Size at first maturity and recruitment into egg production of southern bluefin tuna
CSIRO Oceans and Atmosphere Hobart
The SBT parental stock monitored through the Indonesian longline fishery has undergone changes in size structure since monitoring began in 1992. There has been some reduction in the abundance of larger size classes and more recently, the first clear sign of recruitment of small fish into the parental stock. Changes in the size distribution of the parental stock will have major effects on population egg production. Realistic stock projections to examine the medium to long term consequences of current catches on parental biomass and the probability of recovery to the 1980 levels depend on good information on the dynamics of population egg production. This requires estimates of mean size at first maturity, and an understanding of the relationships between spawning frequency, batch fecundity and size. At present we have little information on the smaller SBT that appear on the spawning grounds and it is these fish that are in the process of recruiting into egg production. The increased availability of small SBT on the spawning grounds in 1997/98 means that it is now possible to obtain reasonable numbers of small fish to determine these parameters.
1. Determine the mean size at first maturity of SBT on the spawning grounds.
2. Determine the relationship between spawning frequency and size.
3. Determine the relationship between batch fecundity and size.
4. Model the recruitment dynamics of population egg production.
Principal Investigator: Tim Davis, Jessica Farley, Mark Bravington & Retno Andamari