What’s a bottom trawl survey?
By Rachel Berman
The ocean is full of a nearly uncountable number of fish, crabs, sharks, and other sea life; the true number may never be truly known. As John Shepherd once said, “counting fish is like counting trees&emdash;except they are invisible and they keep moving.” To help meet this challenge, bottom trawl surveys provide a way for scientists to gather information about what lives in the ocean. As you may have noticed, the OceanAdapt website is built using data from bottom trawl surveys.
In a trawl survey, boats go out to areas that have been pre-selected in the ocean and gather a sample of the aquatic life. These surveys are an important investment because they offer society an unbiased survey of fish and other animals from an area (fishing boats, in contrast, specifically search out certain species).
Demersal trawl diagram
In the U.S., NOAA has some of its own boats to conduct trawl surveys (including some of the boats shown here). NOAA and other agencies sometimes contract with commercial fishing boats as well. Some of the first NOAA survey trawling vessels in the northeast U.S. were in use as early as 1948 (Albatross ΙΙΙ) and in 1950 (Delaware).
For more information about bottom trawl surveys, check out some of these sources:
- FAQ about NOAA trawl surveys in the Northeast U.S.
- NOAA Office of Ocean Exploration explains trawling
- Food and Agriculture Organization’s technical information on bottom trawling
- Atlantic States Marine Fisheries Commission explains its scientific surveys
- Doubleday, W., & Rivard, D. (1981). Bottom trawl surveys. Canadian Special Publication of Fisheries and Aquatic Sciences (Vol. 58)
- Hilborn, R, & Walters, C. (1992). Quantitative Fisheries Stock Assessment: Choice, Dynamics & Uncertainty.