Biological Basis of Maturation and Spawning Waves in Pacific Herring (Clupea harengus pallasi)

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Abstract
Maturation rates (measured as the change in the gonosomatic index (GSI) with time) over the last month of the annual maturation cycle were estimated for male and female herring in British Columbia, [Canada], between 1982-87. The data were analyzed to determine interannual and interregional differences in the maturation rate and its influence on spawning time. The data also indicated that in some areas herring spawned in discrete waves- the largest fish tended to spawn first and the smaller fish in subsequent waves. Each spawning wave lasted about 5-6 d and the interwave interval varied from 8-26 d in the Strait of Georgia. General equations were developed to describe gonadal growth over the entire maturation cycle. These equations accounted for the observed differences in: (1) the maturation rates between the sexes (males initially mature faster), (2) the interregional and interannual variation in the tinning of spawning (herring tend to spawn later at higher latitudes, and earlier than normal when its warmer), and (3) provide an explanation for spawning waves. All of these phenomena derive from the fact that the instantaneous rate at which the gonad grows during the maturation cycle in both sexes depends on the weight of the fish, and the daily sea temperature.