Improving understanding of seabird bycatch in Scottish longline fisheries and exploring potential solutions

Introduction

The Scottish Government is committed to providing a clean, healthy, safe, productive and biologically diverse marine environment that meets the long-term needs of people and nature by managing Scottish waters sustainably to protect biological diversity and to ensure that marine ecosystems continue to provide economic, social and wider benefits for people, industry and society. The Marine Scotland 2018-2019 Programme for Government committed to identify actions to address the significant declines in seabird populations through a new Scottish Seabird Conservation Strategy (SSCS). The developing SSCS highlights the vulnerability of seabird species to a range of human pressures, including incidental bycatch in fisheries. Consequently, estimating bycatch levels and understanding the possible effects of bycatch mortality on seabird populations (and reducing it where necessary) forms a fundamental element in supporting the Scottish Government’s long-term environmental ambitions.

Under the UK Fisheries Act (2020), the ecosystem objective calls for any incidental catches of sensitive species to be minimised and, where possible, eliminated. Sensitive species are defined under the Act and includes those species listed under Annex II or IV of Directive 92/43/EEC (‘The Habitats Directive’), any other species of animal or plant, other than a species of fish, whose habitat, distribution, population size or population condition is adversely affected by pressures arising from fishing or other human activities, and any species of bird.

Scotland’s Fisheries Management Strategy (2020-2030) also includes an ‘International Commitment’ to monitor and reduce incidental bycatch, including bycatch of marine mammals and birds. The Strategy also embraces an ecosystem-based approach to fisheries, with a focus on “conservation of vulnerable and protected species, for example, by limiting unwanted bycatch and encouraging proper handling practices when returning protected species to the sea”. Furthermore, and of relevance to this project, the Strategy calls for management decisions which make the most of fishers’ knowledge: “We want to listen to our fishers and the experience and knowledge they have about the marine environment, using this knowledge to add to the richness of our overall understanding”.

In 2020, data collected by onboard observers from the UK Bycatch Monitoring Programme (BMP) were used to produce the first broadscale UK seabird bycatch estimates for net, midwater trawl and longline fisheries (Northridge et al. 2020). This work highlighted a few fisheries where bycatch rates of seabirds appeared to be relatively high, though the results were highly caveated regarding the small sample sizes from some fisheries metiers and the likelihood that sampling data may be biased for a variety of reasons, including uneven spatial and seasonal coverage. One of the fisheries that appeared to have relatively high bycatch rates was the UK offshore longline fishery that mainly targets European hake (Merluccius merluccius) primarily along the continental shelf break in ICES Subareas 4,6,7. The fishery is currently prosecuted by about 14 UK registered vessels, as well as vessels from some EU member states.

Using available data collected between 2010 and 2018 it was initially estimated that bycatch in the UK offshore longline fishery was likely to be in the region of 4,500 seabirds per year (Northridge et al. 2020). However, confidence intervals around the estimates were wide and the estimates were based on a small sample size of just 14 sampled trips. Furthermore, there may be biases in the data as the sampled trips were spread out over a nine-year period and therefore might not have been representative of the fleet activity in the two years (2016 and 2017) for which the estimates were produced. Most of the recorded bycatch in the fishery was of northern fulmar (Fulmarus glacialis), a species which has shown a shallow decline in numbers at nesting sites in Scotland since the mid-1990s. Although the drivers of this decline are not known in detail, they are thought most likely to be due to a decline in the North Sea whitefish industry and a corresponding reduction in the amount of offal discharged from fishing vessels, which provides an important food source for this species (JNCC 2020).

Following the publication of the Northridge et al. (2020) report, the fishery came under increased attention from some conservation groups. However, well before those preliminary estimates were published, one of the two main industry bodies that represent vessels in the UK longline fleet had already expressed a wish to explore mitigation measures in the fishery to reduce seabird bycatch, and informal discussions about possible mitigation approaches had already begun.

To improve understanding of bycatch in the fishery following the publication of the Northridge et al. (2020) report, and to inform future discussions and possible actions related to bycatch and its potential mitigation in the fishery, the Scottish Government funded this project which specifically focussed on the hake longline fishery and included a broad range of objectives that were addressed using qualitative and quantitative approaches. New data analyses were undertaken, and possible bycatch mitigation approaches were explored by collating relevant information from the wider literature and through discourse with industry and other researchers working on seabird bycatch in similar fisheries.

The report is divided into six sections covering the main project objectives.

The first section provides a literature review of relevant studies on fulmar bycatch and mitigation globally, with the aims of identifying risk factors that may be associated with fulmar bycatch and describing seabird bycatch mitigation measures that have been tested or are used in other demersal longline fisheries around the world.

Using data collected in the UK longline fishery between 2010 and 2021, the second section explores what factors may be linked to seabird bycatch rates in the fishery through statistical modelling approaches to try and identify when, where and in what circumstances seabird bycatch is most likely to occur in the fishery. An assessment of the spatial and temporal sampling coverage was also undertaken to explore the representativeness of existing sampling data.

The third section provides updated bycatch estimates for the longline fishery using additional observer data that has doubled the number of observed hauls since the Northridge et al. (2020) estimates were produced.

The fourth section describes efforts to recover bycaught seabirds from the fishery for later necropsy.

The fifth section summarises the detailed notes collected by the observer during data collection activities in the fishery, and describes work carried out to gain a better understanding of bycatch in the fishery, and the drivers for and willingness to address bycatch directly from skippers involved in the fishery.

The final section draws together the findings in a general discussion on the strengths and weaknesses of the data, highlights improvements in data collection/analysis and indicates some initial candidate mitigation measures for testing based on the literature review, existing sampling data and direct input from vessel skippers.

It should be noted that the work has been constrained by the global Covid-19 pandemic which has resulted in less onboard sampling than projected and limited potential for face-to-face engagement with skippers in Spain. Thus, some parts of the planned work have been constrained and these are described in the report.