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Kan fredningsområden förbättra fisket i Sveriges stora sjöar? : Bilaga till uppföljningsrapport för fas 2 av projektet "Områdesbaserad förvaltning".

Sandström, Alfred; Ragnarsson Stabo, Henrik; Hammar, Johan; Asp, Anders; Axenrot, Thomas

Abstract

The usefulness and function of areas protected from fishing has been a major issue of scientific as well as political debate over the last decade. With a few exceptions, the vast majority of both case-studies and theoretical models are from marine environments. Although fisheries management in lakes faces similar problems as in marine systems, fishery closures has not been as frequently used as a management method and subsequently, the numbers of studies from lakes are few and rather limited. Nevertheless, large lakes in temperate areas could provide excellent study objects of the mechanistic processes that govern the success of protected areas, mainly due to lower number of species and habitat complexity and less complex dispersal mechanisms of early life-stages of fishes. In addition, the lakes are often closed systems that thus facilitate monitoring of whole populations. This report summarizes early results from an assessment of fishery closures in the largest lakes of Sweden. Particular emphasis has been given to monitor the impacts of fishery closures in Lake Vättern, the fifth largest lake in Europe. The commercial catch of the important fish species; whitefish (Coregonus lavaretus, L) and Arctic char (Salvelinus alpinus, L) have declined markedly since the mid 70s and as a means of remediation, three large areas, comprising 15 % of the lake's surface, were closed for all fishing in autumn 2005. We report our results monitoring the response of the fish communities within and outside the protected areas as well as the response of the fishery sector. Almost seven years after the closure, the overall catch per unit effort of Arctic char has increased substantially. There are no clear differences in abundance or biomass of Arctic char between protected and not protected areas. There are, however, some differences between closed areas and fished areas. The mean size and age of Arctic char has a more positive trend in the protected areas. There was also a significant effect of the size of the closures. The development of Arctic char was positively related to closure size. These results indicate that at least 25 % of the feeding areas of a mobile fish such as Arctic char must be protected in order to achieve a clear positive influence on a population under substantial pressure from fisheries. In parallel there was also a significant effect of the distance from the edge of the closures on Arctic char mean size, which decreased with increasing distance from the core of the largest protected areas. Several other species have also increased after the introduction of closures but in those cases there were no clear differences between closures and areas with fishing. Similar to the results in other monitoring programmes there has also been a sharp increase in the density of large fishes recorded in hydroacoustic surveys, particularly in deeper parts within protected areas. It is concluded that the positive development of Arctic char in particular and some other commercial species (particularly brown trout) is a product of a combination of fishery closures and other fishery regulations together with a marked reduction in the effort of the commercial fishery that has switched its attention to the more economically beneficial introduced signal crayfish. The total catch in the fisheries in Lake Vättern, when adding all types of fisheries, has mainly responded positively to the new fishery regulations. After an initial drop after the introduction of closures, the total catch of Arctic char has increased to approximately 38 tonnes in 2010 compared to 23 tonnes in 2003 and 17 tonnes in 2006. A similar positive trend was also observed for the catches of trout, which has more than doubled after the introduction of closures. Besides an increased total catch in many species, the fisheries have shifted in dominance from commercial to recreational fishing. Particularly the catches in trolling have increased markedly over time and at present contribute to the largest part of the overall fisheries mortality in Lake Vättern. 4 Besides permanent no-take closures there are also seasonal closures aimed to protect spawning areas of sensitive species. In Lake Vänern the catches of sander (Sander lucioperca) in areas with seasonal fishery closures were compared to other adjacent areas where fishing was allowed and with other lakes without fishery closures. Two of the investigated areas with spawning closures had low catches of pikeperch and very few young pikeperch in the catch indicating that these areas probably are not very important spawning areas. In the remaining areas in northern Lake Vänern on the other hand the catches of pikeperch were high and a significant part of the catch was constituted of young pikeperch. The comparison with other areas and lakes showed that the size distribution of pikeperch in Lake Vänern did not differ significantly from lakes without fishing closures. This study however is only comprised of data from two years and should be interpreted with care. An analysis of migration patterns and influence of fisheries on asp (Aspius aspius) in Lake Mälaren was conducted in collaboration with Sigtuna Naturskola and the County Administration of Stockholm. The results indicate that asp may migrate downstream for spawning and that the recreational fisheries on the species have changed as a response to introduction of spawning closures. General considerations when arranging zoning activities in Swedish large lakes are discussed. The importance of adapting the size and distribution of closed areas to the life-history and migration tendency of the target species is emphasised. The results from Lake Vättern show that fishery closures could be a powerful tool to remediate fisheries in crisis but since they constitute a significant violation of the livelihood of fishermen they should be used with care and only in situations where they can be fully legitimate. Involving stakeholders in zoning activities and using stakeholders local knowledge combined with modern spatial modelling techniques is concluded as a promising way to implement and facilitate the use of fishery closures in large lakes.

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Publisher: Fiskeriverket