Fish & Wildlife - Region 7
среда, июля 26, 2006
Montana Fish, Wildlife and Parks biologists are trapping soft-shelled turtles in the Yellowstone and Missouri River drainages. The traps are harmless hoop nets that the turtle can swim into but not out of. The turtles are carnivores and the traps are baited with pieces of dead fish. The soft-shell turtle population appears healthy and biologists from several agencies are gathering data over a 5-year period to determine the relative abundance of the population. FWP is spearheading this effort using funding from the State Wildlife Grants program that is administered by the US Fish and Wildlife Service.
Some may envision the turtle as a slow moving critter that likes to have its neck rubbed while munching on a piece of lettuce in your living room. The soft-shelled would just as soon take a bite out of you and they are not the slow moving tortoise that raced the fabled rabbit. In fact, they would probably eat the rabbit if it were lying dead in the water. The shell is unique in the turtle world, as it is composed mostly of skin and is soft, hence the name soft-shelled. The literature describes them as cold-blooded reptiles that are fast swimmers and ambush their prey. They are warm-water carnivores that enjoy a meal of dead fish and basking in the sun. There are four families and fifty different species of soft-shelled turtles worldwide. They can live in a variety of waters: lakes, ponds, streams, rivers and even ditches. Their natural range extends from southern Ontario and Quebec, through northern United States from Montana, Wyoming and Colorado, east to New York, Vermont and south to Georgia and into Florida and Mexico. In Montana, soft-shells appear to be primarily in flowing streams and rivers.
The hot July day found us working a several mile stretch of the Yellowstone River with 15 hoop net traps set strategically to capture soft-shelled turtles. We found eight turtles scattered from one side of the river to the other with traps located every two miles apart. The stretch of river we sampled that day was Miles City to the Powder River confluence. All the turtles we trapped on Wednesday, July 19th were females. Each turtle was measured for shell length and width, tagged and weighed. Another team was sampling the Yellowstone from the Powder River confluence to the Fallon fishing access site. During the four-day survey from Miles City to Fallon, we found 37 soft-shelled turtles. All were returned unharmed to the river where they wasted no time in disappearing. Over the past three years, the Yellowstone River has been surveyed from Miles City downstream to the confluence with the Missouri and the Missouri River has been sampled from Fort Peck Dam to Garrison Reservoir.
Biologists are trying to gather enough survey information to estimate which sections of both the Missouri and Yellowstone Rivers support a population of soft-shelled turtles. Biologists have already discovered some interesting information. Survey efforts in the Missouri River below Fort Peck Dam have not located any soft-shells. Changes in water flows and temperature and possibly substrate composition as a result of the Dam operations could be a major influence on the habitat and its suitability for the turtles. They have had no success trapping any soft-shelled turtles from Sidney to the Yellowstone/Missouri River confluence. According to John Ensign, Region 7 Wildlife Manager, “We don’t know what is the limiting factor in this stretch of river. It may be water temperature or perhaps it’s the river substrate, which is sandy and not gravelly with cobbles. It may be a combination of both factors or other factors we have not discovered yet.”
According to Arnold Dood, FWP Biologist, “Soft-shelled turtles must use the river corridor to move up and down river. They do not seem to be very well adapted for over-land dispersal. Other species of turtles can crawl up on the ground and move along the river back to avoid obstacles. This may not be true of the soft-shells. They either swim or they don’t get around certain obstacles. This limitation will probably define the distribution of the population. The soft-shelled can be characterized as a “canary” species in the river system. It can help us understand the health of the river system for several different species of reptiles and fish.”
Ken McDonald, Fishery Management Bureau Chief with FWP said, “The State Wildlife Grants program provided funding for this 5-year survey. This is a unique opportunity for different divisions within FWP to work together for a common goal. Both fisheries and wildlife divisions want to know biological information about the soft-shelled turtle population. A wide variety of agencies are cooperating in the survey so more river miles can be surveyed and the data can be combined to reveal a broader picture for the biologists to begin to understand the biological and environmental needs of the population. ”