Killer whales and dolphins move in as bay fish dwindle

KILLER whales and ocean-dwelling dolphins are increasingly venturing into Port Phillip Bay, despite fish stocks hitting record lows in some places.

A survey by the Department of Primary Industries suggest a long-term decline for fish species, with two sections of the bay of particular concern.

The survey revealed record low biomass levels for fish in the deep centre of the bay and western waters near Geelong.

By measuring the catch in tonnes, the annual trawl provides an indication of population levels in the bay for bottom-dwelling fish such as flathead.

Despite the study revealing record lows, the department said the results were within "expected variability" and not significantly different from previous years.

But Australian Conservation Foundation spokesman Chris Smyth expressed concern that an all-time low was portrayed as being within an acceptable range of variability.

"Anyone who loves Port Phillip Bay will be shocked by this collapse in the bay's fish biomass," Mr Smyth said.

"The community should be deeply disturbed at the lack of port and government agency response and action."

Department spokesman Peter Appleford defended the method of reporting, saying the results represented the continuation of a trend.

He said while bottom-dwelling species were under pressure, others such as whiting and gummy shark were thriving.

The decline in fish stocks comes as dolphin experts report "an extraordinary influx" of dolphin species that traditionally live in ocean waters outside the bay. Dolphin Research Institute executive director Jeff Weir said ocean dolphins had been hunting and reproducing inside the bay near Frankston in the winter months.

The bay has traditionally been the exclusive domain of another species of dolphin believed to exist only in the bay and the Gippsland Lakes.

Mr Weir said there was no indication that dredging was harming dolphin numbers, and sightings of killer whales inside the bay had also risen sharply.

"They have been observed feeding on salmon in the bay and in winter time they follow the pattern with the southern right whales because they like to feed on the calves," he said.

Monash University dolphin expert Kate Charlton said the influx of ocean dolphins and killer whales was in contrast to the time she started researching the bay 10 years ago.

"We are having more and more sightings of killer whales … we've had killer whales as high up as Dromana and Mount Martha," she said.