Harbour Porpoises & Weirs:
The Nature of the Interaction

The Weir Fishery
Weir fishing in the Bay of Fundy dates back to before European settlers arrived in North Amerca. Local bands of indigenous Canadians (Passamaquody and Mik'maq peoples) used weirs to catch fish for subsistence. Today, the weir fishery is a commercial industry, providing herring for a variety of purposes including cans of "sardines" produced locally and in other places. Chances are that if you live in North America and eat sardines, those fish probably came from the Bay of Fundy, and possibly from a weir on Grand Manan!

What is a Weir?
A weir is heart or kidney shaped structure built from stakes and twine net that acts to catch and concentrate fish as they move laterally along a shoreline. Fish swimming along the shore first encounter a net running perpendicular to the shoreline and alter their course to swim along it. This "fence" directs the fish into the mouth of the weir where they swim across the weir and encounter the back twine. At this point the fish again alter their course and swim along the net. The curved shape of the weir continually directs fish away from the mouth, keeping the them from escaping. When full of fish, the mouth of a weir is often shut off with another net to ensure that the fish don't escape!

Porpoises and Weirs
Although porpoises eat many different species, they feed primarily on herring in the Bay of Fundy. Weirs tend to catch the majority of their herring at night, as they move along the shoreline in relatively shallow waters. Porpoises often follow these shoals of herring into weirs and become entrapped. Sometimes they swim out, but in the majority of cases thay have difficulty finding the mouth of the weir and escaping. This is especially true if the weir is shut off.

Weir Check
Every morning staff members of the GMWSRS check the local weirs for porpoises. This is usually done in a small boat. After approaching a weir the boat is stopped and the weir is scanned for a minimum of 5 minutes - that's about the longest that a porpoise could remain submerged without surfacing to breathe. When the weir checkers are certain that there are no porpoises in the weir, they move on to the next one!

Safe Release:
Removing porpoise from weirs safely.
Development of the Program
Since 1991 the GMWSRS has worked with local weir operators to develop safe methods of removing porpoises from weirs. These methods help conserve porpoises and help scientists learn more about this threatened species - all without compromising herring catches! Weir operators receive a small level of compensation to help pay for fuel and crew costs incurred during the process!

Overview of the Release Process
When a porpoise (or porpoises) is reported in a weir, the first step is to contact the owner/operator of the weir and organize when to help get them out. In many cases this occurs when the herring in the weir are sold for market. This process is called a seine, or seining a weir. The seine process begins with fishers deploying their net (also called a seine) around the inside perimeter of the weir. They go slowly but steadlily to keep the fish in the middle of the net. When they've gone completely around the inside of the weir the ends of the seine are brought together and the bottom of the seine is closed, or "pursed." Now the herring are trapped inside and the net is slowly pulled onboard to concentrate the fish at the surface. A special boat called a herring pumper then pumps the concentrated fish from the siene into a carrier boat which then transports the fish to market. 

During this process GMWSRS staff are working to release the porpoise(s). Several staff members will bring a small boat into the weir along side the seine. Depending on the number of porpoises in the weir, one or two divers with snorkels enter the water at the perimeter of the seine. They scan the water and the net looking for the porpoise(s). As the net comes up their job is to bring the animals to the surface and over to the small boat. After the diver hands the porpoise up to the biologists in the boat, the porpoise(s) are gently layed on a soft foam mat and the boat is driven into open water clear of the weir. Porpoises are released a distance from the weir to reduce the chances of them swimming straight back in by mistake.

Outreach
With the help of our sponsers, the GMWSRS produced a manual detailing the our methods for safely romoving porpoises from weirs. A waterproof flashcard was distributed along with the manual, to help remind people of the methods during a release! The manual and card were aimed at teaching weir operators and community groups in areas other than Grand Manan how to remove porpoises from weirs safely. Both are available in PDF format for download: