213 research outputs found
Selective fishing induces density-dependent growth
Over the last decades, views on fisheries management have oscillated between alarm and trust in management progress. The predominant policy for remedying the world fishing crisis aims at maximum sustainable yield (MSY) by adjusting gear selectivity and fishing effort. Here we report a case study on how striving for higher yields from the Eastern Baltic cod stock by increasing selectivity has become exceedingly detrimental for its productivity. Although there is a successive increase in numbers of undersized fish, growth potential is severely reduced, and fishing mortality in fishable size has increased. Once density-dependent growth is introduced, the process is self-enforcing as long as the recruitment remains stable. Our findings suggest that policies focusing on maximum yield while targeting greater sizes are risky and should instead prioritize catch rates over yield. Disregarding the underlying population structure may jeopardize stock productivity, with dire consequences for the fishing industry and ecosystem structure and function
Comments to Froese et al. (2008): Size matters: Ne quid nimis
Letter to the editor: Comments to Froese et al. (2008
Re-thinking the “ecological envelope” of Eastern Baltic cod (Gadus morhua): conditions for productivity, reproduction, and feeding over time
Hypoxia is presently seen as the principal driver behind the decline of the former dominating Eastern Baltic cod stock (EBC; Gadus morhua). It has been proposed that both worsening conditions for reproduction and lower individual growth, condition, and survival are linked to hypoxia. Here, we elucidate the ecological envelope of EBC in terms of salinity stratification, oxygen content, and benthic animal biomasses, and how it has affected EBC productivity over time. The spawning conditions started deteriorating in the Gotland Deep in the 1950s due to oxygen depletion. In contrast, in the Bornholm Basin, hydrographic conditions have remained unchanged over the last 60 years. Indeed, the current extent of both well-oxygenated areas and the frequency of hypoxia events do not differ substantially from periods with high EBC productivity in the 1970s–1980s. Furthermore, oxygenated and therefore potentially suitable feeding areas are abundant in all parts of the Baltic Sea, and our novel analysis provides no evidence of a reduction in benthic food sources for EBC over the last 30 years. We find that while reproduction failure is intricately linked to hydrographic dynamics, a relationship between the spread of hypoxia and the decline in EBC productivity during the last decades cannot be substantiated.Peer reviewe
A continuous involvement of stakeholders promotes the ecosystem approach to fisheries in the 8-fjords area on the Swedish west coast
The coastal marine environment in the 8-fjords area on the Swedish west coast has been subjected to various stakeholder co-management initiatives since 1999. Stakeholders and authorities have acted by supporting and implementing gradually stricter fishing restrictions following the collapse in the 1970s of several demersal fish stocks and their apparent lack of recovery. Moreover, concerns have been raised regarding a locally sharp depletion of eelgrass meadows, in addition to an apparent increase in the number of seals and cormorants. The present 8-fjords initiative applies a cross-sector approach to environmental management and thus also addresses various types of environmental pollution. This study has compared the environmental work around the 8-fjords to 15 principles regarding the ecosystem approach to fisheries (EAF). The main strength that has been identified among the EAF principles is the continuous involvement of stakeholders. Among weaknesses in the EAF is the scarcity of suitable indicators that are necessary for appropriate monitoring, especially biomasses of functional groups as well as economic and social indicators. Many environmental problems in the fjords remain and it is possible that improved adherence to EAF principles will facilitate solving some problems and alleviating others. Moreover, the application of the EAF in practice in the 8-fjords can serve as a guiding example for co-managing other aquatic ecosystems towards ecological, economic, and social sustainability. The experiences from the 8-fjords initiative, including its extensive stakeholder involvement, may serve as a practical EAF example to be studied by researchers and managers globally
Genome architecture enables local adaptation of Atlantic cod despite high connectivity
Adaptation to local conditions is a fundamental process in evolution; however, mechanisms maintaining local adaptation despite high gene flow are still poorly understood. Marine ecosystems provide a wide array of diverse habitats that frequently promote ecological adaptation even in species characterized by strong levels of gene flow. As one example, populations of the marine fish Atlantic cod (Gadus morhua) are highly connected due to immense dispersal capabilities but nevertheless show local adaptation in several key traits. By combining population genomic analyses based on 12K single nucleotide polymorphisms with larval dispersal patterns inferred using a biophysical ocean model, we show that Atlantic cod individuals residing in sheltered estuarine habitats of Scandinavian fjords mainly belong to offshore oceanic populations with considerable connectivity between these diverse ecosystems. Nevertheless, we also find evidence for discrete fjord populations that are genetically differentiated from offshore populations, indicative of local adaptation, the degree of which appears to be influenced by connectivity. Analyses of the genomic architecture reveal a significant overrepresentation of a large ~5 Mb chromosomal rearrangement in fjord cod, previously proposed to comprise genes critical for the survival at low salinities. This suggests that despite considerable connectivity with offshore populations, local adaptation to fjord environments may be enabled by suppression of recombination in the rearranged region. Our study provides new insights into the potential of local adaptation in high gene flow species within fine geographical scales and highlights the importance of genome architecture in analyses of ecological adaptation
Corrigendum: Compensatory feeding in Eastern Baltic cod (Gadus morhua): recent shifts in otolith growth and nitrogen content suggest unprecedented metabolic changes
Improving the assessment and management of the plaice stock complex between the North Sea and the Baltic Sea
Small-scale biocomplexity in coastal Atlantic cod supporting a Darwinian perspective on fisheries management
Harvesting of marine resources raises concerns about how to identify and preserve biocomplexity, including the diversity of life histories found within and among wild populations of a species. In order to fully accomplish this, there is a need to elucidate the underlying causes of phenotypic variation, and how this variation responds to environmental changes. In general, both evolutionary (genetic) and nonevolutionary (plastic) responses may occur. Plastic responses to environmental change are expected to shift the phenotype along a reaction norm, while an evolutionary response is expected to shift the reaction norm itself. Here, we assess the maturation patterns of coastal Atlantic cod (Gadus morhua) in Skagerrak, where studies using neutral markers have revealed genetically differentiated populations of this harvested fish within tens of kilometres of coastline. Our results suggest that physiological state prior to the spawning season, as well as juvenile growth, both influence the probability of completing sexual maturation at a given age. Furthermore, our results point towards a spatial structuring of this plasticity (i.e. the maturation reaction norms) comparable with population connectivity inferred from neutral markers. We argue that such fine-scale biocomplexity calls for a Darwinian approach to fisheries management
Förvaltningsmål för nationellt förvaltade fiskbestånd
Fisk- och skaldjursbestånd som i huvudsak är begränsade till svenska nationella vatten förvaltas av svenska myndigheter och organisationer. Dessa bestånd kan i motsats till internationellt exploaterade och förvaltade arter utnyttjas av flera olika aktörer (t.ex. kommersiellt- och fritidsfiske). Olika grupper av aktörer kan ha olika syn på vad som är de lämpligaste långsiktiga förvaltningsmålen (t.ex. stor avkastning vs. stora individer). För dessa nationella bestånd är ofta datatillgången sämre än för in-ternationella bestånd, och ofta saknas tydliga mätbara förvaltningsmål, vilket resul-terar i en mindre effektiv förvaltning. Syftet med denna rapport är att ge en överblick över tillgängliga kvantitativa förvaltningsmål med tillhörande metoder som är lämp-liga för ett långsiktigt hållbart utnyttjande av nationella fisk- och skaldjursbestånd. Vi identifierar tre huvudkategorier av kvantitativa förvaltningsmål: 1) Långsiktigt hållbar avkastning, som kräver detaljerade data från många olika källor. 2) Minini-våer av biomassa- eller abundansindex, eller ett specifikt förhållande mellan fångst och biomassaindex, vilket kräver pålitlig övervaknings- eller fångstdata. 3) "Natur-lik" eller "önskvärd" demografisk struktur, vilket kräver information om egenskaper så som storlek, ålder, och könsmognad. Alla tre typerna av mål har sina förtjänster och nackdelar. Mål för hållbar avkastning och biomassa-index tar inte hänsyn till storleksstruktur, och vice versa, och olika mål kräver olika typer av indata. Vi gör en översikt av vilka förvaltningsmål som kan vara lämpliga för olika typer av nationellt förvaltade fisk- och skaldjursbestånd. För närvarande är aktuella data i allmänhet allt-för begränsade för att föreslå specifika förvaltningsmål för de flesta bestånd som kan komma i fråga för nationell förvaltning. Snarare betonar vi vikten av att använda flera olika mål i stället för att förlita sig på ett enda för att underlätta en hållbar användning av akvatiska resurser med hänsyn tagen till olika intressenter. Dessutom finns det ingen klar definition av vad ett nationellt bestånd är och när det är lämpligt att ha en nationell förvaltning. Därför är det viktigt att förvaltningsmålen sätts så att de kan återspegla både internationella, nationella och lokala förutsättningar
Nature’s contributions to people and human well-being in a Nordic coastal context
In this chapter, essential ecological and societal aspects of the Nordic coastal environment are highlighted. These show that local communities and stakeholders need to be more involved in decision-making because their needs and their ecological knowledge are essentialto this process. This also relates to Aichi targets 14, 15, 16 and 18 (see Lucas et al., 2015). There is the need to improve the monitoring of all types of NCP or ecosystem services and to critically review existing indicators that may be used to track the development of biodiversity and NCP. Only by actively analysing data and creating syntheses, is it possible to understand changes in the ecosystem linking biodiversity and NCP
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