SURVIVAL OF EGGS AND ALEVINS 



Estimates of survival of eggs and alevins in 

 this i)a|)er pertain to three periods in the fresh- 

 water hfc of 1965 hrood year pink sahnon: 



Period Months 



1. Egg deposition (hite August through 



Septen\ber) 1.3 



2. Egg deposition and hatching (October 



through mid-November) 1. 7 



3. Hatching and fry emergence (late 



November into lale March) 4. 2 



Total 7. 2 



Survival in the nth [)eriod is calculated by: 



«i • S2 • ■ • S„=S (1) 



>5n = Q Q (2) 



The symbol S is total survival from beginning 

 of spawning to any selected date, and an estimate 

 of S (S) must account for dead eggs and alevins 

 that may have disappeared from the population 

 before the date of sampling. The estimate must 

 also give a value 6"< 1.0. To satisfy these reqvure- 

 ments, the estimate of survival is calculated from: 



1 _^ t 



Sy-~ "i^ (3) 



with the condition that 

 1 * 

 ^^<1.0 (4) 



In equations (3) and (4), 



i designates an individual sampling {i= 1 to k), 

 j designates an individual area (j=l to 3), 

 Qfi is the number of live eggs and alevins 



collected at the ith point of the jth area, 

 T,j is the total number of eggs and alevins 



(live and dead) collected at the ?th point 



of the jth area, 

 Cj is the average potential egg deposition in 



the jth area, and 



A 



Sj IS an estimate of S for the jith area. 

 578 



For the case where 

 1 ' 



ej 

 equation (8) reduces to 



<1.0 



1 ' 



^>j= 



ei 



(5) 



I used equation (5) in an earlier pa|)er (McNeil, 

 1966) to estimate survival of i)ink salmon in 

 Sashin Creek. 



The a\i'i-iige density of eggs and uknins was 

 estimated in earh area from sani])les obtained with 

 hydraulic sampling ccpiipnient described by Mc- 

 Neil (lJ)64a). The jwints sampled, each repi-esent- 

 ing 0.1 m.- of tlie streaniln-d, were selected ran- 

 domly witiiin the three study areas witii tlie aid of 

 tables of random numbers. Eggs were collected 

 aftei- spawning (September Lii1), and eggs and 

 ale\ ins were collected during liatcliing (No\ember 

 '20) and before emergence (March 2G). 



In calculating Sj (equation 3 or 5), I assumed 

 lliat (lie number of eggs collected at each point was 

 '.)'■> percent of the numl)er actually pi'esent at the 

 time of sampling (McNeil, 1964a). Potential egg 

 dejjosition was c^Uculated by nnih iplying the aver- 

 age fecundity by the estimated average munl>er of 

 females tliat liad spawned per square meter (table 

 3). The average tWundity, based on '20 randondy 

 selected unsi)awned females taken at the weir on 

 the four dates females were tagged, was estimated 

 to be 1,78'2 eggs. 



Estimates of sur\ ival from August 20 (l>egin- 

 ning of spawning) to September 29, November 20, 

 and March 26 are given for each area in table 5. 

 These estimates were calculated directly from equa- 

 tion (3). 



The estimated munber of eggs per sipiare meter 

 in the middle area at the end of spawning was 

 greater than the estimatetl potential egg deposition 

 (table ;')). Two soui'ces of error could have con- 

 tributed to this discrepancy: (1) I'otential egg 

 deposition may have been undei'estimated, or (2) 

 tlie number of eggs at the end of spawning may 

 have been o\erestimated. 



The use of an area by spawning salmon can be 

 indexed in two ways — directly by observing the 

 density of spawners (table 3) and indirectly by 



T'.S. FISH ANI> \Vir,l>I,IFK SKKVICK 



