Causes and Consequences of the Miramichi Salmon Decline

Since the 80s, the number of Atlantic Salmon (Salmo salar) returning to the Miramichi River have experienced a drastic decrease compared to previous years. According to Department of Fisheries and Oceans from 1992 to 2014 the Miramichi watershed has seen a 93.5% decrease in the number of returning Atlantic Salmon! While numbers have since showed some improvements, they are nowhere near the numbers from their glory days.

Why has the salmon Popular Diminished?

Atlantic Salmon -  Copyright to Walter Baxter,  image  used under a  creative commons Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0) license. 

Atlantic Salmon - Copyright to Walter Baxter, image used under a creative commons Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0) license. 

There are many propositions as to why the Salmon population has decreased such a significant amount. One that might have already come to your mind is climate change. Salmon are ectotherms, so their internal temperature depends on the external temperatures. With warmer summers, the water temperatures are beginning to stray away from the Salmon’s optimal temperatures (4-12°C) , approaching the upper threshold temperatures in which they can survive (28°C being lethal, and anything over 20°C impeding survival). Over the summer of 2017, the Miramichi River contained periods where water temperature readings of exceeded 30°C! This is much too high for Salmon survivability. Another thing to note is that temperature isn’t uniform in rivers. Some spots will have higher and lower temperatures. Thus, there is an increased competition between Salmon, and other species, for colder habitats which will also act to reduce population size.

Another hypothesis in regards to the decline in Salmon population size is excessive fishing. Atlantic Salmon from the Miramichi River are fished in the river (of course...) but also in the ocean because of their life cycle. Salmon are “anadromous” fish. An anadromous fish is one that is born in freshwater, matures in the ocean and then returns to freshwater to reproduce. Anadromy is important to the nutrient cycle as the participating fish carries essential nutrients from one ecosystem to another. Therefore, throughout their life they have the opportunity to be exposed to countless fishermen from different provinces, and even countries. The exposure of Atlantic Salmon to multiple regions leaves them vulnerable to multiple regulations, some more strict than others.

Habitat destruction is also thought to be a prime candidate to the decrease in the Salmon population. Lots of riparian vegetation (especially trees) is being harvested next to rivers and streams inhabited by Atlantic Salmon. The canopy created by this vegetation is essential to salmon survival as the shade from riparian vegetation acts to cool the shadowed regions. The covered regions then create an ideal habitat for Salmon, allowing them to effectively regulate their temperature. With the introduction of climate change, the canopy plays an even more important role in helping to preserve the Atlantic Salmon population. The riparian vegetation also provides a lot of nutrients to the rivers. While Salmon may not feed on leaves, a lot of the things they eat do. Therefore, if the invertebrates Salmon predate on aren’t getting enough nutrients, neither will they.

While there are many hypotheses’ about why the Atlantic Salmon population has decreased, none thus far have unveiled the entire truth of the matter. Is it over fishing? Climate change? A combination of reasons? Or is it something we have yet to consider?

Why should we care?

If you’re not a fisherman you might be wondering, “why should I care?” If the number of returning Salmon continues to decline, the Salmon population in the Miramichi River will become functionally extinct. Functional extinction means that they are still present, but no longer have an ecological impact. Therefore, if the number of returning Salmon becomes small enough, they will no longer make a significant contribution to the nutrient cycle. Without their contribution, other species such as their predators will become affected as well. As more and more species are affected, a cascade effect will occur eventually affecting plant life, and then potentially spreading to neighbouring ecosystems. This includes us! In biology, things are often more complex than they appear and small changes often have even larger implications.

Salmon also hold a large socio-economic value here in New Brunswick. In 2010 alone, Salmon generated a GDP (gross domestic product) value of 54.7 million dollars (Gardner and Pinfold 2011). Without any Salmon returning to our rivers, that price drops to 0 and can have a huge impact on our province’s economy.

What’s being done?

There are two approaches to the Salmon problem in the Miramichi River. The first is the freshwater approach. The freshwater approach involves catching salmon as seaward migrating smolts, raising and then releasing adult salmon into the wild to reproduce and continue their life cycle. The purpose of doing this is to give Salmon a head start by temporarily guaranteeing their survival in captivity allowing them to safely travel to the ocean with the hopes that they will make it back the following year. Theoretically, smolt-to-adult supplementation should bypass any issues with ocean survival that are causing the salmon population to dwindle.

A CAST member pounding rebar in the Miramichi River to secure a sonar camera to allow accurate counting of salmon  - Photographed by Jani Helminen

A CAST member pounding rebar in the Miramichi River to secure a sonar camera to allow accurate counting of salmon - Photographed by Jani Helminen

While ocean survival has been addressed, the next concern is the marine approach. The marine approach involves tagging Salmon with satellite tags that track their migratory patterns. With this data the team is able to see where Salmon are spending a lot of their time, so they can identify problems or areas of concern.

A team of scientists collectively called ‘CAST’ (Collaboration of Atlantic Salmon Tomorrow) are working together to investigate and act on the decline of the Atlantic Salmon population. CAST’s ongoing research involves accurately counting the number of returning Salmon each year, quantifying and interpolating land use affect on stream temperature, raising and releasing Salmon into the wild as well as many other projects. In doing these things, they will be able to accurately monitor our progress and focus Atlantic Salmon research in the right areas. 

What progress has been made?

The next question that comes to mind is how is the progress going? As this issue is only recent, CAST does not have any reliable data to see nor confirm any results in regards to progress. However, CAST has recently created a website that contains current estimates on the Salmon population size using ARIS sonar technology. The rekindling of the Salmon population can be monitored here.  

The ASRJ is proud to provide this article to you in partnership with the UNB Undergraduate Biology Society. 



DFO. 2017. Update of indicators of Atlantic Salmon (Salmo salar) in DFO Gulf Region

Salmon Fishing Areas 15 - 18 for 2016. Canada Science Advisory Secretariat. Science Response.

Gardner Pinfold. 2011. Economic value of wild Atlantic salmon. A consultant report  prepared for Atlantic Salmon

Federation. Gardner Pinfold Consulting, Canada.

Atlantic salmon, Salmo salar. Accessed on 28 September 2017.

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