Fish Population Dynamic and Stock Assessment

1.3.1. Mixed stock

A mixed stock fishery is a fishery whose stock consists of fish that are of a variety of ages, sizes, species, geographic or genetic origins or any combination of these variables. Mixed stock fisheries offer a challenge to fisheries managers due to the difficulty in targeting fish of a specific type using many commercial fishing methods.

Mixed stock of a species has significant differences in morphological and biological characteristics. The mixed stock population may unite into a unit stock by gene flow.

The morphometric characters and meristic characters are to be taken for different stocks / populations of a species. Using Principal Component Analysis (PCA) statistical test, the population are to be segregated.

Mixed stock of a species is common in tropical waters. Assessment of such tropical stocks becomes difficult by using conventional models. Refinements are needed for proper assessment. The aging becomes difficult in a mixed stock of tropical species.

Usually many cohorts are released from a tropical stock; hence the assessment becomes more problematical on tropical stocks of a mixed species.

Mixed stock of a species has varied spawning seasons and the calculation of length at minimum maturity and growth gets varied.