Fish Stocks of the Pacific Coast: Online Book

INTRODUCTION

Salmon - Coho

Coho salmon (Oncorhynchus kisutch) originate in streams around the North Pacific Ocean, from California and the Sea of Japan north to the Bering Strait. They are swift, active fish, a favourite of the saltwater sport fishery. Next to pinks, they probably have the most consistent life history of west coast salmon.

Juveniles are aggressive, territorial and often vibrantly coloured, with a large orange anal fin edged in black and white. They may be difficult to distinguish from chinook, with which they co-occur. In fresh water, coho feed on aquatic and aerial insects, plankton and occasionally small fish.

Migrating to sea in the spring, some male coho (jacks) will mature and return to their birthplace to spawn in the fall of the same year. The rest continue to grow rapidly, usually within 1,000 km of their home stream. In the ocean, coho feed at first on euphausiids and other plankton, and later on squid, herring, sand-lance and small fish. They return the following summer and fall to spawn in their natal streams, primarily from October to December.

As adults, coho have silvery sides and metallic blue backs with irregular black spots. Spawning males in fresh water may exhibit bright red on their sides, bright green on their backs and heads, and darker colouration on their bellies, as well as marked hooked jaws with sharp teeth.

Coho salmon remain in surface waters near the coast throughout their lives in the ocean, and are readily caught with hook-and-line gear. Prior to 1900, coho were caught using hand lines from rowboats or dugout canoes. Around 1910, powered boats were introduced and commercial trolling, as it is now known, began. Coho are now harvested in directed hook-and-line commercial and recreational fisheries throughout their second year in the ocean.

The 1920s saw the advent of gill net and purse seine fisheries directed at intercepting coho. Although there are currently no directed net fisheries for coho, a substantial bycatch occurs in gill net and seine fisheries for sockeye, pink and chum salmon. Unlike sockeye, pink and chum salmon - but like chinook - most coho are harvested in rearing areas, not during their spawning migrations. As a result, coho fisheries catch individuals from potentially hundreds of populations. Coho are also harvested in "gauntlet" and "terminal" fisheries directed at other salmon species, such as sockeye, as they return from the high seas to their natal streams. A typical coho fishery is thus a mixed-stock fishery, which poses many problems for the assessment and management of the species.

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