Research Document - 2011/034

Spiny Dogfish (Squalus acanthias) Assessment and Catch Recommendations for 2010

By V. Gallucci, I. Taylor, J. King, G. McFarlane, and R. McPhie

Abstract

Spiny dogfish (Squalus acanthias) is a small shark that inhabits temperate waters off the east and west coasts of North America. They are ovoviviparous and gestation is 2 years. Females produce 2-16 pups, averaging between 26-27 cm in length at birth. Spiny dogfish are a long-lived species with maximum ages in the Pacific population of between 80-90 years and a maximum size of 130 cm. Age-at-maturity of females is approximately 35-36 years corresponding to approximately 94 cm. Length-at-maturity for males is 70 cm.

Spiny dogfish have a long history of commercial exploitation in British Columbia dating back to 1870. From 1870-1916, spiny dogfish were harvested for their liver and body oils for use in industrial lubrication and lighting. Spiny dogfish livers were used as a source of Vitamin A, and a large liver fishery took place from 1937-1950 with recorded annual landings between 5,139-31,187 tonnes. Stock declines, market shifts and production of synthetic Vitamin A led to a collapse of the liver fishery. By 1977, market demand for spiny dogfish as food fish revived the fishery and since 1980 annual landings have ranged between 139 tonnes (in 1986) to 4,952 tonnes (in 2003). The longterm mean annual total fishing mortalities for the food fishery era (1978-2008) are 1,599 tonnes for the inside fishery and 1,690 tonnes for the outside fishery.

The spiny dogfish population in British Columbia is assessed as two distinct stocks: an inside stock inhabiting the Strait of Georgia (Statistical Area 4B); and an outside stock inhabiting all remaining coastal areas (Statistical Areas 3C through 5E). This stock assessment employs generalized Schaefer and Pella-Tomlinson surplus production models to estimate the current biomass of each stock. Model parameter estimates for the intrinsic rate of population increase (r) were available from the literature, and a range of estimates between 0.017-0.07 were used. The carrying capacity (K) estimates were based on estimates of biomass at the start of the liver fishery in the 1940s which were 166,667 and 333,333 tonnes for the inside and outside stock respectively. Catch per unit effort data available from the longline and trawl fisheries and from several research surveys were used as indices of relative abundance.

Model runs that use intermediate r values and that allow the model to estimate K are recommended for consideration in assessing the status of the inside and outside stocks and selecting yield limits. For the inside stock both the Schaefer and the Pella-Tomlinson model runs estimate that the population is in the Cautious zone, i.e. between 40-80% of BMSY. The yield limit derived from the Schaefer model is 525 tonnes, and the limit derived from the Pella-Tomlinson model is 168 tonnes. For the outside stock both model runs estimate that the population is in the Healthy zone, i.e. greater than 80% of BMSY. The yield limit derived from the Schaefer model is 5,964 tonnes, and the limit derived from the Pella-Tomlinson model is 10,087 tonnes.

There is some indication from length data collected from research surveys that there are slightly fewer very large spiny dogfish (>100 cm) in the inside stock and fewer large females (>85 cm) in one area (Hecate Strait) in the outside stock. Caution should be taken when interpreting these results. The research survey data for the inside stock requires calibration for a change in gear type and the data for the outside stock is only for one area and is derived from bottom trawl data that targets flatfish habitat.

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