VIMS team studies bay fish diet

[Sea Gristle]

VIMS team can stomach innards of bay fish
Study of diet is raising as many questions as it is providing answers
BY MATT SABO
DAILY PRESS

Apr 18, 2005


GLOUCESTER - Jim Gartland dons latex gloves, grabs a pair of scissors and starts cutting what appears to be a tan, viscous fishwrap with a tail sticking out of it.

He peels away the sticky layers of wrapping to reveal one 10-inch-long menhaden and the meat-and-bone remnants of another "very well-digested menhaden," Gartland said.

The covering wasn't fishwrap, however. It was actually the stomach from a 32-inch, 15-pound striped bass out of the Chesapeake Bay. Gartland was cutting it open as part of a Virginia Institute of Marine Science survey in its fourth year to study the fish-eat-fish world of the bay.

The study, overseen by VIMS professor Chris Bonzek, is compiling the largest database on the diet of fish in the Chesapeake Bay. The idea is to try and determine the health of fish species - for both prey and predators - based on what's in the stomachs of predators.

Every year of the program, about 4,000 to 5,000 fish have their stomachs sliced open to see what was for breakfast, lunch or dinner. That's a lot of seafood, but Gartland isn't tempted to throw a study subject on the barbecue.

"I'm allergic to fish," he said. "There's no conflict of interests."

Previous studies of fish diets were localized, such as a study of stomachs from 500 to 1,000 fish caught in 3-pound nets in the York River, Bonzek said.

Nothing of this kind has been undertaken on such a broad scale, where fish caught year-round from Baltimore to the Capes are examined. The study is raising just as many questions as it is providing answers.

A case in point is an early assumption that 50 percent of the stomach contents by weight of striped bass would be menhaden, said Rob Latour, an assistant professor at VIMS. But data compiled during the study show only about 5 percent to 10 percent of the stomach contents by weight of striped bass are menhaden, he said.

"That's startling," Latour said.

Why such a difference? Latour cannot answer that right now. He does not know if it means there are fewer menhaden or if striped bass are changing their diets.

The study has also found that older striped bass are not eating the amount of fish, such as menhaden, that was anticipated. Instead, fish older than five or six years are eating such invertebrates as sand shrimp.

"Is it random: 'I eat [what's] in front of me?'" he said. "If they're seeking it out, why? Is it high energy? Is it easier to catch?"

Another startling finding has been what is in the stomachs of striped bass caught trolling for food in seagrass, said Deb Parthree, a marine scientist who helps compile data on the project.

In deep water, only 1 percent of the weight of stomach contents of striped bass consists of blue crabs, Parthree said. But in shallower water where seagrass is growing, 80 percent of the stomach contents of striped bass consists of juvenile blue crabs.

Which leads Latour to another question: "Is this interaction for the blue crab a negative impact?"

Perhaps the answers lie in the unopened stacks of 5-gallon buckets in a VIMS office where Gartland and others perform their work. Inside the buckets are fish. Lots of fish.

Said Bonzek, "You need to look at a lot of stomachs of fish to see what's there."

[jwica]

Does Professor Bonzek or VIMS have a website where anglers can post what their rockfish had in their stomachs?

They could pile up alot of info quickly and get info from the entire Bay.

[Digger]

It is to bad the study was not conducted 15-20 years ago since the diet has probably changed. They need to consult some older log books. Otherwise they will only get a snapshot of today.

[Capt Frank]

SG I think that is a good study, however, they seem to have lost funding for the myco research. This is perhaps the most important issue facing stripers in the Bay area. Eris Burgee(Sea Monkey) who is now doing post Doctoral work in SC had indicated that funding had slowed, not good.

[Sea Gristle]

Out of curiousity I made it a point to check what was in the stomaches of the rock I kept last year. Most were small crabs and mantis shrimp and I think only one had a couple of peanuts.

[Tom Powers]

I think that they are seeking some recreational license money for the DNA work on Myco. From what I can tell the work will get the support of the RFAB.

Tom

[rbr]

OK, the study points to diversity of diet re location etc.
But does it also look at historical change due to availability
of food source as it relates to the big picture. Rock like all preditors are oportunistic feeders that will take advantage of
prey available in their migratory range. So as fish move along
Bay and river channels toward inshore haunts what effect
does the abundance or lack of abundance of prey species
(menhaden) have on the overal health of the population?


Bert

[Sea Gristle]

Lack of abundance means fish have to work harder, expend more energy to get the same amount of protien in their diet. If there next best source of food after menhaden is crabs, there aren't an abundance of them either(depending on who you talk to). The former surge in rockfish is one argument for the lack of abundance of menhaden in the Bay.

[stanleybros]

Sea, your second sentence began with an"if". And , you know what an "if" means.

[Sea Gristle]

Yep. Sheer conjecture. If I was a scientist, I'd get to call it a "hypothesis"[wink]