North Atlantic Oscillation, Woods Hole, NOAA, And What It Means

Concept
For a long time we anglers of Salmo Salar have been coming up with every reason possible for reduced returns. Clearly, the Atlantic Salmon rivers of the North Atlantic have been in decline.  My observation is that the further south the river mouth, the greater the decline.  In the United States the greatness of a revolution for wealth was a dagger in the heart of many fish species populations.  Now global warming, if natural or for man made reasons, continues the negative effect on southern waters.

In Canada, where there are many rivers without the blockage of dams, we have seen major disruptions in populations due to other reasons.  Netting, clear cutting, heavy metals mine spills, acid rain and greater angling pressure have all taken a toll.   In Europe the south was hit hard in the same way as the US.   Further north to a lesser degree, but over all declines have been evident.

My simple point is that you can look region by region and river by river and find a great number of reasons for decline.  I am now under the belief that there is one major factor that transcends all others.  One so clear in science it is hard to deny.   It's called The North Atlantic Oscillation(NAO).

Studies by The Woods Hole Oceanographic Institute as well as The National Oceanic & Atmospheric Association(NOAA)  have both been done on this subject.  My writing is but an attempt to understand the information gathered.

Most anglers I talk with about the NAO have no idea what it is.  When I mention El Nino everybody then has a reference.  Although they are not the same, the concept of this Earth phenomenon of open ocean effect on migrating species and weather patterns is understood and more important believed.

Definition
Wickapedia defines the NAO as follows:  "The North Atlantic oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is highly correlated with the Arctic oscillation, as it is a part of it".

During the 1960's and early 70's Atlantic Salmon fishing was having some of the finest years possible.  This continued into mid decade of the 70"s but the decline was noticeable and having a sharp impact.  By the early 1980's things were very different and many fishing regulations and daily limits were changed.  We still had all the river specific effects of man's doing but an overall world wide decline was taking hold.  At this same exact time there was something else that had happened.  The North Atlantic Oscillation moved from a narrow or negative difference in barometric pressure to a wide or positive difference. 

Science
Over the past number of years information has been gathered.  Part of this puzzle has been the need to understand the numbers of smolt going to sea.  Counting wheels and down stream shock counts have proven that the numbers remain strong.  The conclusion has been to look to the ocean for the issue.  Again, lets for a moment agree that man made problems like fish farms and sea lice, acid rain and natural issues as predation have effect, but don't allow us to look at the big picture.  This big picture is in the ocean and what is happening to the Salmon while at sea and the availability of food to eat.  Food availability is the key ingredient to a healthy Salmon population.  This will be especially noticed in the numbers of multi winter, multi spawning very large fish.

If we examine the current NAO history we will find that a positive or large gradient difference has been the pattern for the last thirty five years.   This effect brings strong westerly winds, warmer Southern North Atlantic Ocean temperature and colder Northern North Atlantic Ocean temperature.  When the NAO is in a negative pattern the winds are held to the south of the salmon feeding grounds off Greenland. 

Positive equals a decreased area of feeding or a band of ocean that is battered by high winds and rough seas further north and into the winter feeding areas.  A negative pattern creates a larger feeding ground or wider band of northern ocean that is calmer.  Salmon survive in an average of fourteen feet below the surface while at sea.  A harsh and rough environment means the disruption of the food source.  Can it be that the major populations of salmon thought to winter off Greenland and the Farrows Islands can be directly impacted by the weather conditions of those locations?  Is it also possible that certain river populations do their winter feeding in different locations that are effected more or less?  Are the salmon of the Kola feeding in the same winter areas of those from Scotland?  Do the Inner Bay of Fundy salmon that have been the hardest hit feed in a location not conducive to survival?   Can it be that the salmon of a single river will disperse to different feeding areas for the survival of the species?  

Nature will feed the strong to survive only to the degree of ability.  Should the ability be decreased by food deprivation, the weakest will continue to die until a level of survivability is met.   This is called the Balance of Nature.  Should critical mass be eroded to a tipping point the result will be catastrophic. 

Conclusion
Over the last five years it has been possible for me to predict the size and quantity of the salmon returning to North America.  Food and the availability of food in the ocean alone is the key factor. What man has done to harm the fish has been somewhat countered by all the good that has been done over the last thirty years.  We are now in the up cycle of this science and the next ten years should prove to be a very positive time for an angler of Salar.

So I don't leave this only to the Atlantic, you steelhead fans on the West Coast need only follow the Pacific Decadal Oscillation for your answers. 

William