Estimation of Yelloweye Rockfish and Lingcod Abundance Using a Submerisble for Line Transect Distance Sampling

Rockfishes are long-lived and late maturing species susceptible to overharvest; consequently, it is preferable to use non-lethal methods to assess these species. The use of traditional fishing gear may result in mortality of rockfish through barotrauma and be difficult to operate in the rugged, rocky habitats rockfish inhabit. In situ assessment methods using SCUBA, submersibles, or remote operated vehicles are preferable for measuring abundance. The Alaska Department of Fish and Game has developed an assessment for yelloweye rockfish using a manned submersible to conduct distance sampling methods along line transects. Rocky habitat is delineated by management area using a combination of fishery and sonar data. Fishing locations where greater than 0.04 yelloweye rockfish per hook are caught and habitat where backscatter data are interpreted to be rocky are used to select habitat. Dive transects are performed in locations randomly selected from the rocky habitat designated for the management area. The length of each transect and the number of yelloweye rockfish counted along each transect are used in the Distance program to estimate the density of yelloweye rockfish. These fish densities can be extrapolated to a biomass estimate using the average weight collected through port sampling and the area of rocky habitat estimated for the management area. Recently, we have explored producing similar biomass estimates by management area for lingcod, a species with high variability in density by location. Lingcod data have been collected during line transect sampling for yelloweye rockfish in the past. No stock assessment exists for lingcod in Southeast Alaska; consequently, using these historical data to estimate biomass could inform future management decisions.