The December Bay Journal’s front page article on assessing the Bay’s forage base, “Little things turn out to be big deals in Bay predators’ diets,” illustrated both the value and the challenge of science in unravelling complex Bay issues. In doing so, it may have left a skewed impression of one of the Bay’s key prey species, Atlantic menhaden.
The article reviewed the findings of a recent Chesapeake Bay Program workshop and concluded that menhaden are “apparently not” the most important forage fish in the Bay, as many perceive them to be. The workshop characterized the diets of five representative Bay predatory fish, and University of Maryland scientist Ed Houde was quoted as saying “Menhaden came out not as high on the list as people thought it was going to be.” In the analysis, menhaden was important for only one of the predators, striped bass.
The workshop analysis used the most extensive predator diet data available for the Bay, so the results are solid. What was not made clear in the article, however, is that the data was all collected since 2002, so it only represents current Bay predator/prey relationships. Also not mentioned, menhaden recruitment to the Bay (annual production of young menhaden that are most eaten by predators) has been very poor for the last 20 years. And, a recent scientific assessment of the menhaden population found their numbers coastwide to be near an all-time low. So, to those concerned about menhaden fulfilling their forage role in the Bay food web, the workshop results are not surprising at all — in fact, they bear out the concern that fewer menhaden are being eaten by predators, and some, like striped bass, are being forced to turn to alternative prey — anchovies, blue crabs and baby seatrout — causing other problems.
So, are today’s forage dynamics different from earlier, more stable Bay conditions? Where historical predator diet data are available, the answer is yes, at least for striped bass. Several past diet studies were analyzed in a recent scientific journal article that concluded that striped bass prey consumption in the Bay “changed dramatically” between 1955 and 2001. Menhaden consumption declined 10 to 15 times from what it was in the 1950s, when menhaden numbers were at more normal levels. And, as might be expected, anchovies and blue crabs were relatively uncommon in stripers’ diets back then.
The forage workshop was a strong start to a multi-year task prompted by the 2014 Chesapeake Watershed Agreement to assess the Bay’s prey base and its ability to provide sufficient forage to the Bay’s valuable predators. But the job doesn’t stop at characterizing current conditions. Other historical datasets need to be evaluated and are, in fact, already under way. It is an enormous task, as Houde acknowledged when he said, “Providing estimates of consumption and forage demand is something we [scientists] would like to be able to deliver to managers in the next decade.”