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COSEWIC Assessment and Update Status Report on the Nooksack dace in Canada


Life Cycle and Reproduction

Nooksack dace spawn nocturnally over coarse substrate in riffles (McPhail, 1997) between April and early July (Pearson, 2004). Both male and female Alouette River R. cataractae establish and defend small breeding territories (approx. 10 cm in diameter), which are clustered at the upstream end of riffles. Females leave their territories at night to court and spawn with territorial males, which rarely leave, even to feed until at least 24 h after spawning (Bartnik, 1972; 1973). Fecundity ranges from about 200 to over 2000 eggs depending upon body size and adults are believed to spawn annually (McPhail, 1997); however, given the long spawning period, females may spawn multiple clutches (Roberts and Grossman, 2001).

R. cataractae eggs hatch in 7-10 days at 15.6º C in Manitoba, but remain in the gravel for an additional week until the yolk sac is absorbed (Scott and Crossman, 1973). Young-of-the-year Nooksack dace emerge from substrate in mid-summer feeding on zooplankton and chironomid larvae in shallow, marginal pools with sand or mud substrates. After approximately 4 months (at about 45 mm body length) they become negatively buoyant and move into riffle habitat. Lifespan is four to six years and sexual maturity is attained at the end of the second summer of life, suggesting that generation time is three years (McPhail, 1997).

Hybridization of R. cataractae with several co-occurring cyprinids, including the redside shiner, Richardonius balteatus, a species that occurs with Nooksack dace in the Brunette River, are documented (Scott and Crossman, 1973).


Adults are likely taken occasionally by coastal cutthroat trout (Oncorhynchus clarkii clarkii), rainbow trout (O. mykiss), and prickly sculpin (Cottus asper), which co-occur with all known Nooksack dace populations (Pearson, 2000). Juveniles are likely taken by these species in addition to juvenile coho salmon (O. kisutch). All of the Canadian watersheds occupied by Nooksack dace are also colonized by one or more introduced predators, including bullfrog (Rana catesbeiana), brown bullhead (Ameiurus nebulosus), pumpkinseed (Lepomis gibbosus), and largemouth bass (Micropterus salmoides). Population level impacts of these predators are unknown. None of them are commonly found in the riffle-rich reaches preferred by Nooksack dace.  The nocturnal foraging habit of Nooksack dace (McPhail, 1997) may reduce their susceptibility to diurnal predators (Culp, 1989).


Little information exists on tolerances or preferences of Nooksack dace for water quality parameters such as dissolved oxygen, pH, and temperature. Activity appears minimal at temperatures below 11o C, and fish forage normally at temperatures in excess of 20o C (Pearson, 2004). Nooksack dace were found in streams with temperatures significantly above the average during an Olympic Peninsula survey (17.6o C, range 14.0 – 22.0; Mongillo and Hallock 1997). Nooksack dace are likely poorly adapted to hypoxia, as riffle habitats are typically well oxygenated.


Nooksack dace typically have small home range sizes and show no evidence of long-range dispersal as adults. Pearson (2004) showed that the distribution of Nooksack dace movements within two 200 m long study areas was extremely leptokurtotic (biased towards short distances) relative to the distribution of detectable movements.  Over 50% of recaptured, marked adult dace were caught within 5 m and 92% were found within 50 m of their initial capture positions in the 14-month study. Fully 30% were recaptured in exactly the same location, some after more than a year had lapsed since the previous capture. Fish were as likely to move upstream as downstream, and maximum displacement was 205 m.  None of the recaptured fish moved the 2.2 km between study reaches. Nooksack dace colonists (n=9) did not penetrate more than 560 m into a newly constructed 960 m tributary diversion within 15 months (Pearson, unpub. data), suggesting that maximum annual range is less than 1 km. The data suggest that a large fraction of the population is sedentary. Hill and Grossman (1987) also report small home range size for R. cataractae (mean 13.7 m). The relatively long movements (hundreds of metres) of a few individuals, however, suggests that a fraction of the population may travel considerable distances from the home patch, a pattern demonstrated in a number of other stream fishes (Nakamura et al. 2002; Gowan et al. 1994; Smithson and Johnston 1999). Juveniles may passively disperse downstream, but this has not been studied.

The clumped distribution within watersheds combined with limited adult dispersal raises the possibility that Nooksack dace exist as metapopulations within watersheds. Insufficient data, particularly on juvenile dispersal rates, exists for assessment, however.

Migration links between Canadian populations are highly unlikely as migrants would need to either traverse a minimum of 10 kilometres of largely unsuitable habitat in Washington State or, in the case of the Brunette River, cross the divide between the Fraser and Nooksack watersheds.

Interspecific Interactions

Adult Nooksack dace feed primarily on riffle dwelling insects, while young-of-the-year dace subsist primarily on ostcracods and chironomid pupae (McPhail, 1997). Competitors are probably limited to juvenile coastal cutthroat trout and rainbow trout, the only other fishes that commonly forage in riffles inhabited by Nooksack dace (Pearson, 2004). Little data exist regarding parasitism, but most individuals have light infestations of blackspot (Neascus sp.), a subcutaneous trematode cyst, which appears to have little effect at low infestation rates (Vinikour, 1977).


In aggregate, Nooksack dace life history characteristics (small body size, short generation time, potential for multiple clutches annually) should permit rapid population growth, promoting early recovery from small-scale disturbances, rapid colonization of restored or created habitats within a few hundred metres of existing populations and successful (re)introductions into suitable habitat. Their life history strategy, however, will provide little resilience in the face of large scale or chronic disturbances (Winemiller and Rose, 1992; Detenbeck et al., 1992).