Distribution of the threatened Macquarie Perch (Macquaria australasica) within the Hawkesbury-Nepean catchment, NSW.
The Hawkesbury-Nepean catchment is the largest coastal catchment in NSW. Over 50% is contained within National Park or Sydney Catchment Authority restricted areas, and much consists of very rugged terrain and remains highly inaccessible wilderness. Due to this inaccessibility, the status of Macquarie perch populations within the entire catchment has previously never been comprehensively assessed.
Macquarie perch were recorded at 21 locations during this survey, and new records for the species were collected from five sub-catchments. All except one of these 21 sites were within National Park or Sydney Catchment Authority restricted areas.
The inaccessibility of many of these locations, and the added protection of the surrounding land from environmental disturbance, gives the illusion that fish populations in such streams are generally free from threatening processes. However most of the Hawkesbury-Nepeans major tributaries begin outside of this protective umbrella. As a result, they continue to be subjected to a number of threats in their upstream reaches including flow regulation, pollution, impacts from introduced and translocated species, and habitat degradation such as sedimentation.