Tag Archives: plankton

Sampling Hours in the Ocean of the Midnight Sun

 

 

One thing I find interesting on this cruise is that we only sample in so-called daytime hours.  Despite the fact that we are above the Arctic Circle and have 24 hours of sunlight, the fish still sense the change in time of day.  It is not the darkness that determines the fish behavior but the angle of the sun and light penetration into the water has an effect because of the albedo, the reflectivity of the light on the water.  Even though we are in the land (or ocean) of the midnight sun, the fish still move to deeper waters at night.  For this reason, we begin sampling in the early morning and end in the late evening noting that our highest concentration of fish are caught in the middle of the day. 

We are also finding very small concentrations of plankton in the area.  This is peculiar but apparently has been the case in this region of the Norwegian Sea for some time now.  One theory is that the abundance of the small pelagic species, herring, mackerel, etc is leading to over-grazing driving the populations down.  This will eliminate food for the young salmon on their way to grow and fatten up in the north before heading back to their natal rivers. 

There is so much to learn about the Atlantic Salmon and the possible reasons why they are getting “Lost at Sea.”  We are only just skimming the surface of our understanding and this cruise and the other SALSEA cruises are seeking to answer the question of what is happening to the post-smolt salmon that are leaving the rivers when they enter the ocean…