villegas-ríos at the 2nd icft south africa
TRANSCRIPT
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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
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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 1:391-4052 Pauly D, Hilborn R, Branch TA (2013) Nature 494:303-306
INTRODUCTION
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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: 175-1904 Olsen et al. (2012). Ecology and Evolution, 2(7): 1549-15625 Rudstam (1984). CJFAS, 41(8): 1252-1255
INTRODUCTION
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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
INTRODUCTION
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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
6 Villegas-Ríos et al. (2013). PhD Thesis7 Villegas-Ríos et al. (2013). Journal of Sea Research, 80:61-71
INTRODUCTION
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Relate environmental cues, physiological state, fish behaviour and catchability in a marine costal fish (Labrus bergylta)
HypothesesH1: 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
INTRODUCTION
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Receiver array Twelve receivers (VR2W) Complete overlap in the study area Fixed in sandy bottom with auger anchors September 2011- September 2012
360º
MATERIAL AND METHODS
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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 mm6 g Ø= 9 mm2.9 g
MATERIAL AND METHODS
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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
MATERIAL AND METHODS
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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
MATERIAL AND METHODS
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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
MATERIAL AND METHODS
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ModelTemperature
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
MATERIAL AND METHODS
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Results Significant sinusoidal
cycle in all cases except the home range size
Distance travelled influenced by fish size
RESULTS AND DISCUSSION
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Results216.5
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
RESULTS AND DISCUSSION
reproduction
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Results216.5
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
temperature
feeding
RESULTS AND DISCUSSION
reproduction
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Results216.5
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
activity
temperature
reproduction
feeding
RESULTS AND DISCUSSION
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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
RESULTS AND DISCUSSION
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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.
RESULTS AND DISCUSSION