NOAA Teacher at Sea
Roy Arezzo
Onboard NOAA Ship Oscar Dyson
July 11 – 29, 2007
Mission: Summer Pollock Survey
Geographical Area: North Pacific, Alaska
Date: July 26, 2007
Weather Data from Bridge
Visibility: 8-10 nm (nautical miles)
Wind direction: 220° (SW)
Wind speed: 11 knots
Sea wave height: 3 feet
Swell wave height: 0 feet
Seawater temperature: 10 °C
Sea level pressure: 1014.9 mb (millibars)
Air Temperature: 10°C
Cloud cover: 8/8, Stratus
Science and Technology Log: Special Operations
When a fully equipped research ship goes to sea everybody wants in. Any scientist doing work in a particular region needs access to that region to conduct their fieldwork. Fishery scientists often catch a ride with commercial vessels to do work at sea. A research vessel can be more desirable for certain projects and NOAA has a system for organizing request proposals and prioritizing work. Unfortunately, a boat is limited in the number of passengers, equipment, food and other resources it can carry. For example one scientist, who is not with us, has sent light meters onboard and requested we collect the data for him. The light meter mounts to our trawl net to study if light penetration affects the vertical distribution of walleye pollock. The pollock survey, the main project of the season, has a science team of 8 not including the birders, ship’s staff and Teacher at Sea. With this many scientists onboard the ship becomes a platform for an interesting mix of experimentation.
We finished the transects of the Pollock Survey and are now transiting southeast back towards Dutch Harbor. Tomorrow we launch “the sled”, a large metal-framed instrument equipped with an underwater video camera to record the sea bottom of a special study site. The purpose of the study is to assess the effect of bottom trawling on benthic habitats and measure recovery progress over time. The study site is an area that was bottom trawled back and forth around a month ago. The camera will be pulled in lines perpendicular to the tracks created by the trawling. I got a sneak peak at some of the video footage and the benthic habitat is flat and muddy with strange white sea pens poking upward around 5 feet. Crabs and flat fish scurry around while giant basket stars and sea anemones ornament the bottom. We will use some of our transit time to reflect on some of other side projects that occurred this trip, most of which were designed to refine and validate the survey methodology.
When the trawl catch is unloaded into the lab the sex, weight and length of individual fishes are recorded. To make the work more efficient, a new measuring board has been designed to length fish. This is the first time it was tested and it performed smartly. The board allows scientists to input digital length data by touching the sensor to the board at the end of the fishtail fork. NOAA Scientists, Rick Towler and Kresimir Williams, designed the instrument using magnetic sensors from scratch, and shared with me the details of their first project and how the length board evolved from an acoustic instrument through trial and error to the prototype we tested this year. When processing data from trawling, there is always a concern as to how to best represent biomass estimates. You should not count a fish that is 10 centimeters the same as you would a fish that is 40 centimeters. Although they would both qualify as one fish they have a different size and thus a different biomass. We know we cannot count every fish so we have different methods of estimating biomass.
Not all fish are caught with the same efficiency; the retention of fish in a net must be taken into consideration. To compensate for this, an estimate as to fish escapement is often factored into the calculations for fish density. Fisheries Scientist, Kresimir Williams, wants to quantify fish escapement. He is using handmade “pocket nets” to study selectivity and sample escaped fish. In the evening we conducted experimental trawls to monitor escapement from our main trawl nets. We did this by attaching pocket nets to the outside of the trawl net in random placement and analyzing pollock caught in the smaller nets relative to the catch in the cod end. We have found that smaller fish (one year-old juveniles) more often escape the net from near the cod end as opposed to forward, where there is a larger mesh size. Although the data will not be analyzed until later, observations indicate this could be important in interpreting pollock survey results.
The most exciting project for me is the “Optical Pea Pod”, another Kresimir/Rick design. The pod houses 2 digital cameras, a timed circuit board and a strobe light that is lowered in the net to photograph fish at regular intervals. The setup is designed to produce calibrated stereo images of fish making it possible to measure fish length in deep water. Perhaps, in the future, the cod end can be left open allowing the fish to swim out safely as they are documented. The imaging data can possibly be used to verify the acoustic data that is currently used to estimate the population, reducing the need to handle fish on deck. I would like to thank my technical advisors, Kresimir and Rick, for involving me in their projects and for their support in my work as Teacher at Sea.
Bird of the Day
The Albatross is a seabird steeped in maritime folklore. Mariners of yore would tell stories of the souls of dead sailors rising when they saw the white bird. Famous for being one of the largest seabirds they are a magnificent sight. The Wandering Albatross is capable of extremely long migrations, circumnavigating the globe for years before settling down to breed. Albatrosses, of the biological family Diomedeidae, have recently been reclassified (based on recent DNA evidence) and the number of genii and species is widely disputed. What is clear is that many species are in danger of extinction. The greatest impact to their populations is long line fishing although many were slaughtered for their feathers before being protected after the turn of the last century. Swordfish, monkfish and cod are fished with long-lines involving miles of baited hooks that can attract the birds and lead to their entanglement and subsequent drowning. We have seen two species on this cruise, the Laysan and the Short-tailed Albatross. It is estimated that there are only between 1500 and 2000 Short-tailed Albatrosses remaining the world. Many were harvested for feathers and a volcano eruption at their Japanese breeding grounds decimated the remaining adults. Fortunately juveniles at sea have returned to breed and hopefully with protection, the numbers will continue to rebound. We were lucky to have one spend a fair amount of time of our stern in calm waters the other day as we were stopped for water quality testing.
Personal Log
The Bering is a surprisingly lovely color of blue and if the sun would ever come out I am sure it would accent the aesthetic of the water’s color. When we stop to check the water quality the CTD instrument makes for a decent secchi disk and I have observed anecdotally that the visibility seems to be around 13 meters or 40 feet. On an unrelated topic, the other day Executive Officer LT Bill Mowitt let me in on his “lesson plan” for the weekly drill. We went into a fan room and created an electrical fire scenario. We also left clues around the area for the crew and fire fighter team to assess and react to. When it came time for the actual drill I had front row seats to watch the drill unveil and was then permitted to test the fire house of the leeward side the ship. All went well.
Question of the Day Today’s question: How much fish did we catch? Previous Question: How does one become a Golden Dragon?
The short answer is one sails across the 180-degree line separating the eastern and western hemisphere. We did this going steaming to Russian waters continuing our survey work in the Northwest Bering.
