| 1. |
- Aho, Teija
(författare)
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By-Catch of Grey Seals (Halichoerus grypus) in Baltic Fisheries-A Bayesian Analysis of Interview Survey
- 2014
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Baltic seals are recovering after a population decline. The increasing seal stocks cause notable damage to fisheries in the Baltic Sea, with an unknown number of seals drowning in fishing gear every year. Thus, sustainable seal management requires updated knowledge of the by-catch of seals-the number of specimens that die in fishing gear. We analyse the by-catch of grey seals (Halichoerus grypus) in Finland, Sweden, and Estonia in 2012. We collect data with interviews (35 in Finland, 54 in Sweden, and 72 in Estonia) and analyse them with a hierarchical Bayesian model. The model accounts for variability in seal abundance, seal mortality and fishing effort in different sub-areas of the Baltic Sea and allows us to predict the by-catch in areas where interview data was not available. We provide a detailed description of the survey design and interview methods, and discuss different factors affecting fishermen's motivation to report by-catch and how this may affect the results. Our analysis shows that the total yearly by-catch by trap and gill nets in Finland, Sweden and Estonia is, with 90% probability, more than 1240 but less than 2860; and the posterior median and mean of the total by-catch are 1550 and 1880 seals, respectively. Trap nets make about 88% of the total by-catch. However, results also indicate that in one of the sub-areas of this study, fishermen may have underreported their by-catch. Taking the possible underreporting into account the posterior mean of the total by-catch is between 2180 and 2380. The by-catch in our study area is likely to represent at least 90% of the total yearly grey seal by-catch in the Baltic Sea.
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| 2. |
- Aho, Teija, et al.
(författare)
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Impacts of effective population size on genetic diversity and relatedness in hatchery reared Brown trout (Salmo trutta L.)
- 2006
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Ingår i: Aquaculture. - : Elsevier BV. - 0044-8486 .- 1873-5622. ; 253:1-4, s. 244-248
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Tidskriftsartikel (refereegranskat)abstract
- Many populations of brown trout are managed by hatchery breeding and supportive release. Using a limited number of individuals as founders creates a bottleneck, which can lead to loss of genetic diversity in a population. In this study 17 populations of hatchery-reared brown trout were examined genetically using microsatellite markers. Genetic variation measured as gene diversity and allelic richness were analysed and the effects of effective population size of founders and time since founding on these parameters were explored. Allelic richness and gene diversity decreased with increasing time since founding of the stock, and there was a negative relationship between current effective population size and time since founding. Allelic richness was positively correlated with effective population size at founding. The results indicate that considerations concerning effective population size in hatcheries must be taken seriously to promote high levels of genetic variation among individuals and minimise loss of genetic diversity.
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| 3. |
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| 4. |
- Bergek, Sara, 1979-
(författare)
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Population divergence at small spatial scales : – theoretical and empirical investigations in perch
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Genetically structured populations arise when gene flow between groups of individuals is hindered by geographical, behavioural or temporal barriers. The identification of such groups is important for understanding evolution and has large implications for conservation concern. The field of population subdivision has received a lot of interest throughout the years and gained empirical support from a number of species. However, very little is known about population structure at small spatial scales, especially in a highly mobile species such as fish. The main object for my thesis was to further investigate population differentiation, explicitly at small spatial scales in the Eurasian perch. My results show that in this species, genetic differentiation occurs, even at very small spatial scales, both within lakes and in the Baltic Sea. Additionally, the differentiation can be stable over years and thus have a large impact in the evolution of adaptation to different environments. I also found barriers to gene flow that overlapped with the largest change in spring temperature, suggesting a temporal difference in spawning. Morphological differences were found at these small scales as well which indicates that a difference in food resources might be an underlying cause of change. My thesis work shows that the aquatic environment might not be as homogenous as widely thought and that there could be barriers or adaptations to different environments that hinder the fish from genetic panmixia. Slight patterns of isolation by distance (IBD) were found in the Baltic Sea, implying that the distance (i.e. currents) effect the level of differentiation via drifting of larvae and/or small fish. However, I have also theoretically investigated the IBD model of and seen that it is no longer correct when differences in population sizes are introduced. The pattern of IBD can mean high levels of gene flow or no gene flow at all, solely dependent on population size differences and fluctuations. My thesis has resulted in new and important findings regarding the existence and cause of genetic differentiation at very small spatial scales and thus added new knowledge into the field of evolution and speciation. In addition, my results also give insights into the contemporary state of the Eurasian perch and future evolutionary potential.
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| 5. |
- Bergenius, Mikaela, et al.
(författare)
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Fishing or the environment - what regulates recruitment of an exploited marginal vendace (Coregonus albula (L.)) population?
- 2013
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Ingår i: Advances in Limnology. - 1612-166X. ; 64, s. 57-70
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Konferensbidrag (refereegranskat)abstract
- Fish populations inhabiting marginal areas are generally highly susceptible to environmental variation and therefore show large fluctuations in recruitment. The commercially important, and usually freshwater, vendace (Coregonus albula (L.)) occupying the brackish waters of the Bothnian Bay forms one such marginal population and shows large annual variation in recruitment. Here, we investigate the relative importance of fishing (trawling time), hydro-climatic factors and species interactions in explaining the variability in vendace recruitment using three sets of models. A comparison of the best models in the hydro-climatic model set and the fishing model revealed that the hydro-climatic variables were overall superior to the anthropogenic model in describing recruitment variability. Trawling time and water temperature in winter combined with salinity explained 33 and 63.7% of the variation in recruitment, respectively. The importance of water temperature and salinity, in combination with the effects of trawling time, calls for catch levels to be set with caution in this vendace fishery.
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| 6. |
- Björklund, Mats, et al.
(författare)
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Genetic differentiation in pikeperch (Sander lucioperca): the relative importance of gene flow, drift and common history
- 2007
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 71:Suppl B, s. 264-278
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the relative importance of homogenizing factors, such as gene flow, and diversifying factors, such as drift, genetic variation in pikeperch (Sander lucioperca) in two Fennoscandian regions (North and South) was analysed with microsatellites. Allelic richness and the degree of differentiation were significantly higher in the North (FST = 0·20) than in the South (FST = 0·064). In northern areas, assignments of genotypes were almost exclusively to the population of origin, but in southern areas, the proportion of correct assignments was significantly lower. Most samples exhibited significant heterozygote deficits, and the level of relatedness was higher than expected from randomness. These combined results suggest that there has been more gene flow between populations in southern areas than in northern areas, where the importance of genetic drift has been greater. Effective population sizes were small (c. 100) and did not differ between areas. The effect of a common history appears minor, and thus processes such as genetic drift and gene flow have been more influential in shaping the patterns of genetic diversity in this species.
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| 7. |
- Björklund, Mats, et al.
(författare)
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Isolation over 35 years in a heated biotest basin causes selection on MHC class II beta genes in the European perch (Perca fluviatilis L.)
- 2015
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 5:7, s. 1440-1455
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Tidskriftsartikel (refereegranskat)abstract
- Genes that play key roles in host immunity such as the major histocompatibility complex (MHC) in vertebrates are expected to be major targets of selection. It is well known that environmental conditions can have an effect on host-parasite interactions and may thus influence the selection on MHC. We analyzed MHC class II ss variability over 35years in a population of perch (Perca fluviatilis) from the Baltic Sea that was split into two populations separated from each other. One population was subjected to heating from cooling water of a nuclear power plant and was isolated from the surrounding environment in an artificial lake, while the other population was not subjected to any change in water temperature (control). The isolated population experienced a change of the allelic composition and a decrease in allelic richness of MHC genes compared to the control population. The two most common MHC alleles showed cyclic patterns indicating ongoing parasite-host coevolution in both populations, but the alleles that showed a cyclic behavior differed between the two populations. No such patterns were observed at alleles from nine microsatellite loci, and no genetic differentiation was found between populations. We found no indications for a genetic bottleneck in the isolated population during the 35years. Additionally, differences in parasitism of the current perch populations suggest that a change of the parasite communities has occurred over the isolation period, although the evidence in form of in-depth knowledge of the change of the parasite community over time is lacking. Our results are consistent with the hypothesis of a selective sweep imposed by a change in the parasite community.
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| 8. |
- Ekström, Andreas, 1979, et al.
(författare)
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Chronic environmental warming alters cardiovascular and haematological stress responses in European perch (Perca fluviatilis)
- 2016
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Ingår i: Journal of Comparative Physiology B-Biochemical Systemic and Environmental Physiology. - : Springer Science and Business Media LLC. - 0174-1578 .- 1432-136X. ; 186:8, s. 1023-1031
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Tidskriftsartikel (refereegranskat)abstract
- Environmental warming and acute stress increase cardiorespiratory activity in ectothermic animals like fish. While thermal acclimation can buffer the direct thermal effects on basal cardiorespiratory function during chronic warming, little is known about how acclimation affects stress-induced cardiorespiratory responses. We compared cardiovascular and haematological responses to chasing stress in cannulated wild European perch (Perca fluviatilis) from a reference area at natural temperature (16 A degrees C) with perch from the 'Biotest enclosure'; an experimental system chronically warmed (22 A degrees C) by effluents from a nuclear power plant. Routine blood pressure was similar, but Biotest perch had slightly higher resting heart rate (59.9 +/- 2.8 vs 51.3 +/- 2.9 beats min(-1)), although the Q (10) for heart rate was 1.3, indicating pronounced thermal compensation. Chasing stress caused hypertension and a delayed tachycardia in both groups, but the maximum heart rate increase was 2.5-fold greater in Biotest fish (43.3 +/- 4.3 vs 16.9 +/- 2.7 beats min(-1)). Moreover, the pulse pressure response after stress was greater in reference fish, possibly due to the less pronounced tachycardia or a greater ventricular pressure generating capacity and thermally mediated differences in aortic compliance. Baseline haematological status was also similar, but after chasing stress, the haematocrit was higher in Biotest fish due to exacerbated red blood cell swelling. This study highlights that while eurythermal fishes can greatly compensate routine cardiorespiratory functions through acclimation processes, stress-induced responses may still differ markedly. This knowledge is essential when utilising cardiorespiratory variables to quantify and compare stress responses across environmental temperatures, and to forecast energetic costs and physiological constraints in ectothermic animals under global warming.
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| 9. |
- Gårdmark, Anna, et al.
(författare)
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Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?
- 2012
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 69, s. 1448-1456
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Tidskriftsartikel (refereegranskat)abstract
- Mortality of small pelagic fish due to marine mammals is generally considered to be low compared with other sources of mortality. With recent recoveries of marine mammal predators worldwide, this may no longer hold. The grey seal (Halichoerus grypus) population in the Bothnian Sea has increased fivefold since 1985. Its main prey, herring (Clupea harrengus), is a key species for fisheries in the region. Yet, current stock assessments assume constant natural mortality, leading to a risk of biased stock estimates with increasing predation and misleading analyses of herring population dynamics. We estimated grey seal predation from diet data and reanalysed herring spawning stock biomass (SSB) during 1973-2009. Accounting for predation increased the herring SSB 16% (maximum 19%), but this was within the confidence intervals when ignoring predation. Although mortality in older individuals was inflated when accounting for seal predation, this did not change the conclusions about drivers of herring dynamics. Accounting for grey seal predation is important for abundance estimates of old herring, but currently not for SSB estimates, given the great uncertainties in the standard assessment. The grey seal impact on Bothnian Sea herring will need to be reassessed if stock age composition, grey seal feeding preferences, or total stock development change.
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| 10. |
- Lundström, Karl, et al.
(författare)
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Födoval hos vikaresäl i Bottenviken: Rapport från den svenska forskningsjakten 2007-2009. Aqua reports 2014:1. Sveriges lantbruksuniversitet, Lysekil. 24 s.
- 2014
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Rapport (refereegranskat)abstract
- Bottenvikens vikaresälar har under de senaste årtiondena återhämtat sig från den kraftiga minskningen av sälbeståndet under förra seklet. I takt med ökningen av antalet sälar har konflikterna med fisket tilltagit samtidigt som kraven på kunskap om vilka faktorer som påverkar fiskbestånden har höjts. På grund av att ytterst få sälar samlats in från det aktuella området har dock relevanta uppgifter om vikare-sälarnas födoval, och även hälsostatus, i Bottenviken saknats under en längre tid. Av den anledningen gavs tillstånd att bedriva forskningsjakt på 60 sälar i Norrbottens län under 2007-2009. Syftet med denna rapport är att presentera vikaresälar-nas dietsammansättning och fiskuttag i Bottenviken, baserat på bytesrester från de sälar som samlades in. I samarbete med lokala jägare samlades 45 sälar in av den tillåtna kvoten. Majoriteten av sälarna var unga djur,huvudsakligen insamlade i maj-juni 2008. Innehål-let i de insamlade djurens mage och tarm undersöktes och totalt hittades 12 olika bytesarter. De undersökta sälarnas födoval dominerades av strömming och siklöja, som tillsammans utgjorde nästan tre fjärdedelar av vikten i dieten. Baserat på en uppskattning av antalet sälar år 2009 beräknades vikaresälarnas årliga konsumtion av strömming i Bottenviken vara i samma nivå som det sammanlagda svenska och finska yrkesfiskets landningar, medan sälarnas uttag av siklöja till och med upp-skattades överskrida yrkesfiskets fångstmängder. Sälarnas födoval verkar ha genomgått en förändring sedan 1970-talet, med en ökadbetydelse av strömming, siklöja och storspigg och en minskad betydelse av skorv. Även om undersökningen begränsas av materialets urval ger den ett mått på sam-mansättningen och den potentiella storleken av sälarnas fiskkonsumtion. Resultaten framhåller behovet av att ta med vikaresälen i förvaltningen och betydelsen av fortsatta undersökningar av vikaresälens födoekologi för en ökad förståelse av den ekologiska dynamiken i Bottenviken
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