Stock Assessment Methods used for Cephalopod Fisheries

Cephalopods are of increasing importance as a fishery resource and many species are taken in directed and bycatch fisheries around the world. Owing to the short life-cycles and variable growth rates of most cephalopods, stocks may be highly volatile, both highly susceptible to recruitment overfishing and, conversely, capable of rapid recovery. Many species have protracted spawning seasons so that multiple microcohorts may be present in the population at any one time.

Many assessment methods have been applied to cephalopod stocks, including stock-recruitment relationships (e.g. the Japanese Todarodes pacificus stock), recruitment indices (e.g. Saharan Bank cephalopod stocks), swept-area biomass estimates (e.g. Northwest Atlantic stocks of the squids Loligo pealei and Illex illecebrosus), production models (e.g. Saharan Bank cephalopod stocks), cohort analysis (e.g. Illex argentinus in the Falkland islands), yield-per-recruit models (e.g. Northwest Atlantic squid stocks), length-based cohort analysis (e.g. Dosidicus gigas in the Gulf of California), and depletion estimates of stock size (e.g. Illex argentinus in the Falkland islands).

Despite the widespread application of assessment methods, few stocks are rigorously managed, and the best example of a regulated fishery is the Falkland islands squid fishery. In contrast, although a number of assessment methods are used in the Japanese Todarodes fishery, management activities are designed to ensure harmonious operation of the industry rather than maintain stock size. Fisheries for Loligo forbesi and Loligo vulgaris in the Northeast Atlantic are mainly based on by-catches, although there is some directed fishing, particularly artisanal jig fishing in coastal waters. There is currently nd assessment and minimal management for these species, and available management options are constrained by the nature of the fishery and the generally poor quality of available data.