The Great Lakes shipping season is off to a solid start in 2017, thanks to a mild winter and an upsurge in iron ore exports.

The latest figures from the St. Lawrence Seaway indicate that total cargo shipments via the Seaway during the first six weeks of the shipping season were up 8 percent from the same period a year ago. The season began March 20.

The Duluth Seaway Port Authority is seeing that trend with increased vessel traffic in Duluth and Superior, Wis., said spokeswoman Adele Yorde.

Final April tonnage numbers are not available yet, she said, but show a similar upswing in several commodities.

"With the light ice season at this end of the lakes, we were really able to get started right on schedule," she said.

"We had some strong grain [shipments] through here already this spring, but in March particularly it was iron ore that was up significantly," Yorde said, running 45 percent more than last year for that time period.

Bruce Burrows, president of the Chamber of Marine Commerce, a binational industry group, said that U.S. iron ore pellet exports to Japan and China that started in the fourth quarter have continued this spring.

Year-to-date iron ore shipments via the St. Lawrence Seaway totaled 800,000 metric tons, he said, up 70 percent over 2016 levels during the same time.

The taconite pellets are typically loaded onto U.S. or Canadian domestic carriers at Minnesota ports and shipped to Quebec, where the cargo is transferred to larger oceangoing vessels for transport to Asia.

Road salt shipments via the Seaway between March 20 and April 30 totaled 432,000 metric tons, officials said, up 20 percent over the same period in 2016.

"Actually, it seems like the 2016 shipping season never really ended," said John Loftus, executive director of the Detroit/Wayne County Port Authority. "With the mild weather that we experienced, barge loads of steel continued in January and February with both domestic and Canadian shipments."

Shipping on the Great Lakes includes "lakers" — giant freighters up to 1,000 feet long that typically move between U.S. and Canadian ports with bulk commodities such as iron ore, coal, grain and limestone — and "salties," which move through the system and the St. Lawrence Seaway to and from foreign ports.

Overall on the Great Lakes, shipments were down about 4.5 percent in 2016, the report said. Iron ore began to pick up toward the end of the year as mining and steel production increased, but coal shipments fell by more than 26 percent.

Low natural gas prices and retirement of coal-fired power plants, especially in Canada, have caused western coal sent through Duluth to fall dramatically during the past several years.

Coal, grain and iron ore are the three largest commodity groups shipped from the Twin Ports each year, according to the Duluth Seaway Port Authority's records. In 2016, about 30 million tons of products moved to and from Duluth and Superior on 707 vessels, a decrease of nearly 8.5 percent compared to 2015.

"We're all cautiously optimistic at this end that this is going to be a stronger year based on how the year started," Yorde said.

Tom Meersman • 612-673-7388