Evidence of increased occurrence of Atlantic bluefin tuna in territorial waters of the United Kingdom and Ireland

Thomas W Horton,Hannah Jones,Lucy A Hawkes,Duncan Jones,David Righton,Dave Wall,Matthew J Witt,Barbara A Block,Keith Leeves,Jeroen Van Der Kooij,Rachel Davies,Niall Ó Maoiléidigh,David M Kaplan

doi:10.1093/icesjms/fsab039

Abstract

Abstract Atlantic bluefin tuna (ABT, Thunnus thynnus; Linneaus, 1758) is an ecologically important apex-predator with high commercial value. They were once common off the coast of the United Kingdom (UK), before disappearing in the 1960s. In regions lacking commercial fisheries for ABT, such as the UK and Ireland, spatial data can be scarce. In these cases, sightings and bycatch databases can offset information shortfalls. Here, we document the reappearance of ABT into territorial waters of the UK from 2014 onwards, and increased occurrence off Ireland. We analyse a novel, multi-source dataset comprising occurrence data (2008–2019; 989 sightings and 114 tonnes of bycatch) compiled from a range of sources (scientific surveys, ecotours and fisheries). We show an increasing trend in effort-corrected ABT occurrence in (i) the pelagic ecosystem survey in the western English Channel and Celtic Sea (PELTIC), (ii) an ecotour operator, and (iii) the Irish albacore fishery in on-shelf and off-shelf waters. Sightings of ABT by the PELTIC correlated with modelled abundance estimates of ABT and the Atlantic multidecadal oscillation. These data demonstrate that sightings of ABT have increased off the UK and Ireland since 2014, following the same increasing trend (2010 onwards) as the eastern ABT population.

Highlights

The distributions of migratory species are temporally dynamic, driven by complex dispersal behaviours that reflect variations in the environment (Faillettaz et al, 2019), prey availability (Tiews, 1978), predation risk (Hammerschlag et al, 2010), anthropogenic pressure (Nowacek et al, 2015), and ontogenetic development (De Grissac et al, 2016; Votier et al, 2017)
The observations we present suggest a change in ABT distribution in the northeast Atlantic in recent years, with ABT foraging in territorial waters of the United Kingdom (UK)
Our results suggest an ontogenetic difference in distribution, with larger year classes further North in the waters off Ireland, highlighting the complex nature of ABT dispersal dynamics

Summary

Introduction

The distributions of migratory species are temporally dynamic, driven by complex dispersal behaviours that reflect variations in the environment (Faillettaz et al, 2019), prey availability (Tiews, 1978), predation risk (Hammerschlag et al, 2010), anthropogenic pressure (Nowacek et al, 2015), and ontogenetic development (De Grissac et al, 2016; Votier et al, 2017). Understanding the role of fishing, environment and, concomitantly, population dynamics on the spatio-temporal distribution of ABT has been a key research goal in recent decades. Takeuchi et al, 2009) fisheries detail large fluctuations in ABT abundance over time, driven by fishing pressure (Fromentin et al, 2014) and the environment (Faillettaz et al, 2019). The increased use of electronic tracking tags has added enormously to the understanding of ABT space use (Block et al, 2005; Galuardi et al, 2010; Cermen~o et al, 2015; Arregui et al, 2018) and, in turn, helped inform management and conservation policy (Block et al 2005)

Methods

Results

Discussion

Conclusion