Dynamic ecosystem models and the evaluation of ecosystem effects of fishing: can we make meaningful predictions?

• 1. Fishing is one of the most widespread anthropogenic impacts on marine ecosystems. In recent times, the development of measurable metrics of the resultant ecosystem effects, has become an important aspect of fisheries management. Ecosystem models are often advocated as tools for the evaluation of system effects, but the extent to which models are able to make meaningful predictions, has not yet been fully addressed.
• 2. In order to assess the suitability of models, to evaluate ecosystem effects of fisheries, the direct and indirect effects were catalogued.
• 3. From the literature, 33 applications of marine ecosystem models were identified for analysis of their ability to fully assess these catalogued effects. Analysis was possible for only 24 of the models due to poor documentation of the other 9.
• 4. Each model was examined for their inclusion of nine functional groups, deemed essential for the assessment of impacts of fishing on the whole ecosystem (e.g. detritus, marine mammals). The models were also assessed for their inclusion of several additional factors, either fundamental in the regulation of marine ecosystems (e.g. environmental forcing), or important in the classification of their role as a predictor of changes in ecological processes (e.g. simulation, spatial properties).
• 5. No model formulation provided coverage in all the areas necessary to cover the identified effects of fisheries. Eight models provided good coverage, nutrient dynamics and benthos were the least well represented aspects of the ecosystem.
• 6. The ECOPATH with Ecosim family of models, the European Regional Seas Ecosystem Model (ERSEM) and the Anderson & Ursin multispecies extension to the Beverton & Holt model all seem likely to yield good insights.
• 7. In further developing these models, however, consideration must be given to explicitly incorporate spatial factors and extrinsic forcing functions, such as climate.

Copyright © 2002 John Wiley & Sons, Ltd.     

Managing inequality or managing stocks? An ethnographic perspective on the governance of small‐scale fisheries

A growing volume of recent research on small‐scale fisheries governance has a focus on local perspectives and priorities of small‐scale fisherfolk. This paper develops from this local perspective a novel focus on what is a fundamental priority of many small‐scale fishers: concerns about inequality. The paper begins with a critical review of the literature on small‐scale fisheries governance and suggests how a focus on inequality can make a useful contribution. The paper uses case‐studies of small‐scale fisheries in Papua New Guinea (PNG) and the Philippines to highlight local priorities about inequality and the implications for small‐scale fisheries governance. PNG and the Philippines have very different social, political and environmental contexts, yet in both cases, local inequalities were a key pre‐occupation of fisherfolk and posed major challenges for fisheries governance. While in both of the case‐studies, fishers were aware of and keen to act on resource sustainability, this concern was overridden by concerns over: who obtained benefits from the fishery; who was responsible for resource degradation; and who should bear the costs of regulation. We conclude by discussing how our emphasis on the importance of inequality at a local level can potentially be integrated within many influential approaches to small‐scale fisheries governance.     

Modelling the distribution of marine fishery resources: Where are we?

Ecological niche models (ENMs) and species distribution models (SDMs) have been widely applied to various studies relevant to biogeography, conservation biology, and ecology. These modelling techniques seek to develop spatial maps for projecting, among others past, current, and future species distributions. Born in the field of terrestrial ecology, only in recent years have these models been applied to marine environmental issues, especially to improve the forecasting of the distribution of occurrences and capturing of fishery resources. This study aimed to present through bibliometric analysis the characteristics of articles related to the use of ENMs and SDMs in marine fishery resources considering three main points: (1) state of the art: number of articles over the years, journals, countries, collaborations, and focus of research; (2) characteristics linked to fishery resources: marine biogeographic realms, taxonomic groups, life phases, oceanographic zones, and behaviours; (3) characteristics linked to methods: type of method, type of biological and, environmental data. We provide a list of 378 articles (derived from 930 screened ones), the results, and a discussion of our findings, which represent a baseline for the current status (strengths, limits, and gaps) of the interface between ENMs/SDMs and fishery resources.     

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

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

The European Water Framework Directive: a new era in the management of aquatic ecosystem health?

1. The forthcoming European Commission Water Framework Directive will introduce catchment management throughout Europe, and could have major impacts on the conservation and restoration of aquatic ecosystems. The Directive is outlined, and the proposed mechanisms for determining water quality status under the Directive are described. 2. The Directive is assessed using the developing ideas of ecosystem health. These combine scientific validity with an open acknowledgement of the value judgements inherent in all assessments of ecological quality, and emphasize the importance of public involvement. 3. Permitted derogations and exemptions are identified and their likely consequences discussed. These include substantial reductions in the potential of the Directive to improve water status in some cases. Existing bioassessment methods relevant to the proposed scheme are reviewed, and the sampling and statistical implications of the Directive are explored. Much work is needed on the development of ecological classification and referencing systems if the requirements of the Directive are to be met. 4. The emphasis of the Directive on biological (and not just chemical) quality goals, and the introduction of a consideration of ecological functioning (as well as structure) is welcomed. Although the Directive requires the assessment of hydromorphological and chemical, in addition to biological, variables, in most cases biological assessment is given priority. We advocate inclusion of all three elements in quality assessments. 5. The Directive gives little advice on policy integration for catchment management at European and national levels, and fails to provide for public involvement in the process of ecosystem management. These omissions will limit the ability of the Directive to deliver ecosystem health, and need to be addressed if the goals of the Directive are to be achieved. © 1998 John Wiley & Sons, Ltd.     

Does fishing dismantle fish culture and ecosystem structure? Questions about the implications of social learning among fish and fishers

Scientific awareness of social learning, especially among vertebrates, has expanded rapidly in recent decades. That literature suggests that social learning may be a second adaptive mechanism that interacts with and refines genetic adaptation. For an individual fish, learning from others reduces the costs of acquiring experience-based behaviours and minimizes the hazards that arise from imperfect knowledge of local regularities. For a group of fish, social learning facilitates the evolution of time and place behaviours that work in its locality. It spreads those behaviours within the group and to subsequent generations. Thus, social learning enables persistent adaptation at a finer scale than might be possible through genetic processes alone. Strong evidence of genetic differentiation at less than a panmictic scale and persistent local depletions suggests regular, fine-scale system structure. Social learning may play an important role in creating and maintaining this finer-scale structure. Fishers' learned adaptations to the market and natural system usually lead them to target larger/older fish and fish aggregations at familiar times and places. However, older fish are likely to be the principal repository of the time-and-place experience required for local growth, survival, and reproduction, while social aggregations are important schools in which younger fish acquire the experience of older fish. Consequently, if adaptation through social learning is important among fish, there is reason to be concerned that heavy fishing of social learners reduces their abundance, as usually assumed, and impairs the inheritance of the socially learned experience required for persistent local adaptation.     

How long should we ignore imperfect detection of species in the marine environment when modelling their distribution?

The application of the ‘ecosystem approach’ to marine conservation management demands knowledge of the distribution patterns of the target species or communities. This information is commonly obtained from species distribution models (SDMs). This article explores an important but rarely acknowledged assumption in these models: almost all species may be present, but simply not detected by the particular survey method. However, nearly all of these SDM approaches neglect this important characteristic. This leads to the violation of a fundamental assumption of these models, which presuppose the detection of a species is equal to one (i.e. at each survey locality, a species is perfectly detected). In this article, the concept of imperfect detection is discussed, how it potentially influences the prediction of species' distributions is examined, and some statistical methods that could be used to incorporate the detection probability of species in estimates of their distribution are suggested. The approaches discussed here could improve the collection and interpretation of marine biological survey data and provide a coherent way to incorporate detection probability estimates in the modelling of species distributions. This will ultimately lead to an unbiased and more rigorous understanding of the distribution of species in the marine environment.     

Reinventing residual reserves in the sea: are we favouring ease of establishment over need for protection?

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Is Pseudanodonta complanata the most vulnerable of widespread European species of unionids? An intense stress test leading to a massive die‐off

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An analysis of the effect of diet and genotype on protein and energy utilization by the black tiger shrimp,Penaeus monodon – why do genetically selected shrimp grow faster?

Selected (G8) and wild‐type (W) genotypes of black tiger shrimp (Penaeus monodon) juveniles (initial weight G8 = 9.14 ± 0.36 g per animal and W = 8.44 ± 0.10 g per animal) were fed either of two diet types in a clear‐water tank trial to examine the effects of diet type and genetics on growth and feed utilization parameters. Animals were fed twice daily at one of the five ration levels from starvation to apparent satiety. All uneaten feed was accounted for and moults removed. Starved animals were measured after 3 weeks; those fed were measured at both three and 6 weeks. Diet type varied by protein content, raw material choice and the presence [high‐specification diet (HSD)] or absence [low‐specification diet (LSD)] of bioactive substances. At the end of the study, faecal samples were also collected to determine the digestible protein and energy content of each diet by each genotype. Whole animal protein and energy content were also assessed from samples from the initial populations and those from each tank. Growth after 6 weeks of those animals fed to satiety showed that the G8 animals fed the HSD diet had grown at a rate of 2.56 g week^?1, significantly faster than any other treatment. Those G8 animals fed the LSD diet (1.81 g week^?1) had grown significantly faster than the W animals fed the HSD diet (1.25 g week^?1), while those W animals fed the LSD diet (0.61 g week^?1) grew the slowest. Using the data from the varying ration levels, we were able to define that the growth gains of the G8 animals were achieved not only by a greater appetite, but also through lower maintenance energy costs (29 versus 57 kJ kg^?0.8 day^?1) and a more efficient energy conversion (19.5% versus 11.6% when fed the HSD diet). Use of a low‐specification diet with the G8 and W shrimps limited their growth and impaired their potential as demonstrated by a curvilinear response of growth to intake. By comparison, those shrimp fed the HSD diet had a relatively linear growth response to intake.     

Should we allow human‐induced migration of the Indo–West Pacific fish,barramundi Lates calcarifer (Bloch) within Australia?

Some biologists have expressed concerns about the possible genetic impacts of translocation between stocks of barramundi Lates calcarifer (Bloch) in Australia. Recent genetic, biogeographical studies have provided an understanding of the evolution of the currently observed population structure in Australian barramundi by assessing the impacts of ice‐age, sea‐level changes on their distribution. These studies found that genetic differences between most barramundi populations are extremely small, have arisen in the past 17 000 years, and substantial migration and hybridization between eastern and western populations, isolated for at least 110 000 years, has occurred naturally. Some phenotypic support for these minor genetic differences can be inferred from the lack of adaptation to temperature in growth and survival responses of widely separated stocks (tropical and temperate). Based on a low level of genetic differentiation and high levels of gene flow between populations, with little evidence of local adaptation, translocation between populations should not pose a significant risk or problem.