Comparisons of Shrimp Catch and Bycatch between a Skimmer Trawl and an Otter Trawl in the North Carolina Inshore Shrimp Fishery

Abstract

The skimmer trawl, used in Louisiana exclusively for commercial shrimping, is a gear that is pushed through the water column. The gear consists of two nets, one mounted to each side of the vessel in a rigid frame. Commercial fishermen in North Carolina principally use the otter trawl to harvest shrimp. Each gear catches an unwanted (unmarketable) mix of finfish and shellfish species known as bycatch. The purpose of this study was to compare the skimmer trawl and otter trawl fisheries and the different methods used in each to determine if skimmer trawls can be used in North Carolina to reduce bycatch and improve bycatch survivability. Gear comparisons were conducted at night in inshore protected waters; a skimmer trawl vessel and a comparably sized otter trawl vessel fished in close proximity. For each type of gear, bycatch was quantified by species, and live well experiments were used to determine bycatch survivability. On average throughout the study, the skimmer trawl caught less bycatch (mean, 0.47 kg/min) than the otter trawl (mean, 0.66 kg/min), and had the lower bycatch rate (mean, 0.30 kg/min) and fish-to-shrimp ratio (mean, 1.38) during the peak of the fishing season for white shrimp Penaeus setiferus. The skimmer trawl proved very effective for catching white shrimp, which constituted 23.3% of the total skimmer trawl biomass, compared with 5.1% of the total otter trawl biomass. On the other hand, brown shrimp P. aztecus constituted only 6.1 % of the skimmer trawl biomass, compared with 16.8% of the otter trawl biomass. Of the 20 species tested in live wells, 12 finfish species and all 3 commercial shrimp species exhibited lower mortality when caught by skimmer trawls. Significant differences in length frequencies between the two gears were observed for five finfish species. Use of the skimmer trawl in the North Carolina shrimp fishery may increase white shrimp catch and reduce bycatch and mortality rates of most other species. Additional work is needed to determine skimmer trawl effectiveness in the fisheries for brown shrimp and pink shrimp P. duorarum; however, commercial fishermen have recently modified the gear for use during the brown shrimp season.