Juvenile redfish (Sebastes spp.) behavior in response to Nordmøre grid systems in the offshore northern shrimp (Pandalus borealis) fishery of Eastern Canada

Abstract

A recent rebound of juvenile redfish (Sebastes spp.) in areas where the northern shrimp (Pandalus borealis) bottom trawl fishery in eastern Canada occurs has been challenging the fishing industry to maintain bycatch of this species within acceptable levels. Using self-contained underwater cameras and red lights, this study investigated the behavior of juvenile redfish in response to bycatch reduction devices (BRDs), called Nordmøre grids. Fish behavior was analyzed in grid systems with different bar spacings, including 22- and 19-mm bar spacings. A total of 10.3 h of useable underwater video was collected during commercial fishing conditions, which yielded individual observations of 931 redfish. Generalized linear models (GLMs) and behavioral trees were used to analyze the data. We observed that 52.5% of all redfish passed through the bar spacings and were retained. The duration of the selection process was relatively short (~1.9 s mean), and 57.8% of redfish reacted to the grids by swimming upwards, forward, or towards with respect to the grids. Behaviors exhibited by redfish and redfish retention were similar for both grids. GLM results suggested that as time in front of the grid increased and redfish had upwards or steady grid reactions, retention was drastically reduced. These were important variables that significantly explained the capture fate of redfish. The behavioral sequence that led to higher escape probability was redfish that approached upwards, had no contact with the grid, and reacted to the grid by continuing to move upwards to finally exit through the escape opening. GLM and behavioral trees gave a comprehensive view of redfish behavior, which is extremely useful for perfecting or developing any BRD to address juvenile redfish bycatch.

Effect of the Nordmøre grid bar spacing on size selectivity, catch efficiency and bycatch of the Barents Sea Northern shrimp fishery

“…The results showed while the different grids were effective at reducing bycatch, there was no significant difference in the mean Northern shrimp length captured with either of the grids. In a recent study from the same area (the shrimp grounds off Newfoundland), similar results, i.e., no difference, was obtained for shrimp retention when comparing 19 and 22 mm bar spacings in a Nordmøre grid [29]. Furthermore, it…”

“…Therefore, we designed this study to examine the effect of the grid bar distance. Different bar spacing grids have been tested in other shrimp fisheries around the world (e.g., [ 18 , 26 – 29 , 47 , 48 ]). For example, Hickey et al [ 26 ] tested 22, 25 and 28 mm grids along the fishing grounds of Eastern Canada.…”

“…The trials were conducted using a two-bridle Campelen #1800 trawl built from 3 mm polyethylene (PE) twine with 80-40 mm diamond meshes size in the wing sections and by polyamide (PA nr. [24][25][26][27][28][29][30][31][32] in the belly and codend sections. The trawl was towed behind a set of Thyboro ¨n T2 otter boards (6.5 m 2 and 2.200 kg).…”

“…Changing bar spacing in the Nordmøre grid is an obvious modification to change the selection characteristics of the grid section because it potentially affects the sizes of fish and Northern shrimp that can pass between the bars of the grid. However, no published study has evaluated if or how the selection properties in the Northern shrimp fishery in the Barents Sea change by modifying the Nordmøre grid bar spacing, except a brief notice of initial experiments during 1989–1990 with various bar distances in the grid [ 4 ] with few studies examining the effect of grid bar spacing in other fisheries [ 18 , 26 – 29 ].…”

Towards Shrimp and Prawn Welfare in the Wild‐ Caught Fishing Industry: A Global Review and Recommendations for Research and Policy

“…Almost all of the catch was composed of caridean species (Pandalus borealis and unspecified Pandalus species). The fishery is concentrated off Canadaʹs east coast and is divided into an offshore and inshore fleet (Araya- Schmidt 2022). The offshore fleet consists of around 10 vessels, which range between 50 and 75 metres in overall length and operate from Newfoundland and Nova Scotia (Foley 2012;Araya-Schmidt 2022).…”