NCDMF studying how shrimp trawl bycatch may be affecting decline of gray trout, croaker

Report being prepared for August meeting

North Carolina once had enough gray trout and croaker to support robust recreational and commercial harvests, but over the past decade, those populations have slipped.

The N.C. Division of Marine Fisheries’ most-recent stock status report bears that out, labeling croaker as a species of “concern”, while gray trout, aka weakfish, are “depleted.”

Now, the agency is investigating what role shrimp trawling might have played in the declines of the two species.

Results from two studies by Kevin Brown, a fisheries biologist with NCDMF, point to “bycatch” as a potentially large factor. An independent analysis by an East Carolina scientist says the studies point to staggering numbers of both species killed as “bycatch” by shrimp trawlers.

Dr. Louis Daniel III, executive director of NCDMF, said he isn’t sure if bycatch — usually infantile finfish caught in trawls — is the major culprit, but he has his staff doing more research to make a presentation to the N.C. Marine Fisheries Commission at its Aug. 22-24 meeting in Raleigh, and he said NCDMF has already reduced bycatch significantly by reducing the amount of trawling and areas where it its legal.

Brown’s studies were obtained from shrimp-trawl harvests, and the bycatch was massive. His first study was conducted from July 1, 2007, to June, 30, 2008 and the second was conducted in 2010 and lasted six months.

Dr. Everett Pesci of Greenville, a microbiologist who works for the East Carolina University School of Medicine, crunched numbers from Brown’s 2009 report that his first survey generated. He said the 2007-08 study from the Pamlico Sound, Carteret and Brunswick counties showed that for every pound of shrimp caught by trawlers, bycatch included about one-fifth of a pound of juvenile grey trout, fish weighing slightly less than an ounce and measuring around 3.2 inches long each.

Pesci said that if you compare those numbers with the whole of the 2011 shrimp harvest in North Carolina — the most-recent numbers available — then shrimp trawlers had a bycatch of more than 950,000 pounds of gray trout, or about 20 million juvenile fish.

Brown’s survey estimated that shrimp trawlers in 2009 accounted for 137 million croakers, 58.9 million spot and 25.6 million gray trout as bycatch. The total weight of 951,719 pounds that Pesci arrived at for the weight of the gray trout bycatch in 2011 is, according to his analysis, 8.8 percent of the stock by weight.

“That stock is for the whole east coast — not just North Carolina,” he said.

Daniel said no other states have done studies on juvenile weakfish, so NCDMF has no baseline with which to compare its bycatch figures. Some studies in mid-Atlantic states have suggested that depressed numbers have been caused by predation by striped bass and dogfish sharks. He said some national peer-review panels want shrimp-trawl bycatch numbers, and some don’t.

“What I have directed staff to do is to do a presentation (for the Marine Fisheries Commission, updating the Shrimp Fishery Management Plan),” Daniel said. “It’ll be a full-blown presentation, with all the new bycatch information and landings dates and reductions and (fishing) effort. “If the Commission, at the August meeting, says, ‘What can we do to address bycatch issues?’ We will back up and punt, and that will require full-blown Shrimp (FMP) Amendment. Then we’ll contact a new (Shrimp) Advisory panel.”