DYNAMIC RESPONSE ANALYSIS. III. A CONSISTENCY FILTER AND APPLICATION TO FOUR NORTHERN ELEPHANT SEAL COLONIES

Abstract

AbstractDynamic response analysis, a technique for determining stock size relative to the maximum net productivity level (MNPL), was applied to northern elephant seal populations from the South Farallon Islands, Año Nuevo Island, San Nicolas Island and San Miguel Island. Pup counts were used as indices of population size. The application of dynamic response analysis presented here involved some methodological innovations. We present a moving interval method which involves calculating separate dynamic response analyses for intervals of various lengths ranging from four counts to the total number available for the colony. The sign of the second order polynomial regression coefficient computed from a particular interval was used to indicate the colony's apparent status (relative to its MNPL, += above MNPL, ‐ = below MNPL) on that interval. Consistency in the sign of the second order coefficient, as the interval was moved along the trajectory, was used to determine the minimum reliable interval size. Each colony exhibited growth similar to that of a population below its MNPL. These results are consistent with recent natural history observations at San Nicolas, San Miguel and the South Farallon islands. Natural history observations at Año Nuevo Island suggest that the colony there is now at equilibrium. Thus, if our results from dynamic response analysis of the Ano Nuevo colony are correct, it appears that the MNPL may be close to the carrying capacity for these animals.