Abstract
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.
Highlights
In 1986, a small scale winter (January–May) longline fishery for Greenland halibut (Reinhardtius hippoglossoides) was developed in Cumberland Sound, a large inlet on the east coast of Baffin Island in the territory of Nunavut, Canada
Greenland shark were not captured in experimental longline Sets 2, 8, or 10, Greenland halibut that had been depredated by Greenland shark were captured in these sets (Table 2)
Greenland shark depredated Greenland halibut captured in the stock assessment survey longlines during these three sets and four Greenland sharks were captured in the stock assessment survey longlines during Set 8 (Table 2)
Summary
In 1986, a small scale winter (January–May) longline fishery for Greenland halibut (Reinhardtius hippoglossoides) was developed in Cumberland Sound, a large inlet on the east coast of Baffin Island in the territory of Nunavut, Canada. In this fishery, fishing takes place through holes in the ice and fishers move with land-fast ice as it expands to cover deeper waters (>400 m) where Greenland halibut are abundant. No bottom gillnetting or trawling is permitted in Cumberland Sound (Fisheries & Oceans Canada, 2008b) and future development of a Greenland halibut longline fishery during the ice-free season would increase the likelihood of catching the full quota in years when ice conditions limit winter fishing activities
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