Highlights: Male Sperm Whale, Leatherback Turtle (see below for lat and
long)
___
Departed Eden at 07:30 on the 9th November on board the licensed
vessel ?Spirit of Eden?. Wind speed was Beaufort 2 for most of the day climbing
to Beaufort 3 for just a short period while in deep water. The intention of the
trip was to observe cetaceans and other marine wildlife and record information
to submit to biological databases.
About half an hour into the trip we encountered a group of about 20 Common
Dolphins feeding below a flock of Short-tailed Shearwaters. This area seemed
reasonably productive and on our approach we observed about a one degree
increase in sea surface temperature. We crossed a few surface fronts indicated
by lines of cuttlefish shells and seaweed while seabirds such as Wilson?s Storm
Petrels, White-faced Storm Petrels and Fairy Prions appeared and became
gradually more abundant.
Shortly after the first dolphin sightings the keen-sighted Dave Donnelly
sighted a turtle which turned out to be a Leatherback ? a new species for most
people on the boat. The animal was on the small-side of average for the species:
about a metre and a half in length. Leatherbacks can grow to a size of 3m, dive
to depths exceeding 1000m and may live for forty to fifty years. The largest
recorded animal was just under a tonne at 916kg.
Our Leatherback behaved inquisitively offering good views to everyone on
board. It surfaced repeatedly around the vessel to within about 50 metres over a
period of 20 minutes or so. At the same time another group of about 25 Common
Dolphins appeared.
Leatherback Turtles are rarely seen in SE Australia. They breed in tropical
waters during the austral winter and afterwards are thought to move south to the
colder, more productive waters of southern Australia. Nesting has been recorded
at Wreck Rock and beaches near Bundaberg and in other sites widely scattered
along the coastline (Great Barrier Reef campaign website
http://www.gbr.wwf.org.au/). However, the park authorities suggest these are
probably strays at the extremes of their ranges. Unlike most other reptiles
Leatherback Turtles are not strictly ?cold-blooded? as they can to some extent
regulate their body temperature internally instead of relying on the sun. In
both the northern and southern hemispheres they are more often seen in cold
waters at high latitudes than any other species of marine turtle. For example,
they are regularly recorded as far north as Nova Scotia, Canada. Although they
are not thought to rely on Australian waters for breeding, they are known to
regularly occur in Bass Strait in summer as a number are caught by fishing
trawlers each year. Gillnet fishing for tuna around Maria Island (small island
just north-east of Hobart) during February and March 1936 ? 1986 resulted in a
worrying average of two Leatherbacks caught each week (DPIWE, Tasmania -
http://www.dpiwe.tas.gov.au/intertext.nsf/Attachments/RLIG-5426H6/$FILE/raves3.pdf).
Given that there is so little information on the species in Australia, this
sighting off Eden could be another significant piece in the puzzle about
Leatherback Turtle movements around the continent.
After this initial excitement and given the extraordinarily calm weather
conditions, we decided to head towards the shelf break and search for other
cetaceans such as Sperm Whale and pilot whales. About an hour passed with few
other sightings although four more Common Dolphins were seen. Surface
productivity declined for a period and then rose again just before the
continental shelf break. Again, a few Wilson?s Storm Petrels, White-faced Storm
Petrels and Fairy Prions were observed.
Heading further out into deeper water Jon Hall suddenly spotted a low bushy
whale blow in the distance. We cruised closer but were not convinced that it was
a Humpback as the body of the animal was not appearing so there were thoughts
possibly of species such as Sei Whale. It had escaped our attention that we were
over water in excess of 650m deep. On approach, the animal offered a view of its
back with an unmistakable hump-like dorsal and knuckle-like ridges over the tail
stock and was correctly identified as a male Sperm Whale. Along with the
Leatherback, this was to be one of the highlights of the trip and a new species
for many on board. After one final large blow it threw its tail flukes in the
air and dived vertically out of sight. By this time the swell had picked up
slightly. For the sake of the passengers more than anything else, the decision
was made to move on and leave the animal in peace rather than wait the forty
minutes or so for it to resurface. As the weather conditions were still
favourable we decided to head on and search for more marine mammals over even
deeper water and the vague off-chance that beaked whales or pilot whales may be
around.
As with Leatherbacks, there are little data on Sperm Whales around
Australia?s coastline and this sighting was particularly interesting being an
adult male. Further north around Wollongong and Sydney mostly matriarchal groups
(cows and calves) are seen. Elsewhere in the world the distribution of Sperm
Whales tends to be divided like this with matriarchal groups mainly occupying
tropical and sub-tropical waters and solitary males existing further south or
north as the case may be.
For the remainder of the day we had no other marine mammal sightings over
deep water but did encounter three ocean sunfish, including one particularly
large individual measuring about 3m in length (for a picture of ocean sunfish,
see http://www.orcaweb.org/other_wildlife/sunfish01.jpg). Four Humpbacks were
seen off Tura head just north of Eden on the return trip and another group of
Common Dolphins were observed along with a large flock of Albatrosses including
a single Gibson?s (Wandering) Albatross.
On the 10th November the weather conditions were much worse and we
were forced to spend the day hugging the coastline. An exciting encounter with
Common Dolphins in the first hour was shortly followed up by great views of a
repeatedly breaching calf Humpback just off Green Cape (a short land-based watch
at this location two days earlier had also yielded views of Humpbacks including
a breaching calf). For the rest of the day Humpback Whales continued to pass
south on migration. By the afternoon when the wind swung southerly, adult
Humpbacks began breaching and several times they were seen to completely clear
the water; these dramatic breaches visible for several miles.
Following a trawler back from Green Cape we managed to pick up a few other
seabirds including Southern Giant Petrel and Cape Petrel. Brief views of another
couple of groups of Humpbacks were had on the way back in to Two-fold Bay but by
this time the viewing conditions had worsened and the Humpbacks were being
elusive. We finally headed back in to shore feeling adequately full-filled after
an extra ordinary weekend.
STOP PRESS: Jon Hall just informed us that a friend playing golf at a
headland about 100km north of Eden on Saturday was distracted by a group of
Killer Whales.
Regards,
Simon Mustoe.
Sperm Whale: 1 ad male ; 37° 07.34?S, 150° 23.45?E
Leatherback Turtle: 1 ; 37° 06.89?S, 150°
04.50?E
