Comparing dominance relationships and movement of native marble trout (Salmo marmoratus) and introduced rainbow trout (Oncorhynchus mykiss)

Behaviour observations of the endangered native marble trout (Salmo marmoratus,Cuvier, 1829) and introduced rainbow trout (Oncorhynchus mykiss, Walbaum, 1792)in the laboratory and in a tributary to the Idrijca River in Slovenia were combined tostudy the movements and dominance relationships between individuals of the twospecies in an open field test. Under laboratory conditions, no difference between thespecies was detected for neither time spent actively or distance moved. In speciespaired tests, rainbow trout initiated more aggressive behaviours towards marble troutthanvice versa, and rainbow trout were clearly the dominant individuals. After simul-taneous release in the river, marble trout immediately left the release area and spenttwice as long time as rainbow trout until they settled in an area of the river; there-fore, the release site was immediately occupied exclusively by rainbow trout. Thus,the dominant and aggressive behaviour of rainbow trout seen in the laboratorybefore release might have influenced marble trout's subsequent behaviour in theriver, by marble trout leaving the areas occupied by rainbow trout and moving tolocations further away from the release site. In the field, the marble trout occupiedsites individually, whereas rainbow aggregated at a few locations. Rainbow troutshowed higher movement activity in the morning compared to marble trout. Therewas a positive correlation between swimming speed in the laboratory and movementin the field for marble trout but not for rainbow trout. In conclusion, the results in thisstudy support the need to end stocking of rainbow trout in rivers with native marbletrout. To better understand the interaction between the species, and to develop effi-cient management plans to protect the native marble trout, reference behavioursshould first be understood, and future research in sites where the two species do not co-exist is needed. This is especially important for marble trout for which behaviouralresearch and data are lacking.acceptedVersio

Effekter av kalkning på flodpärlmussla (Margaritifera margaritifera) : Status och trender

I rapporten utvärderas kalkningens effekter på flodpärlmusselpopulationer utifrån data från Musselportalen, Kalkdatabasen, Elfiskeregistret samt vattenkemi från länsstyrelserna. Utvärderingen fokuserar på tätheten av musslor och andelen juvenila musslor och hur dessa förhåller sig i kalkpåverkade, svagt kalkpåverkade, respektive okalkade vattendrag. Förhållanden inom och mellan grupperna utvärderades utifrån ett tidsserie-och nulägesperspektiv. Eftersom det förekommer två olika inventeringsmetoder, enkel statusbeskrivning och statusbeskrivning, utvärderades resultaten separat för vardera metoden

Size-related habitat use in juvenile Atlantic salmon: the importance of inter-cohort competition

In stream-living salmonids, an underlying mechanism for the critical period after emergence has generally been assumed to be size-dependent swimming capacity constraining fry (age-0) to low-velocity habitats with reduced food availability and intense competition. A further plausible mechanism is that inter-cohort habitat exclusion confines fry to marginal habitats. This possibility was tested using a semi-natural stream with 16 test arenas each comprising one high-velocity, deep, habitat and one low-velocity, shallow, habitat. We observed groups of newly emerged Atlantic salmon Salmo salar fry, either alone or in sympatry with one or two age-1 salmon. Salmon fry used high-velocity areas (42.2 ± 0.4 cm s-1) most extensively in the absence of inter-cohort competition, where they obtained more food than in low-velocity areas (3.3 ± 0.3 cm s-1), even though foraging efficiency was lower (though not significantly so). In sympatry with older cohorts, fry increased their use of the low-velocity habitat, with a reduced foraging activity, suggesting that strong older cohorts in natural populations may have the potential to influence the strength of the recruiting cohort by negative density-dependence due to interference competition for habitat.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Local adaptation studies and conservation : Parasite-host interactions between the endangered freshwater mussel Unio crassus and its host fish

Parasite-host interactions can involve strong reciprocal selection pressure, and may lead to locally adapted specializations. The highly threatened unionoid mussels are temporary parasites on fish, but local adaptation has not yet been investigated for many species. Patterns of local adaptation of one of Europe's most threatened unionoids, the thick-shelled river mussel (Unio crassus) were investigated. Eurasian minnows (Phoxinus phoxinus) from two rivers (separate drainage areas) were cross-infested in the laboratory with sympatric and allopatric mussel larvae, while bullheads (Cottus gobio), inhabiting only one of the rivers, were infested with sympatric or allopatric mussel larvae. Larval encystment, juvenile mussel excystment and survival were measured. For one river, but not the other, juvenile excystment from P. phoxinus was highest when infested with sympatric mussels. The opposite pattern was found for C. gobio in this river, where juvenile excystment and post-parasitic juvenile survival from allopatric C. gobio were highest. The results thus cannot confirm local adaptation of U. crassus to P. phoxinus in the study rivers, as excystment was not consistently higher in all sympatric mussel-host combinations, whereas there were potential maladaptive signs of U. crassus in relation to C. gobio. There was no loss of encysted larvae 3 days after infestation until juvenile excystment. Most juveniles were excysted between 17 and 29 days after infestation, and the numbers of excysted juveniles increased with fish size. The results have implications for parasite-host ecology and conservation management with regard to unionoid propagation and re-introduction. This includes the need to (1) test suitability and adaptation patterns between U. crassus and multiple host fish species, (2) evaluate the suitability of certain unionoids and host fish strains after more than 3 days, and (3) determine whether large fish produce more juvenile mussels than smaller fish

Effects of mussel and host fish density on reproduction potential of a threatened unionoid mussel : Prioritization of conservation locations in management trade-offs

Management decisions in conservation of threatened species require trading off social needs against biodiversity values, including the prioritization of conservation locations, i.e. where conservation efforts should take place. To improve conservation decisions for the thick-shelled river mussel, Unio crassus, a highly threatened temporary parasite on fish, we performed a field study on how mussel and host fish density (European bullhead, Cottus gobio, and common minnow, Phoxinus phoxinus) affect reproduction potential of the mussel at different sites along a river. We assumed that the proportions of gravid mussels would be higher at high mussel density, and result in enhanced glochidia (mussel larvae) encapsulation rates on fish. We also expected the highest ‘glochidia density’—a proxy for the potential number of recruits per stream area, assessed by multiplying glochidia encapsulation rates on fish by fish density, to occur at high mussel density sites. Such river sites, producing many offspring and conveying important conservation values, may thus be prioritized. However, contrary to our assumptions, higher glochidia density and higher proportions of gravid mussels occurred at lower density mussel sites. We also found that P. phoxinus had higher glochidia encapsulation rates than C. gobio, possibly related to species-specific behavioural and life-history traits. Even so, glochidia density was similar for both fish species, reflecting comparable ecological functions in hosts. The results of this study suggest that mussel and host fish densities should be considered along with glochidia density in conservation prioritization and management trade-offs.Artikeln ingick som manuskript i Schneiders (2017) doktorsavhandling Conservation ecology of the thick-shelled river mussel Unio crassus: The importance of parasite-host interactions</p

Hatchery selection promotes boldness in newly hatched brown trout (Salmo trutta): implications for dominance

By using newly hatched (approximately 2 weeks old) brown trout (Salmo trutta) from six families of wild and six families of sea-ranched origin (seventh generation), we tested the hypotheses that (1) the hatchery environment selects for increased boldness, and (2) boldness predicts dominance status. Sea-ranched trout spend their first 2 years in the hatchery before being released into the wild at the onset of seaward migration. Trout were presented with a novel object (tack) and with food (brine shrimp), and their responses were measured and scored in terms of boldness. Siblings with increasing difference in boldness were then paired in dyadic contests. Fish of sea-ranged origin were on average bolder than were fish of wild origin, and bolder individuals were more likely to become dominant regardless of origin. Boldness was not related to RNA levels, indicating that bold behavior was not a consequence of higher metabolism or growth rate. Neither was size a predictor of bold behavior or the outcome of dyadic contests. These results are consistent with studies on older life stages showing increased boldness toward predators in hatchery-selected fish, which suggests that behavioral consequences of hatchery selection are manifested very early in life. The concordance between boldness and dominance may suggest that these behaviors are linked in a risk prone-aggressive phenotype, which may be promoted by hatchery selection. However, we also found significant variation in behavioral and growth-related traits among families, suggesting that heritable variation has not been exhausted by sea-ranching procedures. Copyright 2004.boldness; dominance; family variation; sea-ranched; selection; wild

Testing for tax smoothing in a general equilibrium model of growth

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