Natal homing and straying are behavioural tactics of migratory animals that return to nursery habitats to breed as adults. Straying has evolutionary and ecological importance for species flexibility, interpopulation connectivity and success of invasive species in new environments. This study aimed to estimate the relative importance of straying and homing in introduced brown trout Salmo trutta spawning in a model coastal tributary (Silverstream) of a large New Zealand river using otolith microchemistry. The data on natal homing and straying are important for the understanding of the ecological resilience of salmonid populations and metapopulations, and the development of effective management measures at stream or catchment scales. To examine brown trout homing and straying in a river catchment, otolith microchemical analysis was applied. We used linear discriminant function analysis to compare the trace element composition in the otoliths of YoY (young‐of‐the‐year) trout collected at spawning streams across the catchment and adult trout reproducing in Silverstream. The results showed that only six from a sample of 30 spawning adults in Silverstream originated from Silverstream. Another 14 fish likely originated from other Taieri tributaries further upstream, but the origin of the remaining 10 could not be determined. Contrary to published studies based on wild populations of brown trout in Europe, and several other species of salmonids, a large proportion of brown trout spawners collected in Silverstream were strays. The large number of strayers identified in Silverstream may be a consequence of the geomorphology of the Taieri catchment and highlights the adaptability of brown trout to different environmental contexts.
The information on fishery object limited by CPUE data and fragmentary data on age and size is sufficient for production models. However, this type of models is improper for long-living species, as crabs, because of problem with assumption on equilibrium stock. Describing dynamics of a single year-class, these models average the parameters for all generations that impedes to use them for assessment of crabs stocks. Finite-difference models with delay are more promising in this case. Deriso-Snute finite-difference model with delay was used for simulating of the spiny king crab biomass dynamics at southern Kuril Islands and forecasting of TAC for this species. Parameters of the model were estimated using the algorithm of sampling by scheme of Markov chain. The model is relatively simple and undemanding to data - time-series of commercial catch per effort is sufficient for its simplest version. Results of modeling are comparable with the results of cohort models.
Size composition and growth rate of blue king crab males are analyzed on the data of 8 bottom trawl surveys conducted in the western Bering Sea in summer-fall seasons within the period from 2005 to 2017. Significant changes in size structure of this population are revealed. Portion of commercial males was the lowest (18.7 %) in 2010 because of the strong yearclass appeared in the catches in 2005, when its males carapace had the width 20–40 mm, that provided in 2008–2010 the percentage of juveniles with the size < 100 mm about 59–60 %. Then this strong year-class reached the commercial size, so the portion of commercial males increased to 66 % in 2014 and to 85 % in 2015–2016. The portion of juveniles was extremely small (3.1–6.5 %) in these years. The portion of commercial males had reduced again to 67 % in 2017 because of a new strong year-class appearance that provided the juveniles percentage increasing to 24.6 %. The mean size of commercial males has increased since 2012 in 18 mm and reached the value of 160.4 mm in 2017. Age of the crab males entry into the commercial cohort is estimated as 8 years. The observed cyclic changes in size composition of blue king crab and estimated value of its growth rate indicate indirectly a good and stable state of its population in the western Bering Sea.
Generalized additive models are applied for standardization of daily landing per unit effort (LPUE) for opilio crab using the data of fishery statistics for the West Bering Sea fishery zone in 2003–2020. A set of 12 models with various combinations of predictors was examined and the best model with the smallest value of Akaike criterion was selected (information criterion Akaike 21743, explained variance 58.6 %). The selected model reflects the effect of depth, distance from the coast, daily effort and tensor product of geographic coordinates and day of the year. LPUE was standardized using the selected model by substituting median values of nominal predictors and modal values of categorical predictors. Then the crab stock was estimated using the state-space form of Deriso-Schnute delay-difference model. The estimates based on both standardized and nominal indices are compared and a significant difference between them is found: the stock is assessed as 23,040 t with nominal indices but as 17,070 t using the standardized indices.
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