Fish/Shellfish Research and Management - Fish/Shellfish Research
Date Published: December 2008
Number of Pages: 133
Author(s): Farron R. Wallace, Yuk Wing Cheng, and Tien-Shui Tsou
In this document, we include model results from the STAR base model and results based on the "STAT best fit" model, where natural mortality for "old" females is assumed to be 0.24 compared to the assumption of 0.2 in the STAR base model. All other parameter settings remain the same in both models. The "STAT best fit" model is based largely on new and expanded analyses following the conclusion of the STAR Panel. We ran a grid search of natural mortality between 0.1 and 0.3 for "old" females and found that model with natural mortality of 0.24 for "old" females resulted in a better fit to the data with the largest negative change in log likelihood. The mortality of 0.24 agreed with a direct estimate of female natural mortality at 0.27 (SE = 0.26) from historical catch, effort, and length frequency data. Results from the "STAT best fit" model was presented to the Pacific Fishery Management Councils' Science and Statistical Committee (SSC) in September, 2008. The SSC and assessment authors concurred that management should be based on the "STAT best fit" model because it represents the best fit to data. Natural mortality assumptions in "STAT best fit" model were bracketed by increasing and lowering natural mortality +/- 25% to produce "Low" and High" model results that were used to bracket the uncertainty.
This assessment applies to the Northern portion of the black rockfish (Sebastes melanops) stock found between Cape Falcon, Oregon and the U.S. border with Canada. This assessment treats these fish as a separate unit stock. The stock found South of Cape Falcon, Oregon is treated as another unit stock in a different assessment document. Black rockfish are not subjected to a targeted fishery in Canadian coastal waters and are not assessed.
Little information exists on the historical landings of black rockfish prior to the early 1960's. Landings of "rockfish" peaked at nearly 25,000 mt in 1945 in support of the war effort; however, there is no known species composition estimates for these catches. Due to the nearshore habitat of this species it is likely that very little of this catch was black rockfish. Predominate harvesters of black rockfish between 1963 and 1983 were commercial line and trawl fishers. Black rockfish trawl landings typically came from directed tows on nearshore rocky reefs and shipwrecks with few landings incidental to other targeted fisheries. Peak landings in the trawl fishery reached 350 mt in 1976 and declined to less than 10 mt in recent years. Black rockfish comprised less than 1% of total rockfish landings by the trawl fishery during this period.
The "non-trawl" fishery is composed of three distinct line fisheries, and each differs in target species. Oregon and Washington fish receiving tickets show nominal rockfish catches as early as 1970 in the salmon troll fishery, during 1973 in the jig fishery, and during 1979 in the bottomfish troll fishery. Black rockfish are generally caught as bycatch in the commercial salmon troll fishery; landings peaked in the late 70's (151 mt) and steadily decreased coincident with losses in fishing opportunities for coastal salmon. The bottomfish troll fishery generally targeted lingcod; rockfish landings were small and estimated black rockfish catch never exceeded 2 mt. The jig fishery is primarily composed of small vessels less than 26 feet in length that generally fish near their port of access. Black rockfish were targeted in nearshore areas and were a significant fraction of the nominal rockfish landings in the jig fishery. Black rockfish catch in the jig fishery was inconsequential prior to 1980, and peaked in 1982 at 272 mt. Since 1996, nominal rockfish landings have contained no black rockfish due to area restrictions that have forced jig fishers to target other rockfish species found farther offshore.
Black rockfish are the primary target of the coastal groundfish sport fishery, with small catches first reported in the late 1970's that steadily increased to over 300 ton per year by the mid 1990's. Due to the implementation of a 10 fish bag limit in 1995 (Figure 7), and longer salmon seasons, annual catches of black rock declined to 188 mt in 2001. In recent years, sport catches increased to more than 300 mt. The coastal recreational rockfish fishery generally competed with sport salmon, halibut and tuna fisheries, and this is reflected in year-to-year variability in black rockfish catch.
Discard of black rockfish in Washington waters in either the commercial or recreational fisheries is likely very small. "Sebastes complex" trip limits in the line fishery were nonrestrictive prior to 1999 since few landings ever achieved the trip limit, and there was no incentive to discard catch. Furthermore, Washington State waters (inside 3 miles) have been closed to directed non-trawl commercial fishing since 1996 and directed trawl fishing since 1999. Black rockfish represented only a small fraction of the nominal rockfish catch in the trawl fishery and it is unlikely they were discarded. Discard in the sport fishery is also insignificant since the vast majority of recreational fishers do not high-grade their rockfish catch. This is supported by recent sport fishery information that indicates discard is less than 16 mt on an annual basis.