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Recovery Strategy for the Atlantic Whitefish
1.4 General Biology and Description
1.4.1 Physical Description
The Atlantic whitefish is a member of the salmon and trout family (Salmonidae) (Scott and Scott 1988) and belongs to the whitefish subfamily Coregoninae. It appears salmon-like, with silvery sides, a silvery white underbelly, and a back that is dark bluish-black or dark green (Figure 4). There are no spots or upper body markings. It has a deeply forked caudal (tail) fin and an adipose fin (small, fleshy fin between dorsal and caudal fins, typical of salmonids).
Scott and Scott (1988) describe Atlantic whitefish as having between 91 and 100 scales along the lateral line, a terminal mouth (lower and upper jaws equal) and small but well developed teeth.
Figure 4. Schematic depicting an adult Atlantic whitefish.
While growth of the species in the wild has not been studied, anadromous specimens from the Tusket River are known to have been larger than the landlocked Petite Rivière individuals. Records suggest adults can reach 50 cm (20 in) in length and up to 3.63 kg (8 lb.) in weight (Edge and Gilhen 2001). However, anadromous adults typically average 38 cm (15 in) while the smaller landlocked individuals range 20 to 25 cm (8-10 in) (Bradford 2000).
1.4.2 Common and Scientific Name
The common name Atlantic whitefish was employed by Scott (1967) and Scott and Crossman (1973) in reference to its regular occurrence in salt water off Yarmouth County, Nova Scotia, and its upstream fall migration in the Tusket River (Scott 1987). Originally described as Coregonus canadensis by Scott (1967) the species name canadensis was found to be already in use. Hence the name Coregonus huntsmani was recommended by Scott in 1987 in honour of the late Dr. A.G. Huntsman, noted Canadian marine biologist, who was aware of the presence of an unusual whitefish in Nova Scotia waters at least as early as 1921 (Huntsman 1922). The species was also referred to in the past as Acadian whitefish, Sault whitefish, round whitefish, and common whitefish.
1.4.3 Distinguishing Traits
Atlantic whitefish can be recognized on the basis of their external appearance. The species can be distinguished from most other salmonids by its larger scales. Additional features are used to distinguish Atlantic whitefish from the lake whitefish, C. clupeaformis, which is a common species in Nova Scotian lakes. The number of lateral line scales differs (average of 93.8 in Atlantic whitefish versus an average of 76.6 in lake whitefish), as does the number of vertebrae (average of 65.3 in Atlantic whitefish versus 60.6 in lake whitefish), the mouth shape (near- terminal for Atlantic whitefish, sub-terminal for lake whitefish), and Atlantic whitefish have small teeth while lake whitefish do not (Edge et al. 1991; Hasselman 2003). Genetically, Atlantic whitefish differ from both lake whitefish and cisco (Bernatchez et al. 1991; Murray 2005).
The distinguishing external traits of the Atlantic whitefish are published annually in the Nova Scotia Angler’s Handbook, along with a request for members of the public to contact authorities with suspected sightings of the species. Additionally, habitat stewardship initiatives within the Petite Rivière area have included production and distribution of a handbook and brochure which provides information on the Petite Rivière watershed and the endangered Atlantic whitefish.
1.4.4 Life History
Little is known about the life history of Atlantic whitefish and what is known relates primarily to adults.
The Atlantic whitefish was anadromous (sea-going) in the Tusket River (Figure 2); and, despite the lack of recorded evidence, they likely occurred historically in Petite Rivière as well (Figure 3). Individuals on the Tusket were known to occur in the estuary and sea waters in the summer, migrate into freshwater in the early fall (around September), move upstream in October and November with spawning probably occurring in the late fall or winter, overwinter, and return to the sea in the spring (Edge and Gilhen 2001). Specimens captured in the Tusket River during October and November had well developed gonads but had not yet spawned while specimens collected in May and June had poorly developed gonads (Edge and Gilhen 2001). Neither specific locations nor characteristics of the spawning habitat of the anadromous Atlantic whitefish population that once existed in the Tusket watershed are known (Bradford et al. 2004a).
Atlantic whitefish specimens captured in the marine environment contained shrimp, amphipods, fish and marine worms (Edge 1987).
Spawning of the landlocked population in the Petite Rivière lakes also probably occurs in early winter. Neither specific locations nor characteristics of the spawning habitat of the land-locked Atlantic whitefish are known. Fish occurring in Minamkeak, Milipsigate and Hebb lakes are genetically identical (Murray 2005). No eggs or larvae have been collected from the wild. A single juvenile was sampled from an aggregation of Atlantic whitefish of similar size on one occasion in June 2000 in Hebb Lake (Hasselman 2003). The paucity of information on these life stages precludes any understanding of age structure and mortality rates.
Adults feed on a wide variety of aquatic organisms. Stomach analyses of specimens from the landlocked Petite Rivière population indicated a diet that includes aquatic insects and small fish but not benthic organisms (Edge and Gilhen 2001).
As mentioned previously, it is possible that Atlantic whitefish are swept over the Hebbville dam since there is nothing to prevent their downstream passage. However, these fish that do pass over this dam, are not able to re-join the lake resident population since there is no upstream fish passage provided. Furthermore, while there have been records of Atlantic whitefish below the Hebbville dam, there is no evidence to indicate that these fish represent a viable population (Bradford et al. 2004a).
1.4.5 Habitat Requirements
Little is known of the habitat requirements of Atlantic whitefish. Spawning, nursery, and rearing ground locations and preferences are not known, and migration areas are not understood. In the Tusket population, adults were frequently caught in the estuary. Lake resident Atlantic whitefish appear to be more prevalent in warmer surface waters than are lake whitefish. Recent field and laboratory research indicates that the species can tolerate full sea water from an early stage of development (DFO unpublished data).
1.5 Population Size and Trends
While there is insufficient information available at this time to enable accurate quantitative estimates of the Atlantic whitefish populations’ sizes and trends in the Tusket and Petite watersheds, the following general qualitative comments can be made.
Once abundant, the Tusket River population apparently declined rapidly in the 1940s and 1950s, likely a result of the combined effects of construction and operation of the Tusket hydro-electric facility, poaching, and river acidification (Gilhen 1977; Bradford et al. 2004a). The decline continued; by the 1970s it was a novelty for one specimen to be taken in a season by a gaspereau fisherman. The last confirmed specimen captured on the Tusket River was in 1964 (Edge et al. 1991; Bradford et al. 2004a). No individuals have been observed or captured in any of the years of fishway monitoring since 1995 (Bradford et al. 2004a). It is believed that this population no longer exists (Edge and Gilhen 2001; Bradford et al. 2004a).
On the adjacent Annis River, catch also decreased over time, to the point that by the late 1970s a combined catch of fewer than ten individuals per year in the gaspereau fishery was typical (Edge and Gilhen 2001). There are no reports of Atlantic whitefish being captured in the Annis River since 1982 (Edge and Gilhen 2001; Bradford et al. 2004a).
1.5.2 Petite Rivière Population
There are anecdotal reports of Atlantic whitefish in the Petite Rivière watershed as early as the 1870s (Edge and Gilhen 2001). The recent trend for the Petite Rivière lake resident population is uncertain as there is no population estimate for the lakes. There have been records of Atlantic whitefish occurring below the Hebbville dam since its construction; however, a research trapnet set in the estuary during autumn 1999 and spring 2000 failed to capture a single Atlantic whitefish (Bradford et al. 2004a). Therefore, the presence of a viable anadromous population of Atlantic whitefish below the Hebbville dam is unlikely, or it exists below the level of detection currently possible.
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