Variation of Chinook salmon fecundity between the main stem of the Naknek River and a tributary stream , Big Creek in southwestern

I estimated fecundities for two stocks of Chinook salmon Oncorhynchus tshawytscha from the same drainage in southwestern Alaska using a length based linear regression. Female Chinook salmon from the main stem of the Naknek River had a mean fecundity of 9,852 eggs per fish. Big Creek, a tributary stream, had a mean fecundity of 9,060 eggs per female. The observed difference in fecundities was found to be significant (p < 0.001). I was able to attribute this difference primarily to a difference between the size class structures of the two stocks. I also eliminated other alternative hypothesis as to why these stocks had different fecundities. I then speculated that there are selective pressures selecting for smaller spawners in Big Creek mainly due to shallow water depth. Further research is needed before this hypothesis can be validated or management recommendations can be made. Accurate fecundity estimates are important for understanding dynamics of fish populations, predicting trends in population abundance, and estimating spawning-stock biomass (Eldridge and Jarvis 1995). Reproductive potential influences the ability of a species to respond to abiotic and/or biotic stresses. Knowledge of the fecundity of a stock is needed to quantify the effects of external stresses such as fishing, on the reproductive potential of the species (Nitschke and Mather 2001). Fecundity is also of theoretical interest because the energy invested in egg production cannot be used for other functions like growth, escaping predators, or foraging (Healey and Heard 1984). In Pacific salmon Oncorhynchus spp., fecundity varies widely between species, with in populations and even more so between populations (Healy and Heard 1984).