VARIATIONS IN THE DISSOLVED OXYGEN CONTENT OF 



INTRAGRAVEL WATER IN FOUR SPAWNING STREAMS 



OF SOUTHEASTERN ALASKA 



by 

 William J. McNeil 



ABSTRACT 



Inexpensive equipment for sampling intragravel water for dissolved oxygen is 

 described. Water samples were withdrawn from plastic standpipes driven into the 

 streambed. Dissolved oxygen values representative of points sampled were ob- 

 tained from 30-ml. samples of water taken about 24 hours after standpipes were 

 placed. 



Fourfold seasonal and yearly changes in dissolved oxygen levels were ob- 

 served. Spatial differences in dissolved oxygen levels were greatest when dis - 

 charge was low and tennperature was high. 



For routine measurement of dissolved oxygen level random sampling was 

 tried and found to be satisfactory. 



INTRODUCTION 



Pink salmon (Oncorhynchus gorhuscha) and chum 

 salmon (0. keta) spend only brief periods in 

 fresh water as fry and spawning adults, but 

 their eggs and larvae commonly remain in the 

 streambed 6 to 8 months. During this period 

 mortality is influenced largely by physical 

 conditions, and a decline in quality of the 

 streambed environment may cause consider- 

 able mortality. 



Mortality of pink and chum salmon is high 

 in fresh water. Neave and Foerster (1955) 

 summarized data obtained over several years 

 on mortality observed in five British Columbia 

 and Southeastern Alaska streams. The stream 

 experiencing the highest mortality had a ge- 

 ometric mean yearly mortality of 99.7 percent, 

 while the stream experiencing the lowest 

 mortality had a geometric mean yearly mor- 

 tality of 86.8 percent. Because mortality 

 estimates were based on counts of adult 

 females migrating into the streams and of 

 their progeny migrating out of the streams, 

 it was not possible to differentiate among 

 prespawning, egg, larval, and postemergent 

 losses. There is evidence, however, that a 

 considerable portion of fresh-water mortality 

 of pink and chum salmon occurs during em- 

 bryonic development. 



Estimated mortality of chum salmon eggs 

 and larvae ranged from 75 to 95 percent over 

 a 4-year period in a controlled stream 

 (Wickett, 1952). In another experiment (Neave 

 and Wickett, 1955), eyed pink salmon eggs 

 were planted in an artificial spawning channel. 

 Approximately 19 percent were estimated 



Note.--The author is presently with the Bureau of Commercial 

 Fisheries Biological Laboratory, Auke Bay, Alaska. 



to have died prior to hatching. Mortality up 

 to time of migration was estimated to be 58 

 percent. 



Hunter (1948) excavated natural redds in 

 British Columbia streams during January 

 and found that 86 percent of the chum salmon 

 embryos and 97 percent of the pink salmon 

 embryos were dead. Natural mortality of em- 

 bryo pink and chum salmon has been observed 

 in three streams in the Hollis area of South- 

 eastern Alaska by the Fisheries Research 

 Institute. Mortality prior to hatching has been 

 observed to exceed 95 percent in certain im- 

 portant spawning areas. A high mortality during 

 early stages of development was observed to 

 occur in 1957 in association with low levels 

 of dissolved oxygen. 



Embryonic mortality has been attributed to 

 a number of causes. Wickett (1958) proposed 

 that the most important causes of mortality 

 among eggs and larvae were closely asso- 

 ciated with extreme Ioav and high stream 

 discharge. Further, the rate of oxygen supply 

 to eggs was thought to be an important factor 

 limiting survival during certain periods of 

 low stream discharge. 



The rate of oxygen supply to embryos has 

 recently received attention by a number of 

 investigators. Wickett (1954) pointed out that 

 the rate of supply is a function of the flow 

 velocity past the embryo, as well as the 

 dissolved oxygen content of the intragravel 

 water. He devised techniques and portable 

 equipment for measuring seepage rate along 

 with dissolved oxygen content. Other workers 

 (Pollard, 1955; Terhune, 1958) have recently 

 refined Wickett's method of measuring seepage 

 rate. Gangmark and Bakkala (1959) also have 



