Scientists hope a network of Canadian-built sensors capable of tracking marine life for almost 200 km starting from Halifax harbour will provide a better understanding of what lies beneath the surface of the world's oceans.

Researchers at the Ocean Tracking Network announced Friday they had launched a method of keeping tabs on marine animals — from species as small as salmon to those as large as whales.

"Marine ecosystem management is something we're starting to talk about now, but the truth is we know almost nothing about what's going on at the bottom of the sea and even less about the animals that live there," said Ron O'Dor, a Halifax marine biology professor and a senior scientist at the Census of Marine Life, an international network of researchers compiling a comprehensive inventory of ocean life.

"Animals do a lot of things you might not imagine they did," he said.

The $168-million project, headquartered at Dalhousie University, has so far placed almost 30 acoustic receivers on the sea floor that can track the movements of fish and other animals that have been fitted with special tags made by Halifax-based sensor company VEMCO.

The receivers are listening for signals from tagged fish along the first 22 km of the OTN's Halifax Line, which will soon extend 170 km to the continental shelf.

The hope is it will eventually be rolled out to 14 regions around the world.

The project is an effort to marry the precision and data collection methods of larger-scale ocean observation with the specific research of animal tracking, providing a link between the larger studies of climate change and ocean ecology with the more practical efforts at fish management.

O'Dor said his interest in the big picture stems from his research of cephalopods, or squids.

O'Dor found that as larger predators like tuna disappeared from ecosystems, squids — the next marine animals in line in the food web — were more likely to thrive. Likewise, warming waters seem to encourage squids to populate more northern coastal waters.

"I said at one point that to attract attention to the issue we should put out a cookbook of the future for the ocean and have all the recipes be for squid," he said.

But further understanding the squid — or any animal's role — in marine ecosystems requires a more comprehensive approach to monitoring them, he said.

The sensors and tags act in a manner similar to radio frequency identification tags used in shipping and inventory technology. The sensor sends a signal out, and when this signal reaches the tag, the tag will respond with a return signal that passes information about the animal to the sensor.

He said researchers are also working on another type of tag that can pass and record information from animal to animal, allowing scientists to record the interaction between predators and prey on the tags.

"This would allow use to find out everybody a shark, for example, met as it travelled across the ocean," he said.

"It lets us know who is meeting who and who is eating who."