Kartlegging av gytefeltene for norsk-arktisk torsk i Nord-Norge og beregning av eggproduksjonen i årene 1983-1985

Abstract

The population fecundity of Northeast-arctic cod were computed for the years 1983, 1984 and 1985. Repeated and detailed egg surveys were conducted at the spawning sites in Lofoten and along the coast of Troms and Finnmark throughout the spawning season which occurs in March and April. In addition eggs were sampled at selected sites at the spawning ground, spawning intensing stations, twice a week throughout the spawning season. For each egg survey maps of the distribution of stage 1 eggs (approximately 0-2 day old), stage 2 eggs (approximately 2-5 day old) and stage 3 eggs (approximately 5-7 day old) were constructed. Total number of eggs for each of the three stages were computed, and thus three independent estimates of the egg production per day were obtained for each survey. In Lofoten 3-5 survey were conducted, and the total production of eggs during the spawning season was computed by integrating by time the data from the eggs survey throughout the spawning season. At those spawning fields where only one or two egg surveys were conducted, the data from the spawning intensity stations were used to construct the time integration function. The results show that 40% of the eggs are spawned in the Lofoten area. Important spawning fields are also located close to the coast of Troms. In addition several off shore spawning fields are found off the coast of Lofoten. Peak spawning in Lofoten occurs during the first days of April and show very little variation between years. The peak spawning is showed to be delayed with about 14 days at the northernmost spawning field. The egg production estimates for the three years are compared with acoustic estimates of the spawning stock in Lofoten (GODØ, NAKKEN, RAKNES and SUNNANÅ 1983, GODØ, NAKKEN and RAKNES 1984 and GODØ, RAKNES and SUNNANÅ 1985), and the two sets of data agree fairly well. The mean individual fecundity estimated from these data was 1,4x10 eggs, which agrees very well with fecundity measurements for the Lofoten area made by SOROKIN (1961).