The movement ecology of common bream Abramis brama in a highly connected wetland using acoustic telemetry.

Abstract

Evidence increasingly suggests that the movement behaviours of potamodromous fishes can be highly diverse in well-connected systems. Intra-population divergence in spatial and temporal resource-use is an important component of fish distribution patterns and population structure, which can affect population viability and adaptive potential. The common bream Abramis brama (µbUHaP¶) is a potentially strong model species for testing the importance of habitat connectivity and examining variation in movement patterns in lowland rivers. Concurrently, the Broads National Park (µBURadV¶), eastern England, provides a large network of interconnected rivers, lakes and dykes in which to examine unconstrained fish movement. Thus, biotelemetry was applied to investigating the movement ecology of bream in the northern Broads wetland system. Acoustic telemetry is a central tool for fish movement ecology, but robust data interpretation requires detailed knowledge of its efficiency and the fate of tagged individuals. Here, variation in acoustic receiver performance was quantified, along with the post-tagging survival rates of bream and Northern pike Esox lucius. The results demonstrated that acoustic detection range and efficiency were highly variable temporally, being negatively impacted by increased water temperature and precipitation, or reduced transparency (a surrogate measure of algal density). For both bream and pike, post-tagging survival rates were lowest in the reproductive periods of both species, but in bream, fish tagged just prior to spawning actually had the highest subsequent survival rates. Acoustic signal loss, potentially due to tag expulsion, also accounted for the loss of some bream from the study. These results emphasise the need for long-term receiver monitoring and consideration of the relative effects of tagging to be incorporated into telemetry study design. Geostatistical models of stable isotope landscapes (µLVRVcaSHV¶) provide a complementary tool to telemetry for assessing and predicting animal movements. The efficacy of single versus dual-isotope isoscapes in predicting the foraging locations of roach Rutilus rutilus was compared, with the dual-isoscape approach emerging as the most efficient. Dual-isoscapes were then applied to predicting the movement distances of individual bream in comparison to their movements recorded by acoustic telemetry. This revealed that isoscape-predicted movement was a significant predictor of the spatial extent of subsequent movements recorded by telemetry, suggesting repeatable individual activity levels between years. Dual- isotope isoscapes can thus provide a reliable alternative or complementary method to telemetry. Acoustic telemetry was then applied to investigating the diversity of bream migration behaviour throughout the northern Broads wetland system and examining more fine-scale spatial and social preferences during their reproductive period, with the aim to understand their spatial occupancy patterns and spatial population structure. Bream movements showed considerable diversity, with some individuals making repeatable spawning migrations of up to ~25 km, whereas others were relatively sedentary. Behavioural type (resident/ migrant) was highly consistent within individuals, although both phenotypes were detected mixing in space and time during the reproductive period. This suggests the Broads bream population is comprised of several distinct, semi-independent subpopulations that reside in spatially distinct areas throughout much of the year, but converge and potentially interbreed in their spawning period. Thus, this research explores the utility of acoustic telemetry and stable isotope tracking for documenting the movement ecology of lowland wetland fishes. The results emphasise the fundamental importance of connectivity in freshwater systems for enabling and maintaining high phenotypic diversity in the migration behaviours of potamodromous fishes.