Seasonal and Diurnal Vertical Distribution of Herring (Clupea harengus L.) in Passamaquoddy, Bay, N.B.

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Abstract
The depth of schools of immature herring in Passamaquoddy Bay was determined from echo-sounder records taken from 1947 to 1958. The records gave no information on the presence of herring between the surface and 14 ft, and any herring in this zone have been omitted from the calculations. The herring schools showed diurnal vertical movements, being closer to the surface by night than by day in every month of the year. From May until December the median depth varied from 30 to 44 ft by day and from 21 to 26 ft by night. From January to April the schools were deeper in the water by day with a median depth of 83 to 126 ft, though still rising towards the surface at night, to a median depth of 36 ft in February. No correlation was found between the mean solar radiation for the daylight hours and the median depth of herring by day in each month. Between 2° and 4–7 °C there was a significant inverse correlation between water temperature and the depth of the herring by day, but as temperature increased above 7 °C, up to 12°, there was no further decrease in median depth.