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| 2. |
- Bäcklin, Britt-Marie, 1957-, et al.
(författare)
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Sälpopulationer och sälhälsa
- 2016
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Ingår i: HAVET 2015/2016. - : Havsmiljöinstitutet. - 9789198229134 - 9789187967122 ; , s. 116-118
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 3. |
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| 4. |
- Hansson, Sture, et al.
(författare)
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Competition for the fish - fish extraction from the Baltic Sea by humans, aquatic mammals, and birds
- 2018
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 75:3, s. 999-1008
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Tidskriftsartikel (refereegranskat)abstract
- Seals and fish-eating birds have increased in the Baltic Sea and there is concern that they compete with fisheries. Using data from around year 2010, we compare consumption of different fish species by seals and birds to the catch in the commercial and recreational fishery. When applicable this is done at the geographical resolution of ICES subdivisions. Predation by birds and mammals likely has limited impact on the populations of the commercially most important species (herring, sprat, and cod). In the central and southern Baltic, seals and birds consume about as much flatfish as is caught by the fishery and competition is possible. Birds and seals consume 2-3 times as much coastal fish as is caught in the fishery. Many of these species are important to the fishery (e. g. perch and whitefish) and competition between wildlife and the fishery is likely, at least locally. Estimated wildlife consumption of pike, sea trout and pikeperch varies among ICES subdivisions and the degree of competition for these species may differ among areas. Competition between wildlife and fisheries need to be addressed in basic ecosystem research, management and conservation. This requires improved quantitative data on wildlife diets, abundances and fish production.
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| 5. |
- Harding, Karin C., 1968, et al.
(författare)
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Population Wide Decline in Somatic Growth in Harbor Seals—Early Signs of Density Dependence
- 2018
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Ingår i: Frontiers in Ecology and the Environment. - : Frontiers Media SA. - 1540-9295 .- 1540-9309 .- 2296-701X. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The harbor seal populations of Danish and Swedish waters have had turbulent population dynamics during the last century. They were severely depleted by hunting in the beginning of the twentieth century, followed by rapid recovery due to protective measures. They were victims to two mass mortalities caused by Phocine Distemper Virus (PDV) epidemics. Long term monitoring and intensive sampling during the last decades now allow analysis of population level phenomena in response to shifting population size. We compare somatic growth curves from several seal populations including 2,041 specimens with known age, length and population size at birth. Asymptotic body lengths of female harbor seals were 148 cm in all four regions in 1988, when seal abundances had been kept low by hunting for decades. Males were 158 cm, being 10 cm longer. However, in 2002 the asymptotic lengths of seals differed among regions. While seals in the Kattegat showed similar asymptotic lengths as in 1988, seals in the Skagerrak were significantly shorter, where both male and female asymptotic lengths declined by 7 cm. We estimate the area of available feeding grounds in the two sea regions and find the density of seals per square kilometer feeding ground to be three times greater in the Skagerrak compared to the Kattegat. Thus, the shorter body length of seals in the Skagerrak can be an early signal of density dependence. Hampered body growth is known to trigger a suite of changes in life history traits, including delayed age at sexual maturity, higher juvenile mortality and lowered fecundity. These mechanisms all point at a possible “smooth route toward carrying capacity” with gradually reduced population growth rate as the main response to high population density. Recent aerial surveys confirm declining rates of population increase in the Skagerrak.
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| 8. |
- Härkönen, Tero, et al.
(författare)
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Predicting recurrent PDV epizootics in European harbour seals (Phoca vitulina)
- 2010
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Ingår i: NAMMCO scientific publications. - 1560-2206. ; 8, s. 275-284
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Tidskriftsartikel (refereegranskat)abstract
- Phocine Distemper Virus (PDV) caused mass mortality in European harbour seals (Phoca vitulina) in 1988 and in 2002. Both epizootics likely originated from refugia in Arctic seals, where data indicate PDV hops among populations and species. The metapopulation structure of host populations is suggested to be the reason why PDV is preserved among Arctic seals, since the high rate of spread of PDV would require much larger panmictic populations to maintain an infection. The pattern of sudden outbreaks of PDVi s also seen in grey seals (Halichoerus grypus), the only to date identified species that could act as a vector between Arctic and North Sea seal populations. Harbour seal populations along mainland Europe were below critical herd immunity levels by 3-5 years after the events, and thus vulnerable for new outbreaks, but historical data and the 14 years between the 2 epizootics suggest that harbour seals in the North Sea area are only rarely exposed to the infective agent. The risk for new outbreaks of the seal plague in North Sea harbour seals is likely linked to the dynamics of the disease in Arctic seal species as well as vector species.
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| 9. |
- Härkönen, Tero, et al.
(författare)
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Reproduktionsperioder och andra störningskänsliga perioder hos säl : En kunskapssammanställning omgråsäl, knubbsäl och vikaresäl
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- På uppdrag av Naturvårdsverket har författarna sammanställt befintliga fakta om de tre i Sverige förekommande sälarternas biologi med avseende på årstid och störningskänslighet. De har även summerat de sista årens faktiska säljakt och hur den är distribuerad över året. De tre sälarterna, gråsäl, knubbsäl och vikare har olika ekologi och årscykel, men lika för alla är att sälarnas mest störningskänsliga period är då honorna samlas för att föda sina kutar och de efterföljande veckorna av digivning. Under denna period är de beroende av land eller is för att dia sina ungar och låta ungarna vila. Den näst mest känsliga perioden är under pälsbytet. Då går sälarnas metabolism upp till det dubbla och de är även under denna tid beroende av land för att gynna ökad blodtillförsel i den varma torra huden vilket underlättar den nya pälsens tillväxt. Störningar som skrämmer hela kolonin i vattnet (både vid jakt och båtturism) under pälsbytestiden kommer att stressa sälarnas energibudget.Författarna rekommenderar framtida studier av sälarnas beteenden, särskilt vad gäller hur mycket tid de tillbringar på land under olika årstider och i olika delar av utbredningsområdet. De uppgifter som har sammanställts kommer från äldre studier under förhållanden då både sälbestånden var mindre och klimatet kallare. Modern inventeringsmetodik tillåter också en högre grad av upplösning i resultaten och kommer ge ett bättre underlag för adaptiv förvaltning. Författarna har för varje art pekat på specifika kunskapsluckor vad gäller säsongsmässigt beteende och störningskänsliga perioder.
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