An important aspect of the VIMS NEAMAP survey is that it provides "fishery-independent" data. Unlike "fisheries-dependent" datainformation from fishermen and dealers regarding catch, landings, and effortfisheries-independent data are designed to be free from vagaries introduced by changes in factors such as fuel costs, fishing gear, market price, and consumer demand. They are thus much more suitable for assessing the true population characteristics of a particular species.
"Fisheries-dependent data give managers and scientists a picture of the fishery," says Bonzek, "while fisheries-independent data, over the long term, provide information on the stock status of a species."
The NEAMAP team ensures the validity of their data by sampling in a consistent manner from cruise-to-cruise and year-to-year. Whereas commercial fishermen will readily change to a more efficient net and move to where the fish are in an attempt to optimize their target catch, NEAMAP teams always use a standardized trawl net and sample randomly within their study area.
"We select our tows using a stratified random design," says Gartland. "That means we break the survey up into different regions and use a computer to randomly select tows within each. That ensures that we have good spatial coverage and statistical validity."
The team's neta 3-bridle, 4-seam bottom trawlwas specifically designed for survey work by an advisory panel that included commercial fishermen, trawl-gear manufacturers, academic scientists, and federal researchers at the Northeast Fisheries Science Center (NEFSC).
During each tow, the scientists and crew use electronic sensors to ensure that the net's "wingspread," "door-spread," and "headrope height" remain within accepted values. "When you're working with a survey net you want consistency so that your data are comparable across tows and surveys," says Gartland. "That way, you can tell if
|Contact: David Malmquist|
Virginia Institute of Marine Science