Search

Genetic identity analysis and PIT (passive integrated transponder) tagging were used to examine the freshwater return rates and phenotypic characteristics of n = 1791 downstream migrating juvenile Salmo trutta in the Burrishoole catchment (northwest Ireland) across the period September 2017 to December 2020. In this system, juveniles out‐migrate (move from freshwater into brackish or marine habitats) in every month of the year, with distinct seasonal peaks in spring (March through June; mostly silvered smolts) and autumn (September through December; mostly younger, unsilvered fry or parr). Both types exhibited a sex‐bias towards females, which was stronger in spring (78% females) than in autumn outmigrants (67%). Sixty‐nine returning fish were matched back to previous juvenile outmigrants, and similar return rates were found for spring outmigrants (5.0%), autumn outmigrants (3.3%) and fish that out‐migrated outside of spring or autumn (2.8%). Spring and autumn outmigrants returned at similar dates (typically mid to late July), but autumn fish were away for longer periods (median = 612 days; spring outmigrants = 104 days). Autumn outmigrants were 25% smaller than spring outmigrants at outmigration and 6% smaller on their return, and within both groups smaller/younger outmigrants spent longer away than larger/older outmigrants. Autumn outmigrants were more likely to return unsilvered as "slob" trout (84%) than spring outmigrants (31%), suggesting they make greater use of brackish habitats that might be safer, but less productive, than fully marine habitats. Nonetheless, both types also produced silvered "sea trout" (≥1+ sea‐age), implying neither is locked into a single life‐history strategy. The findings emphasise that autumn outmigrants and the transitional habitats that support their persistence should not be overlooked in salmonid management and conservation. [ABSTRACT FROM AUTHOR]

Pass‐through PIT antennae are often used in river and stream habitats to monitor the movement of aquatic species. Where these habitats are prone to high flows that contain suspended debris, traditional pass‐through antennae designs are particularly vulnerable to damage, which can be time consuming and expensive to repair and lead to extended gaps in data collection. We designed and tested a novel pass‐through half duplex (HDX) antenna system that allows the antenna loop to (1) break away from one river bank under predetermined strain and (2) split into two separate cables, thereby shedding entangled debris that could otherwise damage or dislodge the antenna system. After break away events, our system can be rapidly reconnected and redeployed without the need for personnel to enter the water, reducing maintenance time and costs while minimizing gaps in data. In locations where pass‐through antennae are prone to flood damage, this system offers distinct advantages over traditional designs. [ABSTRACT FROM AUTHOR]

The degree of natal philopatry relative to natal dispersal in animal populations has important demographic and genetic consequences and often varies substantially within species. In salmonid fishes, lakes have been shown to have a strong influence on dispersal and gene flow within catchments; for example, populations spawning in inflow streams are often reproductively isolated and genetically distinct from those spawning in relatively distant outflow streams. Less is known, however, regarding the level of philopatry and genetic differentiation occurring at microgeographic scales, for example, where inflow and outflow streams are separated by very small expanses of lake habitat. Here, we investigated the interplay between genetic differentiation and fine‐scale spawning movements of brown trout between their lake‐feeding habitat and two spawning streams (one inflow, one outflow, separated by <100 m of lake habitat). Most (69.2%) of the lake‐tagged trout subsequently detected during the spawning period were recorded in just one of the two streams, consistent with natal fidelity, while the remainder were detected in both streams, creating an opportunity for these individuals to spawn in both natal and non‐natal streams. The latter behavior was supported by genetic sibship analysis, which revealed several half‐sibling dyads containing one individual that was sampled as a fry in the outflow and another that was sampled as fry in the inflow. Genetic clustering analyses in conjunction with telemetry data suggested that asymmetrical dispersal patterns were occurring, with natal fidelity being more common among individuals originating from the outflow than the inflow stream. This was corroborated by Bayesian analysis of gene flow, which indicated significantly higher rates of gene flow from the inflow into the outflow than vice versa. Collectively, these results reveal how a combination of telemetry and genetics can identify distinct reproductive behaviors and associated asymmetries in natal dispersal that produce subtle, but nonetheless biologically relevant, population structuring at microgeographic scales. [ABSTRACT FROM AUTHOR]

This paper reviews the life history of brown trout and factors influencing decisions to migrate. Decisions that maximize fitness appear dependent on size at age. In partly anadromous populations, individuals that attain maturity at the parr stage typically become freshwater resident. For individual fish, the life history is not genetically fixed and can be modified by the previous growth history and energetic state in early life. This phenotypic plasticity may be influenced by epigenetic modifications of the genome. Thus, factors influencing survival and growth determine life‐history decisions. These are intra‐ and interspecific competition, feeding and shelter opportunities in freshwater and salt water, temperature in alternative habitats and flow conditions in running water. Male trout exhibit alternative mating strategies and can spawn as a subordinate sneaker or a dominant competitor. Females do not exhibit alternative mating behaviour. The relationship between growth, size and reproductive success differs between sexes in that females exhibit a higher tendency to migrate than males. Southern populations are sensitive to global warming. In addition, fisheries, aquaculture with increased spreading of salmon lice, introduction of new species, weirs and river regulation, poor water quality and coastal developments all threaten trout populations. The paper summarizes life‐history data from six populations across Europe and ends by presenting new research questions and directions for future research. [ABSTRACT FROM AUTHOR]

Non-invasive methods are needed to enable indirect observation of vulnerable migratory fish populations across their life cycle and spatial distribution. Microchemistry data, such as trace element (TE) concentrations, collected non-invasively from the biomineral in fish scales can be used to characterize fish life history (habitat usage, fish provenance). However, scales are generally underutilized in microchemistry studies, due to conflicting evidence regarding the temporal stability of their composition. Some studies have found TE concentrations from scales are stable and reflect environmental conditions and habitat usage through time, while others have found that TE concentrations can change significantly after deposition in fish which have undertaken migration or spawning. Furthermore, validating TE proxies, such as fish scales, is extremely challenging for vulnerable populations because they have notoriously low survival rates in the wild, making tag and recapture experiments incredibly difficult. This study aimed to directly quantify changes in TE concentrations in scales collected from Atlantic salmon (Salmo salar , L.) at the juvenile and adult life stage. Over 1800 wild Atlantic salmon were tagged with passive integrated tags and, remarkably, 3 fish were successfully recaptured as adults. Individuals were sampled twice in the freshwater as juveniles, and again upon recapture during their return migration as adults. Scales were analyzed for concentrations of Ba, Sr, Mg, Mn, Fe, and Zn, using Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICPMS). Mixed effects models found significant changes in TE concentrations, between the juvenile scale and freshwater portion of the adult scale for all elements. Post depositional alteration may be caused by continued crystallization of scale apatite after migration, or scale reabsorption during the pre-spawning period. Future work could investigate the TE signal of fish recaptured at sea, to determine exactly when TE concentrations become modified. [ABSTRACT FROM AUTHOR]