Stocking program boosts state rockfish population

Outdoors

March 03, 1991|By PETER BAKER

The spring rockfish season proposal announced Friday b Department of Natural Resources undoubtedly is the hottest topic among saltwater anglers at the moment. But there is a side issue that should be recounted: Rockfish are back due, in considerable part, to the efforts of Ben Florence.

Florence runs the DNR's hatcheries program, which, over the past six years, has stocked 4,214,710 striped bass in tributaries of the Chesapeake Bay.

The oldest of those fish, the survivors of the 186,926 hatchery fish stocked in 1985, turned up in sizable number in the sportfishing season last fall and the commercial gill-net season that ended earlier this year.

The average size taken in the gill-net season was 24 inches and about 6 pounds, which compares closely with the average catch during the sport fishing season.

"The real nitty-gritty here is that 7 percent of the more than 5,000 fish that we checked out of the commercial catch were hatchery fish. . ." Florence said early last week. "But that also means the best is yet to come. We have more than 4 million of them out there, and we saw a 7 percent return [from the small stocking class of 1985]. We are having an impact out there."

On Friday, the DNR announced it supports a trophy striped-bass fishery from May 11 to May 27, with a 36-inch minimum size and a creel limit of one fish per fisherman throughout the season.

Although hatchery fish will not be large enough to be taken in that fishery, the hatchery program should supplement such a season for years to come.

Florence and his staff are able to determine whether a rockfish originated in a hatchery by reading a small, encoded magnetic wire tag that was inserted in the fish's cheek before release.

To assist in the monitoring of the program, another 40,000 fish have been marked with external tags. The external tags are easily found by fishermen, and 2,000 have been returned to the DNR from as far away as Canada.

"From these tag [returns], we are making the assumption that the hatchery fish are probably reacting in a very normal %o behavioral pattern. . ." Florence said. "They are schooling with wild fish and behaving the same way.

"What we have determined is that fish exhibit expected migratory behavior, we can determine migration rates from the bay and mortality rates can be determined also from the return [of tags]."

Further, Florence said, the tabs kept on hatchery fish allow biologists to determine the number of rockfish in a given river system and, perhaps, to validate the young of the year index, the sometimes controversial survey that the Atlantic States Marine Fisheries Commission uses to set catch quotas for commercial and recreational fishermen.

As examples, Florence pointed to the Choptank and Patuxent rivers, both of which have been stocked heavily with hatchery fish.

In the vicinity of the Patuxent, Florence said, there has been a 30 percent return from hatchery fish, which is a high figure, because few of the hatchery stock have grown to the minimum size of 18 inches.

"To try to get a handle on these hatchery fish and to give us some prudent management information, we stocked 100,000 fish the Patuxent River for two successive years," Florence said. "Then we went back and had an intensive recovery program. From that, we were able to measure the mortality rates of

hatchery fish vs. wild fish.

"Interestingly enough, the hatchery fish and wild fish do not exhibit different mortality rates."

According to studies of the early life history of striped bass, Florence said, calculations show a 2 percent mortality per day on these fish, both wild and hatchery, from mid-June until the end of September.

"Not only can we get an idea of how many are left over at the end of September," Florence said, "but, by using marked fish, we can recapture and get a pretty good estimate of the total number of fish in any given river system."

In the Choptank River, Florence said, a stocking of 100,000 hatchery fish in 1988 and subsequent investigations of ratios between wild and hatchery fish determined the total number of wild fish in the river to be 90,000.

"In 1989, we had a better year class. It was determined there were about 1.2 million one-year fish in the river," Florence said. "This gets interesting because, by using the same setups and plans, we can actually validate the young of the year index.

"We have the potential now to go into a river system like the Choptank and answer the Hambrooks Bar question forever, maybe."

(An unusually high reading at Hambrooks Bar in 1989 triggered the reopening of the striped-bass season last fall and remains an issue debated among conservationists who feel the figure should have been thrown out.)

In 1990-91, 356,000 rockfish were stocked in the Patuxent River, and 75 percent of the young fish in the Patuxent right now are of hatchery origin, Florence said.

"So we can have a pretty big impact on what is going on in the river," Florence said. "The question now is: How are these fish growing in the overall population?"

To find out, biologists are beginning to look at the adult stocks returning to the Chesapeake Bay and its tributaries and hatchery fish within those stocks.

"In 1990, we looked somewhat," Florence said, "and 11 percent of the fish we sampled in the Choptank River during spawning season were of hatchery origin. In the Patuxent River, a little over 40 percent of the sample was of hatchery origin.

"Now, these are still fairly young fish, but this year we will go back in and look at older fish," Florence said, "and we expect to see even better numbers in the Choptank and the Patuxent."

Perhaps Florence is right when he says the best is yet to come.

Striper stockings

Year Number stocked current size*

1985.. ..186,926.. .. 24-26

1986.. ..419,239.. .. 20-22

1987.. ..828,224.. .. 16-18

1988.. ..971,456.. .. 15-16

1989.. ..993,409.. .. 11-12

1990.. ..815,456.. .. 5-10

*-in inches

Source: Department of Natural Resources.

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