Principle Investigators:

T. Rudolph
J. Pappalardo
M. Sanderson

Cape Cod Commercial Hook Fishermen's Association, 210E Orleans Road, North Chatham, MA 02650, USA [tel: 508 945 2432, fax: 508 945 0981 e-mail: tom@ccchfa.org, johnp@ccchfa.org and mel@ccchfa.org]

H.O. Milliken

NOAA / NMFS / NEFSC, 166 Water Street, Woods Hole, Massachusetts 02543, USA [tel: +1 508 495 2294, fax: 508 495 2066, e-mail: Henry.Milliken@noaa.gov].

M. Farrington

1 Algonquin Rd, Acton,e-mail:mfarr15@verizon.net].

Federal fisheries regulations require that undersized individuals of commercially important species be returned to the sea and the National Marine Fisheries Service (NMFS) has listed investigations into discard mortality rates as a research priority. For demersal longline fisheries, survival of discarded bycatch is uncertain. Sub-legal sized fish can incur injuries in their mouth, gills, and eyes and sometimes in the gut from hooks, as well as undergo pressure and temperature changes as they are brought to the surface. This study built on previous work that investigated the survival of sub-legal cod. The results of the previous study were hard to assess because of the large numbers of control fish that died. Additionally, the results of the previous study were questioned because the study was not conducted using commercial vessels. This study, funded by the Northeast Consortium (NEC), was executed in collaboration with commercial vessels fishing their commercial hook and line gear. Two handling techniques were examined and compared to jigged fish that acted as the control to estimate cage induced mortality. Longline caught fish were either removed from the hook by hand (unsnubbed) or removed by allowing the hydraulic hauler to pull the fish against the parallel steel cylinders placed vertically on the gunwale, causing the hook to pull through the jaw (snubbed). At the extreme, this process can result in breaking the jaw. This study was a cooperative effort between fishermen and scientists using standard commercial fishing practices. 3,764 sub-legal cod were assessed for survival at three different depth ranges and four sea surface temperature ranges. Survival, assessed after holding the fish in cages for a minimum of 72 hours, ranged from 30.8% to 100%. Binomial logistical regression analysis indicated that depth, sea surface temperature, and de-hooking technique all affected survival. Depth and temperature affected survival more than the de-hooking technique. Survival improved as depth and sea surface temperatures decreased. Unsnubbed fish had less mortality compared to snubbed fish. (from final report abstract)

sublegal_cod.csv