Introduction

Aquatic ecologists and conservationists have long been obsessed with trying to understand links between body size, exploitation and conservation (e.g. Adams, 1980; Dickie, Kerr & Schwinghamer, 1987a). There are several reasons for this interest. First, at the individual level, fisheries management for both vertebrate and invertebrate populations tries to minimize the mortality of smaller individuals, in order to increase the probability that individuals have reproduced before they are caught (Jennings, Kaiser & Reynolds, 2001a). Even if other management methods are used, practically every stock assessment that has ever been done on an indeterminately growing species has included size as a key input parameter. Second, at the population level, large-bodied species have life-history traits that lead to slow rates of population turnover, with clear implications for productivity, resilience and recovery potential (Hutchings, 2001; Denney, Jennings & Reynolds, 2002; Reynolds et al., 2005; Goodwin et al., 2006). Third, at the community level, predator–prey relationships are strongly linked to size (Cohen et al., 1993; Woodward & Warren, this volume; Persson & De Roos, this volume), leading to the potential for understanding how fishing mortality may have wider ecosystem impacts through food-web dynamics (Dickie et al., 1987a).

At the population level, studies of the effects of exploitation have long focused on the direct effects of fishing mortality on a single stock, and this is often a pragmatic response to limited information on the indirect effects of mortality on one species affecting other species in the ecosystem (Hilborn & Walters, 1992).