Chapter 1: Ocean Ecology of Pink Salmon
Vladimir I. Radchenko, Richard J. Beamish, William R. Heard, and Olga S. Temnykh
Pink Salmon Oncorhynchus gorbuscha have the smallest body size at maturity, the lowest fecundity, and the shortest life cycle duration among Pacific salmon. However, it is also the most abundant in spawning stocks and the most widely distributed. As a biological species, Pink Salmon emerged about 5 million years ago and is likely the most recently evolved of Pacific salmon. It has a unique population structure represented by two distinct broodlines that spawn in odd and even numbered years, preventing interbreeding between broodlines. As a result, both the abundance level and genetic structure of broodlines are spatially and temporarily distinct. In turn, there are paired seasonal early and late, or “summer” and “autumn,” races with distinct morphological characteristics and spawning areas within river basins.
Mature Pink Salmon enter rivers and streams along the Pacific coast from the southernmost temperate latitudes to high-arctic areas. During feeding migrations, Pink Salmon explore and utilize food resources throughout the subarctic Pacific Ocean as far southwards as 38°–39° N. In the last few decades, the northern boundary limits to spawning Pink Salmon have gradually expanded while their abundance declined at the southern limits of spawning distributions.
Pink Salmon abundance has recently reached record levels. Since the late 1980s, Pink Salmon catch steadily increased to 400,000 metric tons (mt) for odd year broodlines, and 300,000 mt for even years. In the last six years, these figures correspondingly reached 600,000 and 400,000 mt. These record catches occurred due to favorable climate and environmental conditions, proper fisheries management, which included optimum escapements, and a large-scale hatchery propagation. About 80 hatcheries in Russia, Japan, and Alaska annually have produced about 1.4 billion Pink Salmon fry since early 1990s. There is a general understanding that Pink Salmon stock abundance will gradually decline in the future due to physical factors related to long-term climate variability.