Thursday, September 29, 2011

Scientist Tracks Bay's Second Ugliest Fish

Researcher Uses Satellites to Track Cownose Ray
Cownose rays are native to the Chesapeake Bay. They arrive late spring when the waters start warming and leave again in the early fall as waters cool. Where they go during the rest of the year? No one knows!

That’s why Virginia Sea Grant Fisheries and Seafood Technology Specialist Bob Fisher is satellite tagging some rays. The satellite tags will gather data about water quality and depth for 90 days. On December 12, 2011, the tags will disconnect from the ray and float to the water’s surface. There, they’ll send the data gathered as well as information on their current position to a satellite which will pass the data back to Fisher at Virginia Institute of Marine Science.

Although six rays were tagged, it’s uncertain how much data Fisher will get back. Last year, during a similar study, only one of the tags transmitted data after the 90 day period. Fisher suspects that the other tags probably got eaten, along with the rays, by predatory sharks.
Cownose Rays mark the end of the best spring fishing locally.  While there's a chance of catching a big striper after the rays have shown up, it's unlikely, as most of them have migrated back to the ocean.  But catching a big ray on light tackle is amusing in it's own way.  They fight like a freight train, often not even getting off the bottom until pulled at unmercifully and then starting to move slowly and steadily away, picking up speed as they go.  My goal, once I'm sure the fish is a ray, is merely to get as much of my tackle and line back as possible.  Once in a while I succeed.

They do have a powerful "stinger" near the base of their tail, a rather nasty barbed knife like looking thing, equipped with a venom strong enough to make you unpleasantly sick.  In the Bay, few people get hurt by them, as you have to either stand on one while wading (and probably pin it down, which might be tough), or mishandle it on a boat.  I know of at least one scientist who has been stung that way.  I wouldn't jump on one's back like Steve Irwin did, though.

Their quality as a food fish is questionable.  I kept one once, a long time ago, and was not overwhelmed with the quality of the flesh, and a little put off by the bits of red meat among the white.  I know other people swear by them. Trevor claims to like them, but he's never kept one while I've fished with him, but then Trevor likes everything but Oyster Toads (the #1 ugliest fish in the Bay).

Rays can do a number on shellfish and crabs with their crushing jaws, often moving in on planted oysters in packs and nearly wiping them out.  A current theory holds that ray numbers are up because the number of predatory sharks in the ocean is sharply down due to fishing; many sharks dine on their distant relatives (and their close relatives for that matter).  I don't know about that, but I wouldn't be opposed to seeing a commercial fishing for rays under the right regulations.  I'm sure there's an Asian culture somewhere that would prize them.

Another study from Virginia proposes that Cownose Rays help oysters to disperse:
A study published in April’s “Journal of Shellfish Research” indicates that cownose rays’ mouths aren’t strong enough to crush and eat larger oysters, but this physical limitation doesn’t stop rays from trying. The result? Cownose rays pick up and swim away with large oysters, but eventually drop them after failing to crack the shells open. This behavior could help disperse large, reproductively mature oysters throughout the Bay.

Bob Fisher, Virginia Sea Grant Extension Agent and lead author of the study, says industry and other shellfish growers have confirmed his findings. “I had given multiple talks to industry and oyster gardeners on what I was seeing,” Fisher says. “Some oyster growers started to look at their oysters that remained after the rays and come in and fed, and they say that what I found was true—that their larger oysters weren’t eaten, but were moved away from where they were originally planted.”

Cownose rays are native seasonal residents that migrate in groups into the Chesapeake Bay during summer months. Ever since 2003 when a group of rays was seen descending on an oyster bed and eating all but a few of the newly planted oysters, industry and oyster restoration groups alike have been trying to find ways to keep rays out. According to reports, in a couple of hours those rays ate more than 1 million seed oysters, which were about the size of a fingernail.
Considering that oysters have planktonic larvae that can settle many miles from where they are spawned, this may seem like a trivial help, but for oysters, it may be more important than it seems. Larval oysters need a hard substrate to set on, and the best hard substrate in the Bay is another oyster.  So by moving mature oysters off a concentration of oysters into soft or sandy bottom, the ray may actually help establish a new cluster of oysters.

No comments:

Post a Comment