Chesapeake Outdoors ~ by C. D. Dollar

 Vol. 10, No. 15

April 11 - 17, 2002

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Sick Rockfish from a Sick Bay

As if there weren’t enough bad news recently about the deteriorating condition of Chesapeake fisheries, we now hear troubling news from Bay scientists about the growth of a destructive microbe, mycobacteriosis, that could potentially wreak havoc on the rockfish population.

Karl Blankenship’s article in this month’s Bay Journal ( sheds a glaring and necessary light on the chronic disease that, according to researchers, was first identified in 1997, the same year that Pfiesteria reared its flesh-eating head in the Chesapeake. But unlike Pfiesteria, mycobacteriosis has left no massive fish kill to tip off its presence.

External signs include sores and lesions, and fish lose weight. But just because you can’t see lesions doesn’t mean the fish on the other end of your line isn’t infected. Nasty large growths, called granulomas, form inside rockfish to partition off the infection.

Bay anglers will recall that beginning in the mid-1990s, we started to catch skinnier rockfish, some with lesions and open sores. Maryland Department of Natural Resources began to track this trend, and anecdotal evidence suggested that something was amiss, which is now, in part, confirmed by science. Several studies showed that mycobacteriosis was found in more than 50 percent of the fish sampled.

Because it’s a hard germ to identify and is not commonly found in the wild — no cases were reported in wild fish stocks on the East Coast prior to 1997 — scientists aren’t sure if it showed up earlier and slipped past them. To make the situation spookier, scientists in both Maryland and Virginia now think that they have discovered new strains of the disease.

It is clear that the Bay’s rockfish are stressed, but what environmental factors are causing this stress is debatable. One factor that might be stressing the fish, thus making them susceptible to mycobacteriosis, could be poor water quality, the root cause of many of the Bay’s ills. We know that excess nitrogen is choking the life out of the Bay and contributing to oxygen-depleted zones. Couple this with warm water temperatures, and adult rockfish are trapped in what scientists call the temperature-dissolved oxygen squeeze. The fish must avoid these areas, and by doing so squeeze into smaller areas where the habitat is more suitable.

Another key factor frequently mentioned when the problem was first noticed several years ago was lack of menhaden in the diet of rockfish. High in protein, bunkers are valuable fuel for stripers, especially for a population that is at its highest in decades. The forage keeps rockfish immune systems robust. When the food isn’t plentiful, they turn to other food, such as crab, that is not so nutritious.

Combined, these and other factors lead some researchers to think that perhaps the infections simply reflect a stressed population that has outgrown the Bay’s current carrying capacity.

Scientists say its possible that the disease could run its course and then disappear. The flip side, of course, is that the whole striped bass population could bottom out, which would be bitter irony in that the rockfish recovery, like the return of eagles, is testament to our ability to help restore critical species.

In recent years, record spawns gave us even more reason to be optimistic for continued stability. Research to find answers takes time and money and gets us back to two basic questions: How important is a healthy Bay to us, and how much are we willing to spend to aid its recovery? There isn’t much time left to decide.

Fish Are Biting
The doom and gloom of our fisheries didn’t deter a couple of bank fisherman from dunking freshly caught grass shrimp in Black Walnut Creek in hopes of landing a few plump white perch. The Susquehanna flats season, which runs through April, ranges from dynamite to poor, depending on wind and water clarity. Capt. Richie Gaines of the Chesapeake Guides Association, said most of the fish caught are under eight pounds. They might be winter holdovers that have left their wintering holes to feed on shad and herring.

Copyright 2002
Bay Weekly