Different PlacesDifferent Places Different Different DietsDiets

Feeding habits and diet of the Feeding habits and diet of the

Water-rat ‘Rakali’ Water-rat ‘Rakali’ Hydromys Hydromys chrysogasterchrysogaster

in the waters of City of Port Phillipin the waters of City of Port Phillip

Andrew McCutcheon - Earthcare St Kilda Inc

Feeding habits and diet of Feeding habits and diet of rakalirakali

They are amphibious hunters of mostly aquatic and They are amphibious hunters of mostly aquatic and marine organisms. They also hunt on land.marine organisms. They also hunt on land.

Diet consists of larger aquatic insects, crustaceans, Diet consists of larger aquatic insects, crustaceans, molluscs, fish, frogs, birds and even aquatic plants.molluscs, fish, frogs, birds and even aquatic plants.

They are opportunistic and will quickly adapt to other They are opportunistic and will quickly adapt to other types of food if there is a shortage of the normal or types of food if there is a shortage of the normal or preferred food source. preferred food source.

They hunt or forage for food by running on waters edge, They hunt or forage for food by running on waters edge, wading in shallow water or swimming and diving in water wading in shallow water or swimming and diving in water to a depth of 2 metres.to a depth of 2 metres.

Prey is generally taken to a feeding platform such as a Prey is generally taken to a feeding platform such as a rock or log in or beside the water. They will frequently rock or log in or beside the water. They will frequently use moored boats for this purpose.use moored boats for this purpose.

How can we find out what rakali How can we find out what rakali eat?eat?

Direct ObservationDirect Observation

Analyse food left on feeding platforms - Analyse food left on feeding platforms - ‘middens’‘middens’

Middens provide a good indication of prey Middens provide a good indication of prey species that exist in a particular habitat area.species that exist in a particular habitat area.

Rakali eating Red Swimmer Crab - 25 0ctober 04

Rakali resting - Note abundant whiskers

Partially webbed hind-foot

Swimming Rakali

Four Habitat Areas in City of Port Four Habitat Areas in City of Port PhillipPhillip

St Kilda HarbourSt Kilda Harbour

Elwood Canal & Point Ormond Elwood Canal & Point Ormond shore shore

Albert Park Lake Albert Park Lake

East shore of Webb Dock & East shore of Webb Dock & Port Melbourne Foreshore Port Melbourne Foreshore

St Kilda HarbourSt Kilda Harbour Sheltered and exposed marine habitatSheltered and exposed marine habitat

Habitat subject to heavy storms battering Habitat subject to heavy storms battering breakwaterbreakwater

Populations can be reduced or vanish after Populations can be reduced or vanish after storms and/or heavy rain producing flows of storms and/or heavy rain producing flows of turbid/ polluted water from the Yarra River and turbid/ polluted water from the Yarra River and drainsdrains

Prey species consist of crabs, European Prey species consist of crabs, European Fanworms, fish and possibly baby penguins. Fanworms, fish and possibly baby penguins. Red Swimmer Crabs are the preferred diet.Red Swimmer Crabs are the preferred diet.

Main threats are heavy storms, floods and water Main threats are heavy storms, floods and water pollution impacting on prey.pollution impacting on prey.

Inside of breakwater - St Kilda Harbour

Pier and breakwater - St Kilda Harbour

Rakali eating Red Swimmer Crab - 25 0ctober 04

Floodwater from Yarra after storm - 2 February 05

Turbid water 3 days later - 5 February 05

Rakali midden with small Common Shore Crab - 23 march 05

Rakali midden with small clam and European Fan Worms - 23 March 05

Rakali midden with European Fan Worms - 23 March 05

Rakali feeding on European Fan Worm - 23 March 05

Rakali midden with European Fan Worms - 1 May 05

Midden with Common Shore Crab & Fanworm- 2 October 05

Midden with Common Shore Crabs - 16 October 05

Rakali feeding on Sea lettuce - 16 October 05

Elwood Canal & Point Ormond Elwood Canal & Point Ormond shoreshore

Freshwater surface drain, tidal canal and exposed Freshwater surface drain, tidal canal and exposed marine habitatmarine habitat

Habitat subject to complete inundation and rapid Habitat subject to complete inundation and rapid change of water quality (salinity, turbidity) after change of water quality (salinity, turbidity) after heavy rainheavy rain

Populations can be reduced or vanish after storms Populations can be reduced or vanish after storms and/or heavy rainand/or heavy rain

Prey species not fully known as there are no Prey species not fully known as there are no middens. Fish and aquatic insects are the most middens. Fish and aquatic insects are the most likely diet.likely diet.

Main threats are heavy floods and water pollutionMain threats are heavy floods and water pollution

Elster Creek

Elwood Canal -High tide

Elwood Canal -Low tide

Elwood Canal -Very low tide

Foreshore north of Pt Ormond

Silverfish (Hardyhead)

Baby Black Bream

Sea lettuce

Albert Park LakeAlbert Park Lake Freshwater Lake with islandFreshwater Lake with island

Gunn Island appears to be the land based Gunn Island appears to be the land based refuge for rakali.refuge for rakali.

Habitat subject to little change as water level Habitat subject to little change as water level is regulated, and stormwater pollution is regulated, and stormwater pollution minimised by pollution control ponds. minimised by pollution control ponds.

Prey species not fully known as there are no Prey species not fully known as there are no middens. Yabbies and aquatic insects are the middens. Yabbies and aquatic insects are the most likely diet.most likely diet.

Main threats appear to be water pollution Main threats appear to be water pollution impacting on preyimpacting on prey

The Point - Albert Park Lake

Pollution control pond - Albert Park Lake

Yabby

East shore of Webb Dock & East shore of Webb Dock & Sandridge Beach (Port Sandridge Beach (Port Melbourne)Melbourne)

Exposed marine habitatExposed marine habitat

Habitat subject to heavy storms battering Habitat subject to heavy storms battering rock armor and groynesrock armor and groynes

Rakali show great variation in diet. Prey Rakali show great variation in diet. Prey species consist of crabs, mussels, European species consist of crabs, mussels, European Fanworms, and possibly fish. No single Fanworms, and possibly fish. No single species appears to form a preferred diet.species appears to form a preferred diet.

Main threats appear to be heavy storms.Main threats appear to be heavy storms.

Webb Dock East Park

Sandridge Beach Groyne

Midden with Mussels - 1 October 05

Midden with small Spider Crab - 1 October 05

Midden with small Red Swimmer Crab - 1 October 05

Why is it important to find out Why is it important to find out what rakali eat?what rakali eat?

To obtain a better understanding as to how To obtain a better understanding as to how they survive in our urban environment, in they survive in our urban environment, in what are primarily man made habitats.what are primarily man made habitats.

To determine the diversity of aquatic or To determine the diversity of aquatic or marine species that live in our marine or marine species that live in our marine or aquatic habitats.aquatic habitats.

Rakali are good indicators of whether our Rakali are good indicators of whether our marine and aquatic ecosystems are in a marine and aquatic ecosystems are in a healthy environmental condition.healthy environmental condition.