Population Dynamics and Age Determination in Decapod Crustaceans

Decapod crustaceans, encompassing crabs, lobsters and freshwater crayfish, are central to marine and freshwater ecosystems and underpin major fisheries worldwide. Understanding their population dynamics requires reliable estimates of growth, mortality and recruitment, yet conventional ageing has been confounded by periodic moulting, which replaces calcified structures and obscures chronological information. Indirect approaches—length-frequency analysis, mark-recapture studies and growth models such as the von Bertalanffy equation—have long been employed to infer age structure and growth parameters (asymptotic length L∞, growth coefficient K and theoretical age at zero length t₀). However, these techniques rest on assumptions about moulting frequency, cohort separation and constant growth that are not always met in the wild. Recent methodological breakthroughs have demonstrated that certain calcified elements—gastric mill ossicles and eyestalk structures—retain annual growth bands that can be validated and counted to yield direct age estimates. Integration of these direct ageing methods with population models has begun to refine estimates of longevity, mortality rates and life-history variation across diverse environments, from subtropical aquaculture ponds to polar continental shelves. Such advances carry profound implications for ecosystem modelling, stock assessment and the sustainable management of decapod resources under changing climatic and anthropogenic pressures.

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Technical terms

Ossicle: A small calcified element within the gastric mill of a crustacean, which may retain discrete growth bands used for age estimation.

Gastric mill ossicles: Paired or fused ossicles in the foregut that process food, often exhibiting annual band deposition.

Von Bertalanffy growth model: A mathematical function describing the increase in size of an organism over time, characterised by parameters L∞, K and t₀.

Intermoult period: The interval between successive moults, during which somatic growth and calcified band formation occur.

Growth coefficient (K): A parameter in growth models indicating the speed at which an organism approaches its asymptotic size.

References

1. Direct Age Determination of a Subtropical Freshwater Crayfish (Redclaw, Cherax quadricarinatus) Using Ossicular Growth Marks. PLOS ONE (2015).
2. Directly ageing the Caribbean spiny lobster, Panulirus argus with validated band counts from gastric mill ossicles. ICES Journal of Marine Science (2018).
3. 海洋深層水を使用した飼育下におけるベニズワイガニの脱皮成長量と脱皮間隔. Nippon Suisan Gakkaishi (2024).