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CANON Spring 2017 Expedition – Log 1

CANON Spring 2017 Expedition – Log 1

Using sound to locate prey

Meilina Dalit

Despite the early call time of 4:30 a.m., spirits were pleasant the morning of the first day of the expedition. With a great weather forecast for the next couple of days, there was little to complain about other than wishing for another hour of sleep. The R/V Western Flyer headed toward an area called “C1,” where we conducted the first CTD cast of the expedition.

A CTD cast involves lowering a “rosette” of plastic cylinders over the side of the boat to collect water samples at different depths. The rosette also carries a CTD—a device that measures the water conductivity (salinity), temperature, and depth. Throughout the next six days, we will conduct round-the-clock CTD operations in various locations in Monterey Bay. I’ll write more about these operations in future posts.

The CTD rosette on the aft deck of the R/V Western Flyer during an early departure from Moss Landing, California.

This morning, instead of making a straight shot for C1, we zigzagged across Monterey Canyon and used an instrument called a scientific echosounder, which uses sonar to detect physical or biological objects below the ocean’s surface. The presence of humpback whales near Moss Landing the day before we left gave us a good indication that the whales’ favorite prey, anchovies, might be nearby. Indeed, we did see whales and salmon fishermen (salmon also eat anchovies) during our departure.

Research Technician Jeff Sevadjian analyzed the measurements collected from the echosounder and found a strong signal of small organisms close to shore as we steamed out of the harbor; the researchers on board suspect these were anchovies.

Data collected from the scientific echosounder. The top row (38 kHz) shows the strength of the reflected sonar signal at low frequencies (used to detect larger animals); the bottom row (200 kHz) are signals reflected at higher frequencies (showing smaller organisms). The strong red lines show the signal reflected from the seafloor and each dip of the red line shows every time the ship sailed over Monterey Canyon. The dense patches of red above the seafloor line (as shown in the two left panels) are sonar signals reflected by organisms that were likely anchovies.

Schools of fish, such as sardines or anchovies, can be good indicators of hotspots—places where biological resources are highly concentrated. A major goal of the Spring 2017 CANON experiment is to gain a better understanding of ecosystem processes that influence these hotspots and biological responses by improving scientists’ ability to find and follow these hotspots using smart, autonomous instruments.