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