EPS Ecologist finalising PhD on Fish Ecology

EPS ecologist, Alan Midgley, has a background in bush regeneration and ecological research and consulting. Alan, who joined the company as an Ecologist in March 2016, is currently completing final edits to his PhD entitled ‘Ecology of the Australian bass in tributaries of the Hawkesbury-Nepean River’, and contributes strong research skills to the company.

Alan’s PhD was based on the ecology of the Australian Bass in obstacle-strewn and open creeks that run into the Hawkesbury River. He looked at fish, size, diet, age, migrations and aspects of the recreational fishery for this species.

Bass in obstacle-strewn creeks, where the interface of land and water is much higher than that of open creeks, ate a greater diversity of foods, for example, mayfly larvae, cicadas, birds, reptiles, with fish rarely eaten.

To determine fish age, Alan extracted a bone called the otolith from each fish head. By taking a small cross-section of the otolith, age can be determined by counting the visible bands under a microscope, much in the same fashion as counting the rings of a tree.

Bass breed in the estuary in winter and move to freshwater in Spring. Moving back into freshwater is no easy task and often relies on flooding cues to drown out impassable barriers such as those in obstacle-strewn creeks.

Alan was able to detect migrations between fresh and estuarine water throughout the fish’s lifetime through subjecting otolith cross-sections to microchemistry analysis. Higher levels of Barium would indicate occupancy of freshwater, and strontium indicated when they occupied the estuary, where these chemicals naturally occur at higher levels respectively. With this method, the age bands discussed earlier can be used to show where it was at a certain age!

The social aspect to this study involved looking at bass angler survey trends. Most anglers were male, 25-34 years old, use Google maps to identify secluded fishing spots where they practice catch and release sport fishing. Alan found it very interesting that many bass anglers use technology to perform a ‘desktop study’ prior to accessing an area to fish. It is important for ecological management that most of these anglers release this species after capture to limit impacts on this species.

EPS are very pleased Alan is part of the ecology team and look forward to celebrating the completion of his PhD. For more information on EPS ecology capabilities, or some Australian Bass fishing tips, contact the EPS ecology team.