Amanda Peretich: More Trawling Treasures, July 11, 2012

NOAA Teacher at Sea
Amanda Peretich
Aboard Oscar Dyson
June 30, 2012 – July 18 2012

Mission: Pollock Survey
Geographical area of cruise: Bering Sea
Date: July 11, 2012

Location Data
Latitude: 58ºN
Longitude: 173ºW
Ship speed: 11.7 knots (13.5 mph)

Weather Data from the Bridge
Air temperature: 7.9ºC (46.2ºF)
Surface water temperature: 7.3ºC (45.1ºF)
Wind speed: 10.7 knots (12.3 mph)
Wind direction: 323ºT
Barometric pressure: 1007 millibar (0.99 atm, 755 mmHg)

Science and Technology Log
In a recent post, I talked about how one of the things we are doing on board the Oscar Dyson is trawling for fish. The video from that post showed what happens in the fish lab during a midwater trawl. Remember that there are two nets we have been using for a midwater trawl: first, the normal Aleutian Wing Trawl, or AWT, which catches plenty of pollock, but also the 83-112 to which adjustments are being made to use this bottom trawl net for midwater fishing. But what about using the 83-112 for its original purpose: bottom (or benthic) trawling?

Bottom Trawl

I’ve been lucky enough to see two bottom trawls on this cruise, although neither of them were actually during my shift. My wonderful roommate Carwyn, one of the other scientists on board, came to tell me about the bottom trawls so I could see all the neat creatures from below! A bottom trawl is used when the pollock are swimming much lower in the water column for one reason or another, but in trying to catch them, there are always many more “trawling treasures” that find their way onto the fish table. The process is basically the same as a midwater trawl, except the 83-112 net is lower down in the water towards the bottom of the sea floor (hence the term bottom trawl). The net is also much shorter in length than the AWT using in midwater trawling.

DYK?: How do the scientists know exactly how far down the net is in the water column? One of the sensors attached to the net is called the SBE (Seabird) 39. This will measure the depth and temperature during the trawl and determine the average head rope depth (which is the top of the net) and average temperature during the trawl between EQ (equilibrium – start of the trawl) and HB (haul back – end of the trawl). The sensor is then uploaded on the computer and the data is used by the scientific party.

I attempted to classify all of these great bottom trawl treasures, and discovered that this was way easier said than done. There are some books in the fish lab with photos and descriptions just of the species that may be found around the Alaskan waters, and it was incredibly difficult to nail down a specific species for most of the finds!

In the bottom trawl, we found things such as the Oregon hairy triton, an unidentified pretty purple star fish, pink shrimp, basket stars, sheriff’s star, halibut, crabs, pacific cod, sculpin, Pribilof snail, sea anemone, scallop, sponge, sea pens, arrowtooth flounder, flathead sole, chiton, and seaweed.

Enjoy the slideshow below with photos of the bottom trawl treasures (and an interesting fact or two about some of them) or click on the link to open it in a new window!

Bering Sea Bottom Trawl Treasures

Methot Trawl

The other trawl we’ve done outside of the normal AWT (Aleutian Wing Trawl) midwater and 83-112 midwater comparison trawl is something called a methot trawl. This uses a completely different net because the others have mesh that is much too large to catch something so small. The methot net has very fine mesh and a hard square opening with a fixed height. The cod end (very end of the net) is actually a small white container because the organisms collected are so small. A methot trawl is done to collect euphausiids, otherwise known as krill. Sometimes other microscopic (small) organisms are collected as well, including jellies, salps, and amphipods, which must then be carefully sorted out.

DYK?: Krill are part of the phylum Arthropoda, which includes species with an exoskeleton and jointed legs such as spiders, crabs, insects, and lobsters. They are an important part of the ecosystem because these small, reddish-orange animals are a source of food for many larger animals.

Steps to process a methot trawl in the fish lab:
1. Dump contents of the hard cod end container into a large gray bin.
2. Remove any large jellyfish (and weigh those separately).
3. Rinse contents from the gray bin into the sieve to remove any water.
4. Using tweezers, sort through the small microscopic organisms on the sieve and remove anything that isn’t krill.
5. Weigh krill sample.
6. Collect a random subsample in a scoop and weigh it.
7. Count all of the krill in the subsample (yes, this is as tedious as it sounds!).

Personal Log

It continues to be a little slow on the trawling during my shift, but that’s okay, because I was lucky enough yesterday to get a tour of some of the lower bridge levels from the 1^st Assistant Engineer, Tony.

DYK?: There are 8 levels on the Oscar Dyson. They are numbered, starting from the topmost deck, as follows:
O4 – flying bridge
O3 – bridge
O2 – staterooms (CO, XO, chief scientist)
O1 – staterooms (scientists), CTD winch, FRB (fast rescue boat), Peggy D (boat), liferafts
1 – galley, labs (acoustics, chem, dry, fish)
2 – engineering (machinery, centerboard, oceanic winch, trawl winch, and more), staterooms (deck crew and then some)
3 – engineering (machinery, bilge/ballast, workshop, and more)
4 – bowthruster, transducer, fuel oil tanks, ballasting tanks

I plan to share some of the facts I learned related to chemistry and biology from this tour (and other things on board) in one of my next blogs, so be sure to look for all of the info on the generators, sea water purification, MSD, cathodic protection system, and more.

We did have two trawls yesterday (July 10) – the first was an AWT midwater trawl that had caught so many fish it was actually a “splitter”! In a splitter, there’s an extra step between hauling in the net and getting it to the table in the fish lab. The cod end of the AWT net is opened over a separate splitting crate, where there is another net underneath that will only take about half of the fish to release on the table. The rest are then returned to the water.

We also had drills yesterday (these are required once a week) and after gaining permission from the bridge, I checked in to my muster station (which is in the conference room for the science party, away from all of the action) and then went and watched what everyone else on board does. When we have fire drills in school, the alarm sounds, we walk outside, and wait for the “all clear” before heading back in. When they have fire drills on the Oscar Dyson, they use a smoke machine to produce smoke, there is an on-scene crew (first responders), there may or may not be a “victim” involved, the hose team actually dresses out (with the help of another person on the alpha or bravo firefighting teams), and the fire hoses are actually used. It may seem like old hat to everyone else on board, but I found it incredibly interesting to watch!

Following the fire drill, there was an abandon ship drill, where everyone on board grabs their survival suit, PFD, and heads to one of three life rafts (there are actually 6 on the ship). The CO had me stay up in the TV lounge so that my life raft (#5) wouldn’t have a “full muster” until they sent out a search party to find me. Just as there are two people on hose team in both alpha and bravo for the fire drill, people must go in pairs for the search party, so Patrick and Rick came and found me. I think some people thought I’d actually not heard the alarm (I was wearing headphones), but I was instructed to be up there! We will have one more day of drills before we get back to Dutch Harbor, so maybe I’ll actually don my bright orange survival suit, which other Teachers at Sea in the past have affectionately called the “gumby suit” (even though Gumby was green).

Animal Love
In yesterday’s AWT midwater trawl, we had a new visitor in the fish lab. Introducing the lumpsucker!

The lumpsucker is in the family Cyclopteridae, which is derived from Greek words that mean circle and fin in reference to their round-shaped pectoral fins. There is a sucker on the bottom of them, so when we put this little sucker in some sea water while we were processing the fish, he stuck himself to the bottom of the container! Lumpsuckers are poor swimmers, so they are mostly benthic, meaning they stay at the bottom of the sea floor. However, that doesn’t mean they are incapable of swimming (especially since this one was caught during a midwater trawl). We took some photos and tossed this little guy back to sea, so hopefully he makes it!