Suggestions for improving the quality of estimates of the state and trends of small pelagic fish stocks off the Northwest African coast

摘要

Simple random sampling may result in biased age-composition of annual catch off the Northwest Africa. Design-based approach based on the best practical approximation to a probability sampling scheme is felt to be best for collection of basic biostatistical data. Investigated seasonal catch has to be compartmentalized into geographic and temporal sampling parts. The use of CPUE as a measure of abundance becomes more and more questionable due to diversification of the gears, vessels and commercial decisions about fishing locations and times in the area. Other abundance indices, not affected by time-related changes in fishing gear parameters, vessels and fishery management would be more acceptable. Good consistency in the results of young fish surveyswould indicate that they are a suitable source for the virtual population analysis (VPA) tuning. Despite a long series of acoustic surveys, acoustic methods still appear to be at an experimental stage in the region. The observed range of changes in the estimated biomass from year to year seems to be improbable. Nevertheless, on condition that the fitting technique is modified, the numerous data produced by these surveys are acceptable for use in the cohort analysis.