NOAA Teacher at Sea
Aboard NOAA Ship Oscar Dyson
July 1 – 21, 2018
Mission: Pollock Acoustic-Trawl Survey
Geographic Area of Cruise: East Bering Sea
Date: 8 July 2018
Weather Data from the Bridge
Latitude: 66 N
Longitude: 166 W
Sea Wave Height: 2ft
Wind Speed: 25 knots
Wind Direction: SW
Visibility: 15 miles
Air Temperature: 52°F
Barometric Pressure: 1010.61 mb
Science and Technology Log
Although July has just begun, teachers are already anticipating the first day of school. Like every science teacher, we launch our classes with the “Nature of Science” or the “Scientific Investigation.” Unlike past years, I plan on contextualizing these topics by showing my students the “scientific investigation in action” by describing how scientists aboard the Oscar Dyson studying eastern Bering Sea pollock populations apply the scientific method in their research.
To better understand how scientists “do science,” I had a conversation with Dr. Patrick Ressler, our Chief Scientist, about this topic. Dr. Ressler has been involved with the Pollock Acoustic Trawl Survey for many years and stresses that this ongoing research is a way to monitor change over time with pollock populations and to set quotas for commercial fisheries. He shared his ideas about science and how it is a way to understand natural phenomena through testing. In biological research, however, it is harder to assess the outcomes because of the potential effects of outside factors. That is why scientists refine their experiments to get “closer to the truth.” Even being “wrong” about some ideas is beneficial because it facilitates opportunities to learn more. Scientists give testable ideas, or hypotheses, the chance to be wrong through repeated trials.
It was a circuitous path that Dr. Ressler took to become a scientist. He studied environmental science and creative writing as an undergraduate, but after a semester abroad learning nautical science, he decided to study oceanography as a graduate student. For his graduate studies, Dr. Ressler focused on acoustics and has worked on Pacific hake populations along the west coast of the U.S. For the past 16 years, he has worked with NOAA as a Chief Scientist whose responsibilities include being a point of contact between the ship’s commanding officer and the management supervisor on land. He has supported NOAA’s Teacher at Sea program because he feels that a good science teacher can better cultivate and inspire future scientists.
The scientists on the Oscar Dyson have varied academic specialties, yet they are collaborating on the Pollock Acoustic Trawl Survey by contributing their expertise. Dr. Ressler and Dr. Chris Bassett have been monitoring the acoustics on this expedition. The acoustic system was most patiently explained to Joan and me by Dr. Bassett.
On the Oscar Dyson, there are 5 transducers producing vibrations on the drop keel of the boat. Cables are attached that can lower this drop keel to 9.2 meters below so that storms will not interfere with the acoustics. These cables connect the drop keel to the five boxes in the survey room. Voltage signals are sent to the transceiver, which in turn creates a pressure wave. When the signal is sent into the water, some sound bounces back. The pressure waves reflected back to the transducer are converted to an electrical signal and recorded by the computer. For the sound wave to scatter off something, it must have a density or sound speed different from that of the surrounding water. The larger the differences in the properties of the animals from the surrounding water, the more sound will generally be reflected by an animal. As a result, animals with ‘swim bladders’ (an organ inside their body containing air) will generally scatter more sound than animals without them.
When one of the transducers sends out a wave, the wave spreads out as it moves from the ship and it may encounter fish. To assess the number of fish present, the total amount of acoustic energy, the volume of water, the range, and the echo expected from a single fish must be measured or estimated.
The acoustics translate into an ongoing screen display which is observed by both Dr. Ressler and Dr. Bassett in the acoustics lab. The data displayed allows the scientists to decide whether a net sample is needed.
These scientists adhere to the scientific method so that they can make strong conclusions about their data. The acoustics portion is but one part of this ongoing research. The trawls, after which we measure the length and mass of each fish, is a means of supporting the data from the acoustics portion. There are also cameras attached to the net so that the scientists can verify the type and abundances of fish species at each sampling transect. By corroborating findings in acoustics with the data from the trawls, these scientists can use their combined data to give greater insight on pollock populations and abundances.
I am in awe of people who do what they love for a career. The scientists with whom I spoke convey their passion for their areas of expertise and are willing to share their knowledge. These scientists have made me aware of outside resources so that I can learn more about the topic. Collaboration is evident among these scientists as each works to illuminate an aspect of the pollock population. Together, their work sheds light on pollock dynamics.
Scientists aboard the Oscar Dyson participate in the Pollock Acoustic Trawl Survey research as well as projects of their own. Sandi Neidetcher, a research fishery biologist at the NOAA’s Alaska Fishery Wildlife Center, is investigating the reproductive biology of pollock and cod. According to Sandi, the reproductive biology of pollock is important for assessing the stock. By carrying out data collection of pollock length and otolith analysis, scientists can determine whether 50% of the stock is mature. For pollock, using the otolith analysis is a good indicator of age. Otoliths are made of calcium carbonate and are found in the fish’s inner ear and otoliths have annual growth rings, which allows for scientists to accurately assign their ages. Since pollock is a commercial fish, it’s important to know how many of the fish are capable of reproducing and using this data, set quotas commercial fishing. Another facet in researching pollock populations is determining where and when pollock spawn as well as the frequency of spawning. Sandi has been studying pollock, in addition to other commercially caught species, for many years as a commercial fishery observer. Currently, she is sampling pollock ovary tissue to determine fecundity, or fertility, of the population for stock assessment.
Sandi advises high school students who think they’d enjoy this type of career to get a college degree in biology. She also encourages them to network and apply for internships. Effusive when recounting her career in research, Sandi is equally enthusiastic discussing her horse and misunderstood dog.
Did you know?
Otoliths aid fish like pollock in balance and acceleration.
Something to think about….
What are some factors that might affect the growth of otoliths?