The Dirty Secret on Burrowing Shrimp Growth: Verification of Two Alternative Methods of Age Determination in the Burrowing Shrimp N. Californiensis

The burrowing shrimp, Neotrypaea californiensis, is an important ecosystem engineer inhabiting estuaries along the Pacific Northwest coast whose populations have declined over the last decade. Information is needed about this species, including viable aging methods to assist in developing management plans. Obtaining accurate age estimates in crustaceans is difficult because they don’t retain evidence of age over a lifespan. Our study verified two aging methods, lipofuscin analysis and gastric mill rings. Each method was used on known-age shrimp and findings compared with data from wild shrimp populations. Known-age shrimp were kept in outdoor mesocosms from time of recruitment and population samples included animals collected from surveys conducted in Yaquina Bay, Oregon and Willapa Bay, Washington. Lipofuscin values of known-age shrimp related linearly to age while size varied, verifying that this method may be useful in the direct aging of crustaceans.  Number of rings correlated more directly with growth than with lipofuscin, suggesting that rings might not be a direct measure of chronological age, but rather metabolic age, which is more likely affected by environmental factors. The novel methods developed in this study may be applied to other commercially important crustacean species where methods for direct aging are not available.