New Paper’s Deep Dive On Possible Pink Salmon Impact On Sockeye

Fascinating new paper published that suggests the impact pink salmon numbers are having on more coveted sockeye. Here’s some background from the Anchorage Daily News:

The new peer-reviewed paper, published this week in the ICES Journal of Marine Science, analyzed growth rates that could be deduced from the fish scales, similar to trees’ yearly growth rings.

The paper was built on a unique aspect of the life cycle of pink salmon, which are primarily targeted by commercial fishermen: Their abundance is high in odd-numbered years, and lower in even-numbered years. Those booms and busts allowed authors Peter Rand and Gregory Ruggerone to tease out whether sockeye salmon — which are more highly valued by sport and personal use fishermen — were growing at lower rates during odd years, when pink salmon are more numerous.

Their analysis showed that was the case across the Gulf of Alaska — a dynamic that Rand and Ruggerone describe as a “zero-sum game” between the two species. It found that yearly growth of sockeye was depressed by as much as 17% at times when pink salmon abundance was high.

Here’s the paper’s abstract. It was co-written by Peter Rand and Greg Ruggerone, the latter of whom discussed pink salmon’s effect on the state’s other fish and seabirds a few years back in a feature we ran.

In response to ocean heating and hatchery production, pink salmon (Oncorhynchus gorbuscha) returning from the North Pacific Ocean steadily increased after 1975, leading to concerns about their influence on food webs and competition with other species. Using measurements of distance between scale annuli of 24 584 individual sockeye salmon (O. nerka), we examined growth during their 2 or 3 years at sea from 1977 to 2015 for eight populations in Alaska. We found significant, negative autocorrelations at 1 lag year in annual growth of sockeye salmon, with a consistent pattern of lower growth in odd years, i.e. opposite to the biennial pattern of pink salmon abundance. Peak pink salmon abundances reduced growth of sockeye salmon from 7 to 14% during the second year in the ocean compared with growth when pink salmon abundance was low, while third-year growth was reduced up to 17%. The overall effect of pink salmon abundance on sockeye growth was over two times greater than the effect of sockeye salmon abundance. Production hatcheries and ocean heating contribute to the competitive dominance of pink salmon, underscoring the need to consider this unintended anthropogenic effect on the growth and productivity of sockeye salmon throughout the North Pacific.