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Industry-science partnership investigating the short-term and long-term discard mortality of spiny dogfish using commercial hook gear in the Gulf of Maine.
Shelly Tallack (Gulf of Maine Research Institute)
Lara Slifka (Cape Cod Commercial Hook Fishermen's Association)
The unpopular spiny dogfish, Squalus acanthias, represents a resource which, in recent years, despite its apparent high abundance, is considered vulnerable to overfishing. This vulnerability hinges on its characteristics of slow growth, late maturation (~6 years in males and ~12 years in females), high maximum age (35-40 years) and low natural mortality (M=0.09). One immediate problem faced by fishery managers is that while spiny dogfish are periodically caught in high numbers as bycatch (during both recreational and commercial trips), there is little information regarding the survivability of the discarded dogfish. Two recent studies have addressed dogfish discard survival from trawl gear and gillnet gear; the current study addresses survival from commercial hook gear.
This collaborative project represents a partnership between the Gulf of Maine Research Institute (GMRI), the Cape Cod Commercial Hook Fishermen's Association (CCCHFA) and commercial fishermen working with each organization in Gulf of Maine waters and Southern New England waters, respectively. The primary research objective was to investigate the short-term discard mortality rate of dogfish from different commercial hook gears. Survivability was investigated through caging studies.
A total of 2,418 dogfish were sampled between the two regions; of these 682 were caged by GMRI (45% males and 55% females) and 1,234 were caged by CCCHFA (27% males and 73% females). Dogfish were subject to three gear/handling treatments: 1) snubbed, 2) unsnubbed and 3) control. An overall regional difference in short-term discard mortality was observed; GMRI recorded significantly lower total mortality (7%) than CCCHFA (22%). Regional, averaged findings showed a sex effect with males demonstrating higher mortality (26%) than females (14%). The largest dogfish of each sex demonstrated greater resilience to mortality. Treatment effects were observed with mortality being highest in snubbed fish (23%), then unsnubbed fish (16%) and finally control fish (13%). Gear effects were found with highest mortality resulting from long-line gear (22%) while the different hand gear-related mortality ranged from 8-17%. The relationship between hook removal treatment and hooking severity index (HSI) was significant; severe mouth and jaw injury was most frequent in snubbed fish but was rare in control fish and the overall trend was that mortality increased with increased HSI.
Considerable variation was observed between the GMRI and CCCHFA findings; this variation was likely caused by differences in: water temperature, levels of parasitic infestation (i.e. sand fleas) and possible differences in handling, tanking and caging procedures. This study's long-term discard mortality assessments were aborted for logistical reasons and as such, these findings represent the range of likely short-term discard mortality from hook gears across the region.
An electronic jig machine is used to mechanically jig a fish hook or lure with a bait casting reel without using the fishing rod to jig the lure. Normally to jig a fish hook or lure one must move the fishing rod either vertically, horizontally, or jerk the fishing line by hand. The jigging action of this bait cast reel (how rapid and how long in distance the jig will travel) will determine the desired intensity and resonance of the rattle used in the lure to attract or snag the fish. With very simple controls, the equipment functions automatically since it is programmed to suit the actual fishing area, the fishing method and the type of fish.
Used to catch fish.
Longlining employs a central fishing line that can range from one to 50 miles long; this line is strung with smaller lines of baited hooks, dangling at evenly spaced intervals. Longlines can be set near the surface to catch pelagic fish like tuna and swordfish, or laid on the sea floor to catch deepdwelling fish like cod and halibut. (www.montereybayaquarium.org/cr/cr_seafoodwatch/sfw_gear.aspx)
Gulf of Maine or Cape Cod
vessel name + trip number
month of year, local time
day of month
local day and decimal time, as 326.5 for the 326th day of the year, or November 22 at 1200 hours (noon)
bait used to catch dogfish
time from beginning to end of haul
depth at beginning of haul
depth at end of haul
latitude at starting time of measurement (west is negative), in decimal degrees
longitude at starting time of measurement (west is negative), in decimal degrees
latitude at end time of measurement; in decimal degrees (negative denotes South)
longitude at end time of measurement; in decimal degrees (negative denotes West)
temperature at bottom
comments pertaining to the haul
Biological and Chemical Oceanography Data Management Office.
Funded by the U.S. National Science Foundation