1. The University of Southern Mississippi
AN ANALYSIS OF SEA TURTLE STRANDINGS IN LOUISIANA
by
Jessica L. DeJean
A Thesis
Submitted to the Honors College
of The University of Southern Mississippi
in Partial Fulfillment
of the Requirements for the Degree of
Bachelor of Science
in the Department of Biological Sciences
4. Approved by
________________________________
Patricia M. Biesiot
Associate Professor of Biological Sciences
________________________________
Frank R. Moore, Chair
Department of Biological Sciences
________________________________
David R. Davies, Dean
Honors College
7. LIST OF TABLES
Table Page
1. Shrimp Trawling Season Opening and Closing Dates
A. Zone 1……………………………………………………………………….XX
B. Zone 2…………………………………………………………….…………XX
C. Zone 3………………………....…………………………………………….XX
2. Sea Turtle Strandings……………………………………………………………..…XX
3. Sea Turtle Strandings with Strike Marks……………………………………………XX
4. Chi Square Test of Association
A. All Zones Combined………………………………………………………..XX
B. Zone 1…………………………………………………………………….....XX
C. Zone 2…………………………………………………………………….....XX
D. Zone 3…………………………………………………………………….....XX
8. LIST OF FIGURES
Figure Page
1. Louisiana Shrimp Management Zones………………………………...…………….XX
2. STSSN Stranding Form
A. Front…………………………………………………………………….…..XX
B. Back……………………………………………………………………..…..XX
3. Google Earth Maps of Strandings
A. 2002…………..……………………………………………………………..XX
B. 2003…………..……………………………………………………………..XX
C. 2004…………..……………………………………………………………..XX
D. 2005…………..……………………………………………………………..XX
E. 2006…………..……………………………………………………………..XX
F. 2007…………..……………………………………………………………..XX
G. 2008…………..……………………………………………………………..XX
H. 2009…………..……………………………………………………………..XX
5. Alive and Dead Strandings
A. Alive Strandings…………………………………………………………….XX
B. Dead Strandings…………………………………...…………………...........XX
6. Scatter Plots of Sea Strandings
A. Zone 1…………………………………….…………………………………XX
B. Zone 2……………………………………………………………...………..XX
C. Zone 3…………………………………………………………………….....XX
9. ABSTRACT
The Audubon Aquarium of the Americas (AAOA) in New Orleans has been
collecting and archiving observations about strandings of marine mammals and sea
turtles along the Louisiana coast. For the present study, we collated and mapped the data
for 163 sea turtles (5 different species) archived over the past eight years. Recorded
strandings are concentrated primarily in the Lake Charles area and along Grande Isle and
Grand Terre. The strandings peak around the end of April through the beginning of June
and again at the beginning of October through mid-November. About 23% of the sea
turtles had obvious strike marks. The areas with high stranding concentrations are heavily
used by sport and commercial fishermen. The stranding dates overlap with periods of
warm weather recreational boating and with open fisheries seasons for menhaden and
shrimp. We examined the association between strandings and open fisheries seasons
using a chi-squared test. Most strandings occurred during open menhaden season except
in 2002 and 2007 where most occurred when both menhaden and shrimp seasons were
open. Although there was a statistically significant association between sea turtle
strandings and open fisheries seasons, this does not imply that fishing caused the
observed morbidity and mortality.
10. INTRODUCTION
There are seven identified species of sea turtles, including the leatherback turtle
(Dermochelys coriace), Kemp’s ridley turtle (Lepidochelys kempii), olive ridley turtle
(Lepidochelys olivacea), green turtle (Chelonia mydas), hawksbill turtle (Eretmochelys
imbricate), loggerhead turtle (Caretta caretta), and flatback turtle (Natator depressus)
(Castro and Huber, 2007). With the exception of the flatback turtle, which is found only
in Australia, all other species can be found in the waters of the United States, and five of
these six species are currently found in the Gulf of Mexico (Department of Commerce,
2003). The Endangered Species Act of 1973 classified the Kemp’s ridley, leatherback,
loggerhead, hawksbill and green sea turtles as endangered species. The loggerhead and
the green turtles were also classified as threatened at that time.
Over the past 20 to 25 years sea turtle populations have struggled to exist around
the world (Lewison and Crowder, 2007). Various natural factors contribute to sea turtles
dying daily, but determination of the cause of death can be problematic in the marine
environment (Crowder et al., 1995). When sea turtles start to decompose, their bodies fill
with gases, and they float on the surface of the water (Crowder et al., 1995). Some wash
onto shores (referred to as strandings), but many are broken apart, eaten, and may sink
without ever being seen. The strandings washed onto shores can therefore only account
for a small number of dead and injured turtles in a region. These strandings may provide
evidence of the current human impact on sea turtle populations.
The adverse conditions under which sea turtles live can be quite problematic for
their survival. Humans have impacted sea turtle populations in the past with interference
on beaches, by cleaning, artificial lighting, or sand mining. In addition, oil contamination
11. and other types of pollution in waters inhabited by sea turtles have the potential cause
even more declines in sea turtle populations (Lewison and Crowder, 2007). Incidental
capture by fishing gear has been the focus of sea turtle strandings in the past (Lewison
and Crowder, 2007; Wallace et al., 2008). One of the reasons that incidental capture has
such a negative affect on sea turtle populations is because it has a tendency to cause
higher mortality rates in sea turtles of reproductive maturity, decreasing the number of
possible reproductive offspring in the following generations.
When an organism like a sea turtle is incidentally captured, it is commonly
referred to as bycatch. Bycatch becomes a concern when it involves a threatened species
such as a sea bird, marine mammal or sea turtle (Moore et al., 2009). Many countries
including the United States are currently working to protect the threatened species that
are more susceptible to becoming incidentally captured in fisheries practices. Even if
greater efforts are put into other conservation strategies like nest protection for sea turtles,
the populations will not be able to recover without reduction of their bycatch worldwide
(Zydelis et al., 2009).
Managed by the National Oceanic and Atmosheric Administraiton (NOAA),
fisheries activities in the United States are under surveillance to reduce bycatch of species
in recovery (Moore et al., 2009). Surveillance by actual observers on vessels is one way
that NOAA can monitor the bycatch of threatened species. Under the direction of the
Magnuson-Stevens Fishery Conservation and Management Act (MSA) NOAA Fisheries
is sanctioned to place observers on vessels, however these observers are not required, and
the NOAA’s sanctions cannot control fisheries on the state level. Not only is the state
fishery difficult to control, generally very little funding is allocated to cover the expenses
12. for on vessel observers. According to Moore et al. (2009), this is very problematic
because state fisheries are commonly a source of the bycatch of sea turtles.
Various studies state that evidence of bycatch in fisheries can be seen in the form
of strandings (Lewison et al., 2003; Cox et al., 2007). Strandings in this case are defined
as turtles that have washed up on shores dead (Cox et al., 2007) or at times injured.
Lewison et al. (2003) determined that a study of the reduction of sea turtle bycatch could
be carried out by analyzing frequencies of sea turtle strandings and in turn the
effectiveness of various bycatch reduction devices.
Shrimp fisheries are considered the top contributor in the bycatch and stranding of
sea turtles (Lutz and Musick 1997; Lewison et al, 2003; Cox et al, 2007; Casale et al,
2007). In the Gulf of Mexico, the shrimp fishery is dominated by two species, the white
shrimp, Litopenaeus setiferus, and the brown shrimp, Farfantepenaeus aztecus (LDWF,
2006). The coastline of Louisiana is divided geographically into three separate shrimping
zones (Fig. 1). Each zone has its own opening and closing dates for shrimp seasons that
can be tracked by LDWF. The targeted species of shrimp are caught during the open
season using funnel shaped trawl nets that are pulled through the water by a fishing
vessel in a process called trawling. Observing increases in sea turtle strandings during
shrimp trawling seasons can provide evidence that this human interaction is contributing
to more sea turtle mortality (Lewison et al., 2003; Cox et al., 2007).
During the early 1970s, the first instances of shrimp trawler interactions with sea
turtles were indentified (Crowder et al,. 1995). In 1997 Lutz and Musick stated that the
incidental capture of sea turtles in shrimp trawls has caused more sea turtle deaths than
any other human interaction combined, and it has been estimated by NOAA that 62,000
13. loggerhead turtles and 2,300 leatherback turtles have been killed due to interactions with
shrimp trawls (Department of Commerce, 2003).
Over the past 20 years, over 150 bycatch reduction devices have been tested to
establish one that is consistently reliable (Manjarrés et al., 2008). Turtle excluder devices
(TEDs) are the most common bycatch reduction device in shrimp trawling. In order for a
TED to be approved by the National Marine and Fisheries Service (NMFS), it must be
proven to be at least 97% effective during testing (Department of Commerce, 2003).
Approved TEDs have been implemented in the southeastern United States surrounding
the Gulf of Mexico in an attempt to reduce bycatch (Spotila, 2004), and some have been
quite successful, reducing bycatch numbers by up to 50% (Lewison and Crowder, 2005).
Originally met with high opposition, TEDs requirements were challenged in at least ten
different court cases until passing in 1991 (Lewison, et al., 2003). Even though TEDs
have been highly effective in decreasing in incidental sea turtle mortality (Spotila, 2004);
there is evidence that suggests that after the initial two to three years of decreases in
strandings after 1991, turtle strandings in the Gulf of Mexico began to increase once
again (Lewison et al., 2003). Under the regulations of the National Oceanic and
Atmospheric Administration, shrimp and flounder trawlers operating in the southeastern
United States are now required to use National Marine Fisheries Service (NMFS)
approved TEDs. But even with federal law requiring the use of TEDs and trawls,
Louisiana continues to refuse to enforce the laws and regulations (LDWF, 2006).
The use of these bycatch reduction devices has been most effective in smaller sea
turtles, including the Kemp’s ridley, but the effectiveness of these devices on the larger
sea turtles remains a concern. In recent studies, there is evidence that 33-47 % of
14. stranded loggerheads and 1-7 % of stranded green turtles are too large to fit through
TEDs. In addition, 75 % of the Loggerhead turtles in the Gulf of Mexico are too large to
escape through the openings in the devices (Department of Commerce, 2003).
In other parts of the world, TEDs have proven to be highly effective. Since their
implementation in Australia, turtle bycatch has decreased by at least an estimated 90%
(Department of Commerce, 2003). In a field study by Cox et al. (2007), vessels trawled
next to each other, one with a TED and one without; the use of the TED proved to
decrease the bycatch rate by 97%. This proves that it is possible for TEDs to be highly
effective in the reduction of bycatch. However, shrimp trawl TEDs have little
effectiveness if very low compliance exists in using the devices, especially when on
vessel observers are not present (Moore et al., 2009). When states are unwilling to
enforce federal regulations like Louisiana has in the past, there is very little hope for the
device to work to the best of its ability. After decades of federally required TED use, the
success of the device is still greatly determined by how well and accurately it is used not
how long the requirements have been in place (Lewison et al., 2003). The lack of
compliance with TED use in the Gulf of Mexico is a direct contributor to the high
numbers of strandings (Cox et al, 2007).
Another important fishery in the Gulf of Mexico is the purse-seine fishery of Gulf
menhaden, Brevoortia patronus (Smith et al., 2002; Anderson, 2007; Vaughan et al.,
2007). With a history as far back as the 1800s, menhaden fishing is today of the most
valuable fisheries in the United States with the largest tonnage (Vaughan et al., 2007).
Since 1995 when most commercial fishing equipment was banned in Florida (Vaughan et
al., 2007), Louisiana has been the leader in the menhaden industry (Smith et al., 2002).
15. Louisiana is currently responsible for 92% of the menhaden catch annually (Vaughan et
al, 2007).
Menhaden fishing involves the use of two boast and a purse seine net to catch
entire schools of menhaden at a one time (de Silva and Condrey, 1997; Rester and
Condrey, 1999; VanderKooy and Smith, 2002). Once a school of menhaden is spotted,
the two boats encircle it with the net. The net is pulled closed and the contents are
brought on board the mother ship. A flexible hose is used to pump the catch into the
refrigerated hold. This entire process usually lasts no longer than one hour. Though
bycatch numbers are much lower for the menhaden industry compared to shrimp
trawling, the bycatch of large fishes and sharks in these devices is still seen as a major
issue.
As far back as the 1950s, efforts have been made by menhaden fisheries to reduce
incidental bycatch (Rester and Condrey, 1999). Two types of bycatch reduction devices
have been established and are commonly used: hose cages and large fish excluders. Hose
cages are used to prevent larger fishes from getting pumped into the refrigerated hold on
deck and large fish excluders are made of thick bars, also preventing larger fishes from
passing into the holds. In a study by Rester and Condrey (1999) it was determined that
the hose cages needed substantial improvements in order to work effectively as bycatch
excluder devices. The cages allowed the passage of menhaden as well as the fins, heads,
and tails of larger fishes. Less than 28% of the bycatch that encountered the menhaden
fishery survived in the observations. Through the observations of Rester and Condrey
(1999), it was determined that the best way to decrease the mortality of the bycatch is to
make alterations to the hose cages.
16. Another study of bycatch in the menhaden fishery by de Silva and Condrey
(1998), determined that the best way to eliminate bycatch of different species was to
pinpoint what they referred to as “hot spots” in the Gulf of Mexico. These spots included
the waters east of the Mississippi River from April to August. In these areas during these
few months, large numbers of incidental catches of fin fishes, shrimp and sharks were
found in purse-seine nets. De Silva and Condrey (1998) also determined that one of the
best ways to decrease the mortality of the bycatch was to make modifications to the
purse-seine nets.
Though there is no record of sea turtle capture in purse-seine nets thus far, sea
turtles have recently been capture incidentally in gillnets (Carretta et al, 2003). Over
seven years, 132 sea turtles were captured as bycatch in the gillnets that are very similar
to the nets used in purse-seine fisheries like menhaden. Entanglement and drowning in
these nets is the generally what leads to sea turtle mortality, and with no current standards
for bycatch reduction set in the menhaden fishery bycatch of various large species is
inevitable (Rester and Condrey, 1999).
The conservation effort of sea turtles is problematic because it interferes with a
market of high economic value. Fishermen profits can be compromised in the effort to
save a species that they do not find essential to their business. Increases in the
convenience of these devices and possibly some economic benefit could encourage more
fishers to become more accepting of safer materials and practices (Gilman et al., 2006).
Various other coutries have set up incentive programs for their citizens in order to protect
endangered sea turtle (Ferraro and Gjertsen, 2009). These simple and inexpensive
payments to the environmentally conscious have already begun to show increases in the
17. success of juvenile and adult sea turtles. Cox et al. (2007) suggested that TED use for
reduction of bycatch to targeted levels simply will not occur until some sort of incentive
program is established. By implementing small yet effective techniques to decrease sea
turtle bycatch, improvements in survival among sea turtle populations can be made in the
Gulf of Mexico.
MATERIALS AND METHODS
Records of sea turtle strandings in Louisiana from 2002-2009 were reported to the
AAOA. The observer of each stranding filled out a document (Fig. 2) produced by the
Sea Turtle Stranding and Salvage Network (STSSN). The form included the observer’s
name, address, and phone number. The details of each stranding included but were not
limited to date found, number found (if more than one found in one day), species and sex
(if identifiable), condition (i.e. level of decomposition), and geographic location. The
observer made notes on the final state of the carcass (buried, painted, etc.) to insure the
stranding would not be surveyed more than once. Details of injury could also be noted
on an included diagram. Many of these forms were complete and detailed, but others
included only basic information. When possible, photographs were taken and sent via
email. Some species were recorded as unidentified under specific conditions. Some sea
turtles were not complete specimens due to decomposition. In some, only a small portion
of the turtle was found and could not be properly identified. Some sea turtles were found
and referred to “hybrids.” These sea turtles displayed recognition characteristics for
more than one species and could not be properly placed into one species category.
However, these strandings cannot be technically classified as hybrids without proper
DNA analysis (James et al., 2004). Many stranding reports noted instances of obvious
18. boat strikes and propeller marks that were later noted. Few observers included
measurements, and tagging information was usually not available. The documents were
either faxed or emailed to AAOA.
The eight years of sea turtle strandings were collated and entered into Excel
spreadsheets, noting the details of each stranding. The geographic coordinates were also
plotted on maps using Google Earth in order to pin point their location along the
Louisiana coastline. The strandings were categorized by the week of the year that they
occurred.
The Louisiana Department of Wildlife and Fisheries (LDWF) was consulted
regarding the dates for the opening and closing of shrimp seasons each year. The zoning
for shrimp trawling was geographically defined, and the individual strandings were
located within one of the three shrimp trawling zones (Fig. 1). The opening and closing
dates were recorded for each of the three zones set by LDWF (Table 1). The opening and
closing dates were also defined by the week of the year that they occurred. The opening
and closing dates for menhaden fishing season were also obtained from LDWF. The
menhaden dates were also defined by the weeks of the year that they occurred.
My null hypothesis for this study was that open shrimp and menhaden fishing
seasons have no effect on the frequency of sea turtle strandings in Louisiana. A chi
square test of association was performed for the stranding data.
RESULTS
The sea turtle strandings in Louisiana from 2002-2009 included 163 turtles as
follows: 102 Kemp’s ridleys, 27 loggerheads, 20 unidentified, 8 green sea turtles, 4
leatherback sea turtles, and 2 hawksbill sea turtles (Table 2). Strandings were
19. concentrated in Lake Charles (Zone 3) and Grand Isle/Grand Terre (Zone 2) (Fig. 3). On
average, 87.8% of stranding in all zones between 2002 and 2009 involved dead rather
than live sea turtles (Fig. 4).
After the strandings were divided by zone, each was plotted on a scatter plot by
week they occurred during the year (Fig. 5). The weeks of open shrimp season only, open
menhaden season only, and both open shrimp and menhaden fishing seasons were
indicated by shading present in figure 5. Most strandings occurred during open
menhaden season except in 2002 and 2007 where most occurred when both menhaden
and shrimp seasons were open. The strandings peak around the end of April through the
beginning of June and again at the beginning of October through mid-November. About
23% of the sea turtles had obvious strike marks (Table 3) from what was assumed to be
boats and boat propellers.
The chi square test of association demonstrated a positive association between
open fishing seasons and the frequency of sea turtle strandings in Louisiana (Table 4).
The null hypothesis was rejected, and it was determined that open shrimp and menhaden
fishing season have an effect on the frequency of sea turtle strandings in Louisiana.
DISCUSSION
In the present study, it was determined that sea turtle strandings in Louisiana were
influenced by the shrimp and menhaden seasons. The strandings seemed to be
concentrated in two main areas: the Lake Charles area and Grand Isle/Grand Terre.
These areas are heavily used by sport and commercial fishermen. If the strandings were
fairly evenly dispersed then it could be assumed that the chance of incidental bycatch is
evenly spread over Louisiana waters. However, this clustering suggests that sea turtle
20. bycatch is more likely to be encountered in these particular fishing areas (Lewison et al.,
2009).
The stranding dates frequently seen in the data overlap with periods of warm
weather recreational boating and with open fisheries seasons for menhaden and shrimp.
However, the impact of recreation boating on sea turtle strandings was not reviewed in
this study. It is possible that many of the propeller marks on stranded turtles occurred
from these types of activities.
Although there was a statistically significant association between sea turtle
strandings and open fisheries seasons, this does not imply that all sea turtle strandings
were caused by shrimp trawling and menhaden fishing. There are many other factors that
could have influenced the sea turtle strandings throughout the eight years in this study.
Many other human interactions have caused sea turtle mortality in the past, and it is
possible that any of these could have been the cause of some of the strandings. It is also
possible that some of the strandings could have died of natural causes and then washed
up on the Louisiana shores.
All factors must be considered when determining the cause of sea turtle
strandings. While taking all of these factors into consideration, the results of this study
still agree with various prior studies, stating that there are obvious patterns between sea
turtle strandings and trawling fisheries (Crowder et al., 1995; TEWG, 2000; Lewison et
al., 2003). However, necropsies of the strandings were never taken, eliminating almost
all possibility of determining the cause of death.
21. SUMMARY
The strandings in this study were concentrated Lake Charles (Zone 3) and Grand
Isle/Grand Terre (Zone 2). Both are major areas for commercial and recreational fishing
as well as for recreational boating activities. On average, 87.8% of stranding between
2002 and 2009 involved dead rather than live sea turtles. The chi square test
demonstrated a positive association between open fishing seasons and the frequency of
sea turtle strandings in Louisiana. However, we did not investigate the impact of
recreational fishing and boating on strandings. Other factors that may have contributed to
sea turtle strandings are seasonal migrations between feeding areas and spawning areas as
well as migrations based on water temperature changes (Crowder et al., 1995).
There is always room for improvement in the reduction of incidental bycatch in
sea turtles, but as long as budgetary and organizational constraints are affecting fisheries
practices, sea turtles will continue to strand (Moore et al., 2009). Without Louisiana’s
enforcement of federal TED laws, sea turtle strandings will continue in Louisiana.
22. ACKNOWLEGEDMENTS
First and foremost, special thanks go to Dr. Patricia Biesiot for her assistance
throughout the development of this study. Thank you to the Audubon Aquarium of the
Americas and stranding coordinator, Michele Kelley for access to the data used. Special
thanks for their help and expertise go to Paul Cook, Mandy Courville and Keith Ibos at
the Louisiana Department of Wildlife and Fisheries for their assistance with dates of the
shrimp fishing season. Also, thanks to Joseph Smith at the National Oceanic and
Atmostpheric Administration for his help regarding the menhaden fishing industry.
Thank you to Dr. Carl Qualls at The University of Southern Mississippi for his assistance
in statistical analysis of this study.
I would also like to thank the USM Department of Biological Sciences and USM
Honors College for their financial support of this study.
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