Emigration of Juvenile Chum Salmon in the Elwha River and Implications for Timing Hatchery Coho Salmon Releases

摘要

The emigration timing and estuarine residence of chum salmon in the lower Elwha River were assessed using fyke netting and beach seining. Emigration was already underway by 21 March 1995, showed biomodal peaks on 1 May and 15 May 1995 and virtually ended by 12 June 1995. Freshwater rearing was believed to ocur based on increasing fork lengths of chum fry over the sampling period. A model predicting the time to maximum alevin wet weight (MAWW), and calculation of temperature units, failed to accurately estimate chum salmon emigration in the Elwah River. Difference in intragravel water temperatures at the study site versus temperatures at mainstem sampling locations monitored by Lower Elwha Tribe, and freshwater rearing by juvenile cnum salmon, likely caused the failure of these prediction methods. Only four chum salmon were caught in the limited estuary of the Elhwa River, but extensive estuarine residence is suspected based on the size of two of there fish (> 80 mm fork length). No chum salmon fry were observed in the stomach contents of 23 coho smolts and 11 steelhead smolts released from the Lower Elwha Tribe's hatchery and later caught at the mouth of the Elwha River. Although no predation was observed, the limited sample size examined is insufficient to draw strong conclusions. Delaying hatchery releases until June 1 should protect a majority of emigrating chum salmon in the Elwha River.