New research shows that fishing at squaretail grouper spawning sites disrupt mating. Males are repeatedly scared away during their short mating periods, losing time to attract females. A study from Lancaster University, published in Biology Letters, reveals that fishing affects not just the caught fish but also causes behavioral changes in those left behind, reducing their ability to reproduce.
This disruption could lead to fewer offspring and long-term population issues. Squaretail groupers gather at specific sites several times yearly during new and full moons between December and March.
Male groupers arrive at spawning sites a few days before the new or full moon to set up mating territories and attract females. Females arrive just before the new moon, and fish spawn in sync with the moon’s cycles. These gatherings are crucial for reproduction.
However, spearfishing and hook-and-line fishing target these sites, causing significant disruptions. In India’s Lakshadweep archipelago, where fishing was previously restricted to protect local culture and ecology, new markets have led to a 70% drop in grouper numbers over the past decade.
Marine scientists noticed a change in squaretail grouper behavior at spawning sites compared to a decade ago. Unlike before, Dr. Rucha Karkarey from Lancaster University observed that fish were more afraid and swam away quickly.
This change was linked to increased fishing at these sites. Researchers compared fish behavior at fished and unfished sites by simulating threats and observing how close the fish could get before they fled, as well as their time spent defending their territory and courting.
Single male squaretail groupers are twice as likely to flee at fished sites and take two and a half times longer to return to their territories than those at unfished sites. Fewer than half of single males return to fished sites, while two-thirds return to unfished sites.
Although fleeing early can help fish avoid danger, it may also reduce mating chances. Fishing stress makes fish more nervous and affects their ability to mate and defend territories. This can impact the future fitness of the population, as fishing targets more successful paired males.
Spawning events are short, so every hour is crucial. Researchers found that male groupers at fished sites spent much less time defending territories and more time fleeing compared to those at unfished sites. This may be because females are less selective or bolder fish are caught.
Reduced aggression could affect mating, population health, and long-term survival. This study, the first of its kind for these islands, highlights essential implications for fishery management. The findings are in Biology Letters.
Journal reference :
- Rucha Karkarey, L Boström Einarsson et al., Do risk-prone behaviours compromise reproduction and increase vulnerability of fish aggregations exposed to fishing? Biology Letters. DOI: 10.1098/rsbl.2024.0292.