From: http://www.nefsc.noaa.gov/esb/why_nefsc_surveys.htm#neo7
Why:
- Monitor recruitdment: they use nets that catch very small fish, allowing them to predict the number of young fish, which is used to give predictions of upcomming seasons.
- Monitor abundance and survival of harvestable sizes: information from fish in year x can be compared with information in year x-1 to see how the population has changed; the results will indicate mortality rates. (? If mortality rates are drastically different than expected, does this indicate a high level of illegal fishing?)
The estimate population by using the equation: (number caught in sample) / (area of sample) then * (total area of stock)
- Monitor geographic distribution of species: shows how stock distribution moves.
- Monitor ecosystem change: each bottom trawl survey yields data for up to 200 species. Can see how fishing a few species impacts the other species
- Monitor biological rates of stocks: data shows growth rate, sexual maturity rates, feeding rates. Changes in these values predict changes in stock size.
- Collect environmental data/Support other research: surveys are conducted 24 hrs/day while at sea. Crews can monitor pollution, temperature, etc
Types of Surveys:
- Spring/fall bottom trawl: survey from 5 to 200 fathoms from Cape Hatteras (N Carolina) to "well beyond" Canadian border. 300 half hour trawls selected through a stratified random sample. Only two boats have been used.
- 1/2 inch net used to capture recruits.
- All species in each tow are counted and weighed, and all or a subsample are measured for length
- Some hard parts (scales, ear stones, fin rays) are taken from a smaller sample (these parts determine the age)
- Age of whole stock is estimated from this sub-sample
- Checked for gender and sexual maturity
- Stomach contents identified, disease inducing agents recorded
- All the data is available to scientists, which means that there should be a way for us to get it.
- Sea Scallop survey: continental shelf from Cape Hatteras through Georges Bank and Gulf of Maine
- Stratified Random Sample
- 8ft wide commercial scallop dredge with 2 inch ring abg and 1.5 inch mesh liner.
- 15 minute tow
- 15 to 60 fathoms
- Large amount of bycatch; it is used to collect info on the bycatch species (similar to spring/fall trawl I suppose...the article doesn't say much though)
- Hydraulic Clam Dredge: survey for surfclams and ocean quahog. Surveyed ever three years.
More to come.