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Scientific Name:
Maccullochella ikei
Common Name:
Eastern freshwater cod
General Type:
Fish
Status:
Endangered
Other Names:
Eastern cod, Clarence River cod, east coast cod
Family:
Percichthyidae
Status Of Recovery Plan:
Final
Description
The eastern freshwater cod is similar in appearance to the Murray cod (Maccullochella peelii) and the Mary River cod (Maccullochella peelii mariensis). Eastern freshwater cod are a large, elongated, deep-bodied fish with relatively small eyes and a short, rounded, depressed snout with a distinctly concave profile; the lower jaw protrudes. They have a large mouth that extends to below the back of the eye. Eastern freshwater cod have been recorded to 41kg but are mainly less than 5kg and 660mm in length since the 1960s. They are generally a yellow green to golden colour, with a speckled pattern of black to very dark green spots.
Distribution
Eastern freshwater cod were once abundant in both the Clarence and Richmond River systems downstream of tablelands waterfalls, with fish up to 27kg being frequently caught in the Clarence and Orara Rivers. Late in the 1920s and 1930s the easternfreshwater cod apparently declined in the Richmond River and much of the Clarence River system. Wild fish are now currently considered to be extinct in the Richmond River system, and very rare or absent in the major northern tributaries of the Clarence River system. Since the late 1960s small numbers of eastern freshwater cod have only been recorded from tributaries such as the Nymboida, Guy Fawkes, Boyd and Mann Rivers where some pristine habitat still exists. Re-stocking with hatchery-bred cod has been undertaken since 1989. These stockings took place in numerous locations throughout the Clarence and Richmond River systems. Angler reports and recent surveys indicate that stocked fish have survived at many locations.
Habitat and Ecology
- Eastern freshwater cod are often found in clear, flowing streams with rocky beds and deep holes. They are generally found in areas that have plenty of boulders or large woody debris (snags). Riparian vegetation, large boulders and snags provide a complex array of habitats for each stage of the cod life cycle and influence the quality and quantity of food and shelter.
- Eastern freshwater cod are sexually mature at 4 or 5 years old, when 700g to 1.5kg. The breeding season is in spring and spawning commences when water temperatures rise above 16°C. Breeding fish are territorial and aggressive. Cod lay large (3mm) strongly adhesive eggs onto hard surfaces, probably rocks and logs in the wild. The number of eggs produced is relatively low and similar to Murray cod (3.2 – 7.6 eggs/gram of female bodyweight). Hatching begins at 8 days and is complete 12 days after fertilisation at 17°C – 20°C. Larvae start feeding on zooplankton 12 days after hatching.
- Eastern freshwater cod prey upon other fish, frogs, crustaceans and snakes. Zooplankton and aquatic insects are the main food source for eastern cod larvae.
Threats
- Historical decline of eastern freshwater cod is thought to have been caused by a combination of over-fishing, including by the use of explosives, with a series of catastrophic natural events where heavy rains followed severe bushfires, causing a deterioration of water quality and leading to widespread fish kills.
- Releases of contaminated water from tailings dams at gold and tin mines are also thought to have caused the death of cod and other freshwater fish in parts of the Clarence system.
- River regulation and water extraction reduce flows and can affect seasonality of flows, detrimentally impacting on the fish.
- Habitat degradation including reduction of in-stream woody debris, sedimentation of deeper holes, changes to stream substrates suitable for invertebrate production, and reduction of aquatic vegetation.
- Barriers such as weirs, dams, road crossings and farm tracks can prevent fish access to spawning and feeding areas, fragment fish populations, and interrupt exchange of genetic material.
- Loss of riparian vegetation contributing to reduced bank stability, reduction in water quality, reduced shading, increased water temperatures, and reduced habitats for terrestrial and aquatic plants and animals.
- Introduced species such as Murray cod and banded grunter may pose threats from disease, competition, predation, and habitat degradation.
- Illegal fishing practices directly reduce eastern cod numbers, remove breeding age adults, and can disturb breeding activities including egg guarding, leading to increased predation of eggs and juveniles by eels.
What needs to be done?
- Refer to priority recovery strategies.
- Conserve habitats and promote the restoration and protection of aquatic and riparian (river bank) vegetation and in-stream aquatic habitats.
- Allocate and manage environmental water flows in regulated rivers to lessen the impacts of unnatural flows and temperature patterns, and maintain natural flow seasonality.
- Educate fishers about the identification and protected status of eastern cod.
- Continue the research and monitoring of eastern cod populations to assess the effectiveness of recovery plan actions.
- Prevent sedimentation and poor water quality by improving land management practices, restoring riparian (river bank) vegetation and using effective siltation and erosion control measures.
- Develop and implement control programs for introduced pest species and prevent translocation of pest species including banded grunter, redfin and Murray cod.
- Implement the Threatened and Pest Species Sighting Program to improve knowledge of the distribution and abundance of the species.
- Modify on-farm stream crossings in accordance with Department of Primary Industries policy and guidelines for fish firendly road crossings.
- Construct fishways and remove redundant weirs to improve fish passage and reconnect aquatic habitats.
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