Age-at-size relationships of the American lobster (Homarus americanus) from three contrasting thermal regimes using gastric mill band counts as a direct aging technique

Direct age determination of crustaceans has remained a long-standing challenge because all calcified structures are shed with each molt. Cuticle bands in the ossicles of the gastric mill have shown promise as age indicators. We validated the one-to-one relationship between known age and number of cuticle bands for 15 hatchery-raised juvenile American lobsters (Homarus americanus). Additionally, we applied this method to 308 lobsters from three contrasting thermal regimes in New England, USA. Band counts matched our expectations of differences in age-at-size across this thermal gradient; lobsters at harvestable size in southern New England were estimated to be 5.5 (+/- 1.5) years old compared with 7.5 (+/- 1.6) years in the Gulf of Maine. We found 81% of our band count estimates of age fell within 2 years of independent, regionally specified growth model estimates of age-at-size for lobster. Notwithstanding remaining uncertainties regarding the mechanism of band formation, our findings indicate the method may provide an independent and direct means to determine the age of individual American lobsters, which will improve estimates of essential life history parameters.