Tag Archives: Atlantic Salmon

Why are the salmon “Lost at Sea?”


As I have written about in an earlier post, the purpose of this research project, SALSEA-Merge, is to understand the life history of the Atlantic Salmon, and to the figure out why they are not returning to the river after their migration out of the rivers and into the sea.  This expedition is seeking to understand what is happening to these smolts along their journey through genetic testing, etc.  With the knowledge or lack there of about what is actually happening, some of the problems facing these salmon are known.  

Some of the problems facing these salmon include poor water quality in the rivers, over-harvest, discards of post-smolts as bycatch, sea lice, and lack of food when they reach the sea…to name a few.   The first two are clear, the fish need a good habitat to live in and with development, etc, water quality in the river goes down.  This needs to be improved so that the salmon don’t have to battle poor conditions in the beginning (and end) of their lives. 

Overharvest is also straight-forward.  If you take too many fish, there won’t be any spawners left to replenish the populations.  Overharvest is one of the largest problems facing the fisheries of the world and the salmon are right there in this losing battle. 


Two Russian trawlers in the distance


Bycatch is another issue that is key to the decline of many fisheries, but with the salmon, it was a new idea to me.  The post-smolts follow a similar migratory path to the shoals of mackerel that are targeted by the large Russian factory trawlers using massive surface trawls to harvest the mackerel in large numbers.  While the actual impact of these trawlers is unknown, it is hard to imagine that thousands of post-smolts are not captured in these trawls and processed with the mackerel.  The mackerel and post-smolt salmon occupy the same water and having seen the number of mackerel we captured in the sampling trawls, it is hard to imagine that with the size of the trawlers, they are not impacting the population of salmon. 

Mackerel bycatch from the sampling trawl…100 post-smolts were captured in this trawl…can you imagine how many are taken in the large factory trawls?  it must be thousands!

The other problems are distinct possibilities as well.  Many of the post-smolts we collected had sea lice on them.  I learned on the voyage that if a post-smolt has a certain number of sea lice on it, it will certainly die.  The sea lice attach themselves to the smolts on their way out of the river past fish farms.  Fish farms are the culprit in this game.  As the smolts pass, the nauplii (1st stages of development of the sea lice which are copepods, small crustaceans) attach themselves to the smolt and develop into adult sea lice which will remain on the salmon for the remainder of its life.  The level of infestation of the sea lice is tremendous and is one of the major problems arising from the use of fish farms to rear salmon. 

This salmon is infested with sea lice giving way to poor body condition.

Finally, the populations of the small pelagic fish, herring, mackerel, blue whiting, have boomed in the past years impacting the density of zooplankton in the Norwegian Sea.  With the increasing populations due to good management of the stocks for maximum abundance, the zooplankton has been grazed heavily leaving a sea nearly devoid of zooplankton.  Without zooplankton, our post-smolts have nothing to eat so their body condition is not good and they will not be able to survive without food.  This may be a cycle but it is largely unknown at this point…more research must be done.

With all of the potential problems outlined above, it may be something entirely different, but it is hard to imagine how one of our tiny post-smolts can survive its year-long journey in the sea to return to the river to spawn.  In fact, given all of the human obstacles we have put in front of them, it is remarkable that any return at all.  


June 27: Day 2 of Sampling- South and North


With an early start to the day (0500), back up to the north, the CTD was in the water.  The trawl was in and fishing by 0600 for a three hour tow.  At 0900, the tow came up and was as expected with a nice concentration of post-smolts although they are quite small.  The trawl went out again for four hours on the second tow but the haul had far fewer fish than anticipated.  With that in mind, we steamed north a bit for the third tow.  We are kind of zigzagging along a contour in order to find higher numbers of post-smolts. 


After ending the day with a smaller number of post-smolts, we are steaming farther north to sample tomorrow into the northerly current.  We should be above 68°N in the morning to begin sampling so in fact our first proclamation of the northernmost point of the voyage will be incorrect. 

The day was filled with quite a bit of wildlife though.  We saw a few sperm whales cruising on the surface in addition to two minke whales and a fin whale.  There are quite a few fulmars following the ship as well. 



Sperm Whale Fluke

A fulmar soaring past the ship


I am quite excited to be heading so far north.  Perhaps we will get some sunshine but the fog is rolling in so it is not looking promising.  


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…


Day 2- June 24, 2009


I arose to a beautiful calm morning on the North Atlantic with the Hebrides to the east of the ship.  We are moving at quite a fast clip up to our sampling area, cruising at around 14 knots.  We have a southerly wind behind us adding to our speed and the calm seas are helping us along. 



Because today we are steaming (transiting), the chief scientists gathered all hands to talk about the sampling plan.  It seems we are going to begin sampling just below 68° N where the concentration of post-smolt salmon should be high as they funnel along the western side of the Voering Plateau.  We are anticipating a high catch in this area on our way to the more northerly sampling grounds. 




The rest of the day was spent exploring the ship to find good places and interesting angles to shoot photos and video of the net coming in.   And of course, enjoying the sunshine!  It was quite warm and very beautiful as we traveled up north, with gannets and other sea birds flying all around the ship. 

We have another day steaming tomorrow and should reach our first sampling area on Friday morning.  Because we are heading pretty far north, we may lose internet signal for a few days so the posts will be logged when we are back online.

We are now above 61 degrees North…The science should start soon…I am looking forward to seeing some post-smolts and whatever other species we capture in the nets!  


The SALSEA PROJECT- “Lost At Sea” Film


A few months ago, Deirdre Brennan, a fellow member of the Explorers Club, approached me about a film, “Lost At Sea,” she is making with Eamon de Buitlear about Atlantic Salmon and where they go in the ocean once they leave the rivers. The ratio of fish leaving the rivers to those returning has declined dramatically in recent years indicating a high mortality of the salmon at sea. In an effort to learn more about these post-smolt fish, the SALSEA project was created to learn about the oceanic migration of the salmon. Deirdre asked me to come along on one of the SALSEA expeditions to film and assist in the early stages of the film. Being the avid fisherman that I am and of course, my desire to know all there is to know about every fish in the sea, led me to participate on this SALSEA expedition aboard the RV Celtic Explorer into the Norwegian Sea to collect and sample post-smolt Atlantic Salmon on their way to their feeding grounds to the North.

I am very excited to be on this voyage and a part of this project as it is one of the first of its kind to do a comprehensive study of salmon at sea. We will be fishing for the salmon with surface trawls (large nets dragged right at the surface) because the post-smolt salmon, fish just leaving the rivers, are found in only the surface waters no deeper than 3m. Because the scientists are using genetic markers to identify the fish, every fish captured becomes useful as opposed to only tagged fish in the past. There are 1360 known salmon rivers in Europe and many of the highly productive rivers have been “genetically mapped” so that the fish caught in the ocean can be identified to their natal river.

We are heading north to an area west of the Voering Plateau where the salmon funnel into the Barents and Greenland Seas. This “salmon pass” is our target area in our quest to document the salmon migration. In its second year, the SALSEA project will attempt to answer questions of where the salmon go when they leave the rivers and why they are not returning.


Gaelin Rosenwaks & Deirdre Brennan are carrying Explorers Club Flag #81 on this expedition







After a bit of time on land, it is time for Gaelin and Global Ocean Exploration to head back out to sea.  We will be embarking on the R/V Celtic Explorer departing from Killybegs, Ireland and heading north into the Norwegian Sea.  Gaelin is honored to be carrying the Explorers Club Flag #81 on this expedition.  

The purpose of the voyage is to track Atlantic Salmon Migration at Sea.  The scientists I will be working with have completed a comprehensive genetic map of the rivers of Northern Europe and now are taking their sampling out into the ocean where they will collect specimens in order to add the ocean migrations into this map.  Understanding where the Atlantic Salmon go once they leave the rivers is of vital importance to creating conservation strategies for this fish prized for food and sport fishing.  

Currently, I am finishing my preparations to fly out to Ireland this evening where I will visit the Marine Institute, get some final safety certifications and then head out to sea on Tuesday.  Stay tuned to the blog for updates about the voyage and the science, and lots of pictures!  


Map of Voyage


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