NOAA Teacher at Sea
Melissa George
Aboard NOAA Ship Oscar Dyson
July 22 – August 9, 2013
Mission: Pollock Survey
Geographical Area of Cruise: Gulf of Alaska
Date: August 5, 2013
Current Data From Today’s Cruise (2 pm Alaska Daylight Time)
Weather Data from the Bridge
Sky Condition: Partly Cloudy
Temperature: 15.8 ° C
Wind Speed: Light Wind
Barometric Pressure: 1018.7 mb
Humidity: 84%
Sun and Moon Data
Sunrise: 5:13 am
Sunset: 9:35 pm
Moonrise: 4:22 am
Moonset: 8:27 pm
Latitude: 59 ° 09.7 N Longitude: 141° 27.6 W
The ship’s position now can be found by clicking: Oscar Dyson’s Geographical Position
Science and Technology Log
Processing the Catch
My last blog post focused on mid-water trawling; this blog will focus on processing the catch. When we process the catch, we are processing it in a scientific way, not a food production way. The goal of any fish survey is to try to determine how many fish (in this case pollock) are in the sea in order to establish sustainable fishing limits. Ideally, trawling allows scientists to randomly select a sample of pollock to measure a good representation of the pollock population. The survey is undertaken in an ecologically friendly way with a focus to preserve as many fish as possible by releasing them alive back into the ocean. I will go through the steps of this process.
Step 1: Sorting and Measuring
Usually, fish brought in with the trawl net are placed directly on the table. If the catch is especially large, it may be weighed first by attaching a scale to a crane, and then attaching the load to the scale. The entire catch is weighed so the scientists can use the length and gender data taken from the sample to extrapolate for the entire catch. Then a sample (ideally 300 pollock) are kept to process and the rest are released. This data is combined with the acoustics data to estimate the size of the entire stock.
Fish are emptied out of the net and onto the table outside of the fish lab. The number of fish that land on the conveyor belt can be controlled by raising the table and opening the door. The fish on the conveyor belt are separated by species. Although in the catch there are often many types of species of sea animals present, the focus of this blog will be the pollock that are caught.
In the video clip, the vast majority of the fish are adult pollock, but sometimes there are a variety of age stages; Age 0, Age 1, and Adult are what we have seen. Pollock are sorted by age, gathered into baskets, and weighed. Age 0 and Age 1 pollock are weighed and then measured with the icthystick, a magnetic fish measuring board, from the head to the fork in the tail. The icthystick is connected to a computer that automatically records the data. (The icthystick below shows how the length of capelin, a prey of pollock, are measured and recorded; the method is the same pollock).
Step 2: Sexing
Each age group has a somewhat different protocol for processing. Counts and measurements of weight and length are taken for the smaller pollock (and capelin). The larger pollock are grouped by sex. To do this, the abdomen is sliced open with a scalpel, the innards are pushed aside, and ovaries or testes are identified. After determining the sex of the fish, its length is measured with the icthystick. Finally, a subsample of fish are set aside for otolith removal. As we process a catch, samples of fish and other species are collected for various off-board scientists. For example, Age 0 pollock are kept for one scientist; ovaries from mature pollock for another.
Sometimes it is difficult to tell the testes from the ovaries. Generally, both are paired organs that lie along the vertebrae under the guts (stomach, liver, intestines). The ovaries tend to be fuller and more brightly colored; the testes, stringier and paler. However, these organs can vary somewhat depending on the maturity of the fish. Below are examples of the organs from fish that have not yet spawned (photos courtesy of Story Miller, TAS 2010).
Step 3: Removing Otoliths
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 (small ridges on the otoliths) much like one does when counting tree rings. This age data allows scientists to estimate growth rates, age at maturity, and exposure to various environmental conditions.
The otoliths are brought to Seattle for more detailed analysis, so after extracting them from the pollock, they are placed in jars with a preservative called glycerol thymol. The jars have bar codes on the side so that the otoliths are linked to the fish’ weight, length and sex. These results will be used to correspond length to age in the stock assessment report.
Personal Log Accomplishment
Continuing with Maslow’s hierarchy of needs, I will discuss some of the ways that the need of feelings of accomplishment are met on the Oscar Dyson.
- A Version of Maslow’s Hierarchy of Needs
Did You Know?
Something to Think About:
So far we have discussed the following invertebrate animal phyla: Porifera and Cnideria. Today’s episode of Trawling Zoology features other interesting representatives of the invertebrate animal kingdom: Annelida, Mollusca, Arthropoda, and Echinodermata that have turned up in our catches.
Phylum Annelida-from the Latin word anulus meaning “little ring”
Annelids are segmented worms that have a linear series of external segments divided by septa (walls between segments) that house serially repeated nervous, muscle, and excretory systems. Their anterior segments contain jaws, eyes, and cirri (small feelers that help with feeding). Filter-feeding marine annelids capture bacteria and feed selectively on sediment particles within tubes buried in sand or mud.
Phylum Mollusca-from the Latin word mollis meaning “soft”
Mollusca is one of the most diverse groups of animals on the planet, with at least 50,000 living species (and more likely around 200,000). It includes such familiar organisms as sea snails, octopuses, squid, clams, and chitons, all of which we have seen on this mission. They all have soft bodies which typically have a “head” and a “foot” region. Often their bodies are covered by a hard exoskeleton, as in the shells of snails and clams or the plates of chitons. Squid and octopuses have small internal shells.
Phylum Arthropoda-from the combination of Greek words arthron meaning “jointed” and pous meaning “feet”
The Phylum Arthropoda includes organisms such as insects, spiders, and crustaceans (crabs and shrimp). The vast majority of sea dwelling arthropods are crustaceans. For example, the hermit crabs emerging from the mollusk shells in the picture above are members of the most abundant family on Earth, the arthropods. Arthropods have an exoskeleton of a tough compound called chitin that forms a rigid armor with joints in between. This outer shell provides the structure against which arthropod muscles pull, reduces water loss, and protects them from environmental dangers. Below are other examples of arthropods found frequently in trawls.
Phylum Echinodermata-from the combination of Greek words echinos meaning “spiny” and derma meaning “skin”
The adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as starfish, sea urchins, sand dollars, and sea cucumbers. Echinoderms are found at every ocean depth and contains about 7000 living species. Echinoderms are also the largest phylum that has no freshwater or terrestrial (land-based) representatives. Two unique characteristics of this phylum are the ability to regenerate tissues and their ossified limestone exoskeletons.
