For those of you who read Using "Sound" to See Underwater and Everglades at Night, you've learned a bit about the DIDSON (an imaging sonar) and have gathered that some of my work occurs at night in the glades. Below, I'll explain how I'm using the DIDSON to understand the role of predatory fish in canals of the Everglades.
Canals were dredged in the early 20th century to drain the wetlands and have now become a permanent fixture in the Everglades landscape. I could write a whole separate article on the harm canals have done, but for now I encourage you to read The Effects of Canals and Levees on Everglades Ecosystems for a review on their history and role in the landscape. Their relevance to my study is that the canals harbor large, piscivorous fish (fish that eat other fish), which is great for recreational fishermen but bad news for the little fish who have to fight for survival in these canals. Small fish play a very important role in the Everglades, serving as an critical food source for wading birds. As you can see in the video below and infer from the word "wading", these birds hunt for fish in shallow bodies of water. They may not be successful hunters in deep canals.
If we tie all these ideas together you've learned: 1) Small fish are possibly at risk for being eaten by larger fish, making them unavailable to wading birds, and 2) If small fish are congregating in canal habitats instead of shallow water bodies like they would have historically (before the creation of canals), wading birds may not be able to feed on them anyway. A double blow to wading birds.
The part that I'm interested in studying is the "risk" factor. Are small fish at risk for being preyed upon by large, piscivorous fish in the canals and are their certain times of the day or even year that this risk is higher. To answer this question, I'm sampling during the day and night and throughout the year to look at the diurnal and seasonal patterns of this risk. The DIDSON comes into play in that it allows me observe fish behavior and look for evidence of "risk" without disturbing the fish and since it doesn't require light, I can sample at night.
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| Sampling at night. Photo courtesy of Eric Fortman |
Stay tuned for future posts on what it's like to work in the Everglades at night and what I've observed in my DIDSON videos over the last year. If you have any questions about my work, please leave a comment below!
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