NOAA Teacher at Sea
Aboard NOAA Ship Oscar Dyson
July 22 – August 9, 2013
Mission: Pollock Survey
Geographical Area of Cruise: Gulf of Alaska
Date: Sunday, July 28, 2013
Current Data From Today’s Cruise
Weather Data from the Bridge
Sky Condition: Cloudy
Temperature: 14° C
Wind Speed: 4 knots
Barometric Pressure: 1025.1 mb
Sun and Moon Data
Sunrise: 5:57 am
Sunset: 10:34 pm
Moonrise: 11:52 pm (July 27, 2013)
Moonset: 2:35 pm
Latitude: 59° 53.3′ N
Longitude: 149° 00.0′ W
The ship’s position now can be found by clicking: Oscar Dyson’s Geographical Position
Science and Technology Log
How do scientists use acoustics to locate Pollock (and serendipitously other ocean creatures)?
Scientists aboard the NOAA Research Vessel Oscar Dyson use acoustic, specifically hydroacoustic data, to locate schools of fish before trawling. The trawl data provide a sample from each school and allow the NOAA scientists to take a closer look by age, gender and species distribution. Basically, the trawl data verify and validate the acoustics data. The acoustics data, collected in the Gulf of Alaska in systematic paths called transects, combined with the validating biological data from the numerous individual trawls, give scientists a very good estimate for the entire Walleye pollock population in this location.
Hydroacoustics (from Greek words: hydro meaning “water” and acoustics meaning “sound”) is the study of sound in water. Sound is a form of energy that travels in pressure waves. In water, sound can travel great distances without losing strength and can travel fast, roughly 4.3 times faster in water than in air (depending on temperature and salinity of the water).
The Oscar Dyson has powerful, extremely sensitive, carefully calibrated, scientific acoustic instruments or “fish finders” including the five SIMRAD EK60 transducers located on the bottom of the centerboard, the SIMRAD ME70 multibeam transducer located on the hull, and a pair of SIMRAD ITI transducers on the trailing edge of the centerboard.
This “fish-finder” technology works when transducers emit a sound wave at a particular frequency and detect the sound wave bouncing back (the echo) at the same frequency. When the sound waves return from a school of fish, the strength of the returning echo helps determine how many fish are at that particular site.
Sound waves bounce or reflect off of fish and other creatures in the sea differently. Most fish reflect sound energy sent from the transducers because of their swim bladders, organs that fish use to stay buoyant in the water column. Since a swim bladder is filled with air, it reflects sound very well. When the sound energy goes from one medium to another, there is a stronger reflection of that sound energy. In most cases, the bigger the fish, the bigger the swim bladder; the bigger the swim bladder, the more sound is reflected and received by the transducer. The characteristic reflection of sound is called target strength and can be used to detect the size of the fish. This is why fish that have air-filled swim bladders show up nicely on hydroacoustic data, while fish that lack swim bladders (like sharks) or that have oil or wax filled swim bladders (like Orange Roughy), have weak signals.
These reflections of sound (echoes) are sent to computers which display the information in echograms. The reflections showing up on the computer screen are called backscatter. The backscatter is how we determine how dense the fish are in a particular school. Scientists take the backscatter that we measure from the transducers and divide that by the target strength for an individual and that gives the number of individuals that must be there to produce that amount of backscatter. For example, a hundred fish produce 100x more echoes than a single fish. This information can be used to estimate the pollock population in the Gulf of Alaska.
On the first day of our travel, before the Oscar Dyson was far from port at Kodiak, we had three drills. The fire drill and man overboard drill required me to report to the conference room and meet up with the rest of the science team. Patrick, the lead scientist, then reported that we (the scientist team) were all accounted for. The crew had more complex tasks of deploying a small boat and retrieving “the man overboard”.
The other drill was the abandon ship drill. On the ship, every person is assigned to a life boat (mine is Lifeboat 1). When the drill commenced, I reported to my muster, the portside of the trawl deck, with survival gear: jacket, hat, survival suit and life preserver. We will have drills weekly at anytime.
Did You Know?
Something to Think About:
Since I will begin teaching Zoology later in August, I have decided to highlight some of the animals that the scientist team has found in our trawls. Today’s feature will be one of the simplest multicellular animal families, the Porifera. Porifera is a word formed from combining the Latin words porus which means “passage-way” and fera meaning “bearing.” Porifera, commonly referred to as sponges, have tiny pores in their outer walls that filter water to get nutrients.
To learn more about the Porifera Family, click the Porifera on the picture below, and stay tuned for further exploration of this animal Tree of Life.