Photographic identification based on unique, polymorphic colour patterns: a novel method for tracking a marine crustacean

Abstract

Mark–recapture techniques are an important tool for estimating population parameters of vagile organisms. However, the application of marks (tags) to crustaceans is problematic due to tag-loss during moulting of the exoskeleton. Accordingly, we investigated the use of external colour patterns to distinguish (via photographic identification) individuals of a common marine crustacean (painted crayfish, Panulirus versicolor). Colour patterns were found to be highly polymorphic and individually unique, such that all crayfish in a sample of 59 could be individually identified. When 30 of these crayfish were recaptured after 6–36 months at liberty, colour patterns were unchanged, despite moulting during the inter-census period. It was concluded that (1) photographic identification is an effective method for tracking P. versicolor through time and space, and (2) this method of identification may be useful in capture–recapture investigations of other invertebrate species that display polymorphic colour patterns. This result is significant given the logistical, ecological and ethical problems of attaching tags to crustaceans, as well as invertebrates in general.