As the field season comes to a close, the loons are beginning to make their way back to the ocean and Loon Restoration Project interns are wrapping up their field seasons with Maine Audubon. Earlier in the season, after reading a study focused on loons and their reactions to poor water clarity, intern Anne Heissenbuttel dug up a Secchi disk (used to measure water quality) and got out on Maine lakes. Here is her report.
—By Anne Heissenbuttel
A particular segment of a Birds of the World article piqued my attention as I looked for a topic for an independent study as part of my summer internship with Maine Audubon’s Loon Restoration Project. It read, “At Secchi disk readings of ≤ 1.5 m, loons alter their foraging behavior.” It went on to say that water quality readings taken in Michigan found that lakes with poor water quality were not used by loons for nesting. When I read, “Further effort is needed to assess the … nesting success of loons in relation to water turbidity,” I knew I had found my project!
This research article prompted me to question if water quality had an impact on, or even a correlation to, the reproductive success of loon breeding pairs in Maine. More specifically, I decided to look at the loon pairs being monitored by the Maine Loon Restoration Project.
I combed through years of loon nesting data and looked at water quality records from the lakes and ponds where our team was working and developed a hypothesis: If a loon pair’s reproductive success relies on good visibility and high water clarity, then lakes with high turbidity (or cloudiness) and low Secchi disk readings will house loon pairs with a history of poor reproductive success.
For those who don’t spend their time testing water clarity, you may be asking yourself, what is a Secchi disk? A Secchi disk looks a lot like a Frisbee with alternating black-and-white quadrants on the top surface. It is lowered into the water until it can no longer be seen. The cloudier or more turbid the water, the sooner the disk disappears from sight. This depth of disappearance, called the ‘Secchi depth’, is a measure of the transparency or clarity of the water. So, the lower the number, the cloudier and poorer the water quality.
To take a Secchi reading, you drop the disk off the shady side of the boat and lower the disk until it is no longer visible. As the disk is lowered into the water, a tape measure is used to measure the depth where the disk first disappears from sight, as well as the point where it reappears as the disk is raised again. These depths are then averaged to get a Secchi Depth reading.
I prepped the Loon Restoration Team to take Secchi readings while on field visits. Our team was able to collect readings from loon territories on ten different lakes. Back in the office, I compiled the data into a table with poor water clarity indicated by red, and good water clarity with green, with shades of yellow indicating mediocre readings.
While we couldn’t collect enough data points throughout the season to draw solid conclusions, the data generally supported my hypothesis: only lakes with better water quality hatched chicks and lakes with poorer water quality had lower to non-existent reproductive success. Interestingly, the exception was a pond with the highest clarity of any of our samples (with a 5.85 meter Secchi depth reading), which didn’t hatch any chicks. Also interesting, it was the only pond we sampled where a nesting raft had not yet been deployed. As part of the Loon Restoration Project, we place rafts for pairs that continually struggle to hatch chicks due to nest flooding, terrestrial predators, and in some instances of nest disturbance. We will be placing a raft on this pond with high water clarity, but low nesting success, in 2025.
What to make of this exception? I think it underscores that clear water isn’t all that it takes for loons to hatch chicks! While a certain level of water clarity may be necessary for loons to nest successfully, we know that other factors affect loon nesting success as well, such as nest flooding from boat wakes or storm runoff. Maybe what this exception tells us is, perhaps, that rafts can’t help overcome a pair’s nesting issues if the lake doesn’t meet a base level of water clarity.
In short, while this data doesn’t prove that poor water quality adversely affects reproductive success, it shows a correlation between the two. It would be interesting to continue this work next season on more lakes to see if the trend holds true.
So what do we know about lakes with poor water clarity? Increased sediments and nutrients “can increase turbidity and water color while also fueling plankton with energy, which can lead to algal blooms that further diminish water clarity” (Wissel et al. 2003.) In other words, soil and nutrients can directly and indirectly decrease water clarity. In my study, one of the lakes with poorer water quality, with a Secchi reading of 0.9, showed undeniable signs of algal blooms at the time of the reading.
Why does water clarity matter to loons and how might it affect their reproductive success? Loons are visual predators that rely on good water clarity to see fish and other prey. So loons which catch more prey are presumably better able to nourish themselves and feed their young. If foraging success is dependent on being able to spot underwater prey, then clear water would be important to the loon’s health, the resources it has to devote to reproduction, and its ability to care for and feed its young.
It’s clear that the water quality of many Maine lakes and ponds is less than optimal. Poor water quality takes a toll not only on loons but on many species, aquatic and terrestrial. There are many ways you can help by spreading the word and also taking direct actions to improve water quality. Lake Stewards of Maine, the program that graciously lent me a Secchi disk for this project, may be able to help get you set up to take Secchi disk readings on your lake or pond if that role isn’t already covered by another volunteer. LakeSmart, a program run by Maine Lakes, has volunteers who are trained to evaluate lakeshore properties at the owner’s request and provide a voluntary plan of action for reducing nutrient and sediment runoff into your lake or pond. Aquatic nuisance species like Eurasian Watermilfoil and many others can also impact water quality; the state requires boaters to drain and dry their boats and clean off any hitchhikers before launching boats in another lake. You can also reduce your use of chemical fertilizers, clean up pet waste, or, if you live near a lake, increase the amount of vegetation between you and the water. Ultimately, keeping Maine lakes clean for us, the loons, and other wildlife requires all of us to take meaningful steps and lake friendly actions to protect the health of freshwater ecosystems in Maine.
