Steven@HumboldtHerps
11-10-2008, 05:50 AM
Hello everyone! Today I'd like to share what's been happening to some of our California native frogs and garters high up in our alpine lakes. Multiple studies have been done lately that are realizing the detrimental effects of stocking lakes with non-native trout.
In the High Sierras, research has shown that many sub-populations of Mountain Garter (T. e. elegans), which here feed specifically on Mountain Yellow-legged Frogs, are on the decline. Concurrently, yellow-legs are also in severe decline. 2,103 alpine lakes and ponds were monitored (in 2 major locations) with test groups - some lakes were chosen that were stocked with non-native trout, others were free of non-native trout. Results depicted a direct correlation: stocked lakes had scant populations or none of both Mtn Garters and Yellow-legs.
So what is happening? Actually, the effect varies in some localities. In the Trinity Alps of the Klamath Mountains as well as localities near Shasta, stocked rivers and lakes have actually blown garter populations out of proportion and sent both predator and prey on massive migrations. The Oregon Garter (T. atratus hydrophilus) and Valley (T. s. fitchi) are on the rise here.
It should be known that, although garters do feed voraciously on tadpoles, frogs, and yes, locally on baby trout and other fish, adult trout like to exchange the favor by feeding on baby garters as well as tadpoles and the likes.... So there are all these lakes out there that are stocked for fishermen, because these lakes are over-fished.... probably don't even get the chance to grow old enough to breed before they're caught, tortured, and released or eaten. (I do fish by the way, but not for sport...). So, imagine these lakes regularly being stocked with farmed non-native ADULT trout. Those who do not get hooked , will get hungry, and their adult diet threatens younger generations of both frog and snake. So frog populations go first, since they are prey to both fish and snake; most likely their breeding grounds are compromised. In many of these alpine terrains, lakes are isolated by a variey of challenging geographical barriers, which makes migration difficult. Mountain Garters are usually known for being opportunists, in that they feed on a variety of prey species. Many of the Sierra populations feed exclusively on frogs and are not readily adaptable to the rapid change in the feeding heirarchy.
In the case of the Klamath populations, here the study was specifically carried out on the Cascades Frog, which is a remarkable frog (A recent Wildlife study revealed they tunnel under snow to their breeding ponds in early spring and are capable of migrations over 5,000 ft. peaks!), is nonetheless under fire. T. atratus is the most powerful swimmer of all Thamnophis (you should see them in the rapids), and while it relishes frogs and especially larval Pacific Giant Salamanders, it is primarily a fish eater capable of downing fairly good-sized trout. T. s. fitchi, although quite versatile in its diet at times, in this locality it primarily goes after the frogs. So Rana cascadae breeding populations are fleeing the rougher rivers and creeks (to avoid big trout and voracious atratus) for the remaining calmer lakes and ponds. Well, Valley Garters do prefer calmer bodies of water....
And so it's basically a situation where the frogs have nowhere to hide. Even atratus has been found leaving its preferred aquatic habitat in search of frogs on the move. I have seen them in the lakes.
So, it's something I thought you might like to ponder. Please note that there was no mention of any effects global warming or chytrid fungus might be having on the Sierra populations. Chytrid has also recently been found in the Trinity Alps. :( In case you don't know, chytrid, which once established in a particular habitat, can wipe out up to 80% of all amphibians living there within the first year!
That's a big BOO HOO for both frog and snake!
Steven
In the High Sierras, research has shown that many sub-populations of Mountain Garter (T. e. elegans), which here feed specifically on Mountain Yellow-legged Frogs, are on the decline. Concurrently, yellow-legs are also in severe decline. 2,103 alpine lakes and ponds were monitored (in 2 major locations) with test groups - some lakes were chosen that were stocked with non-native trout, others were free of non-native trout. Results depicted a direct correlation: stocked lakes had scant populations or none of both Mtn Garters and Yellow-legs.
So what is happening? Actually, the effect varies in some localities. In the Trinity Alps of the Klamath Mountains as well as localities near Shasta, stocked rivers and lakes have actually blown garter populations out of proportion and sent both predator and prey on massive migrations. The Oregon Garter (T. atratus hydrophilus) and Valley (T. s. fitchi) are on the rise here.
It should be known that, although garters do feed voraciously on tadpoles, frogs, and yes, locally on baby trout and other fish, adult trout like to exchange the favor by feeding on baby garters as well as tadpoles and the likes.... So there are all these lakes out there that are stocked for fishermen, because these lakes are over-fished.... probably don't even get the chance to grow old enough to breed before they're caught, tortured, and released or eaten. (I do fish by the way, but not for sport...). So, imagine these lakes regularly being stocked with farmed non-native ADULT trout. Those who do not get hooked , will get hungry, and their adult diet threatens younger generations of both frog and snake. So frog populations go first, since they are prey to both fish and snake; most likely their breeding grounds are compromised. In many of these alpine terrains, lakes are isolated by a variey of challenging geographical barriers, which makes migration difficult. Mountain Garters are usually known for being opportunists, in that they feed on a variety of prey species. Many of the Sierra populations feed exclusively on frogs and are not readily adaptable to the rapid change in the feeding heirarchy.
In the case of the Klamath populations, here the study was specifically carried out on the Cascades Frog, which is a remarkable frog (A recent Wildlife study revealed they tunnel under snow to their breeding ponds in early spring and are capable of migrations over 5,000 ft. peaks!), is nonetheless under fire. T. atratus is the most powerful swimmer of all Thamnophis (you should see them in the rapids), and while it relishes frogs and especially larval Pacific Giant Salamanders, it is primarily a fish eater capable of downing fairly good-sized trout. T. s. fitchi, although quite versatile in its diet at times, in this locality it primarily goes after the frogs. So Rana cascadae breeding populations are fleeing the rougher rivers and creeks (to avoid big trout and voracious atratus) for the remaining calmer lakes and ponds. Well, Valley Garters do prefer calmer bodies of water....
And so it's basically a situation where the frogs have nowhere to hide. Even atratus has been found leaving its preferred aquatic habitat in search of frogs on the move. I have seen them in the lakes.
So, it's something I thought you might like to ponder. Please note that there was no mention of any effects global warming or chytrid fungus might be having on the Sierra populations. Chytrid has also recently been found in the Trinity Alps. :( In case you don't know, chytrid, which once established in a particular habitat, can wipe out up to 80% of all amphibians living there within the first year!
That's a big BOO HOO for both frog and snake!
Steven