HEARD: PROBABLE CASE OF STREAMBED OVERSEEDING 



Table 5. — Potential egg deposition, number of live and dead eggs and alevins, ratio of live to combined live and dead eggs and 

 alevins, and estimated survival of 1967 brood year pink salmon in three areas of Sashin Creek. 



Area 



Potential egg deposition 

 per square meter 



Mean 

 3,947 



3,672 



2.644 



90°o confidence 

 limits of mean 



Period 



beginning 



10 Aug 



and ending 



Combined live and dead eggs 

 and alevins per square meter 



QO^o confidence 

 Mean limits of mean 



Percentage of live to combined 

 live and dead eggs and alevins 



Mean 



90°o confidence 

 limits of mean 



Percentage 



calculated 



survival 



Upper 



Middle 



Lovi/er 



::;201 



:187 



:136 



Table 6. — Percentage of estimated survival of 1967 brood year 

 pink salmon eggs and alevins for three time periods in three 

 areas of Sashin Creek and for the entire stream, 1967. 



' Data weigfited and adjusted to include spawning grounds not included in tfie 

 three study areas 



completed. Relatively few fry migrated 

 downstream through the weir until mid-April; the 

 daily fry migrations increased steadily through 

 late April, reached a peak in early May, then de- 

 clined rapidly, and were essentially completed by 

 early June (Figure 1). The total number of pink 

 salmon fry estimated to migrate from Sashin 

 Creek from the 1967 brood year spawners was 3 

 million. Similar close agreements between esti- 

 mates based on densities of preemerged fry and 

 those based on number of fry counted at the weir 

 have occurred in previous years (McNeil 1968). 



The 3 million fry migrating from Sashin Creek 

 in the spring of 1968 represent a total freshwater 

 survival of 6.8'''!^ of the 44.4 million potential egg 

 deposition. This is the lowest freshwater survival 

 in the odd-year line of pink salmon spawners in 

 Sashin Creek since 1949 (Table 1). I will sub- 

 sequently attempt to show that this reduced sur- 

 vival was primarily due to excessive seeding of the 

 streambed during spawning. 



DISAPPEARANCE OF EGGS 

 AND ALEVINS 



To determine the number of eggs and alevins 

 that disappeared from the streambed, I compared 

 the potential egg deposition with the numbers of 



live and dead eggs at the end of spawning and the 

 number of eggs and alevins at the time of hatching 

 and just before emergence. In 1967, 55% of the 

 potential egg deposition disappeared during 

 spawning. The fate of these eggs is unknown, but 

 they were probably removed from the stream dur- 

 ing the spawning period by predators, scavengers, 

 or turbulent streamflow. McLarney (1967) and 

 McNeil ( 1968) discussed the roles offish predators 

 (especially sculpins) and water turbulence in re- 

 moving eggs from Sashin Creek during spawning 

 and between spawning and hatching. 



McNeil ( 1968) found that eggs and alevins of the 

 1963 and 1965 brood years disappeared at differ- 

 ent rates in the upper, middle, and lower study 

 areas of Sashin Creek. Most of the 1963 brood year 

 progeny disappeared during spawning, and most 

 of the 1965 brood year progeny disappeared be- 

 tween hatching and emergence (over the winter). I 

 will examine closely the possible fate of eggs and 

 alevins during this period (December to March) 

 because the factors that caused a reduced freshwa- 

 ter survival of 1967 brood year progeny prevailed 

 during this period. 



The estimated percentages of the potential egg 

 deposition that disappeared in the upper, middle, 

 and lower areas of Sashin Creek were similar 

 within each of the three periods. This disappear- 

 ance varied greatly between periods: 55% of the 

 progeny (eggs or alevins) had disappeared by 1 

 October, 4% between October and December, and 

 25% between December and March (Table 7). The 

 disappearance between hatching and emergence 

 (December and March) appears more significant 

 when expressed in terms of numbers present in 

 December; 56-65% of the eggs and alevins in the 

 upper, middle, and lower areas of Sashin Creek on 

 1 December had disappeared by 25 March (Table 

 8). 



573 



