The egg production of Arcto-Norwegian cod (Gadus morhua L.) in the Lofoten area estimated by egg surveys

Abstract

Spawning intensity measurements have been executed in Lofoten each year since 1976. They consist of egg net samples at selected spawning cites . In 1983, in addition, four quasi-synoptic egg surveys were conducted during the spawning ceason coverinq the total spawning area in Lofoten. These data are used to estimate the egg production during the spawning season 1983. The estimates are done by two methods. In the first method stage 1, 2 and 3 cod eggs a r e used i n eaeh survey t o qet 3x4=12 estimates of the egg production per day at different t imes during the spawning season. The 1 2 values are used to construct an egg production curve for the spawning season. The curve is integrated to get an estimate of the total egg productian. By the other method certain assumptions about the egg distribution field have to be done, and the total egg production is computed by combining the spawning intensity data with one quasi-synoptic survey. The first method is the most correc tone. The second method is more rapid and needs less ships time and time for egg analysis. It is discussed how to get the second method more accurate.