The estimation of a mackerel (Scomber scombrus L.) spawning stock size by plankton survey

The International Council for the Exploration of the Sea (ICES)Mackerel Working Group recognises two mackerel stocks in Europeanwaters, the North Sea stock and the Western stock. From Marchto July 1977 an Anglo-French plankton survey was carried outin the shelf waters of the Bay of Biscay, Celtic Sea and westof Ireland to estimate the size of the Western stock. Sampleswere collected with a 76 cm Lowestoft pattern high-speed planktonsampler fished to a maximum depth of 100 m. The number of eggsm^–2 at each of five development stages were raised todaily production estimates with development rate coefficientsmeasured with live material collected in March. The mean numberof stage I eggs m^–2 d^–1 was raised to a total dailyproduction estimate for each month by the area within the minimumcontour level, and a production curve was drawn for the spawningseason. The total egg production was estimated at 1.98 x 10¹⁵eggs, + 30%, – 20%. With a mean fecundity of 361 000 anda sex ratio of 0.64 males per female this is equivalent to 8995 million fish.