A study published in Global Change Biology, a scientific journal, found that brook trout spawn later in the fall and aren't as productive when water temperatures are elevated in the summer months.
The study, which appeared online in March, was performed between 1998 and 2010 on Rock Lake. The body of water is located on private land east of Stillwater Reservoir in the southwestern Adirondacks. The lake hasn't been stocked since 2002.
"Brook trout are cold water fish," said Cliff Kraft, a professor of fisheries and aquatic sciences at Cornell University and one of the authors of the study. "We know they aren't going to thrive in warm water temperatures. I think the thing that surprised us was that they shut down in the middle of the summer and that led them to spawn later because they just didn't have the energy to reproduce."
Photo courtesy of Cliff Kraft
Scientists measure a brook trout from Rock Lake in the southwestern Adirondacks. The trout was part of a study that analyzed how spawning patterns are influenced by warming water temperatures.
The study found that when the water temperature rose an average of one degree celsius (or 1.8 degrees Fahrenheit) in the summer, between June 15 and August 15, that spawning was delayed by about one week. The fish also made fewer spawning beds.
Adirondack brook trout that live in ponds or lakes usually spawn in October by building spawning beds on top of cold water springs along the shorelines.
This activity would be delayed when water temperatures rise to about 70 degrees Fahrenheit in the summer months because the fish would become stressed and not have the energy to feed. The stress delayed the growth of the animals' reproductive organs.
"In unusually warm years such as 2005, when temperatures were elevated throughout the summer, no redds (spawning beds) were observed in the fall and the 2006 year class was lost entirely," the study states.
Kraft said brook trout can bounce back from one off year. However, he said three consecutive warm summers would do serious harm to the population.
This brook trout study comes at a time when climate scientists are continuing to predict increasing air temperatures in the coming years.
A ClimAID report issued last November by the New York Energy Research and Development Authority, that was the subject of a conference recently at the Wild Center in Tupper Lake, forecasts the average annual temperature of 42 degrees Fahrenheit in the Adirondacks will increase between three and five degrees by about 2050 and between four and nine degrees by the 2080s.
Kraft said he couldn't predict what was in store for future brook trout populations because he's not a climate scientist.
"The message is that these types of long term studies are important," Kraft said. "We can make all kinds of predictions. At some level, (when you have) really warm water temperatures, consistent warm temperatures, you're really not going to have brook trout. There's no question about that. But that's not what we have now. We obviously have plenty of cold nights and cold water in the Adirondacks and it sees variable water temperatures that we're trying to understand.
"People are going to make climate forecasts and we're gong to try to connect that to what is happening to animal and plant populations, but the only way we are really going to understand it is to watch how these things play out."
Kraft went on to say that the real threats to brook trout right now is actually not warm temperatures.
"It's introduction of non-native fishes, like smallmouth bass and northern pike and brown trout," he said. "Those have hammered brook trout in places where they have disappeared. Destruction of shoreline habitat and groundwater refuges for them - that's hammered them. So the real threats to brook trout haven't been warming temperatures to date. And I hope that they'll be around for a long time and I expect that they will be."