ESTIMATION OF FISHING AND NATURAL MORTALITY FROM TAGGING STUDIES AN FISHERIES WITH 2 USER GROUPS

We present generalizations of fishery models that allow for the separa te estimation of fishing mortality when more than one user group is pr esent (e.g., a commercial and a recreational fishery). This model also allows for the fisheries to be in operation for any length of time wh ereas previously fisheries were generally considered to be pulse or co ntinuous. Three cases are considered: (i) fisheries operate consecutiv ely, (ii) fisheries overlap for a part of their seasons, and (iii) fis heries are in operation for the whole year. The results of a simulatio n study are included, which provide estimates of fishing and natural m ortality along with their proportional standard errors (CVs). All scen arios had good precision, with most CVs < 25% and usually very little difference between the three cases. Coefficients of interaction, the p otential gain by one fishery if another is closed down, are also given along with a method for calculating them. Factors affecting these coe fficients of interaction were the order in which fisheries operated, a mount of overlap in fishing seasons, and intensity of fishing effort b y each fishery. We believe that these models could provide useful info rmation for the management of fisheries with multiple user groups wher e allocation conflicts may arise.