A Birth-Interval Model for Estimating Cetacean Reproductive Rates from Resighting Data

Three approaches are examined for estimating reproductive rates from data on multiple resighting of distinctly marked animals. The three approaches correspond to parameter estimation for three population growth models. Two of the approaches. parameter estimation for the Leslie matrix and geometric serin models. are based only on known-aged individuals. A third approach. the birth-interval model. is developed making fuller rue of available information. The birth-interval approach uses only known-aged individuals to estimate the first-binh ogive and uscs all females with previous births to estimate the probabilities associated with various birth intervals. A Monte Carlo simulation is rued to examine the bias and precision of the three methods p e n the quantity of data that is usually available in a multiple resighting study. All three approaches appear capable of giving unbiased estimatn of population growth rate. The variance d a t e d with such estimates is greatest for the Leslie model. leu for the geometric series model and least for the birth-interval model.