Abstract
Flow manipulation offers a promising yet under-utilized method for enhancing bycatch escape in demersal trawl fisheries by exploiting fish swimming behaviors, such as flow refuging. We investigated to what extent different Gadoids use a low-flow zone to escape from a trawl. A 360° radial escape opportunity was created by placing a gap in the codend within the low-flow zone generated by a tarpaulin funnel. An additional tarpaulin deflector expanded the low-flow zone to prevent fish from holding around the funnel. This proof-of-concept design was developed using flume tank trials and computational fluid dynamics, and tested at sea. Substantial escape rates were observed for cod ( Gadus morhua), haddock ( Melanogrammus aeglefinus), and whiting ( Merlangius merlangus). Cod showed an increased escape rate with length, while no such trend was seen in haddock or whiting. We tested two gap sizes and found that a shorter gap size resulted in higher escape rates for undersized haddock and whiting, while cod escape was unaffected by gap size. These findings suggest species-specific interactions between hydrodynamics and behavior, useful for bycatch reduction in trawl fisheries.