Abstract

Size-at-age data are critical for understanding the life history of marine organisms, with relevance for fisheries management. Direct aging of crustaceans has been difficult, as they grow by ecdysis of their exoskeleton and it was believed that this process resulted in the complete loss and replacement of all hard structures. Recently, the discovery of banding in the gastric mill ossicles of several decapod crustacean species suggested a promising method for direct aging, and case studies of the Caribbean spiny lobster, Panulirus argus, have shown correlation of band numbers with size and known age. We therefore applied this method to P. argus sampled from the local fishery in Bermuda. Banding was consistently identified in all ossicle structures of the gastric mill plate, however the zygocardiac ossicles had more distinctive banding than the ptero- and meso-cardiac ossicles. Band counts were reliably reproduced by independent readers, and banding patterns give a plausible estimate of age when compared to carapace length. The highest band count observed was 11, in a female with a carapace length of 138 mm. The data indicate larger size at age and faster growth for males relative to females, concurring with established research and observations of size dimorphism in the landed catch. Importantly, there appears to be considerable variation in size-at-age for both male and female lobsters, implying that size -frequency is not necessarily a reliable proxy for demographics. This study suggests that directly aging P. argus in Bermuda using ossicle band counts is feasible, and can be used to inform local fisheries management.

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