Premium
Comparison of the Catch from Tongue and Two‐Seam Shrimp Nets off South Carolina
Author(s) -
Stender B. W.,
Barans C. A.
Publication year - 1994
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/1548-8675(1994)014<0178:cotcft>2.3.co;2
Subject(s) - shrimp , biomass (ecology) , fishing , fishery , tongue , invertebrate , biology , towing , environmental science , zoology , ecology , marine engineering , linguistics , philosophy , engineering
Before the gears were used for catch comparisons, a two‐seam net and a tongue trawl were evaluated for changes in net dimensions with fishing depth and tow direction. When towed as it would be during catch comparisons, the two‐seam net had a width of 16.1 m and was estimated to extend 2.1 m vertically al the center of the headrope. The horizontal spread of the tongue trawl was 13.5 m and its vertical spread was 4.2 m at center. Small, statistically consistent differences in openings (<0.5 m) occurred with depth and direction. The major factor influencing changes in catch (kg/ha) with depth (10‐fold increase in shallow water) appeared to be the faunal distribution with depth, independent of towing characteristics. Differences in biomass (kg/tow, kg/ha), and in the biomass (kg/ha) ratios of taxa to shrimp between the two‐seam and tongue trawls were documented for eight major biological groups. Major differences in total catch by net occurred between years primarily because of changes in the catch of miscellaneous invertebrates and shrimp. Significant differences in the lengths of nine priority species occurred between the two gears. Mean lengths in the two nets differed by more than 1 cm for spot Leiostomus xanthurus (which was larger in the tongue net), Atlantic croaker Micropogonias undulatus (larger in the two‐seam net), and Spanish mackerel Scomberomorus maculatus (larger in the tongue net). Mean ratio of fish to shrimp biomass was 31: 1 overall (21:1 for the two‐seam net and 41:1 for the tongue trawl). Ratios of total biomass and the biomass of any taxonomic grouping to shrimp biomass did not differ statistically between the two gears. Biomass ratios were recalculated from published data by a standard methodology. Subsequent comparisons indicated increases in the ratios over time and highlighted a need to validate the technique of subsampling heterogenous trawl samples. Finfish by‐catch in both gears was dominated by sciaenids (44% by weight ofall fish). Red drum Sciaenops ocellatus , spotted seatrout Cynoscion nebulosus , snappers (Lutjanidae), and groupers (Epinephelinae) were not caught by either net. Catches of Spanish mackerel and king mackerel Scomberomorus cavalla were documented and warrant further investigation to evaluate the effects of by‐catch on local populations.