'The fit die young'

Fisheries management has to start taking fisheries-induced evolutionary changes into account, states a study published in renowned Science magazine. ‘An evolutionarily enlightened approach’
could help to identify the impact of fishing on species and their utility more clearly, the researchers suggest.

According to the paper, a number of studies have already indicated that many widespread changes in fish species are likely to be the result of selection pressure originating from fishing and
cannot be explained by environmental factors alone. Industrial fishing is now the most common cause of death in many fish stocks: figures may exceed natural mortality by 400%, estimates say.

‘Life-history theory [i.e. the theory of the reproductive cycle of animals and plants] predicts that increased mortality generally favours evolution toward earlier sexual maturation at smaller
size and elevated reproduction effort,’ the paper explains. The authors are researchers from Norway, Germany, Denmark, France, Austria, Sweden, Iceland, Portugal and the Netherlands.
Life-history traits are among the primary indicators for population dynamics.

The theory is corroborated by analyses of fisheries data. To make matters worse, the effects, which have repercussions for stock biomass, demography and economic yield, are amplified by fishing
that is selective regarding size, maturity status, behaviour or morphology. Human-induced evolution is considered to be particularly rapid, bringing about unintended changes in a matter of
decades. Some of those changes ‘will even have the potential to cause nonlinear ecological transitions and other unexpected outcomes,’ the paper warns.

Currently, those specimens that have – against all odds – survived all natural dangers and grown to be large and prolific are the ones that end up on the fish hook or the fishing net, says
Professor Robert Arlinghaus of German Leibniz Institute of Freshwater Ecology and Inland Fisheries, who is one of the authors of the report. ‘Consequences on long-term development and the
preservation of natural fish stocks are difficult to predict. At the moment, it is not ‘survival of the fittest’ that rules in many fished stocks, but rather ‘the fit die young’,’ he adds.

The study now suggests ‘evolutionary impact assessment (EvoIA) as a tool for the management of evolving resources’. ‘First of all, this would help to identify those fish stocks that are
particularly sensitive,’ Professor Arlinghaus explains. Next it would be important to find out exactly which evolutionary changes are fisheries-induced, and which impact they have on fish
stock’s utility to industrial fisheries and recreational fishing. Suitable methods are currently being developed in various projects worldwide. Using population dynamics models, researchers
would then be able to develop scenarios as to which management measures will be able to curb fisheries-induced evolution.

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