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Written by Bryan Watts
October 12, 2011
A menhaden in a brown pelican’s nest. Photo by Bryan Watts.
Menhaden, often called the “most important fish in the sea,” are the energy changers of Bay waters. They filter plankton, converting it into oil-rich tissues and making this vast energy reserve available to consumers higher up on the food chain. Demand for this energy-rich oil is at the heart of the conflict between Omega Protein, the largest commercial menhaden fishery on the Atlantic Coast, and many recreational anglers who claim that menhaden harvest levels have greatly compromised the health of striped bass and other prized species that depend on menhaden for food.
But striped bass and Omega Protein are not the only ones chasing menhaden. Menhaden are critical prey for many of our bird populations as well, including bald eagles, osprey, brown pelican, royal tern, and common loons – species that provide the sights and sounds of the visible living fabric that we identify with the Chesapeake Bay experience.
The current ASMFC regulation allows for harvests down to 8% of the projected unfished population (or conversely, catching up to 92 percent of all menhaden in the Bay and ocean). The population is technically classified as overharvested if it is driven below the 8% threshold. Even with this alarmingly generous threshold, a recent scientific assessment has indicated that menhaden have been overfished in 32 of the last 54 years.
In 1971 during the height of the DDT era, Bob Kennedy worked with breeding osprey in Mobjack Bay as a graduate student at the College of William and Mary under Dr. Mitchell Byrd. Kennedy determined that osprey pairs were producing chicks at a rate well below that needed to maintain the population, largely because DDT in their system made their egg shells too thin to be viable. Only 1 in 4 eggs hatched due to DDT contamination, but of the chicks that hatched, nearly 8 of 10 survived to fledge.
Andy Glass weighing an osprey chick as part of a study examining diet, provisioning rates, and chick growth. Photo by Bryan Watts.
During the next few decades, three additional William and Mary graduate students would work with osprey in Mobjack Bay and provide a portrait of a changing population. The United States ultimately banned DDT, and by the early 1980s osprey pairs were producing more than twice as many chicks as in the early 1970s, and their population was growing.
Surprisingly, however, by 2006 osprey productivity in Mobjack Bay had declined again back to levels not seen since the DDT era. This time the underlying cause had completely changed.
More than 35 years after DDT, graduate student Andy Glass found that 9 out of every 10 eggs hatched, but only 4 of every 10 chicks survived to fledge. Chicks were hatching, but they were starving in the nest.
Why? In the 1970s adult osprey were delivering nearly three times more fish to nestlings than in 2006. In the 1980s during the period of highest productivity, more than 70% of the fish delivered to nests were menhaden. By 2006 menhaden represented less than 27% of the diet. None of the other fish species in the osprey’s diet are equivalent to menhaden in energy content. So the adults were providing fewer fish to their chicks, and the fish were of poorer quality.
Significantly, over the same four decades, the menhaden population as measured by haul seines in Maryland had declined by more than 90%.
What is now before the ASMFC are proposals to make no change, as well as one to increase the population threshold from 8% to 15% of unfished levels. Though that would represent a modest change, it would be a welcome movement toward considering the needs of sport fish, birds, marine mammals, and the broader Bay ecosystem.
The Chesapeake Bay is a tremendous and shared resource. We all have a voice in how that resource should be used for the highest public good.
Results of aerial surveys for occupied bald eagle nests (1976-2016) within the lower Chesapeake Bay. The population increased from 30 to 1,052 breeding pairs with an average doubling time of 8 years Data from CCB data.