The Northern Land Council says authorities must take a tougher approach to foreign fishing vessel incursions amid an influx of boats breaching Aboriginal land and waters along the West Arnhem Land coastline.

NLC Chair Matthew Ryan called on Friday for federal and Northern Territory government agencies to work collaboratively to create stronger deterrents to curb the activity which has "increased markedly" in recent months.

Bawinanga (Djelk) Rangers spotted a foreign fishing boat hidden beneath mangroves at an intertidal zone at Maningrida last week, with its crew members swimming and wandering along the beach at Rolling Bay.

In a separate incident, community members at a mainland outstation south of Warruwi said a crew camped on the beach late last week had broken into their cars and stolen fuel and oil.

A third vessel was sighted by Garngi Rangers on the north western side of Croker Island on Sunday morning; and the carcasses of two sharks with the fins and tails removed had washed upon the beach on the east coast of Cape Croker.

The NLC's Aboriginal ranger groups regularly surveil the coastline by sea and air.

The rangers support the work of agencies such as Australian Border Force and Australian Fisheries Management Authority as well as the Australian Defence Force.

The Land Council noted on Monday that Illegal foreign fishing creates biosecurity risks and poses serious threats to the Territory's sustainable fisheries management; marine ecosystems; border security; and community safety. It is also linked to other illegal activities including organised crime and human rights abuses.

The Council previously sounded the alarm last month.

Mr Ryan said the Territory's West Arnhem coastline is being targeted by illegal fishermen because it's so close to Indonesia, and there has been "a distinct spike" in boat numbers.

"These foreign fishing crews have been camping on Aboriginal land and people in our communities are worried because they know the fishermen have a lot to lose and they don't know how far they'll go to protect their stolen stock," he said.

"Illegal fishing needs to be addressed urgently, and the NLC believes offenders should receive the toughest-possible penalties to deter this activity, which places our land and sea at great risk.

"It's not good enough to simply tell these people to leave Australian waters, we need a much stronger approach to stop them stealing our resources. Crew members of each and every illegal fishing vessel should be prosecuted.

"Our rangers are the frontline monitors of our coast and they are in an ideal position to work alongside the federal government agencies to help address this situation. That's why the NLC continues to seek better resources and more on-ground support for our rangers."