Julia Harvey: Determining Population Size/A Day in My Life Cruising, July 27, 2013

NOAA Teacher at Sea
Julia Harvey
Aboard NOAA Ship Oscar Dyson (NOAA Ship Tracker)
July 22 – August 10, 2013 

Mission:  Walleye Pollock Survey
Geographical Area of Cruise:  Gulf of Alaska
Date:  7/27/13

Weather Data from the Bridge (at 1:00 am Alaskan time):

Wind Speed = 3.52 knots
Air Temperature = 13.6 C
Humidity = 94%
Barometric  Pressure = 1025.5 mb

Science and Technology Log:

How can you determine the population size of species?

You could count every member of the population.  This would be the most accurate but what if the population moves around a lot? What if the population is enormous and requires too much time to count each and every one?  Would you want to count all of the krill in the Gulf of Alaska?

The greyish fish are capelin. The pink organisms are krill.

You could mark and recapture.  In this method you catch individuals from the population and tag them.  Data are compiled from the recaptures and the population is mathematically calculated.  Halibut and many other populations are monitored this way and require fishermen to report any recaptures.

Tagged Halibut
Tagged Halibut
photo courtesy of Greenland Institute of Natural Resources

Another method is sampling.  The organisms in a small area are counted and then the overall population in the entire area is calculated.

To determine the population of the organisms of the whole area, find the population density of the dark green area. In this case there are 8 per square meter. Multiply this density by the total area and that will be the population estimate.
Using a transect to sample a population.
Photo courtesy of http://www.kscience.co.uk/as/module5/succession/fieldwork.htm

This picture above illustrates the use of a transect line.  On various increments along the transect line, samples of populations are taken.  Imagine the Oscar Dyson’s path as the measuring tape and the trawl net as the sampling square.

The overall survey area of the pollock study this summer is the northern Gulf of Alaska between the shore and the continental break.  Within this area transect lines were established.  These are pathways that the Oscar Dyson will travel along and periodically take samples of the fish.

Transect Plan
The pollock summer survey is broken into three legs. I am part of leg 3.
Photo courtesy of NOAA

The current set of transects are 25 nautical miles (1 nautical mile is equal to 1 minute of latitude) apart and are parallel but transects in other areas may be 2 or 5 miles apart.  Transects that we are following now are located on the shelf and are perpendicular to the coastline.  Transects in inlets and bays may run differently and may even zigzag.

OD Current Cruise
Leg 3 left from Kodiak and is moving eastward for the survey.
Photo courtesy of NOAA

If fish are located through acoustics, the ship will break transect (a mark is made on the map) and the ship will circle around and a sample of the population is taken by trawling.  The population of pollock can then be mathematical calculated.  After trawling, the ship will return to the break and continue along the transect line.


This afternoon, we were working smaller transect lines near Amatuli Trench that were 6 miles apart.  It is an area that has had good pollock catches.  Just when we were going to fish, a pod of fin whales was spotted in the area.  So we moved to another area and hauled in quite the catch of Pacific Ocean perch.

POP Haul
After fish are caught they are processed in the fish lab. Here we are processing the Pacific Ocean perch.

It is hopeful that the Oscar Dyson will finish a transect line by nightfall and then the ship can be at the next transect by sunrise.  This maximizes the time looking for fish and trawling.

Personal Log:

I am settling into life on the Oscar Dyson and have established a routine that will support my night shift (4 pm to 4 am).  So how do I spend 24 hours on the ship?

I wake up around 11:45 in the morning to be able to eat lunch that is served only between 11:00 and 12:00.  Because of the shift schedules, some people are bound to miss one or more of the meals.  I miss breakfast because I am sleeping.  We are able to request a plate of food be saved for later.

Between the end of lunch and the start of my shift, there are several things that I can do.  The weather has been very nice and so I often go on deck to soak up the sun and whale watch.

Whale watching
Can you spot the fin whales?

I may need to do laundry as my clothes start to smell fishy.

Laundry Room
We are lucky to have a laundry room on board. It meant I did not have to bring many clothes.

I will also workout in one of the two gyms.  The gym at the back of the boat can’t be used when trawling because of the high noise level.  There is a rower, two exercise bikes, two treadmills, a cross trainer, mats and weights.  I got lucky and someone installed a makeshift pull up bar.

Front exercise room
This is the exercise room towards the bow of the ship.
Back Exercise Room
This is the exercise room toward the stern of the ship.

There is also a lounge where I can read or watch DVDs.  Some of the movies are still in theaters.

The lounge for reading and watching movies.

An hour before my shift starts, I read and take a short nap.  Then, I grab a cup of coffee at 4 pm as my shift starts.  I listen as the day shift fills in the evening shift about the happenings of the last 12 hours.

During my shift, there are several things that I may do.  If we have fished, there will be pollock and other organisms to process.

Processing pollock
Here Jodi, Kirsten and I are processing the pollock by determining their sex. Then, they will be measuresd weighed and their otoliths removed.

After processing, we need to clean up the fish lab which involves spraying down everything include ourselves with water to remove scales and slime.

I also keep an eye on the acoustic monitors, to see what I can recognize.  Paul and Darin are always willing to answer my questions (even the ones I already asked).

Acoustics Screens
The four screens of acoustic data. From these screens, Paul will determine whether to fish.

I may look at trawl camera footage or observe camera drops.  Drop Camera

I also have time to work on my blog.

Work Space
I have set myself up an area in the “Cave” to write my blog.

Dinner is served at 5 pm but the mess is always open and is filled with snacks such as sandwich fixings, ice cream, yoghurt, a salad bar and pop tarts.

Go to the mess for meals and snacks.

Whenever I get hungry at night, I just head for the mess.  It is a time that I am able to chat with the crew and NOAA Corps as they come in for snacks too.

At 4 am, I make it a point to head directly to my stateroom and go to sleep.  The room has a window but I can close the curtains on the portlight (window) and around my bed.

Since I work until 4 am, I close the curtains on the window and bed to help me sleep. The bottom bunk is mine.

There are no weekends out here.  Everyone works 7 days a week for the duration of the cruise.

Did You Know?

Usually fin whales show only their back as they surface for air.  Check out my video clip and see if you can spot the whale.  It wasn’t too close.

fin whale
Here is that fin whale closer up.


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