Decreasing body size has been proposed as a universal response to increasing temperatures. The physiology behind the response is well established for ectotherms inhabiting aquatic environments: as ...higher temperatures decrease the aerobic capacity, individuals with smaller body sizes have a reduced risk of oxygen deprivation. However, empirical evidence of this response at the scale of communities and ecosystems is lacking for marine fish species. Here, we show that over a 40‐year period six of eight commercial fish species in the North Sea examined underwent concomitant reductions in asymptotic body size with the synchronous component of the total variability coinciding with a 1–2 °C increase in water temperature. Smaller body sizes decreased the yield‐per‐recruit of these stocks by an average of 23%. Although it is not possible to ascribe these phenotypic changes unequivocally to temperature, four aspects support this interpretation: (i) the synchronous trend was detected across species varying in their life history and life style; (ii) the decrease coincided with the period of increasing temperature; (iii) the direction of the phenotypic change is consistent with physiological knowledge; and (iv) no cross‐species synchrony was detected in other species‐specific factors potentially impacting growth. Our findings support a recent model‐derived prediction that fish size will shrink in response to climate‐induced changes in temperature and oxygen. The smaller body sizes being projected for the future are already detectable in the North Sea.
Spatial management measures are currently being used to manage bycatch and discards, given the spatial heterogeneity of fish distributions. However, permanent fishing closures are often poorly ...implemented, unresponsive to stock dynamics and do not achieve their management objectives. Recently, real‐time spatial management tools for managing bycatch and discards implemented under either a comanagement or self‐governance approach have been introduced in Europe and the US. Real‐time catch and discard information is shared among fishers to incentivise and encourage vessels to leave areas of high bycatch. Here, the similarities and differences, in governance, implementation and management of ten real‐time spatial management systems from across Europe and the US are reviewed. A framework is developed to characterize the attributes associated with voluntary, private and regulatory real‐time spatial management tools. Challenges and management practices in the different case studies are reviewed providing insights for designing these spatial management tools. The results illustrate that real‐time spatial management approaches can create incentives for fishers to develop, use and share information and technology to avoid undesired catch. Compared with Europe, the US has developed spatial management tools with more truly real‐time mechanisms and with greater involvement of the fishing industry in designing and operating the tools.
Since the beginning of the 21st century, electronic monitoring (EM) has emerged as a cost‐efficient supplement to existing catch monitoring programmes in fisheries. An EM system consists of various ...activity sensors and cameras positioned on vessels to remotely record fishing activity and catches. The first objective of this review was to describe the state of play of EM in fisheries worldwide and to present the insights gained on this technology based on 100 EM trials and 12 fully implemented programmes. Despite its advantages, and its global use for monitoring, progresses in implementation in some important fishing regions are slow. Within this context, the second objective was to discuss more specifically the European experiences gained through 16 trials. Findings show that the three major benefits of EM were as follows: (a) cost‐efficiency, (b) the potential to provide more representative coverage of the fleet than any observer programme and (c) the enhanced registration of fishing activity and location. Electronic monitoring can incentivize better compliance and discard reduction, but the fishing managers and industry are often reluctant to its uptake. Improved understanding of the fisher's concerns, for example intrusion of privacy, liability and costs, and better exploration of EM benefits, for example increased traceability, sustainability claims and market access, may enhance implementation on a larger scale. In conclusion, EM as a monitoring tool embodies various solid strengths that are not diminished by its weaknesses. Electronic monitoring has the opportunity to be a powerful tool in the future monitoring of fisheries, particularly when integrated within existing monitoring programmes.
In recent years, scientists providing advice to fisheries managers have been granted access to an increasing range of spatio-temporal data from fishing vessels, using tools such as vessel monitoring ...systems and electronic observation platforms. This information should allow for the provision of more germane advice on the activity of vessels, and hence the likely impact of management measures which are becoming increasingly spatial in nature. However, the development of appropriate management simulation and assessment models has lagged behind the availability of these new data. This paper presents an accessible spatio-temporal simulation framework (Honeycomb) which features a weekly time-step, multiple stocks and vessels, and economic decision rules and applies this to a case study of a spatial evaluation of a simple closed-area fishery policy. We conclude that the development and utilization of such spatio-temporal simulation models is a key research task for fisheries in which both spatial fisheries data and spatial fisheries management are becoming paramount.
Abstract
Needle, C. L., and Catarino, R. 2011. Evaluating the effect of real-time closures on cod targeting. – ICES Journal of Marine Science, 68: 1647–1655. Under its Conservation Credits scheme to ...reduce cod mortality, the Scottish Government has implemented a system of real-time closures (RTCs) since 2008. These are relatively small, temporarily closed areas (50–225 square nautical miles per RTC, closed for 21 d) that are triggered by high cod catches. An important step in evaluating their effectiveness is to determine the response of vessels to RTCs, because the conservation benefit would be reduced if vessels moved to areas of greater cod abundance following closures. Abundance indices from research-vessel surveys and commercial-vessel observer trips are combined to create a time- and space-dependent relative cod-importance index (RCII). Vessel monitoring system data from Scottish vessels fishing during 2008/2009 are used to construct RCII profiles for each vessel, which are then used to determine whether the areas to which vessels move have a higher or a lower RCII, and how far away they move when an RTC is activated. We show that the RCII of the areas moved to tends to be lower than that of the RTC and that vessels travel farther when moving away from a closure than when moving back after reopening. Although not conclusive, this result indicates that RTCs may impact beneficially on cod mortality.
SURBAR is a survey-based fisheries stock assessment model that is used to indicate relative stock dynamics and provide advice for both data-rich and data-poor fisheries. It is a relatively simple ...separable model that requires only a survey index-at-age to determine stock trends (although data on weights and maturity can also be included). This paper evaluates the characteristics and potential utility of SURBAR by applying it to data generated by the model itself, considering the impact of three parameters (survey noise, smoothing, and the time of year of the survey) on the ability of the model correctly to reconstruct self-generated populations. We show that, while SURBAR is generally able to achieve this reconstruction, errors can be induced by either of the three tested parameters that may not be detectable by standard goodness-of-fit measures, and which could lead to inappropriate management advice. The analysis emphasises the importance of understanding the likely characteristics and behaviour of the model before using it to provide advice on fisheries stock dynamics.
Stockrecruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume that the proportion of SSB composed of females and the relative fecundity (number of eggs ...produced per unit mass) are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production (TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period. The proportion of females (FSB/SSB) varied between 24% and 68%, and the variation was systematic with length such that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock (TEP/SSB) varied between 115 and 355 eggs·g
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and was significantly, positively correlated with mean length of spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size (overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference between SSB and FSB in the assessment of stock status; however, in recent years (19802001) TEP fell below the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status.
Part of the European Union (EU) Common Fisheries Policy revision of 2013 is a commitment to implement a land-all policy, under which the practice of discarding caught fish back into the sea will be ...forbidden. This measure will be applied first to the pelagic fleet in 2015, with a phased implementation for the demersal fleet between 2016 and 2019. As part of trials to determine the efficacy of a land-all policy for North Sea cod (Gadus morhua L.), Remote Electronic Monitoring (REM) systems were installed on seven Scottish demersal vessels in 2008. Vessels were permitted additional days-at-sea and cod quota, and were obliged to land all cod caught in the North Sea. This arrangement has been renewed each year as part of the Scottish Cod Conservation Credits scheme, and while the list of vessels involved has not remained constant, the scheme remains attractive to skippers (27 vessels in 2014), has always been oversubscribed, and is likely to remain a key part of the Scottish Government's approach to land-all enforcement. Marine Scotland Science is granted access to all REM data collected from Scottish vessels. This paper summarizes the scientific analyses carried out using these data from 2008 onwards, including the installation and operation of REM systems for scientific purposes; the programme developed to train REM analysts; systems for combining length measurements with fish counts; the potential use of REM data in management advice; and studies on such aspects as discard-rate estimation, activity mapping, estimating the relative costs of on-board and REM observation, morphometric length inference, and automated image analysis. We conclude that, while further development work is certainly needed, REM provides a rich source of fisheries information for science as well as for compliance and management. However, care will need to be taken to ensure that science monitoring and analysis resources do not become overwhelmed.
Probabilistic projections of future fish population dynamics and the determination of many management reference points are both driven by fishery recruitment models. In turn, these projections and ...reference points largely govern perceptions of the likely response of a population to fishery management action. Hence, recruitment modeling is a vital component of stock assessment as carried out for the purposes of strategic fisheries management. This review presents a synopsis of the types of recruitment model that are currently utilised in stock assessments, the reasons that certain models are habitually selected and the problems inherent in their use, and some of the key ongoing research efforts that are attempting to improve the validity of recruitment models. The need for increased multidisciplinary symbiosis in the development of recruitment models is emphasized.
North Sea haddock (
Melanogrammus aeglefinus) are managed under a plan agreed between the European Union (EU) and Norway. This management plan was reviewed during 2006. As part of the review process, ...a quantitative management strategy evaluation (MSE) was undertaken, both of the existing plan and of proposed modifications. The evaluation was implemented in the R programming system, using FLR libraries, and was based on stochastic simulations of the complete fishery system (including a biological operating model, a knowledge production model with “live” stock assessments, and a simple implementation model). The generation of appropriate time-series of recruitment was of key importance for a stock like North Sea haddock which produces sporadic large year-classes. Although some refinement of growth and discard models is still required, tentative conclusions can be reached on the likely efficacy of different management plans. Well-defined MSEs have the potential to impart useful information for assessment scientists, fisheries managers and stakeholders.
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