This document summarizes a study that recorded the ethnoecological knowledge of European pilchard (Sardina pilchardus) held by fishermen in Peniche, Portugal. 87 fishermen were interviewed about the species. Key findings included: 1) Fishermen provided detailed informal data on the taxonomy, habitat, behaviour, migration, development, spawning and fat accumulation season of sardines that was consistent with published biological data. 2) Fishermen identified different names for juvenile vs. adult sardines and described preferred habitats as coasts and high seas or just coasts. 3) The study concluded that incorporating fishermen's local ecological knowledge could help improve management of this important fishery and

1. RESEARCH Open Access
Sharing fishers´ ethnoecological knowledge
of the European pilchard (Sardina
pilchardus) in the westernmost fishing
community in Europe
Heitor de Oliveira Braga1,2*, Miguel Ângelo Pardal1 and
Ulisses Miranda Azeiteiro3
Abstract
Background: With the present difficulties in the conservation of
sardines in the North Atlantic, it is important to
investigate the local ecological knowledge (LEK) of fishermen
about the biology and ecology of these fish. The
ethnoecological data of European pilchard provided by local
fishermen can be of importance for the management
and conservation of this fishery resource. Thus, the present
study recorded the ethnoecological knowledge of S.
pilchardus in the traditional fishing community of Peniche,
Portugal.
Methods: This study was based on 87 semi-structured interviews
conducted randomly from June to September
2016 in Peniche. The interview script contained two main
points: Profile of fishermen and LEK on European
pilchard. The ethnoecological data of sardines were compared
with the scientific literature following an emic-etic
approach. Data collected also were also analysed following the
union model of the different individual
competences and carefully explored to guarantee the objectivity
of the study.

2. Results: The profile of the fishermen was investigated and
measured. Respondents provided detailed informal data
on the taxonomy, habitat, behaviour, migration, development,
spawning and fat accumulation season of sardines
that showed agreements with the biological data already
published on the species. The main uses of sardines by
fishermen, as well as beliefs and food taboos have also been
mentioned by the local community.
Conclusions: The generated ethnoecological data can be used to
improve the management of this fishery
resource through an adaptive framework among the actors
involved, in addition to providing data that can be
tested in further ecological studies. Therefore, this local
knowledge may have the capacity to contribute to more
effective conservation actions for sardines in Portugal.
Keywords: Ethnoecology, Folk knowledge, Fishermen,
European pilchard, Participatory management
Background
Human populations have forced marine coastal ecosystems
to differ from their historical states, which were character-
ized by diversified and productive communities [1]. One of
the biggest human impacts has been overfishing, which has
progressively reduced stocks, geographically expanded its
range and disguises itself through new and improved
technologies [2].
In marine ecosystems, pelagic fish are recognized as
abundant in productive fishing areas, both on a large scale
and on a small scale [3], and are characterized by a history
of large fluctuations in their populations, both due to
overfishing as well as environmental factors [4]. Within

3. this group of fish, we have small pelagic species, such as
sardines and anchovies, which are abundant in several
productive regions of the ocean and are found mainly in
areas of coastal and oceanic upwelling [5]. These clupeoid
fishes are recognized mainly as having a low trophic level
* Correspondence: [email protected]
1Centre for Functional Ecology - CFE, Department of Life
Sciences, University
of Coimbra, Calçada Martins de Freitas, 3000-456 Coimbra,
Portugal
2CAPES Foundation, Ministry of Education of Brazil, Caixa
Postal 250, Brasilia,
DF 70040-020, Brazil
Full list of author information is available at the end of the
article
© The Author(s). 2017 Open Access This article is distributed
under the terms of the Creative Commons Attribution 4.0
International License
(http://creativecommons.org/licenses/by/4.0/), which permits
unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate
credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were
made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to
the data made available in this article, unless otherwise stated.
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52
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in the food web, early reproduction age and rapid growth,
all of which make them more vulnerable to different
environmental factors and climate change [5].
In the central, eastern, and northeastern Atlantic, the
European pilchard Sardina pilchardus (Walbaum, 1792)
stands out among the pelagic fish for fisheries [6]. At the
moment in Iberian waters, this species exhibits low biomass
stocks at age 1 and a decrease in the stock of old fish and
low recruitment rates [7]. In Portugal, European pilchard
are one of the most important species to fishing fleets using
purse seines and are recognized for their socio-economic
values and traditional uses among the Portuguese [3].
With all these processes occurring, it is important to
understand both the perceptions of local fishery man-
agers and users of local resources and to provide strat-
egies for avoiding conflicting shared perceptions among
the stakeholders involved in fisheries management [8].
In small-scale fisheries, for example, local fishermen are
in many cases disadvantaged in relation to the actors be-
longing to large-scale fisheries due to their marginal pol-
itical power, lack of infrastructure and their typical
remoteness [9].
However, it is known that support from the general
public for the management of natural resources is funda-
mental for long-term sustainability [10]. Discussions
should be initiated with these local communities as a
way of transferring responsibility and regulatory power
over available environmental resources [11].
The local ecological knowledge (LEK) in this context

5. serves as an effective tool for monitoring and assisting in
the planning of depleted resources, for the conservation
of biodiversity [12], and for conducting more reasonable
and culturally sensitive research and management plans
[13]. This knowledge can be understood as the lay or ex-
periential knowledge of an individual about the environ-
ment based on daily observations, practical experiences
in nature and learned scientific knowledge [14].
To better understand recent history of artisanal fishing
and the deterioration of the standard of living of the depen-
dents of this resource [15], we can employ ethnoecology,
which according to Marques (2001) can be understood as
the scientific study of traditional ecological knowledge
(knowledge, behaviour, feelings, and beliefs that influence
all interactions between humans and the ecosystem) [16].
More specifically within ethnozoology, we have eth-
noichthyology [17], which aims to report the knowledge
that fishermen have about fish biology and ecology [18],
and the understanding of interactions between humans and
ichthyological resources encompassing the cognitive and
behavioural aspects supported by conservation [19].
From this perspective, extracting ethnoecological data
about European pilchard from the fishing community of
Peniche, as well as the knowledge passed from gener-
ation to generation by the more experienced fishermen,
can be important strategies for the conservation of this
fishing resource. This type of ethnoecological survey
emphasizes the cultural knowledge of fishermen, favours
their dialogue with environmental managers and re-
searchers, and contributes to the improvement of partici-
patory management of natural resources by increasing the
acceptance of management rules [20].

6. Thus, the aim of this study was to record the ethnoecolo-
gical knowledge of the fishing village of Peniche, Portugal,
about the ecology and biology of S. pilchardus. The fisher-
men’s profiles and the likely human uses, beliefs and taboos
related to European pilchard (also known as the Atlantic
sardine, European sardine, or sardine) were also explored.
The ethnoecological data provided by the fishermen who
are in agreement with the published biological data were
interpreted and discussed in the present study.
Methods
Study area
This study was based on interviews with artisanal fisher-
men from the fishing community of Peniche, on the coast
of the western sub-region of Portugal (39° 21′ 32″ N, 9°
22′ 40″ W; Fig. 1). This city has 27,628 inhabitants with
an area of approximately 77,55 km2 [7]. The climate is
temperate with rainy winters and dry and somewhat hot
summers (Köppen type Csb) [7].
One of the world’s first Portuguese protected areas [21] is
located approximately 5.7 miles from Peniche (Cape
Carvoeiro) in the Atlantic Ocean [22]. Formed by an archi-
pelago of islands (Berlenga Grande, Estela and Farilhões),
this marine protected area is located in the transition zone
between the Mediterranean and European sub-regions,
specifically at the top of the escarpment of the Nazaré
Canyon [22]. The Berlengas Marine Natural Reserve
(MNR) is renowned for its great marine biological diversity,
archaeological features, insular ecosystem specificities and
is importance in the life cycle of the marine avifauna [23].
Fishing community
The fishing port of Peniche is recognized as one of the
main ports of the country [24] according to fishing indi-

7. cators for the average value of fish unloaded in this area
[7, 25]. The economic and social development of the city
is directly linked to the fishing activity of this port,
which is one of the busiest in Portugal [26].
This fishing community is considered a local symbol
with remarkable prestige throughout the municipality
[25]. In the maritime captaincy of Peniche, there are ap-
proximately 1105 registered fishermen, with 996 conduct-
ing marine fishing [7]. Polyvalent and seine fishing are
predominant in this area, with sardines being one of the
three main target species for fishing according to the data
on the nominal catch landed in Portugal [7].
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 2 of 13
Fishermen’s Interviews
Semi-structured interviews [27, 28] were conducted
from June to September 2016 to obtain data on LEK
about the European pilchard. The state-owned company
Docapesca - Portos e Lotas granted permission for
administering the interviews to the fishermen of Porto
de Peniche. Fishermen were interviewed over successive
visits in the fishing warehouses of the Port of Peniche
and at the main meeting points of the fishing commu-
nity. Brook and McLachlan (2008) sees this type of
involvement with the community as indispensable
[29]. The objectives of the work and the statement of in-
formed consent to participate in the research were pro-
vided to the fishermen through the Statement of
Informed Consent (IC) [see Additional file 1].
The interviews were mainly conducted through man-

8. ual transcription and occasionally with a digital audio re-
corder. The interviews with fishermen were conducted
randomly - always before or after the arrivals and depar-
tures of the fishing teams and when they were doing net
and fishing gear repairs. The interview script [see
Additional file 2] was structured in 2 parts: Profile of
fisherman (age, schooling, fishing time, time of residence
in Peniche, income source, type and length of boat, fish-
ing time at sea and time to catch sardines) and LEK of
European pilchard (folk taxonomy, habitat, behaviour
and migration, development of sardines, spawning, fat
accumulation season and uses, beliefs and food taboos).
The educational profile of the interviewees followed the
Portuguese educational classification: A (1st Cycle: 1–
4 years of study), B (2nd Cycle: 5–6 years of study), C
(3rd Cycle: 7–9 years of study) and D: (Secondary
Education: 10–12 years of study).
Data analyses
A respect for the stakeholders and communities, the clarifi-
cation of data collection objectives, the interactive approach
and the recognition of information limitations were used as
a basis for analysing the data acquired [30]. All the informa-
tion provided through the surveys was analysed following
the union model of the different individual competences
[31]. The LEK about sardine was analysed through an
emic-etic approach [32], and the data generated by the
community were compared with the scientific literature
[16]. The wealth of information and depth of perceptions in
the data collected were analysed through careful coding
and cross-checking to ensure the objectivity of the study
[27]. Species nomenclature data were analysed following
the Food and Agriculture Organization of the United
Nations (FAO) [33], the International Union for Conserva-
tion of Nature (IUCN) [34], and Fish Base [35]. The data

9. obtained in the interviews were stored and standardized in
EXCEL and analysed (descriptive statistics) in the R Project
for Statistical Computing version 3.3.2 [36].
Results
Descriptive statistics of fishermen’s profiles
A total of 87 interviews were conducted in the fishing
community of Peniche. The interview sites were predom-
inantly in the Port of Peniche (Fig. 2) (N = 71) followed by
the city centre (N = 16). The average age of the respon-
dents was 58.25 years, with a minimum of 25 years and a
Fig. 1 Map of the study area, highlighting the fishing port and
the city center of Peniche where the interviews were conducted
in Portugal.
Credits: B Zucherato
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 3 of 13
maximum of 76 years. More than half of the interviewees
(N = 59) were born in Peniche and are active (N = 49) in
the fishing currently. According to the Portuguese educa-
tional classification, 58 individuals belonged to the 1st
Cycle, 19 to the 2nd Cycle, 5 to the 3rd Cycle and 5 to
Secondary Education. There were no illiterates or individ-
uals with higher education in the sample. The fishing ex-
perience varied from 3 to 60 years, but fishing experience
average was 39.08 years. The average monthly income
source related to fishing, including retirees, is 810.5 Euros,
ranging from 208.0 to 3000.0 Euros. A total of 50 fisher-
men interviewed supplement their income with income
from other activities. Of these fishermen, 31 informants
do so through work related to fishing (maintenance of

10. fishing nets) and the rest in other autonomous activities.
The main types of boats mentioned by the fishermen
were: trawlers, artisanal fishing boats, trawl nets, coastal
boats, and sports boats. Trawlers were further sub-
classified by fishermen into trawlers (larger boats) and
“rapa” (smaller boats). Boats were measured 93 times dur-
ing the interviews. Of these, the boats mentioned were as
follows: trawlers (35), artisanal fishing boats (38), “rapa”
(14), trawl nets (3), coastal boats (2) and sport boats (1). Six
Fishermen have said they have fished in more than one type
of boat, those being 3 in both artisanal fishing boats and
trawlers and 3 in artisanal fishing boats and trawl nets.
Only 17 of the fishermen interviewed are boat owners.
The fishermen interviewed were questioned about their
preferred schedule of sardine capture during the fishing
campaigns. A cycle called "It is six in the morning and six
in the afternoon" was the most cited by fishermen (N = 27).
Other respondents mentioned both sunrise and sunset
(N = 17), day and night (N = 16), preferably day (N = 16),
preferably night (N = 9), and only at sunset (N = 2).
Local ecological knowledge of sardines
Folk taxonomy
In Peniche, besides the name sardine, the artisanal fishermen
attributed popular names to small sardines. A total of 82
fishermen attributed the name “petinga” or “esquilha” to
juvenile sardines. One fishermen mentioned the name “real”
sardine and another fishermen “sueste” fish. In this commu-
nity, only two fishermen mentioned the scientific name
(Linnaean).
Habitat, behaviour and migration
When questioned about the preferential habitat of sardines,

11. 40 of the fishermen indicated coasts and high sea, 39 only
on the coast, 6 more often on the coast, one only on the
high sea and one did not answer this question. The infor-
mants highlighted some specific habitats (rocky seabeds,
areas where the river empties into the sea carrying food,
clean seabeds, more temperate waters, and sandy seabed to
escape from common dolphin (Delphinus delphis Linnaeus,
1758) attacks.
In relation to the most common depth of the sardine in
the sea, 32 informants indicate a forage interval of 0–
50 m, 40 between 0 and 100 m and 11 between 0 and
200 m. Two fishermen did not know how to answer this
question and two others just said they were deep-sea fish.
The locomotion of sardines in the sea, according to all
fishermen, is carried out in shoals. Some fishermen
(N = 15) specified that the schools are enormous. Two
other fishermen referred to a phenomenon that makes
sardines stick together. One informant said that sardines
usually come together to protect themselves from com-
mon dolphins, and the other informant said that com-
mon dolphins make them stay together to feed.
The following types and patterns of sardine migration
have been mentioned by fishermen in the fishing commu-
nity of Peniche: the migration comes from the South (13
times), comes from the North (18 times), comes from the
South and North (32 times), occurs with the tides (3 times),
occurs according to the seasons of the year - summer and
winter (15 times) and migrant/pelagic/moving fish (14
times). Only 7 respondents did not respond to this part of
the interview.
Fig. 2 a Main area of the fishing port of Peniche, Portugal
where the interviews with the fishermen were carried out. b A

12. fisherman doing
maintenance of purse seine nets. Credits: HO Braga. (Images
published under previous consent of the participants)
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 4 of 13
Local fishermen also mentioned the probable areas of
sardine displacement along the Portuguese Coast that
passes through Peniche (Table 1). The areas most cited by
respondents were Figueira da Foz (27 times), Algarve (25
times), Nazaré (19 times), Ericeira (15 times), Sesimbra
(12 times) and Sines (11 times). Other areas of Portugal,
such as Aveiro, Setúbal and Portimão (8 times), Cape Roca
(7 times), São Pedro de Moel and Matosinhos (4 times),
Viana de Castelo, Póvoa de Varzim, Olhão and Santa Cruz
(3 times) and Cascaiz and Leixões (2 times). Foz do Minho
Beach, Vila do Conde, Caparica Coast, Porto Beach, Mira
Beach, Tocha Beach, Sagres and Lisbon were mentioned
only once in the interviews.
Development of sardines
In the development section, the fisherman was asked
about the time of sardine growth. According to 57 of re-
spondents, sardines showed rapid growth, 16 said they
were slow growing, 3 indicated intermediate growth
(neither slow nor fast) and 11 did not know how to an-
swer this question. The vast majority of respondents
(N = 85) said that the sardine exhibit only the roe phase
during their development. One fisherman mentioned
both the larval stage and the roe phase, and another
fisherman did not know how to answer this question.
Only 19 of respondents said that sardine mature after

13. 1 year of age, and 24 did not know how to respond. The
rest of the interviewees (N = 44) said that the sardine is
able to reproduce within a range of 3–7 months old.
Spawning and fat accumulation season
The answers about the spawning time of sardines varied
among fishermen. Most informants cited the spawning
months as the answer to this question. The spawning time
ranged from one to 8 months (72 citations). There was 1
response for 8 months, 2 for 4 months, 3 for 6 months
and 3 for 7 months, 7 responses for 5 months, 16 for
4 months, 17 for 3 months and 20 for 2 months. The rest
of the respondents (N = 3) did not report any months.
According to respondents, spawning occurs mainly in the
months of January and February (20 times). December was
quoted 19 times, November and March 15 times and
October 12 times. The months of April (9 times), May and
September (6 times), June (5 times), July and August (4
times) were the least mentioned by fishermen in Peniche
(Table 2).
Other fishermen still specified the occurrence of spawn-
ing seasons. Along these lines, there were citations only
for winter (N = 12) and summer (N = 8). There were also
fishermen who reported the number of times (2× a year = 4
citations, 2-3× = 4 citations, 3× = 3 citations and 3-4× = 1
citation) that they spawn each year (Table 2).
The fishermen interviewed in Peniche provided some
information from this part of the questionnaire below:
1. “The water becomes creamy and milky when the
sardine spawns”.

14. 2. "From 100% of the spawn, 90% live and 10% die".
3. “The sardine buries itself in the sand to spawn and
escape predators”.
4. “The sardine goes to the rocks to scratch its belly
when it is pregnant”.
Table 1 Probable areas of sardines displacement along the
Portuguese Coast according to the fishermen of Peniche
Fishing spots in Portugal Number of times
cited by fishermen
Figueira da Foz 27
Algarve 25
Nazaré 19
Ericeira 15
Sesimbra 12
Sines 11
Aveiro, Setúbal and Portimão 8
Cape Roca 7
São Pedro de Moel and Matosinhos 4
Viana de Castelo, Póvoa de Varzim,
Olhão and Santa Cruz
3

15. Cascaiz and Leixões 2
Foz do Minho Beach, Vila do Conde,
Caparica Coast, Porto Beach, Mira Beach,
Tocha Beach, Sagres and Lisbon
1
Table 2 The sardines spawning period according to the
fishermen interviewed
Sardines spawning period Number of times
cited by fishermen
Months
January and February 20
December 19
November and March 15
October 12
April 9
May and September 6
June 5
July and August 4
Seasons
Winter 12

16. Summer 8
Time per year
2 times 4
2–3 times 4
3 times 3
3–4 times 1
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 5 of 13
5. “Outside the summer, the sardines are thin and run
away”.
6. “The sardine passes its belly through the sand to
spawn and leaves the eggs for the sea to take
later”.
The informants mentioned the months of the years when
the sardines accumulate (April to December). The months
of June (56 times), July (75 times), August (68 times),
September (47 times) and October (34 times) are the most
remembered by the fishermen. (Table 3). Some local
sayings were recorded in the interview as:
1. "In July, the sardine already drips on bread".
2. "The sardine grows earlier in the Algarve (Portugal)
because of the warm waters".

17. 3. “The more rain, the more the sardine gets fat”.
4. "In June and July, they are fatter, just like the
Christmas sardine".
Trophic ecology: Predators and prey
The LEK of the fishermen of the Port of Peniche showed
important aspects of the sardine food chain, indicating
the main predators and prey according to fishing experi-
ences along the Portuguese coast. The main predators
according to the fishermen (Table 4) are dolphins (atu-
ninha or toninha), sharks and whales (generally), conger
eel (safio) and yellowfin tuna (atum-albacora).
The fishermen also mentioned the following: sea bass
(robalo), wreckfish (cherne-legítimo), red porgy (pargo-
legítimo), chub mackerel (cavala), black scabbardfish (es-
pada-preto), common octopus (polvo-comum), blackspot
seabream (goraz), European hake (pescada-branca), fork-
beard (abrótea), Atlantic “bonito” (sarrajão or serrajão),
raja rays nei (raias), blackbelly rosefish (cantarilho),
monkfish (tamboril branco) and swordfish (espadarte).
The following species were cited only once in the in-
terviews: horse mackerel (carapau), meagre (corvina),
white seabream (sargo-legítimo), Atlantic mackerel
(sarda), pouting (faneca), black moray eels (moréia-
preta) and ocean sunfish (peixe-lua). The “tainha” was
also mentioned in the study in a generalized way. Birds
were generally cited as sardine predators. The yellow-
legged gull (gaivota-de-patas-amarelas) and albatross
(albatroz) and were also mentioned within this group.
According to the ethnoecological data obtained from
the fishing community have a diet (Fig. 3) based on plank-

18. ton (N = 56), algae called “limo” (N = 30), small shrimp
(N = 13), “comedias” or “comedorias” (N = 12), the spawn
of other fish species (N = 8) their own spawn (N = 6). The
fishermen also said that the sardine feed on krill (N = 5),
sediments accumulated after rainfall (N = 5), sea impur-
ities (N = 1), and remnants of other fish species (N = 1).
“Comedorias” or “Comedias” in this study was defined by
fishermen as a mixture of small fish, small prawns, the roe
of other species of fish and sardine roe.
Table 3 The period of fat accumulation of sardines according
to the respondents
Sardines accumulation season Number of times
cited by fishermen
Months
June 56
July 75
August 68
September 47
October 34
Table 4 The correspondence between the Portuguese folk
names of the S. pilchardus predators and the scientific
classification (Linnaean)
Folk taxonomy Scientific names (Linnaean)
Atuninha or toninha Delphinus delphis Linnaeus, 1758

19. Sharkes Generally
Whales Generally
Safio Conger conger (Linnaeus, 1758)
Albacora Thunnus albacares (Bonnaterre, 1788)
Robalo Dicentrarchus labrax (Linnaeus, 1758)
Cherne Polyprion americanus (Bloch & Schneider, 1801)
Pargo Pagrus pagrus (Linnaeus, 1758)
Cavala Scomber japonicus Houttuyn, 1782
Espada-preto Aphanopus carbo Lowe, 1839
Polvo-comum Octopus vulgaris Cuvier, 1797
Goraz Pagellus bogaraveo (Brünnich, 1768)
Pescada-branca Merluccius merluccius (Linneaus, 1758)
Abrótea Phycis phycis (Linnaeus, 1766)
Sarrajão or serrajão Sarda sarda (Bloch, 1793)
Raias Raja spp.
Cantarilho Helicolenus dactylopterus (Delaroche, 1809)
Tamboril branco Lophius piscatorius Linnaeus, 1758
Espadarte Xiphias gladius Linnaeus, 1758

20. Carapau Trachurus trachurus (Linnaeus, 1758)
Corvina Argyrosomus regius (Asso, 1801)
Sargo-legítimo Diplodus sargus (Linnaeus, 1758)
Sarda Scomber scombrus Linnaeus, 1758
Faneca Trisopterus luscus (Linnaeus, 1758)
Moréia-preta Muraena augusti (Kaup, 1856)
Peixe-lua Mola mola (Linnaeus, 1758)
Tainhas Mugil spp.
Gaivota Larus michahellis J. F. Naumann, 1840
Albatroz Generally
Birds Generally
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 6 of 13
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Human uses, beliefs, and food taboos about European
pilchard
The sardine is greatly important to the fishermen inter-
viewed. According to the majority of the interviewees
(N = 81), sardines have a high economic importance in the
region of Peniche. Another 4 fishermen said that the im-
portance of it is average and 2 other respondents have said
that the importance is low. The summer (N = 21) is cited
as the time when the sardine is more important to the
population of Peniche. The main uses of this pelagic species
are as bait for another species (N = 85 fishermen), in the
canning industry (N = 53), for one’s own food (N = 50) and
the fish meal industries (N = 10). Local commerce (N = 2)
and tourism (N = 2) were also identified by Fishermen.
Some informants (N = 6) from this community men-
tioned sardine food taboos. Fish that are restricted were
locally termed “raimoso”. A change in the restriction of
this fish was observed over time. Twenty-three percent
of fishermen said that the sardine was once “raimosa” in
the past and 61 % of the fishermen said it was not “rai-
mosa”. Two informants said that the sardine was little
“raimosa” and that sick people could not eat it. There
were 3 respondents who said that if the joint between
the sardine skins is removed, it is no longer a restricted
food. The fat found in sardines was recognized as a

22. source of omega 3 by fishermen (N = 9), aiding in the
medical treatment of people with problems with choles-
terol or in the treatment of heart disease patients.
Discussion
Folk taxonomy
Local knowledge related to the naming of fish species is an
inherent part of fishermen’s trade and can be considered as
proof of ability in these communities [37]. In Ericeira,
Portugal, the local community also calls the juveniles of this
species “petinga” [38]. In the Autonomous Region of the
Azores in Portugal, the sardine is also called by the same
vernacular name [35]. The designation of sardines as
“esquilha” (small fish), “sueste” and “real” are new to the
scientific literature.
Habitat, behaviour and migration
According to the ethnoecological data extracted from the
interviews, sardine is a predominantly coastal species and
prefers sites near river mouths in the sea. The fishermen
reported that sardines are distributed vertically, predomin-
antly between the depths between 0 to 100 m. In the sci-
entific literature, similar information was found indicating
that this species is predominantly found in coastal shelf
waters [39–43] and prefers areas of great productivity near
the mouths of rivers and estuaries [42]. In a study on the
modelling of habitat suitability for juveniles of S. pilchar-
dus, the results showed that sardines in the growth phase,
in search of food and in the spawning process can be
closely linked to sites that provide nutrient sources that
increase productivity, such as local upwelling or river run-
off [44]. Di Natale and collaborators (2011) report in the
IUCN Red List of Threatened Species 2011 that European
pilchard can usually be found at depths of up to 100 m,
reaching a lower depth limit of 180 m [40]. The PECH

23. Committee of the European Parliament for the sardine
fishery shows that this species can range down to 150 m
[41], and in a study of sardine habitat to the west of
Portugal showed that this species has a preference for wa-
ters with depths of up to 100 m [43] (Table 5).
European pilchard show migratory behaviour, a high
dispersal capacity and schooling behaviour similar to other
pelagic fish [45]. In the present study, respondents exclu-
sively reported this type of behaviour pattern. There was
an account of a fisherman who referred to this ability to
school as a way to ward off predators. Neilson and Perry
(1990) show that the presence of competitors or predators
may change the direction or influence the intensity of
these migrations in schooling [46] (Table 5).
In Portugal, the geographic distribution of this pelagic
fish covers the entire coastline, Madeira Island and the
Fig. 3 Number of citations of S. pilchardus food items by
fishermen in the fishing community of Peniche, Portugal
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 7 of 13
Azores [47]. However, sardine migration patterns are
not yet well understood [42]. There are indications of
seasonal migrations along the Portuguese Coast [48],
and fifteen interviewees mentioned this information.
According to acoustic campaigns performed in April
and May of 2015 by the Portuguese Sea and Atmosphere
Institute (IPMA), the abundance of sardines decreased
from the north to the south of Portugal [28]. Regarding

24. sardine migrations, it is known that they occur during
the growth phase and towards the north coast of Spain
[23]. During the collection of ethnoecological data in
this part of the interview, it was observed that there was
a variation in the responses among the interviewees.
There were 18 fishermen who said that the sardines
come from the north of Portugal and another 32 fisher-
men who say that they come from the north and the
south of Portugal. This pattern of responses among fish-
ermen reinforces the need to investigate and explore the
studies on the migratory behaviour of sardines in the
Iberian Peninsula.
The European pilchard show migratory behaviour, a
high dispersal capacity and schooling behaviour similar to
other pelagic fish is distributed mainly near Póvoa de Var-
zim and Figueira da Foz in the northwestern region of
Portugal and near Peniche and Lisbon in the southwestern
region [49]. In the Algarve (Southern Portion of Portugal),
this pelagic fish is found in greater quantities in Lagos,
Portimão and between Faro and Vila Real de Santo Antó-
nio [49]. According to the fishermen of Peniche’s LEK, the
Figueira da Foz region and the Algarve were cited the
most frequently when asked about where the sardine is on
the coast after passing through Peniche (Table 5). The re-
gions of Portimão, São Pedro de Manoel, Olhão, Tocha
Beach and Sagres were identified by the fishermen in the
southern portion of Portugal, which are included in or
near the range of greater distribution found during the last
acoustic campaign by the IPMA. None of the respondents
specifically mentioned V. Real de Santo Antônio.
Development of sardines
The sardines show a very fast growth rate [42, 45, 50],
growing to approximately 90% of their full size in 2 years

25. [42]. Most fishermen in the community of Peniche
(N = 57) corroborate the scientific research in relation
to rapid growth (Table 5). In relation to the stages of
development of this species, the fishermen only men-
tioned the egg phase as constituting the whole sardine
life history. However, it is known that the larval stage is
one of the development stages of this pelagic fish [51].
Table 5 Matrix cognition compared between the fishers´ LEK
and the scientific literature on the biology and ecology of
European
pilchard in Peniche, Portugal
Topics Fisherman’s citation Scientific literature
Habitat “Coastal species and prefers sites near river
mouths in the sea”.
“Depths between 0 to 100 m”.
Coastal shelf waters [39–43];
Areas of great productivity near the mouths of rivers and
estuaries [42];
Area of local upwelling or river runoff [44].
Depths of up to 100 m, reaching a lower depth limit of 180 m
[40];
Preference for waters with depths of up to 100 m [43].
Behaviour “Migration carried out in shoals”.
“Ability to school as a way to ward off
predators”.
Migratory behaviour, a high dispersal capacity and schooling
behaviour similar to other pelagic fish [45].
Competitors or predators may change the direction or influence
the
intensity of these migrations in schooling [46].

26. Migration “Mainly Figueira da Foz and Algarve”.
“Póvoa de Varzim, Lisbon...”.
Póvoa de Varzim, Figueira da Foz and Lisbon [49];
Algarve (Southern Portion of Portugal), this pelagic fish is
found in greater quantities [49].
Development “Rapid growth”.
“Sardine reach sexual maturity at 1 year”;
“from 3 to 7 months of age”.
Very fast growth rate [42, 45, 50].
Matures early [52, 53].
Spawning “The main months of spawning are also December,
January and February”.
“Spawn time can range from one to 8 months”.
“In the winter, the sardine spawns more”;
“The spawning occurs 2 to 4 times a year”.
October to April [56]; mainly between December and February
along the Portuguese coast [57].
Ranging from 3 months per year up to 8 months [43].
Sardines exhibit a prolonged spawning period during the year,
with more pronounced spawning mainly in the colder months
of the year [43].
Fat accumulation
season
“June through October”. Late summer and autumn [58].
Late spring to autumn [42].
Predator “Mainly dolphins (atuninha or toninha), “sharks,
whales, conger eel (safio) and yellowfin tuna (albacora)”;

27. “yellow-legged gull (gaivota)”, albatross and other birds”.
Common dolphin (D. delphis) [59–62]; species of demersal fish,
seabirds and marine mammals [41, 42, 59, 63, 64].
Prey “Plankton, algae called “limo”, small shrimp, krill,
the spawn of other fish species and their own spawn”.
Zooplankton as their energy source [58, 68]; Phytoplankton [58,
69];
fish eggs and crustaceans [58].
Sardines may predate on their own eggs in winter [69].
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 8 of 13
The European pilchard matures early [52, 53]. Individ-
uals are largely mature at 1 year of age, and all individuals
are reproductively mature at 2 years of age [41, 52]. In the
present study, only 19 of fishermen said that sardine reach
sexual maturity at 1 year of age and 44 of respondents
mentioned that they are ready to reproduce from 3 to
7 months of age (Table 5).
Spawning and fat accumulation season
Regarding reproduction, spawning of sardines occurs in
batches of eggs [54, 55]. The spawning of the Atlantic
sardines occurs mainly on the western coast of Portugal
between the Nazaré Canyon and the Minho river and in
the Cantabrian Sea [56]. Along the western Iberian
coast, the spawning season of this pelagic species ranges
from September to May, with spawning peaking in No-
vember to the north of Portugal from October to April
[56]. Nunes and collaborators (2011) showed that the

28. spawning peak occurs mainly between December and
February along the Portuguese coast. According to fish-
ermen from Peniche, the main months of spawning are
also December, January and February. This period as a
whole (from October to April) included the months
most cited by the respondents (Table 5).
There is a variation in the duration of spawning times
in the European waters of the North-East Atlantic, ran-
ging from 3 months per year up to 8 months to the
south and west of the Iberian Peninsula for large fish
[43]. A similar pattern was found in responses of our in-
terviewees from Peniche, in which 72 fishermen said
that the Atlantic sardine spawn time can range from one
to 8 months (Table 5).
The winter was cited by 12 fishermen as being the sea-
son during which sardine spawn the most along the Por-
tuguese Coast, and others (N = 12) said that the
spawning occurs 2 to 4 times a year. This point aligns
with the scientific information that Atlantic sardines ex-
hibit a prolonged spawning period during the year, with
more pronounced spawning mainly in the colder months
of the year [43] (Table 5).
S. pilchardus begins to store fat reserves before the
breeding season between late summer and autumn [58].
However, sardines can also accumulate fat from late spring
to autumn [42]. Most months cited by fishermen (June
through October) fit the range of months for the accumula-
tion of fat found in the scientific literature (Table 5).
Trophic ecology: Predator and prey
The sardine is one of the main prey species of the com-
mon dolphin (D. delphis) [59–62]. It also serves as a
food base for several species of demersal fish, seabirds

29. and marine mammals [41, 42, 59, 63, 64]. These animals
were also cited by fishermen during the interviews
(Table 5). The common dolphin stood out among all the
other predators [59–62]. Along the Portuguese Coast
specifically, S. pilchardus was the most important species
in the common dolphin diet in a study in which the stom-
ach contents of this animal were examined during acci-
dental catch and when they were stranded [62]. It is also
known that the common dolphin is an opportunistic
predator of small epipelagic fish [61], usually in places
with moderate or high productivity [65] where sardines
seek their energy sources [44]. Given the current popula-
tion decline in the sardine population on the Iberian coast
[66], attention should be given to the conservation of the
common dolphin along the Portuguese coast, as this is
one of the main predators of this clupeoid fish [67].
Sardines primarily seek zooplankton as their energy
source [58, 68]. Phytoplankton are also an integral part
of the diet of this species [58, 69]. Among the zooplank-
ton, we should highlight copepods, decapods and cirri-
peds [58, 69], fish eggs and crustaceans [58]. During the
winter spawning months, sardines may exhibit cannibal-
istic behaviour in which they predate on their own eggs
[69]. Respondents describe a foraging behaviour similar
to that reported in the investigative work on European
sardine prey (Table 5). In general, it is also observed that
fishermen in the fishing village of Peniche show sardines
with migratory behaviour, high dispersal capacity, prey
and school behaviour similar to other pelagic fish.
Human uses, beliefs and food taboos about European pilchard
The great majority of fishermen (N = 81) in our ethnoeco-
logical study indicated the great economic importance of
Iberian sardines, S. pilchardus, to the local community of

30. Peniche. According to data from the Statistics Yearbook of
the Central Region of 2015 made by Portugal’s National
Statistical Institute (INE), sardine fisheries officially yielded
approximately 1223 tons of fish and 3517 thousand Euros
for the municipality of Peniche in 2015 [7]. This fact proves
the strength of this economic activity for this region.
The summer was highlighted among the respondents
as being the most important season for sardine fishing,
local commerce and tourism. In this season, the sardines
are in the fattening stage [42, 58], and their fat content
is high [70]. The sardine in this period has a flavour and
aroma that is more appreciated by the consumers [71],
which makes this species more economically profitable.
When the fat content is low (2–5%), this fish is less pre-
ferred by consumers and is normally sent to the canning
and fish meal industries [70]. In other seasons, sardines
are primarily used as baitfish for demersal fishing or for
the canning industry [72]. All sardine uses known to the
scientific literature were also mentioned by the fisher-
men during the interviews.
Taboos are unwritten social rules that regulate human
behaviour and can both govern and affect human social
life and serve to manage a local biological resource [73].
Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 9 of 13
In the local community of Peniche, there were no sig-
nificant taboos or food aversions regarding sardines by
fishermen (N = 6). In local communities of the Amazon
and in the Atlantic Forest in Brazil, taboos and aversions
were also not associated with herbivorous fish or inver-

31. tebrate eaters [74]. According to Begossi (2004), this can
be an adaptive strategy of local inhabitants to fish of
higher trophic levels that can more easily accumulate
toxins by eating a variety of prey (plants, invertebrates
and other fish) [74]. This may be one of the reasons that
there are few fishermen with taboos or sardine aversions.
Another hypothesis is that these social rules may be los-
ing strength over the years due to the exodus of fisher-
men to other economic activities, many of whom leave
due to the low economic profitability of this profession
and the difficulties imposed by European Union legisla-
tion on Portuguese artisanal fisheries [75].
Regarding medicinal purposes, 9 fishermen indicated
that sardine can treat high cholesterol levels and patients
with cardiac problems. In a study about the fauna and
the role of taboos in the conservation of animals in a
forest reserve in southeastern Cameroon [76], sardine
(Sardina sp.) are used medicinally to treat cardiovascular
diseases, which was also indicated in our survey by some
fishermen (N = 9). In the Sierra de Segura (Albacete,
Spain), S. pilchardus is used for medicinal purposes in
the treatment of sore feet and blisters in modern times
and is marketed in the Spanish markets as food [77].
Conservation concerns and co-management
There is a growing interest in LEK research in order to
provide complementary data for several small-scale fishery
species [78]. With the difficulties and vulnerability of the
marine ecosystem, LEK correctly acquired and aggregated
at appropriate spatial-temporal scales becomes an import-
ant marine species conservation tool [79]. The manage-
ment of these coastal resources in fishing villages can also
be better achieved by exploring data of this nature, which
provide information on the ecology, behaviour and pres-
ence of these species in the environment [80].

32. In the present work, we present LEK data on the ecol-
ogy of sardines that corroborated scientific research.
Other data generated in the interviews that were not val-
idated by the scientific literature can be tested and in-
corporated into new hypotheses before carrying out a
scientific study. According to Drew (2005), an analysis
of the components of traditional ecological knowledge
can reveal new information and thus contribute to the
formulation of testable hypotheses in order to improve
scientific infrastructure. Silva et al. (2014) also reveal
the importance of generating new scientific questions
through ethnoecological data [81]. The LEK about sar-
dines acquired here may complement pre-existing sci-
entific data. Due to the high cost and lack of resources
for investments in traditional samplings, data of this
nature become important for conservation practices
and development [82].
Given the low stock levels of the sardine population in
the Iberian Region [66], participation among the actors in-
volved in fishing regulations should be carried out in an
interactive manner [83]. Ecological knowledge data on
spawning and the time of fat accumulation may provide
researchers an additional source of data to better under-
stand the reproductive behaviour of this species from the
fishermen’s point of view. Analysing this knowledge can
contribute to a better understanding and reduction of in-
ternal conflicts between fishing managers, politicians and
the community about the correct time for harvesting this
species. In addition, LEK data acquired from these trad-
itional communities are important because it reveals the
most recent changes in environmental processes [84].
The new data (trophic ecology, habitat and behaviour)

33. that emerged during the interviews can serve as a start-
ing point for research on the population structure of sar-
dines. On a larger spatial scale, this kind of data, with
adequate treatment, becomes important in the construc-
tion of management and conservation plans for sardines.
Finally, we can note that the LEK of the sardines in
Peniche should (and did) treat all stakeholders as being
within a continuously adaptive framework [85].
Conclusions
The socioeconomic profile of the fishermen of Peniche
was described in this ethnoecological research. Respon-
dents provided detailed informal data on the taxonomy,
ecology and biology of Sardina pilchardus. This informal
knowledge showed agreements with the scientific litera-
ture. We suggest the use of non-corresponding data with
formal knowledge to aid in the construction of testable
hypotheses for new investigative work on sardines. The
data generated here can be used to try to improve the un-
derstanding of the fishermen’s knowledge of the European
pilchard by managers and conservationists. This approach
requires the use of an adaptive framework, which contrib-
utes to an improvement in the relations between the ac-
tors involved with the resource. The food taboos and
social rules about European pilchard were not relevant to
conservation in this community. This species, which is
mainly used as baitfish for other fishes and in the canning
and fish meal industries, provides a great economic value
for the fishing community studied here.
Finally, our results highlighted that artisanal fisher-
men from Peniche show ethnoecological data about
European pilchard that can support scientific know-
ledge, as well as collaborate with future initiatives in
pursuit of viable conservation goals for sardines on the
coast of Portugal.

34. Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 10 of 13
Additional files
Additional file 1: Statement of Informed Consent (IC) and
agreement
to participate in the research. (DOCX 16 kb)
Additional file 2: Script of interview. (DOCX 14 kb)
Abbreviations
FAO: Food and Agriculture Organization of the United Nations;
IC: Statement
of Informed Consent; INE: Portugal’s National Statistical
Institute;
IPMA: Portuguese Sea and Atmosphere Institute; IUCN:
International Union
for Conservation of Nature; LEK: local ecological knowledge;
MNR: Berlengas
Marine Natural Reserve
Acknowledgements
We are also grateful to Henrique M. F. de Oliveira and Bruno
Zucherato who
collaborated in the production of this paper. We also thank the
members of the
fishing community of Peniche who took part in this study by
providing
interviews. A special thank you goes to Dr. Paulo Maranhão and
João G.
Carneiro for the initial support given to the data collection
process in Peniche.

35. Funding
The fieldwork was sponsored by the CAPES Foundation -
Ministry of
Education of Brazil (BEX: 8926/13–1).
Availability of data and materials
Not applicable.
Authors’ contributions
HOB – Collected and analyzed data and drafted the manuscript;
MAP and UMA –
Reviewed the manuscript. All authors read and approved the
final manuscript.
Ethics approval and consent to participate
The objectives of the work and the statement of informed
consent to
participate in the research were provided to the fishermen
through the
Statement of Informed Consent (IC) [see Additional file 1]. No
further
Research Ethics Committee approval was required in Portugal.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional
claims in
published maps and institutional affiliations.
Author details

36. 1Centre for Functional Ecology - CFE, Department of Life
Sciences, University
of Coimbra, Calçada Martins de Freitas, 3000-456 Coimbra,
Portugal. 2CAPES
Foundation, Ministry of Education of Brazil, Caixa Postal 250,
Brasilia, DF
70040-020, Brazil. 3Department of Biology & CESAM - Centre
for
Environmental and Marine Studies, University of Aveiro, 3810-
19 Aveiro,
Portugal.
Received: 13 July 2017 Accepted: 3 September 2017
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53. Braga et al. Journal of Ethnobiology and Ethnomedicine (2017)
13:52 Page 13 of 13
AbstractBackgroundMethodsResultsConclusionsBackgroundMet
hodsStudy areaFishing communityFishermen’s InterviewsData
analysesResultsDescriptive statistics of fishermen’s
profilesLocal ecological knowledge of sardinesFolk
taxonomyHabitat, behaviour and migrationDevelopment of
sardinesSpawning and fat accumulation seasonTrophic ecology:
Predators and preyHuman uses, beliefs, and food taboos about
European pilchardDiscussionFolk taxonomyHabitat, behaviour
and migrationDevelopment of sardinesSpawning and fat
accumulation seasonTrophic ecology: Predator and preyHuman
uses, beliefs and food taboos about European
pilchardConservation concerns and co-
managementConclusionsAdditional
filesAbbreviationsFundingAvailability of data and
materialsAuthors’ contributionsEthics approval and consent to
participateConsent for publicationCompeting
interestsPublisher’s NoteAuthor detailsReferences
Drummond & Leonard: Breeding biology of the Fork-tailed
Storm-Petrel 265
Marine Ornithology 37: 265–273 (2009)
265
INTRODUCTION
The Fork-tailed Storm-Petrel Oceanodroma furcata is an
abundant
and widespread pelagic seabird in the northern Pacific Ocean.
The species nests on islands from California to Alaska and in
northeastern Asia, with most of the birds concentrated on

54. offshore
islands in Alaska (Boersma & Silva 2001). The highest numbers
of Fork-tailed Storm-Petrels occur in the Aleutian Islands,
which
support nearly two thirds of the entire global breeding
population
(Boersma & Silva 2001, Byrd et al. 2005, USFWS 2006).
Despite the importance of the Aleutian Islands for Fork-tailed
Storm-Petrels, data on their breeding biology in this region are
lacking. Studies have been conducted at colonies in the Gulf
of Alaska (Quinlan 1979, Boersma et al. 1980, Simons 1981,
Baird & Gould 1983), British Columbia (Vermeer et al. 1988),
Washington (Boersma & Silva 2001) and California (Harris
1974),
but knowledge of the species’ breeding biology in the Aleutian
Islands is limited to baseline productivity data collected at
several
long-term monitoring sites (e.g. Andersen 2007) and
unpublished
historical data (Byrd & Trapp 1977). Understanding the
breeding
biology of Fork-tailed Storm-Petrels in the core of its range is
important not only to the conservation of the species, but also
for
its potential use as an indicator of changing marine conditions
in
the northern Pacific ecosystem (Boersma et al. 1980, Boersma
&
Parrish 1998, Piatt et al. 2006).
Our goal was to conduct the first detailed study of Fork-tailed
Storm-
Petrel breeding biology in the Aleutian Islands. We examined
timing
of breeding, breeding success, chick growth, parental

55. provisioning
and chick diet at a colony in the central Aleutian Islands during
two
consecutive breeding seasons.
METHODS
Study site
We conducted our study at Kasatochi Island (52°11′N,
175°30′W),
located within the Alaska Maritime National Wildlife Refuge in
the central Aleutian Islands, Alaska (Fig. 1). Kasatochi is a
small
volcanic island of about 300 ha, with a large crater lake in the
center.
The climate is typical of the Aleutian Islands region,
characterized
by rain, thick fog, strong winds and frequent storms. Terrain
includes
rock cliffs, boulder beaches, grassy slopes and vegetated talus
fields,
which provide habitat for hundreds of thousands of breeding
seabirds.
The breeding population of Fork-tailed Storm-Petrels on the
island
during our study was estimated to be at least 2000 birds
(Drummond
& Rehder 2005, Drummond 2006).
After the present study, Kasatochi erupted violently on 7
August 2008,
burying the entire island in lava and ash; the storm-petrel
colony
and all other seabird colonies on the island were destroyed
(Alaska

56. Volcano Observatory 2008, R. Buchhiet & J. Williams pers.
comm.).
BREEDING BIOLOGY OF THE FORK-TAILED
STORM-PETREL OCEANODROMA FURCATA ON
KASATOCHI ISLAND, ALEUTIAN ISLANDS, ALASKA
BRIE A. DRUMMOND1,2 & MARTY L. LEONARD1
1Department of Biology, Dalhousie University, 1355 Oxford
Street, Halifax, Nova Scotia, B3H 4J1, Canada
([email protected])
2Current address: Alaska Maritime National Wildlife Refuge,
US Fish and Wildlife Service,
95 Sterling Highway, Suite 1, Homer, Alaska, 99603, USA
Received 9 October 2008, accepted 1 June 2009
SUMMARY
DRUMMOND, B.A. & LEONARD, M.L. 2009. Breeding
biology of the Fork-tailed Storm-Petrel Oceanodroma furcata on
Kasatochi
Island, Aleutian Islands, Alaska. Marine Ornithology 37: 265–
273.
We present the first detailed account of breeding biology in
Fork-tailed Storm-Petrels Oceanodroma furcata from the
Aleutian Islands,
Alaska, where nearly two thirds of the global breeding
population occurs. We examined timing of breeding, breeding
success, chick growth,
parental provisioning and chick diet during two consecutive
breeding seasons at a colony in the central Aleutians. Most

57. adults laid eggs
before late May, eggs hatched between mid-June and early
August and chicks began fledging in mid-August. Timing of
breeding varied
between years, with an earlier mean hatch in 2005 than in 2006.
Hatching success was consistently high in both years (89% in
2005, 91%
in 2006), but fledging success varied substantially between
years (58% in 2005, 89% in 2006), indicating that factors that
influence chick
survival may drive annual breeding success. Visitation rate,
meal size and composition of chick diets also varied between
years, suggesting
that foraging conditions varied during our study. Food
availability and weather conditions may both have contributed
to the variation we
observed in timing of breeding and fledging success.
Key words: Aleutian Islands, breeding biology, chick survival,
Oceanodroma furcata, storm-petrel
266 Drummond & Leonard: Breeding biology of the Fork-tailed
Storm-Petrel
Marine Ornithology 37: 265–273 (2009)
Study species
Fork-tailed Storm-Petrels are nocturnal, burrow-nesting
seabirds
that breed on islands in colonies ranging from fewer than 100 to
more than 1 000 000 birds (Sowls et al. 1978, Boersma & Silva
2001, Byrd et al. 2005, USFWS 2006). The breeding period
lasts

58. up to four months, prolonged by episodes of egg neglect
(Boersma
et al. 1980, Simons 1981) and slow chick growth (Boersma et
al. 1980). Females lay a single egg and both sexes participate in
incubation and chick-rearing. Adults brood chicks for about five
days post-hatch (Boersma et al. 1980), after which they leave
the
nest and return only briefly every one to four nights to feed
chicks
(Simons 1981). Chicks fledge after about two months (Boersma
et
al. 1980).
Timing of breeding, reproductive success, chick growth and
visitation rate
We followed Fork-tailed Storm-Petrel nests during two breeding
seasons (25 May–23 August 2005 and 21 May–1 September
2006)
to determine timing of breeding (hatch date), reproductive
success
(hatching success, fledging success, overall success), chick
growth
(growth rate, final fledging mass) and visitation rate. In each
year,
we used all accessible nests in which we could view complete
nest
contents by flashlight (n = 79 in 2005, n = 103 in 2006). All
nests
used in 2005 were monitored in 2006 to determine the
proportion
of nest reuse. Once an egg or incubating bird was observed at
the
beginning of the season, we did not check nests again until
close
to predicted hatch in mid-June, when we checked nests daily to

59. determine hatch date. After chicks hatched, we visited nests
every
two days until the nest failed or the chick fledged.
Chicks were considered failed if they died or disappeared from
the
nest at less than 50 days of age and fledged if they disappeared
from the nest at 50 days of age or older. In cases in which we
left
the island while the chick was still in the nest, we considered
chicks
at those nests successful if they were 40 days of age or older
and
apparently healthy at our departure (n = 11 in 2005, n = 40 in
2006).
The foregoing assumption is based on patterns of chick
mortality in
Fork-tailed Storm-Petrels, in which mortality occurs almost
entirely
in chicks younger than 20 days (Boersma et al. 1980, B.
Drummond
pers. obs.). The few chicks that were less than 40 days of age at
our
departure (n = 3 in 2005, n = 4 in 2006) were omitted from
analyses
of fledging success and overall success. We estimated hatching
success as the number of eggs hatched divided by the number of
eggs laid, fledging success as the number of chicks fledged
divided
by the number of eggs hatched, and overall success as the
number
of chicks fledged divided by the number of eggs laid.
We examined chick growth by measuring chicks from a subset
of accessible nests (n = 26 in 2005, n = 43 in 2006), beginning
after the brooding period ended [5.1 ± 2.4 days post-hatch

60. (Drummond 2007)]. On each nest check (except on stormy days
when removing the chick from the nest could be harmful), we
measured mass [±0.5 g using a 100-g Pesola spring scale
(Pesola,
Baar, Switzerland)], wing chord length (±1 mm using a 150-mm
wing ruler) and diagonal tarsus length (±0.1 mm using a dial
calliper). From chick measurements, we calculated mean mass
gain
(g/day) from hatching to peak weight, and wing and tarsus
growth
(mm/day) during the linear growth periods, which we
determined
by fitting regression lines to the data. Because fledging size can
affect post-fledging survival in some seabirds (e.g. Olson 1997,
Sagar & Horning 1998), we also calculated mass at fledging for
chicks that fledged before we departed the island.
We used toothpick knock-downs to record parental visits at
night
(Quinlan 1979), and we present visitation rate as a proxy for
feeding
rate. Toothpicks were placed across nest entrances in the
evening
and were checked the following morning; those that had been
knocked down indicated that the nest had been visited that night
by
a parent carrying food. Visitation rate was defined as the
percentage
of nights a nest was visited between the end of brooding and
death
or departure of the chick from the nest. We assume that
visitation
rate generally represents feeding rate, because once brooding
ends,
adults return to the nest primarily to feed the chick (Simons

61. 1981,
Boersma & Silva 2001). We consider this measure an
underestimate
of true visitation rate, however, because it does not record
incidents
of two parental visits in a single night.
Chick meal size and diet composition
To determine chick meal size and diet composition, we captured
adult
storm-petrels (n = 32 in 2005, n = 53 in 2006) in mist nets at
night,
when birds were returning to the colony with food for chicks.
When
caught, birds spontaneously regurgitated the food they were
carrying
onto plastic sheeting stretched under the net. We captured birds
at three
regularly-spaced intervals during the nestling period: early
(mid-July,
when at least 70% of chicks were 0–20 days old), mid (late
July, when
Fig. 1. Location of the Fork-tailed Storm-Petrel Oceanodroma
furcata colony at Kasatochi Island, Aleutian Islands, Alaska.
Drummond & Leonard: Breeding biology of the Fork-tailed
Storm-Petrel 267
Marine Ornithology 37: 265–273 (2009)
most to at least family) by K. Turco (Falco Consulting,
Fairbanks,

62. AK, USA). Small amounts of partially-digested fish and squid
were unidentifiable and were categorized as such. From prey
data,
we determined diet composition by calculating the percentage
occurrence and percentage biomass of prey items in chick diets
during each of the three sampling periods (Vermeer & Devito
1988). Percentage occurrence was defined as the number of
regurgitation samples containing a specific prey item divided by
the
number of samples. Percentage biomass was the mass of a prey
item
in a diet sample divided by the mass of the diet sample,
calculated
by multiplying the number of individuals of a prey item in a
sample
by a standard laboratory value for mass of that prey item.
TABLE 1
Reproductive performance of Fork-tailed Storm-Petrels
Oceanodroma furcata at Kasatochi Island, Alaska, 2005 and
2006
Parameter 2005 2006 χ2 df P value
Eggs laid 79 103
Eggs failed [n (% of all eggs)] 9 (11) 9 (9)
Abandoned 7 (9) 5 (5)
Broken or cracked 1 (1) 1 (1)
Disappeared 1 (1) 3 (3)
Eggs hatched [n (% of all eggs)] 70 (89) 94 (91)

63. Chicks died 28 (35) 10 (9)
Chicks survived 39 (49) 80 (78)
Chicks 30–39 days at departurea 3 (4) 4 (4)
Hatching success (%) 88.6 91.3 1.10 1 0.294
Fledging success (%) 58.2 88.9 24.66 1 <0.001
Overall success (%) 51.3 80.8 23.21 1 <0.001
a Chicks aged 30–39 days at our departure from the island were
excluded from estimates of chick survival and overall success.
Fig. 2. Distribution of hatching dates of Fork-tailed Storm-
Petrel Oceanodroma furcata eggs at Kasatochi Island, Alaska, in
2005 (n = 53)
and 2006 (n = 53). Arrows indicate mean hatch date (1 July ±
10.1 days in 2005, 6 July ± 10.1 days in 2006).
at least 70% of chicks were 20–40 days old), and late (mid-
August,
when at least 70% of chicks were 40 or more days old).
Sampling
occurred between 23h00 and 03h00 on a single dry, overcast
night
during each period, except during the late nestling period in
2005
when sampling occurred over two nights because of rain.
To measure meal size, defined as the mass of an individual food
load, we weighed regurgitation samples on site (±0.5 g with a
30-g
Pesola scale). Samples were then preserved in 70% ethyl
alcohol

64. and 2% glycerine (2005) or Streck (Streck Laboratories, Omaha,
NE, USA) tissue fixative (2006) and later identified to species
or
lowest taxonomic level possible (many to genus or species, and
268 Drummond & Leonard: Breeding biology of the Fork-tailed
Storm-Petrel
Marine Ornithology 37: 265–273 (2009)
Data analysis
Of all nest sites monitored, 26 were occupied in 2005 only, 50
in 2006
only and 53 in both years. Sites used in both years were likely
occupied
by the same pair each year (Drummond 2007), because Fork-
tailed
Storm-Petrels have high nest-site fidelity (Boersma & Silva
2001).
Therefore, parameters potentially related to individual birds,
such as
hatch date and feeding rate (e.g. Weimerskirch 1990), taken at
the
same nest in different years, are likely not independent. To
account
for this situation, we performed separate analyses for each year
and
restricted between-year comparisons to nests used in both years
(n =
53). Meal size and diet composition were considered
independent
across years, because data were collected from mist-netted birds
presumed not to be the same individuals in different years.

65. All statistical analyses were performed using JMP 5.0. We
report
means ± standard deviation and use α = 0.05 for statistical
significance. For analyses of variance, we report only
interaction
terms that were significant at α = 0.05. Data for visitation rate
and percentage biomass of prey were arcsine-transformed to
better
approximate a normal distribution. All variables otherwise met
the assumptions of parametric tests, except for visitation rates
in
nests in which chicks died, for which we used a nonparametric
test
because of unequal variance (Ruxton 2006).
TABLE 3
Relationships between chick growth parameters and visitation
rate at nests on Kasatochi Island, Alaska, 2005 and 2006
Parameter 2005 2006
r2 n P r2 n P
Linear growth rate
Mass (g/d) 0.001 15 0.942 0.136 33 0.035
Wing chord (mm/d) 0.070 15 0.341 0.089 32 0.097
Tarsus (mm/d) 0.007 15 0.773 0.009 33 0.598
Fledging mass (g) 0.070 3 0.209 0.032 12 0.580
TABLE 2

66. Parameters of chick growth and parental provisioninga
of Fork-tailed Storm-Petrels Oceanodroma furcata at
Kasatochi Island, Alaska, 2005 and 2006
Parameter 2005 2006 t df P value
Linear growth rates
Mass (g/d) 2.1±0.5
(n=25)
1.9±0.4
(n=38)
1.95 47 0.057
Wing chord (mm/d) 3.5±0.4
(n=22)
3.6±0.2
(n=37)
1.21 47 0.268
Tarsus (mm/d) 0.5±0.1
(n=25)
0.6±0.1
(n=38)
3.55 49 0.001
Fledging mass (g) 80.3±9.2
(n=3)

67. 78.6±5.0
(n=12)
0.47 13 0.650
Visitation rate (%) 48.2±8.1
(n=43)
58.3±7.4
(n=73)
5.45 36 <0.001
Meal size (g) 6.5±1.5
(n=32)
8.2±1.5
(n=53)
2.21 82 0.030
a Mean ± standard deviation.
Fig. 3. Mean (± standard deviation) growth of (a) mass, (b)
wing
chord, and (c) tarsus in Fork-tailed Storm-Petrel Oceanodroma
furcata chicks over the nestling period at Kasatochi Island,
Alaska.
Data include all known-age chicks that survived to fledge (n =
25
in 2005, n = 34 in 2006).
Drummond & Leonard: Breeding biology of the Fork-tailed
Storm-Petrel 269

68. Marine Ornithology 37: 265–273 (2009)
TABLE 4
Percentage occurrence of prey items in diet samples collected
from Fork-tailed Storm-Petrels Oceanodroma furcata
at early, mid, and late nestling periodsa at Kasatochi Island,
Alaska, 2005 and 2006
Prey type 2005 2006
Early Mid Late Total Early Mid Late Total
Crustaceans
Amphipods 50.0 50.0 80.0 59.4 81.8 60.0 59.4 64.2
Parathemisto spp. 0.0 0.0 10.0 3.1 0.0 0.0 0.0 0.0
P. pacifica 0.0 0.0 10.0 3.1 36.4 0.0 0.0 7.5
Hyperia spp. 10.0 0.0 0.0 3.1 0.0 0.0 0.0 0.0
H. medusarum 0.0 0.0 0.0 0.0 0.0 0.0 3.1 1.9
Lysianassidae 50.0 50.0 80.0 59.4 63.6 60.0 50.0 54.7
Anoyx spp. 0.0 0.0 0.0 0.0 0.0 0.0 12.5 7.5
Unidentified amphipod 0.0 0.0 0.0 0.0 0.0 0.0 3.1 1.9
Copepods 10.0 0.0 0.0 3.1 45.5 10.0 0.0 11.3
Neocalanus cristatus 10.0 0.0 0.0 3.1 45.5 10.0 0.0 11.3

69. Euphausiids 10.0 0.0 0.0 3.1 18.2 10.0 3.1 7.5
Thysanoessa longipes 10.0 0.0 0.0 3.1 0.0 0.0 0.0 0.0
Unidentified euphausiid 0.0 0.0 0.0 0.0 18.2 10.0 3.1 7.5
Decapods 50.0 8.3 20.0 25.0 63.6 60.0 25.0 39.6
Atelecyclidae megalopa 30.0 8.3 10.0 15.6 63.6 40.0 21.9 34.0
Unidentified shrimp 20.0 0.0 10.0 9.4 9.1 30.0 3.1 9.4
Molluscs
Squid 20.0 16.7 20.0 18.8 0.0 10.0 12.5 9.4
Fish
Myctophids 80.0 91.7 90.0 87.5 63.3 90.0 78.1 77.4
Unidentified fish 0.0 0.0 10.0 3.1 9.1 10.0 25.0 18.9
Other (plastic) 20.0 16.7 0.0 12.5 0.0 0.0 0.0 0.0
Samples (n) 10 12 10 32 11 10 32 52
a “Early” samples collected when 70% chicks were 0–20 days
(18 July 2005 and 16 July 2006); “mid” samples, when 70%
chicks were
20–40 days (25 and 28 July 2005 and 31 July 2006); “late”
samples, when 70% chicks were ≥40 days (14 and 16 August
2005 and
16 August 2006).
RESULTS

70. Timing of breeding
In both years, most birds were incubating eggs upon our arrival
at
the island in late May. Hatching began in mid-June and
continued
to late July (2005) and early August (2006) (Fig. 2). Fledging
began
in mid-August and continued through our departure from the
island
in both years. Eggs hatched significantly earlier in 2005 (mean:
1 July ± 10.1 days) than in 2006 (mean: 6 July ± 10.1 days;
paired
t
20 = 2.14; P = 0.045). Hatch date did not predict fledging
success
in either year (2005: r2 < 0.011, n = 49, P = 0.884; 2006: r2 =
0.050,
n = 48, P = 0.178).
Reproductive success
Hatching success ranged between 89% and 91% and did not
differ
significantly between years (Table 1). The greatest source of
egg
failure was abandonment (Table 1). Fledging success, in
contrast,
varied between 58% and 89%, with significantly higher chick
survival and, ultimately, overall reproductive success in 2006
than
in 2005 (Table 1). Chick mortality occurred primarily when
chicks
were young, with approximately 81% of known-age chick deaths
occurring before 10 days of age and 91% before 15 days of age

71. in both years (n = 34). Only a single chick in each year died
after
the age of 20 days. Of nests used in 2005, 67% were reoccupied
in
2006. As compared with nests that had been successful, nests
that
270 Drummond & Leonard: Breeding biology of the Fork-tailed
Storm-Petrel
Marine Ornithology 37: 265–273 (2009)
failed in the first year were significantly less likely to be
reoccupied
the following year (χ21 = 11.78, P = 0.003).
Chick growth and parental provisioning
Chicks attained a peak body mass (101.5 ± 7.5 g) at an average
of 47.9 ± 5.2 days and then lost mass before fledging (Fig. 3).
Wing chord and tarsus measurements reached asymptotes at
53.2
± 7.2 days and 29.0 ± 2.3 days respectively (Fig. 3). Only tarsal
growth rate varied significantly between years, with faster
growth
in 2006 than in 2005 (Table 2).
Visitation rates at individual nests varied from 32% to 75%
(mean:
54.5% ± 9.1%; n = 116). Visitation rate and meal size were both
significantly higher in 2006 than in 2005 (Table 2). However,
there
was no significant difference in visitation rate between nests
where

72. chicks died and where they survived (2005: t
21 = 0.50, P = 0.623;
2006: t7 = 1.47, P = 0.184). Chicks that were fed more
frequently
gained weight faster in 2006 but not in 2005 (Table 3).
Visitation
rate was not directly related to wing chord or tarsal growth, nor
to
final mass at fledging (Table 3).
Chick diet
Myctophid fish occurred in more than 75% of diet samples
(Table 4) and made up more than 80% of the prey biomass
(Table 5)
in both years. Amphipods and decapods occurred in 25% to 64%
of
samples, but each contributed little to prey biomass (<1% to
1%).
Small plastic particles were found in diet samples in 2005 but
not
in 2006 (Table 4).
The percentage occurrence of myctophid fish in chick diets did
not
vary between years (χ2
1 = 1.41, P = 0.236) or across the nestling
period (χ22 = 2.79, P = 0.248). In contrast, the percentage
biomass
TABLE 5
Percentage biomass of prey items in diet samples collected from
Fork-tailed Storm-Petrels Oceanodroma furcata

73. at early, mid and late nestling periodsa at Kasatochi Island,
Alaska, 2005 and 2006
Prey type Mass
standard
(mg)b
2005 2006
Early Mid Late Total Early Mid Late Total
Crustaceans
Amphipods — 0.2 0.1 0.4 0.3 0.3 0.1 0.2 0.2
Parathemisto spp. 3.0 0.0 0.0 <0.1 <0.1 0.0 0.0 0.0 0.0
P. pacifica 2.0 0.0 0.0 <0.1 <0.1 0.1 0.0 0.0 <0.1
Hyperia spp. 2.0 <0.1 0.0 0.0 <0.1 0.0 0.0 0.0 0.0
H. medusarum 3.9 0.0 0.0 0.0 0.0 0.0 0.0 <0.1 0.0
Lysianassidae 4.0 0.2 0.1 0.3 0.2 0.2 0.1 0.2 0.2
Anoyx spp. 8.0 0.0 0.0 0.0 0.0 0.0 0.0 <0.1 <0.1
Unidentified amphipod 2.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Copepods — 0.1 0.0 0.0 <0.1 40.8 2.0 0.0 9.1
Neocalanus cristatus 13.0 0.1 0.0 0.0 <0.1 40.8 2.0 0.0 9.1
Euphausiids — 7.8 0.0 0.0 2.4 2.4 0.4 1.0 1.1

74. Thysanoessa longipes 75.0 7.8 0.0 0.0 2.4 0.0 0.0 0.0 0.0
Unidentified euphausiid 22.7 0.0 0.0 0.0 0.0 2.4 0.4 1.0 1.1
Decapods — 1.9 1.1 0.5 1.1 4.1 0.9 0.5 1.4
Atelecyclidae megalopa 15.0 1.4 1.1 0.3 0.9 4.0 0.8 0.2 1.1
Unidentified shrimp 50.0 0.5 0.0 0.2 0.2 0.1 0.2 0.4 0.3
Molluscs
Squid 20.0 0.5 0.5 0.3 0.4 0.0 0.1 0.5 0.3
Fish
Myctophids 2100.0 89.5 98.3 90.4 92.9 50.8 95.3 87.6 82.0
Unidentified fish 485.0 0.0 0.0 8.4 2.9 1.7 1.3 10.1 6.0
Samples (n) 10 12 10 32 11 10 32 53
a “Early” samples collected when 70% chicks were 0–20 days
(18 July 2005 and 16 July 2006); “mid” samples, when 70%
chicks were
20–40 days (25 and 28 July 2005 and 31 July 2006); “late”
samples, when 70% chicks were ≥40 days (14 and 16 August
2005 and
16 August 2006).
b Standard laboratory mass value of each prey item used in
percentage biomass calculations.

75. Drummond & Leonard: Breeding biology of the Fork-tailed
Storm-Petrel 271
Marine Ornithology 37: 265–273 (2009)
of myctophid fish varied across year (F1,83 = 4.25, P = 0.042)
and
nestling period (F2,83 = 4.59, P = 0.013), with a higher biomass
in
chick diets in 2005 than in 2006, and later in the nestling
period.
These differences appeared driven by an unusually low amount
of
myctophid fish in chick diets during the early nesting period in
2006, when biomass of myctophid fish was just 51% and
appeared
to be replaced mainly by copepods (Table 5).
DISCUSSION
Timing of breeding
Timing of breeding varied between years at Kasatochi, with
later
hatching in 2006 than in 2005. Annual variation in seabird
phenology
may be driven by food availability (e.g. Bertram et al. 2001) or
weather
(e.g. Payne & Prince 1979). We lack independent measures of
storm-
petrel prey supply during our study to determine how food
availability
relates to timing of breeding at Kasatochi, although variation in
timing
is thought to reflect fluctuation in food supply at other Fork-
tailed

76. Storm-Petrel colonies (Quinlan 1979, Boersma et al. 1980).
However,
differences in timing of breeding at Kasatochi coincide with
differences
in spring temperature, with colder spring temperatures in the
central
Aleutian Islands in 2006 than in 2005 (NOAA 2007). Snow
cover can
postpone breeding in seabirds by preventing access to nest sites
(Payne
& Prince 1979) and has been associated with delayed breeding
of Fork-
tailed Storm-Petrels on Buldir Island, Alaska (Byrd & Trapp
1977). If
snow persisted longer during the colder spring of 2006, storm-
petrel
breeding could have been delayed that year.
Compared with other colonies throughout the species’ range,
phenology at Kasatochi appeared to fit a pattern of later nesting
with increasing latitude. Mean hatch dates on Kasatochi (1 July
in
2005, 6 July in 2006) were earlier than at colonies farther north
in
the Barren Islands [peaking 20–23 July (Boersma et al. 1980)]
and
Semidi Islands [mean: 15 July (Hatch & Hatch 1990)], but later
than those to the south in British Columbia [peaking late May–
early
June (Vermeer et al. 1988)] and California [peaking late May
(Harris 1974)].
Reproductive success
Hatching success was high in both years of our study, with only
about 10% egg loss each year. Egg failure in Fork-tailed Storm-

77. Petrels may be biased by investigator disturbance, because
storm-
petrels are especially susceptible to disturbance during
incubation
and prone to egg abandonment (e.g. Marks & Leasure 1992). We
attempted to minimize disturbance by viewing nests by
flashlight
without physically disturbing the nest inhabitants. In addition,
we
did not check nests with incubating adults until just before
hatch,
and we monitored nests every two days only after chicks
hatched,
when egg abandonment was no longer a concern. Given that
rates of
egg failure at Kasatochi were low compared with those at
colonies
in the Gulf of Alaska [16%–30% (Quinlan 1979, Boersma et al.
1980)] and British Columbia [29% (Vermeer et al. 1988)],
where
more invasive sampling occurred, we believe investigator
effects at
Kasatochi to be minimal.
Fledging success varied dramatically between years and
consequently
drove differences in overall reproductive success. Therefore,
factors
affecting chick survival may be most influential in determining
annual nesting success in Fork-tailed Storm-Petrels at
Kasatochi.
Chick mortality occurred consistently when chicks were less
than 20 days old, suggesting that the early nestling period was
most critical in determining chick survival. This pattern of
heavy

78. mortality in young chicks has been similarly documented at
other
Fork-tailed Storm-Petrel colonies (Byrd & Trapp 1977, Boersma
et
al. 1980, Simons 1981) and likely occurs because, as compared
to
larger chicks, smaller chicks have more difficulty
thermoregulating
and withstanding long fasts between meals (Boersma 1986).
This
hypothesis is consistent with evidence that visitation rates were
higher earlier in the nestling period (Drummond 2007), when
chicks
would presumably require more frequent food deliveries.
Inclement weather can influence storm-petrel chick mortality by
flooding nests or preventing parents from returning with food
(Boersma et al. 1980, Boersma & Silva 2001). Weather during
the
breeding season at Kasatochi varied between years, with colder
summer temperatures and more violent storms in 2005 than in
2006 (Drummond 2006, USFWS unpubl. data). Given that chick
survival was lower in 2005 than 2006, it is possible that poorer
weather conditions in 2005 were in part responsible for lower
chick
survival that year. If inclement weather affects breeding success
of
storm-petrels in the Aleutian Islands, potential large-scale
changes
in climate in the Bering Sea (NAST 2000) could have
implications
for future conservation.
Parasitism by fungus beetles (Leiodidae) and predation both
contribute to chick mortality at other Fork-tailed Storm-Petrel
colonies (Wheelwright & Boersma 1979, Quinlan 1983), but we

79. found no evidence of either chick parasites or nest predators
during
our study. Like most of the Aleutian Islands, Kasatochi lacks
naturally-occurring mammalian predators. Arctic Foxes Vulpes
lagopus were introduced to Kasatochi in 1927 and were present
for
several decades, but all foxes were removed in 1985 (Bailey
1993).
Resident Bald Eagles Haliaeetus leucocephalus and Glaucous-
winged Gulls Larus glaucescens occasionally prey on adult
birds
(Drummond & Larned 2007), but have not been observed
accessing
storm-petrel nest sites on the island (B. Drummond pers. obs.).
Given the vulnerability of storm-petrels to predation at the nest
site
(e.g. Warham 1990), the lack of such predators at Kasatochi and
many other colonies in the Aleutian Islands is likely crucial to
the
success of Fork-tailed Storm-Petrel populations.
Finally, food availability may also affect storm-petrel chick
survival, with higher survival in years of greater food supply
(Boersma et al. 1980, Simons 1981). Feeding rates and meal
sizes
often reflect foraging conditions in seabirds and may be used as
indirect measures of food availability during the breeding
season
(e.g. Granadeiro et al. 2000, Suryan et al. 2000). At Kasatochi,
visitation rates and meal sizes were higher in 2006 than in 2005,
suggesting that food availability may have been better in 2006
when
chick survival was higher. However, without direct independent
measures of food supply during our study, it is unclear exactly
how
foraging conditions contributed to chick survival at Kasatochi.