Cazenovians, especially those who live on Cazenovia Lake, have noticed an unusually high number of dead and dying sunfish in and around the shores of the lake, which has caused many to wonder why and what is the cause.
According to experts, it’s stress.
The larger-than-usual fishkill is a combination of the extremely harsh winter just ended and the presence of a naturally occurring parasite found recently in samples taken of the fish; and the fact that sunfish are spring spawners and the lake is experiencing sudden temperature shifts probably is not helping.
“We are aware of the die-off,” said Dave Lemon, fisheries manager for DEC Region, which encompasses nine counties including Madison. “What you’re seeing isn’t typical winter kill; this is a post-ice out event occurring probably because of the severe winter, and now the warming temperatures are putting more stress on the fish as well.”
Lemon said that three weeks ago, a DEC biologist who was fishing on Cazenovia Lake noticed the high number of dead sunfish and collected six dying fish as samples for testing. The fish were taken to the Cornell University fish pathology lab and the results stated that the fish suffered from a “moderate parasitism,” or a common bacterial infection from naturally occurring parasites.
“Basically, their assessment was that they didn’t anticipate any viral issues. They suspect that moderate-to-heavy loads of the parasite in the gills of the fish, combined with the long cold winter, would have compromised the immune system and has allowed the bacterial infection to flare up,” Lemon said. “It’s not some sort of human-related issue.… We’re pretty confident it’s just circumstances.”
He said the combination of temperature change, plus parasites plus the fact that sunfish as spawning puts their bodies under a lot of stress and contributes to the large death event. He said the fact that it appears to be only one species of fish that is dying is a “good indicator” that the cause is an environmental factor and not a toxic event.
“I would not be surprised if it gets worse again if we have another quick warm-up,” he said. “Rapid temperature change can affect fish as well.”
Thad Yorks, program director for the environmental biology and biology programs at Cazenovia College, who performs an annual fish survey of Cazenovia Lake, agreed that the harsh winter just ended was certainly a contributing factor to the recent fishkill event.
“I think that, given how unusually cold/long/snowy the last two or three months of winter was, it would have been more surprising if people did not see more dead fish than usual,” Yorks said. “Winter fish kills are indeed natural and could be expected to be noticeable after a winter that included the coldest month on record.”
Yorks said that while ice covering the lake does not block too much sunlight from getting to the water underneath, accumulating snow on the ice “absolutely decreases” the amount of light getting down into the water column and bottom of the lake, which reduces the amount of oxygen levels in the water.
Typically, fish die all year round and usually sink to the bottom of the lake where they decompose. During the winter, the cold temperatures slow down the rate of decomposition and when the ice melts off in the spring the dead fish can end up along the shoreline, according to information posted on the town of Cazenovia website.
“Data we’ve collected in the past few years (and presented at the Lake Summit last fall) indicate that the Caz Lake fishery has been in fine shape, so there were a lot of fish competing for what became less and less oxygen,” Yorks said. “Even if the numbers that died amount to something substantial, I’ll be very surprised if those numbers don’t quickly bounce back.”
Jason Emerson is editor of the Cazenovia Republican. He can be reached at [email protected].
