Stock assessments require estimates of reproductive parameters that are used to describe the population dynamics of the species. However, some of the estimates used are uncertain, either because of missing or scarce biological data, or because data had not yet been analyzed. On an ongoing basis OFP undertakes the data collection and analyses to reduce this uncertainty. Sustainable fisheries need continued reproductive output, and so stock assessments use spawning biomass in stock status indicators and reference points.
Past stock assessments reported on spawning biomass as the product of numbers at age, weight at age, and maturity at age. The dynamics of tuna however are more complex. The sex ratio of tuna changes with size, with maturation being an interaction between the age and size of an individual with some faster growing individuals beginning reproduction younger than slower growing individuals, and egg production increasing more rapidly with increasing length. A more accurate method for measuring spawning biomass is spawning potential because it includes age-related and sex related effects on reproductive output. This can be calculated as the product of numbers at age, maturity at age, proportion of females at age, fecundity at age, and the fraction spawning at age. The current focus of OFPs work on reproductive biology is the compilation and estimation of each of these parameters and relationships for bigeye, yellowfin, south pacific albacore and skipjack tuna.
Regional Study of South Pacific Albacore population biology: Year 2 - biological sampling and analysis
ADJUSTED BIOLOGICAL PARAMETERS AND SPAWNING BIOMASS CALCULATIONS FOR ALBACORE TUNA
REVIEW AND PROPOSED INVESTIGATION OF THE AGE, GROWTH, AND REPRODUCTIVE BIOLOGY OF BIGEYE TUNA
REVISED BIOLOGICAL PARAMETER ESTIMATES FOR APPLICATION IN YELLOWFIN STOCK ASSESSMENT
SENSITIVITY OF BIGEYE STOCK ASSESSMENT TO ALTERNATIVE BIOLOGICAL AND REPRODUCTIVE ASSUMPTIONS