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Paper text:
because of the significant depletion in many of the world 's fisheries , there is now considerable interest in fisheries - induced evolution ( fie ) [ 5 - 8 ] from both an evolutionary   and a conservation   perspective .
fisheries have been associated with a plethora of phenotypic changes in wild fish populations [ 9 - 11 ] , manifested in changes in growth , reproduction , morphology , physiology and behaviour , and life history traits such as size and age at maturation [ 13,19 - 24 ] .
modelling studies have also predicted fisheries - induced changes in both life history traits   and spawning migration strategy .
the evolution of traits that genetically co - vary with those under direct selection can also influence the rate of evolution occurring by exploitation alone .
fie has even been invoked to explain vulnerability to recreational fishing . despite the weight of evidence for phenotypic change induced by fishing
, it is generally accepted that unequivocal empirical evidence of underlying genetic change resulting from fishing is lacking , though tantalizing experimental evidence is highly suggestive .
the crux of the problem is that changes in fish density and the environment can act to drive phenotypic plasticity in the absence of any genetic response attributable to selection .
however , there is also widespread acceptance of the notion that fishing causes a change in the selective regime of wild stocks , so that evolutionary change should be inevitable .
the implications are far - reaching ; seemingly minimal shifts in age at maturity ( say from 6 to 4 years in atlantic cod ) can result in reduced annual population growth by up to 30% , and a doubling in the probability of negative population growth .
one of the most promising techniques for understanding the genetic contribution to phenotypic change is probabilistic reaction norms for maturation ( prnm ) - the fish 's probability of maturing as a function of its age and size .
important recent work is helping to quantify selection responses to overfishing , where there has been a dearth of data .
the study of atlantic cod from canada 's southern gulf of st lawrence stands out for estimating selection from an exploited stock .
sexual selection might also be involved in altering the rate of evolutionary change by fishing .
a logical question stems from this work - how much evolution is caused by natural selection and how much is harvest - induced ?
recent studies suggest that fisheries - induced selection acts against and tends to swamp natural selection , leading to changes in populations that may take a long time , if ever , to reverse .
in fact , rates of reversibility in  evolutionary changes due to fie could be extremely low even after fishing pressure ceases , especially when there has been major depletion of fish stocks due to over - exploitation , resulting in lower heritable genetic variation .
such is not surprising in light of the fact that fishing can result in fish mortality far greater than natural mortality - by more than 400% , resulting in far greater selection differentials .
the phenomenon in which current levels of exploitation will require several years of evolutionary recovery has been termed by u dieckmann as the  darwinian debt , which will need to be paid by future generations .
earlier studies showed a reduction in the ability of populations to recover   so fie might keep resilience of fish populations low for long periods .
however , a recent laboratory study demonstrated evolutionary reversibility , despite full recovery taking up to 12 generations in fish with an annual life cycle , ( equivalent to 36 - 84 years in typical harvested fish that have generation times of 3 - 7 years ) .
one of the biggest challenges for proponents of the theory of fie is to disentangle genetic changes from environmental changes - even prnm do not yet have strong empirical support . but does this matter ? only in the sense that evolutionary changes could take longer to recover from once fishing pressure is reduced , as now appears to be the case .
if it occurs on a scale of years to decades , then it is much more relevant to fisheries management than if it occurs on a centennial scale . because it is so widespread and potentially harmful , there is justified and increasing interest in fie to be incorporated into ecosystem - based management of fisheries worldwide [ 5,47 - 49 ] .
others have used fie to stress the recent recommendation of keeping the larger fish around .
but it must also be stressed that effects of fie are variable and , where they occur , might be managed effectively .
experimental studies confirm recovery from fie after selection regimes have been relaxed in the laboratory , supporting the notion that genetic diversity loss does not necessarily accompany fie .
evolutionary scientists will need to work more closely with managers to incorporate fie into conservation management .
the consequences of fie are many and daunting considering the importance of life history traits to population dynamics , biomass , demography and economic yield .
fie may also lead to reduced productivity , lower maximum sustainable yields , slower rates of population growth , and lower probabilities of recovery .
as such , further research should focus on the demographic consequences of fie over multiple temporal scales . while the field is exciting and changing almost daily
, we still have very little information of how species are affected by fie , and the extent to which various traits are vulnerable .
human harvesting of fish results in far greater mortality than natural causes , with enormous potential to affect the phenotypic traits of fish populations , even after exploitation stops . 
 central to understanding these effects is the untangling of the genetic versus environmental components of phenotypic response . 
 evolutionary consequences of harvesting must be incorporated into conservation and management strategies .