Spatial and Temporal Characteristics of Bycatch in Northern Shrimp Fisheries in the Gulf of Maine

The northern shrimp (Pandalus borealis) is an important commercial species for the Gulf of Maine inshore fleet with landings exceeding 5,500 mt ($13.4 million USD) in 2010.  During the past twenty years, efforts have been made to reduce finfish bycatch in this small mesh fishery.  In order to assess and further reduce bycatch this study gathered information from research cruises on the catch rates, size structure, seasonal and temporal variations of the primary bycatch species.  For this study three hundred tows were collected from early February to mid-June over five years using traditional shrimp trawl nets.  All species landed were weighed and measured.  Shrimp catch rates averaged 138.0±67.9 kg/hr while bycatch levels averaged 36.2±51.6 kg/hr (accounting for 18.9±19.7% of the total catch).  Bycatch levels were highly variable ranging from 0.7% to 86.7% of the total catch.  Twenty-six species of fish were identified as bycatch species.  Silver Hake (Merluccius bilinearis) was the primary bycatch species accounting for 51.0 ± 32.3% (28.4±51.1 kg/hr) of the total bycatch landing.  Silver Hake showed a seasonal trend with increasing landings in late spring, peaking in May.  At peak landings, Silver Hake could account for 99.5% of bycatch landings and 85.3% (384 kg/hr) of total catch.  Other bycatch species were pelagic including  Atlantic and blueback Herring (Clupea harengus and Alosa aestivalis), which were a primary bycatch species in February and March.  Flatfish species including American Plaice (Hippoglossoides platessoides) and witch flounder  (Glyptocephalus cynoglossus) were relatively abundant in April, May and June as bycatch.  A length-frequency analysis of Silver Hake, American Plaice and Atlantic Herring showed that most individuals caught ranged from 10-25 cm TL with no distinct seasonal variation.  Based on the information acquired in this study, we hope that future bycatch reduction strategies can be developed to target the main species of concern based on size frequency, natural history and seasonal variations.