DOI: 10.5061/dryad.z34tmpg8c
title: Drivers of spatiotemporal variability in bycatch of a top marine predator: First evidence for the role of water turbidity in protected species bycatch

description: 1. Bycatch of protected species in static net fisheries is a global
 conservation concern and is currently considered the dominant
 anthropogenic threat to many marine mammal species worldwide. Effective
 bycatch mitigation remains challenging, contingent on an understanding of
 the underlying mechanisms that cause individuals to become entangled. 2.
 We combined data collected by scientific observers and fishers to identify
 predictors of seal bycatch in static net fisheries along the west,
 southwest, and south coasts of Ireland. We first analysed the broad
 regional and seasonal trends in seal bycatch before identifying
 environmental variables that could potentially explain these patterns. 3.
 Based on negative binomial generalised linear mixed effects models, the
 rate of seal bycatch significantly varied with season and region, and
 decreased at greater distances to major seal colonies and lower water
 turbidity. 4. Synthesis and applications. Our results suggest that
 distance to major seal colonies was a significant driver of the observed
 regional differences in seal bycatch rates, and water turbidity a major
 driver of seasonal trends. These findings will enable us to identify
 future bycatch risk and target mitigation measures accordingly. This is
 the first study to identify the effect of water turbidity on bycatch of a
 protected marine species. Increasing net visibility in turbid waters may
 provide a novel approach to mitigating against protected species bycatch
 in static net fisheries.05-Nov-2019
description: Field descriptors: vessel_id
 - unique identifier for each fishing vessel net_type
 - one of four entangling net types (see paper for more detailed
 description): gill - gillnets
 tangle - tangle nets trammel - trammel
 nets spider - spider nets (large mesh tangle
 nets) year - year data was
 recorded effort_km - net length in km
 soak_days - number of days the net has been left to soak in the
 water unattended effort_soak_km - fishing effort as
 the product of effort_km and soak_days depth - depth
 of the seafloor where the nets were set mesh_size_cm
 - mesh size of the nets in cm. Note for tangle nets this refers to the
 mesh size of the central net wall seal_byc - was a
 seal caught in the net: TRUE - seal
 bycatch FALSE - no seal bycatch
 seals - number of seals caught in
 net dist_colony_km - distance to nearest major grey
 seal colony in km colony_size - minimum estimate for
 number of breeding seals at nearest major grey seal colony (see paper for
 sources) colony_size_prop - approximate proportion of
 national population at nearest major grey seal colony. colony_size divided
 by the sum of colony sizes at all major grey seal colonies
 dist_colony_s_pop_size - distance to nearest major grey seal
 colony, inversely weighted by the population size. dist_colony_km divided
 by colony_size_prop sdd - Secchi disc depth in m,
 used as a measure of water turbidity (see paper for details)
 spue - rate of seal bycatch in seals per unit effort.
 seals/effort_soak_km season - season data was
 collected: 1 - spring (Mar - May)
 2 - summer (Jun - Aug) 3 - autumn (Sep -
 Nov) 4 - winter (Dec - Feb) 
 Note: To protect the anonymity of fishers
 participating in this study and the commercial sensitivity of the data
 shared, gps locations of observations and the regions in which they were
 collected have been excluded from these data. Please contact the authors
 for more information.