The relatively small state of Sinaloa (surface area of 58,328 km²) is located in northwestern Mexico, between 27°2'32" and 22°28'2"N and 105°23'32" and 109°26'52"W (Figs 1, 2; INEGI 2017). Sinaloa is bordered by Sonora to the north, Chihuahua and Durango to the east, Nayarit to the south, and the Gulf of California to the west.

The topography of Sinaloa can be divided into three large longitudinal strips (INEGI 2017). The first includes the mountain ranges of the Sierra Madre Occidental on the eastern side of the state. In Sinaloa, elevations rarely exceed 2,500 m, with the highest elevations near the border with Chihuahua (Cerro La Bandera: 2,280 m and Cerro Pelón: 2,500 m) and Durango (Cerro Alto: 2,800 m; Cerro Narizón: 2,560 m; and Cordón El Copo Alto: 2,360 m). The second strip is an extensive plain that lies between the foothills of the Sierra Madre Occidental and the Pacific Coast, which is the third strip. In northern Sinaloa the distance between the foothills of the Sierra Madre Occidental and the coast of the Pacific Ocean is greater than in southern Sinaloa, where they can be separated by less than 30 km. Throughout the state, the Pacific coastline is interrupted by large lagoons and mangroves, and although the coastline is straight and low, except for Mazatlán Bay, access to it is difficult due to the presence of these lagoons (Fig. 2; García-Martínez 2008; INEGI 2017).

Figure 2. 

Topographical map of the state of Sinaloa, Mexico (INEGI 2009).

Sinaloa includes two physiographic provinces: Sierra Madre Occidental and Llanura Costera del Pacífico. The Sierra Madre Occidental covers 59.5% of Sinaloa, covering a little more than the eastern half of the state (Fig. 3; INEGI 2017). The Llanura Costera del Pacífico covers 40.5% of the state, including almost all of the western half of the state (Fig. 3; INEGI 2017).

Figure 3. 

Physiographic provinces of the state of Sinaloa, Mexico (modified from Cervantes-Zamora et al. 1990).

The elongated shape of Sinaloa along with its topography characterized by a continuous mountain chain in the east running parallel to the coastline, produces a striped distribution of vegetation types in the state (Fig. 4). The flood plains of the main Sinaloa rivers and adjacent upland slopes have been cleared and cultivated for many centuries, such that the natural plant associations have been considerably altered, and the actual Sinaloa landscape has large areas with an unnaturally high percentage of commercially worthless trees and shrubs, and commercial crops such as corn, sorghum, tomatoes, mango, and sugarcane. The natural vegetation has been replaced by large areas of cultivation (Fig. 4), which also house numerous human populations ranging from small ejidos to large cities (Brand 1936; INEGI 2017). The dominant natural vegetation is tropical deciduous forest found along the western slopes of the Sierra Madre Occidental of Sinaloa. Tropical deciduous forest in southern Sinaloa is separated from the upland oak woodland and pine-oak forest by semi-deciduous tropical forest, a much more tropical vegetation type (Ruíz-Guerrero et al. 2015). The density of this forest is higher in the southern third of Sinaloa and is more open in the northeastern part of the state. In addition, southern Sinaloa has the huge Marisas Nacionales wetlands that abut semi-deciduous forest (T. Van Devender, pers. comm.). Tree species in the southern third are also taller than those in the northern part of the state. This vegetation type is found from the southern third of the state along the foothills of the Sierra Madre Occidental to the northeastern corner of the state. On the highest mountains of the Sierra Madre Occidental, the vegetation often changes to oak and pine-oak forest along the borders with Durango and Chihuahua (INEGI 2017). The coastal plain of the northern half of Sinaloa shows great uniformity in vegetation, gradually changing as one moves to the south (INEGI 2017). The belt immediately along the coast is more arid than the interior and its vegetation is poorer and more open. The flood plains are largely devoted to vast cultivated fields of sugar, garbanzo, tomatoes, and corn. The natural vegetation is more luxuriant than that of the uplands and includes many tropical plants. The vegetation of the hills, which are scattered over the plain, is commonly very similar to that of the plain. In the lowlands of Sinaloa, the coastal plain type of “thorn forest”, a mixture of tropical deciduous forest and thornscrub, predominates in area over the vegetation characterizing the flood plains, the coast, and the hills (Shreve 1937). The vegetation along the coast of Sinaloa north of Mazatlán is a vegetation type that could be considered short tropical deciduous forest (T. Van Devender, pers. comm.). In the northwestern corner of the state near Sonora, the vegetation type is subtropical Mimosaceae-cacti characterized by spiny shrubs and cacti dominated by Mimosaceae and columnar cacti. This vegetation is not distributed uniformly, rather it is arranged in clumps, but with a nearly continuous cover in wetter spots (Brand 1936). In Sonora, thorn scrub is a transitional vegetation type between tropical deciduous forest and the Sonoran Desert to the north and the woodlands and forests of the Sierra Madre Occidental to the east (Martin et al. 1998; Van Devender et al. 2013).

Figure 4. 

Vegetation map of the state of Sinaloa, Mexico (modified from Dirección General de Geografía – INEGI 2013).

In Sinaloa there is a trend for precipitation to decrease from southern to northern Sinaloa. The dominant climate in Sinaloa is warm semi-warm sub-humid which covers 48.4% of the state and is present from the southern tip of the state to the Port of Mazatlán, and from there in a narrow strip along the foothills of the western slopes of the Sierra Madre Occidental of Sinaloa, along the borders with Durango and Chihuahua. This area is characterized by a mean annual temperature over 18 °C. Precipitation of the driest month is < 40 mm. Small scattered locations in the highest mountains of the extreme southeastern and northeastern parts of Sinaloa are characterized by a temperate sub-humid climate, present in only 2.3% of the state. The climate of these elevated peaks is characterized by an average annual temperature between 12 °C and 18 °C. Rainfall in the driest month is < 40 mm; the maximum rainfall occurs in summer. A narrow strip that runs parallel to the foothills of the Sierra Madre Occidental, covering 21.3% of the state surface area, from just north of the Port of Mazatlán to the border with Sonora in northern Sinaloa is characterized by a semiarid climate with a mean annual temperature > 22 °C. Parallel to this strip and next to the coastline the climate is arid, with an average annual temperature > 22 °C. The extreme northwestern corner of the state, from the border with Sonora to just south of the Port of Topolobampo, which covers 9.8% of the state surface territory, is characterized by an extreme arid climate with an average annual temperature above 22 °C, and eight continuous months of dry to very dry conditions. Heavy rains occur in the July-September, which represent more than 75% of the annual total (Fig. 5; Köppen modified by García 1998; INEGI 2017).

Figure 5. 

Climate map of the state of Sinaloa, Mexico (modified from García – Comisión Nacional para el Conocimiento y Uso de la Biodiversidad 1998).

Twenty-one of the 39 species of amphibians in Sinaloa are endemic to Mexico, two of which are restricted to small areas in the Sierra Madre Occidental of Sinaloa and adjacent Durango, or Sinaloa, Nayarit, and Jalisco. Twelve are primarily distributed along the Pacific Coast and western slopes of the Sierra Madre Occidental. Two are characteristic of the Sierra Madre Occidental, and five have a widespread or spotty distribution in the Sierra Madre Occidental, central Mexico, and Sierra Madre del Sur. Of the 18 amphibian species in Sinaloa not endemic to Mexico, one is introduced, nine are found in the United States and Mexico, five are distributed from Mexico to Central or South America, and three have a wide distribution from the United States to Central or South America (Table 1). The American Crocodile (Crocodylus acutus) is widely distributed from southern Florida in the United States, and along the Pacific Coast of Mexico from Sonora to northern South America, including the Caribbean and the Yucatan Peninsula. Twenty of the 42 species of lizards that occur in the state are endemic to Mexico, one is endemic to Sinaloa, three are restricted to localities in the northern part of the Sierra Madre Occidental, one has a spotty distribution in Sinaloa and Colima, and one has a spotty distribution in the Pacific Coast from Sinaloa to Michoacán. Twelve species are found on the western slopes of the Sierra Madre Occidental and the Pacific Coast, one occurs in both the Sierra Madre Occidental and the Sierra Madre Oriental, and one is widely distributed in northern and central Mexico. The remaining 22 species of lizards that inhabit Sinaloa are not endemic to Mexico. Seventeen of the non-endemic species of lizards are found in the United States and Mexico, three are distributed from Mexico to Central America, and two are introduced to Sinaloa (Table 1). Thirty-four of the 64 species of snakes that inhabit Sinaloa are endemic to Mexico. Of the 30 snake species not endemic to Mexico, 19 are found in the United States and Mexico, four range from Mexico to Central or even South America, five are found from central or southern United States to Central or South America, one is a sea snake distributed across the Pacific and Indo-Pacific Oceans, and one is introduced to Sinaloa (Table 1). Six of the13 species of turtles found in Sinaloa are endemic to Mexico, one is found in the United States and Mexico, one is distributed from Mexico to Central America, and five have a circumtropical or circumglobal distribution (Table 1). One of the six endemic species of turtles that inhabit Sinaloa is shared with Baja California Sur (Trachemys nebulosa). This species was probably introduced in the Cape Region of Baja California by Sinaloan miners (T. Van Devender, pers. comm.).

The vegetation type that hosts the highest number of amphibian and reptile species is the Tropical Deciduous Forest, which includes semi-deciduous forest, with 121 species, which represents 77.6% of the total number of species found in Sinaloa. The second highest number of amphibian and reptile species is hosted by “Thorn Forest” with 104 species, which represents 66.7% of the total species of Sinaloa. According to INEGI (2017), these two types of vegetation together occupy approximately 36% of the state. These are the two dominant vegetation types in the state, and they are also the vegetation types that originally appeared in what are now the agricultural areas of Sinaloa, which now occupy approximately 38.5% of the state surface territory (INEGI 2017). In addition, they are the types of vegetation, which due in part to their location, have been more studied from the herpetofaunistic point of view. On the other hand, the Oak Forest of Sinaloa, hosts 70 species (44.9%) of amphibians and reptiles, and the Pine-oak Forest, limited to the highest parts of the Sierra Madre Occidental of Sinaloa, hosts only 14 species (9.0%) of amphibians and reptiles of Sinaloa. Together, these two vegetation types occupy approximately 16.5% of the state surface territory (INEGI 2017). The Subtropical Mimosaceaе Cacti thorn scrub vegetation type of Sinaloa hosts 49 species (31.6%) of amphibians and reptiles. This vegetation type, limited to the northwestern tip of the state, occupies < 3.2% of the state’s territory; however, it houses a unique assortment of amphibians and reptiles, dominated by species typical of thornscrub (Bezy et al. 2017).

For amphibian and reptile species together, 12.7% are IUCN listed (i.e., Vulnerable, Near Threatened, or Endangered), 9.7% are placed in a protected category (excluding NL and Pr, this last category is equivalent to the LC category of IUCN) by SEMARNAT, and 34.0% are categorized as high risk by the EVS (Table 3). For amphibians, 14.3% are IUCN listed, none are protected by SEMARNAT, and 16.2% are at high risk according to the EVS (Table 3; Fig. 7). For reptiles, 17.2% are listed by the IUCN, 12.8% are protected by SEMARNAT, and 40.2% are at high risk according to the EVS (Table 3; Fig. 7). This summary suggests that the herpetofauna of Sinaloa has relatively few species of conservation concern at a global and national scale (IUCN and SEMARNAT lists), but there might be greater conservation concerns using the EVS which is based on information specific to Mexico and Central America and so might be more likely to reflect the conservation status and needs of the Sinaloa herpetofauna. Although the SEMARNAT list is also based on information specific to Mexico, it has not been updated since 2010, and so does not take into account the numerous recent taxonomic changes and the description of new species or more recent changes in conservation status or threats. There are several taxa that, based on their IUCN listing, SEMARNAT category, or their EVS, are of conservation concern. Families with species of particular conservation concern include Craugastoridae, Eleutherodactylidae, Ambystomatidae, Crocodylidae, Dactyloidae, Eublepharidae, Helodermatidae, Iguanidae, Phrynosomatidae, Phyllodactylidae, Colubridae, Natricidae, Viperidae, Cheloniidae, and Dermochelyidae (Table 3). The status of a species in Sinaloa may differ (i.e., be worse or better) from the IUCN, SEMARNAT, and EVS assessments. Thus, assessments at the state level are needed to fully understand the conservation or management needs for the Sinaloan herpetofauna.

Figure 7. 

Proportion of A amphibians and B reptiles listed in protected categories on the IUCN Red List, SEMARNAT, and high EVS for Sinaloa. Green is proportion in Data Deficient and Least Concern (IUCN); Not Listed and Subject to Special Protection (we regarded the category of Subject to Special Protection in SEMARNAT equivalent to Least Concern in IUCN) (SEMARNAT); or low or medium EVS. Red is percentage in protected categories or high EVS. N is the number of species assessed.

The conservation status of species found in different vegetation types in Sinaloa appear to differ (Table 1). For IUCN categories, 6.7% of the amphibian species found in the Tropical Deciduous Forest are listed in a protected category; none in the Thorn Forest of the Coastal Plains or the Subtropical Mimosaceae Cacti, 16.1% in the Oak Forest, and 33.3% in the Pine-Oak Forest. For SEMARNAT categories, no species of amphibian in Sinaloa is listed for any vegetation type (see above). For EVS, 13.3% of the amphibians in the Tropical Deciduous Forest of Sinaloa were in the high category, 5.0% in the Thorn Forest, 10.0% in the Subtropical Mimosaceae Cacti, 19.4% in the Oak Forest, and 16.7% in the Pine-oak Forest. For the IUCN listings, all five vegetation types of Sinaloa have relatively few species of reptiles in the protected categories (Tropical Deciduous Forest, 6.6%; Thorn Forest, 6.0%; Subtropical Mimosaceae Cacti, 5.1%; Oak Forest, 2.6%, and Pine-oak Forest, 0%). However, 66.7% of the reptiles in the Marine region are listed in IUCN protected categories. According to SEMARNAT, 8.8% of reptiles that inhabit the Tropical Deciduous Forest of Sinaloa, 8.3% from the Thorn Forest, 15.4% from Subtropical Mimosaceae Cacti, 10.3% from the Oak Forest, and none from the Pine-oak Forest are in protected categories. Five (83.3%) of the marine reptiles of Sinaloa are in protected SEMARNAT categories. For the Tropical Deciduous Forest of Sinaloa 38.5% of the reptile species were in the high EVS category, 38.1% in the Thorn Forest, 33.3% in the Subtropical Mimosaceae Cacti, 41.0% in the Oak Forest, and 12.5% in the Pine-oak Forest. None of the marine reptile species have been evaluated by the EVS. The marine reptiles of Sinaloa are by far the most threatened of the Sinaloa herpetofauna.

Overall, Sinaloa shares the most herpetofaunal species with Sonora, with 72.4% overlap in species (Table 4). Sinaloa shares the most amphibian species with Nayarit (78.9%). Some families, including Hylidae, Leptodactylidae, Microhylidae, Scaphiopodidae, and Ambystomatidae, show complete overlap between Sinaloa and Nayarit. The higher similarity in amphibian composition between Nayarit and Sinaloa than between Sinaloa and Sonora is due to eleven species that are shared between Sinaloa and Nayarit but not Sonora. All of these species reach their northern most distribution either in Sinaloa or Durango. The five that are shared between Sinaloa and Sonora but not with Nayarit reach their southern or southwestern most distribution in Sinaloa, and one is a species likely to occur in Nayarit. The similarity between the amphibian composition of Sinaloa and Chihuahua and Durango is lower than for Sonora and Nayarit (55.3% Durango, 52.6% Chihuahua). The amphibian species of Chihuahua and Durango have a number of species from the Chihuahuan Desert and the Sierra Madre Occidental, that do not occur in Sinaloa (Lemos-Espinal et al. 2017, 2019a). On the other hand, the Peninsula of Baja California has the lowest similarity with Sinaloa (18.1%), sharing only 28 species (Table 4), of which six are marine species with a wide global distribution. Eight of the other 22 species are only found in the northern part of the Peninsula, in the state of Baja California, far away from Sinaloa, another 10 species have a wide distribution that includes practically the entire Peninsula and the northern Mexican Pacific, four species are limited to the Baja California Peninsula and the northern part of the Mexican Pacific. Although eight to thirteen million years ago most of the Baja California Peninsula was submerged beneath the Pacific Coast and located next to the northwest coast of mainland Mexico (Grismer 2002), since its separation approximately six million years ago the fauna and flora of this peninsula has evolved under conditions of isolation, giving rise to a unique and different biota than that of Sinaloa. These numbers are an indication that Sonora, Sinaloa, and Nayarit are more similar due to the dominance of species distributed along the Pacific Coast, and Chihuahua and Durango are more similar in the composition of amphibians due to the dominance of species from the Chihuahuan Desert and Sierra Madre Occidental. The great similarity in the herpetofauna composition between Sinaloa and Sonora was also found by Enderson et al. (2009). Similarly, reptile composition is more similar between Sinaloa and its neighbors Sonora and Nayarit, than between neighbors Chihuahua and Durango. As with amphibians, Chihuahua and Durango have more reptile species from the Chihuahuan Desert and the Sierra Madre Occidental, and few species characteristic of the Pacific Coast. In addition, Sonora, Sinaloa, and Nayarit share a number of reptile species characteristic of the Pacific Coast. A greater similarity between Sonora, Sinaloa, and Nayarit is also expected by the presence of marine species in these three states, and an absence of those species in Chihuahua and Durango.