Quantitative Video Analysis of Fish and Squid Behavior at the Mouth of a Drop-Chain Trawl

The effectiveness of a trawl configured with drop-chain groundgear to capture target species and release bycatch was evaluated with underwater video recordings in the Nantucket Sound squid fishery off Cape Cod, MA. Entrance into trawl or escape underneath the fishing line was quantified for targeted longfin inshore squid (Doryteuthis pealeii), and two bycatch species summer flounder (Paralichthys dentatus) and skates (family Rajidae). Fish and squid swimming behavior, position at the trawl mouth, orientation, time to entrance, and contact with groundgear were quantified and related to capture or escape. All observed squid entered the trawl; the majority entered in the upper trawl mouth, mantle orientated away, and did not actively attempt escape. Most (60.5%) summer flounder entered the trawl, and those that changed orientation and turned were significantly more likely to enter the trawl (p < 0.05). Conversely, most skates (89.7%) avoided trawl entrance. Both summer flounder and skates were observed to remain on or near the seabed, orientated and swimming in the same direction as the trawl. Some skates (35.4%) had substantial contact with the groundgear. Underwater video analysis showed that a drop-chain trawl is effective at retaining squid and avoiding skate capture, but ineffective at avoiding summer flounder capture.