Migration confers survival benefits against avian predators for partially migratory freshwater fish

Abstract

The importance of predation risk in shaping patterns of animal migration is not well studied, mostly owing to difficulties in accurately quantifying predation risk for migratory versus resident individuals. Here, we present data from an extensive field study, which shows that migration in a freshwater fish (roach, Rutilus rutilus) that commonly migrates from lakes to streams during winter confers a significant survival benefit with respect to bird (cormorant, Phalacrocorax carbo spp.) predation. We tagged over 2000 individual fish in two Scandinavian lakes over 4 years and monitored migratory behaviour using passive telemetry. Next, we calculated the predation vulnerability of fish with differing migration strategies, by recovering data from passive integrated transponder tags of fish eaten by cormorants at communal roosts close to the lakes. We show that fish can reduce their predation risk from cormorants by migrating into streams, and that probability of being preyed upon by cormorants is positively related to the time individuals spend in the lake during winter. Our data add to the growing body of evidence that highlights the importance of predation for migratory dynamics, and, to our knowledge, is one of the first studies to directly quantify a predator avoidance benefit to migrants in the field.

There and back again: migration in freshwater fishes

“…In this framework, we have found it very useful to consider the costs and benefits of different strategies, and how these cost-benefit trade-offs change with habitat-and time-specific changes in selection pressures, to understand the evolution of different migration strategies. Especially, in our own studies we have found that the trade-off between predation risk and growth potential, as first developed theoretically by Werner and Gilliam (1984), is a useful concept for understanding seasonal migration in cyprinids in general, as well as explaining why some individuals migrate while others remain resident (e.g., Brönmark et al 2008;Brodersen et al 2008c;Chapman et al 2011c;Skov et al 2011Skov et al , 2013. Predation-growth trade-offs have also been used to explain the diel and horizontal migrations of fish in deep-water lakes (e.g., Mehner 2012;Muška et al 2013) and in the future we look forward to seeing these applied to other species and other migratory strategies as well.…”

Cormorant predation on PIT-tagged lake fish

“…As the number of PIT tags in the study area increases with time, the risk of PIT tag collisions increases with study period length. PIT tag studies in the vicinity of Lake Viborg, i.e., a study on brown trout in Lake Hald (Boel, 2012) and on lacustrine fishes in nearby Lake Loldrup (Skov et al, 2011;Skov et al, 2013) has most probably increased the collision risk since many tags from tagged cormorant prey fish from these locations also were expelled at the Viborg roosting and breeding sites. Detection efficiency for PIT tags in cormorant colonies has been reported to be in the range of 50-90%, but averaging 57% (Seabring et al, 2010), and specifically for the cormorant colony at Lake Hald, (Boel, 2012) estimated detection efficiency to 78%.…”

Partial migration: growth varies between resident and migratory fish

“…Partial migration may influence population dynamics and persistence [8], as it may confer survival benefits through reduced predation risk (e.g. [9]) and/or increased food availability [6]. Although these factors are frequently cited as the ultimate cause of movement, the proximate cause is debated.…”