Rapid depletion of genotypes with fast growth and bold personality traits from harvested fish populations

Abstract

The possibility for fishery-induced evolution of life history traits is an important but unresolved issue for exploited fish populations. Because fisheries tend to select and remove the largest individuals, there is the evolutionary potential for lasting effects on fish production and productivity. Size selection represents an indirect mechanism of selection against rapid growth rate, because individual fish may be large because of rapid growth or because of slow growth but old age. The possibility for direct selection on growth rate, whereby fast-growing genotypes are more vulnerable to fishing irrespective of their size, is unexplored. In this scenario, faster-growing genotypes may be more vulnerable to fishing because of greater appetite and correspondingly greater feeding-related activity rates and boldness that could increase encounter with fishing gear and vulnerability to it. In a realistic whole-lake experiment, we show that fast-growing fish genotypes are harvested at three times the rate of the slow-growing genotypes within two replicate lake populations. Overall, 50% of fast-growing individuals were harvested compared with 30% of slow-growing individuals, independent of body size. Greater harvest of fast-growing genotypes was attributable to their greater behavioral vulnerability, being more active and bold. Given that growth is heritable in fishes, we speculate that evolution of slower growth rates attributable to behavioral vulnerability may be widespread in harvested fish populations. Our results indicate that commonly used minimum size-limits will not prevent overexploitation of fast-growing genotypes and individuals because of sizeindependent growth-rate selection by fishing.behavior ͉ fisheries ͉ selection ͉ temperament I t is well known that fisheries tend to select for larger and older fish individuals because of preference and/or regulations imposing minimum size limits for harvest. The result of sustained and heavy size-selective harvesting over time has been the removal of larger and/or later-maturing individuals from populations, leaving behind populations consisting of small, earlymaturing individuals, with low fecundity (1-3). Because growth rate affects fish size at age and size at maturity, a size-selective fishery may indirectly remove faster-growing individuals from a population. Studies suggest that this effect may represent contemporary evolution, leaving behind genotypes that are slowergrowing and early-maturing; this then can lead to reductions in harvestable biomass and population fecundity that in turn hinders population recovery from harvest (2-5). The possibility for evolutionary responses should not be surprising given high heritability of growth rate and other life history parameters in fish and the intensity of size-selective fish harvest reviewed in refs. 2, 6, and 7. However, we are aware of only two studies providing strong evidence of fisheries-induced evolution of growth and/or other life history traits (4, 5).A fishery may select upon growth rate through both indirec...

Fishing directly selects on growth rate via behaviour: implications of growth-selection that is independent of size

“…Selection on growth rate via behaviour can occur, because fast-growing individuals tend to be more active, bold and voracious [10,11], and so, in turn, we should expect fast-growers to be more vulnerable to harvest owing to greater encounter rates with fishing gear, and lower gear avoidance. Indeed, at the group level, faster growth is associated with greater catchability, even in the absence of size selection [9,12]. In addition, several recent studies have shown biases towards more active and bold individuals in the catch [7,9,13 -15], but see [16].…”

“…However, one recent study highlighted how fishing may select on life-history traits via a behavioural mechanism, even in the absence of any size selection [9]. Selection on growth rate via behaviour can occur, because fast-growing individuals tend to be more active, bold and voracious [10,11], and so, in turn, we should expect fast-growers to be more vulnerable to harvest owing to greater encounter rates with fishing gear, and lower gear avoidance.…”

Evidence of size-selective evolution in the fighting conch from prehistoric subsistence harvesting

“…When harvesting is intensive, the evolutionary change to smaller size at maturity can be observed over decades [2,7] and under artificial experimental conditions can be forced to appear in just a few generations [8,9]. By contrast, low-intensity subsistence (artisanal) harvesting is widely presumed to lack sufficient directional selection to have an analogous significant evolutionary impact (cf.…”

Trait- and size-based descriptions of trophic links in freshwater food webs: current status and perspectives

“…Behavioural responses may vary between and within taxa; recent research has linked intraspecific variation in prey vulnerability and defensive behaviour to behavioural syndromes (Sih et al, 2004). Boldness may be responsible for differential mortality as bold individual are more likely to take risks during foraging and dispersal and hence have higher mortality (Biro and Post, 2008;Pruitt et al, 2012).…”