The model has four or fewer parameters, the estimates of which are almost invariably statistically stable. Special cases of the model include not only asymptotic growth, but also linear, quadratic, or exponential. growth. A model analogous to the Schnute model proposed by Baker et al. 1991 allows the use of growth increment data from mark–recapture studies to model growth if one of the parameters, usually the starting age, is specified beforehand. Although it would seem of value to employ growth-increment models to validate age-length. estimates of growth, Francis 1988 cautions that age-length models are age-based whereas growth-increment models are length-based, and therefore the two techniques describe different population parameters. However, comparison of growth models that use between-annuli, growth-increment measurements with those that use growth-increment measurements from actual mark–recapture data could circumvent this problem. Once validated, between-annuli growth-increment measurements can serve as a surrogate for growth-increment measurements from mark–recapture methodology and can therefore reduce field time. Mark–recapture methods require the expenditure of time and resources to mark individuals, suffer from the risk of data loss from the mortality of marked individuals or tag loss, and require at least two visits to the field site over the course of at least one year to monitor growth. The annulus growth-increment method requires only one visit to the field when mussels are collected or measured in the field. The method also allows for the comparison of historical growth rates using growth-increment data from geologically preserved assemblages of shells. We report here the results of a comparison of the length-at-age and growth-increment Žversions of the Schnute model applied to the same collection of mussels Mytilus .trossulus Gould 1850 from Prince William Sound, bordering the Northern Gulf of Alaska. We address the problem of using models based on mark–recapture data to validate age-length estimates of growth with the aid of a growth-increment model based on interannular distances on mussel shells. To our knowledge this is the first attempt to model growth in any invertebrate by comparing size-at-age and size-increment versions of the same general growth model in the same population.