New mitigation measures reducing seabird by‐catch in trawl fisheries

This paper provides an update on an earlier review [Fish & Fisheries 8 (2007) 31] of mitigation methods used to reduce seabird by‐catch in trawl fisheries. Interactions of seabirds with trawl vessels fall into two broad categories: those focused on the trawl warps and those focused around trawl nets. For reducing seabird strikes on trawl warps, the use of bird‐scaring lines has been proved to be the most effective mitigation device in the trawl fisheries in which comparative studies have been undertaken. However, the retention or strategic management of fish waste (offal and discards) is recommended as the most effective primary measure for by‐catch reduction, and as such should be viewed as the best long‐term solution to reducing seabird by‐catch in trawl fisheries. Coincident with effective fish waste management, measures such as cleaning the net prior to shooting and reducing the time the net is on the surface should be viewed as best practice measures and incorporated into normal fishing activities. While a number of methods have been trialled to reduce the incidence of warp strikes, there continues to be the need for more work on effective measures for reducing interactions of seabirds with the trawl net.     

Tori‐lines with weighted branch lines reduce seabird bycatch in eastern South Pacific longline fishery

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Reducing seabird bycatch in longline, trawl and gillnet fisheries

With an increasing number of seabird species, particularly albatross and petrels, becoming threatened, a reduction of fishery impacts on these species is essential for their future survival. Here, mitigation methods to reduce and avoid seabird bycatch are assessed in terms of their ability to reduce bycatch rates and their economic viability for longline, trawl and gillnet fisheries worldwide. Factors influencing the appropriateness and effectiveness of a mitigation device include the fishery, vessel, location, seabird assemblage present and season of year. As yet, there is no single magic solution to reduce or eliminate seabird bycatch across all fisheries: a combination of measures is required, and even within a fishery there is likely to be refinement of techniques by individual vessels in order to maximize their effectiveness at reducing seabird bycatch. In longline demersal and pelagic fisheries, a minimum requirement of line weighting that achieves hook sink rates minimizing seabird bycatch rates should be tailored with a combination of strategic offal and discard management, bird‐scaring lines (BSLs) and night‐setting, particulary in Southern Hemisphere fisheries. Urgent investigation is needed into more effective measures at reducing seabird interactions with trawl nets and gill nets. In trawl fisheries, a combination of offal and discard management, the banning of net monitoring cables, paired BSLs, and a reduction in the time the net is on or near the surface are likely to be the most effective in reducing seabird interactions with the warp cables and net. Few seabird bycatch reduction methods have been developed for gillnet fisheries, although increasing the visibility of the net has been shown to reduce seabird bycatch. Further studies are required to determine the efficacy of this technique and its influence on target species catch rates.     

Are bycatch rates sufficient as the principal fishery performance measure and method of assessment for seabirds?

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Bycatch susceptibility in pelagic longline fisheries: are albatrosses affected by the diving behaviour of medium‐sized petrels?

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Seabird bycatch vulnerability to pelagic longline fisheries: Ecological traits matter

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Integrated management to address the incidental mortality of seabirds in longline fisheries

1. Of the myriad of anthropogenic and natural threats to seabirds, one of the most critical global problems is incidental mortality in longline fisheries. Hesitance or failure by fishery managers and longline industries to adequately address this acute problem could result in the extinction of several albatross and petrel species within our lifetimes. 2. An integrated management approach is needed to comprehensively manage longline fisheries to address seabird bycatch. A review of relevant multilateral accords, declarations and actions by regional and international organizations reveals the need to augment international collaboration, especially to address pirate longline fishing. Management authorities and stakeholders need to collaborate to: promote adoption and compliance with effective legally binding accords that cover the ranges of all affected seabirds; ensure that all Range States and relevant distant water fishing nations become contracting parties to these accords; coordinate national implementation of the Food and Agriculture Organization's International Plan of Action on seabirds; set management goals; establish and implement policies to employ seabird deterrent measures; disseminate information on new deterrent measures; locally tailor seabird deterrent measures; standardize data reporting and establish a centralized data repository; coordinate research and monitoring; develop regional surveillance and enforcement systems; and augment less developed countries' capacity and resources to mitigate seabird and longline fishery interactions. 3. Establishing protected areas containing seabird colonies and adjacent waters within a nation's Exclusive Economic Zone (EEZ) is potentially an expedient method to reduce interactions between seabirds and longline fisheries. However, establishing high seas marine protected areas to restrict longline fishing in seabird foraging areas, which would require extensive and dynamic boundaries and large buffer zones, may not be a viable short‐term solution due to the long time it is anticipated it could take to resolve legal complications with international treaties, to achieve international consensus and political will, and to acquire requisite extensive resources for surveillance and enforcement. High seas marine protected areas may eventually become a feasible mechanism to address seabird bycatch if nations develop the will to close ocean areas to commercial fisheries to attempt to rehabilitate depleted pelagic fish stocks. 4. Direct involvement of longline industries, through partnerships with national governments and regional organizations, to develop seabird mitigation measures and policies prescribing the use of these measures, is critical. Direct involvement of stakeholders to find solutions to resource management problems leads to stakeholder groups taking ownership of and supporting rules. Bottom‐up approaches are successful in changing interest groups' attitudes and behaviour, to maximize voluntary compliance and minimize conflict and resources required for enforcement. 5. Data gaps must be filled and scientific uncertainty addressed through multilateral collaboration. Research to develop and improve practicable mitigation measures is most urgently needed. Information on the status and trends of albatross populations, where albatrosses forage, the causes of population declines, seabird mortality rates and levels in each longline fishery, and the type of impacts from longlining on seabird populations is also needed. It is well documented that several seabird species are at risk of extinction, incidental bycatch in longline fisheries significantly contributes to many species' decline, and proven mitigation measures are available. Thus, while additional research is critically needed, we should not delay taking precautionary action to wait for additional information, but should immediately act to protect seabirds from the known acute threat of mortality in longline fisheries. Copyright © 2001 John Wiley & Sons, Ltd.     

Characterizing seabird bycatch in the eastern Australian tuna and billfish pelagic longline fishery in relation to temporal,spatial and biological influences

• 1. Seabirds killed incidentally in Australia's eastern tuna and billfish (ETBF) longline fishery between September 2001 and June 2006 were examined to evaluate species composition and to relate, where possible, capture events to operational and environmental factors.
• 2. During this period 2.129 million hooks on 2202 shots were observed, and 369 birds were reported killed. The majority (78%) of these were flesh‐footed shearwaters (Puffinus carniepes), 53% of which were male and 44% female. Smaller numbers of medium to large sized albatrosses (Diomedeidae, predominantly female) and other shearwaters (Puffinus spp.) and petrels (Pterodroma spp.) dominated the remainder of the bycatch.
• 3. Of the 369 birds reported taken as bycatch, 280 were available for necropsy, and species identifications performed in situ by observers were assessed. While observer identifications were generally correct for common species, performance was poor for less common ones.
• 4. The geographical location (latitude) of shots, season, time of day at which shots were set, and bait type and life status (dead or alive) influenced the seabird bycatch rate. The majority of captures (87% overall) occurred between 30 and 35°S, with bycatch being lowest in winter, and remaining at similar levels across the other seasons.
• 5. The use of live fish bait was generally associated with increased captures of both seabirds overall, and flesh‐footed shearwaters in particular. Copyright © 2010 John Wiley & Sons, Ltd.

     

Characterization of seabird bycatch in eastern Canadian waters, 1998–2011, assessed from onboard fisheries observer data

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Seabird interactions and by‐catch in the anchovy pelagic trawl fishery operating in northern Argentina

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Improving the effectiveness of escape windows in directed Norway lobster Nephrops norvegicus trawl fisheries

A substantial improvement in the bycatch selectivity of Norway lobster Nephrops norvegicus trawls is required, particularly with respect to cod Gadus morhua, whose stocks are at low levels in several areas. Conventional escape windows are not adequate to properly release cod and other bycatch species caught in the trawls. To address this issue, we developed a novel sorting box concept consisting of a four-panel section with a window on the top in order to improve the escape of cod and other bycatch species through an escape window while retaining the target catch of Norway lobster. The concept was tested on a commercial trawler in Kattegat and Skagerrak. Two different window mesh sizes and two different sorting box heights were tested using a traditional codend cover and a dual codend cover. We observed greatly reduced bycatches of both cod and other fish species compared to a standard codend. The reduction in bycatch decreased with decreasing mesh size and increasing height of the sorting box. Escape of Norway lobster through the escape window was limited. A modified version of the sorting box concept was implemented in the Kattegat fishery from 2009 onwards.     

Interactions between seabirds and pelagic squid-jigging vessels in the south-west Atlantic

1. The waters of the Patagonian Shelf in the south-west Atlantic are nutrient rich, support large concentrations of wildlife, and are exploited by several fisheries, including the large Asian squid-jigging fishery. Although the squid-jigging fishery has previously been observed to have few problems with the accidental mortality of seabirds, the deliberate catch for consumption of seabirds by the crew has been identified as a possible issue.
2. Four cruises were made between Uruguay and the Falkland Islands during 2005–2006 to quantify the impact of jiggers on seabirds from indirect observation platforms. Monitoring included closely approaching 116 jigging vessels and boarding seven for inspection.
3. The use of non-jigging fishing gear, either for catching fish or seabirds, was observed at the stern of 33 vessels. Twelve seabird carcasses were observed floating close to vessels during 13 days of monitoring. Although the results recorded here are not sufficient to put a confident estimate on the magnitude of this mortality, the density of carcasses floating in the water among the jigging fleet indicated the potential significance of this problem.
4. The results were considered sufficiently concerning for the Falkland Islands Government to take preventative actions, including educational efforts, improving humanitarian conditions onboard vessels, introducing relevant legislation and licence conditions, and prosecuting intentional seabird take inside the Falkland Islands jurisdiction. This has resulted in the apparent elimination of these mortalities within Falkland waters since the late 2000s.
5. Nevertheless, it is likely that the same initial conditions exist for the crews of squid jiggers on vessels operating on the high seas, and so the possibility of the targeting of seabirds for consumption continues. Squid fisheries with substantial numbers of jiggers overlap with important foraging areas for a range of albatross and other species in high-seas areas such as the Patagonian Shelf, the Humboldt and Kuroshio currents, and the south-west Pacific Ocean. These areas of overlap may be important to investigate, especially in the foraging grounds of declining seabirds.

     

Improved line weighting reduces seabird bycatch without affecting fish catch in the Brazilian pelagic longline fishery

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Hawaii longline tuna fishery temporal trends in standardized catch rates and length distributions and effects on pelagic and seamount ecosystems

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Seabird‐trawling interactions: factors affecting species‐specific to regional community utilisation of fisheries waste

Bottom trawl fishing provides substantial amounts of normally unavailable demersal prey to seabirds (e.g., discards), affecting their life‐history traits and population dynamics, as well as community structure. Within this framework, we studied seabird‐trawling interactions throughout the annual cycle in a poorly studied ecosystem in the Mediterranean, the Balearic archipelago, on a both species‐specific and a community level. Whereas the species‐specific approach showed a significant influence of season (phenology) on shaping seabird’s trawling attendance patterns, the spatio‐temporal coupling of regional community was a result of a complex interaction between fishery‐related variables. The most frequent and abundant species were the yellow‐legged gull Larus michahellis and Cory’s shearwater Calonectris diomedea, the latter attending vessels in higher numbers than expected from local population figures. Conversely, the remaining breeding species occurred in lower numbers than expected according to their local breeding populations, suggesting that discards were of relatively little importance. Discarding activity took place over the entire shelf and continental slope surrounding Mallorca, but especially in the southwest, adjacent to the breeding grounds of approximately 12% of the Balearic total seabird breeding population, including 13% the Balearic shearwater Puffinus mauretanicus world population. Overall discards corresponded to 0.74 of landings (range: 0.09–6.00) and consisted primarily of fish followed by crustaceans and molluscs (approximately 80, 15, and 5%, respectively). Seabird‐trawling interactions should be taken into account in the frame of an ecosystem‐based approach to fisheries management, and particular attention should be devoted to the critically endangered Balearic shearwater.     

Decreasing but still high: bycatch of seabirds in gillnet fisheries along the German Baltic coast

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Can we increase haddock yield within the constraints of the Magnuson–Stevens Act?

Georges Bank haddock is a recently recovered fish stock in the New England groundfish fishery. Due to federal constraints under the Magnuson–Steven Act, however, this stock cannot be optimally exploited due to the bycatch of other critical species in the New England groundfishery such as cod and yellowtail flounder which are overfished. The Ruhle trawl and Separator trawl are examples of recent advances in gear technology that have been shown to significantly increase haddock to bycatch ratios. This study models the groundfish fishery through a mixed-stock yield model which incorporates technological interactions. We also develop a socio-economic model that quantifies the amount of employment and producer surplus associated with three trawl types. Our results explore policy situations regarding the use of the new trawls. By bridging the biological and socio-economic models, we are able to view the fishery as a system that more accurately represents stakeholder views. Our model shows that each trawl, when used exclusively, produces different optimum strategies and therefore an optimum management strategy would most likely include a combination of trawl types. Our results also support the logic of using modified trawls for haddock fishing trips in which bycatch is strictly regulated (“B days”) as the Ruhle trawl is able to maintain 80% of catches caught by a conventional trawl while reducing bycatch up to over 60%. This paper is a first step towards an aid for policy makers to examine fishery gear trade-offs and the resulting biological and socio-economic consequences of different management actions within the constraints of the Magnuson–Stevens Act.     

Trends in carbon flux to seabirds in the Peruvian upwelling system: effects of wind and fisheries on population regulation

We hypothesized that change in the annual population size of guano‐producing seabirds (cormorant, Phalacrocorax bougainvillii; booby, Sula variegata; pelican, Pelecanus thagus) is a response to changes in primary and secondary production of the Peruvian upwelling system. We tested this hypothesis by modeling nitrate input through upwelling to the upper layers of the ocean off Peru between 6° and 14°S using data on wind stress and sea surface temperature. The model predicted the amount of carbon fixed by primary production each year from 1925 to 2000, which was then apportioned to the Peruvian anchovy (Engraulis ringens) biomass and ultimately to the seabird population and the anchovy fishery, the largest single‐species fishery on Earth. The model predicted a marked increase in primary production as a consequence of increasing wind stress. It overestimated the anchovy biomass after the collapse of the fishery in 1972, but closely predicted the growth of seabird populations from 1925 to the mid‐1960s, and their decline thereafter, explaining about 94% of the variation in seabird numbers from 1925 to 2000. The model indicates the seabirds consumed 14.4% of the available anchovies and, thus, that seabirds consumed 2.3% of the new production, before the development of the anchovy fishery, and only 2.2% of the available anchovies and 0.3% of the new production after the development of the fishery. The model results clarify the roles that environmental and anthropogenic factors may have had in regulating the guano‐producing seabird populations. It indicates that the growth of seabird populations from 1925 to 1955 was likely a response to increased productivity of the Peruvian upwelling system and that the subsequent drastic decline in seabird abundance was likely due to competition for food with the fishery, which caught ～85% of the anchovies, which otherwise would have been available for the seabirds. This model also shows that an increase in oceanic primary production promotes reproductive success and population growth in higher trophic level organisms.     

The potential for new Nephrops trawl designs to positively effect North Sea stocks of cod,haddock and whiting

Within commercial fisheries, particularly mixed fisheries, both target and non-target species are often discarded. Discarding represents a potentially significant loss to the productivity of fish stocks; it can have damaging ecological consequences, and is a potential cause of the failure of recovery plans. The Nephrops fishery in the North Sea is classified as a mixed fishery. Nephrops trawls are constructed with smaller meshes than trawls used to target whitefish; consequently, the bycatch of juvenile fish can be substantial. Several new Nephrops trawl designs have been tested in the North Sea. The data from these trials are used to investigate the potential impact of their implementation on cod, haddock and whiting stocks in the North Sea (including the Kattegat and Skagerrak).The model examines five trawl designs, and also the scenarios of a cessation of discarding in all North Sea fisheries and in just the Nephrops fishery. The model is deterministic, and evaluates the relative differences between scenarios assuming all other variables remain constant. If discarding of cod, haddock and whiting in the North Sea fisheries were eliminated, stocks would increase by 41%, 14% and 29%, respectively, within 10 years. Eliminating discarding in the Nephrops fishery alone would increase stocks by 2%, 1% and 13%, respectively, reflecting the relative proportion of catches of these species in the Nephrops fishery. For cod and haddock, the introduction of the Nephrops trawl with a grid with a square-mesh codend was the only scenario in which a notable increase in stock number was observed. This trawl design facilitates the escape of fish of all ages/sizes from the trawl, effectively making the Nephrops fishery a single-species fishery. For whiting, stock numbers and landings increased under all scenarios, but forecasted landings were lower than if current discard patterns continued in all except the no-discards scenario. The dependency of the results on the validity of the assumptions and on the accuracy of the input data is discussed.