Bucke Prize Winner Neff to Speak on the Science of Global Fisheries
By Mitch Zimmer
World GDP figures show that global fisheries contribute 200 billion dollars annually in revenue. Canadian fisheries make up four billion dollars of that. As substantial as this is to the Canadian economy the Pacific salmon in Canada and specifically Sockeye Salmon returns in the fisheries have plummeted from historical levels. In his Bucke Prize lecture on March 29, 7:30 p.m. Somerville House, Room 3345, Bryan Neff of the Department of Biology will examine the current state of the fisheries in a talk entitled, The Ocean’s Bounty: Science and the Changing Face of Global Fisheries.
The scope of the problem facing the Pacific salmon is daunting. “When you look at the time series data, not just any one year; you are looking at returns in the range of 2-10% of historic levels” says Neff. “We have fluctuations that are up and down so you might end up with returns that are twice what they were the previous year but then you’ve gone from 2% to 4%.” The numbers are in stark contrast to “Alaska where they are still at about 100% of historic returns, we’ve plummeted and the Pacific returns are dismal.”
The low levels of fish returns are attributed to a few main factors that lead to a loss of biodiversity says Neff. Overfishing and outdated management practices as well as habitat destruction are the leading causes. Habitat destruction includes things like pollution or where the habitat is altered in some way. “In the case of Pacific Salmon and British Columbia, it’s largely forestry. A lot of these streams, including the Fraser, run thousands of kilometers into the interior where there is a lot of forestry.” Traditionally, the forest companies cut large amounts of forest right up to the edge of the stream. This loss of the canopy results in a number of changes ranging from river runoff erosion and sediments, to the temperature of the water, as well as woody debris. These in turn affects the ecology of the river and the way fish reproduce. Salmon lay their eggs underneath the gravel and the introduction of sediment obstructs the aeration of the eggs eventually suffocating them. Temperature is less obvious, it has been shown that the egg size has evolved to suit the temperature of a river. Larger eggs normally develop in colder water and when the temperature rises, the metabolic rate within the egg increases which in turn raises the demand for oxygen and often stressing the supply. A further complication arises due to the fact that warmer water contains a lower concentration of dissolved oxygen than cold water. So if the forest canopy is removed, the water temperatures will likely rise with the end results of suffocating the eggs.
Neff’s research focuses on evolution by natural selection where organisms are adapted to their local environments via the way their genes are expressed to allow them survive and reproduce well in their local environments. So that even in the scale of a single watershed, different parts of a river and its tributaries might have different ecological characteristics. A single species like Chinook Salmon, one of the Pacific salmons which has a range extending from California right up to Alaska may great many genetic variables.
Forty years ago management decisions within the Department of Fisheries and Oceans (DFO) didn’t keep in mind that a Chinook salmon from Alaska may have a different genetic makeup than a Chinook salmon from British Columbia and so they would take fertilized eggs from different watersheds and plant them in other low yielding rivers where there would be different temperatures, different qualities of river bottoms (rocky versus pebbled) and where the native fertilized eggs would probably be a different size than the transplants. “Now in fairness to the DFO, which is one of the major regulatory bodies for Pacific salmon in Canada, they are much more aware of that” says Neff. “The problem with that is those fish carry genes that have evolved sometimes millions of years to the local environment, particularly with salmon since they return to where they were born. From a research perspective that’s one of the interesting avenues is how they know where they were born? A lot of research has shown it to be smell. Beginning as the embryo in the egg they begin to sense the chemical environment that they’re in and when they leave, it’s probable that they are smelling the odors as they swim out. Some fish swim out thousands of kilometers and when they come back it can be as close as metres to where they were born.” These fish may be away from the site for four or five years and in that time and if the environment is altered, the learned odor may be altered as well (especially if the water polluted) which may mask the odors the fish are trying to sense. If this happens the fish may end up not knowing where they are and make their way up the wrong tributary or the wrong area from where their genes have evolved. “There are also matters of physiological tolerance where the fish themselves are unable to withstand temperature fluctuations” says Neff. “Temperature is a big issue that has being receiving a lot of attention due to global warming. The rivers are warming with an average seasonal temperature warming.” “Climate change is receiving so much attention because it can impact on many species and ecosystems and we really don’t know the ability of these species to respond. So there is a physiological response along with a genetic or evolved response.” We know that climate change is rapid but it is still going to take some time.”