Commercial fishing may severely impact sexual selection 

Large male and female fish are not only the top picks as fishing targets, but are also the preferred choice for sexual selection. In a new study from the University of Jyväskylä, research fellow Silva Uusi-Heikkilä describes the potential consequences of commercial fishing on reproductive success and population viability.

Among most fish species, body size is an important part of the sexual selection process. Large fish are usually preferred over small fish because they can provide better resources and protection for the survival of the offspring.

Sexual selection depends on the advantages that certain individuals have to offer. This process is beneficial to the reproductive success of fish populations by boosting fitness and viability.

A large male can provide more intensive care for the developing offspring than a small male, and this is attractive to females. 

On the other hand, a large female salmon is more fertile than a small salmon and attracts multiple males. Sexual selection in fish has been primarily studied based on certain model species, such as zebrafish and three-spine stickleback.

“Zebrafish females prefer a large male as a mating partner and releases more eggs for him compared to a small male. In some species females also produce higher quality eggs towards large males,” explained Uusi-Heikkilä.

Fisheries often remove the largest individuals from the population, which works against sexual selection. However, the effects of fisheries selection on sexual selection is an issue that has received relatively little attention.

“Studying mate choice in natural conditions can be challenging,” said Uusi-Heikkilä. As a result, the mating systems of many commercially valuable fish species are poorly known, with the exception of salmon and cod. 

Experimental studies have revealed a great deal about cod mating systems, while salmon spawn in their home rivers where it is easy to observe mate choice and mate competition compared to fish who spawn in the ocean.

Uusi-Heikkilä emphasized that more research is needed to understand how size-selective fisheries affect fish mating systems, how persistent these effects are, and how population growth, viability and resilience may be impacted.

“Large females and males often have higher reproductive success than small ones. Thus, size-selective fisheries may impair population growth,” said Uusi-Heikkilä.

“It is tempting to think that sexual selection could buffer the adverse effects of fishing and rescue exploited populations. This is not going to happen, if there are now large females and males left.”

“Overall, if fishing reduces body size variation in a population, sexual selection cannot operate effectively.” 

The study is published in the journal Evolutionary Applications.

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By Chrissy Sexton, Earth.com Staff Writer