Rebecca Kimport, JULY 3, 2010

In a previous post, I briefly mentioned that acoustics helps Oscar Dyson scientists locate aggregations of pollock. I didn’t know much about acoustics surveying before I arrived on board but think its pretty cool.The Oscar Dyson has 5 transducers on its center board and 1 temporary transducer on the side of the center board that looks horizontally. The transducers allow us to see where the fish are. Because of where the transducers are placed, we can only see the pollock from 16m to the bottom. This means that if there are any fish between the surface and 16m they will not be detected. This is the near surface “dead zone”. At right you will see a picture of the acoustic data picked up by the transducers. Why this happens? The transducers are mounted on the bottom of the centerboard about 9 m below the water line, and near the transducer face (first 7 m), no good data are collected. Why it’s okay? Pollock tend to hang out in mid-water. Although a few baby pollock might be in the near surface “dead zone,” the majority of pollock will be in the area we are watching. There is also a bit of a “dead zone” at the other end near the ocean floor.

Why acoustics? 
Ideally, the acoustic data collection would allow us to track aggregations of pollock without actually having to fish them out of the water. All parties involved (scientists, fish, bank accounts) would benefit from this change but scientists are still in the process of perfecting this process. The Oscar Dyson is part of a fleet of five boats that was specifically designed for acoustics. Specifically, it is considered a “quiet boat” where the engine noise is decreased to prevent scaring the fish. Other acoustic projects include: Pacific hake off the coast from California to Vancouver Island (run as a joint project with Canada), herring in the northwest Atlantic, and krill in the Antarctic. Acoustics are used throughout the globe and many countries depend on acoustics for their fish surveys.

Looking in more than one direction
Along with the transducers, there is also a multibeam SONAR that produces the same information as the transducers but with a wider angle range. Scientists use this program to help separate species in the water column. The multibeam ME70 sends its signal out after the transducers information is sent and returned. They alternate about 1.5 seconds apart. Scientists around the world are working to improve this technology and we use information from a group at University of New Hampshire along with a program from Tasmania to analyze these data. Scientists utilize the multibeam ME 70 along with the transducers and fish trawling to ensure they are capturing an accurate picture of the mid-waters.

How the survey data we collect are used.
The data we collect on the Oscar Dyson during the summer pollock surveys are used by scientists and policy makers to determine the fishing quota (the “take”) of pollock for the next season. Quotas are important for maintaining the population of pollock (and other species) for this generation and generations to come. The data we collect on the Oscar Dyson help ensure that maximum stock can be taken without negatively impacting the Eastern Bering Sea pollock population.Thought Question: What could happen if we didn’t regulate the amount of fish that could be caught? Bonus points for anyone who can identify an area where overfishing has impacted the ecosystem.