Communicating Science (2019w109)

You may not have noticed it yet but there has been a steady increase in the price of salmon in consumer stores. The reason for this is due to the high demand and low availability of these fish. Pacific salmon are a very important species of fish that contribute to the economy and play a very critical part in the food chain as the primary source of food for many animals including humans and the iconic black and brown bears. Their annual migration provides an insight into the yearly population and the abundance of their species.

However, the pacific salmon population has decreased in the past few decades due to the effects of global warming causing changes within the habitats they live in. This leads to issues such as suboptimal diets that have caused a decrease in salmon health leading to death. Predators have shifted to a higher salmon diet as their other prey are becoming less abundant due to changes in climate. Rising sea levels, destroying important transition zones for juvenile salmon, has also caused the salmon population to decrease even further.

As ocean temperatures rise, warmer ocean currents pull less nutritious plankton from the central oceans and deposit them to the salmon feeding grounds, at the same time driving out the more nutritious plankton from the coastal waters. (McSheffrey 2016). This can be a disaster for the salmon as the prey they consume also feed on this plankton. As the salmon prey cannot survive on such nutrient-limited plankton they start to die off and the remaining salmon are left with no choice but to substitute their regular feeding habits to accommodate a higher less nutritious plankton filled one. In the short term, this can sustain the fish, however, in the long term this plankton diets lead to lower energy production and a less nutritious diet which in turn makes the fish weaker and more likely to die.

While the salmon prey changes, the predators that prey on salmon have been moving to a higher salmon-filled diet. Global warming has not only affected the salmon’s food source but the food source of many predators that prey on salmon. Predators must change their diets as their other prey has been steadily decreasing. They must also resort to eating a higher percentage of a different species and in this case, it is a higher salmon diet. For decades the salmon and predator population has coexisted, “but salmon populations have come under stress from many sides, reducing salmon numbers and causing an unnatural predator-prey balance” (PBS 2016).  Some of the salmon’s main predators include gulls, sharks, pollack, cod, seals, pike otters, and killer whales. The result of these predators consuming a higher number of salmon causes an overall decrease in the number of salmon. Global warming plays a critical role in the predator to prey ratio and has a very drastic role in the depreciation of salmon.

If suboptimal diets and increased predation was not enough for the salmon to deal with adding habitat loss to the list of challenges is sure to cause a drastic decrease in the salmon population. Most salmon lay their eggs in estuaries that provide an important transition zone from a freshwater habitat to live in saltwater. (National Ocean And Atmospheric 2012). These areas are critical for salmon as it allows juvenile salmon to feed and provide them with a refuge area from predators, allowing for a higher percentage of juvenile salmon to make it to adulthood. As global warming causes ocean levels to rise, the water from the ocean sometimes floods into these low-lying estuaries altering the ecosystem in a way that cannot be reversed (National Wildlife Federation 2009) With these important transition zones being permanently altered, the juvenile salmon are now unable to obtain the proper food and protection from predators, thus, decreasing the probability of the salmon making it to adulthood.

Salmon species are very sensitive to any change in their environment and this can play a drastic role in their population.  These animals are an essential part of the world and their oceanic environment. Global warming is the main reason the salmon population is declining, sustaining the salmon population is critical if one wants to ensure the survival of this species.

Image by BBC’s wildlife photographer Jon Cornforth