Choke Species Research Articles

Quota use in mixed‐stock fisheries

AbstractAlthough most fisheries assessment and management focuses on the status of individual stocks, and regulations are commonly established as single‐species total allowable catch limits (TACs), much of the catch from global fisheries comes from mixed‐stock fisheries where species cannot be harvested separately. We show that in some fisheries where TAC and catch of demersal fish stocks are tracked, the average fraction of TAC harvested ranges from 21% to 68% overall and is declining. This is, in part, related to efforts to protect all species from overfishing, leading to ‘choke species’, which limit fishing pressure on other target species. While some choke species arise from a mix of low and high‐productivity species, others result from allocation processes, which can be aggravated by shifting distributions due to climate change. Underutilization of TACs can also result from market limitations, low value of individual species, undercapacity or management measures. Proposed methods for increasing long‐term yield require species to be managed in stock groups, or allowing the abundance of some stocks to fall below target reference points. We suggest that the observed low and declining aggregate harvests are due, primarily, to the focus on single‐stock sustainability measures, rather than performance of the fisheries in relation to potential overall yield. While there is a growing consensus that single‐species management should be replaced by an ecosystem‐based approach, this will require clear legislative directives regarding management of the trade‐offs involved. Time series considered in this analysis do not extend beyond 2019.

Spatial restrictions hinder avoidance of choke species in an Indigenous rights‐based fishery

Abstract Nutrient‐rich waters along the Pacific coast of North America support diverse fish communities that have helped sustain coastal peoples for millennia. Five Nuu‐chah‐nulth First Nations on the west coast of what is now known as Vancouver Island, Canada, hold constitutional Indigenous rights to conduct a multispecies community fishery, which includes Pacific Halibut (Hippoglossus stenolepis). A 2009 court decision defined the extent of these Indigenous rights to be within 9 nm of the coast, thereby not fully recognizing the knowledge and authority of the traditional leadership and raising concerns about the potential for an increase in rockfish bycatch. Yelloweye Rockfish (Sebastes ruberrimus) are a potential ‘choke’ species for this fishery because the two species occupy similar depth ranges. A choke species is one that is caught incidentally while targeting other species and, if caught in excess of its quota limits, can trigger a halt to fishing on the target species. Guided by the insights of local Indigenous peoples and using both fishery‐independent survey and commercial longline catch data, we investigated the effects of fishing depth and spatial restriction on the relative catch weights of these two species using spatiotemporal models. We find evidence that a confined fishing area can limit opportunities for avoiding choke species. Specifically, fishing at depths deeper than 175 m, which occur outside the court defined area (CDA), would provide more opportunities for catching halibut while avoiding Yelloweye Rockfish than are currently available within the CDA. This Indigenous‐informed, analytical approach to a management problem is just one example of how Western scientists can engage in coproduction of knowledge with Indigenous peoples to transition from the ‘status quo’ towards a practice of ‘Two‐Eyed Seeing’ that more effectively balances Indigenous rights and species conservation. Policy implications: Our study highlights (1) the importance of considering choke species distributions and opportunities for their avoidance when implementing spatial harvest restrictions and (2) how related analytical and management decisions can benefit from being guided by the advice of Indigenous knowledge holders. Read the free Plain Language Summary for this article on the Journal blog.

Reducing the bycatch of undersized whiting (Merlangius merlangus) in flyshooting fisheries using a square mesh escape panel

Flyshooting or Scottish seining is a relatively new but fast growing seining technique. In the English Channel and the North Sea, the main targets are species without Total Allowable Catch (TAC), but whiting (Merlangius merlangus) is a quota-regulated species that is often landed as bycatch. This could make whiting a potential choke species under the current landing obligation. The goal of this study was to evaluate the effectivity of a square mesh panel (SMP) in releasing (undersized) whiting. A catch analysis was done to assess the loss of fish through the SMP. This revealed that over 40% of the undersized and 20% of the marketable whiting escaped through the SMP and was retained in the 55 mm SMP cover. The commercial loss of other species was limited to minor quantities of small red mullet (Mullus surmuletus). We conclude that this SMP can be an effective net adaptation to significantly reduce the bycatch of whiting in the flyshooting fishery with only a marginal commercial loss of other species.

A multispecies TAC approach to achieving long-term sustainability in multispecies mixed fisheries

Abstract The management of mixed fisheries is complicated by the biological and technical interactions among fish species. We tested a multispecies total allowable catch approach to managing mixed fisheries while accounting for the interactions and changes within fish community. A multispecies size–spectrum model was developed to simulate the dynamic of fish community in North Yellow Sea, China. Three scenarios were evaluated: (1) business-as-usual (BAU); (2) Single-species TAC (SSTAC); and (3) Multispecies TAC (MSTAC, assigning an aggregated total TAC to a selected group of species). Our results showed that BAU reduced biomass of target species to a substantially low level, SSTAC led to loss of fishing opportunity by involving “choke species” with discard ban, while MSTAC had a potential for maintaining long-term yields and community structure. We demonstrated the ecological effects of varying levels of MSTACs on the target and non-target species. Species’ responses to MSTAC were stronger when the species had similar feeding and habitat traits to the target species, implying intense competition. Particularly, a 20% decrease in MSTAC could cause an average 17% decline in the biomass of other species through biological interactions in the long-term. MSTAC could be a promising approach to achieving long-term sustainability in data deficient fisheries.

Trial and error: Tactical changes in fishing behaviour can help reduce discards and exposure to chokes, but scientific trials can fail to spot this

Trials conducted on board industry vessels to test gears or alternative fishing tactics are often adopted to test selectivity measures in the field. A challenge trial was conducted on board an Irish demersal vessel in 2015 to assess the potential of tactical and behavioural changes to reduce unwanted catches, in light of the introduction of the EU’s Landing Obligation. Initial analysis of the trial indicated that there had been limited success in avoiding choke species through tactical changes. Feedback from the skipper following the trial, however, indicated that every effort had been made to avoid unwanted catches. Consequently, trial results were further scrutinised to determine what behaviours had been adopted throughout the trial, how catch compositions related to reference vessels at this time and what the major drivers of catch patterns may be. Fishing behaviour and catches for the trial vessel were fairly consistent between both trial months. This was possibly as a result of avoidance behaviours being adopted throughout the whole trial. A comparison with reference vessels indicated that the trial vessel did catch lower proportions of haddock, a key choke, in relation to whiting, a non-choke species. Changes in depth fished and time of day fished could reduce the exposure to discarding haddock but not cod, another key choke. This study highlights the importance of understanding how observation and scientific collaboration with industry may influence fishing behaviour, and how scientists should carefully consider such factors when conducting trials on industry vessels and interpreting subsequent results.

Fishing for euros: how mapping applications can assist in maintaining revenues under the Landing Obligation

Abstract With the introduction of the Landing Obligation (LO) in EU fisheries, there is an increasing need for fishers to avoid unwanted catches while maximizing revenues. Improving understanding of the spatio-temporal dynamics of unwanted catches could assist the fishing industry optimize catches by altering where they fish. How following such advice relates to revenues and fishery dynamics requires more consideration. We take an existing hotspot mapping methodology and examine how it could be used to identify fishing opportunities under the LO in Irish (Celtic Sea) and Danish (North Sea and Skagerrak) demersal fisheries. We consider if fishing effort can be relocated to avoid unwanted catches while maintaining revenues. The value per unit effort of fishing activity in both areas was often linked to high catch rates of key demersal species (cod, haddock, hake, and whiting). Our analyses indicated, however, that there are options to fish in areas that could provide higher revenues while avoiding below minimum conservation reference size catches and choke species. This was evident across both case study areas demonstrating that hotspot mapping tools could have wide applicability. There does, however, remain a need to explore how the displacement of vessels may further alter species distributions and fleet economics.

Why are catches in mixed fisheries well below TAC?

In major mixed stock fisheries of the United States, the actual catch is well below the total allowable catch (TAC). In recent years, only 20–30% of the TAC is caught in the US West Coast non-whiting fishery, whereas 60–80% of the TAC is caught in the Gulf of Alaska groundfish trawl fishery. Possible explanations for the underutilization are (1) lack of infrastructure, (2) lack of market demand, and (3) low quota limits on some species restricting the ability to harvest other species. Using species by species data on catch, TAC and lease price for species under Individual Transferable Quotas, we evaluate the support for these hypotheses. The results suggest that rebuilding plans, under a strict timeline, ultimately created many of the choke species on the West Coast and reduced processing infrastructure, such that the fishery still struggles with low quota utilization even after stocks have been rebuilt. In comparison, the Gulf of Alaska has not had a history of rebuilding plans and generally has higher utilization. The results suggest that rebuilding plans intended to increase sustainable harvest have been successful at increasing abundance but have been unsuccessful at rebuilding the fishery.

Stimulating release of undersized fish through a square mesh panel in the Basque otter trawl fishery

Discards of regulated species in the Basque mixed trawl fishery are a challenge. In 2006, a square mesh panel (SMP) was introduced in the fishery to increase the release efficiency of undersized fish. However, studies have shown that the selectivity in this fishery is based on codend selectivity and the release through the SMP is inefficient due to low contact between fish and the SMP. In order to improve contact, we tested four different gear configurations that use different stimulators to lead fish to the panel: without stimulation, with stimulation based on ropes, with stimulation based on ropes and floats, and with stimulation based on LED lights. The experiment was carried out on three of the potential choke species for the fishery: hake (Merluccius merluccius), horse mackerel (Trachurus trachurus), and blue whiting (Micromesistius poutassou). The results showed that stimulators did not significantly improve the release efficiency of hake and horse mackerel through the panel. For blue whiting, stimulation with floats had a significant positive effect on release efficiency, whereas LED light-based stimulation had the opposite effect. In general, the contribution of the SMP to the overall release efficiency of the selective system (SMP + codend) was low. Underwater recordings confirmed that the stimulators generally were not able to lead fish towards the SMP.

A multi-stock harvest control rule based on “pretty good yield” ranges to support mixed-fisheries management

Abstract Advice for commercially exploited fish stocks is usually given on a stock-by-stock basis. In light of the ecosystem-based fisheries management, the need to move towards a holistic approach has been largely acknowledged. In addition, the discard bans in some countries requires consistent catch advice among stocks to mitigate choke species limiting fisheries activity. In this context, in 2015, the European Commission proposed the use of fishing mortality ranges around fishing mortality targets to give flexibility to the catch advice system and improve the use of fishing opportunities in mixed-fisheries. We present a multi-stock harvest control rule (HCR) that uses single stock assessment results and fishing mortality ranges to generate a consistent catch advice among stocks. We tested the performance of the HCR in two different case studies. An artificial case study with three stocks exploited simultaneously by a single fleet and the demersal mixed-fishery operating in Bay of Biscay and Celtic Sea. The HCR produced consistent catch advice among stocks when there was only a single fleet exploiting them. Even more, the HCR removed the impact of the discard ban. However, in a multi-fleet framework the performance of the HCR varied depending on the characteristics of the fleets.

Use of avoidance behaviours to reduce the economic impacts of the EU Landing Obligation: the case study of a mixed trawl fishery

Abstract The EU Landing Obligation (LO) is designed to reduce bycatch (i.e. unwanted catch) through more selective fishing practices, such as avoidance behaviours which consist in allocating fishing effort to other species, fishing grounds or seasons. Incentives for fishers to change their behaviours depend on their economic performances as well as their ability to avoid bycatch. Changes in economic performances under the LO are evaluated based on cost and revenue equations. The nested grid method is then used to explore the spatial and temporal distribution of landings and discards, and to suggest alternative effort allocation to avoid bycatch. This article is focussed specifically on the French otter trawl fishery in the eastern English Channel and southern North Sea. Results suggest that under the LO the choke species problem will curtail fishing activities earlier in the year, leading to significant economic losses. In the absence of significant quota top-ups (at least 75%), a change in fishing practices consisting in reducing overall bycatch by 30% is insufficient to reduce losses. With a particular attention to choke species, more economically efficient avoidance strategies can be found thanks to the nested grid method.

Likely status and changes in the main economic and fishery indicators under the landing obligation: A case study of the Basque trawl fishery

We modelled fleet dynamics and the economic impact of three implementations of the EU landing obligation for fisheries, and contrasted the results with those obtained under a scenario of no landing obligation. Simulations were performed using a dynamic state variable model of effort allocation for the Basque trawl fleet, assuming that the landing obligation had been implemented in 2012. The three implementations of the landing obligation involved different policy arrangements: (i) quota increases; (ii) international swapping of quotas; and (iii) inter-species quota flexibility. All three scenarios resulted in changes to fishing patterns caused by choke species and improved selectivity of harvest, but also resulted in a negative short-term impact on the economic performance of the fleet. We report average reductions in net revenue of up to 60% when compared with results obtained under a no landing obligation scenario. Our model results suggested that these negative short-term impacts could be alleviated by incorporation of inter-species quota flexibility in the implementation of the landing obligation. Our results indicate that there will be a strong incentive to use this policy arrangement to alleviate the choke effect problem where species with limiting quotas constrain the fishery.

Identifying choke species challenges for an individual demersal trawler in the North Sea, lessons from conversations and data analysis

A likely side-effect of introducing the landing obligation of the 2013 Common Fisheries Policy into mixed fisheries is the occurrence of the “choke species” problem. When discarding no longer is an option, leasing quota or changing fishing practices remain important tools to avoid choke species. Here, the scale and tactics linked to using avoidance behaviour to reduce choke species is investigated by analysing the fishing behaviour of a single demersal trawler in the North Sea. Analysis combined qualitative information collected from through interviews with the vessel owner and skipper, along with quantitative analysis on fisheries data. From the interviews, saithe and cod were identified as potential choke species and subsequent analysis focused on these two species. The analysis of catch and quota composition showed that cod would choke the fishery early if no catch-quota balancing options were available, resulting in a 87% reduction in revenue, while saithe could choke the fishery later, resulting in a 43% reduction in revenue. Avoidance behaviour was difficult to detect from fisheries data, which was explained by avoidance taking primarily place through very fine-scale tactical choices rather than large displacements. Catch composition showed that saithe is distributed more patchily than cod, with most hauls containing small amounts of saithe and a few hauls containing large amounts. In conclusion this paper supplies an view on the choke species problem seen from the perspective of an individual fisher and highlights the amount of real-time tactical decisions and trade-offs that need to be made when operating in mixed-fisheries.

Reducing discards without reducing profit: free gear choice in a Danish result-based management trial

The 2013 Common Fisheries Policy introduced a landing obligation on a range of species, bringing more focus on the full accountability of all catches. To investigate the potentials and challenges of these paradigm shifts, a 6-months ‘unrestricted gear’ trial was performed in Denmark in 2015. Twelve trawlers were challenged to test their own solutions to reduce unwanted bycatch and/or choke species, while maintaining profitable. The participating fishers tested different options depending on their fishery and the type of issues they faced individually, and adjusted their test fishery over time through incremental small steps. Nine vessels reduced discard ratio in the test fishery, one showed no difference between test and control fishery, while two vessels displayed an increase in discard ratio. Catch compositions also differed, with fewer “choke species” occurring in the test fisheries and a more valuable size composition. Ultimately, despite smaller landings in multiple vessels, no vessel showed reduction in value-per-unit-effort (VPUE) and one Baltic vessel significantly increased the VPUE. This trial showed that relaxing technical regulations combined with proper incentives has a potential to provide some flexibility to cope with the landing obligation, where unwanted catches could be reduced to some extent without negative effects on economic viability.

The bad, the good and the very good of the landing obligation implementation in the Bay of Biscay: A case study of Basque trawlers

Landing obligation (LO) has become a core element on the Common Fisheries Policy (CFP). In this work a bioeconomic simulation tool is used to anticipate the effects of LO in a particular fleet that by its nature is likely to be highly affected by its implementation. These effects are measured in terms of biologic, economic and fleet indicators.Results show how LO has a negative short term effect in the economic performance of the fleet (the bad). That the exemption and flexibilities foreseen in the CFP alleviate, in the short term, the effects of the choke species and the redistribution effects created (the good). Furthermore, results show that there are private incentives to improve the selectivity and to reduce the discard levels of the fleets. It is concluded how a breeding ground for a more sustainable and productive system is created (very good).

Temperature-based targeting in a multispecies fishery under climate change

Temperature controls important physiological processes in fish and determines aspects of their niches. In an effort to inform selective fishing and spatiotemporal management in the U.S. Northeast Multispecies fishery, we used 16 years of data from the Northeast Fisheries Science Center Spring and Fall Scientific Trawl Surveys to determine if bottom temperature can be used to differentiate the distribution of Atlantic cod (Gadus morhua) from other species within the fishery management plan (FMP). We identified two separate regimes in spring temperatures and used empirical cumulative distribution functions to calculate biomass availability by temperature for each species. We applied a bagged approach to find optimum thermal threshold values that maximize the difference in cod biomass from each of the other species. For our study area, 38% to 54% of the species considered were well separated from cod by temperature in spring, whereas only 17% were separable in the fall. This study suggests that temperature targeting can be used seasonally to separate cod from many other species in the FMP including top catches and no‐retention species. The use of temperature targeting may allow fishermen to better meet multiple quotas while avoiding choke species. Our results also suggested increasing thermal overlap between cod and species inhabiting higher median temperatures (e.g., spiny dogfish, Squalus acanthias) under the current warming temperature regime. These results indicate that the ability to selectively fish in the US Northeast Multispecies fishery will become more difficult under a warming ocean.