SEA 



SCIENCE 



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JLhere is no shortage of opinions 

 in North Carolina about the environmental 

 impacts of inshore trawling. 



Some say trawling is good for 

 productivity of inshore waters, "cultivating" 

 the bottom sediments and stimulating 

 growth of the tiny creatures that live there. 

 Others say trawling is bad for these waters, 

 unsettling the communities and disrupting 

 their biomass (weight and volume) and 

 ability to reproduce. 



The actual effects of this traditional 

 fishing technique have not been studied in 

 North Carolina until now. 



As the N.C. Marine Fisheries 

 Commission (MFC) begins to examine the 

 effects of inshore shrimp and crab trawling, 

 a research team is launching a two-year 

 study to measure the impact of trawling on 

 sand and mud estuarine bottoms. The work 

 is funded by the MFC through the Fishery 

 Resource Grant Program, administered by 

 North Carolina Sea Grant. When complete, 

 the research will help the MFC better 

 manage inshore trawling. 



"Right now, the argument for or 

 against trawling can be made either way," 

 says Sea Grant researcher Martin Posey, a 

 benthic ecologist at the University of North 

 Carolina at Wilmington. "That's why the 

 study is so timely. The bottom line is that 

 we just don't know. There are so many 

 areas where assumptions have to be made 

 that we cannot make any conclusions about 

 positive, negative or neutral effects." 



At issue is the biological productivity 

 and composition of bottom organisms — or 

 benthos — in the estuaries. These areas are 

 prime habitat for soft-bottom organisms 

 that are important food for larger fish, 

 shrimp and crabs. 



Part of the study, which begins in 

 February, evaluates the short-term impacts 

 of moderate crab trawling on a previously 

 untrawled area in the Pamlico River region. 

 The research boat, owned and piloted by 

 Henry Daniels of Belhaven, will pull an 

 open trawl and sample the benthos in three 

 areas that are not usually trawled. It will 



also sample comparable untrawled zones 

 near each area. 



Daniels' research team includes Posey 

 and researcher Larry Cahoon, a biological 

 oceanographer at UNC-Wilmington, who 

 will analyze the results. The team will pull 

 the open trawl long enough to have a 

 moderately heavy impact on the bottom. 

 They will work at three locations in both 

 February and July of 1999 and 2000, 

 sampling before and after their trawls. Their 

 research targets three types of organisms: 

 benthic microalgae, which are important 

 plant producers, especially for small bottom- 

 dwelling animals; meiofauna, which are 

 prey for shrimp and small bottom-feeding 

 fishes; and macrobenthos, such as worms, 

 amphipods and clams, which are food for 

 larger fishes, shrimp and crabs. 



The second part of the study examines 

 the cumulative effects of trawling, again 

 pulling an open trawl. The researchers will 

 sample the benthos in two heavily trawled 

 areas of the Pamlico River and two that are 

 untrawled but not closed. The dates — in 

 February, May, July and November of 1999 

 and in February, May and June of 2000 — 

 will bracket the shrimp and crab trawling 

 seasons and offer good comparisons for 

 seasonal effects. 



"The two methods have different 

 strengths and can complement each 

 another," Posey says. 



The study focuses on crab trawling 

 because it has more impact on the benthos 

 than shrimp trawling, Daniels says. The 

 research team will avoid state-protected 

 grass beds and primary nursery areas, which 

 serve as crucial habitat for juveniles of many 

 marine species. It will instead focus on 

 nearby sand and mud bottoms, which lack 

 grasses. The mud bottoms are much quieter 

 than sand bottoms and usually are found in 

 deeper channels. Sand bottoms are more 

 comparable to grass beds and contain many 

 of the same organisms. 



To date, research on the effects of 

 trawling has been inconclusive, the 

 researchers say. Some studies indicate that 



trawling can impact the biomass and produc- 

 tivity of benthic organisms that support 

 fishery species. It may also change the 

 composition of benthic species, which can 

 be critical in the role of benthos as food for 

 shrimp, crabs and fish. 



One point of view is that trawling is 

 beneficial, cultivating the bottom and 

 stimulating growth of food organisms. If so, 

 the researchers expect to see relatively high 

 abundances of the sampled food organisms 

 or at least rapid recovery after trawling. 



On the other hand, if trawl impacts are 

 significantly negative, then appropriate 

 management strategies — managing catch, 

 trawling areas or seasons — would be worth 

 investigating for specific fisheries, the 

 researchers say. The study results will at 

 least provide some direction on this issue. 



Another possibility is that trawling has 

 no significant impact either way. 



Although the impacts of trawling have 

 been long discussed, few studies have 

 addressed the well-being of benthic organisms. 



For example, a trawl impact study in 

 South Carolina waters focused on bycatch 

 issues, not on the effects of trawling on the 

 food chain organisms that support fisheries. 

 Some critics have charged that trawling not 

 only damages the benthos, it also catches 

 untargeted species. A study of the Carteret 

 County shrimp fishery also addressed 

 bycatch issues. 



Studies in other regions are beginning 

 to look at such effects. Researchers found 

 impacts of scallop dredging on soft-bottom 

 communities in Maine coastal waters, and 

 another team found that sheltered, untrawled 

 muddy bottoms in a Scottish sea loch were 

 susceptible to damage by bottom dragging. 

 However, it is not clear how relevant these 

 studies would be to North Carolina's waters. 



The MFC has asked the Division of 

 Marine Fisheries to prepare reports on the 

 known impacts of trawling inshore waters, 

 says Nancy Fish, division spokesperson. 

 From these, the commission will identify 

 the research needed to fill in the gaps in 

 data. □ 



COASTWATCH 33 



