Using redd counts to estimate salmonids spawner abundances: A Bayesian modelling approach
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Summary The species–area relationship, which is closely linked with the more general species‐energy theory, is one of the most well‐known patterns in geographical ecology, but the underlying causes remain contentious. The more individuals hypothesis ( MIH ) articulates a causal path from resource availability to population abundance to species richness. The MIH has been tested with a range of taxa including plants, invertebrates and land birds but never with migratory waterbirds. Using multiyear simultaneous survey data of wintering waterbirds in 10 lakes at Poyang Lake, China, and remotely sensed habitat condition measurements, we applied structural equation modelling ( SEM ) to test three causal paths: (A) good habitat conditions (e.g. habitat availability and heterogeneity) attract more species (high richness); (B) habitat conditions promote abundance (more individuals); and (C) habitat conditions promote abundance, which in turn increases richness. We also modelled responses of species richness and abundance to habitat conditions using generalised additive mixed modelling ( GAMM ) to assess their co‐variation. While our analysis confirmed the first two paths, we found no support for the third, which is the central postulate of the MIH . In addition, in agreement with GAMM , SEM indicated that species richness was more closely related to habitat quality than to abundance. Our findings suggest that wintering waterbird species richness and abundance are two intrinsic community indices that covary with environmental variables.
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ABSTRACT
Migration is common among populations of brown trout (Salmo trutta) and Atlantic salmon (Salmo salar). However, not all individuals in the same population migrate, a phenomenon referre ...
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Department of Agriculture, Food and the Marine, Ireland (Beaufort Maritime Research Awards Fish Population Genetics)
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Abstract There are more than 3,000 Atlantic salmon aquaculture sea‐cages distributed along the coastline of Norway. Many of these sea‐cages are located along the migration routes of wild Atlantic salmon ( Salmo salar ) postsmolts. This study documents for the first time that wild Atlantic salmon postsmolts can enter sea‐cages stocked with farmed Atlantic salmon. In addition, wild sea trout ( Salmo trutta ) and salmon/trout hybrid postsmolts were found inside the sea‐cages. The extent of such “bycatch” in commercial aquaculture is vital knowledge for the conservation of Atlantic salmon and sea trout. Further studies are encouraged in order to evaluate the extent of this possible ghost fishing phenomena.
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High levels of hybridization between Atlantic salmon Salmo salar and brown trout Salmo trutta have been reported in the River Driva. This study presents the underlying mechanisms of development of seawater (SW) tolerance and marine migration pattern for S. salar × S. trutta hybrids. Migrating S. salar × S. trutta hybrid smolts caught in the River Driva, Norway (a river containing Gyrodactylus salaris ), displayed freshwater (FW) gill Na + , K + ‐ATPase (NKA) activity levels of 11·8 µmol ADP mg protein h −1 , which were equal to or higher than activity levels observed in S. salar and S. trutta smolts. Following 4 days of SW exposure (salinity 32·3), enzyme activity remained high and plasma ion levels were maintained within the normal physiological range observed in S. salar smolts, indicating no signs of ion perturbations in S. salar × S. trutta hybrids. SW exposure induced an increase in NKA α 1b‐subunit mRNA levels with a concurrent decrease in α 1a levels. Salmo salar × S. trutta post‐smolts migrated rapidly through the fjord system, with increasing speed with distance from the river, as is often seen in S. salar smolts. The present findings suggest that S. salar × S. trutta smolts, as judged by the activity and transcription of the NKA system, regulation of plasma ion levels and migration speed more closely resemble S. salar than S. trutta .
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Abstract. Monthly catches of Atlantic salmon, Salmosalar L., and sea trout, Salmo trutta L., by anglers in a west of Ireland fishery were analysed. Data were available for 50 months from the years 1971 to 1981. The most important single determinant of catch was found to be fishing effort measured in boat-days. An additional 10 boat days were found to correspond to a catch of almost 6 salmon and 23 sea trout. The relationship between catch and stock was weaker, though a relatively high catchability of sea trout at low stock levels was recorded. Slock levels, fishing effort and environmental factors accounted for much, but not all, of the variation in catch from month to month and from year to year. Most of the effect of rainfall, sunshine and water level was attributable to variations in fishing effort associated with these factors.
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