Pighead prickleback COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

In Canada, pighead pricklebacks appear to be more abundant during the months of August and September, after floodwaters subside and the mixing of saline and river waters produces elevated levels of salinity (Bond and Erickson 1989a, 1991, 1992, 1993; Hopky and Ratynski 1983; and Ratynski 1983). Numerous surveys have been undertaken in the Beaufort Sea area (e.g., Galbraith 1975; Galbraith and Hunter 1976); however, very few pighead prickleback were caught. Sampling by the private sector has not yielded specimens (Millman 2003, pers. comm.; Chiperzack 2003, pers.comm.). The limited sightings and their presence in apparently only a few localities make it difficult to obtain data on population structure. This, along with ill-defined population boundaries, produces considerable margins of error when estimating population sizes. The population in Tuktoyaktuk Harbour is the best known due to their confinement in an enclosed harbour basin (Hopky and Ratynski 1983).

Among the 15 fish species captured in Tuktoyaktuk Harbour from otter trawls, pighead pricklebacks ranked 5th in abundance with 177 being captured (Hopky and Ratynski 1983); however, these captures are only from two trawled stations and not necessarily representative of the entire harbour. In Wood Bay, pighead pricklebacks were caught in fewer numbers through use of stationary gillnets and trapnets at four stations (Bond and Erickson 1989, 1990, 1991). In Wood Bay, they were found to be 12thin abundance of 23 fish species captured. Finally, in Phillips Bay, Yukon Territory, only 2 specimens have been captured and no ranking is possible (Bond and Erickson 1989).

In Tuktoyaktuk Harbour, a rough estimate of population density (below the 7 m depth contour) is about 29 individuals per km² (Hopky and Ratynski 1983). The population size of trawlable pighead pricklebacks within this area is 2,160 with approximately 1,600 of these being mature fish. Because the smallest fish within the population undoubtedly slip through the mesh netting, actual total population size may be higher than the 2,160 estimate. If similar densities were found throughout the harbour, pighead numbers could reach some 16,000. Factors impairing accurate estimates include variation in bottom topography, salinity, and temperature preferences causing clumped aggregations within and outside the areas sampled. Population densities of 500 to 720 per km² are reported in Asiatic waters (Schetninnikov 1983; Houston 1988).

The distribution of pighead pricklebacks is clumped, with aggregations shifting location in response to seasonal and day-to-day environmental changes.  For example, changes in salinity and temperature during early summer may cause populations of pigheads near the Mackenzie estuary to aggregate in deeper areas and therefore avoid fresh surface waters above the halocline. Populations in Wood Bay (Anderson River estuary) have very free access to deep water at all times (Bond and Erickson 1991, 1992; Hopky and Ratynski 1983). Summer capture rates at Wood Bay varied from 4 at one site to 1749 at another in 1990. Daily samples varied between 901, 317, 130 and 3 at one site, whereas the combined total was 401 for the remaining 52 days of sampling (none were caught on 13 days). 

The whereabouts of pighead pricklebacks elsewhere in the world are speculative and numbers too variable to provide accurate population estimates.

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