The Greenland shark (Somniosus microcephalus) is the main bycatch species in established and exploratory inshore longline fisheries for Greenland halibut (Reinhardtius hippoglossoides) on the east coast of Baffin Island, Canada. Bycatch and entanglement in longline gear has at times been substantial and post-release survival is questionable when Greenland sharks are released with trailing fishing gear. This study investigated the effect of the type of fishing line used in the gangion and gangion breaking strength on catch rates of Greenland shark and Greenland halibut in bottom set longlines. Circle (size 14/0, 0° offset) hooks were used throughout the study. Behavior of captured sharks, mode of capture (i.e., jaw hook and/or entanglement), level of entanglement in longline gear, time required to disentangle sharks and biological information (sex, body length and health status) were recorded. Catch rates of Greenland shark were independent of monofilament nylon gangion breaking strength and monofilament gangions captured significantly fewer Greenland sharks than the traditional braided multifilament nylon gangion. Catch rates and body size of Greenland halibut did not differ significantly between gangion treatments. Although most (84%) of the Greenland sharks were hooked by the jaw, a high percentage (76%) were entangled in the mainline. The mean length of mainline entangled around the body and/or caudal peduncle and caudal fin was 28.7 m. Greenland sharks exhibited cannibalistic behavior with 15% of captured sharks cannibalized. All remaining sharks were alive and survived the disentanglement process which can be attributed to their lethargic behavior and lack of resistance when hauled to the surface. Thus, as a conservation measure fishers should be encouraged to remove trailing fishing gear prior to release. Our results are used to demonstrate benefits to the fishing industry with regard to an overall reduction in the period of time to disentangle sharks and damage to fishing gear by switching from braided multifilament to monofilament gangions in Greenland halibut longline fisheries.
Abstract:We developed and evaluated an innovative trawl technology that reduces seabed contact while targeting northern shrimp (Pandalus borealis) off the east coast of Canada. The innovative footgear, referred to as the "aligned footgear", was evaluated in a flume tank to estimate contact area with the seabed and then tested at sea for engineering performance and catchability. Results demonstrated that the aligned footgear trawl produced a substantial reduction (i.e., 61%) in the predicted contact area with the seabed compared with the identical trawl equipped with traditional rockhopper footgear. A total of 20 paired tows (n = 40 tows) were subsequently conducted at sea to evaluate fishing performance. The aligned footgear trawl caught significantly more northern shrimp (+23%), capelin (Mallotus villosus) (+71%), and Greenland halibut (Reinhardtius hippoglossoides) (+99%) compared with the traditional rockhopper bottom trawl.Résumé : Nous avons mis au point et évalué une technique novatrice de pêche au chalut qui réduit le contact avec le fond marin en ciblant la crevette nordique (Pandalus borealis) au large de la côte est du Canada. Le bourrelet novateur, appelé « bourrelet aligné », a été évalué dans un bassin à circulation d'eau afin d'estimer l'aire de contact avec le fond marin, puis a fait l'objet d'essais en mer pour évaluer la performance technique et la capturabilité. Les résultats démontrent que le chalut à bourrelet aligné entraîne une réduction importante (c.-à -d. 61 %) de l'aire de contact prévue avec le fond marin par rapport au même chalut équipé d'un bourrelet sauteur classique. Un total de 20 traits appariés (n = 40 traits) ont ensuite été effectués en mer afin d'évaluer la performance de pêche. Le chalut à bourrelet aligné a pris des quantités significativement plus grandes de crevettes nordiques (+23 %), capelans (Mallotus villosus) (+71 %) et flétans noirs (Reinhardtius hippoglossoides) (+99 %) que le chalut de fond à bourrelet sauteur classique. [Traduit par la Rédaction]
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