For centuries, blueback herring swam from their home turf in the Atlantic Ocean up into the Hudson River to spawn.
   Today, with the help of a system of canal locks that make waterway travel possible past the Cohoes Falls, the herring continue their journey into the Mohawk River.
   Some make it all the way to Rome.
   But in recent years, the number of these anadromous fish — those that live in the ocean and return to freshwater to spawn — have been dwindling.
   The reason still is not clear, but researcher Karin Limburg is one of numerous scientists hoping to learn why.
   Limburg and Chris Legard, a professor and graduate student, respectively, at the SUNY College of Environmental Science and Forestry in Syracuse, joined staff from the state Department of Environmental Conservation on Tuesday for a bioassessment below Lock 7.
   Despite more than an hour of surveying, DEC aquatic biologist Scott Wells said it was no surprise that they weren’t fi nding herring.
   The small fish have been seen as far upstream as Lock 15 in Fort Plain and have likely gone even farther west, Wells said. After decades of herring runs in the Mohawk River, Limburg said scientists are only now in the early stages of studying them there.
   What’s most fascinating, she said, is the fact that fish that live hundreds of miles away in the Atlantic are fi nding areas of the Capital Region a fi ne place to lay their eggs.
   “They really represent an amazing connection between here and the sea,” Limburg said. TEAM EFFORTS
   The state DEC’s new Mohawk River Basin Program — a smaller version of the Hudson River Estuary initiative — is making use of cooperation to gather data on fish in the Mohawk River, and that’s where Limburg’s research comes in.
   There isn’t a lot of money available for studies, and the state’s resources in terms of its scientists are limited.
   With eyes on the need for data for the new Mohawk River Basin Program, the DEC is joining forces with Limburg, who has funding from the U.S. Geological Survey administered through the Cornell Water Resources Institute. Limburg, who conducted some major research on herring migration from 1999 to 2001, was willing to get involved in more research. The DEC, for its part, has staff and boats available but has limited time to crunch numbers and evaluate data from two months of bioassessments.
   So the DEC is gathering data on fish pulled up during surveying expeditions, and Limburg and her students will be evaluating the data.
   DEC aquatic biologist Scott Wells said the cooperation is important.
   He said he’s most interested in data gathered on all of the fi sh during electrofishing trips. The length, weight and general condition of the fish — which are temporarily stunned by electric shocks, studied and released — help determine the quality of the river water. The data also enable the DEC to spot any issues the health of fi sh could shed light on.
   Bioassessment trips this season began in late May with a focus on the areas around Erie Canal locks 7, 9, 11 and 15.
   Tuesday’s trip produced a healthy collection of carp, drum, brown bullhead, common carp, white suckers, smallmouth bass and one large northern pike — a wide variety of fish that Wells said is a good sign.
   “The more diversity the better,” Wells said.
   Wells said the fish in the river found this season have been healthy in the vicinity of locks 7, 9 and 11.
   But special notes were made for some fish caught near Lock 15: They appeared to be having difficulty healing from wounds, and a few had sores. That’s an indication of contamination, but the source is unclear. It could be anything from sewage fl owing into the river farther west to the effects of roadwork, he said.
   Limburg said that according to her research, the herring were so prolific in the 1800s that they numbered in the millions — people could see the annual spring run in massive numbers.
   But the herring’s numbers are shrinking in the Atlantic Ocean and elsewhere. Commercial fi shermen have to travel farther out into the ocean to find them.
   Overfishing, Limburg said, is often blamed for declining fi sh numbers. She suspects the herring, currently listed as a species of concern, could be elevated to threatened or endangered.
   “We’re worried about them,” she said.