Marine mammals' influence on ecosystem processes affecting fisheries in the Barents Sea is trivial

Biology Letters, Apr 2009

Some interpretations of ecosystem-based fishery management include culling marine mammals as an integral component. The current Norwegian policy on marine mammal management is one example. Scientific support for this policy includes the Scenario Barents Sea (SBS) models. These modelled interactions between cod, Gadus morhua, herring, Clupea harengus, capelin, Mallotus villosus and northern minke whales, Balaenoptera acutorostrata. Adding harp seals Phoca groenlandica into this top-down modelling approach resulted in unrealistic model outputs. Another set of models of the Barents Sea fish–fisheries system focused on interactions within and between the three fish populations, fisheries and climate. These model key processes of the system successfully. Continuing calls to support the SBS models despite their failure suggest a belief that marine mammal predation must be a problem for fisheries. The best available scientific evidence provides no justification for marine mammal culls as a primary component of an ecosystem-based approach to managing the fisheries of the Barents Sea.

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Marine mammals' influence on ecosystem processes affecting fisheries in the Barents Sea is trivial

Peter J Corkeron * Subject collections Articles on similar topics can be found in the following collections Receive free email alerts when new articles cite this article - sign up in the box at the top right-hand corner of the article or click here - Email alerting service To subscribe to Biol. Lett. go to: http://rsbl.royalsocietypublishing.org/subscriptions Biol. Lett. (2009) 5, 204206 doi:10.1098/rsbl.2008.0628 Published online 6 January 2009 Marine mammals influence on ecosystem processes affecting fisheries in the Barents Sea is trivial Some interpretations of ecosystem-based fishery management include culling marine mammals as an integral component. The current Norwegian policy on marine mammal management is one example. Scientific support for this policy includes the Scenario Barents Sea (SBS) models. These modelled interactions between cod, Gadus morhua, herring, Clupea harengus, capelin, Mallotus villosus and northern minke whales, Balaenoptera acutorostrata. Adding harp seals Phoca groenlandica into this top-down modelling approach resulted in unrealistic model outputs. Another set of models of the Barents Sea fish fisheries system focused on interactions within and between the three fish populations, fisheries and climate. These model key processes of the system successfully. Continuing calls to support the SBS models despite their failure suggest a belief that marine mammal predation must be a problem for fisheries. The best available scientific evidence provides no justification for marine mammal culls as a primary component of an ecosystem-based approach to managing the fisheries of the Barents Sea. 1. BACKGROUND Managing the way that people impact the marine environment requires understanding the ecological processes being affected, including those driving fish fisheries systems. There is a long-standing belief in some quarters that consumption of fishes by marine mammals must be a problem for commercial fisheries (Lavigne 2003). Despite research suggesting that marine mammal predation is a relatively trivial issue (e.g. Trzcinski et al. 2006), some stakeholders want ecosystem-based fishery management (EBFM, Pikitch et al. 2004) to include culls of marine mammals (e.g. Jones 2008). Culling as part of EBFM is implemented in Norways current policy on marine mammal management (Corkeron 2006). It is also implicit in the St Kitts & Nevis Declaration, drawn up by the prowhaling bloc of the International Whaling Commission in 2006 (Anonymous 2006). Probably the strongest scientific argument for culling comes from Norwegian research into marine mammals diet and their role in the Barents Sea ecosystem, which has been ongoing for over two decades (e.g. Blix et al. 1995; Smout & Lindstrm 2007). This work includes the Scenario Barents Sea Study (SBS) model (Schweder et al. 2000), which indicated that more northern minke whales, Balaenoptera acutorostrata, equate to less cod, Gadus morhua, and herring, Clupea harengus. Results of this model, and other aspects of the programme, were used when developing Norways current policy on marine mammal management ( Norwegian Ministry of Fisheries and Coastal Affairs 2004). 2. MODELS OF THE BARENTS SEA SYSTEM There are (or were) three major finfish fisheries in the Barents Sea, for Northeast Arctic cod, juvenile Norwegian spring-spawning herring and capelin, Mallotus villosus (Hjermann et al. 2004a). Northeast Arctic cod is the largest remaining cod population, with a spawning stock biomass currently estimated at over 600 000 ton (ICES 2008). Having recovered from collapse in the 1960s ( Toresen & stevedt 2000), the Norwegian spring-spawning herring population, at almost 12 000 000 ton (ICES 2007a), is the largest fish stock in the eastern North Atlantic, and the worlds largest herring stock. Cod and herring are fished. In recent years, herring total allowable catches (TACs) have been set at around those recommended by ICES (2007a), but for cod, agreed TACs have generally been higher than advised, and there is also an illegal fishery estimated in the tens of thousands of tonnes per year (ICES 2008). The capelin population in the Barents Sea has gone through three crashes in the past three decades. Since the first closure in 1987, the capelin fishery has been open 8 years and closed for 14 (ICES 2007b). A more detailed summary of this system is available in Hjermann et al. (2004b) There have been two main approaches used to elucidate the processes driving the fishfisheries system in the Barents Sea. One has focused on interactions within and between the three fish populations, fisheries and climate, primarily using statistical models: time-series analysis and regressions of varying sophistication (Hjermann et al. 2004a,b,c, 2007; Cury et al. 2008). Data for most of these models were available for the last two or three decades of last century, and so coincide with the research on marine mammal diet in the same area. These models explained up to over 80 p (...truncated)


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Peter J Corkeron. Marine mammals' influence on ecosystem processes affecting fisheries in the Barents Sea is trivial, Biology Letters, 2009, pp. 204-206, 5/2, DOI: 10.1098/rsbl.2008.0628