Tidal Influence on Spawning Time of Pacific Herring (Clupea harengus pallasi

Abstract

Dates of over 17 000 records of Pacific herring (Clupea harengus pallasi) spawns from 1951 to 1986 in British Columbia were examined by tidal or lunar phases. The frequency of spawns was significantly higher during neap tides following a new moon. The effect was greatest in spawning areas close to the open Pacific and least in the inside waters of the Strait of Georgia. The mechanism of tidal influence on spawning is uncertain but may involve inhibition of spawning during periods of strong spring tides corresponding to periods of full and new moons. An association between spawning time and tidal phases requires that the annual calendar dates of spawning times change between years. A tidal cycle (or a synodic month) is about 29.6 d, and 12 synodic mo equals 355.4 d, whereas a calendar year is about 365.2 d. Therefore, the dates of tidal phases, such as the springtide, are either about 10 d earlier or 5 d later relative to the previous year. Other possible consequences of tidal influence include the timing of spawning waves and differences in size composition and egg size between waves.