CORRECT AND INCORRECT USE OF RECRUITMENT RATES FOR MARINE MAMMALS

Abstract

AbstractAdults of long‐lived, birth‐pulse populations (e.g., many cetaceans, polar bears and walrus) may not breed every year because of parental care, long gestation periods or nutritional constraints. Estimates of adult annual recruitment rates for such populations are necessarily an oversimplification since these rates are applied to both breeding and non‐breeding females.The weighted mean of age‐specific recruitment is insufficient for non‐stable age projections of multi‐annual populations beyond the first time interval. Restated, conventional or collapsed Leslie matrix and life‐table projections are not adequate for non‐stable age simulations of populations with multi‐annual reproduction cycles.These difficulties may be avoided by employing a parameterization that accommodates a dynamic age structure and proportion of breeding females within a given age class. This parameterization is a true description of the multiple‐year reproduction schedule.Examples, broadly mimicking the life history of polar bears, were used to identify potential qualitative errors that may occur from using overly simplified projection models.