Research Document - 2008/055
A review of yellowmouth rockfish Sebastes reedi along the Pacific coast of Canada: biology, distribution, and abundance trends
By R. Haigh, and P. Starr
Abstract
We summarize the available information on yellowmouth rockfish Sebastes reedi. Specifically, this paper reviews the current data on the biology, distribution, and abundance trends, primarily for citation by COSEWIC stock status reports. This species has a mean weight of 1.467 kg/fish, representing the samples from the observed commercial fishery. Growth relationships shows no strong difference between the sexes. Allometric analyses yield curvature parameter estimates b all> 3, suggesting non-isometric growth. Length-age analyses also show little difference between males and females, although the models consistently predict slightly higher values for females. Natural mortality M is estimated to be 0.047, based on an exponential decay model and a maximum observed age of 99. The total mortality Z estimate from catch-curve analysis of the 2003 data is 0.063 (95% confidence interval = 0.044-0.083). Maturity ogives yield ages at 50% maturity k of 10.1 y for males and 10.6 y for females. Assuming k = 10.5 y and M = 0.047, the generation time is 31.8 y. Depth-of-capture frequency in commercial trawl tows suggests that most of the population occurs between 130 m and 357 m. Using this bathymetry interval, the estimated potential habitat is 48,368 km². The estimated area of occupancy based on trawl tow observations covers 33,092 km² using a DFO grid (0.1° longitude × 0.075° latitude) or 11,332 km² using a COSEWIC grid (2 km² × 2 km²). Within its preferred depth range, yellowmouth rockfish is caught with numerous other species including Pacific ocean perch Sebastes alutus, arrowtooth flounder Atheresthes stomias, redstripe rockfish S. proriger, silvergray rockfish S. brevispinis, and yellowtail rockfish S. flavidus. Total removal of yellowmouth rockfish from BC coastal waters by Canadian and US commercial fleets since 1930 equals at least 60,000 t. The long-term surveys are generally not useful for tracking abundance of this species due to low index precision. Two of these surveys (Hecate Strait assemblage and WCVI shrimp) are too shallow and rarely catch yellowmouth rockfish. The current series of synoptic groundfish surveys being conducted on the BC coast may provide indicators of population trends in future, but the available biomass indices are not precise (relative error = 30–50%), which may reduce the capacity of these surveys to track abundance changes for yellowmouth rockfish. The survey imprecision is likely associated with a substantial mid-water presence for this species. The commercial trawl CPUE indices coastwide show a decline of 2.5% per year from 1996 to 2006. It is not known if the trend in CPUE indices represents a change in abundance of this species or in fishing practices associated with the introduction of IVQ management.
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