USGS Challenges Menhaden Study Linking Fish Decline to Osprey Reproduction Issues in Chesapeake Bay

WASHINGTON — A U.S. Geological Survey (USGS) letter sent to the House Natural Resources Committee last week indicates that multiple environmental factors — not just prey availability — are likely responsible for recent osprey reproduction challenges in the Chesapeake Bay, pushing back against claims from menhaden fishery critics.

The letter directly questions findings from a 2024 study by Dr. Bryan Watts of the Center for Conservation Biology, which linked a decline in osprey reproduction in Virginia’s Mobjack Bay to reduced menhaden availability. According to the USGS, the Watts study did not demonstrate a biologically significant change in the proportion of menhaden in the osprey diet over time. In fact, menhaden made up a slightly higher portion of the diet in 2021 compared to 2006-07, though the difference is statistically insignificant.

“Although the proportion of menhaden as a percentage of total diet in 2021 is numerically larger than the 2006-07 value, the two values are bounded by overlapping error bars, and are thus not different in a biologically meaningful way,” the letter stated.

The USGS also noted that striped bass, another key prey species, is overfished in the Chesapeake Bay, potentially impacting osprey reproduction. The Atlantic States Marine Fisheries Commission recently found that striped bass stocks remain overfished, with recreational catch-and-release mortality cited as a major factor in the decline.

Meanwhile, the Chesapeake Bay osprey population has surged by 1,800% since the 1960s, with similar trends observed in other coastal areas without menhaden fisheries, including Florida, the Pacific Coast, and New Jersey, suggesting broader environmental factors are at play.

The letter concludes that complex ecosystems like the Chesapeake Bay are influenced by a wide range of variables, including weather, predation risk, and nesting site availability, making it difficult to isolate a single cause for declining osprey reproduction.