Life-history and activity shape catchability in a sedentary fish

Abstract

Catchability, a key parameter in stock assessment, is often considered constant in time and space. However, when fishing with passive gears like traps or gillnets, fish behavior determines the odds of encounter with the fishers and thus catchability. Few studies have presented comprehensive empirical evidence of the link between behavior measured in the wild and catchability from a life-history strategy perspective. Here, a suite of different variables, including environmental cues, physiological states, fish activity, home range and catchability, were modeled using a sinusoidal function to describe their seasonality over the year and the degree of coupling among them in a sedentary coastal fish (Labrus bergylta). All the variables except the home range size showed a significant variation over the year, following a sinusoidal pattern. The models showed a tight match between the seasonality of catchability and fish activity, with high values of both variables occurring in late spring to early summer, when the highest levels of feeding and the period of reproductive inactivity occurred. Lower catchability values were predicted in late autumn to early winter, coinciding with the spawning season and the associated reduced activity. This integrative research shows that the spatio-temporal dimension of fish life-history strategy has a key role in shaping catchability even in highly sedentary species. Timevarying catchability needs to be incorporated into stock assessment models that aim to accurately describe fish population health and to estimate abundance indices.