Decreased availability of menhaden fish in the Chesapeake Bay is causing young ospreys in saltier parts of the bay and its tributaries to starve, a new study finds.
Scientists with the College of William & Mary’s Center for Conservation Biology compiled data on 511 osprey pairs across 12 study areas.
Osprey pairs in parts of the Chesapeake Bay where salinity was above 10 parts per thousand rely on Atlantic menhaden to feed their chicks.
But a reduced menhaden population has left these osprey nests without a major food source. This has led to loss of young due to starvation, smaller brood sizes, or nest failure, according to the study.
Meanwhile, in the freshwater study areas, where salinity levels were lower than 1 part per thousand, ospreys depended on catfish and gizzard shad for food. Osprey chicks in these nests had higher rates of survival due to the higher availability of those fish species compared to the menhaden.
Osprey pairs in the saltier waters lost an average of 1.1 chicks between hatching and fledging. By comparison, pairs in the less salty waters lost only 0.3 chicks on average.
Other factors can contribute to nest failure, including disease, competition, predators, and pollution. However, the William & Mary scientists found that these did not appear to be significant causes of the reproductive failure they observed.
Instead, they attribute the failure to food shortage, which resulted in poor breeding performance and asymmetric broods – in which the young vary in size and development.
In a nest on the Eastern Shore, a female osprey laid and hatched three eggs but early on the brood faced food stress.
The two smallest chicks died over a period of three days. The third survived another four days, but died overnight after 38 hours without food.
“The next morning the male delivered a fish and the female attempted to feed the dead young,” the scientists wrote. “The female continued to shade the young for the rest of the day. This is a typical starving sequence where an extended period without food pushes the young past the breaking point.”
Potential decline of the osprey population more broadly could depend on the relationship between saltier and fresher parts of the Chesapeake Bay, the scientists concluded.
“A determination of whether or not the Bay population as a whole is sustainable given the current prey situation is a topic of ongoing investigation,” they wrote.
The Chesapeake Bay Foundation highlighted Omega Protein and affiliate Ocean Harvesters as major harvesters of menhaden in the Chesapeake Bay.
“The management of the menhaden fishery, one of the most critical species in the Bay ecosystem, is operating with a question mark,” Chesapeake Bay Foundation Virginia Executive Director Chris Moore said in a statement. “We don’t have a full understanding of the impacts of industrial fishing in the Bay because Omega Protein continues to delay much needed scientific answers to this urgent question.”
The Atlantic States Marine Fisheries Commission in August voted to create a workgroup to consider additional ways to protect the Chesapeake Bay’s menhaden from industrial fishing.
“This year’s osprey data adds to the growing concerns about the number of menhaden in the Bay and the importance of a robust menhaden population for species that depend on them for food and Virginia’s economy,” Moore said.
He added, “We must follow a precautionary, ecosystem-based approach to setting limits on the menhaden fishery. That approach must include the study of the industrial fishing impacts to the Bay, as well as considering seasonal fishing closures from the Atlantic States Marine Fisheries Commission.”
