Table of Contents

  • This report summarizes talks, discussions and conclusions from a multidisciplinary workshop on genetic consequences of fisheries and fisheries management held in Rönne, Bornholm in October 2006. The idea of arranging the workshop was put forward during an expert-seminar at Hólar College on Iceland in 2004 arranged by the Nordic Council of Ministers, where selected expert scientists discussed the current knowledge regarding the effects of commercial fishing activities on the genetic diversity of wild, marine fish species in Nordic waters.

  • A multi-diciplinary workshop on genetic consequences of fisheries and fisheries management was held in Rönne, Bornholm in October 2006. The main objectives of the meeting were to 1) improve communication between parties involved in fisheries management, 2) present current knowledge regarding genetic consequences of fisheries and highlight the importance of including genetic/biological data in the management of exploited fish species, and 3) agree upon recommendations how genetic considerations could be implemented in management and decision making processes. The following topics were discussed in detail: 1) Identification of populations and management units, 2) Co-management of fish resources as an alternative management strategy, 3) Evolutionary consequences of fisheries, 4) Genetic effects of fish releases, 5) Effects of fisheries on other species in the ecosystem, and 6) Genetic effects of marine protected areas. For each topic, invited experts gave plenary talks, followed by discussions by all participants in smaller working groups.

  • A future challenge is to manage and protect natural resources while meeting the socioeconomic needs of a rapidly increasing human world population. This challenge is perhaps particularly evident when it comes to aquatic organisms for which exploitation rates have increased dramatically in recent decades. High exploitation rates pose threats to biological diversity at several levels, including diversity at the gene level. For example, high fishing pressures may reduce population sizes to levels where inbreeding and loss of genetic variability become serious problems. Fishing in areas which are used by several populations of the same species (mixed stock fisheries) may result in overexploitation or even extinction of genetically unique populations. Furthermore, the high and selective mortality induced by fishing is likely to cause evolutionary changes in functional traits such as growth rate and maturation age.

  • Most exploited fish species are divided into genetically distinct local populations that evolve more or less as independent units (depending on the amount of genetic exchange between them). Natural selection may favour different gene variants in different geographic areas, and this could give rise to local adaptation, i.e. populations become adapted to different environmental conditions. Fishing and aquaculture may affect the genetic population structure in several ways. For example, extinction of genetically unique populations will result in loss of local adaptations and a reduced overall genetic diversity. Therefore, genetic population structure must be identified and accounted for in the management of exploited fish species.

  • Co-management implies that fishermen and other stakeholders (scientists, managers, governments etc) are involved in decision-making processes and the development of management strategies. One advantage with this way of managing aquatic resources is that decisions concerning for example exploitation rates tend to get higher acceptance among all stakeholders. Previous experiences indicate that co-management has the best potential to work on a local scale. Freshwater systems and coastal regions seem to be areas where opportunities for success are the best. A contributing cause could be that we generally have a better knowledge about the biology of freshwater fish as compared to marine species, which makes it easier for scientists to give clear recommendations and get support for their ideas among other stakeholders. Multi-national fisheries on marine species on international waters most likely are to politically contaminated for co-management. Politicians from different countries negotiate during international meetings and stakeholders from the different countries will not have direct influence on the decision-making process. Under these conditions, co-management is unlikely to work.

  • Exploitation rates on fish stocks have increased considerable during recent decades, and statistics from the Food and Agriculture Organization of the United Nations show that an increasing proportion of the world fish resources are overexploited, depleted, or recovering from depletion. Fishing induces high mortality, and the harvesting is not random: due to the size-selective fishing practices we employ, we are selectively killing large and fast-growing individuals. Also, fishing mortality is often nonrandom with respect to geographical location. The high and selective mortality induced by fishing has the potential to cause evolutionary changes in several important traits, such as growth rate, maximum length, age and size at maturation, and migration behaviours. These changes can have severe consequences for the exploited stock itself, e.g. reduced recruitment rates, but also on other species in the ecosystem through changed ecological interactions in for example the food web. Fishing has also been found to change the species composition in some ecosystems. Evolutionary changes are likely to affect the profitability due to lower yields and a lower commercial value. Evolutionary changes in life history or behaviour are likely to have consequences for maximum potential population growth rate at low density, and may thus have important consequences for the ability of stocks to recover from overexploitation.

  • The practice of releasing (stocking) fish into the wild is common in the management and conservation of a number of fish species. Releases are performed for different purposes, the most important being to increase the yield for commercial and recreational fisheries, to support endangered wild populations at risk of extinction or to reintroduce populations that have become extinct. There is a general concern, however, that releases of fish into the wild may constitute a threat to the genetic and ecological integrity of wild populations, and several guidelines on this subject have been produced.

  • The ecosystem approach is a strategy for management of land, waters and living resources that promotes conservation and sustainable use. The approach does not aim for short-term economic gains, but aims to optimize the use of an ecosystem without damaging it. Ecosystem has been defined in Article 2 of the Convention on Biological Diversity: “Ecosystem means a dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit”. The scale of analysis should be determined by the problem being addressed, and could, for example, be a pond, a lake or part of a sea. The ecosystem approach requires adaptive management to deal with the complex and dynamic structure of many ecosystems. “Learning by doing” and research feedback are important corner stones, and measures may need to be taken even if cause-and-effect relationships are not yet fully scientifically established. The ecosystem approach is comprehensive in that it includes, besides all biological resources, the economic health of communities that are affected. An important characteristic of ecosystem based management is that all parties involved, including fishermen, managers, scientists etc, are preferably involved in management decisions (see “co-management as an alternative management strategy” above).

  • The concept of allocating areas where fishing is prohibited or strongly restricted is not a new idea, but the use of Marine Protected Areas (MPAs) as a tool to conserve biodiversity has become increasingly popular in fisheries management. However, genetic effects of the establishment of MPAs have rarely been examined.

  • Scientists dominated among the participants. A few people working with management issues participated, whereas only one representative from an angler association and none from the fishermen’s federations participated (see list of participants in the appendix), which was a disappointment. One way to draw more managers could be to invite a few managers to give talks on subjects directly related to the practise of their profession. To meet fishermen and their organisations, it may be necessary to initiate meetings like this on a national or regional level.

  • Virtually every exploited fish species is subdivided genetically and/or phenotypically. This differentiation is often associated with local environmental conditions (e.g. habitat heterogeneity) and/or historical processes (e.g. deglaciation). The objective of this presentation is to broadly illustrate to managers and decision makers the relevance of recognizing and maintaining such differentiation for viable fisheries. To do so, I critically address several key questions: (i) why is maintaining within-species diversity important for management? (ii) What exactly are we trying to maintain? (iii) How do we go about maintaining it? Lessons learned from historical approaches to recognizing and maintaining diversity within species (e.g. the concept of an evolutionarily significant unit) are used to exemplify important principles to be considered when defining management/ conservation units within fish species at any given spatial scale. I then illustrate how these principles should be considered in practice through a detailed example of a migratory salmonid fish. Lastly, I address the controversial issue of how to prioritize population diversity within species to aid management. Indeed, although the loss of any one population is clearly unwanted, limited resources in the face of increasing human influences may require such prioritization for future management actions.