Estimates of natural mortality are currently unavailable for Patagonian toothfish. Such estimates are needed for estimating recruitments and for use in assessing yield. This paper proposes a method for jointly estimating natural mortality and cohort strength at age 4 using a negative log-likelihood function based on one or more cohorts for which their abundance has been estimated in two or more years. A worked example is provided in an appendix.
Abstract:
The results of mackerel icefish (Champsocephalus gunnari) trawling survey carried out by Russia at R/V Atlantida in February 2000 in Subarea 48.3 are presented. During that period C.gunnari were feeding. In all parts of the Subarea, except the North-Western one, C. gunnari of 22-28 cm in length and 2-3 years old predominated. Fish biomass distributed near the bottom estimated with different methods amounted to 47-87 thous.t. The estimation also was presented taking into account catchability coefficient. The objective evidences are submitted to prove that a certain part of C.gunnari stock may stay in the pelagic layer in the feeding period. Therefore, the bottom survey estimates only the population proportion distributing near the bottom at that moment. It is proposed to review the survey method. Arrangement of regular trawling-acoustic surveys in the area may improve the accuracy of this important commercial species abundance estimates and will answer some questions which currently have no grounded solutions.
