NEW BEDFORD — Transformed in the 1970s from illicit drug runner to federal research vessel, the shrimp boat Gloria Michelle has spent most of its life tracking fish for science.

Visitors got a chance to tour the boat in New Bedford on Thursday, when it was docked at State Pier as part of a public outreach effort. A branch of the National Oceanic and Atmospheric Administration operates the vessel, whose home port is in Woods Hole.

The 72-foot Gloria Michelle makes three primary trips each year for NOAA's Northeast Fisheries Science Center: two, in the spring and fall, with Massachusetts state scientists to count and study fish populations, and a summer trip focused on shrimp in the Gulf of Maine. It works in coastal waters from Virginia to the Canadian border; a larger vessel does surveys offshore.

Visitors heard from crew members and scientists, toured the vessel’s living quarters, and got a look at the fishing net and a table full of fish typical of a near-shore Massachusetts catch.

“We could’ve stayed there for hours, truly,” said Tobey Eugenio, a teacher from Our Sisters’ School in New Bedford. She and two other teachers brought 17 students and a few parents. They enjoyed hearing about life on board, she said.

Matthew Camisa, a senior biologist with the Massachusetts Division of Marine Fisheries, said the crew does a 20-minute tow in each of 103 randomly assigned locations off Massachusetts each May and September. Fish get dumped onto a table, sorted into baskets and buckets, and examined.

The catch typically includes silver hake, scup, monkfish, skate, and Atlantic mackerel, among other species.

Crew members record characteristics such as length, weight, and sex, and they collect the fishes’ ear bones, which are used to determined their age, much like the rings of a tree.

“It’s pretty neat,” said Nina Shepherd, a biological technician who was showing ear bones to visitors.

The bones can reveal a lot about a fish population.

“They’re not living as long, because we’re catching the big ones,” she said.

Visitors met the vessel's second-in-command, Chris Gallagher, a member of the NOAA Commissioned Officer Corps. The corps is a little-known uniformed service whose officers train at Coast Guard Officer Candidate School and pilot NOAA's research vessels.

Trips aboard the Gloria Michelle usually include a captain and first mate from the Commissioned Officer Corps, plus two deck hands and up to six scientists.

The vessel has been collecting fish in the same way, with the same gear, for some 40 years. That consistency helps ensure reliable results, Camisa said.

“You want to be confident that any trend you see in the data, it’s reflective of what’s actually happening with the fish,” he said. “That’s the only true way of saying what a population is doing.”

The drawback to using old gear is that fishermen view the gear as out of date, according to NOAA biologist Anne Richards.

NOAA also works with fishermen on modern commercial vessels, but on the Gloria Michelle, science comes first.

"We’re not fishing for fish; we’re fishing for information,” she said.

Follow Jennette Barnes on Twitter @jbarnesnews.