Spiny softshell turtle (Apalone spinifera) COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
In general spiny softshells inhabit soft-bottomed bodies of water with an abundance of prey sources and an availability of nesting sites. Initial studies into the habitat requirements of softshell turtles on the Thames and Sydenham Rivers have revealed the following specific habitat requirements:
Nesting Areas: Eggs are typically laid from mid-June to mid-July in sunlit areas above the summer high water level but still within view of the water. Female softshells appear to have a preference for laying eggs in substrates that range from sand to fine gravel. On the Thames River, this habitat is most frequently found downstream of eroding sandy slopes where sand has been deposited on the inside of a meander or where islands have formed. Where there is a lack of sand, such as on some parts of the Thames River and most of the Sydenham River, turtles have been observed to nest on top of sun-baked clay banks or in gravel areas.
Shallow Underwater Muddy/Sandy Areas: Softshells bury themselves in these areas, juveniles and males in particular, perhaps to avoid potential predators and for thermoregulation. These areas also appear to be vital nursery habitat for young softshells because predation by animals such as great blue heron and mink is highest in the first few years of life. Unfortunately, these areas also provide habitat for some prey species of the softshell.
Basking Areas: Most frequently, softshells are observed basking on riverbanks where vegetation does not block sunlight or prevent them from climbing onto the bank. They have also been observed basking on rocks, logs, rip rap and even the cement spillway of Fanshawe Dam in London. They do not, however, appear to be able to use areas where gabion baskets or sheet-pile walls line the river bank.
Deep Pools: In the Thames and Sydenham Rivers, pools that are more than one metre deep during the low water levels of summer will not freeze completely in the winter. During the summer, deep pools may also provide cover and food and allow the turtles to moderate body temperature.
Foraging Habitat: Softshells are known to eat crayfish, tadpoles, minnows and aquatic insects. An adequate food source appears to be available in river reaches containing riffle areas, adjoining creeks, shallow inlets, shallow muddy/sandy areas, vegetative debris and aquatic plants.
Although all of these habitat features appear to be required for the river populations studied, they are not all utilized to the same extent. Nesting areas and deep pools, which are only used at certain times of the year, are not always plentiful or located in close proximity of one another. This lack of proximity may require the turtles to migrate long distances prior to nesting or hibernation. Shallow muddy/sandy areas, basking areas and food sources are more common than nesting sites and deep pools and must be close together as they are used every day. Hence, the quality of the land joining these habitat elements is also critical. If access to any one of these five features is blocked (e.g. if access to basking areas is blocked by gabion baskets) then areas will become useless to the turtles even if all of the five features are present.
GIS mapping has shown a distinct pattern of softshell sightings on the Thames and Sydenham Rivers in that most sightings are at or just downstream of bends in the rivers. This pattern correlates with the above-mentioned availability of critical habitat features in these areas and suggests that along these rivers any river bend and the area directly downstream of it may be potential softshell habitat (Fletcher et al. 1995).
Trends
The information available, although limited, indicates that there has been extensive habitat loss from the historic range (Bonin 1993). In addition, it is the opinion of several researchers (Campbell and Donaldson 1985, Fletcher and Gillingwater 1994, Bonin 1994) that the remaining habitat is not ideal and continues to be degraded by development pressures from agriculture, recreation and road/bridge building. I am currently providing comments on the possible impacts of a proposed bridge and pipeline crossing of the Thames River as well as construction of a sewer treatment plant that will discharge into the river. Currently, human recreational activities at nest sites are having the biggest impact on softshell turtles. In addition, recreation impacts seem to have increased during the past six years at the two Lake Erie sites (Rondeau and Long Point).
Protection/ownership
In Ontario, one of the nesting sites used by softshells is located on federal land (in Big Creek National Wildlife Area) and another is located on provincial land (in Rondeau Provincial Park), whereas all other known nesting sites are on private land. Although the sites located on government land are protected from future development, these two sites experience the highest levels of recreational activity of all the Ontario nest sites. The national wildlife area is signed as no access and periodically patrolled to keep people out, but staff levels are not sufficient to monitor the area adequately and there is a significant amount of disturbance at the nest sites. In the provincial park, there is no restriction of access to the nest sites and not only is there disturbance at these sites, but protective cages placed over the softshell nests are tampered with and the eggs destroyed by vandals each year. In addition to increased human activity directly affecting the turtles (disturbance, possibility of collision with watercraft, etc.), there are also large populations of raccoons in these areas. There are a few softshell records from other protected areas in Ontario (e.g. St. Clair NWA, Point Pelee National Park, Hillman Marsh Conservation Area, Tremblay Beach Conservation Area, Komoka Provincial Park, Coote’s Paradise, Lighthouse Provincial Nature Reserve) and although there is no evidence of nesting from these sites, it is probable that the species has nested or does nest in some of them (M. Oldham, pers.comm.).
In Quebec, nesting sites are being protected on Lake Champlain. The Nature Conservancy is negotiating agreements with the private landowners of these sites and programs such as the St. Lawrence Action Plan offer financial support for land acquisition opportunities.
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