Port Phillip Baykeeper

whales just wanna have fun!

BayKeeper — Sun, 25 Jul 2010 11:25:35 +0000

If you had to choose a magic marine moment, it would be hard to beat the spectacular breach of a Humpback whale. They just love to leap, roll in mid air, and land on their back. Why do they do it? Perhaps just cos they can! Baykeeper is truly envious of Ron, Tania, Duke and Sofia, who photographed this fantastic sight off St Leonards in late June.

Humpback at play in the Bay (pic courtesy of Ron,Tania, Duke & Sofia)

Winter is whale watching time in Victoria as Southern Right Whales (Eubalaena australis) and Humpbacks (Megaptera novaeanglidae) move from the Southern Ocean to warmer waters along the coast. The 2010 winter is reportedly one of the best yet for local sightings. Let’s hope it will continue to get better as both of these Endangered species gradually increase in number. The key concerns are to maintain suitable habitat and food supplies. They feed mostly on copepods, krill, and other swarming zooplankton.

The Southern Right Whale Recovery Plan (2005 – 2010) notes numbers are increasing, suggesting that habitats are not degraded. Logan’s Beach at Warrnambool is one of 6 known Southern Right whale calving areas scattered along the southern coastline from WA to Vic. The Australian population of Southern Rights is believed to be around 1,500, with less than 10% of those occurring east of Adelaide. So it’s quite a privilege if you spot one! The ‘eastern’ population may be more vulnerable to threats due to their lower numbers and the larger human population along the south east Australian coast.

North Pacific Seastar population decline?

BayKeeper — Sun, 25 Jul 2010 10:04:20 +0000

The beautiful, but destructive North Pacific Seastar (Asterias amurensis) first arrived in Port Phillip Bay in the 1990s in ship ballast water. As they eat practically anything live or dead that they can climb onto, they thrived in the local conditions where they have few natural predators. In less than 10 years they became the most common animal in the Bay. The fact that that the females are estimated to produce over 20 million eggs could have something to do with it! Naturally, there are concerns that they could out-compete native sea star species.

North Pacific Seastar - it's own worst enemy?

NPS’s tend to spend the summer months in the deeper, central Bay waters, and move nearer to shore in winter. Over the past 5 winters Earthcare volunteers have taken advantage of this seasonal migration to remove thousands of these pests from St Kilda harbour. The most recent cull, conducted today, found hundreds compared to the usual thousands; and young native seastars were noted.

Along with this promising result, several divers have reported not seeing NPS’s in the south of the Bay over the past year. Have they disappeared altogether, or simply eaten themselves out and moved to another area? Baykeeper is keen to hear any reports of NPS’s from around the Bay. Have you seen more or less this winter?

‘average tide’ hides local reality

BayKeeper — Wed, 07 Jul 2010 12:39:09 +0000

The fact that the tidal range at ‘the Entrance’ is around twice that at Port Melbourne highlights the fact that there are very different tidal zones in the Bay. Incoming tides are impeded by the Bay’s narrow Entrance, and then by ‘the Sands’, the vast triangular area of shallow sand flats which are a barrier to waters moving to or from the north of the Bay. Wind strength and direction, and barometric pressure also affect sea level in localised areas.

Many people raised concerns that deepening the shipping channel at the Entrance (completed in September 2008) would open up the Bay to greater swell wave force, increasing tide levels, scouring ‘the Sands’, and eroding beaches. Swell waves generated by storms over Bass Strait can be quite destructive on the seabed and coast. In turn, changes to the seabed affect tidal current speeds and direction.

Portsea - a swell place for a beach!

Baykeeper and friends have found that average daily highest tides at 4 stations in the south of the Bay are all different, between 48 and 100mm higher than before dredging the Entrance. According to our humble methods, the increase at Williamstown has only been 2mm. Much longer periods (at least 5 years) of monitoring tidal current speed, direction, and levels are needed before channel deepening could possibly be ruled out as a cause of beach erosion. Meanwhile, talk of a “10mm increase” in tides across the whole bay does nothing to explain local realities. Our findings are available as Pdf downloads on this website.