Pam Schaffer: Sampling the Food- Assessing Krill Populations July 5, 2018


NOAA Teacher at Sea

Pam Schaffer

Aboard NOAA Ship Bell M. Shimada

July 2-10, 2018

Mission: ACCESS Cruise

Geographic Area of Cruise: North Pacific:  Greater Farallones National Marine Sanctuary, Cordell Bank National Marine Sanctuary

 

Weather Data from the Bridge

Date July 5 2018
Time 1100
Latitude 37 30.1’N
Longitude 123 08.5’W
Present Weather/ Sky Cloudy
Visibility (nm) 12
Wind Direction (tree) Light
Wind Speed (kts)  Variable
Atmospheric Pressure (mb) 1021.3
Sea Wave Height (ft) <1
Swell Waves Direction (true) 270°
Swell Waves Height (ft) 1-2
Temperature  Sea Water (C) 13.0°
Temperature Dry bulb (C)

Air Temperature

16.7°
Temperature Wet Bulb (C ) 13.7°

 

Science and Technology Log

Krill are small crustaceans (think shrimp-like) that inhabit the world’s oceans.  They are an essential component of marine ecosystems, residing near the bottom of the food chain.  Krill are a staple in the diet of whales, squid, octopuses and fish.  Understanding the variability of krill populations is an important way of monitoring ocean health.    In order to track the krill population, scientists do two things; they use acoustics to estimate the biomass and use nets to verify the results from the acoustics.

Deploying the Tucker Trawl

Deploying the Tucker Trawl

Scientists use a large net mechanism called a “Tucker Trawl” to collect samples of krill and other zooplankton at various depths in the water column.  A Tucker Trawl is a set of opening and closing cone shaped nets made of fine mesh (holes that are 333 microns in diameter).  The unit we are using has three sections, each with a mouth diameter of 1 meter by 1.5 meters and a sample collector container on the bottom. Krill is collected by dropping the net in a specific location to a specified depth while the ship is slowly moving at a rate of approximately two knots per hour (2.3 mph).  An onboard crane deploys and retrieves the mechanism using a heavy cable. On this cruise we’ve sampled to depths as much as 200 meters deep.   The Tucker Trawl depth and when the nets are opened can be adjusted in order to sample several vertical positions in the water column during a single trawl.

Processing Samples

Processing Samples

Once the samples are back onboard the nets are sprayed down and the collectors are carefully emptied into storage containers for later analysis onshore.  The content analysis will count and identify the various species collected in the sample, as determining sex, size, lifecycle which vary by species.    We’ve observed two different species in our samples; Euphasia pacifica (smallest and most abundant) and Thysanoessa spinifera (larger with a spiny back).  Data collected via these Tucker Trawl sessions is used to construct models for assessing krill biomass using acoustic measuring technology.

 

Thysanoessa spinifera upclose

Thysanoessa spinifera upclose

Loads of Krill

Loads of Krill

Personal Log

Tucker Trawling is wet business but really interesting.   It’s a great learning experience working with Dr. Jaime Jahncke to deploy the nets and process the samples.  We’re doing several trawls each day throughout the cruise- one session around noon and another set around midnight.   I’ve adjusted my sleeping schedule to get a few hours of rest before we start the midnight shift and then I sleep a few hours after we finish working around 4:30 am.  I’m tired but really happy to be here.

 

Did You Know? 

                       

The name “krill” is Norwegian for “small fry of fish”.

2 responses to “Pam Schaffer: Sampling the Food- Assessing Krill Populations July 5, 2018

    • Hi Jenny, My sleep schedule on-board was shaped around Tucker Trawl times. We collected samples a couples of times a day. We worked from noon to until around 4 pm and again from midnight until around 4 am. I also helped in the wet-lab during the day. My sleep was basically broken into two, four hour chunks. I was tired when I first got home but it wasn’t too severe. It’s been hard getting back on a regular sleep schedule though. I keep walking up at midnight.

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