Sunday, November 4, 2007
The metre long dark brown Eel was lying immobile in the middle of the trail. At times I've seen fishers at the creek but until now have not encountered their discards. Perhaps they just forgot to take the Eel with them or perhaps they didn't think to put it back its watery home. I read that Eels can live up to 48 hours out of the water because of their very oily skin; they can also travel short distances across land - slithering from place to place in search of a new pond or pool if theirs is drying up. I didn't know how long this one had been out of the water so, hoping it would revive, I picked it up and placed it back in the creek.
The day before I'd seen another Eel swimming in a nearby lake, so finding one more Eel told me something about the creatures who live here but are often out of sight.
Eels live for 50 to 60 years and have an amazing life story to tell. They live as both saltwater and freshwater creatures. And throughout their lives they journey vast distances, up to 6000 kilometres, from their ocean home in the middle of the Pacific (for Australian species) to the particular river, creek and pool where their relatives had once lived. They find their way back, it's believed, due to their remarkable ability to recognise the specific chemistry of the water from their parents' original freshwater pool site (Planet Patrol, 2007).
When they start their journey from the ocean they're known as Elvers. These tiny leaf-like creatures drift on the currents for two to three years but, it's said, only about one percent of them actually make it back to their freshwater refuge. According to British research there has been a huge decline in the numbers of young Eels reaching estuaries and rivers, estimated at over 90 percent in the past two decades (BBC Science & Nature, 2004).
As the Eels move from waterplace to waterplace they also shapeshift from the tiny Elver transforming into a translucent juvenile 'glass Eel' and eventually to the lustrous dark brown Eel I met on the trail. After another 20 or so years living in local creeks, lakes and ponds the Eels hear the call of the ocean. They need to return to their spawming grounds to breed. And then they die.
Journeying across such vast distances is dangerous. Dams act as barriers stopping the Eels moving up and downstream but sometimes stairways are created to help Eels and other migrating fish to reach their destination. Toxic pollution, agricultural, chemical and sewerage runoff also damages the Eel and other river species. Overfishing is another problem. In Brisbane and other areas in SE Queensland, urban development can also affect the Eel population. By filling in channels, swamps and pools, building weirs, disturbing riverbank ecologies and water quality the Eels can lose their pathways to the ocean.
Along Australia's east coast there are two types Eel, the longfinned Eel (Anguilla reinhardtii) which enjoys tropical environments and the shortfinned Eel (Anguilla australis) which lives in temperate waters. The ABC Science informative website says that: 'Longfinned Eels prefer flowing rivers and creeks more than the calm ponds and lakes the Shortfinned tends to inhabit'.
Longfinned and long lived, these Eels need safeguarding. A lot of attention is now going into breeding Eels in fishfarms at the 'glass Eel' stage. If you are interested have a look at work being conducted at the Bribie Island Aquaculture Research Centre in Queensland (e.g. Langdon and Collins, 2000).
Langdon SA and AL Collins, 2000, 'Quantification of the maximal swimming performance of Australasian glass eels, Anguilla australis and Anguilla reinhardtii, using a hydraulic flume swimming chamber,' New Zealand Journal of Marine and Freshwater Research, 34: 629-636