Scientists have studied the evolution of fish and whether commercial trawling has driven a change in how fish evade capture, creating a new league living up to Charles Darwin's theory of "survival of the fittest." During their trials, they noticed an evolutionary change in females trying to avoid unwanted male attention.
Let's say you're out at the bar. Some smarmy guy sidles up and starts hitting on you. What do you do? If you were a female guppy, you'd outswim him.
Researchers from the University of Glasgow and the University of Exeter have been studying guppies in various scenarios, including commercial trawling, but they are less interested in the fish that get caught - it's the ones that get away that intrigue them.
"There is a lot of concern on how overfishing is affecting the abundance of wild fish, consequences for the economy, employment and the ecosystem as a whole," said Shaun Killen of Glasgow's Institute of Biodiversity, Animal Health and Comparative Medicine, according to a Glasgow press release. "But one aspect that is often overlooked is that intense fishing pressure may cause evolutionary changes to remaining the fish that are not captured."
"Sexual coercion of females by males is widespread across sexually reproducing species," Killen explained in a press release from Exeter. "Typically, male reproductive success is limited by access to females, and males of many species will try to overcome this using a number of behaviors, such as chasing and even attacking females in an attempt to gain a mating.
"These types of behaviors are considered sexually harassing as males are attempting to coerce females into mating with them. Females can spend a lot of energy avoiding males in these situations and can even be injured.
"To reduce these costs, one possibility is that females may be able to change their own behavior or physiology in ways that reduce the negative energetic consequences of harassment or allows them to more easily escape male coercion."
In a recent study, groups of female fish who faced varying levels of harassment from male fish were tested, and the researchers discovered that some females, over time, were able to outswim their male counterparts.
"After five months (of male harassment), females exposed to higher levels of harassment were able to swim much more efficiently, using less energy to swim at a given speed compared to those exposed to lower levels of harassment," said co-author, Safi Darden, from the University of Exeter.
"An important factor appears to be swimming technique, and female guppies that experienced lower levels of harassment spent more time swimming with their pectoral fins extended, an indicator of an inefficient swimming technique," Killen added. "This change is very similar to that seen in human athletes who train to become better at their sports."
Killen suggested that the removal of the poor swimmers (by commercial fishers) will lead to "better swimming fish" with higher metabolic rates. "Over time, the selective removal of poor-swimming fish could alter the fundamental physiological makeup of descendant populations that avoid fisheries capture."
The study on how fish evade commercial trawling was published on Aug. 5 in the Proceedings of the Royal Society of London B.
The study regarding male sexual coercion affecting swimming technique of female fish was published on Aug. 24 in the journal Functional Ecology.
