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Trawl fishing constitutes an important part of the marine fisheries sector in Southeast Asia. It provides livelihoods and food for millions of people in coastal communities as well as feed for the ...

Bycatch in fisheries can have profound effects on the abundance of species with relatively low resilience to increased mortality, can alter the evolutionary characteristics and concomitant fitness of affected populations through heritable trait-based selective removals, and can alter ecosystem functions, structure and services through food web trophic links. We challenge current piecemeal bycatch management paradigms, which reduce the mortality of one taxon of conservation concern at the unintended expense of others. Bycatch mitigation measures may also reduce intraspecific genetic diversity. We drew examples of broadly prescribed ‘best practice’ methods to mitigate bycatch that result in unintended cross-taxa conflicts from pelagic longline, tuna purse seine, gillnet and trawl fisheries. We identified priority improvements in data quality and in understanding ecological effects of bycatch fishing mortality to support holistic ecological risk assessments of the effects of bycatch removals conducted through semi-quantitative and model-based approaches. A transition to integrated bycatch assessment and management that comprehensively consider biodiversity across its hierarchical manifestations is needed, where relative risks and conflicts from alternative bycatch management measures are evaluated and accounted for in fisheries decision-making processes. This would enable managers to select measures with intentional and acceptable tradeoffs to best meet objectives, when conflicts are unavoidable.

Derelict abandoned, lost and discarded fishing gear have profound adverse effects. We assessed gear-specific relative risks from derelict gear to rank-order fishing methods based on: derelict gear production rates, gear quantity indicators of catch weight and fishing grounds area, and adverse consequences from derelict gear. The latter accounted for ghost fishing, transfer of microplastics and toxins into food webs, spread of invasive alien species and harmful microalgae, habitat degradation, obstruction of navigation and in-use fishing gear, and coastal socioeconomic impacts. Globally, mitigating highest risk derelict gear from gillnet, tuna purse seine with fish aggregating devices, and bottom trawl fisheries achieves maximum conservation gains. Locally, adopting controls following a sequential mitigation hierarchy and implementing effective monitoring, surveillance and enforcement systems are needed to curb derelict gear from these most problematic fisheries. Primary and synthesis research are priorities to improve future risk assessments, produce the first robust estimate of global derelict gear quantity, and assess the performance of initiatives to manage derelict gear. Findings from this first quantitative estimate of gear-specific relative risks from derelict gear guide the allocation of resources to achieve the largest improvements from mitigating adverse effects of derelict gear from the world’s 4.6 million fishing vessels.

Bottom trawl fishing is a controversial activity. It yields about a quarter of the world's wild seafood, but also has impacts on the marine environment. Recent advances have quantified and improved understanding of large‐scale impacts of trawling on the seabed. However, such information needs to be coupled with distributions of benthic invertebrates (benthos) to assess whether these populations are being sustained under current trawling regimes. This study collated data from 13 diverse regions of the globe spanning four continents. Within each region, we combined trawl intensity distributions and predicted abundance distributions of benthos groups with impact and recovery parameters for taxonomic classes in a risk assessment model to estimate benthos status. The exposure of 220 predicted benthos‐group distributions to trawling intensity (as swept area ratio) ranged between 0% and 210% (mean = 37%) of abundance. However, benthos status, an indicator of the depleted abundance under chronic trawling pressure as a proportion of untrawled state, ranged between 0.86 and 1 (mean = 0.99), with 78% of benthos groups > 0.95. Mean benthos status was lowest in regions of Europe and Africa, and for taxonomic classes Bivalvia and Gastropoda. Our results demonstrate that while spatial overlap studies can help infer general patterns of potential risk, actual risks cannot be evaluated without using an assessment model that incorporates trawl impact and recovery metrics. These quantitative outputs are essential for sustainability assessments, and together with reference points and thresholds, can help managers ensure use of the marine environment is sustainable under the ecosystem approach to management., T. Mazor was supported during her research by a CSIRO Postdoctoral Fellowship and CSIRO Ruby Payne‐Scott Award.

Bottom trawl fisheries are the most widespread source of anthropogenic physical disturbance to seabed habitats. Development of fisheries-, conservation- and ecosystem-based management strategies requires the selection of indicators of the impact of bottom trawling on the state of benthic biota. Many indicators have been proposed, but no rigorous test of a range of candidate indicators against nine commonly agreed criteria (concreteness, theoretical basis, public awareness, cost, measurement, historical data, sensitivity, responsiveness, specificity) has been performed. Here, we collated data from 41 studies that compared the benthic biota in trawled areas with those in control locations (that were either not trawled or trawled infrequently), examining seven potential indicators (numbers and biomass for individual taxa and whole communities, evenness, Shannon–Wiener diversity and species richness) to assess their performance against the set of nine criteria. The effects of trawling were stronger on whole-community numbers and biomass than for individual taxa. Species richness was also negatively affected by trawling but other measures of diversity were not. Community numbers and biomass met all criteria, taxa numbers and biomass and species richness satisfied most criteria, but evenness and Shannon–Wiener diversity did not respond to trawling and only met few criteria, and hence are not suitable state indicators of the effect of bottom trawling. Synthesis and applications. An evaluation of each candidate indicator against a commonly agreed suite of desirable properties coupled with the outputs of our meta-analysis showed that whole-community numbers of individuals and biomass are the most suitable indicators of bottom trawling impacts as they performed well on all criteria. Strengths of these indicators are that they respond strongly to trawling, relate directly to ecosystem functioning and are straightforward to measure. Evenness and Shannon–Wiener diversity are not responsive to trawling and unsuitable for the monitoring and assessment of bottom trawl impacts. Fil: Hiddink, Jan Geert. Bangor University; Reino Unido Fil: Kaiser, Michel J.. Bangor University; Fil: Sciberras, Marija. Bangor University; Fil: McConnaughey, Robert A.. National Marine Fisheries Service; Estados Unidos Fil: Mazor, Tessa. The University of Queensland; Australia. Csiro Oceans And Atmosphere.; Australia Fil: Hilborn, Ray. University of Washington; Estados Unidos Fil: Collie, Jeremy S.. University of Rhode Island; Estados Unidos Fil: Pitcher, Clifford Roland. Csiro Oceans And Atmosphere.; Australia Fil: Parma, Ana María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Suuronen, Petri. Natural Resources Institute Finland; Finlandia Fil: Rijnsdorp, Adriaan D.. University of Agriculture Wageningen; Países Bajos Fil: Jennings, Simon. University of East Anglia; Reino Unido. International Council for the Exploration of the Sea; Dinamarca. Centre for Environment, Fisheries and Aquaculture Science. Lowestoft Laboratory; Reino Unido

Fishing gears are marked to establish and inform origin, ownership and position. More recently, fishing gears are marked to aid in capacity control, reduce marine litter due to abandoned, lost or otherwise discarded fishing gear (ALDFG) and assist in its recovery, and to combat illegal, unreported and unregulated (IUU) fishing. Traditionally, physical marking, inscription, writing, color, shape, and tags have been used for ownership and capacity purposes. Buoys, lights, flags, and radar reflectors are used for marking of position. More recently, electronic devices have been installed on marker buoys to enable easier relocation of the gear by owner vessels. This paper reviews gear marking technologies with focus on coded wire tags, radio frequency identification tags, Automatic Identification Systems, advanced electronic buoys for pelagic longlines and fish aggregating devices, and re-location technology if the gear becomes lost.

Bottom-contact fishing gears are globally the most widespread anthropogenic sources of direct disturbance to the seabed and associated biota. Managing these fishing disturbances requires quantification of gear impacts on biota and the rate of recovery following disturbance. We undertook a systematic review and meta-analysis of 122 experiments on the effects-of-bottom fishing to quantify the removal of benthos in the path of the fishing gear and to estimate rates of recovery following disturbance. A gear pass reduced benthic invertebrate abundance by 26% and species richness by 19%. The effect was strongly gear-specific, with gears that penetrate deeper into the sediment having a significantly larger impact than those that penetrate less. Sediment composition (% mud and presence of biogenic habitat) and the history of fishing disturbance prior to an experimental fishing event were also important predictors of depletion, with communities in areas that were not previously fished, predominantly muddy or biogenic habitats being more strongly affected by fishing. Sessile and low mobility biota with longer life-spans such as sponges, soft corals and bivalves took much longer to recover after fishing (>3 year) than mobile biota with shorter life-spans such as polychaetes and malacostracans (

Monitoring live and dead discarded catch contributes to effective fisheries management and ecological and socioeconomic sustainability. We determined contemporary rates and levels of discards in global tuna fisheries. An estimated 265 279 t (52 283 to 478 275 t 95% CI) is annually discarded by global tuna fisheries, composing about 5% of the weight of the total catch. Pelagic longline and purse seine fisheries contributed about 64 and 36% of discards, respectively. Other gear types composed < 1% of discards. Discards in tuna fisheries are now 63% lower than estimated 1 decade earlier, mainly due to large declines in discards in longline tuna fisheries, possibly from increased retention of formerly discarded species and sizes of catch and increased gear selectivity. The decline also resulted, in part, from employing different methods to categorize caught sharks whose fins were retained and carcasses discarded following processing. Discard rates were greater in shallow-than deep-set longline fisheries, and higher in purse seine sets associated with fish aggregating devices and other floating objects than in other purse seine set types. The quality and availability of data on discards in global tuna fisheries were extremely limited. Filling gaps in monitoring, improving observer data fields and collection protocols, and providing public access to amalgamated discard data held by fisheries management organizations will improve the certainty of future discard estimates, supporting effective management of discards in global tuna fisheries.

Aim: Trawling is the most widespread direct human disturbance on the seabed. Knowledge of the extent and consequences of this disturbance is limited because large-scale distributions of seabed fauna are not well known. We map faunal distributions in the Australian Exclusive Economic Zone (EEZ) and quantify the proportion of their abundance that occurs in areas 1) that are directly trawled and 2) where legislation permanently prohibits trawling—defined as percentage exposure or protection, respectively. Our approach includes developing a method that integrates data from disparate seabed surveys to spatially expand predicted benthos distributions. Location: Australia. Methods: We collate data from 18 seabed surveys to map the distribution of seabed invertebrates (benthos) in nine regions. Our approach combines data from multiple surveys, groups taxa within taxonomic classes and uses Random Forests to predict spatial abundance distributions of benthos groups from environmental variables. Exposure and protection of benthos groups were quantified by mapping their predicted abundance distributions against the footprint of trawling and legislated boundaries of marine reserves and fishery closures. Results: Trawling is currently prohibited from more area of Australia´s EEZ (58%) than is trawled (

Bottom trawling is the most widespread human activity directly affecting seabed habitats. Assessment and effective management of the effects of bottom trawling at the scale of fisheries requires an understanding of differences in sensitivity of biota to trawling. Responses to disturbance are expected to depend on the intrinsic rate of increase in populations (r), which is expected to be linearly related to the reciprocal of longevity. We examine the relationship between the longevity of benthic invertebrates and their response to bottom trawling; both in terms of the immediate mortality following a trawl pass and their subsequent rates of recovery. We collate all available data from experimental and comparative trawling studies, and test how longevity influences these aspects of sensitivity. The shortest lived organisms (1 year decreased by ~9% immediately following a trawl pass. The effect of bottom trawling in comparative studies increased with longevity, with a 2–3× larger effect on biota living >10 years than on biota living 1–3 years. We attribute this difference to the slower recovery rates of the long-lived biota. The observed relationship between the intrinsic rate of population increase (r, our metric of recovery rate) and the reciprocal of longevity matches theoretical expectation and predicts that the sensitivity of habitats to bottom trawling is higher in habitats with higher proportions of long-lived organisms. Synthesis and applications. Where the longevity of a species or the longevity distribution of a community is known or can be inferred, our estimates of depletion and intrinsic rate of increase can be combined with high-resolution maps of trawling intensity to assess trawling impacts at the scale of the fishery or other defined unit of assessment. Our estimates of r may also be used to estimate recovery times following other forms of seabed disturbance. Fil: Hiddink, Jan Geert. Fil: Jennings, Simon. Fil: Sciberras, Marija. Fil: Bolam, Stefan G.. Fil: Cambiè, Giulia. Fil: McConnaughey, Robert A.. Fil: Mazor, Tessa. Fil: Hilborn, Ray. Fil: Collie, Jeremy S.. Fil: Pitcher, Clifford Roland. Fil: Parma, Ana María. Fil: Suuronen, Petri. Fil: Kaiser, Michel J.. Fil: Rijnsdorp, Adriaan D..

The eastern Baltic cod (Gadus morhua) stock is at a critically low level and recruitment of the western Baltic cod stock is at the lowest observed level in over 30 years. The EU (European Union) landing obligation was introduced in 2015 for cod and in 2017 for plaice (Pleuronectes platessa). Size selective codend designs have been used in the Baltic cod trawl fishery for 25 years; however, there are still relatively high discard rates for cod, plaice and European flounder (Platichthys flesus; henceforth flounder) in the trawl fishery and landings of individuals below the minimum conservation reference size (MCRS). These problems call for additional improvements of species and size selectivity in the cod trawl fishery. In this study, two trawl codend designs were developed and tested to improve species and size selectivity in the Baltic cod trawl fishery. The codends were tested onboard a commercial trawler and the test codends were compared to the conventional Bacoma codend, which was fished simultaneously in a twin trawl rig. New codend designs were based on the Bacoma design, where the first test codend had a bottom net panel made of larger diamond meshes (nominal 130 mm mesh size) to improve selectivity in a cod fishery with high catch rates of flatfish. This codend showed a reduction of plaice and flounder, and cod below 45 cm, in the catches. The other test codend was a full square mesh codend (nominal 120 mm mesh size) developed for a cod directed fishery with low flatfish catches, and showed a marked reduction in the catch of cod below 50 cm, with no differences for flounder and plaice catches. With cod stocks at critically low levels and relatively high discard rates of cod, plaice and flounder, the simple codend designs tested in this study could benefit the sustainability of the Baltic cod trawl fishery, but with some loss of commercially targeted sizes.

When synthetic non-biodegradable fishing nets are lost, abandoned or discarded at sea, they may continue to catch fish and other animals for a long period of time. This phenomenon is known as ‘ghost fishing’. Biodegradable fishing nets, on the other hand, are intended to degrade or decompose after a certain period of time under water and thereby lose their ghost fishing capacity more quickly than conventional gear. A biodegradable net material, a blend of 82% polybutylene succinate (PBS) and 18% polybutylene adipate-co-terephthalate (PBAT), was developed. We examined the physical properties and degradability of the biodegradable monofilament, and compared the fishing performance of driftnets made of conventional nylon and of the biodegradable material. When dry, conventional nylon monofilament exhibited a greater breaking strength and elongation than biodegradable monofilament of the same diameter. When wet, the biodegradable monofilament exhibited a stiffness of c. 1.5-fold than nylon monofilament. This suggests that a net made of the less flexible biodegradable monofilament would have lower fishing efficiency than conventional nets. The fishing performance comparisons between the biodegradable and conventional nylon nets, however, revealed similar catch rates for yellow croaker Larimichthys polyactis. Biodegradable monofilament started to degrade after 24 months in seawater by marine organisms. We conclude that biodegradable netting may become a feasible alternative to conventional nylon netting and can contribute to reducing the duration of ghost fishing. Nonetheless, there remain many uncertainties, challenges and knowledge gaps that have to be solved before we are able to draw firm conclusions about the overall benefits of these materials in driftnet fisheries.

Accurate data on discards, the proportion of the catch that fishers do not retain, is necessary to achieve socioeconomically and ecologically sustainable fisheries. We review conventional and emerging approaches to monitor and manage discards. At-sea human observer programs currently produce the most accurate data on discards. Electronic monitoring may become the most effective method to monitor discards, as it has the capacity to overcome most sources of statistical sampling bias of conventional human onboard observer programs. Other monitoring approaches, including logbooks, fishery-independent surveys and fisher interviews, produce relatively unreliable discard estimates, while port sampling only provides information on landed catch. Modifications to fishing practices and gear to increase selectivity are main approaches used to reduce discards. Managing the temporal and spatial distribution of fishing effort by employing tools such as dynamic spatial management and fleet communication are additional discards management tools. Landing obligations, retention bans, bycatch caps, effort limits and size restrictions are additional approaches for which strengths and weaknesses are discussed. Continual evaluation is necessary to understand ever-changing causes of fishers' discarding decisions so that important factors can be accounted for in designing monitoring programs and discard models, and guide the adaptation of measures to manage and reduce discards.

Significance We conducted a systematic, high-resolution analysis of bottom trawl fishing footprints for 24 regions on continental shelves and slopes of five continents and New Zealand. The proportion of seabed trawled varied >200-fold among regions (from 0.4 to 80.7% of area to a depth of 1,000 m). Within 18 regions, more than two-thirds of seabed area remained untrawled during study periods of 2–6 years. Relationships between metrics of total trawling activity and footprint were strong and positive, providing a method to estimate trawling footprints for regions where high-resolution data are not available. Trawling footprints were generally smaller in regions where fisheries met targets for exploitation rates, implying collateral environmental benefits of effective fisheries management., Bottom trawlers land around 19 million tons of fish and invertebrates annually, almost one-quarter of wild marine landings. The extent of bottom trawling footprint (seabed area trawled at least once in a specified region and time period) is often contested but poorly described. We quantify footprints using high-resolution satellite vessel monitoring system (VMS) and logbook data on 24 continental shelves and slopes to 1,000-m depth over at least 2 years. Trawling footprint varied markedly among regions: from 50% in some European seas. Overall, 14% of the 7.8 million-km2 study area was trawled, and 86% was not trawled. Trawling activity was aggregated; the most intensively trawled areas accounting for 90% of activity comprised 77% of footprint on average. Regional swept area ratio (SAR; ratio of total swept area trawled annually to total area of region, a metric of trawling intensity) and footprint area were related, providing an approach to estimate regional trawling footprints when high-resolution spatial data are unavailable. If SAR was ≤0.1, as in 8 of 24 regions, there was >95% probability that >90% of seabed was not trawled. If SAR was 7.9, equal to the highest SAR recorded, there was >95% probability that >70% of seabed was trawled. Footprints were smaller and SAR was ≤0.25 in regions where fishing rates consistently met international sustainability benchmarks for fish stocks, implying collateral environmental benefits from sustainable fishing.

Bottom trawling is the most widespread human activity affecting seabed habitats. Here, we collate all available data for experimental and comparative studies of trawling impacts on whole communities of seabed macroinvertebrates on sedimentary habitats and develop widely applicable methods to estimate depletion and recovery rates of biota after trawling. Depletion of biota and trawl penetration into the seabed are highly correlated. Otter trawls caused the least depletion, removing 6% of biota per pass and penetrating the seabed on average down to 2.4 cm, whereas hydraulic dredges caused the most depletion, removing 41% of biota and penetrating the seabed on average 16.1 cm. Median recovery times posttrawling (from 50 to 95% of unimpacted biomass) ranged between 1.9 and 6.4 y. By accounting for the effects of penetration depth, environmental variation, and uncertainty, the models explained much of the variability of depletion and recovery estimates from single studies. Coupled with large-scale, high-resolution maps of trawling frequency and habitat, our estimates of depletion and recovery rates enable the assessment of trawling impacts on unprecedented spatial scales. Fil: Hiddink, Jan Geert. Bangor University; Reino Unido Fil: Jennings, Simon. Centre for the Environment; Reino Unido. University of East Anglia; Reino Unido Fil: Sciberras, Marija. Bangor University; Reino Unido Fil: Szostek, Claire L.. Bangor University; Reino Unido Fil: Hughes, Kathryn M.. Bangor University; Reino Unido Fil: Ellis, Nick. Commonwealth Scientific and Industrial Research Organization Oceans & Atmosphere; Australia Fil: Rijnsdorp, Adriaan D.. Institute for Marine Resources and Ecosystem Studies; Países Bajos Fil: McConnaughey, Robert A.. National Oceanic and Atmospheric Administration; Estados Unidos Fil: Mazor, Tessa. Commonwealth Scientific and Industrial Research Organization Oceans & Atmosphere; Australia Fil: Hilborn, Ray. University of Washington; Estados Unidos Fil: Collie, Jeremy S.. University of Rhode Island; Estados Unidos Fil: Pitcher, C. Roland. Commonwealth Scientific and Industrial Research Organization Oceans & Atmosphere; Australia Fil: Amoroso, Ricardo Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Parma, Ana María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Suuronen, Petri. Food and Agriculture Organisation of the United Nations; Italia Fil: Kaiser, Michel J.. Bangor University; Reino Unido

Jigging with artificial lights (squid jigging) and deploying of large scale trap-net (also known as a set-net in Japan), are the major methods to capture Japanese common squid Todarodes pacificus in western Japan. Squid jigging is a highly selective fishing method. However, it consumes large amount of energy for steaming to the fishing ground and for lighting. In contrast, trap-net fishing requires substantially less energy but its capture efficiency is strongly influenced by its stationary mode of capture. The primary objective of this study was to analyze how various environmental and biological factors such as the lunar cycle, tidal condition, wind direction and squid abundance affect the capture efficiency of squid jigging and trap-net fishing. We analyzed the effect of these factors on squid catch in five Fisheries Cooperative Associations located on four islands in Nagasaki Prefecture, western Japan. Our analysis shows that squid catch in jigging and trap-net fishing is mainly influenced by the lunar cycle but also tide and wind direction play a marked role. In addition, squid abundance significantly affects the catches in trap-net fishing. Recommendations are made to improve the overall profitability of squid fishing by proper choice of the capture method, location and season., Fisheries Science, 80(6), pp.1145-1157; 2014

Cryptic, not readily detectable, components of fishing mortality are not routinely accounted for in fisheries management because of a lack of adequate data, and for some components, a lack of accurate estimation methods. Cryptic fishing mortalities can cause adverse ecological effects, are a source of wastage, reduce the sustainability of fishery resources and, when unaccounted for, can cause errors in stock assessments and population models. Sources of cryptic fishing mortality are (1) pre-catch losses, where catch dies from the fishing operation but is not brought onboard when the gear is retrieved, (2) ghost-fishing mortality by fishing gear that was abandoned, lost or discarded, (3) post-release mortality of catch that is retrieved and then released alive but later dies as a result of stress and injury sustained from the fishing interaction, (4) collateral mortalities indirectly caused by various ecological effects of fishing and (5) losses due to synergistic effects of multiple interacting sources of stress and injury from fishing operations, or from cumulative stress and injury caused by repeated sub-lethal interactions with fishing operations. To fill a gap in international guidance on best practices, causes and methods for estimating each component of cryptic fishing mortality are described, and considerations for their effective application are identified. Research priorities to fill gaps in understanding the causes and estimating cryptic mortality are highlighted.

Balanced harvesting (BH) has been proposed as an alternative to the paradigm of more selective fishing as practiced in most European and North American fisheries management. We examine options for the implementation of BH and evaluate the issues raised in such an implementation. Implementation is considered at the whole ecosystem level, in terms of the patterns of removal for all species, both commercial and bycatch. We suggest that a “laissez-faire” approach analogous to the African lakes where BH was first observed is inappropriate in managed developed world fisheries. We consider two further approaches: focusing on either the species caught or on the sizes of animal alone. We find that aiming to harvest all species with an exploitation rate appropriate to their productivity would require a degree of micro-management that is probably unachievable, with all captured species “choking” the fishery in sequence. The size-based approach works with an exploitation rate appropriate to the productivity at size, with no consideration of the species involved. This might superficially be easier to implement, as management would involve a limited number of size classes only. However, problems may arise due to the likely faster capture of the more easily catchable fish, and also likely targeting of the more valuable species within a size class. We identify a possible third option of “broad brush” métier-based management that may resolve some of these problems. Other issues include the management of protected, endangered, and threatened species (including mammals, reptiles, and birds), the management of already severely depleted stocks, and the capture of benthic invertebrates.

We examined the digestive tract contents of 63 Baltic grey seals (Halichoerus grypus) and 37 Baltic ringed seals (Phoca hispida botnica) collected during May to November in 2008 and 2009 in the northern part of the Bothnian Bay to assess the role of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) in the diet of seals. For grey seals the three most common prey species in numbers were vendace (Coregonus albula), Baltic herring (Clupea harengus) and common whitefish (Coregonus lavaretus). Thirteen grey seals contained remnants of a total of 93 salmonids (Atlantic salmon and sea trout). Salmon ingested were, in general, older and larger than the ingested sea trout. Six grey seals had in their digestive tract Carlin-tags which are used to mark stocked salmonid smolts. Stocked sea trout appear particularly vulnerable to predation during the first months after the stocking. Our study suggests that salmonids may play a marked role in the diet of grey seals during the season when salmonids aggregate in coastal waters in the Bothnian Bay. Three-spined stickleback (Gasterosteus aculeatus), Baltic herring, smelt (Osmerus eperlanus) and vendace dominated in the ringed seal's diet. No salmonids were found in the dietary tracts of ringed seals.

The Finnish coastal fishery of Atlantic salmon ( Salmo salar ) in the northern Baltic Sea is regulated using multi-annual, pre-fixed, opening dates of harvests that aim to enhance spawning escapement of early migrating wild salmon. Such an inflexible management regime does not set regulations that track varying run sizes of salmon. We introduce an array of computational intelligence techniques to estimate and forecast coastal run size and escapement of salmon into three spawning rivers in the northern Baltic Sea. Our results indicated that the present management pattern, driven largely by regional fisheries policy, contrasts greatly with a “run-size driven” (i.e. abundance-based) management approach. Introducing run-size driven management, i.e. setting regulations annually by tracking preseason forecasts, would better ensure adequate escapement and at the same time allow the maintenance of coastal catch at sustainable level. Setting regulations annually would allow effective harvesting in years when the run is high, and would effectively restrict harvests when the run is low.

Much of the research that concerns the impacts of management measures in the eastern Baltic cod fishery has focused on fish stock rather than understanding fishermen's attitudes towards regulations. Hence, there is little information available on fishermen's responses although they are the ones whom the regulations affect most profoundly. This study analyses the views of fishermen towards management measures with an emphasis on fishing closures (marine protected areas, MPAs). Swedish log-book data from 1996 to 2005 were used to describe MPA induced fishing effort displacements. Fishermen argued that MPAs have been inefficient in conservation of cod stock. The enlargement of Bornholm MPA in 2005 caused substantial effort displacement towards areas dominated by smaller sized fish. This contributed to the increased discarding of juvenile cod. Enlarged MPAs also intensified competition between different fleet segments and reallocated fishing areas. To reduce fishing mortality, fishermen suggested days-at-sea (effort) regulation and an effective landings control system for all fleets that exploit cod stocks in the Baltic Sea Main Basin. These measures would better motivate fishermen for mutual rule compliance, which is a prerequisite for a sustainable cod fishery.

Return migration of Atlantic salmon, Salmo salar L., was studied in the Gulf of Bothnia, northern Baltic Sea, by a mark-recapture experiment and catch records from commercial trap-nets. Coastal salmon fishing is regulated by delayed opening of the fishery in consecutive regions based on the assumption that the wild fish migrate before reared ones and the migration is unidirectional and continuous from south to north. Neural network modelling suggested that the migration does not progress linearly from one regulation region to another, but shows variation between origin and sea age among and within regions. Further evidence of the non-linear migration included a noticeable part of salmon on their way to two major estuaries first visiting the northern-most Bothnian Bay before turning back south. Salmon returning to the different homing sites in the north showed no differences in run timing in the southern Gulf whereas the same individual fish showed differences in catch accumulation further north. Run timing estimates indicated only a slight tendency towards earlier migration for wild salmon compared with reared fish.

The conference ‘Fish Stock Assessment Methods for Lakes and Reservoirs: Towards the True Picture of Fish Stock’ (FSAMLR) was held in September 2007 in Ceske Budejovice, Czech Republic. A total of 110 participants from 34 countries attended the meeting and 93 lectures were presented. Great advances were reported in fish surveys using hydroacoustics and multimesh gillnet techniques, with nearly 60% of all presentations dealing with these topics. In contrast, the use of other active sampling gear, especially trawling and purse seining, received relatively little attention and still requires substantial further development. Reviews of standardization of fish sampling in the European Union, Russia and North America were also presented and clearly showed the benefits of standardized procedures. A number of contributions emphasized the need to use a combination of several methods for the same habitat. A true picture of the fish stock includes knowledge of the abundance, biomass, number of species, size and age compositions. Obtaining results of assured quality for all important lake and reservoir habitats and time periods still presents a significant challenge, although good progress is being made towards this important objective.

Suuronen, P., Tschernij, V., Jounela, P., Valentinsson, D., and Larsson, P-O. 2007. Factors affecting rule compiance with mesh size regulations in the Baltic cod trawl fishery. – ICES Journal of Marine Science, 64: 1603–1606. In this study, we evaluate the efficiency and applicability of a series of gear-based management measures, enforced since 1990, whose purpose was to improve size selectivity in the trawl fishery for Baltic cod (Gadus morhua). In general, our study revealed that these measures had no marked effect on the capture and discard of young cod. Legal and illegal manipulation of selective codends was widespread. The adoption of a codend design that offered a modest increase in selectivity, but had a good match with the legislated minimum landing size (MLS), led to greater compliance, demonstrating that a mismatch between MLS and selectivity should be avoided. It was also obvious that, generally, the fishing industry did not tolerate large short-term losses. Our evaluation is that overly ambitious rules will be circumvented, and frequent and incoherent changes in the regulations represent bad management practice. A gradual introduction of restrictions and participation by fishers in the decision-making process will increase compliance.

4 pages, 4 figures, 1 table, The management scheme in the northwest Mediterranean multispecies demersal fishery is based largely on technical measures such as minimum mesh and landing sizes. However, selectivity of the trawls used is poor, and large numbers of juvenile fish are caught. We assess the consequences of improved gear selectivity for European hake, Norway lobster, poor cod, and greater forkbeard by assuming that the whole fleet would switch from the current 40 mm diamond-mesh to a 40 mm square-mesh (SM40) codend. The results suggest that, immediately after implementation, the yield-per-recruit (Y/R) would be reduced by up to 20% for the three fish species but that, within five years, the Y/R of European hake would increase by .50%, provided fishing effort did not change markedly. For poor cod and greater forkbeard, the comparable increases would be more moderate, whereas for Norway lobster, the gains would only be small. Overall, marked long-term benefits might be obtained by changing to SM40 codends, The study was supported financially by the European Commission, Contract SSP8-CT-2003/501605 (NECESSITY)

11 pages, 4 figures, 5 tables, Commercial fishing trials with 40mm diamond (DM40) and square (SM40) mesh codends made of 5mm diameter knotted PE-netting were conducted in July 2005 on the continental shelf (~100 m) and upper slope (~400 m) of the Catalan Sea (NW Mediterranean) to assess the size selectivity of European hake (Merluccius merluccius), Norway lobster (Nephrops norvegicus), poor cod (Trisopterus minutus) and greater forkbeard (Phycis blennoides) in the demersal multi-species trawl fishery. In total, 28 tows were done using the standard covered codend method. For all four species, the SM40 showed a significantly higher mean selection length (L50) than the DM40. For hake the L50 was 16.0 cm in SM40 and 10.1 cm in DM40; the corresponding figures were 13.0 cm versus 9.2 cm for poor cod and 14.9 cm versus 9.8 cm for greater forkbeard. For Norway lobster, DM40 did not show any size-selectivity whereas SM40 produced a L50 of 22 mm. The selection range (SR) between DM40 and SM40 was not significantly (p > 0.05) different for any of the three fish species. Our trials indicate that substantial improvement in size-selectivity for these commercially important species is achieved by switching from the conventional 40mm diamond mesh codend to a 40mm square mesh codend. Our analysis also suggests that by using a 40mm square mesh codend the short-term economic losses of commercial species, compared to the losses of 40mm diamond mesh codend, will be low in the slope fishery (less than ~5% of the total catch value), whereas in the continental shelf losses could be up to ~30% of the total catch value., This study was financially supported by the European Commission, Contract SSP8-CT- 2003/501605 (NECESSITY).

The major wild Atlantic salmon stocks in the Baltic Sea began to recover in the late 1990s. This recovery has been partly due to strict regulations in the Gulf of Bothnia that effectively prevent salmon fisheries during the peak migration. About half of the migrating salmon, however, are reared fish that could be harvested. We simulated a limited trap-net fishery that selectively harvested reared salmon and released wild fish, and studied the survival and migration of the released salmon. We tagged and released 1970 salmon caught in the trap-nets along the coast in 2001 and 2002. The mean maximum capture and release induced mortality of salmon was 11%, ranging between 4% and 21% in different release groups by year, sea age and number of releases. The cumulative mortality for the total salmon population on their spawning migration in the Gulf of Bothnia was below 5%, and it would not increase considerably after the first capture and release events, provided fishing effort is not excessive and fish are handled properly. Survival of trap-net captured and released Baltic salmon appears high and their migration behavior is not altered due to this handling. Several preconditions, however, should be considered before selective fishing is introduced in the Gulf of Bothnia salmon fishery.

More than 50% of the world’s total marine catch (approximately 81 million tonnes) is harvested using towed fishing gears (i.e. Danish seines, dredges and otter and beam trawls). As for all methods, the total fishing mortality of these gears comprises the reported (landed) and unreported catch and other unaccounted, collateral deaths due to (i) avoiding, (ii) escaping, (iii) dropping out of the gear during fishing, (iv) discarding from the vessel, (v) ghost fishing of lost gear, (vi) habitat destruction or subsequent (vii) predation and (viii) infection from any of the above. The inherent poor selectivity of many towed gears, combined with their broad spatial deployment, means that there is considerable potential for cumulative effects of (i)‐(viii) listed above on total fishing mortality, and subsequent wide-scale negative impacts on stocks of important species. In this paper, we develop a strategy for minimizing this unwanted exploitation by reviewing all the primary literature studies that have estimated collateral, unaccounted fishing mortalities and identifying the key causal factors. We located more than 80 relevant published studies (between 1890 and early 2006) that quantified the mortalities of more than 120 species of escaping (26 papers) or discarded (62 papers) bivalves, cephalopods, crustaceans, echinoderms, elasmobranches, reptiles, teleosts and miscellaneous organisms. Seven of these studies also included the estimates of mortalities caused by dropping out of gears, predation and infection [(iii), (vii) and (viii) listed above]. Owing to several key biological (physiology, size and catch volume and composition), environmental (temperature, hypoxia, sea state and availability of light) and technical (gear design, tow duration and speed) factors, catch-and-escape or catch-and-discarding mechanisms were identified to evoke cumulative negative effects on the health of most organisms. We propose that because the mortalities of discards typically are much greater than escapees, the primary focus of efforts to mitigate unaccounted fishing mortalities should concentrate on the rapid, passive, size and species selection of nontarget organisms from the anterior sections of towed gears during fishing. Once maximum selection has been achieved and demonstrated to cause few mortalities, efforts should be made to modify other operational and/or post-capture handling procedures that address the key causal factors listed above.

During the last decade, seal-induced catch and gear damage have increased dramatically in the coastal trap-net fishery in the northern Baltic Sea. Our trials show that it is possible to markedly reduce seal damage by appropriate gear modifications and by careful choice of netting material. Five trap-net modifications and two traditional traps (four replicates of each) were compared under commercial fishing conditions. Modified traps were equipped with various types of fish bags made of strong seal-safe netting and a wire-grid in the funnel to prevent seals from entering into the bag. Four of the five modified models caught as much or more salmon as the traditional traps. In traditional traps, 30–50% of the total observed salmon catch was damaged. Trap modifications that were equipped with a fish bag made of double-layer netting held under tension offered the best protection; only 1–2% of the catch was damaged using these modifications. The proportion of seal-damaged catch varied between 16 and 27% for other modified trap designs. The use of thick and stiff polyethylene netting in the wings and middle chambers effectively prevented entangling of fish and thereby reduced their vulnerability to seal predation. Moreover, the seal-induced damage in the thick net was negligible compared with that of the thinner and more elastic nylon net of traditional traps.

Experiments were conducted in the Baltic Sea to measure mortality of cod that escape through trawl codend meshes under commercial fishing conditions. Three codend types were tested: a 120 mm diamond mesh codend, a Danish type 105 mm escape window codend, and a 105 mm square mesh top-panel codend (Bacoma-window). In total, 30 tows were carried out in three different experiments. Mean tow duration was 3 h and average codend catch 536 kg (range 47–2592 kg). Escapees were collected during the last 20 min of each haul by a caging method. These fish were then held in cages anchored on the seabed and checked daily by divers. Average number of escapees in cage was 133. Average caging duration was 9.5 days. The mortality of escapees was low in normal water temperatures (

Short-term effects of an increase in mesh size of a square mesh window codend were modelled with a stochastic size-selective simulation model using the 1999 fisheries data from the southern Baltic Sea (SD 25). Vessel-type-dependent selectivity estimates and catch per unit of effort (CPUE) data from Baltic cod ( Gadus morhua ) demersal trawl fishery were utilized to estimate the catch losses. When the window mesh size is increased by 15 mm (from 105 to 120 mm), overall catch loss of marketable size of fish during the first month would be 36–49%. Due to the marked effect of vessel type on overall codend selectivity, the decrease in marketable catch for side trawlers would be 42–60% and for stern trawlers 31–45%. With a 38-cm minimum landing size, discarding would decrease by 66–71%. In case fishermen would like to compensate the loss in the marketable catch by increasing their fishing effort, they would have to increase the effort by 55–90%. A 62–123% increase in fishing effort would be required to compensate the decrease in the marketable catch if both the window mesh size (from 105 to 120 mm) and the minimum landing size (from 38 to 40 cm) are increased. Fishermen would likely not be able to increase effort to such an extent. Instead, they might try to circumvent the regulations by intentionally decreasing the selectivity of their gear, i.e. by gear manipulation.

During the past decade, seal-induced gear and catch damage has increased dramatically in the Baltic Sea. The problems are most severe in the coastal trapnet fisheries for salmon (Salmo salar) and whitefish (Coregonus lavaretus), where grey seals (Halichoerus grypus) in particular frequently visit the traps. There is an acute need for gear modifications and other solutions that can prevent seals from entering the fish bag of the traps. Modifications that have been tested in Finland include a wire grid installed in the funnel of the trap and a fish bag made of extra-strong netting material. In comparative fishing experiments conducted in 2001 in the Gulf of Finland the grid was made of 2-mm steel wires with 175-mm spacing. The average undamaged salmon catch per haul in the fish bag of modified trapnets was significantly higher (70%) than that of traditional traps (Mann–Whitney, p < 0.01). In the whitefish experiments, the average undamaged catch of whitefish per haul was 16% higher in modified trapnets than in traditional traps, but the difference was not significant (Mann–Whitney, p > 0.05). These results indicate that the wire grid did not prevent fish from swimming into the fish bag. Experiments also suggest that the wire grid and the extra-strong netting prevented seals from entering the bag. However, on some occasions seals were able to tear the fish through the netting. Underwater observations confirmed that the wire grid kept adult seals outside the bag while salmon and whitefish could be seen entering through the grid into the bag.

Seal-induced catch damages have increased dramatically in the coastal trap-net fishery in the Baltic Sea. Most damage is caused by the rapidly growing grey seal (Halichoerus grypus) population. These seal–fishery interactions require practical and sustainable solutions. A potential measure is capture of live seals using fishers’ commercial trap-nets. The benefit of this approach to fishers would be to catch “nuisance” seals that have learned to use commercial fishing gear for finding their food sources and to remove them in an ethical way while endangered species could be released. We developed a capture system that can easily be installed into a modern salmon trap-net, commonly referred to as the pontoon trap. The aim was to develop a technique that enables undisturbed fishing while allowing live-capture of seals. Development work involved the testing of various structures and recording the behaviour of seals and fish on video. This paper demonstrates the criteria for a successful trap design and presents some observations of seal behaviour. The technique developed provides a unique method for scientific studies where seals have to be captured alive.

The objective of this study is to develop and test a practical field method for measuring survival of fish that pass through trawl cod-end meshes under commercial fishing conditions. This method permits the collection of escaping fish during any moment of a haul. Hence, survival can be assessed for short and long tows, small and large catch quantities, and for any desired depth using this technique. The method involves the use of a cage (with front and rear gates) that is attached to the terminal end of a cod-end cover. The front and rear gates can be held open during the tow, allowing cod-end escapees to pass freely through the cage and into the open sea. The rear gate is closed using a pre-set timer when a sample of escapees is needed. After a suitable sampling duration, pre-set timers activate the closure of the front gate and trigger the release of the cage from the cover. The cage is then left on the sea bed at the place of release for subsequent monitoring of fish condition (e.g., by divers). Trials were conducted on a demersal trawl vessel in the Baltic Sea in 1996–1997. We found that the method performed well under all circumstances for Baltic cod ( Gadus morhua L.) that escaped through trawl cod-end meshes. The method itself was not detrimental to the escapees.

The efficiency of modern, fully motorized under-ice winter seining technique was studied in the selective mass removal of coarse fish in the eutrophicated Lake Vesijarvi, southern Finland in 1992–1994. The total catch in 57 seine hauls was 69000 kg and the average catch per haul 1210 kg (250–6500 kg). The average biomass removed from the fishing area per haul was 120 kg ha−1 (SD 116) in the deepest basins (depth > 15 m), where smelt (Osmerus eperlanus L.) dominated the catches. The corresponding catch was 192 kg ha−1 (SD 187) in a shallower basin (< 15 m) where the catch comprised mainly cyprinids, all age classes of bream (Abramis brama L.) and bleak (Alburnus alburnus L.) and juveniles (1 + and 2+) of roach (Rutilus rutilus L.) and bleak. The catches were composed of aggregated fish since there was no correlation between the length of the haul and weight of the catch and the biomass removed from the fishing area was high. The under-ice pelagic schooling pattern of fish distribution was confirmed by scanning sonar monitoring which was effectively utilized in fishing. Winter seining is a suitable method for selective fish removal both in fisheries management and in biomanipulation of temperate lakes which are ice-covered for several months during a year.

The main objective of this study was to assess how and to what extent Baltic herring avoid and escape midwater trawls under commercial fishing conditions. Information was obtained by acoustic, visual and direct sampling techniques. The majority of herring schools in the path of an approaching trawl were observed to enter the trawl. When they did avoid the trawl it was by swimming downwards. The frequency of strong avoidance reactions was significantly higher during daytime than at night. Herring entering the trawl passed quickly into the funnelling rear part of the trawl, where they swam vigorously, trying to maintain their position in relation to the trawl. Fish often struck against the netting and their scales were seen passing through the meshes. Some herring escaped through the meshes of the upper rear panels of the trawl body, especially in the dark. Escaping herring were significantly smaller than those caught in the codends. Nevertheless, most herring ended up in the codend. We conclude that, although herring occasionally avoid and escape midwater trawls, the majority of fish in the trawl path are caught in the codend.

Studies on herring, Clupea harengus (L.), were conducted in the northern Baltic to assess whether the mortality of herring escaping through a rigid sorting grid (12 mm bar spacing) placed in front of the codend was diVerent from that of herring escaping from a 36 mm diamond mesh codend. Escapees were collected into netting cages, and subsequently transferred into large holding cages (85 m 3 ) where they were held for up to two weeks to assess mortality. 76‐100% of small (

Many young (0 group) vendace (Coregonus albula) are thought to die after passing through trawl cod ends during commercial vendace fishery in Finnish lakes. Survival of 2- to 4-month-old vendace (5–10 cm) after escaping from a 24-mm square mesh trawl cod end was therefore studied in Lake Puulavesi, Finland, during July–August 1993. Escapees were collected in a hooped netting cage that was released from the cod end after the tow, closed, and left at the depth of capture for 3–7 days. The data consist of 59 cagings. On average, 50% of the escaped vendace died, although mortality varied considerably. Most mortality occurred during the first day after escaping. Hauls conducted in the late evening and at night were accompanied by the highest mortality (60–80%). Mortality was 30–40% in the afternoon and early evening hauls. Generally, higher mortality was observed in August than in July. Comparisons with caged fish caught by a purse seine suggested that the experimental procedure did not substantially contribute to the observed total mortality of escapees. Scale loss and exhaustion experienced by vendace during trawl capture may have caused the rapid death of escapees through loss of osmoregulatory control.

A twin codend trawl was fished in the northern Baltic to study the size selectivity of square mesh and diamond mesh codends of 36-mm nominal mesh size. For each codend, 15 hauls were completed with a small mesh (20 mm) codend deployed on the other side of the trawl. The relative size of the catches in the two sides of the trawl varied considerably from haul to haul (the separator section was not operating properly) and selection curves were estimated from each individual haul using a method that incorporated the differences in catching efficiency of the two sides. The length of 50% retention decreased with increased catch for both the diamond and square mesh codends, although in neither case was this relationship statistically significant. Selection curves fitted to the combined haul data were asymmetric. The square mesh codend retained significantly less small herring than the diamond mesh codend, and for larger herring the two codends had similar selectivity. In both codends, most escapes occurred at the front of the catch bulge, from the upper side of the codend. At high catch rates, mesh blockage was observed for several metres ahead of the catch bulge during the later part of the tow.

17 pages, 9 figures, 6 tables, We explored the potential ecosystem effects of improved selectivity in the South Catalan Sea demersal trawl fishery. A calibrated food web model representing current conditions of the ecosystem and selectivity data from recent fishing experiments were used to perform temporal dynamic simulations. This enabled the evaluation of direct and indirect impacts of fishing and provided insights into the sustainability of various management options for the trawl fishery. This fishery has the biggest fleet in the area, it is highly multispecies, and catches are largely composed of juveniles of target species and non-target species, which are often discarded in large quantities. Simulations indicate that improvement of trawl selectivity would have noticeable and complex direct and indirect effects on target and non-target demersal species. The biomass and catch of various commercial species (e.g. anglerfish, adult hake) would increase, while that of invertebrates (e.g. suprabenthos, Norway lobster) and juvenile and small-sized fish species (e.g. juvenile hake, blue whiting) would decrease due to higher predation mortalities and trophic cascades in the food web. Impacts on the pelagic compartment would also be noticeable. A slight increase in the mean trophic level of the community and of the catch is predicted, as well as of ecosystem biomass diversity. Generally, however, a greater reduction of fishing effort would be necessary for the recovery of highly exploited or overexploited demersal species. Trawling would experience moderate decreases in catches, while long-lining and bait-trolling would benefit. This work highlights the importance of including the mortality incurred during or post-escape from trawl nets when assessing the ecosystem effects of improved trawl selectivity., This work was developed within the context of the NECESSITY project (SSP8-CT-2003, 50/605).

38 pages, 6 figures

3 pages, 1 figure

10 pages, 7 figures, 3 tables, 1 appendix, Interactions between grey seal, Atlantic salmon, and harvest controls on the salmon fishery in the Gulf of Bothnia, northern Baltic Sea, were investigated for the period 1999-2003. We assessed the effects of seal-induced catch losses (fish damaged or eaten by seals in the fishing gears) and harvest restrictions (delayed sequential opening of the fishery from south to north) on the Finnish coastal salmon catch and on escapement of salmon into the Tornionjoki River, the major breeding ground of the species in the Baltic Sea. Commercial logbook data on catches and seal-induced catch losses were used in a stochastic Monte Carlo analysis, indicating that mainly because of the stricter harvest controls enforced in 1996 and 1997, the average annual spawning run abundance that approached the Finnish coastal area increased by ca. 56 700 fish between 2000 and 2002. However, these fish were caught increasingly in the northern Gulf of Bothnia (Management Areas, MAs, 3 and 4), and relatively few salmon escaped into the Tornionjoki River. The landings in MAs 3 and 4 increased by 57% and 144%, respectively, whereas in the southern Gulf of Bothnia (MA 1), landings decreased by 23%. Over the five years of the study, seal-induced catch losses in MA 1 ranged from 24% to 29% of the total catch, whereas in MAs 2, 3, and 4 it ranged from 3% to 16%. The analysis suggests, however, that in MA 1 the regulation-induced catch losses were even higher than seal-induced catch losses, indicating that the salmon fishery was being impacted by both major factors. To increase escapement into the river and potentially to increase the future wild salmon catch, the opening of the harvest in the northernmost MAs should be delayed. Seal-induced catch losses should be reduced by extensive introduction of seal-safe fishing gears and by sustainable control of the grey seal population. © 2006 International Council for the Exploration of the Sea, The research was partly supported by the EC study 2003/502482 ‘‘Critical interactions between species and their implications for a precautionary fisheries management in a variable environment e a modelling approach’’ (BECAUSE)

11 pages, 5 figures, 4 tables, We estimated the total size of the Atlantic salmon (Salmo salar) population complex (wild and cultured) in the Gulf of Bothnia, northern Baltic Sea, using a stratified mark-recapture method. In 2001 and 2002, 1970 salmon were captured by the commercial trapnet fishery and tagged with external arrow tags. A total of 349 tagged fish was later recaptured among 65 180 salmon screened for tags. Recoveries were gathered by the commercial trapnets and by screening fish entering counting facilities in rivers and broodstock fisheries at the river mouths. In addition, tags were recovered from recreational river catches. Our estimates suggest that the total size of the migrating population in both years was about 230 000 fish. Proportions of wild and cultured salmon differed between the two years. In 2001, the proportion of wild salmon was 37%; the corresponding figure for 2002 was 62%. Based on estimates of wild salmon smolt production and the number of released smolts, the estimated proportion of cultured smolts that survived the feeding migration and returned to the Gulf of Bothnia (2-4%) was approximately 2.5-4.5 times lower than that of wild smolts (9-10%). © 2006 International Council for the Exploration of the Sea

11 pages, 7 figures, 4 tables, Seal-induced damage in the traditional trap-net fishery increased dramatically during the 1990s in the northern Baltic Sea. Most damage is induced by a rapidly growing grey seal (Halichoerus grypus) population. We evaluated seal damage in the coastal trap-net fishery of the Gulf of Bothnia, where different gear constructions and netting materials are used. A total of 72 commercial fishermen with 136 trap-nets were involved in the study. Catch and gear-damage observations made by fishermen were consistent with our own. The largest catch losses of salmon (Salmo salar) were recorded in the Bothnian Sea, where seals damaged at least 37% of salmon catch (by number). In other regions, losses were notably smaller, at between 3 and 9%. The number of salmon caught in a trap on any one occasion correlated significantly with the number of damaged salmon. However, the more salmon were present in a trap, the smaller was the proportion damaged by seals. Observed catch losses in the whitefish (Coregonus sp.) fishery varied between regions from 5 to 7%. Gear damage was observed in 2-15% of trap-net emptyings, depending largely on region. The extent of gear damage followed the trend of catch damage in each region. Fish entanglement in trap-nets increased the amount of gear damage. The type of netting material significantly affected gear-damage frequencies and salmon entanglement. Seal-induced catch and gear damage could be reduced by gear modification and operational changes. The choice of suitable netting materials and the development of seal-safe fish-bags are essential in protecting the gear and catch from seals. © 2005 Elsevier B.V. All rights reserved

The effects of three catching methods; trawling, gillnetting and poundnetting, on the quality of Baltic herring when stored at 8–16 °C were studied. The proportion of dead fish in the catch increased when the trawling time was increased from 2 to 5 h. Rigor mortis appeared soonest in fish caught by the gillnetting method being practiced. The inosine monophosphate (IMP) content was also lowest in gillnet-caught fish, indicating a loss of freshness. Differences between fish caught by the different methods could not be detected by sensory testing or on the basis of the dielectric properties of fish as measured by a Torrymeter GR device.

Impacts of bottom fishing, particularly trawling and dredging, on seabed (benthic) habitats are commonly per-ceived to pose serious environmental risks. Quantitative ecological risk assessment can be used to evaluate actualrisks and to help guide the choice of management measures needed to meet sustainability objectives.2.We develop and apply a quantitative method for assessing the risks to benthic habitats by towed bottom-fish-ing gears. The method is based on a simple equation for relative benthic status (RBS), derived by solving thelogistic population growth equation for the equilibrium state. Estimating RBS requires only maps of fishingintensity and habitat type–and parameters for impact and recovery rates, which may be taken from meta-ana-lyses of multiple experimental studies of towed-gear impacts. The aggregate status of habitats in an assessedregion is indicated by the distribution of RBS values forthe region. The application of RBS is illustrated for atropical shrimp-trawl fishery.3.The status of trawled habitats and their RBS value depend on impact rate (depletion per trawl), recovery rateand exposure to trawling. In the shrimp-trawl fishery region, gravel habitat was most sensitive, and though lessexposed than sand or muddy-sand, was most affected overall (regional RBS = 91% relative to un-trawledRBS = 100%). Muddy-sand was less sensitive, and thoughrelatively most exposed, was less affected overall(RBS = 95%). Sand was most heavily trawled but least sensitive and least affected overall (RBS = 98%).Region-wide, >94% of habitat area had >80% RBS because most trawling and impacts were confined to smallareas. RBS was also applied to the region’s benthic invertebrate communities with similar results.4.Conclusions. Unlike qualitative or categorical trait-based risk assessments, the RBS method provides a quanti-tative estimate of status relative to an unimpacted baseline, with minimal requirements for input data. It could beapplied to bottom-contact fisheries world-wide, including situations where detailed data on characteristics ofseabed habitats, or the abundance of seabed fauna are not available. The approach supports assessment againstsustainability criteria and evaluation of alternative management strategies (e.g. closed areas, effort management,gear modifications). Fil: Pitcher, C. Roland. CSIRO; Australia Fil: Ellis, Nick. CSIRO; Australia Fil: Jennings, Simon. Fisheries and Aquaculture Science; Reino Unido. University Of East Anglia; Reino Unido Fil: Hiddink, Jan G.. Bangor University; Reino Unido Fil: Mazor, Tessa. CSIRO; Australia Fil: Kaiser, Michel J.. Bangor University; Reino Unido Fil: Kangas, Mervi. Western Australian Fisheries and Marine Research Laboratories; Australia Fil: McConnaughey, Robert A. National Ocean And Atmospheric Administration. Alaska Fisheries Science Center; Estados Unidos Fil: Parma, Ana María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Rijnsdorp, Adriaan D.. IMARES Wageningen UR; Países Bajos Fil: Suuronen, Petri. FAO Fisheries and Aquaculture Department; Italia Fil: Collie, Jeremy S.. University of Rhode Island; Estados Unidos Fil: Amoroso, Ricardo Oscar. University of Washington; Estados Unidos Fil: Hughes, Kathryn M.. Bangor University; Reino Unido Fil: Hilborn, Ray. University of Washington; Estados Unidos