North American Recent Soft-shelled Turtles (Family Trionychidae) Part 19

A juvenile of _hartwegi_ was seen by Mr. Wendell L. Minckley on a gravel bar jutting into a small, shallow creek having a mud-gravel bottom (Carnahan Creek, Pottawatomie County, Kansas); the impounding of the Big Blue River by the Turtle Creek Dam will obliterate this habitat. Mr. J. Knox Jones, Jr. reported seeing a large softsh.e.l.l in a narrow, shallow, clear sandy creek in Holt County, Nebraska.

_T. s. emoryi_ occurs in large rivers having generally turbid waters, a moderate to swift current and mud or sand bottoms such as the Rio Grande; this habitat corresponds to that of large rivers in the western parts of the range of _T. s. pallidus_ (Red and Was.h.i.ta) and _T. s. hartwegi_ (Canadian and Cimarron). These last-named rivers, in periods of low water level, often have shallow, clear, flowing water in parts of the river bed. _T. s. emoryi_ has also been taken from small creeks having bottoms of rocks and large boulders (Black River Village, Eddy County, New Mexico; field notes of Sydney Anderson and Kenneth Shain, June 12-14, 1958).

I received a hatchling _T. s. guadalupensis_ that was obtained in a clear, shallow-water stream (Hondo Creek, Bandera County, Texas, on April 12, 1958). The larger streams and rivers known to be inhabited by _guadalupensis_ are generally clear having greenish-tinted waters.

The geographic distribution of _guadalupensis_ indicates that that subspecies occurs princ.i.p.ally in those waters that drain the limestone-mantled, Edward's Plateau off the Balcones Escarpment; the headwaters are characterized by clear, calcareous streams having occasional travertine deposits. It is probably this type of habitat to which Aga.s.siz's statement (1857:408) of "clear, bold and rocky streams" refers.

There are a few specimens whose locality data indicate a tolerance of brackish-water habitats. An adult male _spinifer_ was obtained at Delacroix Island, St. Bernard Parish, Louisiana, a locality said to have exceedingly brackish waters (Dr. George H. Bick, St. Mary's College, Notre Dame, Indiana); this adult male (TU 16170) is unique in having a mottled and blotched pattern. Another adult male (_spinifer_, TU 16071) was obtained in shallow water in Lake Pontchartrain at the mouth of Tchefuncta Creek; the salinity at the time of capture was recorded as 1.7 (datum from Dr. Royal D. Suttkus, Tulane University), indicating only slightly brackish water. Two _spinifer_ (USNM 100409-10) and one _muticus_ (USNM 100406) were taken at Berwick Bay, near Morgan City, St. Mary's Parish, Louisiana; the waters at this locality are probably brackish. The tolerance of brackish waters doubtless facilitates the dispersal of these turtles along coastal marshes and swamps, and into adjacent drainage systems. The greater number of records in the literature pertaining to _ferox_ suggest that this species may be more tolerant of brackish and marine waters than are _spinifer_ or _muticus_.

In summary, _T. ferox_ occurs in all fresh-water habitats, but chiefly in lentic habitats in the northern part of its range where it and _T. s.

asper_ are sympatric. _T. ferox_ possibly is more tolerant of brackish and marine waters than are the subspecies of _spinifer_ and _muticus_.

The subspecies of _T. spinifer_ occur in all fresh-water habitats. In the southern part of the geographic range, which overlaps that of _T.

ferox_, _T. s. asper_ occurs princ.i.p.ally in running-water habitats. _T.

s. pallidus_ and _T. s. asper_ are tolerant of brackish-water habitats.

_T. s. guadalupensis_, known at present only from rivers and streams, occurs princ.i.p.ally in river systems that drain the Edward's Plateau of southcentral Texas. _T. ater_ is confined to crystal-clear ponds in central Coahuila.

The subspecies _muticus_ occurs in large rivers and streams throughout its geographic range, but is known from lakes and impoundments princ.i.p.ally in the southern part of its range (the northernmost record is from Reelfoot Lake, Obion County, Tennessee); there is only one record of _muticus_ from a small, shallow, headwater creek (Reno County, Kansas), and only one from a lentic habitat (Meredosia Bay, Illinois) in the northern part of its range. _T. muticus calvatus_ is known at present only from rivers and streams.

The seemingly greater restriction of _muticus_ to running-water habitats suggests less vagility than in _spinifer_ (Netting, 1944:86).

Size and coloration are adaptations to habitat. Soft-sh.e.l.led turtles of large size are best adapted to mesic, essentially continuous swampy or marshy habitats, whereas small size is an adaptation to less continuous, semi-isolated habitats. A turtle of the maximum size attained by _ferox_ in the habitat of _emoryi_ would, in a general way, probably be more conspicuous and exposed to its enemies, both in the aquatic environment and during overland excursions; perhaps the kind and amount of food would be insufficient. In any event, small size is correlated with the more arid habitats of the southwest, and large size with mesic ones in the southeast. _T. ferox_, the largest species, and the smallest population of _T. spinifer_ (resembling _muticus_) both occur in the southernmost part of the range of the genus. This situation does not support the corollary of Bergmann's Rule, that pertains to some groups of terrestrial reptiles, in which those subspecies occurring farther north, or in cooler climates during their season of activity, tend to be smaller.

Within the species _spinifer_, the _emoryi_ group of subspecies are pallid having whitish dots on the carapace and lack extensive black pigmentation; these features seem to confer protective coloration on the inhabitants of arid, essentially sandy or muddy habitats having sluggish, turbid waters, whereas the more contrasting patterns of the _spinifer_ group of subspecies eastward seem more suited to existence in clearer, swifter waters.

The occurrence of the two clines, _spinifer-hartwegi_ and _pallidus-guadalupensis_, in the species _spinifer_ are notable in that the former occurs mostly in one large continuous drainage system, that of the Mississippi, and shows no sharp break in the one character distinguishing the two subspecies whereas populations composing the _pallidus-guadalupensis_ cline are separated into several river drainages, and show a relatively sharp break in several characters at the Brazos-Colorado river divide. This situation seemingly supports the thesis that clines are maintained by some sort of parallel gradient in ecological or geological conditions. It is notable that streams draining the Edward's Plateau (inhabited by _guadalupensis_) differ in quant.i.ty (more) and quality (especially CO_{3}^{--}, Ca^{++}, and Mg^{++} ions) of their solutes, and probably pH (higher) from those farther east (Hubbs, 1957:102). The gross difference in habitats mentioned above (sandy, turbid, sluggish streams in the west _vs._ clear, swift streams in the east) may affect the differentiation recognizable in the _spinifer-hartwegi_ cline.

Daily and Seasonal Activity

_Diurnal Habits_

Softsh.e.l.ls bask on debris in the water or on banks close to the water; basking presumably raises the bodily temperature. In general in the southeastern and southwestern United States, I have seen softsh.e.l.ls basking only rarely but once saw six at one time close together on logs in Bowie Creek, Hattiesburg, Mississippi (species undetermined). Surface (1908:122) saw _spinifer_ in rows on rocks or logs in tributaries of the Ohio River. Duellman and Schwartz (1958:271-72) stated that _ferox_ basks on banks or beds of aquatic vegetation. Deckert (1918:31) mentioned large _ferox_ "sunning in shallow water at edge of pond."

Minton (1944:447) wrote that _muticus_ and _spinifer_ sun on steep mud banks (Wabash River). Cahn (1937:180) stated that _muticus_ (in Illinois) basks on banks at the water's edge but seldom on logs, and suggests that _muticus_ is less p.r.o.ne to leave the water than _spinifer_. According to Carr (1952:438), _muticus_ never basks on logs or rocks. In Ohio, Conant (1951:159) mentioned _spinifer_ as occasionally basking upon a log or rock, or sometimes on steep clay banks of streams. On banks, quick escape is facilitated by directing the head toward the water, thus eliminating the time that it would take to turn around on land (Conant, _loc. cit._; Newman, 1906:129). Evermann and Clark (1920:593) mentioned _spinifer_ as basking on sandy or gra.s.sy sh.o.r.es, and large boulders. Muller (1921:181) wrote that _muticus_ basks four to ten feet from the water's edge on gently sloping sand and mud sh.o.r.es of small islands in the Mississippi River (near Fairport, Iowa).

Muller stated that basking usually occurs in the morning, up until 2 p.

m., and that beaches with a northern exposure were preferred; he observed 37 turtles within a 50-foot stretch of beach. In captivity, hatchlings bask on wire-mesh supports.

I have frequently observed softsh.e.l.ls 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 softsh.e.l.ls 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 ma.s.ses 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 a.s.sist in forcing it down." Surface (1908:123) suggested that softsh.e.l.ls 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 Ca.n.a.l, 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 pa.s.sing fish, or other food. Presumably all kinds of softsh.e.l.ls 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 Aga.s.siz (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 softsh.e.l.ls by observing these particular schools of fish. No mention was made of the turtles attempting to catch the fish. Other a.s.sociations of soft-sh.e.l.led turtles and fish have been described. Kirtland (_in_ DeKay, 1842:7) observed several large ba.s.s 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 ba.s.s stay not far away from swimming softsh.e.l.ls; the same author also mentioned the observations of Jacob Reighard, who suggested that ba.s.s may be feeding upon minnows that he noticed following softsh.e.l.ls. Seemingly some sort of commensalistic relationship exists whereby fish acquire food that is dislodged by grubbing and scurrying of softsh.e.l.ls. 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."

Marchand (_loc. cit._) also wrote of other notable underwater observations on _ferox_ in Florida. He commented on this turtle's inquisitiveness in deep water and unconcern upon being touched or even upon being handled to some degree. Calf-deep in soft mud, he noted a turtle that "emerged from the mud of the bottom, headed up toward sh.o.r.e, circled, and when about three feet above the bottom dived suddenly and completely disappeared." Marchand wrote that some areas on the bottom (Crystal Springs), which are rooted up by the burrowing of softsh.e.l.ls, are bare and soft, and a.s.sume a characteristic, easily recognized, appearance.

Cahn (1937:180, 189) stated that the burrowing process consists of "flipping" the loose sand or silt over the back, whereas Conant (1951:159) described the process as a rapid lateral movement of the body. My observations of captives agree essentially with Conant's observations. The initial movement, directed at a slight angle, is princ.i.p.ally with the forelegs although complemented by lateral movements of the body. When the turtle is approximately half buried, it makes rapid lateral movements of the body, which completely bury the turtle and orient its body in a horizontal position.

_Behavior and Adaptations_

Some characteristics of softsh.e.l.ls that are often mentioned in the literature are: extreme shyness or wariness, ferociousness as captives, dazzling speed and agility on land and in water, and great dependence on aquatic environment. Certainly they are wary; and this wariness may account, in part, for the scarcity of observations of basking, and statements attesting to their great speed on land. To my mind, their reported ferociousness and savage disposition as captives is overrated; of the many softsh.e.l.ls that I have collected, only a few attempted to bite. The extensibility of their long neck does warrant more careful handling than needs to be employed with other species. Holbrook (_in_ Hay, 1892:145) even wrote that they "will sometime leap up and give a loud hiss," and Newman (1906:130) wrote that "they hiss violently and thrust out the head." Wright and Funkhouser (1915:120) reported a captive _ferox_ that "could jump forward practically its own length." I have been bitten by individuals of _Kinosternon_, _Sternothaerus_, _Pseudemys_ and _Graptemys_, and cannot support the contention that softsh.e.l.ls are more p.r.o.ne to bite than those species, a view shared by LeConte (_in_ DeKay, 1842:7); many softsh.e.l.ls on initial capture will tend to withdraw the head completely for a short time. Newman (_loc.

cit._) also wrote that recently captured specimens exude a thick, yellow, semi-fluid resembling yolk of an egg from the inguinal glands; the substance, however, is odorless but "undoubtedly h.o.m.ologous with the emission of the inguinal glands of the musk and snapping tortoises."

Perhaps there is a difference in aggressiveness a.s.sociated with geographic location, the age of the turtle or individual temperament.

Smith (1956:159), referring to _muticus_, wrote that they are the best swimmers of all fresh-water turtles, and perhaps of any turtles.

Corresponding statements of other authors attesting to their speed and agility (including _spinifer_ and _ferox_) in water and on land are based princ.i.p.ally on the published comments of Muller (1921:181), who observed that females disturbed while laying eggs "about fifty feet from water ... covered the distance faster than a man can run." Cahn (1937:180) also stated that _muticus_ on a "level, un.o.bstructed sand beach ... can outrun a man," and (_op. cit._:181) can "capture fish with ease"; Cahn supported the latter statement by relating his observation of a _muticus_ that captured a small brook trout in a large tank. Smith (_op. cit._:162) wrote that _spinifer_ is "said to overtake ba.s.s."

Doubtless they are good swimmers and they do scurry rapidly on land.

Published statements relating to the strictly aquatic existence of softsh.e.l.ls especially _muticus_, are based on recognition of "its drastic adaptations to aquatic existence" (Carr, 1952:428); these adaptations presumably include pharyngeal respiration and the marked depression of body form. Pharyngeal respiration was demonstrated for _muticus_ and _spinifer_ (Gage, 1884; Gage and Gage, 1886), and was considered the princ.i.p.al type of aquatic respiration (some dermal and some cloacal) in _Trionyx spinifer asper_ by Dunson (1960). Cloacal bursae (a.n.a.l respiration) are lacking in trionychids (Smith and James, 1955:88). Accessory pharyngeal respiration is meaningful in light of the information furnished by Aga.s.siz (1857:282-83), who found that _Trionyx_ has a smaller lung capacity (weight of body in ounces/capacity of lungs in cubic inches = 16.9) than do some other genera (_Pseudemys_, 2.8; _Testudo_, 2.7; _Terrapene_, 1.1); corresponding values for more aquatic species were _Chelydra_, 9.3 and _Kinosternon_, 16.0. Cahn (1937:181), however, wrote that he has demonstrated pharyngeal respiration in individuals of _Pseudemys_, _Chrysemys_ and _Sternothaerus_, and Allen and Neill (1950:13) suggested that it occurs in _Macroclemys_. More conclusive data are required to detect a positive correlation between small lung capacity, pharyngeal respiration, and degree of restriction to an aquatic habitat.

The depressed, soft-margined carapace of softsh.e.l.ls has been mentioned as an adaptation to facilitate burrowing in soft sand or mud, and more suited for concealment than for speed in aquatic locomotion (Carr, 1952:429; Smith, 1956:162). Nielsen (1951:264-65), commented that in various lotic invertebrates, dorsoventral flattening of the body was no commoner than in lentic invertebrates; he wrote that a dorsoventral flattening is a disadvantage to an animal in a strong current and is an adaptation "probably ... not to withstand the current directly, but to avoid it by seeking shelter in narrow crevices." Probably another aid to concealment, mentioned by Williams and McDowell (1952:272), is the plastral hinge.

Concealment of softsh.e.l.ls is not enhanced by growths of algae on the carapace. Proctor (1958:637-38) reported that the common, epizoophytic alga of chelonians, _Basicladia_, has never been reported from _Trionyx_; the same author recorded a large amount of filamentous algae, princ.i.p.ally _Stigeoclonium_, but the algae could be easily wiped from the turtle, and Vinyard (1955:64) recorded an alga, _Dermatophyton radians_, attached to the skin of the legs of _Trionyx_. I noted a small patch of greenish sc.u.m growing near the insertion of the neck on a softsh.e.l.l (_spinifer_ from Lake Texoma); cursory examination by Dr. R.

H. Thompson, disclosed one of the colonial ciliate protozoans (resembling _Opercularia_) with enmeshed green or blue-green algae.

Evermann and Clark (1920:592) mention a _spinifer_ from Lake Maxinkuckee, Indiana, having a growth of _Opercularia_, covering the plastron.

_Movement_

The reported proclivity of softsh.e.l.ls for a strictly aquatic existence has been over-emphasized; they are no more confined to aquatic habitats than some chelydrids (including kinosternids). In fact, there is a general parallel in habits between members of the two families, namely, a tendency toward a bottom-dwelling existence, and a burrowing habit.

The alligator snapping turtle (_Macroclemys_) is probably the most aquatic fresh-water turtle in the United States. The common snapping turtle and some kinosternids are known to migrate overland. Kinosternids and trionychids bask frequently, and trionychids have been observed moving overland. c.o.x (1894:50) reported a _spinifer_ attempting to climb a narrowly-stepped, 12-foot dam on Mud Creek at Ravenna, Nebraska; the turtle failed after repeated struggles, once reaching a height four inches shy of the brim before tumbling back into the water. Duellman and Schwartz (1958:271) commented that adults of _ferox_ are often seen on roads bordering ca.n.a.ls, and informants have told me verbally of similar observations. Conant (1930:61) reported an individual of _ferox_ that was "... walking across the main street in Venice [Sarasota County, Florida]." Softsh.e.l.ls will travel overland in search for suitable nesting sites; Newman (1906:130) wrote that _spinifer_ will climb "steep railway embankments with considerable ease, in order to reach a sand pit some fifty yards from the water."

From an a.n.a.lysis of species-composition of large reservoirs and lakes and their adjacent smaller ponds in southern Illinois, Cagle (1942:162) concluded that softsh.e.l.ls "travel overland far less often than do ..."

other species, but that they are "probably the first to move as the water level falls." On the basis of further observations in the same region, Cagle (1944:15) wrote that softsh.e.l.ls rarely move overland, and once trapped in a pool of water, they bury themselves and remain there.

He related instances of several individuals having been dug from dried mud where the last remnants of a water pool had evaporated and he concluded that the home range is probably confined to one body of water.

That fluctuations in water level affect the movement of softsh.e.l.ls is suggested by Mr. William E. Brode's comment that a commercial fisherman trapped numerous softsh.e.l.ls in the Pearl River, south of Monticello, Mississippi, in unbaited hoop-nets in late May and June when the water level was receding after heavy rains.

The meager data available concerning the aquatic movements of softsh.e.l.ls indicate that individuals wander but little. Breckenridge (1955:6, table 1) found that among 30 recaptured turtles that had been marked, the greatest distance traveled was 600 yards over a two-year interval; after a three-month interval one originally captured 30 miles distant, moved only 200 yards. The statement of a professional turtle trapper mentioned by Breckenridge (_loc. cit._) and data previously presented (see page 436), to the effect that over-trapping results in increasingly diminished returns, tends to support the idea that there is little aquatic movement in soft-sh.e.l.led turtles.

Breckenridge (_loc. cit._) mentioned methods of marking softsh.e.l.ls and found that notching the edge of the carapace with a leather punch was satisfactory; the notches healed but were discernible as shallow sinuses. The same author mentioned a tattooing device (mentioned also by Cagle, 1939:171), but no turtles so marked were ever recognized as recovered. Tagging with a radioactive isotope and detection with suitable instruments should prove applicable to turtles (see Karlstrom, 1957).

_Nocturnal Habits_

Anderson (1958:212) wrote that hatchlings (_muticus_) leave nests within the first three hours after sunset, and are active on the surface of the sand at night. Muller (1921:183) reported hatchlings (_muticus_) leaving nests at night or early in the morning. Lagler (1954) stated that _spinifer_ is nocturnal. To my knowledge there are no other published statements concerning nocturnal activity of soft-sh.e.l.led turtles. I have noted them at night on only four different occasions. In two instances (Clear Fork Brazos River, Texas, and Lake Concordia, Louisiana), the turtles were resting immediately below the surface of the water on submerged branches, as one would expect _Pseudemys_ and _Graptemys_ to do. Another individual was seen swimming near the surface (Ocmulgee River, 1-1/2 mi. S Jacksonville, Georgia); this observation possibly represents nocturnal activity, or inquisitiveness owing to the disturbances caused by the motor of the boat and/or our head lights. A final observation tends to support the view of nocturnal habits. My field notes record at least four softsh.e.l.ls collected by hand, and a few other seen in a shallow (approximately four feet deep), quiet, clear water side channel of the White River (Cotter, Arkansas); the turtles were seen resting and slowly moving on the bottom or swimming.

_Seasonal Occurrence_

The length of the season of activity increases with decrease in lat.i.tude. Aquatic species in general have longer periods of activity than terrestrial species at the same northern temperate lat.i.tudes. The southernmost populations of all species of softsh.e.l.ls may be active throughout the year, a.s.suming temperature to be the limiting factor.

There are few published statements relative to the length of the annual period of activity; all records refer to _spinifer_. In Lake Maxinkuckee, northern Indiana, Newman (1906:128) wrote that individuals were first seen in early April on the lake sh.o.r.e in a weak condition with neck and legs extended, and were easily captured. Lesueur (1827:262) wrote that _spinifer_ in Indiana appears toward the end of April. Observations of Evermann and Clark (1920:592) in Lake Maxinkuckee, and Butler (1894:224) in east central Indiana concurred in finding that of all kinds of turtles there, softsh.e.l.ls appeared last in spring and disappeared first in fall. Evermann and Clark found small softsh.e.l.ls, benumbed or dead, along the sh.o.r.e as early as March 18 and also late in fall. The earliest observation for large softsh.e.l.ls was April 29, and the latest was September 7; Butler found that these turtles rarely appear before April 15 and sometimes not until May 1.

Cahn (1937:191) stated that softsh.e.l.ls in Illinois hibernate toward the end of October and emerge in May or the latter part of April; the same author mentioned that in southern Illinois the species might remain sluggishly active all winter. In Ohio, Conant (1951:160) wrote that individuals were collected every month from March to October, and one was even taken in December, 1929, in northwestern Ohio. Wright (1919:8) mentioned observing softsh.e.l.ls on April 20 and September 20 (presumably these were the earliest and latest observations of them) in Monroe and Wayne counties, New York. Blatchley (1891:34) listed dates of early and late activity as March 19 and December 11 for Vigo County, Indiana.

Webster (1936:22) recorded the earliest and latest dates of collection of _spinifer_ in central Oklahoma as June 10 and November 8.

Moore and Rigney (1942:80) found an individual of _muticus_ under six inches of ice in water about one foot deep on January 31, 1940 (Cimarron River, Payne County, Oklahoma).

The published information suggests that the length of the normal annual period of activity of _spinifer_ in lat.i.tudes of about 40 and 43 is approximately five months, from April into September, depending upon the weather. There are numerous published statements to the effect that the period of hibernation is pa.s.sed under a shallow covering of mud in deep water. Evermann and Clark (_op. cit._: 593) found a softsh.e.l.l (presumably in a quiescent state) on September 6 that was "buried up to its eyes in mud at the edge of Lost Lake." Softsh.e.l.ls possibly hibernate in shallow water or in soft mud flats. Conant (_loc. cit._) found that captives would not hibernate in a pond in a zoo having a bottom of leaves.