NOAA Teacher at Sea
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|
|Present Weather/ Sky||Cloudy|
|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)
|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.
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.
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.
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”.