The objectives of the project are: (1) to develop expertise in the Annual Egg Production (AEP) method in different European laboratories; (2) to obtain AEP estimates of spawning biomass of cod, plaice and sole in the Irish Sea and (3) to provide independent estimates of biomass for comparison with the results of analyses carried out by ICES Working Groups on data from commercial fisheries.
The abundance of cod, plaice and sole eggs in different stages of embryonic development will be estimated repeatedly over the spawning season by means of a series of ichthyoplankton surveys of the Irish Sea. Approximately 100 stations will be sampled during each survey. The identification of the eggs will be aided by carrying out isoelectric focussing on additional samples of eggs taken during the surveys.
Rates of egg production will be computed from the estimates of egg abundance of each species in each survey using relationships between temperature and stage duration of egg development obtained from controlled laboratory experiments. Total annual egg production and its variance will then be calculated for each species from the series of survey estimates.
Spawning biomass will be estimated from the values of total annual egg production of each species using estimates of fecundity, seasonal incidence of egg atresia, sex ratio in the population and size composition of females in the population. These reproductive parameters will be estimated for spatially separated spawning areas and for the populations as a whole, based on data and samples obtained from trawl survey programmes, surveys carried out by chartered commercial vessels, and from sampling of commercial catches, as appropriate for each species. Variances will be computed for each population parameter, and the overall variance of the biomass estimates will be obtained.
