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Stokes National Park

Stokes Inlet, in the 10,667-hectare Stokes National Park, is one of the most picturesque and interesting estuaries along Western Australia's southern coast. East of Albany, where rainfall and river flow are small, Stokes is the largest estuary and one of few that always hold water while their bars stay closed, often for years at a time.

The inlet lies in a relatively deep valley with high dunes on either side. Dense bush and shady paperbark trees grow right to the beaches along the water's edge. With an area of 14 square kilometres, Stokes Inlet is the largest of a number of estuaries around Esperance and the only one with reasonably deep water.

The Young and the Lort Rivers flow into the upper reaches of the inlet but, when the water level is low in summer, they are cut off from the lagoon by a wide river delta. The mouth of the estuary lies in the middle of Dunster Castle Bay. It is closed by a high sand bar which cuts the estuary off from the sea and only breaks every few years, and then only for a few weeks. As a result, salinity and water level in the estuary vary greatly with river flow and evaporation.

Pre-History

Only 20,000 years ago, during the last ice age, the sea level was more than 100 metres lower than it is now. Dry land extended for some kilometres beyond the present coastline, across which rivers flowed to the sea. Submarine canyons along the edge of the continental shelf show where these former rivers once flowed. However, as the ice caps melted, the sea rose to its present level by about 6,000 years ago, flooding the estuary and forming Stokes Inlet. The estuary is set in a valley (it appears to be located along a fault).

The riverine part is in a narrow valley through ancient granitic rocks (migmatite), while the seaward part lies between high limestone dunes formed in Pleistocene times (in the last two million years). At first, the nearby swamps and Lake Cobinup would have been part of the estuary and it would have been a highly productive marine embayment similar to Princess Royal Harbour near Albany.

The coastal dunes on either side of the inlet were formed during previous interglacial periods, when the sea level was about the same as at present. Beneath the surface, they have hardened to form limestone rock, which is exposed in cliffs and shore platforms. Waves brought sand from the sea bed to form beaches and finer sand was blown up into dunes, covering dunes from previous times, and then stabilised by vegetation. As waves moved sand onshore, offshore and alongside the shore, the channel of the estuary was gradually narrowed from the east by a tongue of dune that has probably only recently been stabilised by vegetation, and from the west by a dune that is still mobile. The mouth of the estuary is now only 200 metres wide.

For a time, the channel remained open to the sea, but the mouth gradually closed as waves built a sand bar that reduced the exchange of water between the estuary and the sea. Eventually, neither the seasonal river floods or the small tides of the South Coast could prevent the bar from closing. The extensive deposits of sub-fossil marine shells in Stokes Inlet indicate that the bar probably closed the estuary off from the sea about 4,000 years ago. The two lines of nearshore reefs parallel to the ocean beach suggest that the beach and bar were once located farther out to sea.

Thus the estuarine environment of Stokes Inlet is far from static. During the last 6,000 years much river sediment has collected in the estuary and has formed the wide river deltas, the swamps and Lake Cobinup, and has shallowed the upper part of the estuary. On the eastern shore a long narrow sand spit, crowned by a well-vegetated dune, now separates the estuary from a large shallow pan that is sometimes flooded. The lower part of the estuary is still relatively deep (10 metres), except where waves have washed beach sand in over the bar. Sand from the western dune is blown by the prevailing south-westerly wind, to drop on the steep sheltered face and cascade into the deepest part of the inlet.

Modern History

Stokes Inlet and the Lort River were named by Surveyor-General John Septimus Roe in 1848, after his friend John Lort Stokes.

In 1863, Charles and William Dempster took up a 41,000 acre pastoral lease west of Esperance which included land on either side of Stokes Inlet. Then, in 1873, Alexander and John Moir were granted a lease of 14,000 acres around Stokes Inlet, extended by 57,000 acres in 1888. The Moirs established a homestead near the eastern shore of the Inlet and grazed sheep through the coastal vegetation, which they burned in patterns to provide fresh feed. They shipped their wool from nearby Fanny Cove, together with sandalwood from the surrounding country.

In the 1890s the Cove was used by miners going to the Dundas and Norseman goldfields. A small area was cleared near the homestead and first barley and then other grain crops were grown as feed for the stock. The limestone walls of the Moir homestead still stand, though roofless, within the national park.

Despite these activities, the area around Stokes Inlet was largely spared from agricultural development until recent times. There was little further development around or inland from Stokes Inlet until pastoralist Noel White established the Young River Station at the head of the inlet in 1950. The upper part of the Stokes catchment was only released for agricultural development in the 1970s and 1980s. Subsequent clearing in the catchment has greatly accelerated the deposition of sediment in the estuary, and half a metre of soft sediment has collected in the lagoon in the last 30 years.

Today, the seaward part of the estuary remains surrounded by an extensive area of uncleared bushland. People visit Stokes National Park via a six-kilometre-long gravel road which leaves the South Coast Highway two kilometres west of the Young River crossing. It leads to camping areas on the western shore of the inlet. The eastern shore can only be reached by boat or by negotiating a four-wheel-drive sand (and mud) track off Farrells Road, leading to the Old Moir homestead and Fanny Cove.

Estuarine Plants & Animals

The plants and animals that inhabit Stokes Inlet are fairly typical of those found in other estuarine environments, providing a snapshot of the wildlife living in and using estuaries along the southern coast of Western Australia. The fringing vegetation reflects both the character of the shoreline and the hydrology of the estuary, including the variation in water level. Saltwater paperbarks (Melaleuca cuticularis) fringe the shoreline. Some even grow among the rocks. There are also sedges along the water or low sandy beach ridges, alternating with samphire.

The aquatic plants are dominated by three salt-tolerant species. A small green alga (Polyphysa peniculus) grows in shallow water throughout Stokes Inlet, sometimes forming continuous cover both on sand and rock. Seagrass (Ruppia megacarpa) is sometimes abundant, even on the eastern shallows of Stokes Inlet when they are flooded, and it also grows in the riverine reaches of the estuary. At times it is heavily grazed by swans. A species of stonewort (Lamprothamnium papulosum) also grows in the shallows.

Swimming in the water are microscopic plankton, such as the common estuarine copepod (Gladioferens imparipes), which are food for juvenile fish. The bottom-living animal life reflects the changing salinity of the water. A few common estuarine worms, snails, bivalves and shrimps, which tolerate a wide range of salinity, are always present and provide abundant food for fish and waterbirds.

When the bar is open, sea water may bring the larvae of mussels, cockles, prawns and even crabs, which grow rapidly until they die in the retreating shallow water that evaporation has made too saline. Sometimes there are millions of small salt lake snails (Coxiella) that feed on microscopic plants on the salt flats while these are still moist.

Similarly, the composition of the fish fauna depends largely on the time and duration of bar openings and the salinity of the water. At one stage the Stokes Inlet bar had been closed for more than 30 years and black bream was the only commercial fish caught (apart from a few very large, blind, sea mullet). Black bream is an estuarine species that also lives in river pools. A few non-commercial estuarine species such as the common minnow and species of hardyheads and gobies also survive under these conditions.

When the bar breaks, however, fertilised eggs, larvae and juveniles of a variety of marine species such as sea mullet enter and survive for as long as conditions favour their growth and survival. Large numbers of Australian salmon, whiting and bream entered Stokes Inlet when the bar opened in 1968. Adults of marine species must return to the sea to spawn at the next bar opening and then continue their growth in coastal waters.

Quite a variety of fish species were reported in the estuary before the bar again broke in November 1975, but after the opening only black bream were caught. Mass mortality has been reported in times of severe drought, when the waters dry up and become too saline, such as in 1983.

At least 29 species of waterbirds have been observed at Stokes Inlet, including large numbers of Australian shelduck, grey teal, little black cormorants, black swans and chestnut teal. Migratory species include the common sandpiper and red-capped plover. Australasian grebes, Australian pelicans, little pied cormorants, white-faced herons, great egrets and pied oystercatchers also visit the inlet.

Stokes Inlet, far from being constant, is a place of change. Influenced by the fascinating events that led to its present condition, the water level and salinity is constantly changing. This change affects the plants and animals that live on and within the inlet. Watching the waterbirds of Stokes Inlet is like watching a wildlife documentary constantly unfolding - as the seasons change new birds arrive or leave, and different birds become active at different times of the day. So too the less visible animals - those living below the surface of the water - change according to the movements of the sand bar and other factors.

THINGS YOU NEED TO KNOW

Where is it?
80 km west of Esperance.

Travelling time:
About one hour from Esperance.

What to do:
Birdwatching, camping, fishing, canoeing, walking. Stokes Inlet itself is the most visited site, but Fanny Cove and Shoal Cape offer attractive coastal scenery accessible only by four-wheel-drive. The ruins of the Moir homestead can be seen en route to Fanny Cove.

Facilities:
Barbecues, Picnic Areas, Camping Areas, Toilets

Information:
Brochure Available, Interpretive information, Rangers present (all year)

Best season:
Spring to Autumn