By Bina Venkataraman, Globe Correspondent

Fishing gear that is being used increasingly in New England waters to catch schooling fish such as mackerel and Atlantic herring came under fire recently after fishermen spotted an expanse of floating dead striped bass east of Chatham. The striped bass stretched for three miles, according to a fisherman who saw it, though video footage showed that the dead fish were scattered sporadically.

UPDATE: The reason for the dead fish is not clear. A group of striped bass fishermen are arguing that a type of fishing gear, the mid-water trawler, may be responsible. Used by commercial fishermen, mid-water trawlers are cone-shaped nets dragged behind either one or two boats at a certain depth, aimed at targeting fish that school, as opposed to bottom-trawlers that drag their nets along the sea floor to capture scallops or groundfish. However, the Sustainable Fisheries Coalition, which represents nearly all of the mid-water trawling vessels from Maine to New Jersey, said that none of their boats were near where the dead fish were spotted on October 5. It is therefore unlikely that mid-water trawlers were responsible for the appearance of the dead striped bass.

Striped bass stocks in New England have rebounded since the early 1980s and are not overfished or being overfished, say several fisheries scientists. (Fish stocks may be depleted without active overfishing going on, or vice versa, but neither is occurring for this species.) UPDATE: Nevertheless, several fishermen's associations have come out in opposition to the mid-water trawlers in recent years because of their suspected impact on river herring, an anadromous fish that is distinct from Atlantic or ocean herring and includes alewives and bluebacks. Striped bass, tuna, cod, and many other commercial fish species feed on river herring, which turn up as bycatch in mid-water trawlers.

Scientists are uncertain what the impact of the mid-water trawlers is on the river herring, as dams, pollution, and the rebound of striped bass are also suspected in their decline in particular areas. The lack of data on mid-water trawlers’ impact on these and other fish populations has frustrated conservation groups that believe the commercial gear is at least partly responsible for the decline of various Atlantic fisheries. They have called for more on-board observation of the trawlers’ bycatch.

UPDATE: The dead striped bass found about 20 miles east of Chatham were likely migrating; this is the time of year when young striped bass move to warmer waters near Virginia and North Carolina for the winter. Striped bass cannot be landed from federal waters, so if any kind of trawler, including a bottom trawler, caught them, they would have had to release them back into the ocean before returning to shore. A delay in separating the stripers from the catch could have led to their death.