Research Document - 2009/094
Redfish Catch Results from the Summer 2007 Survey in Unit 2
By J. McClintock and M. Teasdale
Abstract
To enhance the fisheries research database in Unit 2, NAFO Subdiv. 3Pn, 3Ps, 4Vn, and 4Vs, the Groundfish Enterprise Allocation Council (GEAC) has funded redfish surveys during winter 1997, and summers from 1998 to 2001, 2003, 2005, and 2007. These surveys are the only available index of stock condition given the Department of Fisheries and Oceans (DFO) last conducted a Unit 2 redfish survey in 2002 and there are no plans to continue with the DFO surveys. GEAC funded and performed the surveys with scientific guidance from DFO in the design and execution of a stratified random survey and the associated sampling. The data collected during these surveys have been subsequently analyzed on behalf of GEAC and for the additional intent of providing this information to DFO, for their databases and their assessment work. This is the eighth such GEAC redfish survey in Unit 2 following on the previous 1997 to 2005 surveys. The number of sets conducted in the 2007 survey increased by about 40% from previous surveys, in an attempt to reduce the variability/range of uncertainty of results. Catch statistics, length distribution, and stratified analysis estimates of redfish abundance and biomass, and interpretation of results are presented.
The 2007 Unit 2 total redfish biomass estimate is 98 ktonnes which is about 7% greater than the 2005 survey estimate of 92 ktonnes and 20% greater than the 2003 estimate of 82 ktonnes. The total abundance estimate for Unit 2 in 2007 is 336 million (M), an increase of 12% from the 2005 survey estimate of 299 M, and the largest since the 2001 survey estimate of 404 M. In 2007, estimates of 227 M in 3Ps were 2.4 times those from 2005: 3Ps biomass estimates in 2007 were double those of 2005. In the other three Unit 2 subdivisions 2007 abundance and biomass estimates were down compared with the 2005 counterparts. Abundance in 3Pn and 4Vn were each one third of their 2005 estimates, while the 4Vs estimate of 73 M in 2007 was 82% of the 2005 estimate of 89 M. 2007 biomass estimates in 4Vn and 4Vs at 13.4 and 23.0 ktonnes respectively were down by about 25% from 2005. An approach was considered to apportion abundance and biomass estimates based on maturity of the various population components of redfish in Unit 2. This was achieved by considering fish length, and for biomass, a length/weight relationship. Under this approach, in 2007, it was determined that one third of the total abundance estimates and three quarters of the total biomass estimate for Unit 2 are for mature redfish. Utilizing assumptions for illustration, about 68% of the population are Sebastes fasciatus, 25% S. mentella, and 7% heterozygotes. The 2007 Unit 2 abundance estimate is apportioned as follows: 229 M S. fasciatus, 84 M S. mentella, and 23 M heterozygotes. These percentages suggest 9% fewer numbers and about a 5% reduction in biomass for mature redfish in 2007 compared with 2005 for which similar approximations were made.
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