Economic repercussions of fisheries-induced evolution

Abstract

Fish stocks experiencing high fishing mortality show a tendency to mature earlier and at a smaller size, which may have a genetic component and therefore long-lasting economic and biological effects. To date, the economic effects of such ecoevolutionary dynamics have not been empirically investigated. Using 70 y of data, we develop a bioeconomic model for Northeast Arctic cod to compare the economic yield in a model in which life-history traits can vary only through phenotypic plasticity with a model in which, in addition, genetic changes can occur. We find that evolutionary changes toward faster growth and earlier maturation occur consistently even if a stock is optimally managed. However, if a stock is managed optimally, the evolutionary changes actually increase economic yield because faster growth and earlier maturation raise the stock's productivity. The optimal fishing mortality is almost identical for the evolutionary and nonevolutionary model and substantially lower than what it has been historically. Therefore, the costs of ignoring evolution under optimal management regimes are negligible. However, if fishing mortality is as high as it has been historically, evolutionary changes may result in economic losses, but only if the fishery is selecting for medium-sized individuals. Because evolution facilitates growth, the fish are younger and still immature when they are susceptible to getting caught, which outweighs the increase in productivity due to fish spawning at an earlier age.Atlantic cod | genetic adaptations | harvest control rule | marine governance | adaptive management L ife-history theory, experiments, and field-based studies strongly suggest that fishing is capable of inducing genetic adaptations, especially when it removes individuals with characteristics such as large body size (1-5). Even if fishing is not size-selective, high fishing mortality may be sufficient to induce genetic change (6, 7). It is difficult to predict how genetic changes at the individual level affect population-level properties. Genetic adaptations may, in principle, be beneficial for the state of a stock, by enabling individuals to invest more into reproduction and growth (1, 8). As a consequence, the stock may become more productive, allowing exploited populations to withstand higher fishing mortalities than they could in the absence of such adaptation, possibly permitting higher yields. However, although an individual's increased reproductive investment leads to larger gonads, this happens at the expense of slower postmaturation growth. Maturing earlier may also reduce fecundity, because individuals are smaller when they reproduce (9). Moreover, adapting to fishing may bear a cost of maladaptation, resulting in increased natural mortality (10, 11). Therefore, fisheries-induced evolution (FIE) may reduce yield (2, 4, 12, 13) and may even imply a "Darwinian debt" (14) to be paid back by future generations, at least if genetic changes are difficult to reverse (1,15,16). Clearly, FIE has the potential for causing positiv...

Evolution of boldness and life history in response to selective harvesting

“…However, the sign of the selection differentials on reproductive investment remained identical whether density-632 dependence was acting on growth or not. Moreover, the key predictions emerging from our stylized model were roughly similar to the predictions of more complex eco-genetic 634 models in terms of the expected evolution of fast life histories under most situations in fisheries (Eikeset et al 2013;Dunlop et al 2015b). Nevertheless, it is clear that our 636 work shall be extended and replicated with other model frameworks to analysis its stability.…”

“…Fast life-histories can be characterized by fast juvenile growth, young age and small size at maturation and high reproductive investment, which reduce post-80 maturation growth rate and increase natural mortality. From a management 5 perspective, it is important to understand the population dynamical and social and 82 economic consequences of fisheries-induced evolution, to, if possible, design management tools that minimize undesired evolutionary effects on outcomes valued by 84 humans, such as yield, recovery or the catch prospects of exceptionally large fishes (Matsumura et al 2011;Eikeset et al 2013;Zimmermann & Jørgensen 2017). 86…”

Impact of minimum catch size on the population viability of Strombus gigas (Mesogastropoda: Strombidae) in Quintana Roo, Mexico

“…Furthermore, selective fishing pressure based on size may lead to the appearance of small adult individuals, as observed in Turks and Caicos Islands (Clerveaux, Danylchuk, & Clerveaux, 2005) and Berry Island, Bahamas (Stoner et al, 2012b). Fish stocks experiencing high fishing mortality show a tendency to mature earlier and at a smaller size (Eikeset, Richter, Dunlop, Dieckmann, & Stenseth, 2013), which may also reduce fecundity (Marshall, Needle, Yaragina, Ajiad, & Gusev, 2004). Large queen conch have higher reproductive potential than smaller individuals (Stoner et al, 2012a), so it can be concluded that fishing regulations based on shell length may also decrease the reproductive potential of a population through size selection.…”

Global connectivity and cross-scale interactions create uncertainty for Blue Growth of Arctic fisheries

“…The evolutionary effects of fishing, particularly on age and size at maturation, have been studied in the northern cod stocks of the Baltic Sea, Norwegian Sea and Icelandic shelf [72][73][74], and also in the Norwegian Spring-spawning herring stocks [75]. Harvest-induced evolution can affect the fishery's yield and therefore have economic repercussions for society as shown for the Barents Sea cod [76]. Perhaps counter intuitively evolutionary change may be mostly beneficial for the stock productivity and economic yield of the stock, as long as the fishing mortality is low because in this case, the adaptive capacity of the fish stock is maintained [76].…”

“…Harvest-induced evolution can affect the fishery's yield and therefore have economic repercussions for society as shown for the Barents Sea cod [76]. Perhaps counter intuitively evolutionary change may be mostly beneficial for the stock productivity and economic yield of the stock, as long as the fishing mortality is low because in this case, the adaptive capacity of the fish stock is maintained [76]. However, if fishing mortality is particularly high, productivity is actually lower if the fishery is catching all fish above a certain minimum size, which is currently the case for the Barents Sea cod.…”