ANNAPOLIS, Md. – Ospreys nesting at multiple sites around the Chesapeake Bay this year failed to produce enough young to sustain their numbers, new data shows. The scientists collecting the data say many chicks apparently starved in areas where the birds subsist mainly on Atlantic menhaden for food.
That observation, which builds on previous findings of poor osprey reproduction in Mobjack Bay in Virginia, is sure to increase public pressure on fisheries managers to curtail commercial harvests of menhaden in the Chesapeake.
Scientists with the Center for Conservation Biology at the College of William and Mary and with the U.S. Geological Survey monitored 571 pairs of ospreys from March through August at 12 locations on both shores of the estuary.
Ten sites were in brackish areas bordering the Bay’s mainstem where water salinity exceeded 10 parts per thousand and ospreys rely largely on menhaden for food. Those included the Lynnhaven, Elizabeth, York and Piankatank rivers in Virginia as well as Mobjack Bay, plus the Patuxent and lower Choptank rivers in Maryland.
Two other study areas were in freshwater far up the James and Rappahannock rivers where osprey tend to feed on catfish and gizzard shad.
Ospreys nesting in menhaden-dependent areas hatched and raised the fewest chicks on average, and many breeding pairs did not lay any eggs, reported Bryan Watts, director of the Center for Conservation Biology.
The overall reproductive rate for osprey pairs in the mainstem of the Bay was about half of what scientists believe is necessary to maintain the birds’ population, Watts said. That threshold is 1.15 young per nesting pair.
Ospreys in six menhaden-dependent areas experienced major reproductive shortfalls, producing fewer than 0.6 young per nesting pair. The other four brackish sites had moderate or mild shortfalls, still producing fewer than one young per nest.
By comparison, ospreys nesting over freshwater in the upper James and Rappahannock rivers produced 1.36 young per pair, well above the minimum needed to sustain their number.
Watts said that “the largest contributing factor to poor breeding performance was seemingly the loss of young due to starvation.”
In recent years, Watts and his research team have documented a steep decline in breeding performance among ospreys in Mobjack Bay, an offshoot of the Chesapeake between the York and Rappahannock rivers. They blamed that decline on a seeming shortage of menhaden in local waters, which deprived the young birds of needed nutrition. Watts decided to expand the nest monitoring this year to see if the problem was widespread in the Bay.
Female ospreys usually lay two to four eggs, and the young will spend 55 days in the nest being fed by their parents before fledging. When food is lacking, Watts said, chicks fail to flourish and die. More than half the nests monitored this spring and summer successfully raised just one bird, he noted.
“I’ve never seen nest failure like this in my entire career,” said Barnett Rattner, a veteran scientist with the U.S. Geological Survey who has monitored osprey reproduction periodically over the decades in the Chesapeake and Delaware bays. In collaboration with Watts, Rattner and USGS biologist Dan Day kept tabs on about 90 nesting sites this spring and summer in Maryland’s Harris Creek and around Tilghman Island, which are part of the Choptank.
Osprey nests can fail for a variety of reasons. Storms might blow them off their perches, while predators could poach eggs or chicks. Diseases may take a toll. Toxic chemicals ingested from contaminated fish also have been found to harm reproduction, a problem Rattner has focused on in his prior research.
This time, though, Rattner said he saw evidence that young birds were suffering from malnutrition. Based on footage from cameras mounted on a few of the nests, he said, “Fish are just not being brought to the nests at the rate they need to be.”
In one case cited by Watts, a female osprey on the Eastern Shore laid and hatched three eggs, but the two smallest young died within three days. The third nestling survived another four days but died after 38 hours without food. The next morning, the male adult osprey delivered a fish, and the female attempted to feed the dead young. The female continued to shade the young for the rest of the day.
Even with such evidence from this year’s nest survey, Rattner said he believes more research is be needed to prove unequivocally that a food shortage is causing the problem.
“Whatever is going on, it’s widespread,” Rattner added.
Environmentalists, recreational anglers and some scientists maintain that the Bay’s fish and wildlife don’t have enough menhaden to eat. They have pressed without success to curtail Omega Protein’s fishing fleet, which operates out of Reedville, VA. The Canadian-based company harvests huge quantities of the fish and processes them for use in animal feed and human nutritional supplements.
So far, East Coast fisheries managers are not convinced there’s a problem. A 2022 stock assessment for the Atlantic States Marine Fisheries Commission concluded that the coastwide population of menhaden is not being overharvested. Conservationists contend that Omega’s Bay-based fishing fleet depletes the menhaden stock in the Chesapeake, but to date there has not been a study to tell if that is so. Virginia lawmakers called for development of such a study in 2023, only to postpone funding it this year.
But, spurred by reports of osprey nesting problems, the fisheries commission has directed a working group to consider whether additional harvest restrictions might be warranted. The group is to report back at the next commission meeting in October.
