Sonar

INFORMATION BULLETIN

NOVEMBER 2, 2012

HAIDA SALMON RESTORATION DEVELOPS NEW MULTISPECTRAL SONAR

A biotechnology company funded by the First Nations community of Haida Gwaii is pioneering their way into ocean science- using multi-frequency sonar to study open-ocean plankton ecosystems.

Innovative sonar technology used by the Haida Salmon Restoration Corporation during its first research mission has provided scientists with an improved methodology to classify and measure plankton levels in the open-ocean. The company, funded by the Old Masset Village Council, Haida Gwaii, is using leading-edge sonar instrumentation to achieve ocean stewardship. The scientific experiment was carried out this summer in a large upwelling eddy off the coast of Haida Gwaii, an area that was previously unexplored. The HSRC Senior Oceanographic Engineer, Peter Gross, facilitated the project by reconfiguring the standard design of multi-frequency sonar to provide a vastly more economical and more versatile alternative to current models.

HSRC crew attaching the multi-spectral sonar transducer to the MOCNESS © HSRC 2012

The instrument and processing software, developed and tested by ASL Environmental Services and Mr. Gross is smaller, more lightweight and much more affordable than other multi-spectral sonar. The standard device was modified to enable the acoustic signals to effectively determine the stratification of zooplankton and phytoplankton layers in the water column. Its smaller size and upgraded design allows the HSRC team to use it in numerous configurations that would not be possible with conventional sonar.

With this compact design, HSRC scientists were able to collect data consistently by mounting it directly onto sampling instruments being towed by the boat such as the Multi-Opening and Closing Net Sampling System (MOCNESS) and a winged tow body. The four frequencies simultaneously survey plankton species which can be identified by the reflected wavelengths as they travel into the net, differentiating between plankton species and other organic matter or debris floating by.

Using the sonar in conjunction with the MOCNESS is a new idea that will be used to calibrate acoustical data with the hard data of the net samples. “The purpose of this experiment is not only to measure what is in the water but to classify the type of life and how much there is.” explains Mr. Gross, “Attaching it directly onto the MOCNESS will allow us to take multi spectral sonar measurements of all biomass going in the net which we can then extrapolate to calculate how much biomass is in water column from all the previous net samples we’ve collected.” This technology, once calibrated, could eventually replace tedious net sampling techniques by monitoring, counting and differentiating species in real time. HSRC scientists hope to use this information in the future, to create an acoustic “fingerprint” database to easily identify and classify plankton species.

In addition to the MOCNESS analyses, the sonar was attached to a tow body to perform acoustical surveys of a growing phytoplankton bloom roughly 300km off the coast of Haida Gwaii. During the 3 week research mission, the sonar was towed behind the boat regularly, as well as vertically casted to survey plankton rich areas. In order to actively monitor the behavior and abundance of zooplankton, tows were executed both day and night, at a range of 300m (at low frequency) to 75m (high frequency). An accurate calculation of the quantity of zooplankton portrays growth and plankton bloom consumption thus providing a detailed perspective into the carrying capacity of this area of the ocean.

In order to aid the oceans in responding to recent phytoplankton decline, oceanographers need a better understanding of how marine food webs, nutrient cycles, and the biological pump responds to changes in the marine environment. This unique sonar technology provides HSRC scientists with a valuable insight onto the lifecycles of plankton and allows the scientific community to better represent carbon capture models in the ocean.