Marine Distributions of Coho and Chinook Salmon Inferred from Coded Wire Tag Recoveries
Abstract.—The coded wire tag (CWT) database contains detailed information on millions of Pacific salmon Oncorhynchus spp. released from hatcheries or smolt traps and recovered in the Pacific Ocean and its tributaries. I used this information to compare marine distribution patterns of hatchery coho O. kisutch and Chinook O. tshawytscha salmon, based on recoveries of an estimated 1.99 million tagged salmon in coastal areas from southern California to the Bering Sea. Both species show distinct region-specific distribution patterns. Within these release regions, coho and Chinook salmon marine distributions were often similar, with fish distributed largely in local waters. In other regions, Chinook salmon were distributed father north than coho salmon originating from the same region. Only in two regions did the two species have fundamentally different marine distributions, with coho south of, and Chinook salmon north of, the natal stream. The analysis also revealed several “hot spots” of salmon diversity, identified by numerically few recoveries that represented many of the hatcheries used in the analysis. These hotspots may serve as important reservoirs for the continued existence of populations that are particularly vulnerable to climate change due to their restricted marine distributions. Although CWT technology is primitive by modern standards, the enormous amount of data collected in a consistent fashion over decades and contained in an online database provides a unique and underutilized opportunity to address many elusive questions about Pacific salmon.