Juvenile rockfish thrive in Chesapeake nursery

On The Outdoors

September 27, 1998|By Peter Baker | Peter Baker,SUN STAFF

Each fall, the Department of Natural Resources releases the results of its juvenile fin fish survey, which measures the reproductive success of many species that use the Chesapeake estuary as a nursery ground.

The focal point of the survey is rockfish and its young-of-the-year index, which has been recorded annually since 1954. This year the rockfish YOY index is 12.7, two points above the 45-year average of 10.7.

This marks the seventh consecutive year the index has been at or above the level indicating healthy reproduction and well exceeds the standards set by the Atlantic States Marine Fisheries Commission.

The survey is carried out at 22 stations in the four major rockfish spawning systems: the Choptank, Potomac and Nanticoke rivers and at the head of the bay.

From July through September, fisheries biologists take samples from each site, completing two hauls of a 100-foot beach seine at each location each month. Each catch is cataloged and counted by species, resulting in the young of the year average.

In this year's survey there were some surprises -- both encouraging and discouraging.

For rockfish, the Choptank (24.4) and Potomac (10.8) rivers had good reproduction, but the head of the bay (8.3) and the Nanticoke River (1.1) were below the long-term average.

Atlantic croaker (hardhead) numbers were the highest recorded by the survey since the mid-1970s at 5.9. This is the second successive year of strong recruitment for croaker.

American shad numbers were the highest recorded since 1960 at 4.2, up from 0.84 last year.

"This survey was developed specifically for striped bass [rockfish], and while it does work well for white perch, too, it is not so good for shad and herring, for example," said Harley Speir, chief of DNR's biological monitoring and analysis program. "Remember, we are working the shore zone with a 100-foot seine, so the survey can discriminate for other species."

Young of the year striped bass and white perch share the same shallow, inshore habitat, while shad and herring are more often found in deeper water.

Speir said, however, that a relationship between the increased shad numbers found in the survey in the past couple years has been found to coincide loosely with increased numbers of shad in certain areas.

"We have seen nice increases in shad at the head of the bay," he said, "and we are pretty sure we are getting good reproduction there. There is an increase, but the magnitude of the number of young in the sample may not be well related to overall indexes."

The survey catalogs and indexes 16 species, from silver-sides to rockfish, as well as incidental catches as bizarre as lizard fish. But some sample sizes are too small or too fragmented to draw simple conclusions from.

"In some cases -- bluefish come to mind -- we sample areas where we don't expect to find young bluefish, way up at the head of the bay, for example, or off the Tuckahoe," Speir said. "But by eliminating some habitats you can play with the numbers and get a better read."

Over the next several weeks, fisheries personnel will complete calculations for the rest of the species, but for the moment the good news is about shad, croaker and, especially, rockfish.

While this year's index is well below the post-moratorium banner years of 1993 (39.9) and 1996 (59.4), the future of striped bass appears extremely bright into the next millennium.

According to DNR's Fisheries Service, the last great fishery for rockfish was in the late 1960s and into the mid-1970s, a period in which the average juvenile index was 13.78.

The average juvenile index over the past seven years is 22.02, including the two largest year classes ever recorded in Chesapeake Bay.

Pub Date: 9/27/98

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