Hook modification study to reduce rockfish bycatch on circle hooks

Transcription

1 Hook modification study to reduce rockfish bycatch on circle hooks Stephen M. Kaimmer and Stephen Wischniowski Abstract A pilot study was conducted to see if circle hooks could be modified to reduce rockfish bycatch. We attached spring wires across the gap of the hook, hypothesizing that fish with less aggressive hook attacks might not hook as readily due to the wires. Although previous camera work showed hesitant hook attacks by rockfish, this study encountered larger individuals, and their attacks were aggressive enough that they could easily bend the wires across the hook gaps to become hooked. Introduction Rockfish bycatch continues to be a problem in hook-and-line fisheries targeting Pacific halibut (Hippoglossus stenolepis). This is particularly so for yelloweye (Sebastes ruberrimus) and quillback rockfish (Sebastes maliger), which in some areas are under varying degrees of regulatory protection to reduce catches. Halibut hook attacks typically include taking the entire hook into the mouth. If the fish becomes hooked, this will occur as it attempts to swim away: the gangion and then the hook is pulled from the gullet, and as the hook curves around the corner of the jaw, the point catches in the cheek area from inside the mouth, and the fish is hooked. Previous camera observation of halibut and rockfish (Kaimmer 1998) suggested that hook attacks by halibut are much more forceful than those made by rockfish, and we hypothesized that spring wires across the hook gap might be able to reduce rockfish hooking while not impeding halibut captures. A spring wire affixed to the shank of the hook and spanning across to the point would flex during a forceful attack, allowing the hooking event to continue unimpeded. A less forceful hook attack would not cause the wire to flex, and the hook would be pulled from the mouth without hooking the fish. In order to test this hypothesis, the International Pacific Halibut Commission (IPHC) conducted a hook-modification experiment in southeastern Alaska in May Methods The 58-foot F/V Towego was chartered to deploy a drop camera to evaluate the effects of different wire configurations on the hooking success of circle hooks for halibut and rockfish. Hooks were modified to resemble weedless hooks sold to sports fishermen, with a short piece of spring wire attached to the hook shank near the eye so that it would lie across the gap of the hook (Figure 1). Different configurations of single and double stainless steel spring wires were tested in five different wire diameters: 0.032, 0.037, 0.039, 0.047, and inch. All hook attacks were monitored and recorded. A light aluminum frame holding a GoPro Hero2 1 camera was focused on a single baited hook (Figure 2). The frame was made of 6061 aluminum stock with arms made from 5/16-inch-by-1.25-inch flat bar with 1-inch pipe welded to one edge for rigidity (Figure 2). The body of the frame was a piece of 3/8-inch-by-8-inch

2 aluminum plate cut to allow two 12-inch trawl floats to fit on aluminum rod pylons. A custom camera mount was constructed from stainless steel. The gear was weighted with a 4-foot long piece of 2.5-inch diameter round steel shaft weighing approximately 40 pounds, and the entire assembly weighed 23 pounds in water. The trawl floats each had a buoyancy of 22 pounds. The gear was deployed using an electric EZPull 2 pot hauler modified with a slip-ringed drum instead of a sheave. The drum contained 500 feet of Wireline A 1/10-inch cable for gear deployment. The Wireline provided an insulated inner core which allowed transmission of a live video signal from the camera to the surface. The GoPro camera was contained within a modified Sartek 4 SGP-DHSG deep housing, which allowed deployment at depths of over 500 feet. Modifications to the housing included lengthening to allow use of an extended battery back for the camera and addition of a bulkhead connection to allow the passage of video signals from the camera through the wireline cable to a surface TV monitor. Illumination was provided by two Sartek EBL1000D 1000 lumen LED flashlights mounted to the ends of the deployment frame arms. An oval cone of light 60 by 40 inches generated a usable field of view; rockfish were required to enter the bright field (the brighter lighted area that allowed for rockfish identification) of 40 by 30 inches before enumeration. Realtime video signals were sent up the Wireline cable, allowing precise control and evaluation of the gear sets. Because the length of cable was over 200 feet, an Intertek 5 ISL59605IRZ-EVALZ MegaQ signal equalizer was used to boost the signal definition. HDTV high definition 1080p (1920x1080 megapixel) video at 30 frames per second and a viewing angle of 170 degrees was captured on a 36-gigabyte flash card within the GoPro camera. All video was downloaded onto a laptop computer after each gear retrieval. All caught fish were carefully removed from the hook and released. Captured rockfish were repressurized using a SeaQualizer 6 pressure-activated release mechanism set to release the fish at 100 feet depth. The research design involved an iterative process, testing single and double wires of varying strengths. This was a pilot study, the see whether this type of hook modification would give any practical advantage in reducing rockfish bycatch through a reduction of hooking success. Results Fifty-two gear deployments were completed, with durations of time on bottom ranging from 35 to 135 minutes (Table 1 for a summary and Figure 3 for a chart of fishing locations). The gear was deployed in depths ranging from 20 to 65 fathoms. We observed 215 hook attacks by eleven species or species groups. We observed 201 attacks by our target groups of halibut (12 attacks), quillback rockfish (25 attacks) and yelloweye rockfish (164 attacks). We caught and released 4 halibut (33.3 percent total hooking success, among all hook treatments), 6 yelloweye rockfish (3.7 percent total hooking success), and no quillback rockfish (Tables 2 and 3). We observed no decrease in hooking success for yelloweye over 4.5 kg using various spring wire configurations. Too few quillback rockfish were encountered to make a definitive statement regarding this species. The fishermen on our charter boat commented that the wired hooks were very awkward to work with, both in baiting and in removing fish from the hook, and it would take a major improvement in bycatch avoidance to make these hooks feasible for use in a fishery. 2 EZ-Pull Products PO Box 1307, Shelton, Washington United States 3 RochesterWire and Cable,LLC, 9450 Clarewood, Houston, Texas United States 4 Sartek Industries, Inc 34 Jamaica Ave.,Port Jefferson Station, New York United States 5 Intersil 1001 Murphy Ranch Road, Milpitas, California, United States 6 SeaQualizer LLC, Miami, Florida, United States: theseaqualizer.com 488

3 Discussion In previous camera studies (Kaimmer 1998), an 8-percent hooking success was observed for 237 yelloweye rockfish hook attacks, and the average weight of the hooked fish in 1998 was 3.8 kg. We had hoped to decrease the hooking success for this species without affecting the catch of halibut. While the overall yelloweye hooking success in this current study was only 3.7 percent, all of the attacks by larger yelloweye resulted in captures. Yelloweye over about 20 inches and 4 kg, which constitute a large part of the yelloweye bycatch on setlines, took the hook and struggled violently, making our hook modification ineffective at keeping them off the hook. Twenty-five quillback attacks were observed with no captures. It is possible that the spring wires reduced the hooking success for this species, but the number of observations was too small to make a definitive statement. Bycatch mortality reduction measures currently in use include area avoidance and recompression of rockfish once caught. Hook modification as an additional measure to reduce bycatch mortality does not seem to be a fruitful avenue for future research. The similarity in hooking behavior between halibut and large yelloweye negates the likelihood of a hook modification that could be selective for one species over the other, although this would depend to some extent on the size of the yelloweye encountered. Acknowledgements We would like to thank Tor A. Bjorklund, an oceanographic equipment fabricator at the University of Washington, for his innovative design help in constructing our deployment frame, and Captain Leonard Leach of the F/V Towego for sharing his knowledge of fish behavior and distribution during the field portion of our project. References Kaimmer, S.M Direct observations on the hooking behavior of Pacific halibut, Hippoglossus stenolepis. Fish. Bull. 97:

4 Table 1. Summary of fishing locations for the hook modification charter. Date Approximate location Description Depth range (fm) May N W North end of Clarence Strait May N W North end of Clarence Strait May N W Snow Pass 30 May W Eastside Coronation Island May N W Warren Island Table 2. Catch and catch disposition during 2012 hook modification charter. All catch was taken off Coronation Island; all weights were determined on a handheld digital scale. Date Set Location May W May May May May May May May N W May N W May N W Depth (fm) Species captured Length (in) Weight (lb) Disposition 30 Halibut Careful release 32 Yelloweye Recompress to 100 ft 32 Yelloweye Recompress to 100 ft 32 Halibut Careful release 31 Yelloweye Recompress to 100 ft 35 Yelloweye Recompress to 100 ft 37 Yelloweye 20 5 Recompress to 100 ft 33 Yelloweye Recompress to 100 ft 31 Halibut 37 ~15 Careful release 31 Halibut Careful release 490

5 Table 3. Hooking success for the target species: halibut, quillback and yelloweye rockfish. Yelloweye rockfish numbers are given for both small and large specimens. Weights for escaped fish are estimated from length estimates in camera image. Species Number of hook attacks Number caught Hooking success Halibut % Quillback (all under 2 kg) % Yelloweye (2-3 kg) % Yelloweye (4.5+ kg) % 491

6 Figure 1. Modified hook showing double and single wires across hook gap.

7 Figure 2. Camera deployment frame used in hook modification charter in southeastern Alaska during 2012.

8 Figure 3. Locations for hook modification charter in southeastern Alaska during 2012.