Reports & papers By category Symposium on Ocean Conditions

Changes in size at maturity of salmon before and after the ocean regime change of 1976-77: management implications

John H. Helle
National Marine Fisheries Service
Alaska Fisheries Science Center
Auke Bay Laboratory
Juneau, Alaska

Salmon catches increased greatly in Alaska after the ocean regime change of 1976-77 (Fig. 1). Catches in most years during the mid 1980s to mid 1990s in Alaska exceeded the large catches in the first half of this century. I think most biologists working in the 1950s, 1960s, and early 1970s never expected future salmon catches in Alaska to surpass those banner catches of the teens through the mid-forties.

About the same time as the regime change (and this was a coincidence because nobody had recognized the regime shift until later), interest in pink and chum salmon hatcheries was rejuvenated This new interest was the result of a breakthrough in hatchery technology -- the substrate incubator. This new incubator provided critical physical support for alevins. Japanese chum salmon hatcheries had been using physical support for alevins in their alevin rearing channels since at least the 1940s. Both wild and hatchery stocks in North America as well as Asia enjoyed enormous increases in marine survival following the regime change. However, even if the North American hatchery contribution were subtracted, the catch of wild fish in the 1980s and 1990s would still have greatly exceeded those early century catches.

Along with the dramatic increase in catches of salmon in Alaska in the late 1970s and early 1980s the size at maturity started to decline. This decline continued through the early 1990s. The decline in size was as dramatic as the increase in abundance (Fig. 2). Four-year-old chum salmon at Fish Creek, near Hyder, Alaska, in the early 1990s declined in weight by about 46% compared to the same age fish in the early 1970s. Four-year old chum salmon at Quilcene National Fish Hatchery in Hood Canal, Washington also showed a sharp decline in size from the early 1970s through the early 1990s (Fig. 3). Similar declines in size at maturity were recorded in Japan. Catches of chum salmon in Asia following the regime change increased more than catches in North America during the same time (Fig. 4).

While size at maturity declined, age at maturity increased following the enormous increases in abundance in both North America and Asia. We do know that North American and Asian stocks of chum salmon intermingle on the high seas. These changes in size and age at maturity associated with large increases in salmon abundance provide evidence for an inverse relationship between body size and abundance of salmon in the North Pacific Ocean. This evidence suggests that carrying capacity for salmon on the high seas may be limited under certain conditions. And, these changes in size at maturity were not just limited to chum salmon. Most stocks of all species of Pacific salmon showed reductions in size after 1980.

Most biologists attribute the enormous increases in salmon survival in Alaska following the regime change to improved conditions in the early marine experience and in freshwater. We do know that coastal waters were warmer after the mid- 1970s and offshore waters cooler. We also know that final size at maturity, at least in chum salmon, is determined during the last two years at sea.

So, what have we learned from the regime change and all the associated changes in size, age and abundance that we can use in salmon management and run predictions? One, maybe we can learn to recognize ocean regime changes. Fish Creek chum salmon show a significant increase in size at maturity starting in 1995 (Fig. 2). Quilcene chum show a significant increase in size at maturity starting in 1994 (Fig. 3). However, the abundance of chum salmon did not show a significant decline in 1994 or 95 or 96 (Fig. 4). The negative relation between size at maturity and abundance that was clear during the 1980s and early 1990s was not evident in these years. Therefore, conditions on the high seas for growth must have changed or improved. And, in most years, trends in sea surface temperatures in the central North Pacific Ocean and coastal areas tend to be opposite. So, are we in the midst of another ocean regime change? Are we switching from warmer coastal waters to cooler coastal waters? North American chum salmon catches have remained at high levels during 1994-98. Japanese catches did drop in 1997 and 1998 however, they remain at historic high levels (Fig. 4).

Another bit of evidence that suggests that we are in the midst of an ocean change is that 3-year old chum salmon are starting to show up again in southeast Alaska during the past four years. Age composition of chum salmon in southeast Alaska has been skewed toward 4-and 5-year old chum along with a small increase in 6-year old chum salmon since the mid-1980s. Six-year old chum salmon were rare south of Prince William Sound during the 1950s through the mid-1980s.

Why the emphasis on chum salmon? I think chum salmon are an excellent "barometer" of ocean conditions. They respond to changes in ocean conditions and competition by changing their age and size at maturity and these changes are relatively easy to monitor. Chinook and sockeye salmon may also change their age and size at maturity but their freshwater life history is more complex than that of the chum salmon. Pink and coho salmon apparently have little opportunity to change their ocean age.

While Alaska and Asia were blessed with very beneficial ocean conditions for salmon survival during the mid-1970s through the mid-1990s, ocean conditions off California, Oregon, Washington, and southern British Columbia were generally not good for salmon production. It has been suggested that marine conditions for optimal salmon production are opposite between Alaska and the Pacific Northwest. Then, if ocean regimes are cyclical, marine conditions in the Pacific Northwest may improve if conditions in Alaska deteriorate. So, we may be in the midst of improving conditions in the Pacific Northwest?

What other evidence is there that ocean conditions may be improving for salmon production in the Pacific Northwest? Chum salmon runs were very strong from central British Columbia to Puget Sound, Washington in 1998. This fact may not show on the catch statistics because they were not fished in relation to their abundance because of low prices. Chinook salmon returns during the past several years have improved to southern Oregon and northern California. Chinook salmon from about Newport, Oregon, on south have a different marine migration pattern than do chinook salmon from Newport on north. From Newport north chinook salmon make a "right-hand turn" and migrate along the coast northward and westward. South of Newport chinook apparently go south and westward before they go north? So, does this mean that marine conditions are improving in the southern areas? If so, can we expect marine conditions to deteriorate in the North Pacific off of Alaska? There certainly is some indication that salmon production in parts of Alaska is changing, particularly in the most northern areas in the Bering Sea. Bristol Bay sockeye salmon returned in 1997 and 1998 in numbers much below predictions. Chum and chinook salmon returning to western Alaska, especially the Yukon River in 1998, were definitely below expectations and subsistence and commercial users suffered. A test fishery for Bristol Bay sockeye salmon operated by the University of Washington's Fisheries Research Institute reported that June 1999 sea surface temperatures off Port Moller are the coldest since 1971. The winter of 1971-72 was a record cold winter in Alaska. That could mean delays in adult salmon arrival and maybe not good conditions for the juveniles leaving Alaska streams in that area?

If conditions are improving for marine survival of salmon in the Pacific Northwest, is the freshwater habitat ready to produce large runs again? During the highly favorable marine conditions off Alaska after the regime change - mid-1970s through mid 1990s - the freshwater habitat was only mildly affected by urbanization and conflicting land use policies. That just is not true for the Pacific Northwest. Is the salmon habitat in streams and rivers of the Pacific Northwest of sufficient quality to take advantage of improving ocean conditions for the young salmon that make it to sea? What has been the impact of straying and competition from many years of hatchery "mitigation" on wild stocks of salmon? Is the genetic diversity of the remaining wild salmon populations sufficient to generate large diverse increases in salmon abundance if the ocean environment improves? The habitat issues are simpler to deal with than the more subtle genetic issues. Habitat restoration has shown some promising opportunities recently. But, time is short. How long do the favorable ocean conditions last if they are cyclical?

One of the lessons from the last 30 years that is clear to me, is, that it is especially during times of poor ocean conditions that we need to pay close attention to the health of the salmon's freshwater habitat and impacts of hatcheries on wild stocks. We need to maximize the quality and numbers of our freshwater output of salmon during the lean ocean years to make sure that we do not lose the resource or lose the opportunity to recover the resource during periods of favorable ocean conditions.

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