Research Document - 2011/001

Atlantic Halibut Fishing Mortality Estimated from Tagging on the Scotian Shelf and the Southern Grand Banks

By C. den Heyer, C. Schwarz, and K. Trzcinski

Abstract

In 2006, Fisheries and Oceans Canada (DFO) and the Atlantic Halibut Council (AHC) began the Halibut All Sizes Tagging (HAST) program to estimate exploitation rate and evaluate the distribution of halibut within the Scotian Shelf southern Grand Banks management unit. More than 2,000 halibut were double tagged with t-bar anchor tags, during the DFO-industry halibut surveys between 2006 and 2008. As of 26 August 2010, 409 of these halibut were recaptured and reported. The HAST study is an example of a band-recovery experiment.  The models in this paper follow a similar development to Hoenig et al. (1998a&b), but also incorporate tag loss. We assume that survival after tagging and tag reporting are constant and that fishing mortality is equally spread over the year.  We also estimate instantaneous fishing mortality for each cohort in the first year after release to allow newly tagged animals to mix with the population. Most tag loss occurs in the first year of release. Based on the multiyear models with incomplete mixing and two parameters to describe tag retention, tag loss is estimated at 17%/year in the first year and 9%/year in the second and subsequent years. Assuming 90% tag reporting and 80% survival from tagging, instantaneous natural mortality (M) for halibut that were greater than 81 cm was estimated to be 0.26 (SE=0.08), and instantaneous fishing mortality (F) was estimated to be 0.20 (SE=0.04) in 2007, 0.29 (SE=0.04) in 2008, and 0.21 (SE=0.04) in 2009.

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