- The Enterprise
- The Recorder
In a letter published Dec. 19 [“Menhaden contribute little to quality of water here,” Maryland Independent], Ben Landry takes columnist James Drake to task for misleading statements in his Dec. 12 column [“Deciding the fate of menhaden”] on the role of menhaden in the Chesapeake Bay.
Mr. Drake can defend his column, but Mr. Landry makes a misleading comment of his own. In the second paragraph, he quotes a 2012 study from the Virginia Institute of Marine Science as concluding that “menhaden contribute little, if any, to improving water quality.” However, the authors of the study are not nearly so definitive in their conclusions.
David Malquist of VIMS has published a summary of the study at www.vims.edu/newsandevents/topstories/archives/2010/menhaden_water_quality.php.
The VIMS researchers do conclude that their feeding experiments with menhaden in fish tanks seem to show that it is unlikely that menhaden can remove enough nitrogen to have a significant effect on water quality in the Chesapeake Bay as a whole.
However, they note that uncertainty about actual numbers of menhaden in the bay needs to be taken into account before concluding that there is little effect.
“We face a big scaling issue,” says Latour in the study. “We take what we find in the lab on a per-fish basis, and scale it to the population level by multiplying by total numbers. But since we have little idea what the total number is, we have a lot of uncertainty.”
In other words, until we know how many menhaden are actually in the bay, it is impossible to draw conclusions based on feeding by a small number of confined fish. Furthermore, the authors go on to say that they cannot rule out the possibility of local positive effects on water quality:
“A better understanding of spatial variations in menhaden abundance within the Bay would also give us a better idea of where menhaden may play a larger role,” adds Brush. “While our calculations show little impact at the Baywide scale, menhaden may still be locally important if large numbers overlap with large phytoplankton blooms.”
In other words, it is possible that large schools of menhaden play a significant role in mitigating negative effects of large phytoplankton blooms and thus have a positive effect on local water quality. And, it stands to reason that enough improvement in local water quality could eventually improve water quality in the bay as a whole.
The Chesapeake Bay is a complex ecosystem. We should not draw conclusions about the importance of menhaden to the health of the Chesapeake Bay based on one laboratory study, however well done. The study needs to be replicated and considered along with other studies of menhaden, as well as studies of other species and direct measurements of water quality, such as turbidity and oxygen levels.
Herb Reed, Prince Frederick
The writer is an agricultural and natural resources educator with the University of Maryland Extension, Calvert County office.