Working Group on Mackerel and Horse Mackerel Egg Surveys (WGMEGS)

SUMMARYThe Working Group addressed the problem of estimating spawning stock sizes of mackerel and horse mackerel in thewestern spawning area (VI, VII, VIIIabde) and southern spawning area (VIIIc and IXa). The annual egg productionmethod was implemented using international egg surveys completed in 1998 from 17 January to 5 July and associatedestimates of fecundity and atresia. Sampling was completed as planned, but the WG concluded that the surveys begantoo late in the year to cover fully the mackerel spawning event in the western area, and ended too early to cover fullythe horse mackerel spawning event in the western area. Spawning events for both species in the southern area were notcomprehensively covered. Egg production estimates for both species in the western area are therefore consideredminimum estimates.Estimates of egg production and of spawning biomass for both species in both areas are provided. In the western area,egg production of mackerel is estimated to have decreased by 8 % but as total corrected fecundity is estimated to havedecreased by 23 % this indicates an increase in spawning biomass of 19 % to 2.95 Million t in 1998. In the southernarea, estimated mackerel egg production has increased by 122 % from 1995 to 1998 and fecundity has increased by8 %, indicating an increase in spawning biomass of 106 %. Overall the ratio of southern:western component biomassesis revised from 15 % in 1995 to 26 % in 1998. Mackerel biomass for the southern and western components of the NorthEast Atlantic mackerel is estimated at 3.73 Million t, but is subject to revision.Estimation of horse mackerel fecundity in 1998 has not been possible. Horse mackerel egg production in the westernarea has fallen by 18 % from 1995 to 1998. An estimate of biomass of 1.4 Million t is provided on the assumption thatfecundity in 1998 was as estimated for this stock in previous years. In the southern area, estimated horse mackerel eggproduction excluding a small number of very abundant egg samples is 18.6 10 13 (s.e. 7.7 10 13). If these samples areincluded the estimate is 100.3 10 13 (s.e. 80.7 10 13).Comparison of egg staging among participating countries indicated good consistency of mackerel staging for stage Ieggs but poor consistency of horse mackerel staging. GAM- based egg production estimates for mackerel were similarto estimates calculated using the WG’s usual method. A mackerel egg survey in the North Sea is planned for summer1999 and is expected to report preliminary results by September 1999.