Lake Erie watersnake COSEWIC assessment and status report: chapter 6

Biology

Life cycle and reproduction

The longevity of the Lake Erie Watersnake is up to 12 years in the wild (USFWS 2004). Females reach sexual maturity at 3 years of age, whereas males become sexually mature at 2 years. Typically, females reach sexual maturity at 60 cm snout to vent length (SVL) and males at about 44 cm SVL (King 1986).

Courtship and mating occurs from early May to early June and, as in other natricine snakes, involves scramble competition (several males court one female simultaneously), resulting in a large aggregation of snakes (King 1986; USFWS 1999, 2003). Some females reproduce annually and the frequency of reproduction is size dependent with larger females being more likely to reproduce annually than smaller females (King 1986; Bishop and Rouse unpubl. data 1999).

Parturition occurs in late August and early September. Litter size ranges from 9 to 50 with an average of 23 neonates (NatureServe 2005). On Pelee Island, Bishop and Rouse (unpubl. data 1999) found litter sizes ranging between 13-46 with a mean of 27 neonates. Litter size is positively correlated to female size with larger females not only producing more young but also larger neonates (King 1986). Average neonate size is 18.1 cm SVL and 4.8 g (King 1986). Neonates do not grow much prior to entering hibernation and often emerge at the same size at which they entered (USFWS 1999, 2003).

Predation

Predators of the Lake Erie Watersnake have not been well documented. Known predators include the Herring Gull (Larus argentatus), Great Blue Heron (Ardea herodias), American Robin (Turdus migratorius), raccoon (Procyon lotor), red fox (Vulpes vulpes), Blue Racer (Coluber constrictor), and domestic animals such as cats and dogs (King 1986; USFWS 2003). Dead Lake Erie Watersnakes with wounds from bird attacks have been found on islands inhabited by Double-Crested Cormorants (Phalacrocorax auritus) (D. Jacobs pers. comm. November 2004), but it is not known if cormorants killed the snakes. Neonates and juveniles are more likely to be preyed upon than are adult snakes; however, predation has apparently not contributed greatly to the species’ population decline (USFWS 2003).

Physiology

Female Lake Erie Watersnakes feed over a longer portion of the active season than do males. Females grow faster than males at 0.014 versus 0.012 cm/day, respectively, and females attain a larger body size (82.1 cm mean SVL) than males (62.4 cm mean SVL) (King 1986).

Similar to many reptiles, Lake Erie Watersnake activity depends heavily on seasonal and local weather conditions. Lake Erie Watersnakes have been observed entering water in the first week of May when water temperatures were approximately 5°C (King 1986). However, emergence from hibernation typically starts when the mean maximum daily air temperature rises to 12.8°C (April/May) and entrance into hibernation commences when the mean minimum daily air temperature drops to 15.5°C (September/October) (King 2003).

Dispersal/Migration

Lake Erie Watersnakes have been known to travel several kilometres from island to island, or island to mainland; however, movements over such distances are rare (King 1987a). Individuals rarely move more than 50 m off shore during the active season (King 2003; D. Jacobs pers. comm. November 2004). King (2003) estimated that 50% of all aquatic movements occurred within 8 m of shore, 75% were within 13 m, 90% were less than 21 m, and only 1% ranged more than 47 m from shore. Maximum extent of shoreline used by an adult Lake Erie Watersnake in Ohio ranges from 30-1360 m, averaging 252 m among individuals (King 2003). King (2003) found 50% of the watersnake population hibernated within 27 m of the shore, 75% within 69 m, 90% within 161 m and 99% hibernated within 700 m of shore. In Canada, radiotelemetry studies show that the distance of hibernation sites from shore ranged from 13-105 m and averaged 53 m; with 50% of the hibernation sites within 56 m of the shore, 75% within 69 m, and 90% within 95 m of shore (D. Jacobs pers. comm. September 2005).

Although migration between islands and from island to mainland is rare, one Lake Erie Watersnake was determined to have travelled a straight-line distance of 11 km to Middle Island from Kelleys Island in 2002 (D. Jacobs unpubl. data 2002/2003). However, less than 3% of adults move even among sites on a given island and movements between islands occur much less often (King 1987a). Migration may occur between islands and the mainland in Ontario at an estimated rate of nine snakes in each generation (King and Lawson 1995). Small home range and short distance movement of the Lake Erie Watersnake are mirrored in distinct and local geographic variation in contamination levels found in samples taken from watersnakes along 34 km of shoreline on Pelee Island (Bishop and Rouse unpubl. data 1999).

Interspecific interactions

Lake Erie Watersnakes now feed almost exclusively on the round goby that has recently invaded Lake Erie (King 2004a). It is not known what effect this shift in diet has had on the Lake Erie Watersnake’s former prey of logperch (Percina caprodes) and other darters. Conant (1951) mentions that watersnakes may scavenge for fish that have washed up onto the beach.

Adaptability

Lake Erie Watersnakes appear to adapt somewhat to modification of shoreline habitat. Kelleys Island supports the most dense concentration of Lake Erie Watersnakes in Ohio despite the fact that this island is the most heavily developed of the islands in the watersnake's U.S. range (USFWS 2003). Lake Erie Watersnakes have been documented using anthropogenic structures such as riprap, rock-filled timber or steel crib docks for basking and resting habitat (King 2001, 2003; USFWS 2003). However, sheet steel docks and poured concrete for erosion control are not used by snakes and destroy what would otherwise be suitable watersnake habitat (USFWS 2003). In the U.S. and Canada, radiotelemetry studies demonstrate that individual Lake Erie Watersnakes show fidelity to hibernation sites and specific stretches of shoreline for summer habitat (D. Jacobs pers. comm. September 2005). It is not known how adaptable individuals are to being displaced by habitat development/destruction from their preferred sites.

Lake Erie Watersnakes feed almost exclusively on aquatic prey (King 1986, 1998). The previous COSEWIC report (Campbell et al. 1991) noted that fish comprised over 50% of the watersnake’s diet on Pelee Island and that half of that percentage consisted of logperch and other darters. Since the early 1990s, the round goby has invaded feeding areas of the Lake Erie Watersnake (Jude et al. 1992) and are now the dominant bottom-dwelling fish in the island region (King 2003). In 1998, gobies represented 24% of the Lake Erie Watersnake’s diet (King et al. 1999) and by 2003, gobies made up over 92% of the Lake Erie Watersnake's diet (King 2004a). The effects of this change in diet may be significant. King (2004a) found that watersnakes of all size and age classes consumed gobies, and watersnakes less than one year old had a larger body size after the invasion of gobies compared to before the increase in gobies as prey. The same results were found for body size of adult snakes, with higher growth rates after gobies became a large portion of the diet.

Page details

Date modified: