Mike Marsh — Unsucessful striper stockings are puzzling biologists
By Rudy Coggins
Published in Sports on November 28, 2008 1:46 PM
Stocking is a traditional response to declining fish. In bygone days, fish were stocked helter-skelter with no forethought of chances for success.
Sometimes, stocked fish supplanted native fish populations ... examples being snakehead and common carp.
As a consequence, today's biologists study aquatic ecosystems carefully before stocking fish. They also monitor their stockings for results. Poor results in the aftermath of a carefully conceived striper-stocking program in the Neuse River have biologists puzzled.
"We stocked stripers into the Neuse River to help recover the spawning stock," said Bob Barwick, the N.C. Wildlife Commission's District 2 fisheries biologist. "We stocked 146,340 Phase I fish in the river in 2006 and 173,382 in 2007. In the winter of 2006-07, 100,000 Phase II fish were stocked."
Phase I stripers are tiny juveniles, while Phase II stripers are six to eight inches long. The larger fish, in theory, are better able to migrate downstream to saltwater then return upstream to spawn. With the removal of Quaker Neck Dam a few years ago, striped bass are accessing more spawning habitat as far as Raleigh's Milburnie Dam.
"We know these fish are attempting to spawn," said Barwick. "Eggs and larvae produced have been encountered in an NCSU study. But spawning effort is very diffuse, occurring near Goldsboro and between Goldsboro and Raleigh.
"Effort depends on stream flow, with higher flows creating better spawning conditions. But we see no concentrated spawning in the Neuse like we see in the Roanoke River."
Biologists sampled the Neuse in 2006 using a 100-foot seine. They caught no stripers. In 2007, the introduction of an electric current into along with the seine netted five juvenile stripers.
"We measured and weighed them," said Barwick. "We didn't return them because we were looking for OTC-marked fish."
All Phase II and most Phase I fish were marked by exposure to oxytetracycline, an antibiotic, shortly after hatching. OTC is deposited in the otoliths or "ear bones" giving a greenish glow under epifluorescent light. Some Phase II fish were also marked with yellow tags.
"Of five fish collected, three were stocked by our Watha Hatchery into the Neuse River System," said Barwick. "The others were wild fish, probably from the Roanoke-Albemarle System, but we don't know that for sure."
Barwick conceded collection results are extremely low compared to stocking numbers. It was also disappointing that stockings are responsible for most juvenile stripers in the river, not natural reproduction. As a result, the WRC tightened fishing regulations earlier this year.
"If very few fish are surviving to maturity, it's important to reduce mortality," said Barwick. "Reducing harvest allows more fish to reach maturity."
Barwick said Neuse River stripers suffer 50 percent mortality from fishing, disease, predation and other causes. Biologists age them by examining scale growth rings. Most Neuse River stripers are 3 and 4 years old, with extremely low numbers of older fish. Lack of older fish is the biggest concern because they produce more eggs and their offspring have higher survival rates than younger fish. Female stripers spawn beginning at age 6 and 24 inches long.
The striper season is now closed to harvest in summer months on the Neuse. The creel limit has been reduced from three to two fish per person in conjunction with an expansion in the area with a protected slot limit of 22-27 inches from inland waters. (For specific regulations, anglers should consult the WRC's regulations digest.)
"Coastal systems are highly variable, making survival difficult," said Barwick. "Harvest also works against striped bass. South of Roanoke Island, 67 percent of mortality comes from commercial discards, striped bass caught as bycatch in the commercial fishery and thrown back dead. DMF is making regulations changes to decrease bycatch mortality."
Environmental factors affecting Neuse River stripers include water flows and water quality. The WRC is working out flow agreements for Falls Lake with the U.S. Army Corps of Engineers that will ensure flows to help stripers spawn. But the water quality picture is much murkier.
"Water quality needs to be studied," said Barwick. "We don't know what role sedimentation has on egg and larvae survival."
Until these issues are resolved, the fate of the stocking program is on the table. Stocked fish may be diluting any spawning effort by any wild fish in the river.
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