Catchability: a key parameter for fish stock assessment

The fishing process in a particular fishing ground involves the existence of one or more fish populations in different stages of their life cycles, with a particular behaviour according to natural or foreign challenges; their abundance depends on biological and environmental conditions and they must be captured by fishermen with sophisticated equipment known as fishing gears. This capture is known as fishing mortality and depends on the resource abundance and the efficiency of the fishing gear. The relationship between these two variables is known as catchability. In other words it measures the interaction between the resource and the predation effort. If the catch or fishing mortality is taken as an indication of population size, it is necessary to learn how representative is this catch of the whole population. The implications of such an assumption have been incorporated in the following relationship: C = sqEN or U = C/E = sqN (1) where C denotes catch, which is equal to F (the fishing mortality), U is catch per unit effort, E is the fishing intensity or fishing effort, s is a constant related to the particular fishing gear, q is the catchability coefficient, and N is the population size. The importance of the catchability coefficient cannot be overestimated.