SEATTLE — The mass of warm water known as “the blob” that heated up the North Pacific Ocean has dissipated, but scientists are still seeing the lingering effects of those unusually warm sea surface temperatures on Pacific Northwest salmon and steelhead.

Federal research surveys this summer caught among the lowest numbers of juvenile coho and Chinook salmon in 20 years, suggesting that many fish did not survive their first months at sea. Scientists warn that salmon fisheries may face hard times in the next few years.

Fisheries managers also worry about below average runs of steelhead returning to the Columbia River.

Returns of adult steelhead that went to sea as juveniles a year ago so far rank among the lowest in 50 years.

Scientists believe poor ocean conditions are likely to blame: Cold-water salmon and steelhead are confronting an ocean ecosystem that has been shaken up in recent years.

“The blob’s fairly well dissipated and gone. But all these indirect effects that it facilitated are still there,” said Brian Burke, a research fisheries biologist with the Northwest Fisheries Science Center.

Marine creatures found farther south and in warmer waters have turned up in abundance along the coasts of Washington and Oregon, some for the first time.

“That’s going to have a really big impact on the dynamics in the ecosystem,” Burke said. “They’re all these new players that are normally not part of the system.”

Researchers with NOAA Fisheries and Oregon State University Cooperative Institute for Marine Resources Studies have been surveying off the Pacific Northwest for 20 years to study juvenile salmon survival.

In June, they caught record numbers of warm-water fish such as Pacific pompano and jack mackerel, a potential salmon predator.

But the catch of juvenile coho and Chinook salmon during the June survey – which has been tied to adult returns – was among the three lowest in 20 years.

Burke and other scientists warned in a memo to National Oceanic and Atmospheric Administration fisheries administrators last month that poor ocean conditions may mean poor salmon returns to the Columbia River system over the next few years.

“There was hardly any salmon out there,” Burke said. “Something is eating them and we don’t know what and we don’t know precisely where.”