Old Crow Basin Ecoregion

The Old Crow Basin Ecoregion, the rim and sides of the bowl, contains the pediments, slopes, foothills, and mountains surrounding the Old Crow Flats, including the Old Crow Range. The major water courses in this ecoregion are the headwaters of the Old Crow River (including Ammerman and Bilwaddy Creeks) and Thomas Creek in the northwest; most of the headwaters of Timber, Black Fox, and Johnson Creeks in the north and east; and the headwaters of Schaeffer, Potato and Surprize Creeks in the southwest. Most of the Driftwood River, to the east of the Old Crow Special Management Area (SMA), is also within this ecoregion. Only a few small lakes in the eastern part of the Park and SMA, including Sam Lake and Little Sam Lake, and a few lakes near Thomas Creek are within the Old Crow Basin Ecoregion (see Plate 1).

A system of categorizing streams in the Porcupine River system was devised by Brunskill et al. (1973) in their studies of streams along the proposed arctic gas pipeline route. Within the same watershed, streams may have different physical and chemical characteristics, different velocities and substrates, and correspondingly different biological communities. Of the three categories of streams (alpine creeks, foothill streams, and floodplain rivers), two are represented in this ecoregion.

i) Alpine Creeks.

These creeks are found partly above the treeline, with at least half of the stream consisting of riffle areas. (Riffles are areas of shallow water flowing over a rough bottom, causing turbulence). Both riffles and pools have a rocky bottom. These creeks are usually clear (except after heavy rainfall) and contain large numbers of invertebrate animals. From sampling conducted on the upper reaches of the Old Crow River (precise localities are not given), the most abundant life forms in these creek bottoms are the insects (in larval form): midges or chironomids, stoneflies, caddisflies, and mayflies. Smaller numbers of other insects such as blackflies, and craneflies are expected to be present in some creeks. Based on the Old Crow River sampling results, the only invertebrates other than insects to be expected in most alpine creeks are water mites (Hydracarina). Snails (gastropod molluscs) were found in only two of the sampling sites in alpine creek portion of the Old Crow River (Brunskill et al. 1973). The diversity and abundance of invertebrates indicates that there is water of sufficient quality and quantity to support life throughout the year, and for most or all years.

Areas of open water at the headwaters of the Old Crow River identified in April 1973 were located between Ammerman Mountain and Yankee Ridge (68^o 20' N, 141^o 12'W), about 10 km west of the Yukon-Alaska boundary (Steigenberger et al. 1974). These open water areas often have dissolved oxygen levels high enough to allow overwintering of some fish species. The Old Crow River headwaters, including Bilwaddy Creek (68^o 11' N, 141^o 02'W) and Timber Creek (68^o 34' N, 140^o 04'W) support large numbers of arctic grayling, sculpins, and other species during the winter (Steigenberger et al. 1974). Sampling in October 1973 indicated a population estimate of as high as 20,000 grayling localized for overwintering (Steigenberger et al. 1974). Only arctic grayling and slimy sculpin were caught at these locations. Arctic grayling may move upstream in the fall to open water areas (Steigenberger et al. 1974). A documented over-wintering area for arctic grayling in the headwaters of the Old Crow River was fished in 1973 (Steigenberger et al. 1974). Fish captured in Thomas and Timber Creeks in 1971 included only grayling and slimy sculpin (Bryan et al. 1973).

In Ivvavik National Park, open water and stream channels near river icings (aufeis) support spawning, rearing, and overwintering populations of arctic char and year-round populations of arctic grayling (Steigenberger et al. 1974). The higher temperatures of the groundwater sources probably keep these areas ice-free for some distance below the upwelling. The populations of grayling overwintering in Timber Creek appear to be associated with the river icings (aufeis) in that area, but this needs field confirmation.

ii) Foothill Streams.

These streams are deeper with a generally slow current and low gradient. Over half the stream bed consists of pools (regardless of water level) and sand is deposited in the pools. In each habitat there were areas where coarse sand and gravel was deposited and bottom sediments were relatively unstable. The banks of these streams are steeper, with overhanging vegetation. These streams characteristically have the lowest numbers of stream-bottom animals (Brunskill et al. 1973).

As the Old Crow River moves towards the Flats, and becomes a foothills stream, the composition of the river's aquatic invertebrate life changes. Midges are the most dominant of the insects, followed by caddisflies (but only in one sampled area), mayflies and stoneflies. Water mites (Hydracarina) were found in three of the seven sampling sites (Brunskill et al. 1973). It is likely that the stoneflies and mayflies were associated with ground water discharge areas or areas with well-developed hyporheic (saturated area beside and under stream surface) zones. Midges are generally considered to be insensitive to the presence or absence of winter flows. (REF). Mayflies collected in the Old Crow River are Rhithrogena futilis, and Siphlonurus sp.and in Black Fox Creek, Rhithrogena futilis (Harper and Harper 1997).

In the upper reaches of the Old Crow River between Surprise Creek and the border (near Thomas Creek) Geist saw many fish in the clear water; grayling, suckers, whitefish, and northern pike, especially where there were deep holes (Geist 1955). Arctic grayling move both upstream and downstream to overwintering sites in the Old Crow River (Bryan et al. 1973). The dividing point for upstream versus downstream migration of overwintering grayling was described as being between the mouths of Thomas and Surprise Creeks. Only the arctic grayling was captured at a sampling site on Surprise Creek in 1971 (Bryan et al. 1973).

iii) Lakes and Ponds

The few lakes in this ecoregion are found in the far western part of the Park in the lower reaches of Thomas Creek and in the far east at Sam Lake. No published information on the aquatic species of these few lakes has been located.