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- Dannewitz, Johan, et al.
(författare)
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Kunskapsunderlag för hållbar förvaltning av svenska laxbestånd
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Havs- och vattenmyndigheten (HaV) ska under 2023 revidera den nationella förvaltningsstrategi för landets lax- och öringbestånd som ursprungligen togs fram 2015 inom ramen för ett regeringsuppdrag (HaV 2015). I strategin från 2015 inkluderades endast havsvandrande lax och öring i svenska vattendrag upp till första vandringshindret. I den reviderade versionen ska även lax i Vänern ingå, samt öring i samtliga inlandsvatten. HaV har inför revideringen av förvaltningsstrategin beställt två separata kunskapsunderlag från SLU Aqua - ett som behandlar landets laxbestånd och ett med fokus på öring. I detta underlag beskrivs kunskapsläget för landets laxbestånd, som kan delas in i tre geografiska grupper – lax i Östersjön, lax på svenska västkusten och lax i Vänern. Nedan benämns dessa grupper som östersjölax, atlantlax respektive vänerlax. Sammanställningen fokuserar i första hand på hur kunskapsläget och situationen för svenska laxbestånd förändrats sedan den förra förvaltningsstrategin presenterades 2015. I avsnitt 2 beskrivs olika typer av förvaltningsmål, från produktionsmål till mer bevarandeinriktade mål. Avsnitt 3 innehåller resultat från de senaste analyserna av beståndens status och utveckling. Avsnitt 4 sammanfattar dagens laxförvaltning på internationell och nationell nivå. Avsnitt 5 fokuserar på nyvunnen biologisk kunskap av relevans för vidareutveckling av en bestånds- och ekosystembaserad förvaltning, medan tänkbara framtida förvaltningsmodeller för både yrkes- och fritidsfiske efter lax diskuteras i avsnitt 6. Avsnitt 7 behandlar kunskaps- och datainsamlingsbehov, dels i relation till dagens förvaltningssystem och dels med fokus på den framtida förvaltningens förväntade krav på biologisk rådgivning. Vi har i underlaget främst fokuserat på biologisk kunskap och hur denna kan användas för att utveckla laxförvaltningen, men går inte in på andra relevanta aspekter (samhällsekonomi, juridik mm) som ligger utanför vårt kompetensområde.
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- Jacobson, Philip, et al.
(författare)
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Growth variation of Atlantic salmon Salmo salar at sea affects their population-specific reproductive potential
- 2021
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 671, s. 165-174
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the processes shaping the dynamics of anadromous fish populations is essential for their management and conservation. Yet, little is known about how variation in performance at sea affects their population dynamics. Here we show that variation in body growth at sea contributes to explaining variation in the reproductive potential for 2 Atlantic salmon Salmo salar populations, but to a varying extent. To this end, we assembled data collected during 50 yr for 2 Baltic salmon populations of hatchery origin, including annually released smolts, survival at sea estimates, size-specific growth at sea, annual length distributions of returning adult females and their reproductive potential. The regression models fitted to explain the reproductive potential of our 2 study populations improved when growth at sea was included as an explanatory variable, in addition to smolt year class abundance and estimates of their survival at sea. This link between body growth at sea and population-level reproductive potential suggests that growth at sea can be important to consider when resolving variation in recovery and dynamics among salmon populations sharing the same sea.
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- Skoglund, Stefan, et al.
(författare)
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From spawner habitat selection to stock-recruitment: Implications for assessment
- 2022
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between the spawning stock size and subsequent number of recruits is a central concept in fisheries ecology. The influence of habitat selection of spawning individuals on the stock-recruitment relationship is poorly known. Here we explore how each of four different spawner behaviors might influence the stock-recruitment relationship and estimates of its parameters in the two most commonly used stock-recruitment functions (Beverton-Holt and Ricker). Using simulated stock-recruitment data generated by four different spawner behaviors applied to multiple discrete habitats, we show that when spawners were distributed proportionally to local carrying capacities, there was small or no bias in estimated recruitment and stock-recruitment parameters. For an ideal free distribution of spawners, larger bias in the estimates of recruitment and stock-recruitment parameters was obtained, whereas a random and a stepwise spawner behavior introduced the largest bias. Using stock-recruitment data corresponding to a "realistic " range of population densities and adding measurement error (20%-60%) to the simulated stock-recruitment data generated larger variation in the estimation bias than what was introduced by the spawner behavior. Thus, for exploited stocks at low population density and where spawning stock size and recruitment cannot be observed perfectly, partial observation of the possible spawner abundance range and measurement error might be of higher concern for management.
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- Whitlock, Rebecca
(författare)
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Flexible use of a dynamic energy landscape buffers a marine predator against extreme climate variability
- 2021
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 288
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Tidskriftsartikel (refereegranskat)abstract
- Animal migrations track predictable seasonal patterns of resource availability and suitable thermal habitat. As climate change alters this 'energy landscape', some migratory species may struggle to adapt. We examined how climate variability influences movements, thermal habitat selection and energy intake by juvenile Pacific bluefin tuna (Thunnus orientalis) during seasonal foraging migrations in the California Current. We tracked 242 tuna across 15 years (2002-2016) with high-resolution archival tags, estimating their daily energy intake via abdominal warming associated with digestion (the 'heat increment of feeding'). The poleward extent of foraging migrations was flexible in response to climate variability, allowing tuna to track poleward displacements of thermal habitat where their standard metabolic rates were minimized. During a marine heatwave that saw temperature anomalies of up to +2.5 degrees C in the California Current, spatially explicit energy intake by tuna was approximately 15% lower than average. However, by shifting their mean seasonal migration approximately 900 km poleward, tuna remained in waters within their optimal temperature range and increased their energy intake. Our findings illustrate how tradeoffs between physiology and prey availability structure migration in a highly mobile vertebrate, and suggest that flexible migration strategies can buffer animals against energetic costs associated with climate variability and change.
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- Whitlock, Rebecca
(författare)
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Informing Management of Atlantic Bluefin Tuna Using Telemetry Data
- 2022
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Ingår i: Frontiers in marine science. - : Frontiers Media SA. - 2296-7745. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Sustainable management of exploited marine fish and wildlife populations requires knowledge about their productivity. Survival from natural causes of mortality is a key component of population productivity, but is notoriously difficult to estimate. We evaluate the potential for acoustic telemetry as a long-term monitoring tool to estimate rates of natural mortality. We present a Bayesian multistate mark-recapture model for telemetry data collected over a decade from 188 Atlantic bluefin tuna (Thunnus thynnus) and apply it to estimate the rate of natural mortality using only acoustic tag detections for all animals, or using acoustic tag detections for 96 single-tagged tuna plus acoustic tag detections combined with estimated positions from pop-up satellite archival tags for 92 double-tagged animals. We support the model for bluefin tuna with a simulation study to quantify bias in estimates of population dynamics parameters and investigate the effect of auxiliary information from satellite tagging on mortality rate estimates for different acoustic tag detection probability scenarios.We obtained posterior estimates of the instantaneous annual natural mortality (survival) rate across a decade of tagging for Atlantic bluefin tuna of 0.17 yr(-1) (0.84 yr(-1)) both using only acoustic tagging data, and using a combination of acoustic and satellite tagging data. Use of a prior implying a higher rate of fishing mortality yielded an instantaneous annual natural mortality (survival) estimate of 0.10 yr(-1) (0.90 yr(-1)), with combined acoustic and satellite tag data. Results from the simulation study indicate that the use of satellite tags can improve the precision and accuracy of estimates of detection probabilities, area-specific movement probabilities and mortality rates, where the extent of the improvement depends on true underlying acoustic tag detection probabilities. Our work demonstrates that long-term acoustic tagging data sets have strong potential for monitoring of highly migratory marine fish and wildlife populations, providing information on a number of key parameters, including survival and movement rates. However, improved information on tag reporting rates or fishing mortality is needed to better separate natural and fisheries mortality for Atlantic bluefin tuna.
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- Whitlock, Rebecca
(författare)
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Risk and Reward in Foraging Migrations of North Pacific Albacore Determined From Estimates of Energy Intake and Movement Costs
- 2022
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Ingår i: Frontiers in marine science. - : Frontiers Media SA. - 2296-7745. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- North Pacific albacore (Thunnus alalunga) is a commercially important tuna species known to undertake extensive migratory movements between nearshore waters of the California Current and offshore environments in the central Pacific. However, these migration behaviors are highly variable, with some individuals traveling thousands of kilometers within a season, and others largely resident in the southern California Current throughout the year. In this study, we use data from 33 archival-tagged albacore (released between 2003 and 2011) to examine the movements, physiology and ecology of tuna following different migratory pathways. We used direct measurements of body temperature and ambient water temperature from internal archival tags to estimate energy intake via the Heat Increment of Feeding (HIF), the increased internal heat production associated with digestion of a meal. Our results indicate that HIF was variable in space and time, but it was highest for individuals foraging in the offshore North Pacific Transition Zone and southern California Current during spring and summer, and lowest in the Transition Zone in fall. None of the migratory strategies examined appeared to confer consistently higher energetic benefits than the others. Fish remaining resident in the southern California Current year-round incurred lower migration costs, and could access favorable foraging conditions off Baja California in spring and summer. In contrast, fish which undertook longer migrations had much higher energetic costs during periods of faster transit times, but were able to reach highly productive foraging areas in the central and western Pacific. HIF was generally higher in larger fish, and when ambient temperatures were cooler, but was not strongly correlated with other environmental covariates. Our analyses offer new avenues for studying the physiology of wild tuna populations, and can complement diet and isotopic studies to further understanding of fish ecology.
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