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Winter and Spring Transition

April 29, 2021

It’s been an exciting 2021 for the NHL team. Not surprising, winter weather prevented sampling on some of our small and large boat trips. We are patient and pounced whenever the swell was manageable.

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Washed up pyrosomes on an Oregon beach in mid-February. There were many sightings of these pelagic tunicates in the winter of 2020/2021, but they have been absent this spring.
Washed up pyrosomes on an Oregon beach in mid-February. There were many sightings of these pelagic tunicates in the winter of 2020/2021, but they have been absent this spring.

Water temperature in winter was slightly colder than average and the water column was well mixed. During winter, the plankton were characterized by familiar winter (southern) species, but species indicative of summertime cool ocean conditions made an early appearance at our mid-shelf station. These are copepod species such as Calanus marshallae, a lipid-rich northern species, and Neocalanus. Pyrosomes  were spotted up and down the Oregon coast in winter, likely transported from southern waters where they have remained more prevalent in recent years.

In early April we felt the strong, persistent North winds which usually herald the start of the spring transition. An upwelling data product compiled by Pierce and Barth, OSU physical oceanographers, calculate 2021 as the year of earliest spring transition in their 36-year dataset. We sampled during a period of wind relaxation in late April and encountered our first batch of ‘gunky’ samples. From nearshore to mid-shelf, the water was full of phytoplankton, making our nets and samples a deep, dark green. We also captured a strong pulse of meroplankton including barnacle nauplii and polychaete larvae. This is in stark contrast to our offshore stations which were full of krill, Pseudocalanus (cold water copepod), and Neocalanus (cold water copepod); creating a beautiful pink color in the samples.

Water temperatures were cold and CTD casts along the NHL showed characteristic upwelling dynamics. Check out contour plots and oceanographic data graphs that are updated after each cruise.

We could be looking at another early biological transition and a productive upwelling season.

 

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Vertical net samples from our NH-5 (left) and NH-25 (right) stations.
Vertical net samples from our NH-5 (left) and NH-25 (right) stations.

 

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An up-close look at NH-25 vertical net sample. The pink color is coming from the abundance of Pseudocalanus, Neocalanus, and krill. Can you make out the torpedo-shaped copepods interspersed with the krill?
An up-close look at NH-25 vertical net sample. The pink color is coming from the abundance of Pseudocalanus, Neocalanus, and krill. Can you make out the torpedo-shaped copepods interspersed with the krill?

 

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Hauling up the vertical net.
Hauling up the vertical net.

 

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Last updated by Northwest Fisheries Science Center on May 06, 2021