Virginia Institute of Marine Science
VIMS Marine Resource Report No. 2000-6
This report presents the preliminary results of the commercial survey of the Hudson Canyon Closed Area. The survey was conducted aboard the FN Alice Amanda from June 8-15, 2000. A systematic grid design was utilized with survey stations located approximately 5 nm apart (Figure 1). Survey stations were located both inside and outside the boundaries of the closed area. Additional stations were added along the western, northern and southern boundaries in an attempt to resolve the boundary effects on sea scallop abundance and size distribution. Survey tows were 10 minutes in duration at a speed of 4.5-5.0 kts. The sampling gear consisted of two standard 15 ft. New Bedford style sea scallop dredges with 8 inch twine tops, ring bags knit with 3.5"·(88.9 mm) rings, and no tickler or rock chains. An inclinometer was attached to the frame of the starboard dredge to measure dredge angle and bottom contact time. The results of the initial data analysis are shown in Figures 2-8. Catch data are shown in Figures 2-4 with scallop catches separated into two categories of shell height: less than 90 mm (Figure 2) and greater than or equal to 90 mm shell height (Figure 3). A total scallop catch at each station is shown in Figure 4. Differences in sea scallop abundance and size structure were examined with respect to samples taken inside or outside of the closed area (Figure 5), strata calculated by dividing the closed area into equal North and South portions along the 39° 01.566' latitude (Figure 6), and by depth regimes within the closed area (Figure 7). Catch data stratified by two factors: 1). North and South 2). inside and outside the closed area are shown in Table 1. The initial biomass estimate is shown in Table 2.
The following assumptions were used in calculating biomass:
1. Stratification of the closed area into two roughly equal portions.
2. Utilizing a systematic grid design, number of stations was proportional to area of strata.
3. Tows that fell on closed area boundary were included in the calculation.
4. All scallops harvested were included
5. The coefficients of the shell height-meat weight relationship a=-12.1628 b=3.2539.
6. A nominal tow length of 1 nm. Each tow covered 0.00494 nm2
7. A dredge efficiency of 40%
8. Harvest represents a removal of 25% of the standing stock
The next iterations of biomass estimates will follow accordingly:
1. The number of scallops from 80-100 mm will be corrected for the selectivity of the 3.5" ring dredge. This means that the total number of scallops at each 5 mm interval from 80-100 mm will increase. Consequently, their contribution will also increase the biomass estimate. We will still use the nominal tow length of l nm and a 40% dredge efficiency.
2. The biomass estimate in l will be calculated to account for growth and natural mortality (0.1) to project the standing stock in 2001.
3. The biomass estimate in l and 2 will be calculated to account for actual tow length and changes in dredge efficiency based on the 1999 depletion experiments in the Hudson Canyon Closed Area on 100+ mm scallops
Scallops, Fisheries, Monitoring, Virginia
Sea Scallop Plan Development Team New England Fishery Management Council New Bedford, Massachusetts July 24-25, 2000
DuPaul, W. D., Rudders, D., & Rago, P. J. (2000) Preliminary Results of Commercial Sea Scallop Survey in the Hudson Canyon South Closed Area June 2000. VIMS Marine Resource Report No. 2000-6. Virginia Institute of Marine Science, College of William and Mary. https://doi.org/10.21220/V5Q17W