Four habitat types are described for the island1: Altered Riparian Forest, Open Areas and Silt Mounds, Phragmites Reed Beds and Riverine Habitat. A map of habitat types is presented in Figure 1 (inside back cover).
Altered Riparian Forest
Vegetation and Structure: Forest to woodland structure with an overstorey of mixed exotic, introduced native and indigenous native species. Numerous indigenous River Red Gums Eucalyptus camaldulensis occur around the perimeter of the island with a small number of Red Gums inside the levee bank at the western corner. Most of the overstorey consists of planted non-indigenous native species including Southern Mahogany E. botryoides. A middlestorey of mixed indigenous and non-indigenous native species including some indigenous wattles. Woody weed species are widespread. The ground flora is dominated by introduced grasses which form a dense rank thatch in some areas. The groundlayer contains a mixture of log and leaf litter.
Characteristic Fauna Species: Typical fauna species in this habitat include: introduced mammals including Black Rat and foxes, skinks such as Southern Water Skink and Weasel Skink, honeyeaters and other small forest birds, and arboreal mammals Brushtail and Ringtail Possums. Black Rats are abundant throughout the outer perimeter of the island.
Open Areas and Silt Mounds
Vegetation and Structure: Herbaceous ground flora dominated by Couch and Kikuyu. Some areas have poor vegetation growth and correspond to either currently or previously saline soils (DCE 1991, Costello 1994). Some dense patches of Spiny Rush. Plantations of mixed introduced native and indigenous native species occur throughtout the open areas.
Characteristic Fauna Species: Introduced bird species such m Starlings and Mynas (forage at groundlayer and roost in plantations), introduced mammals such as foxes and Black Rats, native skink Eastern Three-Lined Skink, open-country native birds such as Willie Wagtail and Australian Magpie Lark.
Phragmites Reed Beds
Vegetation and Structure: Common Reed Phragmites australis grows in patches along the river bank at the water's edge. Reeds generally grow in shallow water but are emerged on exposed silt beds at low tide. Densities vary from mid dense to sparse stands. Refuse and other detritus collects at the base of these reed beds and is an attractant to rats.
Characteristic Fauna Species: Clamorous Reed Warbler occurs in foliage of denser stands. Waterbirds shelter and forage within the reeds including Pacific Black Duck, Dusky Moorhen and Maned Duck. Waders forage within the reed beds at low tide. Brown Rat and Black Rat are abundant at the river's edge and forage in the reed beds.
Condition: Poor: The lower reaches of the Yarra River are generally identified as poor quality habitat for aquatic life (Department of Water Resources 1989) due to elevated levels of nutrient, E coli and toxicant, high turbidity and reduced dissolved oxygen levels.
Structure: Riverine habitat refers to the aquatic and river-bed habitat of the Yarra River. The bulk of water flow occurs along the main channel along the northwestern bank Of Herring Island. The bank is fortified by blue-stone boulders along much of this channel. The eastern and southwestern banks of the island are, more natural in structure. Bare areas of silted rock and silt are exposed at low tide. Some sections of the river, notably opposite the stormwater outfall at Como Park, are very shallow and larger areas of mudflat are exposed at low tide.
Characteristic Fauna Species: Common wader species such as the White-faced Heron, cormorants, ducks and moorhens. Introduced fish species.
No amphibians were recorded in the present study. Some ephemeral surface water collects on the island in wet seasons (K.Grover pers. comm.). These areas are Generally located on saline soils (Costello 1994) and are therefore not suitable for amphibian inhabitation. The riverine habitat around the island is suitable for a restricted -group of amphibians notably the locally common Southern Brown Tree Frog, Litoria ewingii. On the whole the island offers low habitat value for amphibians.
Wildlife Corridor Values
Herring Island forms part of a corridor of remnant vegetation along the Yarra River valley.
Remnant Red Gums around the island perimeter make the greatest contribution to the corridor values of the island providing a roosting and feeding site for birds and bats.