Population Dynamics and Marine Mammal Management Policies

Some criteria for appraising population level relative to the maximal or carrying capacity point are listed. Simple population-dynamics models are then used to explore some of the criteria. Age at first reproduction does not seem as important as in some more prolific and shorter-lived species, being at most equivalent to a few percentage points of adult survival. Age-specific reproductive rates are very much the same for a number of pinniped species. For most marine mammal species, survival through immature stages is an unknown quantity, but appears to be a factor of major importance in determining population trend. Data on the Pribilof fur seals (Callorhinus ursinus) lead to the speculative conclusion that the maximum sustained yield (MSY) point may be to the right of the median value frequently assumed, so that "optimal" population levels may be closer to the asymptotic or carrying capacity level. Such a view is proposed as a conservative management policy.