Are Abundant Pink Salmon Hampering Other Fish, Seabirds?

Photos by Katrina Mueller/USFWS (above; pink salmon and Dr. Greg Ruggerone (below; sockeye salmon) 


The following appears in the September issue of Alaska Sporting Journal: 


Though the smallest of salmon species, pinks appear to be taking an outsized bite of the available forage in the North Pacific and Bering Sea, and that’s affecting more prized stocks – even seabirds – according to a building body of research. 

Some experts have concluded that the huge numbers of humpies in the saltwater – as many as 500 million to 600 million in some recent odd years – are impacting both the survival and growth rate of sockeye returning to Bristol Bay, the world’s last great untouched salmon habitat. 

“Over the years we’ve published a lot of studies on this, especially the relationship between pink salmon and sockeye salmon,” says Seattle-based biologist Dr. Greg Ruggerone of Natural Resources Consultants ( Ruggerone has been studying Alaskan waters for just about 40 years, working for the University of Washington along the way. 

“Back in 2003, we published what I think was a key paper looking at how pink salmon impact sockeye growth and we documented this in part by using the pink salmon’s biennial or alternating year pattern of abundance. You can see the pink salmon’s effect on the growth of Bristol Bay sockeye salmon scales and by analyzing the length at age of returning adult sockeye.

“We looked at annual sockeye scale growth at sea back to the 1950s and discovered a very strong alternating year pattern of growth during the sockeye’s second and third years at sea. In odd-numbered years the pinks are very, very abundant in the North Pacific and the Bering Sea, and sockeye growth is greatly reduced. And in even years it’s just the opposite: there are relatively few pink salmon (around), and the growth is much better.”  

The primary pink salmon stocks that interact with Bristol Bay sockeye are those from Russia, especially eastern Kamchatka, though sockeye have a broad distribution at sea and probably interact with other pink salmon, too.

Female pink salmon photo by Katrina Mueller/USFWS

ONE OF THE MAJOR factors in the connection between pink and sockeye salmon is their diet, which is very similar on the high seas. A key source of food is zooplankton, tiny aquatic creatures that drift along in the saltwater. Since pinks are the most prolific species of Pacific salmon – comprising nearly 70 percent of all five species in the North Pacific – it becomes a numbers game for the available food options among reds and humpies. Are pinks crowding the buffet line and grabbing all the good stuff before the sockeye can fill their plates?

“Pink salmon do not directly interfere with foraging sockeye; rather they eat the same types of food, and pink salmon are exceptionally abundant compared with sockeye,” Ruggerone says. “And pink salmon grow fast, spend only one year in the ocean, and then come back at a fairly large size.”

A 2018 publication by Sonia Batten, Ruggerone and Ivonne Ortiz provides substantial new data showing the impact of pink salmon on zooplankton abundance in the southern Bering Sea, where many Bristol Bay sockeye feed. This study provides three lines of evidence for this impact, which had been previously described in less detail by Japanese scientists 20 years ago.   

“Zooplankton are very important to both species. But as the pinks and sockeye grow, like in their second year at sea for both species, they will eat much bigger prey. If you look at the diet data that (salmon scientist) Nancy Davis collected in the North Pacific and Bering Sea, both sockeye and pinks are eating a lot of the same food – a lot of fish and squid in addition to the zooplankton as they get older,” Ruggerone says. “As sockeye and pinks get older and bigger, they’ll eat bigger prey such as fish and squid that Chinook also like to eat.”

Ruggerone thinks that the exceptionally high abundance of pink salmon and the large quantity of prey consumed by them, as reflected in their high growth rate, makes pink salmon the dominant salmon competitor in the North Pacific. 

“One way to look at that is they are growing so fast. They enter the ocean with little or no rearing in freshwater as a tiny fry,” he says. “They spend one winter and then come back the next August or so at a pretty big size. So in other words, their growth rate is probably faster than the growth rate at sea of other species of salmon.”

While pinks outnumber their Chinook and sockeye counterparts in the North Pacific, they are not only not as big but are less desirable for sport anglers and foodies who have made wild salmon such a coveted delicacy. 

So in some ways, pinks might be considered villains among their more celebrated salmonid cousins. 

One of several papers Ruggerone has co-authored in his career studying Alaskan and West Coast salmon was a 2005 entry on pinks’ places as the most dominant species in the North Pacific.

“It’s not that they’re beating up on sockeye salmon or Chinook salmon. They’re just so abundant and growing up so rapidly, they have to eat lots of food. They scarf up a lot of the food like the zooplankton,” he says. “They may be the a bit lower on the trophic food chain compared to, say, Chinook salmon, but they impact Chinook in two different ways; one being simply that pinks are feeding on zooplankton, the building block for all squid and forage fishes that Chinook like to eat. And then as the pinks get older in their second year in the ocean, we see more diet overlap with species like Chinook.”

Dr. Greg Ruggerone

ONE MAJOR QUESTION THAT biologists are continually researching is whether pinks affect not only the growth rate but the survival rate of sockeye originating from Bristol Bay and other regions. In 2015, Ruggerone teamed with Canadian biologist Brendan Connors on a paper that looked at sockeye and pink salmon interaction from the state of Washington all the way up the coast to Southeast Alaska. 

The study found that British Columbia’s Fraser River had similar patterns to what’s gone on in the Bering Sea.

“We found that the size and age of sockeye salmon has been reduced during years of high pink salmon abundance. The survival of 35 populations declined consistently with pink salmon abundance,” he says. “We also incorporated oceanographic variables such as sea surface temperature. And also, there was a delay in sockeye maturation when competing with higher abundances of pink salmon, which is what you would expect; a reduction in growth can lead to a delay in maturation of salmon.”  

Consistent with these patterns, Ruggerone and colleagues also documented how pink salmon have influenced forecast error of Bristol Bay sockeye salmon since 1968. ASJ


Like his colleague Greg Ruggerone, biologist Dr. Alan Springer, research professor of marine sciences emeritus at the University of Alaska Fairbanks, has done his own research on how pink salmon are affecting sea life off the Alaskan coast. Springer’s work has an ornithological twist in relation to pinks. 

“My research has been looking for an apparent effect of pink salmon on seabirds,” he says. “We have found very strong evidence that, just as with other species of salmon, pinks negatively affect aspects of the breeding biology (such as laying date, number of eggs laid, productivity) of several species of seabirds nesting in the Bering Sea,” 

Among the birds most impacted include black-legged kittiwakes, red-legged kittiwakes, tufted puffins and horned puffins. 

“We have just published a paper where we present evidence that pinks also negatively affect short-tailed shearwaters,” Springer adds. “These birds nest in Australia and Tasmania, and spend the rest of the year (their winter, our summer) primarily in the Bering Sea. Not only are the birds affected, but so too are indigenous residents there who depend upon the shearwaters for traditional lifestyles, and the very ecology of the islands where the birds nest because of the role they play in soil aeration and fertilization that affect plant communities.” CC