The Regularity of the Spawning Season of Some Fishes

The spawning periods of four temperate or high-latitude fish species - Pacific sockeye salmon, herring, plaice and cod - have been examined. The mean date of peak spawning was established and it was found that the standard deviation of this mean date was low, often less than a week. For three species no trend of date of peak spawning was found; a trend towards later spawning was detected in the Arcto-Norwegian cod stock, about eight ays in seventy years. In contrast the Californian sardine was shown to spawn at very variable periods and it is likely that tuna in the North Pacific anticyclone spawned during most of the year. It is likely that production is continuous in the anticyclonic regions and discontinuous in the high-latitude cyclones; this would be sufficient to account for the differences found between the two groups of fish.