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Recovery Strategy for Cultus Pygmy Sculpin (Proposed)


1. Description of the Species

1.1 General Biology

Sculpins are members of the Cottidae, a family with more than 300 species (Scott and Crossman 1973; ITIS 2006). They are bottom-living, primarily marine fishes of arctic and temperate waters of the Northern Hemisphere (Scott and Crossman 1973). Sculpins are distinguished by a large head and heavy body; the body tapers from head to a relatively narrow caudal peduncle (Scott and Crossman 1973). The genus Cottus is widely distributed in freshwater (Scott and Crossman 1973). Species of freshwater sculpin are generally less than 18 cm in length, lack a swim bladder and are usually benthic (Heard 1965; Scott and Crossman 1973).

The Cultus pygmy sculpin (Figure 1) was first identified in 1934 and most of what we know about it comes from a single paper, published by Ricker in 1960. Ricker (1960) described this taxon as a dwarf form of the coastrange sculpin, Cottus aleuticus, which has pelagic larvae but adopts a benthic habit after about 32 to 35 days (Krejsa 1965 cited in McLarney 1968). The Cultus pygmy sculpin shares many physical features of the coastrange sculpin and of sculpins in general, but there are also important differences in morphology and ecology, most importantly small body size, retention of larval features, and a limnetic existence. The Cultus pygmy sculpin retains larval features (suggesting neotenic evolution), and has a number of adaptive traits characteristic of a limnetic existence, rather than the benthic habits typical of sculpins. These features include reduced bone density, enlarged head pores and an increase in subcutaneous lipids (Ricker 1960; McPhail and Carveth 1992; Cannings and Ptolemy 1998). Observed diets of plankton corroborate the findings of limnetic habits (Ricker 1960). Details of habitat use are not known.

Cultus pygmy sculpin and C. aleuticus differ in size, meristic traits, and overall shape (Taylor 2006). Typical length for the Cultus pygmy sculpin is 2.9 to 4.5 cm with a maximum observed length of 5 cm. This compares to a typical range of 5 to 10 cm for adult coastrange sculpin. Based on size-frequency analysis, Ricker (1960) suggests Cultus pygmy sculpin typically live a maximum of five years.

It is generally assumed that Cultus pygmy sculpin reproduce in a manner similar to C. aleuticus, which lay egg masses under stones that are then guarded by males. Based on frequency of observations of gravid females, Ricker (1960) suggests that most Cultus pygmy sculpin begin to breed in their third year, with spawning beginning in late May or early June, peaking in late June through July, and tapering until early September. Spawning behaviours and habitats are not known, but spawning apparently does not occur in tributary streams or in shallow littoral areas (Ricker 1960). Some tributaries to Cultus Lake dry up in the summer and are therefore not available as spawning and incubation habitat.

The taxonomic status of Cultus pygmy sculpin is currently undetermined, a common problem with post-glacial taxa in British Columbia. The form may be derived and reproductively isolated from C. aleuticus and may be a distinct biological species (D. McPhail, Professor (Emeritus), Dept of Zoology, UBC, Vancouver, pers. comm.). Additional studies are required to determine the taxonomic status of Cultus pygmy sculpin relative to C. aleuticus.

Figure 1. Drawing of coastrange sculpin, Cottus aleuticus, a close relative of Cultus pygmy sculpin.
Illustration by Susan Laurie Bourque, reproduced courtesy of the Canadian Museum of Nature, Ottawa, Canada.

Drawing of coastrange sculpin. Illustration by Susan Laurie Bourque, reproduced courtesy of the Canadian Museum of Nature, Ottawa, Canada.


1.2 Distribution

The Cultus pygmy sculpin is an extreme endemic. It is found only in Cultus Lake, British Columbia (Figure 2). Cultus Lake drains via Sweltzer Creek into Vedder River, a tributary of the Lower Fraser River mainstem approximately 112 km upstream of its confluence with the Strait of Georgia. No other populations have been documented in BC although a similar form has been observed in Lake Washington, WA (Larson and Brown 1975), and is believed to have evolved independently (D. McPhail, pers. comm.). There has been no systematic search for additional populations similar to those in Cultus and Washington lakes. However, fisheries surveys of lakes have occurred frequently in the past and would likely have detected limnetic coastrange sculpins if they were moderately widespread beyond these locations.

Distribution of Cultus pygmy sculpin within Cultus Lake is not known in detail, but the species is described as a limnetic form that lives primarily within the pelagic zone of the lake (Ricker 1960). It has been caught regularly in offshore, midwater trawls during enumeration studies of sockeye juveniles, and it is a common prey item of char in the lake, which inhabit offshore areas of the lake (DFO unpublished data; Ricker 1960). During extensive trapping and shore seining Cultus pygmy sculpin were not observed in shallow littoral areas or in tributary streams (Ricker 1960). Cultus pygmy sculpin have not been observed reproducing. Since coastrange sculpin (the species from which Cultus pygmy sculpin are assumed to have been derived) lays eggs under rocks in streams, it seems likely that Cultus pygmy sculpin also use benthic substrates for egg laying.

Figure 2. Distribution of Cultus pygmy sculpin.
(Map base obtained from Ministry of Energy, Mines and Petroleum). The detail map indicates roads, tributaries and parks.

Distribution of Cultus Pygmy Sculpin in the area of Cultus Lake and Cultus Lake Provincial Park.


1.3 Abundance

There has been little research done on Cultus pygmy sculpin, and at no time has an empirical population estimate been made. Ricker (1960) described the species as abundant in deep waters of Cultus Lake. It was regularly captured during early work and was a frequent prey item in the stomachs of char (Ricker 1960). Sampling for Cultus pygmy sculpin has generally not occurred in shallow or deep littoral areas. Cultus pygmy sculpin have been regularly caught in trawls conducted during the last 30 years to enumerate Cultus Lake sockeye. At no time have the counts of Cultus pygmy sculpin been high (usually < 100 individuals), but counts have fluctuated considerably within and among years (Taylor 2006). Available data indicate a slight downward trend in abundance, but since data come from efforts to enumerate juvenile sockeye the data are considered inappropriate for quantitative trend analysis for Cultus pygmy sculpin. In summary, no firm conclusions can be drawn with the current data.

1.4 Importance to People

The Cultus pygmy sculpin has special scientific and educational value due to its extreme endemism and unique life history. The species has no commercial value, except indirectly as prey for salmonids that contribute to recreational fisheries. Cultus pygmy sculpin is a member of the native fauna, with its own intrinsic value and ecological role.