The 2018 Bristol Bay sockeye salmon forecast is for a chart-topping 51.3 million fish and a harvest of over 37 million.

That compares with a 2017 forecast of 40 million sockeye, although the run came in 42 percent above forecast and the harvest of 37.7 million fish was 37 percent above forecast, the second-largest on record.

Greg Buck, Bristol Bay area research biologist for the Alaska Department of Fish and Gama, said data collected in 2017 helped inform the 2018 forecast.

“Last year we had some really spectacular returns from a couple of different brood years, particularly 2013 in the Nushagak district,” he said. “Really kind of set records in the Nushagak and Wood Rivers for 1.2’s (fish that spend one year in fresh water and two years in salt water), and that tees us up nicely for Nushagak River 1.3’s.”

He added that the 1.3 year class can be about three fourths of that run.

“If that brood year continues to perform as well as it did last year, we could have another really large year.”

Buck said that there is a record amount of uncertainty in the forecast because “we are literally off the edge of the map” with these returns.

“It’s quite hard to say whether it continues to go up or at what point it rolls over and dies.”

He said the Nushagak set records last season with a 20 million sockeye return, and there is a “non-trivial” chance that will happen again.

He added that there is no conventional wisdom that has coalesced around the cause of the large returns, and that it could be a combination of reasons.

“Most of it revolves around either better smolt out-migration (due to early break-up), better survival post smolt, or better smolt productivity. Something that somehow got that brood year group over the traditional hump of that great limiting step of early marine survival somehow worked really, really well that year.”

Historically, sockeye salmon runs to Bristol Bay have been highly variable. The Bristol Bay total run has averaged 33.8 million from 1963 through 2017 and has averaged 42.7 million fish during the most recent 10-year period.

ADF&G has used similar methods since 2001 to produce the Bristol Bay sockeye salmon forecasts, which have performed well when applied to Bristol Bay as a whole, but not quite as well when applied to individual rivers.

Cristy Fry can be reached at realist468@gmail.com.