Gannets are not attracted to fishing vessels in Iceland—potential influence of a discard ban and food availability

Stephen C Votier,Freydís Vigfúsdóttir,Thomas W Bodey,Julian M Burgos,Mark J Jessopp,Bethany L Clark,Kees Camphuysen

doi:10.1093/icesjms/fsz233

Abstract

Abstract Fisheries produce large amounts of waste, providing food subsidies for scavengers. Discards influence seabird movement, demography and community structure, but little is known about seabird–fishery interactions where discarding is banned. Here, we investigate how northern gannets Morus bassanus respond to fishing vessels in Iceland, where discarding commercial species is illegal, but birds may still access bait, offal, or catch. We GPS-tracked 82 foraging trips for 36 breeding gannets from two colonies (Skrúður and Hellisey) and obtained time-matched vessel locations. We classified bird behaviour using Hidden Markov Models and then tested the effect of vessel distance on behavioural state-switching using multi-state Markov models. Fishing vessels were present during 94% of foraging trips. However, the likelihood of gannets switching from travelling to foraging was unaffected by vessel proximity, regardless of gear type or activity. When encountering vessels, gannets rarely foraged but instead were more likely to continue travelling. When controlling for population size, gannet foraging trips at both colonies were shorter than expected, suggesting favourable conditions. The lack of behavioural responses to vessels among Icelandic gannets is likely driven by the discard ban and availability of pelagic fishes. Our findings have implications for understanding bycatch risk and the consequences of discard reforms.

Highlights

Fisheries provide food subsidies in the form of discards, attracting large numbers of scavengers (Oro et al, 2013)
While reducing discards is key for a sustainable fishing industry, this may considerably impact the large numbers of scavenging individuals (Bicknell et al, 2013)
To quantify behavioural responses to nearby vessels, we investigated the effect of vessel distance on the probability of switching from travelling to foraging behaviour

Summary

Introduction

Fisheries provide food subsidies in the form of discards, attracting large numbers of scavengers (Oro et al, 2013). Seabirds are one of the most conspicuous consumers of fisheries waste (Sherley et al, 2019), with at least 52% of seabird species eating discards (Oro et al, 2013). While reducing discards is key for a sustainable fishing industry, this may considerably impact the large numbers of scavenging individuals (Bicknell et al, 2013). Many birds that feed at vessels are killed as bycatch (Lewison et al, 2004) and reducing discarding may in turn reduce mortality. Subsidies from fishing vessels affect seabird diet (Votier et al, 2004), movement patterns (Bodey et al, 2014), population As a result, understanding the consequences of variation in discard availability is valuable for the study of marine ecology, as well as for ecosystem approaches to fisheries management (Zeller et al, 2018).

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Conclusion