Atlantic Salmon Starve As Plankton Pastures Perish - We Can Feed Them

Atlantic Salmon Starve As Plankton Pastures Perish – We Can Feed Them

We are working now to bring our methods and ideas to the world of Atlantic Salmon.

We recently stumbled across a great post about the crisis Atlantic Salmon face. It was originally published in the Conversation January 2014 ( Author — Chris Todd: Professor of Marine Ecology at University of St Andrews

It’s all uphill for salmon right now. David Cheskin/PA

It is an enduring mystery how juvenile salmon, at 12cm long and weighing perhaps only 20g, can leave a Scottish river in springtime, undertake a sojourn of thousands of kilometers around the North Atlantic, and return between one and four years later to their rivers to spawn. This is for good reason. A returning salmon, known as a grilse, will have grown 100-fold in size from the rich feeding to be found at sea.

But the journey is not without risk. Between 80-90% of grilse, and fewer still multi-winter fish, will not survive their journey. The serious problems wild salmon now face at sea go beyond the hardships of their itinerant life-cycle. These have been intensively researched throughout Europe and North America, and it’s clear that in recent decades salmon mortality rates at sea have increased enormously. While possible causes include natural predation, disease and parasites, or being caught up in fishery by-catch, the truth is we just don’t know.

My research, in collaboration with Marine Scotland Science, has focused not on mortality rates and population decline, but on the changes in size and quality of salmon returning to Scottish rivers over the past 50 years. This variation seems to stem from the effects of climate change on the ocean, and the anomalously high temperatures salmon find in the North Atlantic.

Shrinking salmon

In 2008 we published a study of quality, or condition factor, of adult salmon returning to Scotland between 1993-2006 . This was measured by dividing the observed weight by the expected weight for a fish of that length. The skinny fish, top, is less than its expected weight by more than a quarter (26%), while the bottom fish is illustrative of the long-term norm, being only 4% underweight for its length.

The plankton diet isn’t working for them. Chris Todd

Some individual salmon return in spectacularly good condition, perhaps by chance finding areas of rich feeding. But far more common in recent years are less well nourished salmon showing poor growth. Examining extensive salmon records dating back to 1963, we can see the long-term pattern. Between 1963-1993 there was nothing unusual. During the late 1990s the average condition increased to a high in 1997, but then fell precipitously until 2006. Salmon anglers in Scotland recall 2006 as the “year of skinny grilse” – understandably so, because that year’s salmon were not only in poor condition but also unusually short.

Since 2006 the average salmon length of salmon has increased slightly but the average condition factor is consistently low, fluctuating around at least 7% below average. The data up to 2013 show no signs of improvement. For example, between 1997-2010 the average weight of grilse returning to the River North Esk in east Scotland fell by 29% from 2.35kg to 1.67kg. And for summer-returning salmon that stayed at sea for two winters the average has plummeted from 6.18kg to only 3.63kg. Clearly, salmon are currently having a tough time of it at sea.

(Ed note: Clearly replenishment and restoration of ocean plankton pastures has worked in the NE Pacific resulting in recovery of Pacific Salmon species to all time high abundance. See more here… The Fish Came Back…   Experiments that parallel the spectacular success of Ocean Pastures 2012 NE Pacific restoration are now planned in Atlantic Salmon territory with expectations of similar success… the fish can be helped to come back.)

This approach might be considered as “lambs to the slaughter”, but over millions of years salmon have survived ice ages and eras of global warming. Helping salmon populations recover naturally is clearly a better strategy than rearing them artificially. Read the full article by Prof. Todd here

Chris Todd is Professor of Marine Ecology at University of St Andrews. He receives funding from the European Commission, the Atlantic Salmon Trust, the Association of Salmon Fishery Boards for Scotland, and the Fishmongers Company.

Some of his recent publications include:  Friedland, K & Todd, CD 2012, ‘ Changes in Northwest Atlantic Arctic and Subarctic conditions and the growth response of Atlantic salmon ‘ Polar Biology , vol 35, no. 4, pp. 593-609.

Gargan, P, Forde, G , Hazon, N , Russell, DJ & Todd, CD 2012, ‘ Evidence for sea lice-induced marine mortality of Atlantic salmon (Salmo salar) in western Ireland from experimental releases of ranched smolts treated with emamectin benzoate. ‘ Canadian Journal of Fisheries and Aquatic Sciences , vol 69, no. 2, pp. 343-353.

Russell, I, Aprahamian, M, Barry, J, Davidson, I, Fiske, P, Ibbotson, A, Kennedy, R, Maclean, J, Moore, A, Otero, J, Potter, T & Todd, CD 2012, ‘ The influence of the freshwater environment and the biological characteristics of Atlantic salmon smolts on their subsequent marine survival ‘ ICES Journal of Marine Science , vol Advance Access.

Finstad, B, Bjorn, P-A , Todd, CD , Whoriskey, F, Gargan, P, Forde, G & Revie, C 2011, ‘ The Effect of Sea Lice on Atlantic Salmon and other Salmonid Species ‘. in O Aas, S Einum, A Klemetsen & J Skurdal (eds), Atlantic Salmon Ecology. Wiley-Blackwell, Chichester, UK, pp. 253-276. Todd, CD ,

Friedland, K, MacLean, J , Hazon, N & Jensen, A 2011, ‘ Getting into Hot Water? Atlantic Salmon Responses to Climate Change in Freshwater and Marine Environments ‘. in O Aas, S Einum,

A Klemetsen & J Skurdal (eds), Atlantic Salmon Ecology. Wiley-Blackwell, Chichester, UK, pp. 409-443. We can restore Atlantic Salmon pastures and bring back those fish.