Science Advisory Report 2009/036

Assessment of Atlantic Halibut on the Scotian Shelf and Southern Grand Banks
(NAFO divisions 3NOPs4VWX5Zc)

Summary

• Based on three catch rate analyses of the halibut survey (industry/DFO longline survey), there appears to be relative stability in the adult population of 3NOPs4VWX Atlantic halibut. The preferred analysis suggests a statistically significant increasing trend over the 11 year time series, although not all sources of uncertainty have been evaluated.
• The size composition of halibut from the halibut survey in 4VWX indicates there has been no depletion of large fish from the population over the survey time series.
• The commercial index catch rate for 4VWX shows a statistically significant decline over the time series. This index is more difficult to interpret than the halibut survey abundance indices, and not all sources of variability have been considered at this point.
• The number of pre-recruits (fish < 81 cm) is above the long-term mean (0.192 halibut per standard tow) of the DFO research vessel (RV) survey (1970-2008), and has been increasing since 2004 in both the DFO RV survey and the halibut survey.
• Exploitation rate of the exploitable biomass (> 81 cm) was estimated to be 17.7 % (90 % confidence interval, CI: 15.7 - 19.8 %) in 2006, and 20.1 % (90 % CI: 17.7 - 22.7 %) in 2007 based on the tagging results. This is approximately double natural mortality (10 %) and F0.1 (9 %), and it is not known whether this rate is sustainable.
• Surplus production for the period 1998 to 2007 was estimated to average approximately 1,700 mt, 76 % of which was taken as catch and 24 % was left for future growth of the population.  Utilizing 76 % of the surplus production in more recent years (2,183 mt), would result in a catch of 1,700 mt.
• Although the exploitation rate is double natural mortality (M) and F0.1, given that the abundance indices from the halibut survey have been increasing recently and there are good signs of recruitment, a 15 % increase in the TAC for the 2009/2010 fishing season is not expected to increase the risk to the stock as compared to the previous 4 years. However, the longer-term consequences of utilizing the relatively high catch to production ratio (3.2:1) should be evaluated in the context of stock management objectives, reference points, and a risk management framework.
• Atlantic halibut can move large distances creating some uncertainty in stock structure. Other sources of uncertainty including vessels, bait and temperature effects on the halibut survey and commercial index, have not been fully analyzed. A lack of a population model and biological reference points make it impossible to know whether the stock is rebuilt or what is precautionary.

Complete document (PDF, 236 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.