THE EPITHALASSA OF THE STRAIT OF GEORGIA: SALINITY, TEMPERATURE, pH AND PHYTOPLANKTON

Abstract

The investigation was initiated in order to determine the extent of the Fraser River's effect on temperature, salinity, currents, and fish food, probable factors in the direction of salmon migrations. A correct valuation of the Fraser River in these respects has necessitated a survey of the Strait of Georgia waters and an estimate of the relative importance of water entering the Strait from other sources, from the sea through the passes and from other rivers. It is believed that the data presented may have a potential economic value as a basis for a further knowledge of the habits of fish, the establishment of oyster beds, the development of clam beaches and of crab and shrimp industries and the location of summer resorts. Conclusions regarding the interrelations of salinity, temperature, pH, tidal movements and phytoplankton, may be of scientific interest.The following conclusions discussed in the paper may be emphasized: (1) The Strait of Georgia is a great basin, connected with the sea by narrow passes, which receives water from a number of large rivers, notably the Fraser River. (2) The river water is conserved during the summer and forms a marked upper layer, epithalassa, which is characterized by low salinity and high temperature. The increase in temperature as compared with sea water may amount to 10 °C. or 18° F. (3) Throughout the greater part of the region this epithalassa has a stability which is sufficient to resist tidal and wave movements. (4) Since time is a factor, the heating effect of the sun, insolation, upon the epithalassa becomes most evident at regions some distance from the river mouth. In the case of a large river, as the Fraser, this distance may exceed ten miles. (5) Abundant fish food in the form of plankton is present and the amount is greatest at the regions where the most complete mixing of the river and of the sea water takes place. Evidently each water source contributes certain conditions or factors favorable for plankton growth. Further investigation to determine the exact nature of these conditions is in progress. (6) Mass movements of the epithalassa accompany tidal changes, resulting in variations of salinity, temperature and plankton at any point according to the source of the translocated water and the phase of the tide.