Harbour porpoise (Phocoena phocoena) predation on cod (Gadus morhua) in the Kattegat : a review of current knowledge and implications for stock assessments
Kattegat is an area between Denmark and Sweden that connects the Atlantic Ocean to the Baltic Sea. It has long been an important source for fishery of cod (Gadus morhua). In a time where the future of the Kattegat cod stock is uncertain, the relationship between the predator harbour porpoise (Phocoe...
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| Formato: | M2 |
| Lenguaje: | Inglés sueco |
| Publicado: |
SLU/Dept. Of Aquatic Resources
2017
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| Materias: |
| _version_ | 1855571726691205120 |
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| author | Wallin, Adam |
| author_browse | Wallin, Adam |
| author_facet | Wallin, Adam |
| author_sort | Wallin, Adam |
| collection | Epsilon Archive for Student Projects |
| description | Kattegat is an area between Denmark and Sweden that connects the Atlantic Ocean to the Baltic Sea. It has long been an important source for fishery of cod (Gadus morhua). In a time where the future of the Kattegat cod stock is uncertain, the relationship between the predator harbour porpoise (Phocoena phocoena) and the Kattegat cod remains relatively unknown. In this study, available data that can be used to assess this prey-predator relationship are compiled and evaluated, and the information gaps that need to be filled are identified and discussed. The most recent harbour porpoise abundance assessment from SCANS-III can be approximately remodelled for the Kattegat area to 23 190 (15 550-30 830) animals, eating an estimated average of 3.7 (1.9-5.5) kg of prey each day. Of this, an estimated average of 22 % (5.5-29.3) in weight is comprised of cod, a number which varies seasonally, annually and depending on age and sex of the predator. These results give a mean total annual consumption of 7 020 (593-18 150) tonnes of cod from harbour porpoises in the Kattegat.
When applying harbour porpoise predation to the stock assessment model of Kattegat cod, it is important to have accurate representations of harbour porpoise abundance and diet
composition of harbour porpoise from the Kattegat region specifically. As a stock assessment model is to be used to assess potential threats in the future of the Kattegat cod stock, it is important to be able to connect these values to the variations of prey compositions available in the Kattegat, so that the harbour predation can be assessed for the future. Sufficient data is currently unavailable, and the timeframes in which the samples have been collected are too long and too old to be able to take variations over time into account. More samples from the Kattegat and would be required to make an accurate harbour porpoise predation assessment, ideally in timeframes that are comparable to the ongoing assessments of the cod stock in the Kattegat. As such data is not currently being collected, it could be possible to use available diet composition data, combined with knowledge of seasonal variations in feeding habits to make an approximation of how harbour porpoise predation varies with varying availability of cod in the Kattegat. These approximations may be used to create vague prognoses for the cod stock assessment model. |
| format | M2 |
| id | RepoSLU10643 |
| institution | Swedish University of Agricultural Sciences |
| language | Inglés swe |
| publishDate | 2017 |
| publishDateSort | 2017 |
| publisher | SLU/Dept. Of Aquatic Resources |
| publisherStr | SLU/Dept. Of Aquatic Resources |
| record_format | eprints |
| spelling | RepoSLU106432017-08-24T12:43:46Z Harbour porpoise (Phocoena phocoena) predation on cod (Gadus morhua) in the Kattegat : a review of current knowledge and implications for stock assessments Vanlig tumlares (Phocoena phocoena) predation på torsk (Gadus morhua) i Kattegatt : en översikt över befintlig kunskap och implikationer för beståndsanalyser Wallin, Adam Atlantic cod diet Gadus morhua harbour porpoise Kattegat Phocoena phocoena prey Kattegat is an area between Denmark and Sweden that connects the Atlantic Ocean to the Baltic Sea. It has long been an important source for fishery of cod (Gadus morhua). In a time where the future of the Kattegat cod stock is uncertain, the relationship between the predator harbour porpoise (Phocoena phocoena) and the Kattegat cod remains relatively unknown. In this study, available data that can be used to assess this prey-predator relationship are compiled and evaluated, and the information gaps that need to be filled are identified and discussed. The most recent harbour porpoise abundance assessment from SCANS-III can be approximately remodelled for the Kattegat area to 23 190 (15 550-30 830) animals, eating an estimated average of 3.7 (1.9-5.5) kg of prey each day. Of this, an estimated average of 22 % (5.5-29.3) in weight is comprised of cod, a number which varies seasonally, annually and depending on age and sex of the predator. These results give a mean total annual consumption of 7 020 (593-18 150) tonnes of cod from harbour porpoises in the Kattegat. When applying harbour porpoise predation to the stock assessment model of Kattegat cod, it is important to have accurate representations of harbour porpoise abundance and diet composition of harbour porpoise from the Kattegat region specifically. As a stock assessment model is to be used to assess potential threats in the future of the Kattegat cod stock, it is important to be able to connect these values to the variations of prey compositions available in the Kattegat, so that the harbour predation can be assessed for the future. Sufficient data is currently unavailable, and the timeframes in which the samples have been collected are too long and too old to be able to take variations over time into account. More samples from the Kattegat and would be required to make an accurate harbour porpoise predation assessment, ideally in timeframes that are comparable to the ongoing assessments of the cod stock in the Kattegat. As such data is not currently being collected, it could be possible to use available diet composition data, combined with knowledge of seasonal variations in feeding habits to make an approximation of how harbour porpoise predation varies with varying availability of cod in the Kattegat. These approximations may be used to create vague prognoses for the cod stock assessment model. Kattegatt är ett område mellan Danmark och Sverige som sammankopplar Atlanten med Östersjön. Det har länge varit ett viktigt område för fiske utav torsk (Gadus morhua). Framtiden hos torskbeståndet i Kattegatt är osäker, och trots det är fortfarande sambandet mellan predatorn vanlig tumlare (Phocoena phocoena) och Kattegattorsken relativt okänt. I denna studie samlas och utvärderas den tillgängliga data som kan vara till användning för att uppskatta detta samband mellan byta och predator, och de informationsluckor som finns identifieras och diskuteras. Den senaste uppskattningen av abundans för tumlare, SCANS-III, kan ungefärligt omräknas till 23 190 (15 550-30 830) tumlare i Kattegatt. Dessa äter uppskattat 3.7 (1.9-5.5) kg fisk om dagen, och uppskattat 22% (5.5-29.3%) av detta är torsk, en siffra som varierar med säsong, årsvis och beroende på predatorns ålder och kön. Med dessa resultat kan en årlig medelkonsumption beräknas till 7 020 (593-18 150) ton torsk för de tumlare som finns i Kattegatt. När man ska applicera predation från tumlare på befintliga beståndsanalyser av torskbeståndet I Kattegatt så är det viktigt att variablerna för tumlarabundans och tumlarnas dietsammansättning är representativa specifikt för tumlare i Kattegatt. Då en beståndsanalys används för att uppskatta potentiella framtida hot mot Kattegattbeståndet av torsk så är det viktigt att man kan koppla dessa värden till variationer i sammansättning hos bytesfisk i Kattegatt, så att predationen kan uppskattas baserat på framtida antagna förändringar i bytessammansättning. I nuläget är en tillräcklig mängd data inte tillgänglig, och den tidsramar som de prover som finns har samlats in inom är för långa och för gamla för att temporala variationer ska kunna tas hänsyn till när man analyserar dem. Fler prover från Kattegatt skulle behövas för att kunna göra en precis uppskattning av tumlarpredationen, optimalt hade varit prover som tidsmässigt stammer överens med de nuvarande beståndsuppskattningar som finns för torsken i Kattegatt. Denna data samlas för nuvarande inte in, dock, så en alternativ lösning vore att kombinera nuvarande dietdata med de säsongsvisa och årvisa variationer i diet som har observerats under dietanalyser. Dessa data skulle kunna användas för att skapa en approximativ modell som visar hur tumlarnas diet varierar med förändrade bytesförutsättningar i Kattegatt. Dessa approximationer skulle sedan kunna användas för att göra en ungefärlig prognos över den framtida predationen på Kattegattorsken från tumlare. SLU/Dept. Of Aquatic Resources 2017 M2 eng swe https://stud.epsilon.slu.se/10643/ |
| spellingShingle | Atlantic cod diet Gadus morhua harbour porpoise Kattegat Phocoena phocoena prey Wallin, Adam Harbour porpoise (Phocoena phocoena) predation on cod (Gadus morhua) in the Kattegat : a review of current knowledge and implications for stock assessments |
| title | Harbour porpoise (Phocoena phocoena) predation on cod (Gadus morhua) in the Kattegat : a review of current knowledge and implications for stock
assessments |
| title_full | Harbour porpoise (Phocoena phocoena) predation on cod (Gadus morhua) in the Kattegat : a review of current knowledge and implications for stock
assessments |
| title_fullStr | Harbour porpoise (Phocoena phocoena) predation on cod (Gadus morhua) in the Kattegat : a review of current knowledge and implications for stock
assessments |
| title_full_unstemmed | Harbour porpoise (Phocoena phocoena) predation on cod (Gadus morhua) in the Kattegat : a review of current knowledge and implications for stock
assessments |
| title_short | Harbour porpoise (Phocoena phocoena) predation on cod (Gadus morhua) in the Kattegat : a review of current knowledge and implications for stock
assessments |
| title_sort | harbour porpoise (phocoena phocoena) predation on cod (gadus morhua) in the kattegat : a review of current knowledge and implications for stock
assessments |
| topic | Atlantic cod diet Gadus morhua harbour porpoise Kattegat Phocoena phocoena prey |