Acoustic telemetry reveals strong spatial preferences and mixing during successive spawning periods in a partially migratory common bream population

Abstract

Partial migration, whereby a population comprises multiple behavioural phenotypes that each have varying tendencies to migrate, is common among many animals. Determining the mechanisms by which these phenotypes are maintained is important for understanding their roles in population structure and stability. The aim here was to test for the temporal and spatial consistency of migratory phenotypes in a common bream Abramis brama (‘bream’) population, and then determine their social preferences and extent of mixing across three successive annual spawning periods. The study applied passive acoustic telemetry to track the movements of bream in the River Bure system of the Norfolk Broads, a lowland wetland comprising highly connected riverine and lacustrine habitats. Analyses revealed that individual migratory phenotype was highly consistent across the 3 years, but this was not predicted by fish sex or length at tagging. During the annual spawning periods, network analyses identified off-channel areas visited by both resident and migrant fish that, in non-spawning periods, were relatively independent in their space use. Within these sites, the co-occurrence of bream was non-random, with individuals forming more preferred associations than expected by chance. These associations were not strongly predicted by similarity in fish length, sex or behavioural phenotype, indicating that the resident and migrant phenotypes mixed during their annual spawning periods. The results suggested these different phenotypes, with spatially distinct resource use in non-spawning periods, comprised a single population, with this having important implications for the management of this wetland resource.

The effect of temperature on the dynamics of common bream Abramis brama migrations between the reservoir and its tributary

“…Similarly, common bream spawn when the water temperature is above 15°C (Maitland & Campbell, 1992); hence, reproduction did not drive intensive upstream migrations from the reservoir. The search for feeding resources has often been reported as the reason for common bream migrations (Borcherding et al, 2002; Le Pichon et al, 2017; Molls, 1999; E. R. Winter et al, 2021b); in our study, this appears to be a reason for migrations from the reservoir to the tributary. The drive to find suitable feeding habitats corresponds with the findings that, compared to stationary individuals, migratory individuals had lower somatic conditions (Brodersen et al, 2019; Grift et al, 2001).…”

“…Similarly, common bream spawn when the water temperature is above 15°C (Maitland & Campbell, 1992); hence, reproduction did not drive intensive upstream migrations from the reservoir. The search for feeding resources has often been reported as the reason for common bream migrations (Borcherding et al, 2002; Le Pichon et al, 2017; Molls, 1999; E. R. Winter et al, 2021b); in…”

“…In our study, most individuals migrated between the reservoir and the tributary, some stayed in the tributary inflow to the reservoir and one individual was found in the reservoir. Similarly, local groups of the common bream occurred separately, except during the reproductive period (E. R Winter et al, 2021aWinter et al, , 2021b…”