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Processes responsible for population structuring across spatial and temporal scales represent key components in understanding speciation and evolution. We use a hierarchical approach to investigate the degree and mechanisms of structuring in landlocked and diadromous populations of the facultatively amphidromous fsh Galaxias brevipinnis (kōaro) across various temporal and spatial scales in southern New Zealand. To determine long-term structuring of kōaro, populations in multiple lakes and coastal sites were compared genetically. Short-term population structuring was assessed using otolith microchemistry for a subset of sites, and behavioural mechanisms driving population structuring were assessed via larval distributions. Genetic data show that lakes foster divergence of lake-developing kōaro populations from each other and from coastal stream populations, but there is relatively little structuring within coast or lake populations. Otolith analyses, however, indicate that on a shorter timescale, most kōaro larvae do not disperse widely, i.e. recruitment is local. Thus, lake and coastal populations show a distinct meta-population structure based on catchment, in contrast to the prevailing assumption of widespread dispersal, with implications for management. Most kōaro larvae were distributed in river plumes, suggesting that a simple larval behavioural mechanism, e.g. positive rheotaxis, may result in larval retention within catchments and lakes. Larvae not retained in plumes create opportunities for genetic exchange within-lake or among coastal sites. Genetic divergence of lake populations of kōaro, resulting from both intrinsic behavior and extrinsic landscape, provides insight into the potential of G. brevipinnis to diversify and speciate when landscape and circumstances align, with implications for the management of this and other facultatively amphidromous species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Understanding the role different habitats play in the life histories of fishes is important for the development of holistic aquatic ecosystem management plans. We used otolith trace element analysis to reconstruct the life history of estuarine triplefin Forsterygion nigripenne and infer its habitat use. Analysis of otoliths using laser ablation inductively coupled plasma mass spectrometry showed an elemental profile without prominent changes in elemental concentration. The otolith elemental profiles were not indicative of movement between waters with substantial Sr:Ca and Ba:Ca differences. The Sr:Ca and Ba:Ca profiles were indicative of within—and near—estuary movements encompassing short time periods. Overall, the otolith microchemical profile was likely indicative of a life history closely associated with estuaries. However, it is difficult to rule out brief excursions to the marine environment given that may not have been of sufficient duration to be recorded in the elemental composition of the otolith. This suggests that F. nigripenne is the only species in southern New Zealand known to be closely associated with estuarine habitat for its entire life cycle. [ABSTRACT FROM AUTHOR]

Determining the factors driving population dynamics of stream salmonids across broad landscapes is important for understanding stream ecosystem functioning and for the management and conservation of the populations of such fish. A few studies have described the determinants of the early life history of salmonids across catchments, but none of them have examined how this spatial variation develops temporally.We hypothesised that: (1) spatiotemporal dynamics of young‐of‐the‐year (YoY) trout populations vary within the catchment, with loss rates (emigration plus mortality) being higher in lower elevation, downstream reaches than in higher elevation, upstream ones; and (2) loss rate would be density dependent, leading to reduced intra‐ and inter‐cohort competition and supporting establishment of resident populations.We tested the first hypothesis by examining relationships between geomorphic characteristics of spawning streams and temporal dynamics of YoY brown trout density, loss rate and biological traits through an austral summer across the catchment of New Zealand's fourth‐longest river, the Taieri River. To test the second hypothesis, we examined whether initial YoY density in spring and other biotic determinants affected loss rate and cohort structure dynamics, resulting in density‐dependent self‐thinning of YoY fish to avoid resource limitation.Spring YoY density and subsequent loss rate was higher in low elevation sites, corresponding to stream accessibility to migratory spawners. These significant correlations of YoY density and related biotic variables with elevation disappeared later in the season, indicating that regardless of their origin, brown trout YoY tend to form stream resident populations with multicohort structure and densities low enough to limit intraspecific competition.Our findings provide evidence that geomorphological features of the landscape affect temporal dynamics of YoY trout populations driven by density‐dependent self‐regulatory mechanisms that can control the abundance of growing fish. [ABSTRACT FROM AUTHOR]

New Zealand has a complex recent history of climatic and tectonic change that has left variable signatures in the geographic distribution and genetic structure of the region's flora and fauna. To identify concordant patterns, a broad range of taxa must be examined and compared. In New Zealand's North Island, a consensus is forming as to the dominant biogeographic barriers in the region although obligate freshwater taxa have not been considered in this framework. We use single-nucleotide polymorphisms to investigate phylogeography in the widespread obligate freshwater fish Gobiomorphus basalis on the North Island. Phylogeographic patterns within G. basalis reveal biogeographic disjunctions that are in some ways consistent and in other ways at odds with established patterns, providing insight into the processes that have shaped the islands' biogeography. We also use phylogeography to delineate species boundaries within the entire New Zealand radiation of Gobiomorphus and find that it contains several morphologically cryptic species. We resolve two clades within G. basalis that correspond to areas north and south of the Taupo Volcanic Zone. We confirm the distinctiveness of Gobiomorphus alpinus relative to Gobiomorphus cotidianus , as well as the presence of two lineages within Gobiomorphus breviceps that were previously identified based on mitochondrial data. [ABSTRACT FROM AUTHOR]