Scientists probe food chain theory
New research suggests an age-old assumption that long-fin eels are naturally slow-growing animals could be out the window, with the real reason being a lack of food thanks to low ınanga (whitebait) levels.
Freshwater scientist Dr Simon Stewart said it was a ‘‘eureka moment’’ when he and his research team first made the connection, and a recent announcement of $360,000 in this year’s Te Aparangi Royal Society Marsden Fund awards means more research can be done to look closer into the connection between whitebait population levels and tuna (eel) growth.
Stewart said the new funding would enable the research team to go back into Te Waihora Lake Ellesmere’s historical record of eel otoliths – ear bones which have growth marks similar to rings on a tree – to see if eel populations in the lake used to grow faster before a severe storm in 1968 which ‘‘flipped’’ the lake.
‘‘It ripped up all the lake bed, and after that the lake was turbid and didn’t have any macrophytes [aquatic plants] in it, and it was at that time the ınanga population declined,’’ Stewart said.
The research is also being done in partnership with Dr Jessica Lueders-Dumont from Princeton University, who can help ‘‘fingerprint’’ the eels’ diet using isotopes – matching the profile in the otoliths to either marine or non-marine sources.
If the hypothesis proves correct, and eels in the lake grew faster when ınanga were still plentiful and the otoliths confirm a marine-fish diet, Stewart said he hoped it would lead to more a more holistic approach to ecological protection.
‘‘If we are thinking about eel conservation and improving their population, it is looking at more than just where they are – you have to be looking at, say, our coastal lowlands and waterlines. I see that being a big target of this work.’’
Stewart compared the potential conservation approach to one taken on the west coast of the United States and Canada, where it was discovered that spawning salmon were key ecological drivers for the wider forest thanks to animals like bears and eagles taking the fish from the rivers and spreading them throughout the forest.
‘‘Now they have an ecosystem quota for salmon fishing: there needs to be enough salmon to support the population, and after that enough going on to fertilise the forest and feeding the bears, and once those quotas have been met fishermen can go in.
‘‘We may start thinking about whitebaiting the same way: do we have enough to feed the tuna and our birds as well?
‘‘I am speculating on the results ... but that is a dream I would like to see come from this.’’