Eastslope sculpin COSEWIC assessment and status report: chapter 5

COSEWIC Status Report
on the
"Eastslope" Sculpin
Cottus sp.
in Canada
St. Mary and Milk River populations
2005

Species Information


Name and Classification

Class:
Actinopterygii
Order:
Scorpaeniformes
Family:
Cottidae
Genus:
Cottus
Species:
Cottus sp.
Scientific name:
Cottus sp.
Common names
English: "Eastslope" sculpin (provisional; the quotations are used to indicate the provisional nature of the name.)
French: chabot du versant est


Description

The morphology of sculpins is distinct, reflecting the bottom-dwelling nature of species of this family. They are large-headed and heavy-bodied fish (Figure 1) with a body that tapers from the head to the tail, and lack an air bladder (Peden 2000, 2001). The dorsal and pelvic fins have protective spines (Scott and Crossman 1973). The maximum fork length (FL – straight-line distance from the tip of the snout laterally to the central margin of the tail fin) recorded for the sculpin in Alberta is 114 mm from the Milk River (R.L. & L. 2002).


Figure 1: Illustration of Cottus bairdii

Figure 1. Illustration of Cottus bairdii.

After Bailey and Dimick, 1949 from Peden 2000 by permission.

The mottled sculpin (C. bairdii) and the shorthead sculpin (C. confusus) are morphologically distinct from other sculpins in Canada based on several features (summarized in Peden 2001). These features include the following: (1) no prickles covering the entire body (i.e., only found behind the pectoral fin); (2) well-developed pelvic fin rays; (3) vomerine and palatine teeth; (4) 11-15 anal fin rays and 13-16 pectoral fin rays; and (5) an upper preopercular spine not strongly hooked. However, the two species are very difficult to differentiate from one another visually, and a combination of several morphological features is required to distinguish them in western Canada. Large shorthead sculpins do not have papillae on the top of their heads. In general, they have fewer pectoral fin rays (13 versus 15), reduced preopercular spines (2 versus 3), and fewer lateral line pores (average of 23-25 versus 27-29) than mottled sculpins. A live specimen of the shorthead sculpin is noticeably more slender, often uniformly dark and appears smooth in texture with a shorter head (Peden 2001). In addition, the lateral line of the shorthead sculpin does not extend into the base of the tail fin (i.e., does not usually reach the fin rays). In comparison, the mottled sculpin is broader across the gill area and mottled in pigment with more visible papillae on the top of the head of larger specimens (Peden 2001).

Significant variation for these morphological features also exists within western mottled sculpins throughout their range, making the classification of specific populations of these sculpins even more difficult. Two forms of mottled sculpin had previously been described in western Canada, including the Columbia mottled sculpin [now recognized as the Columbia sculpin, C. hubbsi, Bailey and Dimick 1949 (Nelson et al. 2004)], which is endemic to the Columbia Basin, and a Rocky Mountain form most closely allied with the sculpin found in the St. Mary and Milk rivers, provisionally, C. bairdii punctulatus Gill (Troffe 1999; Peden 2000). A recent morphological study on western Canadian mottled sculpins described populations from the Flathead River in British Columbia and the St. Mary River as the Rocky Mountain form (Troffe 1999). The Rocky Mountain form is distinguished from the Columbia sculpin based on several morphological features (Troffe 1999; Peden 2000). The Columbia sculpin has a complete lateral line with an average of 29 ± 3 pores, and prickles are present behind the pectoral fin. In contrast, the lateral line of specimens from the Flathead and St. Mary rivers is not complete, with an average of 22 ± 3 pores, and prickles behind the pectoral fin are absent (Troffe 1999; Peden 2000).


Taxonomy

The taxonomy of sculpins in western Canada is complex and unresolved. This fish was first recognized as the mottled sculpin, C. bairdii Girard, in the late 1960s (summarized by Nelson and Paetz 1992), but later described as the shorthead sculpin, C. confusus, based on morphological studies (Roberts 1988). Peden et al. (1989) described two forms of C. confusus from British Columbia; one from the Flathead system and another from the Columbia and Kettle rivers. The form found in the Flathead system is similar to that of the St. Mary-Milk rivers, and the other resembling those described as shorthead sculpin by Bailey and Bond (1963) is now recognized as a new species, Cottus hubbsi (Nelson et al. 2004). Some researchers (Troffe 1999; Peden 2000; D. McPhail, Professor Emeritus, Department of Zoology, University of British Columbia, Vancouver, BC; personal communication 2003) suggested that this fish was an unrecognized taxon within the western Cottus bairdii complex and should not be confused with the shorthead sculpin (C. confusus) found elsewhere.

Recent morphological and genetic data suggested that the sculpin in the St. Mary and Milk rivers may be the same species as that found in the Flathead River in British Columbia (Figures 2, 3), as well as the one found in the upper Missouri River system (Troffe 1999; Peden 2000; McPhail pers. comm.). More recently, Neely (D.A. Neely, Post Doctoral Research Associate, Department of Biology, Saint Louis University, St. Louis, MO; personal communication 2003) has suggested that this may be a new species that is closely allied with the Rocky Mountain sculpin, C. bairdii punctulatus recorded by Bajkov (1927) and Schultz (1941) based on specimens collected from both slopes of the Rocky Mountain region and from Glacier National Park in Montana, respectively. Troffe (1999), Peden (2000) and McPhail (pers. comm.) suggested that the sculpins in the St. Mary and Milk rivers, along with the Flathead populations, should provisionally be identified as C. bairdii punctulatus.


Figure 2: Distribution of Mottled Sculpins (Cottus bairdii) in North America

Figure 2. Distribution of mottled sculpins (Cottus bairdii) in North America.

Based on Lee 1980; Peden 2000.
Note the disjunct distribution of the eastern subspecies, C. b. bairdii, from the western subspecies, C. b. punctulatus of the Missouri drainage, and the Columbia sculpin, Cottus hubbsi, which are separated by the Continental divide (roughly along the Montana/Idaho border). It now appears that there are no bairdii in western North America, and the Missouri form is also a distinct species, provisionally “Eastslope” sculpin, Cottus sp.

 


Figure 3: Distribution of Mottled Sculpins in Western Canada

Figure 3. Distribution of mottled sculpins in western Canada.

The dots represent collection sites for C. b. punctulatus (now provisionally “Eastslope” sculpin, Cottus sp.); the shaded area is the Flathead population. Diamonds represent C. hubbsi sites.

In terms of genetic characterization, a large geographic (separated by the Great Plains) and molecular genetic gap appeared to separate western and eastern groups of mottled sculpin C. bairdii, and the eastern groups appear to be monophyletic (i.e., evolved from one group) (Neely pers. comm.). However, the genetic relationships among western C. bairdii and C. confusus populations are still in the process of resolution. Peden (2000) used allozyme variation to demonstrate that the Flathead River population of sculpins was actually an unrecognized Canadian taxon, which he provisionally named C. bairdii punctulatus, distinct from those of the Columbia system, provisionally named C. b. hubbsi (Bailey and Dimick 1949; McAllister and Lindsey 1961; McPhail 2001) and is in agreement with the morphological results reported by Troffe (1999). Most recently, higher resolution molecular genetic results (based on variation in cytochrome b and the control region genes found in the mitochondrial DNA) demonstrated that the Flathead population of sculpins appears to be genetically similar to the St. Mary River (Alberta) and upper Missouri River populations in Montana (McPhail pers. comm.). In addition, these results demonstrated that the Columbia sculpin was quite distinct from the sculpins from the Flathead and St. Mary systems (McPhail pers. comm.). Again, this work supports the morphological work by Troffe (1999). Subsequently, the form in the Columbia River basin has formarlly been recognized as a valid species (see Nelson et al. 2004), Cottus hubbsi, (Bailey and Dimick 1949) based on work by Markle and Hill (2000) supported by the ongoing study of D.A. Neely (pers. comm.).

In a parallel genetic study of western Cottus species in the United States, at least five taxa within the former C. bairdii complex are believed to occur (Neely 2002; Neely unpublished in preparation; J. Nelson, Professor Emeritus, Department of Biological Sciences, University of Alberta; personal communication 2005). As indicated above, the Columbia sculpin (Cottus hubbsi) has already been recognized (Nelson et al. 2004) as a new species. According to Neely (2002; Neely, pers. comm. 2005), the upper Missouri River population, and therefore most likely the St. Mary/Milk and Flathead populations, which were provisionally described as Cottus bairdii punctulatus (Peden 2000), is also a new taxon, not Cottus punctulatus, which is confined to the Colorado River, USA (Nelson, pers. comm. 2005). This new species is provisionally being referred to as the “Eastslope” sculpin, Cottus sp., until a formal description is available (Neely, unpublished data, in preparation). It will require a new name, as it has no synonyms (Nelson, pers. comm. 2005). It now appears that there may be no mottled sculpin in western Canada and C. bairdii exists only in the east (Nelson, pers. comm. 2005).

Unfortunately, the Canadian and American data sets have yet to be combined, but Neely is in the process of completing this task in his ongoing research. In addition, none of the recent morphological work by Troffe (1999) or genetics work has incorporated any Milk River or Flathead specimens. However, Neely’s ongoing research will address these problems, but results are not as yet available. Therefore, it is assumed, based on the earlier morphological data (e.g., Roberts 1988), that the population in the Milk River is the same species as the St. Mary River population.


Designatable Units

As discussed above, all researchers currently pursuing the taxonomic questions regarding these taxa concur that the St.Mary-Milk and upper Missouri sculpins represent an unrecognized taxon, provisionally called “Eastslope” sculpin, Cottus sp. (Neely 2002; Nelson, pers. comm. 2005). Since the St. Mary-Milk River populations are disjunct and biogeographically isolated [COSEWIC National Freshwater Ecological Areas 4, 7 COSEWIC (2004)] from those of the Flathead system (Area 11), they may be considered a Designatable Unit. The flathead population may comprise another designatable unit, but its status is not assessed in this report.

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