Fourhorn sculpin COSEWIC assessment and status report: chapter 8

Limiting Factors and Threats

Little is known concerning the limiting factors and threats affecting the freshwater fourhorn sculpin; however, a considerable amount of work has been conducted with the marine form in the brackish Gulf of Bothnia (Bengtsson and Bengtsson 1983; Hansson et al. 1984; Bengtsson et al. 1985; Bengtsson 1991,1993). A large proportion of fourhorn sculpins suffer from vertebral and spinal abnormalities due to metal-ore smeltery and pulp mill effluents highly concentrated with heavy metals and chlorinated hydrocarbons. Other abnormalities can include delayed first maturity, deformed gill rakers, blackening of the tail, and impaired hematology and ion balance. This susceptibility to pollution presented the marine fourhorn sculpin as a candidate indicator species for monitoring effects of various types of pollution on natural fish populations in Sweden (Gyllensten and Ryman 1985) and the Arctic (Khlebovich 1997). 

Pollution problems are as yet minimal in the Canadian range of the species, but may become more prevalent if and when development, particularly petrochemical exploration and exploitation, intensifies in the Arctic. Moulton and George (2000) described the adverse effects Arctic oil-fields can place on freshwater fish populations. Oil-field activities can alter, delay, or block migrations and can affect the quantity and quality of overwintering habitats. Migration blockage has occurred in scour pools on the downstream side of culverts within the active floodplain of the Sagavanirktok River, Prudhoe Bay, Alaska. Fish moving through the culverts during breakup flows became trapped in pools when water levels dropped. According to Moulton and George (2000), these fish are usually lost to the population because of stress related to high summer temperatures or freezing of the pools during the following winter. Many of the migration and habitat needs of the freshwater fish, and activities that would affect these needs, were recognized early in oil-field development, and facilities in or around the oil-fields were normally designed or modified to avoid or minimize effects to freshwater fish populations. The authors sampled 279 Arctic coastal plain lakes in an oil-field region of Alaska. Seventeen species of freshwater fish were collected with ninespine stickleback (Pungitius pungitius), Arctic grayling (Thymallus arcticus), least cisco (Coregonus sardinella), broad whitefish (C. nasus), and round whitefish (Prosopium cylindraceum) being dominant with respect to abundance and distribution. Only 11 fourhorn sculpins, representing 3.9% of the total catch, were collected with the majority caught in tapped lakes (i.e. lakes that have an active connection to a river channel during the summer). The authors concluded that oil development posed little risk to freshwater species because (1) freshwater habitat capable of supporting fish year-round was in limited supply in the oil-fields compared to nearby regions and (2) the design and placement of facilities, such as bridges and culverts or water withdrawal facilities, have incorporated features to minimize impacts to the fish populations that are present.

The conclusion that oil-field development does not adversely affect fish populations does not apply to all industrial development. An exception to these conclusions may be Garrow Lake. Teck Cominco Limited, in an attempt to reduce the ecological footprint left by the recently decommissioned Polaris lead-zinc mine, has incorporated the use of divers to remove tailing disposal pipes in the lake as well as nearshore structures, such as docking wharves. A diving company has conducted work for the Polaris mine since its incorporation in 1981 and its divers have recently observed fourhorn sculpins to be of high abundance in relatively shallow water (6-9 m). However, it is difficult to assess how the present abundance compares to historic levels because the divers tended to work in deeper waters, beyond the observed range of the resident sculpin population (Gzowski, pers. comm., 2003). There was never any attempt to estimate the size of the Garrow Lake fourhorn population. When the mine was proposing to use the lake as a tailings facility, there was no significant concern raised about the health of the sculpin population. When Teck Cominco Limited was given approval to use Garrow Lake their licence indicated that the company did not need to protect the sculpins in any way (Donald, pers. comm. 2003). Considering these factors it is surprising that the Garrow Lake fourhorn sculpin appears to be in good health and has not been extirpated. 

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