PREDATION OF ANADROMOUS SALMON FRY BY BLACK CRAPPIE IN LAKE WASHINGTON AT THE OUTLET OF ITS LARGEST TRIBUTARY

Black Crappie (Pomoxis nigromaculatus) is a widespread introduced species in the Pacific Northwest; however, little is known about its impact on native fauna including predation of juvenile anadromous salmonids. We collected diet information on Black Crappie in the south end of Lake Washington near the outlet of the Cedar River (Renton, WA), a major spawning tributary for anadromous salmonids. Black Crappie were collected for 4 y (2022–2025) from mid-February through April to coincide with peak migration of juvenile anadromous salmonids. Roughly half of the Black Crappie had consumed salmonid fry, with Sockeye Salmon (Oncorhynchus nerka) representing 89% of the total salmonid weight and 98% of the observed number of salmonid fry. Predation of Sockeye Salmon fry was commonly observed during all 4 y and generally occurred throughout the sampling period. Juvenile salmonids represented about 20% of the diet (mean proportion by weight). Opossum Shrimp (Neomysis mercedis) was the principal prey item of Black Crappie. Other major prey types included aquatic insects, zooplankton, Longfin Smelt (Spirinchus thaleichthys), and sculpins (Cottus spp.). We also collected Black Crappie diet samples from other areas of the lower Lake Washington basin (March–June) and no juvenile salmonids were observed. Instead, their diet consisted largely of Opossum Shrimp and zooplankton. In summary, Black Crappie appears to be an important predator of Sockeye Salmon fry as they enter the lake. The current overlap between the distribution of Black Crappie and Sockeye Salmon nursery lakes is limited to a few lakes but could become more of a concern for fishery managers if Black Crappie expands their distribution to more northern lakes in the Pacific Northwest.