Movement of tagged lingcod and rockfishes off Depoe Bay, Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/x633f382d

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  • A tagging study was conducted from June 1978 through January 1982 to provide information on the movements of adult neritic reef fishes off the central Oregon coast. To evaluate the cause of low tag returns of previous tagging studies of reef fish in this area, tag retention, post-tagging mortality, and tag reporting rates were analyzed. The retention of Floy FD-68C tags was analyzed in a double tagging study in the research area. Short term tag retention (0-450 days) was good (0.66) at the dorsal position. However, tag retention over the long term (0-900 days) was low (0.28) at the dorsal position and contributed to reducing the number of tag returns. The tag at the operculum position had a significantly lower rate of retention than the tag at the dorsal position. The activity at release and extent of air bladder inflation were assessed to determine if these factors affected rates of survival of tagged rockfishes. The results were inconclusive. However, the results suggest that mortality of rockfishes exhibiting inflated air bladders can be reduced by puncturing their air bladders with a syringe either through the mouth or through the side of the abdomen. The rate of tag reporting by fish cleaners and personnel of charter offices was estimated by seeding the catch of charter vessels as they were unloaded at the docks. The rate of tag reporting was 71.4%. An intensive educational program and frequent spot-checking of the catches were largely responsible for this favorable rate of tag reporting by charter fishing personnel. The rate of tag reporting by private sportfishermen was not assessed. A total of 8,471 reef fish was tagged during a 27-month period. The tagged fish were predominately black rockfish (Sebastes melanops) (69.7%) with relatively small percentages of other species of reef fishes. Over a 44-month period the average return rate of tags from all species was 1.71%. The zero return rate (of 859 tagged) of blue rockfish (Sebastes niystinus) was significantly (X2, p 0.005) lower than the average return rate for the other species except cabezon (Scorpaenichthys marmoratus) and China rockfish (Sebastes nebulosus). The low return rate may indicate low utilization of this species. Analysis of tag returns indicates that the population of yelloweye rockfish (Sebastes rubberimus) is characterized by local sedentary stocks. Recaptures of tagged black rockfish, lingcod (Ophiodon elongatus), yellowtail rockfish (Sebastes flavidus), and canary rockfish (Sebastes pinniger) suggest that some individuals of each species are resident while others move extensive distances. However, the actual amount of movement and stock mixing of each of these species could not be quantified. The results of this study suggest that this fishery can best be managed by catch limits of combined species of rockfishes on a statewide basis. Other species of reef fishes including lingcod could effectively be managed separately. Because of significant increases in fishing pressure and advances in fishing techniques considerations should be given to reducing the total catch.
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