Wednesday, 11 January 2017

What’s the deal with fish kills?

Part-two of my exciting* investigation into ocean health and its relation to climate change – a discussion on the recently emerging concern over fish kills, or mass fish deaths, that have been occurring at home and around the world! To tackle this topic a general background of the impact on climate change on fish will take place, followed by a more in-depth look at what seems like a newly emerging trend of something called a fish kill.

In the previous post about the impact of climate change on the oceans, it was discussed that fish migrations are one of the biggest concerns. This was due to rising water levels and temperatures, changes in circulation cells and current patterns, as well as ocean acidification leading to a lack of nutrients for fish species to feed on. But related specifically to fish populations, there is a bit more to it than simply understanding ocean health, itself. Of course, all the aspects noted in the previous post have impacts on the habitats of fish species, which was discussed briefly. This first section will look at two much broader issues, that do impact aquatic ecosystems: ocean acidification and rising water temperatures.

The rise in acidity prevents species such as shellfish and coral to produce their shells. But it’s not just the species that appeal to humans – either visually or deliciously – that are impacted directly by this process. Ever hear of a thing called zooplankton? Well, this is one of the main staples for a good chunk of aquatic species. Zooplankton, like the above mentioned species, also have shells, which are prevented from developing through the process of acidification. If zooplankton cannot form, what will the fish that rely on it as a source of nourishment use to supplement it? In other words, ocean acidification doesn’t just hurt our own food sources, but that of the aquatic species we like to eat!

Rising water temperatures are linked to ocean acidification, meaning this, too, impacts the food sources for many fish species. But, this aspect of ocean-related climate change actually impacts fish in another way. Fish require specific temperatures in order to maintain healthy, happy lives. When water temperature fluctuates – one way or another – it can affect their ability to metabolise the foods they have consumed. When this ability has been compromised, it leads to a species’ inability to grow to full capacity, reproduce, and therefore continue to repopulate – thus completely altering its lifecycle. This, obviously, leads to a variety of challenges, both related to the fish populations themselves, but also, to us human-folk who rely heavily on many of these affected species as a source of food. This problem, of course, is further exacerbated as we continue to participate in over-fishing practices, which lead to additional decreases of the aquatic populations.  Which leads me to my next point/topic: fish kills.

The discussion of fish kills became a widely discussed subject in Nova Scotia in recent months. Some of you may recognize this article, or one of several-like ones. You may have even seen a variety of Facebook posts including pictures of shorelines covered with various aquatic species. And, yes, this does appear to look quite alarming… but is it really?

The basis of the above CBC article and subsequent posts on social media put into question a recently placed tidal turbine in the Bay of Fundy, as a possible source of these washed up fishies. The article did debunk this suggestion, and knowing the extent of research that has been conducted over the years related to this topic, I was sceptical of these allegations, myself. Any large scale project, such as this, would have been subject to fairly substantial environmental impact assessments (EIA) – even despite Harper’s rewrite of EIA law and processes in Canada a few years back. But, given that there were 4 reported cases of fish kills between the end of November and throughout the month of December, it is understandable to think there might be something related happening in Nova Scotia’s waters.

So, to get started on the topic of fish kills, perhaps a brief definition is in order!

Also known as fish die-offs, a fish kill relates to the occurrence of mass, or highly noticeable, fish population deaths. They are usually made noticeable when the group of dead fish wash up on shore, creating a rather alarming sight. While they can be caused by human-related activity, most cases of fish kills happen as part of some natural process. These causes include:
  • Algae blooms and red tides
  • Biological decay
  • Diseases and parasites
  • Droughts and overstocking
  • Oxygen depletion
  • Pollution and Eutrophication
  • Toxins
  • Underwater explosions
  • Water temperature

But, for the purposes of this post, I will be focusing on oxygen depletion, water temperature and toxins.

Lack of oxygen has been frequently noted as the number one reason for the occurrence of fish kills. Like us, fish also require oxygen in order to breathe – although their method of accessing it is a bit different from ours! While you or I would get oxygen through the natural processes above water, fish retrieve it through dissolved oxygen found within the water, itself. When fish aren’t able to gain enough oxygen, just like we would, they begin to struggle to live, and eventually, if that isn’t corrected, will die.

Now, there is a pretty substantial link between oxygen levels and water temperature rise. You see, cooler waters hold greater amounts of oxygen. So, as water temperature rises, the amount of oxygen found within a particular body of water will begin to drop. However, fish kills can also occur when cooler temperatures happen rapidly, because, let’s face it, any drastic change in temperature affects most living things. By this, I ask that you think about how extreme temperature changes affect us, as humans, with an ability to bundle up or peel down. Fish don’t have this luxury; therefore, they are more directly affected by these fluctuations. These warmer temperatures can also breed algae blooms, parasites, and other forms of aquatic disease, all of which have a direct impact on fish populations.

Finally, it is important to touch on the topic of toxins**. This, of course, is a much less natural occurrence, and is something that we actually have some degree of control over changing. It isn’t overly difficult to understand how toxins can negatively affect not only fish species, but the ecosystems in which they inhabit. Depending on the size of the body of water contaminated, the outcomes of the introduction of a toxin can have varying results. In other words, contaminating an entire ocean requires far more toxins than, say a small lake. But, toxins can come in several forms, some of which we may not think of. Oil spills are usually what comes to our minds in these cases, but are only one of many ways that toxins can enter a body of water. These situations can also occur through agricultural run-off, improper disposal of chemicals or hazardous waste, and sewage, to name a few.

So, while the appearance of fish kills can certainly provide us with a sense of alarm, these are actually natural processes. However, there have been few reports of total population losses as a result of these occurrences. This doesn’t mean we shouldn’t keep an eye on things, but rather that when it does happen we shouldn’t be quick to blame things we might feel are the obvious causes. Either way, there are some correlations between human activity and fish kills. Climate change is also certainly having an impact of fish species, making it all the more important to make conscious efforts related to how we are interacting with the natural world – both as individuals and a wider species.

-the Orange Canadian

*Perhaps it’s only exciting to me…

**Say that 10x fast!

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