| 1. |
- Bryhn, Andreas, et al.
(författare)
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Which factors can affect the productivity and dynamics of cod stocks in the Baltic Sea, Kattegat and Skagerrak?
- 2022
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Ingår i: Ocean and Coastal Management. - : Elsevier BV. - 0964-5691 .- 1873-524X. ; 223
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Forskningsöversikt (refereegranskat)abstract
- Stocks of Atlantic cod (Gadus morhua) in the Baltic Sea, Kattegat and Skagerrak (N. Europe) have been strongly exploited for decades bringing them into an enduringly depleted status. Scientific cod stock related advice for targeted and mixed fisheries is provided on an annual basis by the International Council for Exploration of the Sea. This advice forms a basis for ministerial decisions on, e.g., the total allowable catch and management plans. Despite measures to reduce fishing-induced mortality of cod, such as catch and effort restrictions, increased gear selectivity, closed areas and seasons, clear signs of recovery are yet to be seen. Thus, traditional advice for the management of these stocks may have to be complemented by advice on supporting measures focusing on other pressures hampering the recovery of cod. The present study elaborates on potential supportive measures for cod stock recovery in the Baltic Sea, Kattegat, and Skagerrak (including local populations where applicable), based on current knowledge. The list of measures presented here is the outcome of in-depth discussions on the state-of-the-art knowledge, among cod experts and further with stakeholders with the aim to follow principles of ecosystem-based fisheries management. Following the identification of different pressures on and prerequisites for the separate stocks, the listed measures differ between stocks and include cod bycatch mortality reduction, alterations in fisheries affecting food sources for cod, restocking, protection of juvenile habitats, and reduced predation. The literature review and the list of measures are intended to provide decision-support for managers and policymakers aiming to provide conditions for the cod stocks to recover.
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| 2. |
- Sköld, Mattias, et al.
(författare)
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A no-take zone and partially protected areas are not enough to save the Kattegat cod, but enhance biomass and abundance of the local fish assemblage
- 2022
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 79, s. 2231-2246
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Tidskriftsartikel (refereegranskat)abstract
- To supplement catch and effort regulations with the purpose to rebuild the cod (Gadus morhua) stock in Kattegat, Sweden and Denmark established a large (426 km(2)) year-round no-take zone (NTZ) surrounded by partially protected areas (PPAs) in 2009. The purpose of these spatial regulations was to prohibit cod fishing on the spawning grounds and to displace fisheries bycatch of cod from areas where mature cod aggregate in the Kattegat. The aim of this study is to evaluate the effects of the established NTZ and PPAs on the local fish assemblage, including cod. Based on a spatially high-resolution bottom trawl survey in the Kattegat (covering 2008-2021), multivariate analyses revealed significant shifts in the fish assemblage. A closer analysis indicated that six to seven fish species, including cod increased in the NTZ relative to control areas depending on if abundance or biomass was used as dependent variable. Univariate analysis showed that two flatfish species dab (Limanda limanda) and lemon sole (Microstomus kitt), and Norway lobster (Nephrops norvegicus) significantly increased in biomass in the NTZ, and turbot (Scophthalmus maximus) in the PPA relative to the control areas. These results suggest that the NTZ protected even relatively mobile species in an open sea system, such as the Kattegat. However, neither cod abundance nor biomass showed a significant increase as an effect of the NTZ and PPA despite two relatively strong year classes in 2012 and 2013, which possibly would have helped the recovery of the cod stock. As assessed by the International Council for the Exploration of the Sea in 2022, Kattegat cod continuously suffer from being severely overfished with low recruitment, and high discard rates in the mixed N. norvegicus fishery, is considered the major driver behind the reinforced depletion of the stock.
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| 3. |
- Snoeijs-Leijonmalm, Pauline, 1956-, et al.
(författare)
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Unexpected fish and squid in the central Arctic deep scattering layer
- 2022
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 8:7
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Tidskriftsartikel (refereegranskat)abstract
- The retreating ice cover of the Central Arctic Ocean (CAO) fuels speculations on future fisheries. However, very little is known about the existence of harvestable fish stocks in this 3.3 million-square kilometer ecosystem around the North Pole. Crossing the Eurasian Basin, we documented an uninterrupted 3170-kilometer-long deep scattering layer (DSL) with zooplankton and small fish in the Atlantic water layer at 100- to 500-meter depth. Diel vertical migration of this central Arctic DSL was lacking most of the year when daily light variation was absent. Unexpectedly, the DSL also contained low abundances of Atlantic cod, along with lanternfish, armhook squid, and Arctic endemic ice cod. The Atlantic cod originated from Norwegian spawning grounds and had lived in Arctic water temperature for up to 6 years. The potential fish abundance was far below commercially sustainable levels and is expected to remain so because of the low productivity of the CAO.
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| 4. |
- Snoeijs-Leijonmalm, Pauline, 1956-, et al.
(författare)
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Review of the research knowledge and gaps on fish populations, fisheries and linked ecosystems in the Central Arctic Ocean (CAO)
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents a review of the research knowledge and gaps on fish populations, fisheries and linked ecosystems in the Central Arctic Ocean (CAO). The CAO comprises the deep basins of the Arctic Ocean beyond the shelf break, which largely overlap with the High Seas of the Arctic Ocean, i.e. the marine areas outside the Exclusive Economic Zones (EEZs) of the Arctic coastal nations. The authors of the report are members of the European Fisheries Inventory in the Central Arctic Ocean (EFICA) Consortium. This study was funded by the European Commission as an EU contribution to the international cooperation within the Agreement to Prevent Unregulated High Seas Fisheries in the Central Arctic Ocean.
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| 5. |
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| 6. |
- Bland, Barbara, et al.
(författare)
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Expeditionsrapport IBTS, augusti 2019
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Havsfiskelaboratoriets trålexpeditioner i Västerhavet (Skagerrak och Kattegatt) genomförs två gånger årligen, i kvartal 1 och 3. Fisket utförs med den franska bottentrålen GOV. Under denna expedition gjordes totalt 45 giltiga tråldrag i hela området, 26 i Skagerrak och 19 i Kattegatt. Totalt fångades 8,4 ton sill, 6,8 ton skarpsill och 69 kg torsk. I Skagerrak visar sillens 0-grupp en markant ökning. Skarpsillen som förra året dominerades av Kattegatts 1-åringar har minskat men 2+-gruppen i både Skagerrak och Kattegatt har ökat. Torsken visar en stark ökning av 0-gruppen, framför allt i Skagerrak men i jämförelse med den starka årsklassen 2011 är siffrorna måttliga. Övriga åldersklasser hos torsken är fortsatt extremt låga. Biologiska parametrar på individnivå samlas in på sill- och torskfiskar samt några plattfiskar. Totalt provtogs 4 191 individer från 11 olika arter med avseende på ålder och könsmognad.
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| 7. |
- Bland, Barbara, et al.
(författare)
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Expeditionsrapport IBTS, januari 2019
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Havsfiskelaboratoriets trålexpeditioner i Västerhavet (Skagerrak och Kattegatt) genomförs två gånger årligen, i kvartal 1 och 3. Den franska bottentrålen GOV används för fisket dagtid. Under kvartal 1 används också en mindre finmaskig trål (MIK) nattetid för provtagning av fisklarver. Under expeditionen genomfördes totalt 45 godkända tråldrag med GOV-trålen, tre i Nordsjön, 24 i Skagerrak och 18 i Kattegatt. Svenska Försvarsmakten medgav tillstånd för fiske på 24 stationer istället för de ordinarie 27 stationerna i Skagerrak. Den totala fångsten uppgick till drygt 13,1 ton och inkluderade 70 fiskarter. Den biologiska provtagningen, som inkluderar insamling av otoliter för åldersbestämning, gjordes på de viktigaste kommersiella arterna. Totalt togs 5 555 otoliter från 11 olika arter. MIK-trålningen resulterade i 60 godkända tråldrag med fångst av bland annat 607 sillarver, 2 skarpsillarver och 12 ållarver.
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| 8. |
- Cardinale, Massimiliano, et al.
(författare)
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Comments on Local cod (Gadus morhua) revealed by egg surveys and population genetic analysis after longstanding depletion on the Swedish Skagerrak Coast by Svedang et al.
- 2019
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 76, s. 1209-1211
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Tidskriftsartikel (refereegranskat)abstract
- Svedang et al. (2018) concluded that the occurrence of locally spawned cod eggs suggests that spawning on the Swedish Skagerrak coast takes place, which belong to either a coastal subpopulation that is a remnant stock of a once much larger cod population, or a newly formed subpopulation that is now successfully inhabiting the coastal ecosystems along the Swedish Skagerrak coast. However, after carefully reviewing the results and the data presented by the authors, we were no longer convinced that the information presented provided enough evidence for a local, distinct, coastal cod population in the Swedish Skagerrak. Thus, we requested the original genotype data, which the authors kindly provided to us. This allowed us to explore the substructure of these samples further using STRUCTURE 2.3.2. Re-analysis of the data consistently rejects the existence of an independent coastal Swedish stock in contrast with Svedang et al. (2018) conclusions. We acknowledge the observation of cod spawning in the area but, based on re-analysis of the original genetic data of Svedang et al. (2018), we currently lack the scientific basis to assume the existence of established local stocks, and even less the demographic expansion of an older, relict population in the area.
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| 9. |
- Hjelm, Joakim
(författare)
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Designing spawning closures can be complicated: Experience from cod in the Baltic Sea
- 2019
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Ingår i: Ocean and Coastal Management. - : Elsevier BV. - 0964-5691 .- 1873-524X. ; 169, s. 129-136
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Tidskriftsartikel (refereegranskat)abstract
- Fisheries management measures often include spatio-temporal closures during the spawning period of the fish with an overarching aim of improving the stock status. The different mechanisms how a spawning closure potentially can influence the stock are often not explicitly considered when designing such closures. In this paper, we review and synthesize the available data and knowledge on potential effects of the implemented spawning closures on cod in the Baltic Sea. The Baltic cod example represents a relatively data rich case, which allows demonstrating how a closure might affect different parameters of stock status via different mechanisms, including potential unintended negative effects. We conclude that designing relatively small area closures appropriately is highly complex and data demanding, and may involve tradeoffs between positive and negative impacts on the stock. Seasonal closures covering most of the stock distribution during the spawning time are more robust to data limitations, and less likely to be counterproductive if suboptimally designed.
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| 10. |
- Olsson, Jens, et al.
(författare)
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The first large-scale assessment of three-spined stickleback (Gasterosteus aculeatus) biomass and spatial distribution in the Baltic Sea
- 2019
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press. - 1054-3139 .- 1095-9289. ; 76:6, s. 1653-1665
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Tidskriftsartikel (refereegranskat)abstract
- Declines in predatory fish in combination with the impact of climate change and eutrophication have caused planktivores, including three-spined stickleback (Gasterosteus aculeatus), to increase dramatically in parts of the Baltic Sea. Resulting impacts of stickleback on coastal and offshore foodwebs have been observed, highlighting the need for increased knowledge on its population characteristics. In this article, we quantify abundance, biomass, size structure, and spatial distribution of stickleback using data from the Swedish and Finnish parts of the Baltic International Acoustic Survey (BIAS) during 2001-2014. Two alternative methods for biomass estimation suggest an increase in biomass of stickleback in the Baltic Proper, stable or increasing mean size over time, and larger individuals toward the north. The highest abundance was found in the central parts of the Baltic Proper and Bothnian Sea. The proportion of stickleback biomass in the total planktivore biomass increased from 4 to 10% in the Baltic Proper and averaged 6% of the total planktivore biomass in the Bothnian Sea. In some years, however, stickleback biomass has ranged from half to almost twice that of sprat (Sprattus sprattus) in both basins. Given the recent population expansion of stickleback and its potential role in the ecosystem, we recommend that stickleback should be considered in future monitoring programmes and in fisheries and environmental management of the Baltic Sea.
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