Few fishing areas in the EU provide a better example of the challenges presented by the complexities of mixed fisheries management than the west of Scotland (ICES Division VIa). These challenges provide an opportunity for the fishing industry to develop innovative measures to prevent closure of grounds while contributing to effective fisheries management and long-term sustainability of fish stocks.
Fisheries management decisions can occasionally lead to scenarios where catch quotas set annually by the EU can appear to contradict official scientific advice produced by the International Council for the Exploration of the Seas (ICES). This was the case in 2019 when the EU set a bycatch quota for cod and whiting in the west of Scotland, despite ICES advising a zero catch for these species. Zero catch advice for individual species presents a significant challenge in mixed trawl fisheries, where several commercially important species are unavoidably caught together. Much work has been done in recent years to develop and test trawls that can improve selectivity in order to reduce unwanted catches although, while progress has been made in some areas, a range of factors linked to the size and behaviour of different species in these fisheries continue to prevent effective selectivity within the trawl.
Demersal trawl fisheries on the west coast of Scotland predominantly comprise two general gear types, nephrops trawl and whitefish trawl. Nephrops trawlers predominantly catch their target species with an incidental bycatch of several whitefish species. Significant advances have been made in recent years to improve selectivity of nephrops trawls. This is partly due to the considerable difference between the size and behaviour of nephrops and whitefish as they encounter and interact with the trawl. These differences have allowed for the development of adaptations that have successfully reduced unwanted catches. Improvements in selectivity for the whitefish fishery may be less straightforward because many of the unwanted species are of a similar size and exhibit similar behaviour to the target species, making it difficult to separate them in the trawl. Selectivity improvements that reduce catches of unwanted species often also significantly reduce catches of target species, reducing the commercial viability of the fishery.
The recent introduction of the obligation to land all catches of quota species adds further complexities, giving rise to the ‘choke’ phenomenon, where restrictions on catching opportunities for one species in a mixed fishery may ultimately lead to early closure of the fishery. Under the landing obligation, a mixed fishery will close when the available quota for any of the quota regulated species in the fishery has been exhausted. In the west of Scotland mixed fishery, the zero-catch advice for cod and whiting, if imposed, would result in the fishery remaining closed because these species are a common and unavoidable component of mixed catches in the area. The closure of the fishery and resultant loss of landings of the species in the mixed fishery whose stocks are considered to be in a healthy state would have a significant economic impact, not just for fishing vessels but also for the onshore processing sector.
Taking all of the complexities associated with mixed fisheries, zero catch species and the landing obligation into consideration, the EU set a bycatch quota for cod and whiting in the west of Scotland in 2019. They noted that this was done in order to strike the right balance between continuing fisheries in view of the potentially severe socio-economic implications, and the need to achieve a good biological status for those stocks, considering the difficulty of fishing all stocks in a mixed fishery at maximum sustainable yield at the same time. The quid pro quo was the development of measures to ensure that unavoidable by-catches are reduced where possible. These could include specific measures such as more selective gears, area closures, real time closures, avoidance measures and move-on rules.
The most effective way to minimise unwanted catches is to avoid areas where significant volumes of these species may be concentrated. With that in mind, the SFO is in the process of developing and trialling a modern, real-time system that will help facilitate this in the west of Scotland mixed fishery. The system will enable the sharing of information related to catches of unwanted species in real-time, allowing fishermen to avoid areas of high concentrations. This will help improve the management of these species and contribute to their long-term recovery.
While these measures may help reduce unwanted catches of cod and whiting in the short term, additional challenges relating to the future management of these species remain. One such challenge relates to uncertainties over the accuracy of the assessment on which ICES catch advice for cod is based. In recent years fishermen have reported that the quantities of cod they have been catching are at odds with the perceived status of the stock in the stock assessment. An independent review of the stock assessment has highlighted a potential underestimation of the spawning stock biomass and overestimation of fishing mortality, with concerns that some of the underlying model assumptions may not be accurate. This may mean that the current advice for a zero catch is unnecessary. ICES is currently undertaking an ‘inter-benchmarking’ exercise to investigate some of the issues relating to the current stock assessment. This may result in a different perception of the state of the cod stock.
There is also growing evidence that there are several different cod sub-populations within the current west of Scotland management area defined by ICES, with some in better condition than others. For example, fishermen report significant catches of cod north of 59 degrees latitude (roughly north of the Butt of Lewis) while some populations south of this are reportedly struggling. Several proposed factors, including an explosion in the seal population, may be contributing to the lack of recovery in some of the southern parts of the area. To add further complexity, there is a growing belief (although it requires further investigation) that the population north of the Butt of Lewis may in fact be part of the wider North Sea population. This suggests that the arbitrary 4-degree line separating the North Sea and west of Scotland management areas is doing little to help in the management of the stocks. In fact, advice for many species is now moving towards a Northern Shelf management approach (west of Scotland and North Sea combined), which recognises that populations are often straddled across the two management areas.
Paul Macdonald, Senior Fisheries Analyst