The Effects of Water Temperature on the Timing of Spawning and Spat Settlement of the Yesso Scallop (Mizuhopecten yessoensis Jay, 1857) in Minonosok Cove (Posyet Bay, Peter the Great Bay, Sea of Japan)

摘要

The effect of water temperature on the timing of spawning and spat settlement of the Yesso scallop (Mizuhopecten (=Patinopecten) yessoensis Jay, 1857) in Minonosok Cove (Posyet Bay, Peter the Great Bay) has been studied based on the most complete dataset of observations for 1970-2011. The date of onset of spawning varied from May 1 to June 9 (within 40 days) and the onset of spat settlement varied from June 4 to July 5 (within 32 days). It has been found that the timing of spawning shifts to later dates due to the longer preceding cold periods with a greater accumulated sum and lower average values of below-zero temperatures, due to the short pre-spawning periods (from the date when the sea surface temperature (SST) reaches 0 degrees C to May 1) with decreased sums and low average temperatures over these periods, as well as due to the decreased sums of temperatures in April. Later settlement dates were also recorded in the years with severe winter conditions. The onset of settlement shifts to a later date also in case of low average above-zero temperature in the pre-spawning period (correlation coefficient (R) = -0.46). Early settlement on collectors was observed in the years when SST reached 0 degrees C on earlier dates in spring (at the Posyet Hydrometeorological Station). The higher the sum of above-zero temperatures was accumulated by May 1 and June 1, as well as in April and May, the earlier the scallop spat settled on collectors (R = -0.58, -0.60, -0.55, and -0.42, respectively). Prognostic equations are proposed to predict the dates of the onset of spawning and spat settlement with a lead time of 10 and 15 days, respectively; the equations are tested on the results of a correlation analysis. The accuracy of these predictions based on 10-year independent samples constitutes 70% for the spawning onset date and 60% for the spat settlement onset date.