Eastslope sculpin COSEWIC assessment and status report: chapter 8

Biology

General

Life history information for the “Eastslope” sculpin is somewhat limited, and much of the information available is based on a limited number of studies of C. bairdii populations from other western systems. It appears that Bailey (1952) may refer to the same taxon. The only study to specifically describe the life history of the “Eastslope” sculpin in Alberta was conducted by Roberts (1988).

Roberts (1988) noted that all Cottus species in Alberta, including the “Eastslope” sculpin, spawned during the late spring. Specifically, he observed male sculpins protecting eggs in Lee Creek, a tributary of the St. Mary River, during mid-May when the water temperature was 15°C (Roberts 1988). He noted that only gravid females (no males were observed protecting nests) were observed in the St. Mary River mainstem when the water temperature was 7.5°C, suggesting a threshold temperature triggering spawning somewhere between 7.5°C and 15°C.


Reproduction

The spawning season for Cottus species is highly variable and may range from February to August, depending on location (summarized by Bailey 1952). A fairly detailed study on spawning ecology was conducted for Rocky Mountain sculpin in southwestern Montana by Bailey (1952). In general, males arrived earlier than females at the breeding sites, and were ripe earlier. In addition, these males were considered highly polygamous, usually spawning with 1.5 to 4 females, but sometimes up to 12 females. Single egg clusters are deposited by the female C. bairdii on or under rocks, and the single male remains near the nest site for up to several weeks during oviposition, incubation and early embryo stages (Peden 2000; Bailey 1952). Rather than behaving as guardians of these nest sites, Bailey (1952) believed that these males kept the nests clean of silt and other debris. Finally, the study of Rocky Mountain sculpin in southwestern Montana found that more than one female might use a particular nest site (Bailey 1952).

The fecundity of sculpin specimens collected from the Milk and St. Mary rivers generally ranged from 100 to 250 eggs, although one large female of 80.7 mm total length (TL – straight-line distance from the tip of the snout to the end of the tail fin), contained 354 eggs (Roberts 1988). Peden and Hughes (1984) noted a female of 53 mm standard length (SL – straight-line distance from the tip of the snout to the end of the tail spine) with 128 eggs and a female of 99 mm (standard length) with 690 eggs from the Flathead River. Eggs of the “Eastslope” sculpin likely hatch within 2 to 3 weeks, depending on temperature (Roberts 1988). Young of the year were 30-40 mm TL by the end of their first summer, and yearlings achieved a length of at least 50 mm (Roberts 1988). These data are similar to data from the Flathead River, where young-of-the-year were on average 37.0 mm SL by late summer (Hughes and Peden 1984). In the Flathead River, one-year-old males were on average 64.4 mm SL and one-year-old females were 48.6 mm SL by October (Hughes and Peden 1984). Growth of shorthead sculpins in Big Lost River in Idaho was approximately 10 to 20 mm per year (Gasser et al. 1981).

For the “Eastslope” sculpin, both sexes are believed to be sexually mature at the age of 23 months, although no specimens have been aged (Roberts 1988). The only mature two-year-old female collected from the Flathead River was 71.4 mm SL (Hughes and Peden 1984). The smallest mature female examined from the Milk or St. Mary rivers was 52.3 mm in TL, but age was not estimated (Roberts 1988). These observations are consistent with data collected for C. confusus and C. bairdii elsewhere. The youngest age of first maturation for C. confusus in British Columbia is probably 2 years, with the smallest standard length recorded at 42 mm for a mature female (Peden 2001). Similarly, all specimens of Rocky Mountain sculpin in southwestern Montana found to be sexually mature were at least 2 years old and 57 mm TL (Bailey 1952).


Survival

No longevity information is available for this species, but shorthead sculpins in British Columbia are not thought to live beyond 5 years of age and probably breed annually (Peden 2001). Shorthead sculpin females from Big Lost Creek, Idaho were also observed to breed annually (Gasser et al. 1981).


Physiology

There is very little information available on the physiology of the “Eastslope” sculpin. In the Milk River, they are found only in the upper, and middle reaches, which suggests that they have a preference for colder temperatures and clearer water as was indicated for the Columbia sculpin (Peden 2000). Willock (1969) postulated that water temperature was the single most important factor affecting sculpin distribution. Temperature may also play a role in spawning with a threshold between 7.5 and 15°C (Roberts 1988).


Movement

It is unlikely that “mottled” or shorthead sculpins migrate extensively throughout the year, as surveys found specimens of both species at the same sites in British Columbia during spring, summer, fall and winter sampling (Peden 2001). Similarly, Peden and Hughes (1984) did not find either juvenile or adult shorthead sculpin to undergo extensive migrations. Furthermore, Peden (2000) noted that the home range was less than 5 m2 for “mottled” sculpins in British Columbia. An older study by Bailey (1952) found that, over a one-year period, the maximum dispersal by tagged C. bairdii punctulatus in Montana was only approximately 143 m. Finally, genetic differences among small tributaries within streams (based on allozyme electrophoresis) suggested virtually no movement (or at least gene flow) among C. confusus populations intributaries 10 km or more apart in British Columbia, and similar small-scale differences were noted for C. bairdii (Peden 2000). Although no information for the “Eastslope” sculpin exists regarding movement, in all likelihood these fish would demonstrate similar behaviour patterns to those observed in the above studies.


Nutrition and Interspecific Interactions

Sculpins are mainly nocturnal foragers, but foraging behaviour is somewhat dependent on the species. A recent study found that shorthead sculpins in the Columbia River system tended to remain in the fast water areas during the night, where they foraged on drifting insects on the upstream side of rocks (McPhail 2001). In general, food habits appear to be similar for C. bairdii and C. confusus (Peden 2000, 2001). Aquatic insect larvae appear to make up the majority of the diet, but molluscs, fish, and even sculpin eggs may also contribute (Bailey 1952, Peden 2000, 2001; Paetz 1993). Similarly, Bailey (1952) found that the diet of C. bairdii punctulatus in Montana was made up almost exclusively (99.7%) of bottom-dwelling aquatic insects, with snails, clams, water mites, sculpin eggs and fish making up the remaining 0.3%.

Sculpins may forage on eggs of other fishes and may form part of the diet of other fishes such as brook trout (Salvelinus fontinalis) and smallmouth bass (Micropterus dolomieu) or even snakes (Deason 1939, Scott and Crossman 1973). Parasitic interactions are not known for the “Eastslope” sculpin, but larval cestode (Proteocephalus ambloplitis, P. sp.), and trematode (Tetracotyle sp., Diplostomum sp.) infestations have been noted in C. bairdii from eastern Canada (Bangham and Hunter 1939; Bangham 1955), and it is a carrier of Aeromonas salmonicida, the bacterium responsible for furunculosis in fishes (Rabb and McDermott 1962). In addition to trematodes and cestodes, Hoffman (1967) lists several protozoans, nematodes, acanthocephalans, molluscs and crustaceans as associated parasites.


Behaviour/Adaptability

As indicated above, water temperature is an important factor in the distribution of the “Eastslope” sculpin; however, water level also seems to be an important factor (R.L. & L. 2002). Given the restricted area of occupancy (<300 km2) and the periodic episodes of extreme drought that can, and do occur in the prairies, the survival of “Eastslope” sculpins is susceptible to such stochastic events. For example, changes in distribution have certainly occurred since the 1960s as a result of inadequate water flow resulting from drought conditions and impoundments, diversions and water removal (Paetz 1993; R.L. & L. 2002). Populations in the upper Milk River have been extirpated as a result of inadequate water flow, although Clayton (pers. comm. 2004) views this as an unsuccessful range extension; i.e., when the mainstream Milk River dries up some fish are trapped and die. When it does have water some fish may swim up from the North Milk River and if it has sufficient water for a few years, they move further up, and then in dry years the cycle reverses. Therefore, he (Clayton) sees this as habitat limitation through water availability.

It is also possible that those downstream of the reservoir on the St. Mary River were extirpated. There may have been “Eastslope” sculpin in the St. Mary River downstream of the dam prior to construction of the reservoir, but they would have been intolerant of the resultant higher water temperatures (Clayton, pers. comm. 2004). There is evidence that fragmentation within the river systems is possible (see Canadian Range – Alberta), so local extirpations may affect gene flow and lead to further fragmentation. Genes/sculpins from St. Mary sculpin in Montana, above the St. Mary canal, can end up in the Milk River or in the St. Mary River in Canada. But sculpins cannot go from the Milk River to the St. Mary River, and sculpins from the St. Mary River in Canada can not go to the Milk River (Clayton, pers. comm. 2004). In a catastrophic situation the “Eastslope” sculpin might well be eradicated from Alberta.

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