The Angling Mortality Syndrome in Marine Sedentary Fish

Neither recreational nor commercial fishing “samples” fish at random. Larger and older fish have larger probabilities of being fished than smaller ones because of either, management policy (e.g. minimum legal sizes) or gear selectivity (e.g. mesh size and hook selectivity). The outcomes of biased mortality on life-history traits such as growth, reproduction investment and behaviour remain not fully understood. Here, we present both some empirical evidences and computer-simulation experiments supporting that angling may affect life-history traits of marine sedentary fish. In accordance with the optimal life-history strategy hypothesis, our empirical results suggest that angling mortality biases against large size and small reproduction investment. Therefore, it is expected that size-dependent fishing mortality could favour slow growing fish because these fish will maximize their fitness in a scenario of high (and biased) fishing mortality. Some computer-simulation experiments have been completed to better understand the possible processes driving to the “small and slow growing fish” syndrome. Specifically, we compare a simpler model that assumes no behavioural differences between fishes with a more complex one which assumes that fish can display different movement characteristics. Most littoral fish are more sedentary than it has been previously assumed and they spend most of the time moving within a well-defined and relatively small home range. An specific fish can explore its home range at an specific rate, which results in different degrees of boldness or shyness. We propose that this behavioural characteristic could be related with the parameters of a simple movement model for sedentary fish (Palmer et. al., in press). Fish that are more active and mobile would expend more effort looking for food resources (bold personality). Therefore, more food resources would be available to these individuals that, in consequence, would display higher growth rate. The trade-off is that they would be more vulnerable because higher mobility implies larger chance of encountering a fishing gear in comparison with reduced mobility fish. After simulating fishes with different characteristics, out results suggest that angling could bias fishing mortality not only for size, growth rate and reproductive investment, but also for behavioural traits.

Palmer, M., Balle, S., March, D., Alos, P., Linde, M. Estimating the size of circular home range from fish Mark-Release-(single)-Recapture data: the case of a small labrid targeted by recreational fishery. Marine Ecology Progress Series (in press).