Stable isotope (SI) analysis studies rely on knowledge of isotopic turnover rates and trophic-step discrimination factors. Epidermal mucus ('mucus') potentially provides an alternative SI 'tissue' to dorsal muscle that can be collected non-invasively and nondestructively. Here, a diet-switch experiment using the omnivorous fish Cyprinus carpio and plant-and fishbased formulated feeds compared SI data between mucus and muscle, including their isotopic discrimination factors and turnover rates (as functions of time T and mass G, at isotopic half-life (50) and equilibrium (95)). Mucus isotope data differed significantly and predictively from muscle data. The fastest d 13 C turnover rate was for mucus in fish on the plant-based diet (T 50 : 17 days, T 95 : 74 days; G 50 : 1.08(BM), G 95 : 1.40(BM)). Muscle turnover rates were longer for the same fish (T 50 : 44 days, T 95 : 190 days; G 50 : 1.13(BM), G 95 : 1.68(BM)). Longer half-lives resulted in both tissues from the fish-based diet. d 13 C discrimination factors varied by diet and tissue (plant-based: 3.11-3.28%; fishmeal: 1.28-2.13%). Mucus SI data did not differ between live and frozen fish. These results suggest that mucus SI half-lives provide comparable data to muscle, and can be used as a non-destructive alternative tissue in fish-based SI studies.

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The nal publication is available at Springer via https://doi.org/10.1007/s10750-016-2720-z Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. anadromous brown trout (Salmo trutta), however the precise timing, extent and ecological 15 significance of such behaviour remains ambiguous. We investigated the phenology of downstream 16 migration of wild juvenile trout using passive integrated transponder (PIT) telemetry over an eight 17 month period in two European rivers; the River Deerness, north-east England, and the River 18 Villestrup, Denmark. The incidence of autumn-winter seaward migration was greater in the Deerness 19 than the Villestrup, with at least 46 % of migrating juveniles detected prior to spring smoltification in 20 the Deerness. Timing of migration was strongly regulated by factors associated with river discharge 21 in both systems. While autumn and spring downstream migrants did not differ in size at the time of 22 tagging in either system, evidence that spring migrants were of better condition, travelled faster 23 (autumn: 11.0 km day -1 ; spring: 24.3 km day -1 ) and were more likely to leave the Deerness suggests 24 autumn and spring migrant conspecifics respond to different behavioural motivations. Further 25 investigation into the sex of autumn migrant juveniles, as well as the temporal and geographical 26 variability in the incidence and fitness consequences of autumn emigration by juvenile trout would 27 be beneficial. 28

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Stable isotope analysis (SIA) was used to examine the isotopic relationships between dorsal muscle and fin, scale and epidermal mucus in pike Esox lucius. δ 13 C and δ 15 N varied predictably within each tissue pairing, with conversion factors calculated for the surrogate tissues, enabling their application to the non-lethal sampling of E. lucius for SIA.

Epidermal mucus (‘mucus’) is increasingly applied to fish ecological studies based on stable isotope analysis (SIA) due to its non-invasive collection. However, knowledge on mucus SI turnover rates of individual fish remains limited, including uncertainty over how they are influenced by fish body sizes. Here, a diet switch experiment predicted mucus SI turnover rates (δ13C and δ15N) as a function of time using samples taken over 200 days from 10 individually tagged common carp Cyprinus carpio covering two size groups. Non-linear mixed effects models revealed rapid turnover of both δ13C and δ15N (T50: 2–5 days; T95: 9–22 days); δ15N turnover rates were slower for the larger cohort, while δ13C turnover rates were independent of body size. Within size groups, turnover rates were not expected to vary between individuals. These experimental results suggest that due to these fast turnover rates, epidermal mucus can provide insights into the diets of fish over very short timeframes, although for δ15N the body size of the fish needs consideration.

Acoustic telemetry is an important tool for assessing the behavioural ecology of aquatic animals, but the performance of receivers can vary spatially and temporally according to changes in environmental gradients. Studies testing detection efficiency and/ or detection range are, therefore, important for data interpretation, although the most thorough range-testing approaches are often costly or impractical, such as the use of fixed sentinel tags. Here, stationary tag data (from study animals that had either died or expelled their tags) provided a substitute for the long-term monitoring of receiver performance in a wetland environment and was complemented by periodic boat-based range testing, with testing of the effects of environmental variables (water temperature, conductivity, transparency, precipitation, wind speed, acoustic noise) on detection efficiency (DE) and detection range (DR). Stationary tag DE was highly variable temporally, the most influential factors being water temperature and precipitation. Transparency was a strong predictor of DR and was dependent on chlorophyll concentration (a surrogate measure of algal density). These results highlight the value of stationary tag data in assessments of acoustic receiver performance. The high seasonal variability in DE and DR emphasises the need for long-term receiver monitoring to enable robust conclusions to be drawn from telemetry data.

Studies suggest the migratory behaviours of potamodromous fishes can be highly variable in barrier‐free systems, where differing movement types enable populations to exploit a wide range of food and space resources. This intra‐population diversity in spatial and temporal resource use is important to our ecological understanding of fish distribution patterns and population structure. Despite this, freshwater ecosystems are increasingly characterised by high levels of fragmentation and degradation that restrict mobile fauna, and limit opportunities to study natural, unconstrained movement behaviour. Common bream Abramis brama (bream) is a potentially strong model species for testing the importance of diverse migration patterns in lowland rivers, but existing studies have been largely restricted to spatially confined and/or anthropogenically modified systems. This study's principal focus was to examine the diversity of bream movement behaviour in a highly connected, lowland system using passive acoustic telemetry, which provided continuous, multi‐year data on the movements of 181 bream across a tidally influenced, lowland wetland in eastern England (c. 60 km of continuous river length plus numerous interconnected shallow lakes and dykes). Tracked bream were grouped according to their initial location and timing of tagging. Bream migratory behaviours varied considerably between tagging groups, but with greater consistency within groups. There was little mixing of groups outside of spawning periods, with season and tidal phase being significant predictors of movement. Rates of movement and swimming speeds were highest in spring, with movements also generally occurring in the direction of tidal flows. For fish sampled just prior to spawning, there was considerable diversity in their post‐spawning behaviour, with some remaining in the immediate vicinity of the sampling location and others that moved to areas c. 25 km away. These spatially discrete patterns remained until the following spawning period. These results suggest that this lowland fish population is comprised of several distinct, semi‐independent subpopulations that only share space resources in their spawning period. This indicates the importance of connectivity in lowland freshwater systems for enabling and maintaining high phenotypic diversity in the movement behaviours of potamodromous fishes.