Mission: Walleye Pollock Survey
Geographical Area of Cruise: Gulf of Alaska
Date: August 3, 2013
Weather Data from the Bridge (as of 00:00 Alaska Time):
Wind Speed: 26.5 knots
Temperature: 13.6 C
Barometric Pressure: 1014.6 mb
A low pressure system is in the north Pacific and we are having increase winds and swells.
Science and Technology Log:
We listened. We fished. Now what?
Before reporting to the fish lab, I must gear up. Slime gear keeps the scales and goo off of my clothes.
Fish are emptied out of the net and onto the table outside the fish lab.
We can control how many fish land on the conveyor belt by raising the table and opening the door.
The fish on the conveyor belt are separated by species.
In this blog we will focus on the pollock that were caught.
Pollock are gathered into baskets and weighed.
We group the pollock into 3 groups; age 1, age 2 and age 3+. Each group as an entirety is weighed. Each age group has a somewhat different protocol for processing. Fifty specimens that are age 1 will be measured with the ichthystick and 10 will also be weighed.
Fish that are age 2 are processed as age 1 but are also sexed.
When measuring a pollock on an icthystick, one measures from the head to the fork in the tail. The icthystick (a magnetic board for measuring fish) is connected to a computer that automatically records the data.
The larger pollock are grouped by sex. To do this, we cut open their abdomen and look for ovaries or testes.
Then all of the fish (or at least 300) are measured on the icthystick. Forty will be measured and weighed and set aside for otolith removal.
Otoliths are made of calcium carbonate and are located directly behind the brain of bony fishes.
They are involved in the detection of sound and the process of hearing. The age of the fish can be established by counting the annuli much like one does when counting tree rings.
This age data allows scientists to estimate growth rates, maximum age, age at maturity, and trends of future generations. This data is vital for age based stock assessment models. These fish are weighed and measured. Otoliths are removed and placed in jars with glycerol thymol.
The jars have bar codes on the side so that the otoliths are linked to the fish’ weight, length and sex.
The otoliths are sent to Seattle for more detailed analysis of age. These results will be used to correspond length to age in the stock assessment report.
Sometimes, ovaries are removed and sent to other scientists for further histological study.
Other organisms that are caught alongside the pollock are counted and measured as well. The catch might include Pacific ocean perch, salmon, herring, viper fish, lantern fish, jellyfish, squid, and capelin. Below are a few of the normal finds and the rest can be found in my personal blog account “the beautiful, the odd and the interesting”.
The beautiful, the odd and the interesting
This trip is not just about pollock. When we bring any of the nets in there is the possibility of weirdness and other things that catch my eye. Jodi is always filling me in on the uniqueness of our discoveries. And Darin lets me save organisms for photographing later.
My favorite find so far is the lumpsucker. As Jodi says, they have gentle brown eyes and they do. They also have suckers on the bottom that allow it to stick to substrate.
The Methot trawl went close to the bottom and picked up a handful of brittle stars. At first, when they were mixed with all of the krill, it looked like a bunch of worms.
Pollock do eat young pollock. We found evidence of this when Darin opened the stomach of an adult and discovered partially digested age 1 pollock.
Lanternfish (Myctophids) make up a huge amount of the deep sea biomass. They have photophores along their sides for producing light.
The adult Pacific sandfish bury themselves in the sand with only their mouths protuding.
Prowfish lack pelvic fins. They have continuous teeth to feed on jellyfish.
When I think of deep ocean fish I think of the viperfish with its needle sharp teeth.
This cute mud star came up with the brittle stars. It was also referred to as the cookie cutter starfish because it resembles a shortbread cookie.
Salmon are good swimmers and usually escape the net. A few are caught at the surface.
When we were in Kodiak, I would watch the moon jellies drift by. Now we are catching several different species of jellyfish like this sunrise jelly.
Jodi always has a keen eye for finding nearly invisible creatures. The arrow worm is a voracious predator. They immobilize their prey with neurotoxins.
I had never heard of a sea mouse before this cruise. Now I have. Except it is not a rodent. It is a carnivorous worm that feeds on hermit crabs and other worms. It is also a scavenger like a vulture.
Some isopods are parasitic and will feed off of the blood of fish in the gill chamber. I prefer their cousins the pill bugs.
Did You Know?
When we are all measuring and weighing away in the lab, it sounds like a video game. Each machine has it’s own unique sound effects. This allows scientists to have confidence that their data was recorded.