Mark Van Arsdale: Night Work, September 12, 2018

NOAA Teacher at Sea

Mark Van Arsdale

Aboard R/V Tiglax

September 11 – 26, 2018


Mission: Long Term Ecological Monitoring

Geographic Area of Cruise: North Gulf of Alaska

Date: September 12, 2018


Weather Data from the Bridge

Partially Cloudy, Variable Winds, Seas to 3ft

59.43 N, 149.21 W (Gulf of Alaska Line)


Science Log

Night Work

Loading gear on the Tiglax
Loading gear on the Tiglax

Most of day one was spent loading, sorting, unpacking, and storing gear.  Scientists do not travel light.  There were more action packers on board than I have ever seen in once place. At midday, we had a safety training, which consisted of learning how to put on a survival suit and how to use the coffee machine without flooding the galley.  For night work, I was assigned a mustang float coat, a water activated flash light, and satellite locator, so that they could find my body if I went overboard.

After dinner, work shifted to putting together various nets and the CTD which I will describe in more detail later.  We got underway at about 8:00 PM, just as the sun was setting. I slept for an hour and was woken at 10:30 to begin my shift doing zooplankton tows.

The first tow uses a Methot net, which is a large square steel frame attached by d-rings to a heavy mesh net, ten meters long.  The net ends in a plastic sieve tube called a “cod end” that keeps any jellies from escaping.  The net is quite heavy, and it takes four of us to guide it as a crane raises it off of the deck and then lowers it over the side.  The net is dragged at the surface for twenty minutes.  In the darkness of night, it glows slightly green as ctenophores and other bioluminescent jellies smash into it.

Dave demonstrating the proper technique for putting on a survival suit
Dave demonstrating the proper technique for putting on a survival suit

After the Methot net is retrieved and secured on deck, we leave the collected jellies for a few minutes to go deploy the next net, called a Multi-net.  The Multi-net is a steel box about the size of a dishwasher with a funnel entrance and five separate fine-mesh nets hanging off of the back.  The net also has a heavy “fish fin” that acts to drag it down and keep it moving straight.  The four of us work the net to the edge of the boat, open the back gate, and use two winches to lower it overboard.  Once in the water and if the bottom depth allows it, the Multi-net gets dropped to a depth of two hundred meters and the first net is opened.  The Multi-net allows you to “carve up the water column.”  Each net can be triggered remotely to open and collect a horizontal sample of zooplankton at a specific depth.  The electronics also allow you to measure how much water volume flows through the net.  Each net is about two meters long, made of a fine mesh that funnels plankton into a soft sieve or “cod end”. While the Multi-net is “fishing,” we sort, classify, and measure the jellies collected in the Methot net tow.

A Methot Net Tow
A Methot Net Tow

The Seward Line Transect is made up of fifteen stops or stations.  Each one designated as GAK1, GAK2, etc. Once we finish sampling a station, the boat speeds up and drives us ten nautical miles to the next station.  Last night we managed to sample four stations, finishing the last one just as the sun rose around 7:00 AM.  When daylight comes, the Tiglax makes its way back to the place the night shift began.  All of the day-time sampling has to be done at each of the stations we sampled the night before.  The day-time sampling uses different tools, the main tool being the CTD Rosette Sampler.  The Rosette is a steel cage with water collecting “Niskin Bottles” and lots of other instrumentation strapped into the cage. There are fifteen bottles and each is triggered by computer to close at a specific depth.  This allows the scientists on board to measure a variety of physical and chemical properties of the water at depth.

Personal Log

The night shift was surprisingly dark.  That may sound obvious, but after a long Alaskan summer, with campfires and hikes that often went past midnight in perfect daylight, dark is an adjustment.   The night was beautiful and warm, but the work of deploying and retrieving nets was tedious and physical.  By morning I was exhausted, but I was reminded repeatedly that there are no cutting corners.  No matter how tired you get, each sample needs to be meticulously cared for.

After the sun came up, I forced myself to eat some breakfast and then I fell in bed for a hard sleep.  I could only stay there for a couple hours before my well-trained, morning-self wanted to greet the day.  The day was flawless, picture-perfect, sunny and calm, the kind of days you don’t often seen in the stormy Gulf of Alaska.

Animals Seen Today

  • Dall Porpoise
  • Lots of seabirds, including black-legged kittiwakes, pelagic cormorants, and sooty and flesh-footed shearwaters.
Shearwater taking off
Shearwater taking off, photo credit Callie Gesmundo





Leave a Reply

%d bloggers like this: