Atlantic menhaden (Brevoortia tyrannus) supports a major commercial fishery along the U.S. East Coast and serves as essential prey for fishes, seabirds, and marine mammals, may be less able to sustain fishing pressure than some assessments suggest. A new study finds that a key estimate of deaths from natural causes was substantially overstated, potentially making the population appear more productive than its biology supports.
Led by Jerald Ault, professor emeritus at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, with co-author Jiangang Luo, a scientist at the Rosenstiel School's Cooperative Institute for Marine and Atmospheric Studies, the study revisits a landmark federal tagging experiment. The research, published in the journal Fisheries Research, examines how historical records and assumptions about tag recovery influence estimates used to guide fisheries management.
Why it matters
Managers rely on population assessments to determine how much fishing a species can sustain. A central input is natural mortality, the rate at which fish die from causes other than fishing. Setting that rate too high can underestimate fishing's impact and overestimate the size of the breeding population, leading to overly optimistic harvest advice.
"Getting this number right matters for both the fishery and the coastal ecosystems that depend on menhaden," said Ault. "If natural mortality is set too high, the population can appear able to support more fishing than its biology allows."
The researchers estimated a natural mortality rate of 0.50 per year, less than half the 1.17 estimate reported in a 2019 reanalysis by Liljestrand et al., which was incorporated into the SEDAR 69 benchmark stock assessment by the Atlantic States Marine Fisheries Commission. The new result was also substantially below the corrected value of 0.92 adopted in a 2025 stock assessment update.
Ault and Luo returned to original records from a federal tagging program conducted from 1966 through 1971 along the Atlantic coast, from Massachusetts to Florida. The experiment involved more than 1 million tagged menhaden and more than 100,000 recovered tags.
Over approximately three years, they reconstructed two versions of the historical data, checked release and recovery counts, rebuilt fishing-effort records and examined how tags were detected at fish-processing plants.
"Our investigation identified discrepancies involving the numbers of released and recovered tagged fish, reconstruction of historical fishing effort, treatment of tag-detection efficiency at processing plants, and aspects of the statistical model," said Ault.
A critical issue was the performance of magnets used to recover metal tags from harvested fish. Detection varied widely among plants and over time. After correcting the underlying records, the researchers found that accounting for this variation was the principal reason their mortality estimate differed from earlier analyses.
Models that allowed tag-detection efficiency to vary by location and month better matched the recovery records. Both reconstructed datasets produced natural mortality estimates near 0.50 per year. Additional computer simulations tested uncertainty in the assumptions, with the best-fitting results consistently supporting a similar value.
The estimate also aligned with earlier research and biological evidence showing that Atlantic menhaden historically lived at least 10 years.
The findings concern a historical estimate, rather than a newly observed change in survival. The authors recommend that future assessments evaluate natural mortality values centered at 0.50 per year while accounting for uncertainty. The study does not establish a new catch limit.
"If natural mortality is high, fishing appears to account for a smaller share of population change. If it is closer to 0.5, as this study and earlier historical estimates suggest, fishing may account for a larger share of the losses," added Ault. "For a species that is both heavily harvested and ecologically central, that distinction matters not only to the menhaden fishery but to the many managed predators that rely on menhaden."
The study titled "Investigation of Atlantic menhaden mortality rates" was published on September 16, 2026 in the journal Fisheries Research. The authors are Jerald S. Ault and Jiangang Luo of the University of Miami Rosenstiel School.
