Fish scared away from coral reef spawning site due to fishing, study finds

(CN) — Fisheries targeting coral reefs north of the Maldives could be jeopardizing the health of squaretail grouper populations by scaring fish away from their mating sites, according to a new study by a team of scientists at Lancaster University.

Access to the Lakshadweep archipelago in India has been restricted to protect the culture and ecology in the area, but as new fishery markets have opened there has been an increase in fishing around the archipelago over the last five years. The archipelago is home to squaretail grouper spawning aggregation sites, where the fish meet only a few times a year to mate.

The study was prompted when scientists who had researched the squaretail grouper spawning sites more than a decade ago returned to the area and noticed the groupers had a much different reaction to their presence than before.

“We discovered that we couldn’t film or study the fish as easily at the aggregation sites as we could in the past,” Rucha Karkarey of Lancaster University and lead author of the study said in a statement. The findings were published in the journal Biology Letters on Wednesday.

Karkarey said the fish would swim away from researchers as soon as they approached the area as though the scientists were predators.

“It was obvious to us that there was a difference in their behavior and we realized that the major thing that had changed in the decade since our previous study was the start of fishing at the site,” Karkarey said.

Squaretail groupers only gather at spawning aggregation sites to mate during the new and full moons between December and March and spawn in synchrony with the cycles of the moon. Males arrive at the sites a few days before females arrive to establish mating territories.

Fisheries have started to target squaretail grouper spawning sites during the short mating gatherings to ensure catches while the fish are distracted.

“Our findings suggest that the stresses caused by fishing are making the fish more nervous and on guard,” Karkarey said.

The scientists tested this by simulating a threat by diving toward spawning groupers at both fished and unfished spawning sites.

Single males at fished sites were found to be twice as likely to flee from the threat and took longer to return to their mating territories than fish at unfished sites.

Two-thirds of single male groupers returned to their territory at the unfished site, and less than half of the single males returned to their territories at the fished site.

Karkarey said the behavior is reducing the opportunities for single male groupers to reproduce with a mate, and males that are fitter and successful at reproducing are the ones being captured by fishers, potentially affecting the fitness of the population in the future.

“If a spawning aggregation event only lasts for a short period of time then every hour counts,” Karkarey said.

Males who had already mated with females fled their territories later and returned earlier at the fished site. They also spent less time and energy vigorously defending their territory, according to the study. At the unfished site, male groupers spent almost 10 times longer engaged in aggressive behavior.

“Decreased aggression can hold significant evolutionary implications in mating aggregations, specifically through a relaxation in sexual selection, which could have implications for mate choice, population fitness and long-term resilience,” co-author Sally Keith of Lancaster University said in a statement.

The scientists suspect the change in aggression levels could be explained by several factors, such as females in high-risk fishing situations being less discerning about mates or bolder fish lingering at the site being caught by fishers. Those potential factors were not studied.

The aggregation densities of groupers at the fished site went down 70% compared to the last time the researchers studied the area. The scientists said the findings of this study could impact oversight of the area.

“This study is the first of its kind in these atoll reef islands, and the findings can play an important role in fishery resource management in this archipelago,” Idrees Babu from the Department of Science and Technology, U.T. of Lakshadweep said.

Subscribe to Closing Arguments

Sign up for new weekly newsletter Closing Arguments to get the latest about ongoing trials, major litigation and hot cases and rulings in courthouses around the U.S. and the world.

Email *

Submit