North American Recent Soft-Shelled Turtles (Family Trionychidae)Webb, Robert G. (Robert Gravem)
Science
North American Recent Soft-Shelled Turtles (Family Trionychidae)
Webb, Robert G. (Robert Gravem)
Soft-shelled turtles
hatchlings bask on wire-mesh supports.
I have frequently observed softshells floating at the surface of the
water, a habit previously mentioned by Surface (1908:122) and Pope
(1949:305, 311). Individuals of _Pseudemys_ and, to a lesser extent,
_Graptemys_ also float at the surface; those kinds of turtles and
softshells at least, often appear at the surface of the water, seemingly
as a result of an inquisitiveness, following repeated disturbances that
cause submergence.
Newman (1906:131) described the active pursuit of food: "They crawl or
swim along the bottom, thrusting their snouts under stones and into
masses of aquatic vegetation, occasionally snapping up a crayfish or
larva that they have succeeded in dislodging. They do not tear up their
food, but swallow it whole, using the forefeet to assist in forcing it
down." Surface (1908:123) suggested that softshells may feed "upon
insects which may be found floating on the water," and I have had
captives take insects from the surface of the water. Carr (1940:107)
also wrote that _ferox_ and numerous gars in the Tamiami Canal, often at
the mouths of the tributary ditches, snap at each other furiously as
floating bits of food are washed in from the Everglades. Another habit
that has been mentioned as an aid in acquiring food (Breckenridge,
1944:186; Conant, 1951:156; Hudson, 1942:101) is burrowing just below
the surface in a soft bottom in shallow water, to ambush passing fish,
or other food. Presumably all kinds of softshells do this in both
shallow and deep water of lakes or rivers having a suitable substrate;
_spinifer_ and _muticus_ have been reported to burrow in shallow waters
(no observations in deep water) by Agassiz (1857:333), Cahn (1937:180,
189), Conant (1951:159) and Weed (1923:48). Marchand (_in_ Carr,
1952:417-19) noted that _ferox_ burrows in deep water, and mentioned
that in areas of bare white sand a group of fish invariably surrounds
them, and one can locate buried softshells by observing these particular
schools of fish. No mention was made of the turtles attempting to catch
the fish. Other associations of soft-shelled turtles and fish have been
described. Kirtland (_in_ DeKay, 1842:7) observed several large bass
that closely followed large numbers of turtles floating at the surface.
Newman (1906:131) reported the observations of fishermen in Lake
Maxinkuckee that large-mouth black bass stay not far away from swimming
softshells; the same author also mentioned the observations of Jacob
Reighard, who suggested that bass may be feeding upon minnows that he
noticed following softshells. Seemingly some sort of commensalistic
relationship exists whereby fish acquire food that is dislodged by
grubbing and scurrying of softshells. Probably food is pursued on
occasion from a buried position, but this habit probably is not executed
specifically for obtaining food. Newman (_op. cit._:129) was of the
opinion that burrowing in shallow water is a habit to facilitate
"warming up."
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