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Canadian Stock Assessment Secretariat
Research Document - 2000/154
Assessment of the Canadian
longspine thornyhead (Sebastolobus altivelis) for 2000
By P. Starr and R. Haigh
Abstract
A detailed compilation and analysis of the available
data for longspine thornyheads (Sebastolobus altivelis) found in
west coast Canadian waters is presented. This analysis was prompted by
concerns over the rapid development of a new bottom trawl fishery
directed at this species since 1996. An analysis of the available length
frequency data from the commercial fishery showed that these
distributions have been quite stationary over the four years of the
fishery. Relative abundance indices estimated from CPUE data using
general linear modelling methods showed a 16% decline in biomass over
the four year history of the fishery. Population modelling using a
dynamic age-structured model fitted to the estimated relative biomass
indices and the annual observations of length structure in the
commercial fishery estimate that the population has declined between 10
and 30% over the four years of the fishery. These estimates are
unreliable due to the lack of a validated growth function and uncertain
estimates for natural mortality. This report recommends the development
of an independent biomass survey for this species and further research
on growth rates. This report also hypothesises that this species may
have very wide stock boundaries due to its extended pelagic larval phase
(18-20 months) and the consequent opportunity for wide dispersal due to
prevailing ocean currents.
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66 pages (2876K)
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