Nexus

 

Australia Network
Nexus

Print | Close


print friendly page for http://australianetwork.com/nexus/stories/s2193030.htm

12 May 2008

Sea Lions


Rob Morrison: Sea lions are the undersea acrobats of the animal kingdom. With the smallest flick of their tails and flippers they can twist and turn effortlessly to catch fish or simply play. And they do a lot of playing. But on land, it's a different story. There, they are ungainly and cumbersome. Most of the time they sleep and a walk among them shows just how easy it was for seal hunters 200 years ago to club them as they lay - killing them by the thousand for their skins.

Unlike true seals, sea lions have small ears visible on their heads. There are five species of sea lions worldwide and the Australian sea lion, which is only found in southern Australia is one of the rarest, as a threatened species that needs protection. But for that to be effective, much more needs to be known about how these animals live, where they travel and what they eat. Dr Simon Goldsworthy is a leading expert on Australian sea lions and he's using space-age technology to reveal the hidden secrets of these elusive animals.

Dr Simon Goldsworthy: Like many seal species around the world the Australian sea lions were subject to fairly unregulated, uncontrolled sealing in the early to late 1800s. Many of those populations have still not recovered. And the range of the species also contracted. They are listed as a threatened species and so we need to understand more about where they go to sea to feed. We use satellite transmitters which are small microprocessors we glue to the backs of seals. And they produce a signal when the animal surfaces and that signal's transmitted up to an orbiting satellite and we can get information on the locations of these animals when they're at sea.

All other seal species in the world breed every 12 months, roughly. The Australian sea lion's breeding seasons occur about every year and a half. It's very easy to access their breeding colonies. Some colonies we've been tracking are at the base of the Bunda Cliffs on the Great Australian Bight. That's very challenging. They're 70-metre cliffs so it's a very long drop on a rope. We used the State Emergency Service to make sure that we could get our crew down to the bottom of the cliffs, into the colony safely.

Sea lions are very shy animals and they don't like being disturbed. They can get rather anxious. So we have to keep very low to the ground and sneak up on it and place a hoop net over its head. The Australian sea lion is quite a large animal and they're very, very powerful and muscular so it's important that we restrain them physically very quickly, so that requires two or three people to sit on top of the animal and hold it in as many places as it can. And then there's a delicate moment where we've gotta set up our gas anaesthetic machine so we can place a mask around the mouth. And that's quite a dangerous activity, as you can imagine, because these seals have got very large, sharp teeth. Once that's happened we only need the animal to take two or three breaths and it goes to sleep.

We're actually gluing the transmitter to the hair of the animal - not to the skin. The transmitter can remain on for many months and not harm the animal. And when we go to recover the instrument - this could be anywhere between several weeks or several months after we've actually attached the transmitter - we can then just carefully cut away the glue against the hair of the animal. Instruments we don't recover, the animals simply moult the transmitter off - it's usually just after breeding season.

All our transmitted data goes to France initially and gets processed there and we can then access it directly online from our office, on the computer. Here's a track for one individual. What we can do is connect the location points with lines and you get a trace - or a foraging route - of the animal while it's been at sea. That essentially tells you when the animal has left the colony, where it's foraged and where it's gone while it's at sea. Put all the foraging tracks together and we can get an idea about where that population of animals is actually feeding at sea.

One of the really incredible things we've found is that no two Australian sea lion colonies are the same. Sea lions on three of the islands specialised in feeding in very shallow, inshore waters that were about 10m in depth. The other three islands were very, very different. The animals on those islands were travelling much greater distances, feeding out into mid to outer continental shelf waters.

This species - I call them the seal of superlatives. Everything about them is amazing. The only non-annual and asynchronously breeding seal, they have the longest gestation period, one of the longest lactation periods and they're really unique - there are no other seal species does things the way that sea lions do. We have no real understanding what the evolutionary pressures, if you like, were that actually shaped this animal. So the more research we're doing into their feeding, into their breeding biology, we're slowly learning what are the critical things that may have shaped this most unusual life history.