Field Methods
At each station the net is trawled along the bottom for 20 minutes, at an average speed of 3 knots.
The Multispecies fisheries research trawl surveys use Netmind sensors to assure the net if fishing properly.
At each sampling location atmospheric data are recorded along with water quality parameters at 2-meter intervals from suface to bottom (these include, but are not limited to):
- Station identification parameters - date, station number, stratum
- Tow parameters - beginning and ending tow location, vessel speed and direction, engine RPMs, duration of tow, water depth, tidal stage.
- Atmospheric conditions - wind speed & direction, air temperature, relative humidity, barometric pressure, and sea state
- Hydrographic conditions - water temperature, water depth, salinity, dissolved oxygen
- Invertebrate species - crabs, shrimps, hydroids, dead mans fingers, sponges, etc.
- Habitat - ghost crap pots, tires, wood, rocks, etc.
After the completion of each tow, the catch is sorted by species and modal size groups. The catch at each station is sorted by species and size class. Aggregate weights, counts and individual length measurements are recorded from all species collected. For subsampling, we have determined that 3 individuals, for very common species, and 5 individuals all others per species-size group per tow is suffient for full processing. The data recorded from each of these subsampled specimens include length (mm), weight (kg), sex (macroscopic), maturiy stage (macroscopic). In addition, eviscerated weights for calculation of condition indices are recorded for select species. Stomachs are removed, and those containing prey will be preserved onboard for subsequent examination at the shore-based laboratory. Otoliths or other appropriate ageing structures (e.g.) opercles,vertebrae, etc) will be removed fom each subsampled specimen for age determination. For the remainder of the sample, aggregate weights and individual lengths are recorded for each species-size class. All data are recorded electronically using an integrated database and Scantrol fish measuring boards.
Stomachs and otoliths (or other appropriate aging structure) are removed and taken back to our laboratories at VIMS for further analysis.