Evolution discovery for rare whitebait

By ANGELA GREGORY

DARGAVILLE - Scientific studies may have saved three new native fish species even before they have evolved in isolated Kaipara sand-dune lakes.

Research shows that the threatened dwarf inanga (whitebait), found only in Kaipara freshwater lakes, appears to be evolving into a new species.

Landcare Research scientists have studied the slender-bodied fish in their freshwater habitats using nocturnal netting and taking blood samples from anaesthetised fish.

Project leader Dr Dianne Gleeson said the research by Masters student Simon Binzegger found that in three separate lake locations the dwarf inanga seemed to be evolving.

"They could be developing into new species.

"We will have to rethink how we can manage them better."

Dr Gleeson said the work highlighted the need in conservation to not just focus on saving existing species.

The creamy transparent dwarf inanga, which grow up to 6cm long, are found only in 10 dune lakes.

They are in two clusters - the Pouto lakes next to the Kaipara harbour and 80km north in the Kai Iwi Lakes.

Dr Gleeson said DNA extracted from blood samples showed distinct groupings at the Kai Iwi Lakes, Lake Rototuna at North Kaipara Head, and the remaining Pouto lakes.

While the DNA sequences revealed the fish must have had a common female ancestor, the dwarf inanga populations had been isolated for a long time.

She said the oldest of the lakes dated back to the mid-Holocene period 10,000 years ago.

Assessing how long it might take for new species to develop was like measuring a piece of string.

"That's one of the big questions of evolutionary biology. Some speciate faster than others, possibly tens of thousands of years to hundreds of thousands."

Dr Gleeson said it was the dwarf inanga's isolation that made them likely to take separate evolutionary paths, unlike increasingly homogenised humans.

"Humans are not allowing natural selection because of the use of medicines and life-saving techniques. We will never now evolve into some super being."

Landcare Research has recommended that the Department of Conservation manage the populations in the Kaipara Lakes as independent, "evolutionary significant" units.

Dr Gleeson said that without the research, restocking and translocation activities of dwarf inanga might have been carried out.

"This had the potential to result in the loss of distinct genetic information, reducing fitness and rendering the remaining stock vulnerable to future habitat and climate modification."

The dwarf inanga were discovered in 1967. They are found in shoals in the open lake waters or among vegetation in the margins.

Dr Gleeson said threats to their habitat included the conversion of surrounding land to pasture and exotic pine plantings.

Predation from rainbow trout and the liberation of mosquito fish had already harmed the dwarf inanga populations.

Mosquito fish had been seen attacking and killing adult dwarf inanga, which had led to their extinction in Lake Kai Iwi and a decline in their abundance in the other lakes within that group.

Northland conservancy scientist Dr Ray Pierce said the results would help to better manage the dwarf inanga populations by giving priority to habitat protection.

Already the department was working on fencing, planting and maintaining riparian buffers.