Has cannibalism hindered the recovery of weakfish?

A research team studied data on weakfish stomach samples from the past 20 years.

Research Need

The weakfish, located throughout the coastal United States, is a highly predatory species with a diet as diverse as the range it inhabits. Variations in diet typically depend on the size and age of the individual weakfish, as well as the season and availability of local prey. Because of the high variability in its diet, the weakfish is a good indicator of energy transfer through the food chain.

The size of the weakfish population has been low since the 1990s, which is likely the result of natural mortality (starvation, predation, and disease) and excessive fishing mortality during that time period. But even when fisheries removals were significantly reduced, the population didn’t rebound.

Could weakfish’s diet affect its ability to recover?

What did they study?

A research team studied publicly available data regarding weakfish stomach samples from the past 20 years. Sample 150 sites spanned from Cape Cod, Massachusetts, to Cape Hatteras, North Carolina, during winter, spring, and fall.

The team then categorized the samples by size of the fish and season.

What did they find?

Weakfish prey field did not significantly change during the 2007–2019 period. The most-identified prey overall were anchovies, bony fish, and small crustaceans, with anchovies accounting for the vast majority . 

As suspected, size of the individual weakfish and sample season accounted for significant variation in prey types and proportions, with the biggest differences occurring with fall versus spring. Medium-sized weakfish tended to eat larger prey fish, particularly Atlantic menhaden, while smaller weakfish preferred larvae, smaller fish, and crustaceans.

What else did they find?

Cannibalism accounts for a significant part of weakfish diets. This could be due to diminishing sources of other prey or competition for resources with other predatory species and larger weakfish. Regardless, cannibalism likely has contributed to the species’ inability to recover from the 1990s population decline.

So what?

Understanding the diet of a fish species, especially when it covers a wide range of habitats and sources, is crucial to understanding energy transfer through the food chain, predator-prey interactions, and interactions among fish of the same and different species. The information gathered in this study also could help scientists better understand how predatory species other than weakfish interact with fish both inside and outside of their own species.

Reading

Reyes Delgado, A., & Smith, B. E. (2024). Diet variation and trophic impact of weakfish, Cynoscion regalis, within multiple marine habitats of the eastern United States. Journal of Fish Biology, 105(6),1628–1642. https://doi.org/10.1111/jfb.15897

This study was funded by National Oceanic and Atmospheric Administration, Office of Education, Educational Partnership Program, Award numbers: NA16SEC4810007; NA21SEC4810005.

The text from Hook, Line & Science is available to reprint and republish at no cost, but only in its entirety and with this attribution: Hook, Line & Science, courtesy of Scott Baker and Sara Mirabilio, North Carolina Sea Grant.