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Fish abundance data from MOC-10 trawls.
Field work was done on four cruises conducted during the austral fall and winter. Cruises 1 (2001) and 3 (2002) were aboard the Antarctic Research Support Vessel (A.R.S.V.) Laurence M. Gould from April to June; cruises 2 (2001) and 4 (2002) were aboard the Research Vessel Ice Breaker (R.V.I.B.) Nathaniel B. Palmer from July to September.
Samples were collected with a 10m2 MOCNESS (MOC-10) outfitted with six 3mm mesh nets. The initial net fished obliquely to depth with each subsequent net fishing a discrete depth layer upward to the surface. At stations with depths>1000 m, layers sampled were 0-1000, 1000-500, 500-200, 200-100, 100-50, and 50-0 m. At stations with depths >500 m, layers sampled were 0-500, 500-300, 300-200, 200-100, 100-50, and 50-0 m. At stations with depths <500 m, sample layers were modified to provide optimal coverage of the water column with the five discrete-depth nets.
A total of 62 MOC-10 trawls were done, 22 each in the fall of 2001 and 2002, and 9 each in the winter of 2001 and 2002 (Table 1). Trawls were conducted at various times throughout the day. In the fall, 37 trawls occurred at night (18:00-06:00 h), 1 in daylight, and 6 at dusk. In the winter, seven trawls occurred at night, seven in daylight, and four at twilight. Towing speed for all tows was 1.5-2.2 knots. Tows in pack ice were conducted in leads created by the ship's wake with the A-frame in to minimize the chance of hooking the wire on ice floes. When ice conditions dictated, the ship first traversed a trawling transect prior to deployment and then backtracked over the same course through the created lead to insure that adequate speed could be maintained for the duration of the tow.
Fig. 1. Trawling sites for (A) fall and (B) winter SO GLOBEC cruises; blue circles: 2001 and red circles: 2002.
All samples were preserved in a 5-10% buffered formaldehyde solution, shipped to the laboratory for analysis, and then stored in 50% isopropanol. Fish were sorted from each sample, identified to lowest possible taxon, enumerated, measured (mm; standard length (SL)), and weighed (mg; wet mass (WM)). WM of formalin preserved specimens has been found to not differ significantly from fresh specimen WM (Lancraft, Donnelly and Torres, unpublished data). For many catches, selected specimens were removed from the sample prior to preservation and stored frozen. These specimens were identified to species and measured prior to freezing and their WM determined from regressions generated from numerous previous datasets (Donnelly and Torres, unpublished data).
Species' abundance and biomass are expressed as normalized values (#, gWM104 m3 water volume filtered). Discrete-depth values were calculated for each species by dividing their number or WM in the catch by the water volume filtered for a particular depth stratum.
Donnelly, J. and J.J. Torres, Pelagic fishes in the Marguerite Bay region of the West Antarctic Peninsula continental shelf. Deep-Sea Research II, 2008. 55: p. 523-539.
The Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) is based on the Tucker Trawl principle (Tucker, 1951). The MOCNESS-10 (with 10 m^2 nets) carries 6 nets of 3.0-mm circular mesh which are opened and closed sequentially by commands through conducting cable from the surface (Wiebe et al., 1976). In this system, "the underwater unit sends a data frame, comprising temperature, depth, conductivity, net-frame angle, flow count, time, number of open net, and net opening/closing, to the deck unit in a compressed hexadecimal format every 2 seconds and from the deck unit to a microcomputer every 4 seconds" (Wiebe et al., 1985).
Cruise identifier, e.g. en9402 R/V Endeavor cruise 9402
Year, e.g. 1995.
Consecutive station number
MOCNESS_10 tow number
Net number or identification
Observation or sample depth
Depth at which the net is opened (specific to MOCNESS tows)
Depth at which the net is closed (specific to MOCNESS tows)
volume of water filtered by the net
Family. One of the levels in the taxonomic system of classification; typically ends in 'ae'.
A binomial that consists of a genus name followed by the species name of an organism.
Number of individuals counted in sample or sample fraction
Number of the specific taxa/group counted per meter3
Wet weight of a specific taxa/group identified, in units milligrams per meter3
Wet weight of a specific taxa/group identified
GMT day and decimal time, as 326.5 for the 326th day, or November 22 at 1200 hours (noon), for start of tow. Decimal portion of yrday is from time_start.
month of year, GMT time , i.e. 01-12 at start of tow
day, GMT time, e.g. 22, at start of tow.
starting time of observation, GMT time, 24 hour clock, GMT time
latitude- north is positive, negative denotes South
longitude - east is positive, negative denotes West
Biological and Chemical Oceanography Data Management Office.
Funded by the U.S. National Science Foundation