Artisanal longline fishing for Greenland halibut (Reinhardtius hippoglossoides) operated under sea ice using a metal plate kite in northwest Greenland

Abstract

Understanding the deployment ranges and behavior of fishing gear in relation to fishery efficiency will help us grasp the potential impact of future shifts in the fishery on resources and fishing activities. Fisheries for Greenland halibut are conducted by boat in open water during the summer. However, in winter, fishermen travel to fishing grounds on the sea ice using dog sleds, drill holes in the ice, and deploy longlines using metal plate kites. While the scale of deployment varies between boat and ice longlining, the movement of kites used in ice longlining and their effect on the deployment range of the line is not well understood. We conducted experiments using an accelerometer to determine the underwater movement of kites and their effect on the horizontal range of longline deployment. This is the first report describing specific operational information on longline fishing under sea ice, specifically on the effects of the kite on longline deployment. The kite is attached to the leading end of the mainline and deploys the longlines horizontally as it moves downward towards the sea floor. When the kite and mainline are dropped into the sea, the kite extends the line horizontally while shifting forward-facing long side, and forward-aligned short side. The motion resembles a fluttering action primarily influenced by the Reynolds number and moment of inertia. When the mainline is held, the kite descends in a circular motion. With repeated fishing operations and the passage of time, the kite's movement is expected to decrease in both range and speed due to the buoyancy and tension of the mainline. These kite movements suggest that the deployment range of longlines could extend several hundred meters. Therefore, it can be inferred that the impact of winter ice fishing on the Greenland halibut stock is relatively low due to the limited deployment range of the longline when using the kite.