November 25, 2016 — Scientific surveys of fish are often done by trawling. This means towing a net and then hauling it up to count the catch. Estimates are then made about how many of each species are in a square mile. They are generally done in the same area for the same amount of time on a periodic basis.
The Rhode Island Department of Environmental Management does trawl surveys in Narragansett Bay, the National Oceanographic & Atmospheric Administration and a regional fisheries commission do trawl surveys too. Fish managers and scientists simply do not have the resources to do a proper job with survey trawls in our coastal waters, never mind areas outside our territorial waters (200 miles). Large tracts of the ocean are not monitored so we have no idea what fish are in the water globally, never mind how many are being taken out.
But a reliable and inexpensive way to monitor fish populations is being developed by scientists. Philip Thomsen and his team from the Natural History Museum of Denmark, are developing a a far less costly way to count fish.
The team is examining fragments of floating DNA which fish slough off in slime and scales, or excrete into the water.
A Nov. 19 Economist blog post said scientists “Hope they are able to link the quantity of this ‘environmental’ DNA to those species’ abundances, as measured by a trawl survey that took place at the same time… Given the fragmentary nature of environmental DNA, they found it easier to recognize families than species (a family, in this context, is the taxonomic level above a genus; herring, sardines and shad, for example, all belong to the family Clupeidae). The trawls picked up fish from 28 families. The team found DNA from members of 26 of these in their samples, and also detected three families that had no representatives entangled in trawl nets.”