This document summarizes a study on the seasonal patterns of behavior and catchability of the fish species Labrus bergylta. The study found that (1) there was a significant seasonal cycle in sea surface temperature, reproductive activity, feeding activity, and catchability, (2) higher activity and catchability occurred in summer when the fish were feeding more, and (3) lower activity and catchability occurred in winter when the fish were reproducing less. These seasonal patterns in behavior influence the vulnerability of the fish and have implications for how catchability is modeled in stock assessments.

1. Seasonal patterns of behaviour of a temperate coastal
fish: drivers and implications for vulnerability
David Villegas-Ríos, J. Alós, M. Palmer, R. Bañón, S. Barbieri,
A. Alonso-Fernández, F. Saborido-Rey
Grahamstown, 15th July 2013
1

2.  If catches represent fish abundance is an
old question1,2
 CPUE=q·N
 Catchability:
 Probability of a single fish to be caught
by a defined unit of fishing effort
 Often considered constant in stock
assessment
 Affected by a number of variables , e.g.
fish behaviour:
 Migrations
 Spawning aggregations
 Fish personality (boldness, activity)
 …
Background
1 Cooke JG, Beddington JR (1984). Math Med Biol 1:391-405
2 Pauly D, Hilborn R, Branch TA (2013) Nature 494:303-306 2
INTRODUCTION

3.  Relationship between environment (T)
and catchability (e.g. lobster3)
 Relationship between environment and
activity
 Relationship between activity and
catchability with telemetry (e.g.: cod4)
 The probability of catching a fish with
passive gears depends on (1) the
probability of the fish encountering
the gear and the (2) probability of being
trapped in it5
 In passive gears, fish behaviour is
important
Background
Catchability of lobster in Tasmania
(Ziegler et al., 2004)
3 Ziegler et al. (2004). Marine Biology, 145: 175-190
4 Olsen et al. (2012). Ecology and Evolution, 2(7): 1549-1562
5 Rudstam (1984). CJFAS, 41(8): 1252-1255
3
INTRODUCTION

4.  Many harvested nearshore fish species are
sedentary and move within a small home
range
 Many of them are fished in coastal areas
with passive gears (hook and line, gillnets,
traps…)
 In temperate environments, those fish are
subject to seasonal environmental cues
that may determine seasonal patterns in
the physiological state (feeding,
reproduction)
 More evident in capital breeders with
determinate fecundity
Background
Serranus cabrilla
Serranus scriba
Diplodus sargus
4
INTRODUCTION

5. Labrus bergylta
 NE Atlantic, Mediterranean
 Commercial and recreational interest
 Fished with gillnets (95%)6
 Sedentary species, small home range
(~0.1 km2)7
 High residency and site fidelity 7
 Diel behaviour, more active during
daytime 7
 Capital breeder, determinate fecundity 6
 Feeding in summer, reproduction in
winter 6
5
6 Villegas-Ríos et al. (2013). PhD Thesis
7 Villegas-Ríos et al. (2013). Journal of Sea Research, 80:61-71
INTRODUCTION

6.  Relate environmental cues, physiological state, fish behaviour and
catchability in a marine costal fish (Labrus bergylta)
Hypotheses
 H1: The existence of a seasonality in the environmental cues
determines physiological variations over the year which in turn
influence the behavioural pattern
 H2: The existence of a seasonal pattern of behaviour should
determine a pattern of fish catchability with passive gears
Objective
6
INTRODUCTION

7. Receiver array
 Twelve receivers (VR2W)
 Complete overlap in the study area
 Fixed in sandy bottom with auger anchors
 September 2011- September 2012
360º
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MATERIAL AND METHODS

8. V13
V9
Fish tagging
 Hook and line and night diving
 25 individuals
 Surgery
 Residence index (DD/TP) in the
study area during the duration of the
experiment=0.99
Ø= 13 mm
6 g
Ø= 9 mm
2.9 g
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MATERIAL AND METHODS

9. Behavioural variables
 Centers of activity (COAS) at 30 min time bins
 Home range based on Kernel utilization distributions
 Distance travelled: distance between consecutive centers of activity
 Estimated for 10d periods to reduce the inherent variability of the data
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MATERIAL AND METHODS

10. Additional sampling
 Sea surface temperature (2 yr):
oceanographic buoy
 Biological sampling (2 yr)
 Reproductive activity: gonads from
1529 individuals collected in the local
fish markets. Reproductive state
(spawning vs. Non-spawning) based
on GSI and maturity ogive
 Feeding activity: gut weight from 570
individuals. F=stomach weight/gutted
weight
 Catchability (10 yr): artisanal fishing data
from a monitoring program (>800 hauls)
by scientists. Abundance index from UVC
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MATERIAL AND METHODS

11.  Simple approach!
 Variables
 Drivers: temperature, reproductive activity and feeding activity
 Behaviour: home range size and distance travelled (activity)
 Catchability
 Difficult to assess cause-effect relationships from observational data
 Our strategy: to estimate and compare the phase (φ) of each variable
individually fitted to a sinusoidal function (julian day)
 Assumed sinusoidal cycle if β1 or β2 ≠ 0
Model
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MATERIAL AND METHODS

12. Model
Temperature
 Temporal autocorrelation term
Home range size and distance travelled
 Temporal autocorrelation term
 Fish as random factor (mixed-model)
 Fish size as a continuous variable (β3)
Catchability
 Offset: panel lenght and haul time
12
MATERIAL AND METHODS

13. Results
 Significant sinusoidal cycle in
all cases except the home
range size
 Distance travelled influenced
by fish size
13
RESULTS AND DISCUSSION

14. Results
216.5
232.4
214.0
 Significant sinusoidal cycle in
all cases except the home
range size
 Distance travelled influenced
by fish size
 Clear relationship between sea
surface temperature and
physiological state
temperature
feeding
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RESULTS AND DISCUSSION
reproduction

15. Results
216.5
232.4
214.0
176.0
 Significant sinusoidal cycle in
all cases except the home
range size
 Distance travelled influenced
by fish size
 Clear relationship between sea
surface temperature and
physiological state
 Relationship between
physiological state and activity activity
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temperature
feeding
RESULTS AND DISCUSSION
reproduction

16. Results
216.5
232.4
214.0
176.0
173.8
 Significant sinusoidal cycle in
all cases except the home
range size
 Distance travelled influenced
by fish size
 Clear relationship between sea
surface temperature and
physiological state
 Relationship between
physiological state and activity
 Clear relationship between
activity and catchability
catchability
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activity
temperature
reproduction
feeding
RESULTS AND DISCUSSION

17. Conclusions
 We used a simplistic approach that facilitated the interpretation of
the results
 Forced the variables to a lag of 6 months between maximum and
minimum
 There is an alternation between:
 a predominantly reproductive state with low activity in winter
and
 a predominantly feeding state of high activity when catchability
is higher in summer
17
RESULTS AND DISCUSSION

18. Conclusions
 The pattern of behaviour determines the pattern of catchability and
thus vulnerability, in agreement with other theoretical (Alós et al.,
2012) or experimental results (Biro and Post, 2008)
 Implications for stock assessment since catchability decouples
catches and abundance (temporal variation) and should be
considered in stock assessment models
 Highlights the need to study fish behaviour in coastal sedentary
fish, not only in migratory or highly-mobile species.
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RESULTS AND DISCUSSION

19. Thanks!
villegas@iim.csic.es
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