NOAA Teacher at Sea
Aboard NOAA Ship Oscar Dyson
July 23 – August 11, 2012
Mission: Alaskan Pollock Mid-water Acoustic Survey
Geographical Area: Bering Sea
Date: July 31, 2012
Latitude: N 61°39’29″
Longitude: W 117°55’90″
Ship speed: 11.7 knots (13.5mph)
Weather Data from the Bridge
Wind Speed: 26 knots (30mph)
Wind Direction: 044°
Wave Height: 4 meters (12 ft)
Surface Water Temperature: 8.2°C ( 46.8°F)
Air Temperature: 7.4°C (45°F)
Barometric Pressure: 994 millibar (0.98 atm)
Science and Technology Log:
Last blog, we learned about the different trawl nets and how the NOAA scientists are comparing those nets while conducting the mid-water acoustic pollock survey. We left off with the fish being released from the codend onto the lift table and entering the fish lab. Here is where the biological data is collected.
The fish lab is where the catch is sorted, weighed, counted, measured, sexed, and biological samples such as the otoliths, or earbones, are taken (more about otoliths later in this post). First, the fish come down a conveyor belt where they are sorted by species (see video above). Typically, the most numerous species (in our case pollock) stay on the conveyor and any other species (jellyfish and/or herring, but sometimes a salmon or two, or maybe even something unique like a lumpsucker!), are put into separate baskets to weigh and include in the inventory count. In the commercial fishing industry, these species would be considered bycatch, but since we are doing an inventory survey, we document all species caught. Here are some pictures of others species caught and included in the midwater survey.
The goal of each trawl is to randomly select a sample of 300 pollock to measure as a good representation of the population (remember your statistics! Larger sample sizes will give you a better approximation of the real population). If more than 300 pollock are caught, the remainder are weighed in baskets and quickly sent back to sea. All of the catch is weighed so the scientists can use the length and gender data taken from the sample to extrapolate for the entire catch. This data is combined with the acoustics data to estimate the size of the entire fishery (more on acoustic data in a future post). Weights are entered via touch screen into a program (Catch Logger for Acoustic Midwater Surveys – CLAMS) developed by the NOAA scientists onboard.
The 300 pollock are sexed to determine the male/female ratio of this randomly selected portion of the population. Gender is determined by making an incision along the ventral side from posterior to anterior beginning near the vent. This exposes the internal organs so that either ovaries or testes can be seen. Sometimes determining gender is tricky since the gonads look very different as fish pass through pre-spawning, spawning, or post-spawning stages. When we determine gender, the fish are put into two separate hoppers, the one for females is labeled “Sheilas” and the hopper for males is labeled “Blokes.”
We use an Ichthystick to then measure the males and females separately to collect length data for this randomly selected sample. Designed by NOAA Scientists Rick and Kresimir, the Ichthystick very quickly measures lengths by using a magnet placed at the fork of the fish’s tail (when measuring fork-length). This sends a signal to the computer to record the individual fish’s length data immediately into a spreadsheet and the software creates a population length distribution histogram in real-time as you enter data.
A randomly selected subset of 40 pollock get individually weighed, length measured, sexed, evaluated for gonadal maturity and have the otoliths removed. Otoliths (oto = ear, lithos = bone) are calciferous bony structures in the fish’s inner ear. These are used to determine age when examined via cross-section under a dissecting scope. The number of rings corresponds to the age of the pollock, similar to rings seen in trees. The otoliths are taken by holding the fish at the operculum and making an incision across the top of the head to expose the brain and utricle of the inner ear. The otolith is found inside the utricle. Forceps are used to extract the otoliths, which are then washed and put in individual bar-coded vials with glycerol-thymol solution to preserve them for analysis back at the Alaska Fisheries Science Center.
Watch this short video to see what the entire process of data collection looks like.
So… why collect all of this data? How is this data analyzed and used? Stay tuned to my next blog!
Well, I can officially say… the honeymoon is over. The Bering Sea had been so extremely kind to us with several days of great weather while we had a high pressure system over us. We enjoyed spectacular sunrises and sunsets, cloudless days and calm seas.
Now… we have a low pressure system on top of us. Last night, we experienced 35 knot winds and 12 foot seas. I have spent a lot of time in my room in the past 24 hours… Late this morning, the sun came out and the winds calmed down, but the barometric pressure was still very low (around 990 mbars) which basically meant we were in the center of the low pressure system (similar to the eye of a hurricane, but not as strong… thank goodness!). We had a few hours relief, but we are back to pounding through the waves as the wind picks back up. It will be another long and sleepless night for this landlubber…
On a positive note, we did see two Laysan Albatrosses (Phoebastria immutabilis) from the Bridge as the winds began to kick up. They seemed to really enjoy the high winds as they soared effortlessly around the ship. The Officer on Deck (OOD) also said he saw a humpback breaching, but by the time I got up to the Bridge, it had moved on…
Next blog, I will share pictures of my room, the galley, “the cave,” the Bridge, etc. Right now, I am just trying to hold on to my mattress and my stomach…