Habitat Rankings

We selected sediment type, water quality, current (m³/s), pH, and threat factors in different stations as indices of R. euphraticus status and investigated each to identify suitable habitats for the species. Habitat characteristics were investigated and habitats were ranked from 1 (poor) to 4 (excellent) based on these factors (Table 2).

Table 2. Rankings of sediment type, water quality, discharge, pH, and threat factors at different stations in Khuzestan Province, Iran.

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Sediment Type. — Sediment types were ranked based on nesting site suitability (4 = fine-grained alluvial soil; 3 = large-grained alluvial soil; 2 = sand and stone; 1 = boulders).

Water Quality. — Water quality was ranked based on pollutant sources discharging into the river (4 = without pollution; 3 =domestic discharge; 2 =industrial discharge; 1 = domestic and industrial discharge). For this ranking, we investigated the source of pollutants (factories and local people that released waste into the rivers) in addition to information obtained from the Khuzestan Water and Waste Water Organization.

Current (m³/s). — Softshell turtles are rarely seen in fast-flowing sections of the river. Thus, we ranked current based on the nature of the flow [4 = stagnant (0–5 m³/s); 3 =slow (5–500 m³/s); 2 =fast (500–2000 m³/s); 1 =very fast (2000–3500 m³/s)].

pH. — We ranked pH of the water at each station as follows: (4 = 6–7; 3 = 7–8; 2 = 8–9; 1 = 5–6).

Threat Factors. — We ranked threat factors, which included presence of fishermen and nets, periodic fluctuations of the water level in probable nesting sites, and pollution and toxic substances that could promote water-based disease (such as malaria).

Study Site

Khuzestan is one of the 30 provinces in Iran, located in the southwest, adjacent to Iraq, and its area is 6.3 million ha. The east and north of the province are bordered by the Zagros Mountains running from northwest to southeast, and to the south is the Persian Gulf. The main rivers in the province are the Karoon, Dez, and Karkheh, flowing from the east; all of them join the Tigris–Euphrates before entering the Persian Gulf (Figs. 2, 4, and 5).

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The Karoon River enters the province from the northern plain of Shushtar, passing Ahvaz, the capital of the province, to Abadan and it joins the Tigris–Euphrates at Shat-al-Arab before entering the Persian Gulf (Fig. 2). The Dez River enters the province from the northern plain of Dezful flowing to the southeast and connecting to the Karoon River in Band-e-Ghir. The Karkheh River flows in the far west towards the south of the Shush, where it changes direction to the west. It changes its direction again at 40 km north of Ahvaz as it enters Iraq and joins the Tigris–Euphrates (Fig. 2). Parallel to the Karkheh River, the small Shahoor River flows southwards in the Khuzestan plain, which is a western tributary of the Karoon. The River Dez flows further southwards joining the Karoon River. After draining the northern lowland of Andimeshk, the Balarood River reaches the Dez River (Fig. 4). The length of Balarood River from its source to reach the Dez River is 100 km.

In Khuzestan 3 main areas were investigated for R. euphraticus habitat. These 3 areas were as follows: 1) Karkheh River (in the range of Karkheh Protected Area and Wildlife Refuge), 2) Dez River (in the range of Dez Protected Area and Wildlife Refuge), and 3) Karoon River (within the Ahvaz city limits). Eleven stations were chosen in order to investigate habitat characteristics, as well as the occurrence of R. euphraticus in these 3 main habitats (Fig. 2).

Dez Protected Region (Protected Area 18,711 ha and Wildlife Refuge 6127 ha; located at 31°35′to 32°15′N and 48°51′to 48°22′E) was established in 1967. A proposal to create a wildlife park on the Dez was approved in early 1969, and the park was established in 1970. Similarly, Karkheh Protected Region (Protected Area 10,763 ha and Wildlife Refuge 5422 ha; located at 32°57′ to 31°36′N and 48°32′E) was established in 1960 and a wildlife park in 1970. These sites consist of 2 noncontiguous areas along the Dez and Karkheh rivers. Both rivers are deep and wide and meander considerably.

The headwaters of the Karoon River are in the mountain cluster Zard Kuh in Isfahan. In its upper course, until it reaches Shushtar, it is called Ab-e-Kuhrang. From the junction of the 2 principal sources in the Zard Kuh, the Ab-e-Kuhrang is a powerful stream, full, deep, and flowing with great velocity for most of its upper course between precipices. In general, the steepness and height of its banks make it useless for irrigation purposes. From its principal sources to Shushtar the straight distance is only about 75 km, but the course of the river is so tortuous that it travels 250 km before it reaches that city. Besides being fed on its journey through the Bakhtiari country by many mountainside streams, it receives various tributaries, the most important being the Ab-e-Bazuft from the east and the Ab-e-Barz from the west. At Shushtar it divides into 2 branches: Gerger (an artificial channel cut long ago and flowing east of the city) and Shutait (flowing west). These 2 branches, which are navigable to within a few kilometers below Shushtar, unite after Band-e-Ghir, 60 km south of Shushtar, and there are also joined by the Dezful River. From Band-e-Ghir to a point 2 miles above Muhamrah the river is called Karoon and is navigable all the way with the exception of about 2 miles at Ahvaz, where a series of cliffs and rocky shelves cross the river and cause rapids. A major city that is close to the river is Ahvaz, where the Karoon River has divided the city into western and eastern parts.

Climate

The climate of Khuzestan is generally hot and humid, particularly in the south. The mean diurnal ambient temperatures (Anonymous 2006) from February 2002 to June 2005 were between 19.1°C and 33.7°C (minimum 7.9°C in January 2002 and maximum 47.1°C in August 2003).

The province of Khuzestan can be basically divided into 2 regions (i.e., the plain [the south and west of the province] and mountainous regions [the north and east of the province]). The plains are irrigated by the Karoon, Karkheh, and Jarahi rivers. The mountainous region is considered to be the southern extreme of the Zagros mountain ranges. In the elevated and mountainous regions of the province, a moderate summer and cold winter are experienced, but in the foothills of the mountains semidesert conditions prevail. In the plains and lower regions to the south and southeast, a variable climate ranging from semidesert to coastal desert predominates. Thus this region experiences long, warm summers and short, moderate winters.

Morphology

Morphological features of the 5 specimens we captured during our study are given in Table 3. The carapace is smooth and peripherally thick and fleshy in adult R. euphraticus. The outlines and sutures of the bony disc are easily discernible from above. In some specimens (usually large adults), a slight vertebral depression is present. The ground color of the carapace is uniformly olive-green with some irregular cream-colored spots, especially on the lateral margins. Larger and more abundant spots are visible on the head. Occasionally, the ground coloration of the whole dorsum is uniformly brown instead of the usual olive-green. The lateral septal ridges (or septal papillae) have small longitudinal troughs with sharp edges (Taskavak and Atatur 1995; Taskavak 1998).

Table 3. Morphometric measurements (in mm) of 5 captured specimens.

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Adult R. euphraticus are flattened and dorsally compressed. Carapace length measurements given in the literature range from 420 mm (Basoglu and Baran 1972) to 535 mm (Duméril and Bibron 1835). The largest specimen captured by Taskavak (1992) had a straight carapace length of 680 mm. Among our Iranian specimens, maximum straight carapace length was 520 mm (Table 3).

According to Lortet (1883), Basoglu and Baran (1977), Griehl (1981), and Gramentz (1991) nesting and egg laying occur towards the end of April to early June. One of our specimens (straight carapace length of 355 mm) captured in the Looreh River on 22 May 2005 laid 5 eggs on 2 June 2005 in captivity. Based on the observation of several small juveniles (probably post-hatchlings; 15 September 1988; Habes Creek) at the tributaries of Euphrates River, Taskavak and Atatur (1998) also claimed that egg laying occurs during the spring months. These 5 brittle-shelled eggs were approximately spherical with a mean diameter of 28.7 mm (range 28.2–29.2 mm). The mean egg weight was 14.1 g. None of them hatched. The mean diameter was somewhat larger than that given by Taskavak and Atatur (1998) for 19 fully developed eggs dissected out from 2 female specimens (23.3 ± 0.13 mm).

Based on the criteria used for determining sexual maturity (i.e., in males, the size and condition of testes and appearance of vasa deferentia; in females, the presence of oviductal eggs and size of ovarian follicles), Taskavak (1998) determined that the smallest mature female had a carapace length of 320 mm. The female specimen that laid 5 eggs was somewhat larger than the smallest mature female reported by Taskavak (1998); however, it is smaller than the length of mature females examined by Basoglu and Baran (1972) and Gramentz (1991). In their samples the smallest size and the mean were 365 and 382.5 mm, respectively. Our sample size is insufficient to speculate on the dimensions reached by mature females in Iran.

Conservation

The Euphrates softshell turtle has been listed by International Union for Conservation of Nature and Natural Resources in the “Red List of Threatened Species” as Endangered (EN A1ac+2c; Anonymous 2008).

The greatest single threat to this species in Iran is habitat destruction. In Khuzestan Province, industrial development causes ever-increasing pollution of the water sources. Wastes discharged into the Karoon, Dez, and Karkheh Rivers and their tributaries have caused the worst habitat loss.

Local fishermen believe this species to be a competitor for fish, and it is often killed for this reason. Also, those turtles that escape from fishing lines may retain the hook inside their throats, causing eventual mortality. One of the specimens that we obtained from a fisherman had an old hook deep in its throat. Similarly, Taskavak and Atatur (1998) reported that a large specimen was captured by hook and line and released by cutting the line. In general, local people are hostile towards the softshell, and incidentally hooked specimens do not usually escape with their lives.

One of the threats of concern is the potential introduction and establishment of Pelodiscus sinensis as an invasive species. In Iran, P. sinensis hatchlings are sold in pet stores in Tehran and also in Ahvaz city. Thus it is quite likely that area residents, few of whom were familiar with the Euphrates softshell turtle, may release unwanted captive P. sinensis into Khuzestan's freshwater habitats. Habits and characteristics of P. sinensis are close enough to R. euphraticus to cause potential competition. In the pet trade they are explicitly purchased by individuals whose goal is to keep turtles alive and healthy. The majority of these species can become quite aggressive and quickly outgrow most aquariums or outlast the owner's commitment to care for them. As a result, some pet owners unwilling to care for their turtles may release them into nearby bodies of water. This scenario is implicated for invasive introductions elsewhere (Luiselli et al. 1997; Chen and Lue 1998). The impact of introduced turtles on native turtle populations is difficult to assess, but is almost certainly negative (Spinks et al. 2003). However, we do not yet have any records of released P. sinensis in Iran.

The majority of the water-polluting industries are located in the Karoon River basin followed by the Jarahi and Dez basins. There is not yet any significant industry causing water pollution in the Karkheh basin. Based on research carried out by Jafarzadeh et al. (2004), a quantity of 56,502 tonnes/y of organic load and 26,0186 tonnes/y mineral load from various industries are discharged into the Karoon River. In the Dez River basin, 87,716 tonnes of organic and 93,380 tonnes of inorganic loads from industries are discharged annually. In the Karoon River basin, metal pollution load is greater than in the other basins in Khuzestan, and a major part of this pollution is caused by metal industries concentrated within Ahvaz city limits (Table 4). There is no information about the effect of this pollution on R. euphraticus in Iran. However, these pollutants may accumulate in tissues and kill turtles in the long term.

Table 4. Active plants (factories) that discharge their sewage into the rivers.

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Although freshwater turtles are heavily exploited as a food item in many countries, the meat of this turtle is generally not consumed in Iran. Similarly, Taskavak and Atatur (1998) reported that the local people inhabiting the same region as the Euphrates softshell turtle in southeastern Anatolia do not consume the meat, but a few Armenian families at Diyarbakir are reported to eat softshells.

In addition to these factors endangering the survival of the Euphrates softshell in Iran, we should mention the mechanical destruction of its habitat and the heavy chemical pollution which resulted from the Gulf Wars. Van Dijk (1990) was of the opinion that the species had been negatively affected by the Ataturk Dam in the north, and by the Iran–Iraq War in the south. We also believe the physical and chemical damage inflicted upon the southern parts of the species' range during Gulf War I in 1991 and Gulf War II in 2003 has also been quite serious.

Conclusions

Rafetus euphraticus exists in most rivers and marshes of Khuzestan Province in southwestern Iran. Nevertheless, although no published literature is available to ascertain the conservation status of R. euphraticus in Iran, based on our findings given above, R. euphraticus in Iran is in jeopardy. Habitat destruction seems to be the major cause of its decline.

The majority of the water-polluting industries are located at the Karoon River, which in the recent past, based on fishermen's reports, was one of the best R. euphraticus habitats in Iran. Now, it is the most threatened habitat, the main reason being the high level of pollution of this river, especially within the limits of Ahvaz city. Also, the Kharkheh River, in the range of the Karkheh Protected Area and Wildlife Refuge have heavy pollution that has caused habitat loss.

In the south of Dezful in a narrow creek there is a high density of R. euphraticus, but wastewater is released directly into it and is likely to cause problems in the future. If these conditions continue in R. euphraticus habitats, it could be devastating.

To ensure the survival of the species, immediate action is required. This should include the following: drafting an action plan for conservation and management; conservation of the most important nesting sites; establishment of undisturbed areas for mating and egg laying; protection against persecution by fishermen (public awareness and education programs); and establishment of measures against drowning in nets.