CONVEX PROFILE 



CONCAVE PROFILE 



SPAWNING BED 



Figure 1. — Changes in direction of interchange with 

 changes in curvature of the stream bottom (from Vaux, 

 1962). Arrows indicate direction of interchange. 



The temperature of intragravel water in pink 

 salmon spawning beds is controlled largely by 

 stream water temperature. Sheridan (1961) 

 obtained a linear correlation coefficient of 0.99 

 when he related intragravel and stream water 

 temperatures. 



Pink and chum salmon embryos and larvae 

 survive in streams where water temperatures drop 

 to 0° C. James (1956) reported water tempera- 

 tures slightly below 0° C. in pink and chum salmon 

 spawning streams. In an experiment with pink 

 salmon embryos, Combs and Burrows (1957) 

 varied water temperature to coincide with varia- 

 tions observed in Sashin Creek, Southeastern 

 Alaska. They found that embryos reared at 

 5.5° C. for 30 days and then at 0.5° C. to hatching 

 had almost no mortality. 



Information is lacking on tolerance of pink and 

 chum salmon eggs and larvae to high tempera- 

 ture, but studies with other salmonid species 

 suggest that temperatures of 15° C. or higher may 

 be tolerated. Chinook salmon embryos exposed 

 to 20° C. water died at all developmental stages, 

 while embryos exposed to 17° C. water died only 

 at hatching (Donaldson, 1955). Larvae of Atlan- 

 tic salmon, Salmo salar, and brown trout, S. trutta, 

 survived 16 days in 20° C. water (Bishai, 1960). 



Pink and chum salmon normally spawn on 

 declining water temperature after maximum sum- 

 mer temperatures. Sheridan (1962b) reported 

 that pink salmon typically spawned in South- 

 eastern Alaska streams after water temperatures 

 declined to 10° C. or less in late summer. Mean 

 water temperature in Hook Nose Creek was 

 reported to be 12° C. or less when pink and chum 

 salmon spawned (Hunter, 1959). It would appear, 



therefore, that high temperature seldom exerts a 

 direct lethal stress on pink and chum salmon eggs 

 and larvae. 



DISSOLVED OXYGEN SUPPLY 



Oxygen is transported to the embryo by diffu- 

 sion. After water hardening, the capsule of a 

 newly fertilized egg is permeable to oxygen mole- 

 cules but impermeable to water molecules (Krogh 

 and Ussing, 1937). 



The oxygen consumption rate per unit mass of 

 embryonic tissue appears fairly constant over most 

 of the developmental period. During the last 

 two-thirds of the period, the oxygen consumption 

 per gram of embryo remained almost constant for 

 Atlantic salmon (Hays, Wilmot, and Livingstone, 

 1951). The rate of oxygen consumption for chum 

 salmon was highest but variable during the first 

 one-third of the developmental period and fairly 

 constant thereafter (Alderdice, Wickett, and 

 Brett, 1958). 



The rate at which oxygen is consumed by salmon 

 embryos decreases with decreasing dissolved 

 oxygen content of the water below a certain "limit- 

 ing level" while at dissolved oxygen levels higher 

 than the limiting level, the rate is independent of 

 pressure or content of dissolved oxygen. The 

 limiting level corresponds to the dissolved oxygen 

 content or partial pressure below which normal 

 metabolic functions are affected. There is evi- 

 dence, also, that the limiting level may vary in a 

 complex manner with temperature and stage of 

 development (Lindroth, 1942; Hays, Wilmot, and 

 Livingstone, 1951). 



Alderdice, Wickett, and Brett (195S) calculated 

 theoretical values of the limiting dissolved oxygen 

 level for chum salmon embryos by using an equa- 

 tion originated by Harvey (1928) and later 

 modified by Krogh (1941). The equation is 



C D = 



SKT 



(1) 



where delimiting level of oxygen dissolved in the 

 external medium in atmospheres 

 i?=radius of the egg in cm. 

 S=ml. of oxygen consumed/g. of embryo/ 



minute. 

 T= thickness of the capsule in cm. 

 U= diffusion coefficient of oxygen through the 

 capsule in ml. 2 /cm. 2 of surface/cm. of 

 thickness/minute. 



.SPAWNING BED ENVIRONMENT OF PINK AND CHUM SALMON 

 774-711 O— 66 14 



497 



