Winter can be cruel to animals. Food is scarce. Water is frozen. Temperatures are inhospitable. In Northwest Montana, the scene is played out before our eyes each season. Deer nibbling at dried grass that would not appear to offer much substance. A path through the snow, where the mountain lion dragged the deer. A carcass half buried in the woods, the lion's "refrigerator". It can be distressing, but it is the circle of life, the delicate balance that keeps the weak out of the gene pool and a check on overpopulation of any one species. Recently, my "back yard" gave me a ring-side seat to one of these events. Don't worry, it's not too terribly gruesome.
On January 24, I was walking along the lake at the bottom of our property, ever hopeful that the otter might have returned to the spring (see this post for my otter encounter last winter). As I approached the open water, a slight ripple broke the surface and I held my breath. Closer, and no sign of an otter. No slide marks, no sleek sable-brown body. Sigh. Instead, fish. Dozens of fish, roiling the water. What? Check out this video.
link about low oxygen levels under ice.
In especially long, harsh winters a winter fish kill can occur. During periods of prolonged ice cover, the lake is sealed off from the atmosphere and cannot be recharged with oxygenated air. Furthermore, ice and snow reduce the amount of sunlight reaching aquatic plants, thereby reducing photosynthesis and oxygen production. All the fish and aquatic organisms in the lake use up the oxygen, and when it does not get replenished, oxygen levels can get too low for fish to survive. Winter kill begins with distressed fish gasping for air at holes in the ice and ends with large numbers of dead fish which usually show up as the water warms in early spring.
We don't know for certain this is the problem, but it is one theory. It might also explain why the fish have not returned to the main body of the lake. (An alternate theory is that the passage back to the lake is now frozen.) In any event, within a couple days of my first sighting, several of the fish had died.
This site is visible from our house by spotting scope and binoculars, and although you cannot see the fish, you can easily detect critters around the open water. Not surprisingly, crows began to gather, sometimes a dozen at a time.
But they were not the main attraction. One afternoon, three bald eagles and 2 golden eagles were in the vicinity simultaneously! At my next opportunity, I placed my trail cam at the site, and I was thrilled to see these majestic raptors on film the next time I downloaded photos. (I apologize in advance for the number of pictures - trust me, these are the best of hundreds that the trail cam snapped in a span of two hours!)
In the two hours caught on film, the golden eagle ate at least 7 fish.
Interestingly, the article noted that perch and pike are generally tolerant of low oxygen. If that's the case, then the dead fish you see floating here might have died for other reasons. (I can't be certain, but it would appear, from the color of "dinner", that the eagle was selecting live fish.)
And then it got even better; the bald eagle arrived!
Before these pictures, if you had asked me about relative stature, I would have guessed the bald eagle to have the size advantage. Wrong! Having the bald eagle in the shot emphasizes the gigantic frame of the golden eagle.
The bald eagle wasted no time in snagging a fish, and departed as soon as the prey was consumed.
The golden resumed fishing, with vigor. I am sad for the fish, but the raptors are clearly benefiting from this ready source of sustenance.
I was rewarded with one blurry photo of a coyote; based on the position of the camera and the fact that it takes three photos in one go, I suspect that the coyote did not stop at the spring.
Only one raptor appeared on the trail cam, and that was a bald eagle in flight. My theory? Most of the live fish have been consumed and the raptors have therefore lost interest. (By the way, isn't it fabulous technology that the camera detected the eagle AND took this shot?)
So, now I wonder what we will face when the spring season arrives. Is the open pool of water an isolated case, or will the entire lake be awash in dead fish because of low oxygen levels throughout the lake? Can the lake replenish itself with fish? If some fish remain, breeding will restore the fish stocks. If all of them are gone, since the lake is spring-fed, the only natural source of new fish would be those that might swim UP the stream from lakes lower down in the system. Could be a tough putt - there is a substantial beaver dam where the stream meets the lake! But, in my experience, nature finds a way. That's the circle of life!