PARIS — French authorities have arrested and convicted a top smuggler and his accomplice who had reigned over desperate migrants trying to sneak to Britain, earning 300,000 pounds ($390,000) a month and hiding travelers amid onions to keep police off their trail.

Across northern France, police are cracking down on smugglers profiting from migrants who fled war or poverty-stricken homelands and took treacherous journeys to reach northern France en route to Britain.

The arrests cracked the centerpiece of a lucrative network run out of Britain, where the investigation continues, according to Dunkirk deputy prosecutor Amelie Le Sant, who handled the case.

A Dunkirk court convicted Twana Jamal, a 35-year-old Iraqi Kurd known as “the Pasha,” earlier this month along with Kadir Pirout, 33. In a single month the two arranged passage for more than 80 migrants, and their monthly take was evaluated at 300,000 pounds, Le Sant told The Associated Press.

Jamal received a five-year sentence while Pirout got four years, plus fines and lifelong bans from France once their terms are served.

The people smuggling operation was out of the Grande Synthe camp outside Dunkirk, about 45 kilometers (27 miles) east of Calais, site of a massive makeshift migrant camp that French authorities plan to dismantle before year’s end.

“The arrest was a bit messy. Police officers were set upon” by migrants trying to prevent the operation, Herve Derache of the regional border police told reporters Thursday.

“The networks are indeed very well organized,” he said. He added that the smugglers are increasingly moving away from Calais and its increased security presence, to attract less attention as they try to sneak onto trucks crossing the English Channel on ferries or trains.

Authorities in the area have arrested 619 suspected smugglers so far this year, up from 586 over all of 2015, Derache said, primarily Afghans, Kurds and Albanians. He said 49,000 migrants have been caught hiding in trucks this year, up sharply from 38,000 over all of 2015.

Jamal ran his business out of the Grande Synthe camp, receiving clients and negotiating prices — usually 4,500 – 5,000 pounds for the ride in a freight truck with no guarantee of safe passage, Le Sant told the AP. Phone taps showed he brought some potential clients into the camp, providing directions.

“Pasha was a big fish … the nickname Pasha shows the place he had in the camp,” Le Sant said. “He has lots of charisma. He had a reputation.”

His accomplice, Pirout, played a crucial role as the drop-off man. He would sometimes drive migrants as far away as the Rouen area in Normandy or the Somme region south of Dunkirk “where truckers are less vigilant,” the deputy prosecutor said. Pirout would try to find the most desirable trucks — those carrying onions — or pack onions in with the migrants, to sneak the human cargo past carbon dioxide scans at the port. Onions, she said, purportedly mask the CO2 from the migrants’ breath.

Le Sant, who has handled numerous migrant smuggling cases, described another network run by Vietnamese who guaranteed passage to Britain for migrants using paid drivers. Seven were convicted in the scheme earlier this year. Those trips, in which migrants hidden in Paris were first taken to Dunkirk or nearby Belgium, cost 10,000 pounds each.

Morgane Railane and Corentin Escaillet in Dunkirk contributed to this report.