A large scale BACI experiment to test the effects of prawn trawling on seabed biota in a closed area of the Great Barrier Reef Marine Park, Australia

A multiple Before-After-Control-Impact experiment was conducted to estimate the large scale effects of a single coverage by prawn trawlers on an offshore inter-reef area in the northern Great Barrier Reef that was closed to fishing. Prospective power and cost-benefit analyses facilitated the design and optimization of the experiment, the effect size of which was guided by prior publications at the time that had indicated impacts of 10–100×. The optimal design, given the number of factors to be tested and the constraint of available ship time (100 days) and resources needed to process samples, was for 12 control and 12 impact plots each measuring 2.8 km × 1.2 km. The final design specification was capable of detecting an average −80% effect size (5×). The experiment was divided over two seasons, wet and dry. During the experimental trawl impact phase, a total of 32 t of benthic biota was removed from six shallow plots (15–25 m depth) and 6 t from six deep plots (30–50 m depth). Sampling before and 6 months after impact was conducted by an epibenthic dredge, a prawn trawl and a fish trawl. Analysis of means before and after impact, relative to controls, showed very few significant differences. This indicated that the impact of a single prawn trawl was less than the design specification. The lower than expected impact, compared to previous studies, may have been partly because this study included all benthic groups, not just the most sensitive as earlier studies had focussed on. Comparison of catch rates from the prawn trawl and the dredge indicated the overall impact on total biomass was around −3% but ranged from close to 0% for some species to around −20% for sensitive sessile species. A review of effect sizes in 30 other recent trawl experiments indicated that this result was not exceptional; i.e. the reported effects of single trawls generally were not large, and prawn trawls appeared to have smaller effect sizes than fish trawls, beam trawls and scallop dredges—also, several studies reported recovery within ca. 6 months. Analysis of fishery effort data indicated that this result was appropriate for the majority of trawl fishing grounds, where effort is sparse and infrequent. Many published experiments had confounded designs and most had not used a priori power analyses or pre-specified effect sizes. Nevertheless, recurrent trawling can be expected to have cumulative impacts on benthos, as has been demonstrated by repeat-trawl depletion experiments. On the other hand, the spatial extent of fishing grounds trawled as intensively as these depletion experiments is quite limited.     

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.     

High mortality of adult female Magellanic penguins by gillnet fisheries in southern Brazil

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Bycatch Beknown: Methodology for jurisdictional reporting of fisheries discards – Using Australia as a case study

Bycatch remains one of the most important issues in the world's fisheries so its estimation and reporting have been highlighted in many international, regional and jurisdictional guidelines and policies. This paper describes a simple methodology to estimate jurisdictional discards, using Australia's first national bycatch report as a case study. The methodology involves: (a) identifying annual landings for all fisheries and methods; (b) deriving retained:discard ratios for each; (c) where ratios are lacking, using substitute ratios from similar fisheries; (d) applying the ratios from (b) and (c) to the data from (a) to obtain totals; and (e) scoring the quality of the discard information using the US Tier Classification System weighted by estimated discard levels. The results for Australia revealed that, during the last decade, commercial fisheries annually discarded 42.5% of what was caught (87,983t). 70% came from just eight fisheries/methods with 30% coming from the other 299. The Queensland East Coast Prawn Trawl fishery contributed 28.5% of the national total. The quality of discard information was reasonable across most jurisdictions, with a national score of 59.1%. The best quality data came from the Commonwealth due to its observer and (more recent) Electronic Monitoring programmes. Those data also showed that fishers’ logbook information under‐estimated levels of discards (determined from observer data) by 89.7%. This paper provides: (a) the means to develop benchmarks in bycatch management and estimation against which jurisdictions can be compared and performances tracked; and (b) for Australia, priority areas for management intervention to reduce discarding and improve its monitoring.     

An interview-based approach to assess marine mammal and sea turtle captures in artisanal fisheries

Recent case studies have highlighted high bycatch mortality of sea turtles and marine mammals in artisanal fisheries, but in most countries there are few data on artisanal fishing effort, catch, or bycatch. With artisanal fisheries comprising >95% of the world’s fishermen, this knowledge gap presents a major challenge to threatened species conservation and sustainable fisheries initiatives. We report on results from an intensive pilot study to evaluate whether interview surveys can be effective in assessing fishing effort and threatened species bycatch. Fisheries and bycatch data from interviews with >6100 fishermen in seven developing countries were collected in <1 year for approximately USD $47,000, indicating that this approach may rapidly yield coarse-level information over large areas at low cost. This effort provided the first fisheries characterizations for many areas and revealed the widespread nature of high bycatch in artisanal fisheries. Challenges to study design and implementation prevented quantitative estimation or spatial comparisons of bycatch during this pilot research phase, but results suggested that annual sea turtle bycatch may number at least in the low thousands of individuals per country. Annual odontocete bycatch may number at least in the low hundreds per country. Sirenian bycatch occurred in all study areas but was frequent only in West Africa. We discuss lessons learned from this survey effort and present a revised protocol for future interview-based bycatch assessments.     

Fyke-netting and coarse fisheries in lowland Britain: practical advice for fishery owners and managers

Abstract  The by-catches of fish, mammals and birds from a fyke-net survey of eel, Anguilla angilla (L.), stocks (total effort 1593 end days) at 45 sites in rivers and lakes in the Thames catchment and tidal river were examined. Sizes and compositions of by-catches varied between sites, yielding a total of 21 fish species representative of the types of water body sampled. The largest catches were of shoaling juvenile perch (especially in lakes). Small roach, perch and ruffe were also fairly frequent in running waters (especially the tidal and non-tidal Thames). Carp, tench and pike were less frequently caught (mainly in still waters and upper tributaries). Juvenile flounders and smelt were fairly common in the tidal Thames. Salmonids were rarely caught and fish mortalities overall were very low. Few mammals, wildfowl or crustaceans were trapped, but it is important that nets are set below water level to avoid trapping birds swimming on the surface, and the use of otter guards is recommended. Fouling of fishing tackle was rare. Recommendations are made for practical steps that can be taken to minimize undesirable impacts of commercial fyke-netting, whilst realizing the potential financial and management benefits. The cost-effective uses of fyke-nets for sampling and culling fish for management purposes are discussed.     

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

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Report card on ecosystem‐based fisheries management in tuna regional fisheries management organizations

International instruments of fisheries governance have set the core principles for the management of highly migratory fishes. We evaluated the progress of tuna Regional Fisheries Management Organizations (tRFMOs) in implementing the ecological component of ecosystem‐based fisheries management (EBFM). We first developed a best case tRFMO for EBFM implementation. Second, we developed criteria to evaluate progress in applying EBFM against this best case tRFMO. We assessed progress of the following four ecological components: target species, bycatch species, ecosystem properties and trophic relationships, and habitats. We found that many of the elements necessary for an operational EBFM are already present, yet they have been implemented in an ad hoc way, without a long‐term vision and a formalized plan. Overall, tRFMOs have made considerable progress monitoring the impacts of fisheries on target species, moderate progress for bycatch species, and little progress for ecosystem properties and trophic relationships and habitats. The tRFMOs appear to be halfway towards implementing the ecological component of EBFM, yet it is clear that the “low‐hanging fruit” has been plucked and the more difficult, but surmountable, issues remain, notably the sustainable management of bycatch. All tRFMOs share the same challenge of developing a formal mechanism to better integrate ecosystem science and advice into management decisions. We hope to further discussion across the tRFMOs to inform the development of operational EBFM plans.     

Catch rate and at‐vessel mortality of circle hooks versus J‐hooks in pelagic longline fisheries: A global meta‐analysis

We conducted a meta‐analysis of literature reporting on the use of circle hooks and J‐hooks in pelagic longline fisheries. Our study included more data than previous meta‐analyses of the effects of hook type, due to both a larger number of relevant studies available in recent years and a more general modelling approach. Data from 42 empirical studies were analysed using a random effects model to compare the effects of circle hooks and J‐hooks on catch rate (43 species) and at‐vessel mortality (31 species) of target and bycatch species. Catch rates with circle hooks were greater for 11 species, including four tuna species, six shark species and one Istiophorid billfish. Catch rates on circle hooks were lower for seven species, including two Istiophorid billfishes and two species of sea turtle. At‐vessel mortality was significantly lower with circle hooks in 12 species, including three tuna species, three Istiophorid billfishes, swordfish (Xiphias gladius) and three shark species. No species had significantly greater at‐vessel mortality when captured with a circle hook rather than a J‐hook. While our general approach increased model variability compared to more detailed studies, results were consistent with trends identified in previous studies that compared the catch rates and at‐vessel mortality (between hook types) for a number of species. Our results suggest that circle hooks can be a promising tool to reduce mortality of some bycatch species in pelagic longline fisheries, although the effects depend on the species and the metric (catch rate or at‐vessel mortality), emphasizing the need for fishery‐specific data in conservation and management decisions.     

The physiological consequences of catch‐and‐release angling: perspectives on experimental design,interpretation, extrapolation and relevance to stakeholders

Over the past 20 years, there has been a dramatic increase in the use of physiological tools and experimental approaches for the study of the biological consequences of catch‐and‐release angling practices for fishes. Beyond simply documenting problems, physiological data are also being used to test and refine different strategies for handling fish such that stress is minimised and survival probability maximised, and in some cases, even for assessing and facilitating recovery post‐release. The inherent sensitivity of physiological processes means that nearly every study conducted has found some level of – unavoidable – physiological disturbance arising from recreational capture and subsequent release. An underlying tenet of catch‐and‐release studies that incorporate physiological tools is that a link exists between physiological status and fitness. In reality, finding such relationships has been elusive, with further extensions of individual‐level impacts to fish populations even more dubious. A focus of this article is to describe some of the challenges related to experimental design and interpretation that arise when using physiological tools for the study of the biological consequences of catch‐and‐release angling. Means of overcoming these challenges and the extrapolation of physiological data from individuals to the population level are discussed. The argument is presented that even if it is difficult to demonstrate strong links to mortality or other fitness measures, let alone population‐level impacts of catch‐and‐release, there remains merit in using physiological tools as objective indicators of fish welfare, which is an increasing concern in recreational fisheries. The overarching objective of this paper is to provide a balanced critique of the use of physiological approaches in catch‐and‐release science and of their role in providing meaningful information for anglers and managers.