MULTIYEAR TAGGING STUDIES INCORPORATING FISHING EFFORT DATA

The Brownie models for multiyear tagging studies can be used to estima te age- and year-specific annual survival rates and tag recovery rates . The latter are composites of the exploitation rates and rates of tag reporting, tag shedding, and tag-induced mortality. It is possible to estimate the exploitation rates if the other components of the tag re covery rates can be quantified. Instantaneous rates of fishing and nat ural mortality can be estimated if information is available on the sea sonal distribution of fishing effort. The estimated rates are only mod erately dependent on the timing of the fishing; consequently, the rela tive effort data can be crude. Information on the timing of the catch over the course of the year can be used as a substitute for the effort data. Fishing mortality can also be assumed to be proportional to fis hing effort over years; consequently, if fishing effort is known then the tag reporting rate, natural mortality rate, and a single catchabil ity coefficient can be estimated (instead of natural mortality and a s eries of fishing mortalities). Although it is possible in theory to es timate both the tag reporting rate and the natural mortality rate with all of these models, in practice it appears necessary to obtain some additional data relating to tag reporting rate to obtain acceptable re sults. The additional data can come from a variable reward tagging stu dy, a creel or port sampling survey, or from tagged animals that are s ecretly added to the fishers' catches.