HEARD: PROBABLE CASE OF STREAMBED OVERSEEDING 



4. Survival of progeny of the 1967 spawners 

 was determined a) from stream entry to end of 

 spawning, b) from end of spawning to hatching, c) 

 from hatching to shortly before fry emergence, and 

 d) from shortly before emergence to emergence 

 and downstream migration of fry. In general, sur- 

 vival in each of these time periods was greatest in 

 the upper area, lowest in the lower area, and in- 

 termediate in the middle area, a pattern consis- 

 tent with previous survival studies at Sashin 

 Creek. Total freshwater survival from potential 

 egg deposition to preemerged fry was 107f , 79c , and 

 49c in the upper, middle, and lower areas, respec- 

 tively, and 6.8% for the entire stream. The total 

 number of migrating fry agreed closely with the 

 estimates of preemerged fry in the streambed in 

 late March. 



5. Mortality of eggs and alevins was high dur- 

 ing spawning, low between spawning and hatch- 

 ing, and high between hatching and emergence. 

 Between 1 December 1967 and 25 March 1968, 

 11.1 million eggs or alevins disappeared within 

 Sashin Creek streambed; 10.7 million of these 

 were alive on 1 December. The high densities of 

 eggs and alevins in the streambed after spawning 

 and at hatching are believed to exceed the 

 streambed capacity for fry production. High over- 

 winter mortalities appear to have occurred shortly 

 after hatching, probably from critical levels of dis- 

 solved oxygen in intragravel water. Critical oxy- 

 gen levels apparently developed under average 

 winter streamflow conditions due to the high 

 biochemical oxygen demand placed on the 

 streambed by high egg and alevin densities. 



6. Recently hatched dead alevins disappear 

 rapidly within the streambed because of biochem- 

 ical decomposition and invertebrate scavenging. 

 In comparison with dead alevins, dead eggs disap- 

 pear slowly. In Sashin Creek, insect larvae and a 

 planarian, probably Polycelis borealis, may be 

 particularly important in removing dead salmon 

 eggs and alevins from the streambed. 



7. Several aspects of the historical patterns of 

 pink salmon fry production in Sashin Creek 

 suggest that streambed overseeding occurred in 

 1967. Fry production from the 1967 spawners falls 

 on the descending limb of the fry production 

 curves, both for the stream as a whole (since 1940) 

 and for the individual stream areas (since 1961). 

 From the historical pattern of time of adult entry 

 and resulting freshwater survival, freshwater 

 survival of 1967 brood year progeny should have 



been around 18% (or a production of 8 million fry). 

 Survival of progeny during spawning and between 

 spawning and hatching was adequate to reach 

 these predicted levels. Overwinter mortalities (be- 

 tween hatching and emergence), however, were 

 higher than any previously recorded. Compensa- 

 tory losses during this period were probably due to 

 the presence of too many eggs and alevins in the 

 gravel for existing environmental conditions — 

 streambed overseeding. 



8. Overseeding does not invariably occur at 

 some precise density of eggs, but rather is a 

 dynamic interaction between densities of eggs and 

 alevins in the gravel, certain ecological charac- 

 teristics that define the fry production capability 

 of the streambed, and the prevailing climatologi- 

 cal features during the 6- to 8-mo period eggs and 

 alevins reside in the streambed. 



ACKNOWLEDGMENTS 



The following people assisted with field studies 

 on the 1967 spawners and freshwater survival of 

 the progeny: David Brickell, Robert Coats, 

 Richard Crone, Calvin Fong, Henry Kopperman, 

 Derek Poon, and Roger Winchester. 



LITERATURE CITED 



Brickell, D. C. 



1971. Oxygen consumption by dead pink salmon eggs in 

 salmon spawning beds. M.S. Thesis, Univ. Alaska, Col- 

 lege, 53 p. 

 BRIGGS, J. C. 



1953. The behavior and reproduction of salmonid fishes in 

 a small coastal stream. Calif. Dep. Fish Game, Fish 

 Bull. 94, 62 p. 



1955. Behavior pattern in migratory fishes. Science 

 (Wash., D.C.) 122:240. 



Chapman, D. W., and T. C. Bjornn. 



1969. Distribution of salmonids in streams, with special 

 reference to food and feeding. In T. G. Northcote ( editor), 

 Symposium on salmon and trout in streams, p. 153-176. H. 

 R. MacMillan Lect. Fish. Inst. Fish. Univ. B.C., Van- 

 couver. 

 CLAIRE. E. W., AND R. W. PHILLIPS. 



1968. The stone^y Acroneuria pacifica as a potential pred- 

 ator on salmonid embryos. Trans. Am. Fish. Soc. 97:50- 

 52. 



Ellis, R. J. 



1969. Return and behavior of adults of the first filial gen- 

 eration of transplanted pink salmon, and survival of their 

 progeny, Sashin Creek, Baranof Island, Alaska. U.S. 

 Fish Wildl. Serv., Spec. Sci. Rep. Fish. 589, 13 p. 



1970. Alloperla stonefly nymphs: Predators or scavengers 

 on salmon eggs and alevins? Trans. Am. Fish. Soc. 

 99:677-683. 



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