Electronic deterrent for hungry harbour seals
Marcel Tetrault
Comox Valley Echo
Tuesday, April 17, 2007
New technology is currently being tested beneath the Fifth Street bridge to see if an endangered salmon run can be protected from hungry harbour seals.
The electronic deterrent device--a series of cables that are anchored across the river and emit pulses of electricity--was designed and built by Washington-based Smith-Root, Inc., a company that develops technologies for fisheries conservation.
"Based on some tests we did at the Vancouver Aquarium, we know that seals are very sensitive to electric current," said Carl Burger, senior scientist with Smith-Root. "It doesn't take much to stop them."
The device works by direct current, not the more dangerous alternating current, and produces fields of force like a magnet. The larger the animal that comes within range of the electric pulses, the more electrical field it will feel.
That is why it could be effective at deterring seals while still allowing salmon to pass by.
"Juvenile salmon won't even notice it," said Burger.
He described the effect of the field as an uncomfortable pins and needles sensation, similar to when a limb goes to sleep.
"It's very safe, very non lethal," he said. "Everybody thinks of electricity as a hair dryer being tossed into a bath tub. That's alternating current, that's completely different from direct current.
"This is a very milder form and a very safe form of electricity and we hope to be able to show that it will deter the seal predation on salmon."
Sports fisherman as well as salmon conservation groups and the Department of Fisheries and Oceans want to stop the seals from hiding in the shadows beneath the bridge created by city lights.
Seals wait in those shadows until they see juvenile salmon pass by in the lights overhead and then snatch them for a quick and frequent meal.
The ease with which the seals are able to kill the salmon due to the lighting in that area are making it very difficult for the fish produced at the hatchery on the Puntledge River to make it out to sea.
"They have a significant impact on both the out-migrating fish this time of year, and in-migrating fish in the fall," said Bruce Adkins, the south coast area director of DFO's oceans, habitat and enhancement branch.
It is hoped that the electronic device will force the seals to stay far enough away from the bridge that they will no longer be able to use the shadows to hide. The salmon will then have a better chance of avoiding the seals and making it either out to sea to grow or back into the river to spawn.
The goal is to prevent a repeat of the 1998 harbour seal cull, when about 50 harbour seals were killed for similar reasons.
"We're hoping that this will be a non-lethal method that we can use," said Adkins.
The summer chinook run on the Puntledge has been significantly impacted over the years, not only be seals but also by the hydroelectric dam, habitat degradation and increasing summer temperatures in the river.
"Seals are only a part of the picture here," said Adkins. "It's a stock of concern and we'd like to take some measures to enhance that stock more fully."
Last year, about 1,000 of the summer chinook salmon run returned to the river. For the run to be sustainable, DFO would like to see about 4,000 salmon return to the river to spawn.
Tests so far have been inconclusive because high and fast water as well as debris in the river, caused by the weather and an increased water release from the hydroelectric dam, have kept seals away from the area recently.
When they return, DFO staff will be able to determine whether the seals remain far enough away from the bridge that they can no longer hide in the shadows and fill their bellies with salmon.