However, no eggs or mature eels have been reared anywhere nearby. So the question remains unanswered… until now.
Pop-up satellite archival tags are a relatively new tracking device that allows scientists to map the movements of marine life in a way that was not possible before.
The tags record where the animals travel, how fast they move and even how deep they dive. Then, the tags detach and surface, where the data can be transferred into the hands of eager scientists.
The migration of European eels is impressive, but they are still shrouded in mystery. All mainland eels come from the same spawning grounds – yes, even backyard pond eels can drift from land to sea after a little rain. Eels can even climb huge dam walls! But how do they know where to go? When do they decide?
Australia also has its famous eels. They usually keep to themselves so much that most of us don’t even know they’re there. But with all this rain and flooding, chances are you’ll run into one soon.
So I thought it would be a good time to share five things you didn’t know about eels, including Australia.
1. We have our own amazing migration story in Australia
Although not as long as the journey of the Australian Shortfin, it makes a massive migration.
In a study published last year, researchers from the Arthur Rylah Institute and the Gunditj Mirring Traditional Owner Aboriginal Corporation used satellite tracking tags to map the path of 16 eels from Port Phillip Bay, near Melbourne, to the Coral Sea outside the Great Barrier Reef. Some have traveled almost 3000 km in just five months.
It is a difficult journey. The tags showed that some eels used currents and dived almost 1,000 meters below the ocean surface to avoid predators. Not all were successful, though—at least five of the tracked snakes were eaten by sharks or whales.
2. Eels are masters of the obstacle course
When you stop to think about it, there are more than a few barriers between inland freshwater and the ocean. Many of the swamps and marshes that traditionally offered safe passage have been filled in, replaced by farms, dams and cities.
And yet, the eel finds a way. One of the main characteristics is the ability to breathe through their skin, which means that even the shallowest drain or puddle-soaked lawn is enough water for them to pass through.
According to urban legends, eels have been seen gliding over city traffic jams, sports ovals or university campus fountains, following ancient trails out to sea.
3. Eels are expert transformers
Imagine having to go through puberty four or five times, each body change more dramatic than the last. Then you will understand well what it is to be an eel.
Migrating eels must switch from saltwater fish to freshwater fish and back again unbelievable life cycles. They begin as tiny larvae in the ocean in the Sargasso or Coral Sea, where they spawn, then transform into transparent “glass fish”.
After that, when they return to fresh water, they turn into darker “elvers” at about one year of age, eventually becoming the adult eels that live in our rivers, lakes and dams.
In time, they eventually transform into lean, medium, migratory machines known as silver eels.
Their eyes are enlarged and their heads are pointed and flat. They also stop eating as their stomachs shrink to make room for larger reproductive organs (better for spawning).
Moment surfer takes the ‘world’s heaviest wave’
4. Sigmund Freud was also an eel lover
Speaking of gonads, Sigmund Freud (yes, that Freud) spent the early years of his research career trying to understand the sexual anatomy of eels.
Unfortunately, Freud and the only way to tell if an eel is male or female is to dissect it to observe its internal reproductive organs.
Despite hundreds of dissections, Freud rarely found a male eel. It turns out that this is because eels don’t develop their reproductive parts until later in life – usually at least ten years old.
5. Eel can live a very long life
Yes, these long fish have long lives, with some eels living for over 50 years.
A man in Sweden claimed that his backyard fish lived to be 155 years old, and another man in a Swedish aquarium lived to be 85 years old.
Eels spend the first few years of their lives moving from their spawning grounds to fresh water and the last few years returning to the sea. They only spawn once – after that they die.
Why is this kind of research important?
There’s still a lot we don’t understand about eels around the world. But satellite studies published this week bring us one step closer to putting all the pieces together.
This has real implications for how we view eel populations. European eel (Anguilla anguilla) is critically endangered, the species has experienced a decline of up to 95% in the last 50 years.
We really don’t know how well Australian snakes track. If we understand where animals breed and how they get there, it means we can find ways to help and protect the places that matter, rather than hinder them.