It’s 5am as we head out onto the outermost pier, where our trusty vessel awaits. Fog clings to the surface of the water as harbour seals play in the marina’s kelp beds below. Our team from UBC, under the supervision of Dr. Mei Sato, is on a mission to examine the impacts of food availability on killer whales residing in the Juan de Fuca strait. Mildly exhausted from our early-morning wake up, the 6 of us cram ourselves into a boat designed for 4, squeezing ourselves in amongst scientific equipment worth more than our cumulative annual salaries. Today we’re measuring the accuracy of the most expensive instrument on our boat – a special underwater sonar that will – hopefully- provide UBC’s marine mammal unit with unprecedented levels of detail.
Designer of the sonar and project lead Dr. Mei Sato describes how it works: “It [the sonar] uses four different frequencies. The lower frequencies pick up only on larger objects like salmon while the higher frequencies pick up on objects both large and small – a range that spans everything from salmon to plankton. By subtracting the small objects that show up only on the high frequency reading, we are then left with only the larger objects, at a higher level of detail than would be available had we only performed the lower frequency reading.”
Commercial and sport fishermen have been using consumer grade sonars to find fish for decades, but the accuracy of this sonar is considerably higher. The sonar is so accurate in fact, that Mei is using it to discern between different fish species – for example, to tell the difference between a chinook and coho salmon. In order to test the accuracy however, we have to validate the reading by catching the fish that show up on the reading, and checking to see if our prediction was right.
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Image via University of British Columbia.