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Variation in brown trout (Salmo trutta L.) population recruitment and structure is related to migratory patterns, which should depend on ease of access to habitats providing increased opportunity for growth. We quantified the number of young of year (YOY) as a proportion of the total number of brown trout at 24 locations on 11 streams within the Taieri catchment, New Zealand, including back calculated growth rates and emergence dates from otoliths. Locations with high absolute and relative abundance of YOY fish were related to elevation and distance from the river mainstem (habitat used by migratory fish), fish density, and the interaction between invertebrate food biomass, distance and elevation. Hatch date and growth were not related to the proportion of YOY fish, though growth was negatively correlated to total fish density. We suggest landscape features play a large role in determining recruitment and population structure. Locations at lower elevations have a high YOY density, high competition and lower growth, likely prompting out‐migration. These conditions could be created by successful return migration and spawning of large fecund fish resulting in YOY densities exceeding the habitat carrying capacity. Environmental factors, such as food availability, also played a role in determining population structure. These results provide an example of how population structure and recruitment might be controlled by local conditions and access to high growth environments in wild populations of introduced brown trout across a catchment. [ABSTRACT FROM AUTHOR]

Identifying the environmental factors that affect freshwater fish can be crucial for their conservation and management. Despite the widespread investigation of relationships between fish habitat use and environmental variables, there is a paucity of knowledge on how abiotic and biotic factors jointly influence stream fish habitat use. Three New Zealand South Island streams were selected to investigate the habitat preference of a stream-dwelling galaxiid, banded kokopu ( Galaxias fasciatus). Fish abundance in several permanent pools was determined by spotlighting at night once a month from June 2008 to May 2009. Drifting invertebrates and key physical features of each pool were measured at the time of fish sampling. An information-theoretic approach ( AIC) indicated that the most parsimonious candidate model to predict banded kokopu biomass was the one that included pool area, undercut banks, water velocity, overhanging vegetation, invertebrate drift density and an interaction term between invertebrate drift density and water velocity. Banded kokopu biomass was positively related to pool area, undercut banks, overhanging vegetation and invertebrate drift density. Our study suggests that fish resource use patterns need to be understood in the context of multiple interacting ecological factors, including prey abundance. [ABSTRACT FROM AUTHOR]

Dairying is an intensive form of agriculture influencing stream ecosystems worldwide via increased levels of nutrients, deposited fine sediment and other contaminants. However, it is not fully understood how dairy farming affects food supply for stream fish. We investigated relationships between dairy farming prevalence in the catchments of nine tributaries of a New Zealand river (0% to 79% of the catchment area) and fish and invertebrate communities. Streams were sampled four times at monthly intervals for brown trout density, fitness/growth-related trout response variables, native fish density, invertebrate community metrics as well as physical and chemical water quality variables. Densities of both brown trout and native fish declined as dairying increased, with no trout found in streams where dairy farms covered more than 50% of the catchment area. Increasing dairy farming prevalence was also associated with higher in-stream levels of dissolved nutrients and deposited fine sediment. These findings suggest that increasing the extent of dairy farming in New Zealand based on practices at the time of sampling results in less abundant and diverse fish communities. [ABSTRACT FROM AUTHOR]

The article offers information on the study that focuses on the microhabitat use of a native New Zealand galaxiid fish, Galaxias fasciatus. It highlights the materials and methods used in the study including microhabitat use and availability, and data analysis. It also presents the results derived from the study with respect to fish frequency distribution, microhabitat occupied, and habitat availability.