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

Section 6: General Discussion

The work undertaken during this project has improved our overall understanding of the complexities of bycatch in the hake longline fishery and has highlighted useful improvements to data collection procedures and sampling designs which will continue to enhance our knowledge of the factors that lead to bycatch in the fishery and its possible effects on affected seabird populations.

Factors influencing bycatch rates: The modelling exercise to explore what environmental or operational factors might influence bycatch rates was largely inconclusive, though this is not surprising given the limited amount of data on which the analysis was based. Analyses of much larger datasets in Alaska (Melvin et al.2019) and Norway (Fangel et al.2017) also failed to find clear links between northern fulmar bycatch rates and specific operational or behavioural factors, which alongside the current analysis, the notes collated by the observer (that consolidated his and some skipper’s observations and insights) and the questionnaire responses from skippers, serves to highlight the complexity and high variability of seabird, and particularly northern fulmar, bycatch in the hake fishery and is in line with the general findings from other similar northern hemisphere demersal longline fisheries.

Bycatch estimates: Based on the analytical approach used, which was largely determined by the limited amount of data available, overall bycatch in the fishery is estimated to have increased over the last two decades as total fishing effort in the fishery increased over that period. However, the latest modelled estimates produced within this project are considerably lower than the preliminary estimates presented in Northridge et al.(2020). The modelling approach undertaken within this project was a more sophisticated analysis that considered potential seasonality in bycatch rates (which was not incorporated in the preliminary estimates) and used additional data collected since 2018 that almost doubled the available data. Therefore, the modelled estimates presented here are considered to be more reliable than the Northridge et al.(2020) estimates, and should supersede the earlier estimates in future discussions about the possible impact of the hake fishery on seabird populations. Nevertheless, the data from which these latest estimates are derived are likely to be spatially and temporally biased and overall data levels remain low, so uncertainty around the true level of bycatch in the fishery remains high. Further data collection efforts, and where possible designed to address existing biases, will help to improve the accuracy of future estimates. Sampling levels in the fishery are currently quite low and may be insufficient to elucidate inter-annual trends in bycatch rates, but there is no obvious signal in the data of changes in rates over the last decade, and information provided by skippers through the questionnaires does not suggest any clear trend either, so it is likely that the increase in overall mortality is driven by an increase in the number of vessels participating in the fishery rather than operational or behavioural changes that may have increased underlying bycatch rates.

Seabird samples: One of the major gaps in the current understanding of the potential population level implications of bycatch is a lack of information about the population affinity of affected birds. Baetscher et al.(2022) used genetic stock identification techniques to assign bycaught northern fulmars to regional breeding colonies based on over one thousand sampled individuals and found large differences in the susceptibility of different colonies to bycatch that was driven mainly by differences in the summer foraging areas used by different colonies. This research has shown that with close industry collaboration it is possible to collect whole bycaught individuals from the hake fishery and return them to shore within existing monitoring efforts. If sufficient samples are obtained, and funds are available for genetic analysis, a similar approach could be attempted in the UK which would be an important step in understanding the possible population level impacts of the fishery. Whole bycaught samples also provide a unique source of biological material for studies into the biology, population dynamics and feeding ecology of seabirds so have significant scientific, conservation and management value. Consequently, we recommend that this data collection exercise continues going forward.

Data collection: To further improve understanding of bycatch in the longline fishery several improvements to data collection protocols have already been implemented and will assist in understanding how (1) bird density and behaviour, (2) the use of mitigation measures and (3) other operational and environmental factors, may influence the likelihood of bycatch occurring. Consideration of how future sampling coverage might be increased, and how improvements to the spatio-temporal distribution of sampling might be achieved, will be required to address the sampling biases that this work has highlighted. This will require continued open discussions between industry, scientific institutions and Government, and a commitment to continued funding for data collection activities in the fishery.

Potential mitigation approaches: The literature review, questionnaire responses from skippers and the summary of the observers’ notes all provide important and insightful information on the types of mitigation approaches that might be suitable for testing in the fishery. Industry has already made voluntary efforts towards reducing seabird bycatch in the fishery, but some bycatch still occurs. Given industry’s desire to reduce bycatch to improve fish catch rates and for reputational and environmental reasons, further efforts will be required to develop new, or fine tune existing, mitigation practises, and these should be tested within controlled trials to properly test their efficacy. Based on the skipper questionnaire responses, the most favourable routes for achieving bycatch reduction are related to: (1) the use of bird scaring lines, (2) offal management approaches, (3) night setting (including turning off deck lights) and, (4) the deterrence of birds from the line hauling area. Alterations to the line weighting configuration do not appear to be widely acceptable due to vessel and crew health and safety concerns, operational considerations and potential but unknown impacts on fish catch rates. However, a short research project undertaken on a single vessel in the hake longline fishery by Rouxel et al.(2022) found that the line sink rates on some parts of the gear were well below ACAP recommended standards and indicated that baited hooks might be within the foraging depth range of near surface feeding species beyond the typical range of bird scaring lines. The results from Rouxel et al.(2022) may not be representative of sink rates throughout the fleet and there are clearly industry concerns and reservations about altering line weighting configurations in the fishery, however, the results do highlight some potential for altering line sink rates as a bycatch mitigation approach. The skippers’ questionnaires also produced some potential mitigation solutions including the use of water cannons/spray or acoustics to keep birds from the line hauling areas and bird of prey kites to keep seabirds from the general vicinity of the vessel. Industry led suggestions such as these are worth serious consideration.

The literature review provides a comprehensive compilation of bycatch mitigation options that have been tested in demersal longline fisheries elsewhere in the world. This broadens the selection of candidate mitigation approaches that industry may be willing to trial or may even inspire new ideas to help reduce seabird bycatch.

Some of the approaches described in the review, such as swivel hooks, appear to show potential as possible mitigation approaches for the fishery and could be tested. Others, such as underwater line setters, have encountered technical problems during development and testing but nonetheless already appear to be of possible interest to industry (pers. comm. M. Hermida (Hooktone Ltd)).

This project has highlighted a range of mitigation approaches from a variety of sources that are of potential relevance to the hake fishery, but key to ensuring the successful mitigation of seabird bycatch is that industry is properly engaged and central to any decisions that are taken about which candidate approaches should be tested in the fishery.

Next steps: The UK Government and devolved administrations are committed to reducing bycatch in UK fisheries through a range of UK legislative drivers, including the UK Marine Strategy and the Fisheries Act 2020. Within these instruments the main underlying principle is one of managing human activities to ensure the long-term sustainability of the ecosystems on which those activities depend. This provides an important basis for contextualising the need for addressing bycatch in particular situations. Demonstrable population level impacts would require action to reduce bycatch levels to within appropriate thresholds. In situations where population level impacts are not occuring or are unclear, there is a requirements to minimise, and where possible, eliminate bycatch under the Fisheries Act 2020, and this can be addressed by incrementally reducing bycatch levels, assuming that is achievable within the context of maintaining a productive, safe and profitable fishing industry.

Some sections of the UK offshore longline fishery have been engaging openly and constructively with the scientific community on the issue of seabird bycatch for well over a decade and are keen to reduce bycatch levels in the fishery (pers. comm. M. Hermida (Hooktone Ltd)). Northern fulmar (and other species at lower levels) bycatch is known to occur in the fishery, but it is not clear to what degree bycatch mortality in the fishery is a factor in the apparent population declines of northern fulmar in the Northeast Atlantic over the last 30 years. In fact, the perceived positive relationship between fulmar abundance and fishing activity levels and practises over the last century (Camphuysen and Garthe 1997; JNCC 2020) means it is likely that the species population status has benefitted more than suffered from commercial fishing operations historically, and recent declines are considered to be more likely associated with declines in commercial catch levels and changes in discarding practices that have reduced foraging opportunities for many scavenging seabirds (JNCC 2020).

However, given an industry sector that are engaged, interested and potentially willing to adapt their fishing practises to minimise bycatch levels, there is a strong argument for exploring and testing mitigation options that are proposed by, or at the very least acceptable to industry from the outset. This will help ensure that mitigation measures, if they are proven to be effective, are more likely to be adopted in the fishery on a routine basis. At the same time, continued monitoring in the fishery will further improve knowledge of the factors influencing bycatch rates and the possible population impacts of the fishery. This dual approach should fulfil the objectives of incrementally reducing bycatch levels whilst maintaining a profitable, productive and safe fishery while simultaneously improving assessments of the overall impact of the fishery in a way that meets industry needs and Governments environmental ambitions.