The net could soon tighten around foreign and unauthorised boats fishing in restricted areas or without a licence around New Zealand and the South Pacific.
Several agencies, including the Defence Technology Agency, the Navy, Air Force and the National Institute of Water and Atmospheric Research (Niwa) are holding trials to seeif military sonar buoys can be used to tell if a fishing boat is trawling or towing fishing nets in restricted waters or without a licence.
The sonar buoys are dropped near the boats and send an acoustic signal through the water to bounce off fishing nets or underwater fishing gear such as the otter boards, which hold open the mouth of a net. The data is sent to an Air Force Orion flying overhead.
Sonar buoys are traditionally used to detect military targets such as submarines, but scientists hope the trials will allow them to fine-tune the acoustic reflection from nets or fishing gear to produce evidence of illegal fishing.
John Kay, from the Defence Technology Agency at the Devonport Naval Base in Auckland, said the trials might be a world first, although sonar had been used for a long time to track fish stocks.
He said the trials were still in their infancy, but it was hoped they would eventually give an Orion captain enough evidence to immediately challenge a fishing boat.
Trials with the Niwa research vessel Tangaroa, and the Navy's hydrographic survey and oceanographic ship HMNZS Resolution off the east coast of Australia this year had shown a lot of promise.
Dr Kay said that even with the Orion's infrared equipment, which could show if winches used to haul in nets were hot and had therefore been used, it was hard to tell by a visual inspection if a boat had been fishing illegally.
"But if you had an acoustic capability [to] ... look under the water, it may give us additional information about what he is doing."
The Defence Technology Agency was still assessing the data from the trials with Tangaroa last year and Resolution off Australia, he said, but results were very promising.
New Zealand has one of the largest exclusive economic zones in the world, but also has obligations to patrol and monitor fishing zones throughout the South Pacific and south to the Southern Ocean, where the highly prized patagonian toothfish is under increasing threat from poachers.
