CHINOOK SALMON OCCURRENCES IN LAKE MERRITT, OAKLAND, CALIFORNIA, FROM 2021 TO 2025

Anadromous adult Chinook salmon (Oncorhynchus tshawytscha) appeared recently in Lake Merritt in Oakland, California on their final journey from the ocean to fresh water. Carcasses were monitored by a volunteer organization through a CA Department of Fish and Wildlife Scientific Use Permit. The lake is capable of supporting a broad diversity of fish, but most of the salmon entering the lake soon died, most likely as a result of their semelparous life cycle. The carcasses recovered from the lake were mostly males with a ratio of 2 males/1 female. Some individuals had spots on the lower lobe of the caudal fin (an identification character of chinooks), while others had no spots. Of the 30 specimens recovered from the lake during the 2024-2025 season, 5 were hatchery-raised as determined by the clipped adipose fin. Only 25% of fish from hatcheries are fin-clipped, suggesting that the 2024-2025 Lake Merritt fish are predominantly but not entirely hatchery-raised. Where did the other, wild fish come from? Rotary Nature Center Friends is pursuing answers to this question. We are having coded wire tags read and, potentially, isotope analysis of the ear bones (otoliths) of unclipped fish. The ratio of strontium isotopes can indicate the stream of origin, if the water from that stream has been analyzed.