NOAA Teacher at Sea
Caitlin Thompson
Aboard NOAA Ship Bell M. Shimada
August 1 — 14, 2011
Mission: Pacific Hake Survey
Geographical Area: Pacific Ocean off the Oregon and Washington Coasts
Date: August 4, 2011
Weather Data from the Bridge
Lat. 46 degrees 22.4 N
Long. 124 degrees 41.1
Present weather: cloudy
Visibility: 10 n.m.
Wind direction: 330
Speed 11 kts
Sea wave height: 2-3 feet
Swell waves – direction: 310
Swell waves – height: 3-4 feet
Sea level pressure: 197.3 mb
Temperature – dry bulb: 17.0 degrees C
Temperature – wet bulb: 15.0 degrees C
Science and Technology Log
Yesterday, I saw, sexed, and measured my first hake. And my second hake, and hundredth hake, and two hundredth hake. Most of the time, the scientists on the acoustics team watch computer monitors that show acoustic data as colors to represent life under the ship. Twice today, however, they identified large populations of hake and decided to fish for them in order to get more accurate data.
Both times, the ship went into immediate action. Upstairs in the bridge, or command room, the NOAA officers slowed and repositioned the ship. Two scientists watched for marine mammals. If mammals were too close, we would have to abort the operation entirely. On the fish deck, John Pohl, on the acoustics team, taught me to assemble the pressure housing and attach it to the net. Objects attached to the net include the video camera, which will film anything passing by the mouth of the net, a four-beam laser to judge the length of the images that are filmed, a light to illuminate the water, batteries for power, and another camera for storing the data. The crew began lowering the net.
For me, the real excitement began once the fish began pouring onto a conveyor belt into the fish lab. First, we sorted the fish by species. In the first haul, the fish were mostly hake, as intended, but we also caught three yellow-tail rockfish and three eulachons, a type of smelt. In the second haul, there was largely yellow-tail rockfish and hake, with several Pacific Ocean perch and widow rockfish. The rockfish were difficult to sort: they have dangerous spines and fight hard. Alicia Billings, a fisheries biologist on the acoustics team, taught me how to pick them up with one hand over their eyes and the other firmly grasping their tails. Even so, we both had a few close calls. We threw most of the fish right back into the ocean but kept about three hundred hake to sex and scale. With another fifty hake, we put then stomachs in individual bags so that the lab on shore can determine what the hake were eating. We also stored the otolith, or ear bones, in order to determine the age of the hake. Just like the rings of a tree, otoliths show growth rings every year.
Finally, we cleaned up and settled back in the acoustics lab to watch for the next batch of fish.
The monitors use echosounders, which are exactly how they sound: Signals (sound waves) are emitted from beneath the ship and echo back once they hit something. The computer records the distance of an object by how long it takes for the signal to return. For example, suppose a fish were right at the surface. The signal would hit it and return in very little time.
On the other hand, in deep water the signal would take much longer to hit the bottom of the ocean and return. See the thick red line on the graph to the left? That’s the ocean floor. Notice how it curves down on the right at the edge of the continental shelf. The flat line at the top of the graph is the surface of the ocean. The scattered dots in between are most likely fish. The scientists can guess the kind of fish and the number of fish by the pattern and color of dots. All the color below the ocean floor is meaningless noise. Look to the upper left-hand corner of the graph to find the frequency of the signal, measured in kilohertz (KHz). The lower frequencies (20 kHz and 38 kHz) tend to measure larger objects and to go deeper in the water. These frequencies are perfect for finding hake. The higher frequencies (120 kHz and 200 kHz) measure smaller objects. For example, shortly before we started the first haul, we saw a large number of plankton, which showed up bright blue on the 120 kHz and 200 kHz frequencies but barely showed at all on the lower frequencies.
You can follow the progress of the Shimada at shiptracker. We’re headed for Port Angeles on August 14, making East-West transects along the way.
Personal Log
I am so happy to be at sea. The journey was delayed an entire day because of a problem with a valve, and we finally set sail yesterday. The skies are blue and the ocean calm, and I am constantly learning new stuff. I’ve had to learn to lift my feet when stepping through a doorway (I forgot once and went sprawling!) and to memorize the complicated series of halls and ladders to get from the fly deck to the bridge to the mess room to my stateroom. I’ve had to memorize thirty-some names. The scientists have been incredibly patient, explaining each part of their work while I take copious notes. Working in the fish lab is my favorite part so far. It’s fascinating and satisfying work.
I am impressed by the sense of camaraderie on this ship. The scientists on the acoustics team – also known as the hake people – keep up a constant, teasing banter, which only turns serious when discussing science. With science, they all have a different opinions. Before fishing today, Chief Scientist Larry Hufnagle worried that there were too few fish shown on the monitor. He said, “I don’t even know how you would fish on this stuff.” Dr. Rebecca Thomas, a research fishery biologist on the acoustics team, seemed to think there were plenty of fish, but suggested leaving the net in for a longer amount of time for a larger sample. After much more discussion, the team decided on a strategy and put in the net. I’m impressed how often they disagree and how carefully they listen to one another’s ideas.
