Publication Abstract

Estimation of fish biomass in the Irish Sea by means of the annual egg production method

Estimation of fish biomass in the Irish Sea by means of the annual egg production method

M. Armstrong, P. Connolly, M.G. Pawson, R. Nash and R. De Clerck

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 focusing 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. The quantity of mature fish in a stock can be determined using surveys to estimate the total number of eggs spawned by the stock during the year and the average number released by each female. Project AIR3-CT94-2263 transferred expertise in this method between several European laboratories and applied the method to stocks of cod, plaice and sole in the Irish Sea in 1995. The egg production estimates of spawning biomass were substantially higher than given by the catch-at-age analyses which ICES currently uses as the basis for annual scientific advice on management of the fisheries.

Reference:

M. Armstrong, P. Connolly, M.G. Pawson, R. Nash and R. De Clerck, 1998. Estimation of fish biomass in the Irish Sea by means of the annual egg production method. pp250-254 In: Third european marine science and technology conference (MAST conference), Lisbon, 23-27 May 1998: Project synopses Vol. 5:Fisheries and Aquaculture (AIR: 1990-94) European Commission DG 12 Science, Research and Development, Luxembourg.

M. Armstrong, P. Connolly, M.G. Pawson*, R. Nash and R. De Clerck

pp250-254 In: Third european marine science and technology conference (MAST conference), Lisbon, 23-27 May 1998: Project synopses Vol. 5:Fisheries and Aquaculture (AIR: 1990-94) European Commission DG 12 Science, Research and Development, Luxembourg