Nursery Areas as Essential Shark Habitats: A Theoretical Perspective
Michael R. Heithaus
Abstract.—Nursery areas are widely considered to be essential habitats for sharks. While there have been many efforts to determine the locations of nurseries in coastal waters and studies of movements within these nurseries, few studies have attempted to identify the factors that influence nursery area selection and habitat use within nurseries. Such data are critical for identifying essential habitats within nurseries and determining the factors that might set the carrying capacity of these areas. Behavioral and ecological theory provides important insights into nursery area use and the definition of essential habitats. For example, simply measuring the density of animals in various habitats can lead to (1) incorrect identification of critical areas because animal density and habitat quality (or importance) do not always coincide, and (2) incorrect assumptions about the factors limiting population sizes. Food abundance and predation risk are likely important determinants of nursery area selection, habitat use within nurseries, and carrying capacity of nurseries. Currently, we know little about how these factors and the physical features of the environment (e.g., water temperature, habitat structure) influence juvenile sharks. Here, I review our current understanding of shark nurseries in a theoretical context to identify areas where future studies are required and generate testable hypotheses regarding the use of nursery habitats.