Differential Catchability by Zone, Fleet, and Size: The Case of the Red Octopus (Octopus maya) and Common Octopus (Octopus vulgaris) Fishery in Yucatan, Mexico

Abstract

Catchability (q) is a key parameter for the assessment and management of stocks because it is widely used to estimate other parameters such as fishing mortality and resource abundance. However, the common assumption in fisheries assessment that q remains constant through time, individual size, and space can mask the effect of fishing gear, or fleet, when applicable, and the behavior of the organisms, especially when different behavior can be portrayed by different components of the population structure. In the current study, the parameter q was evaluated for the octopus fishery (Octopus maya and Octopus vulgaris) in Yucatan, Mexico, using two deterministic techniques. In the first, q is assumed to be constant by size, age, and type of fleet, whereas the second technique assumes different sources of variation in q associated with the size of individuals, fleet characteristics, and fishing zone. Results suggest that q estimated using the second technique provides information that allows understanding the effect of fishing gear, fleets, and fishing sites at different levels of the population structure. Differences were observed in the patterns of q among fishing zones, with a high vulnerability of small organisms in the central and western zones of the study area throughout the fishing season, whereas the opposite was found in the eastern zone. Differences were also observed in the catchability of octopuses by fleet and species. The results suggest the presence of multiple intra-annual cohorts, which are not considered if q is assumed constant, as currently applies for the official assessment of the resources, with the corresponding fisheries management implications. The results are explained within this framework, and the potential effects of sequential externalities are discussed.