Old methods produce new data
21 September 2015
Old fishing methods are providing the raw data that modern techniques can't match in the Rotorua Lakes.
University of Waikato alumnus Dr Ian Kusabs is a fisheries adviser to Te Arawa and Ngāti Tuwharetoa and is researching the state of kōura (freshwater crayfish) in the central North Island lakes.
He presented his research during Kīngitanga Day and says the aim is to examine catch rates for kōura and use those to develop a sustainable management plan for the delicacy.
Kōura were an important food source for Te Arawa, were used in trade and Dr Kusabs says they are a "keystone" species, crucial to the health of the ecosystem.
"There was anecdotal information that numbers have declined
since the arrival of Pākeha," he says.
In 2006 the Te Arawa Lakes Settlement Act allowed Te Arawa to manage the fishery and Dr Kusabs says they are looking at developing regulations and management plans.
However, with limited information available, Dr Kusabs says gathering credible data was an important issue.
"We needed to develop suitable monitoring methods. We tried spot lighting, scuba, underwater cameras and baited traps but they all had problems."
Traps had a low catch rate, caught mainly larger specimens and mostly the more aggressive males. They were also susceptible to theft and needed to be retrieved early each day.
Scuba, spot lighting and underwater cameras also had issues with things such as murky water or being weather dependent.
So Dr Kusabs consulted local kaumatua who suggested using traditional methods of catching kōura.
That includes tau kōura, which were - in effect - bundles of fern which sit on the lake bed.
The kōura move into the fern fronds, which provide habitat for them. When the bundles are removed from the lake, a net is placed below it to ensure kōura don't escape.
Dr Kusabs says the tau kōura they worked with – consisting of ten bundles of ferns in each - delivered outstanding results.
"We got a wide size range – from 7mm to 50mm OCL (Orbit Carapace Length) - an unbiased sex ratio, a good catch rate, it is cheap to set up, it can be retrieved whenever, it's sustainable and actually enhances the fishery."
Orbit Carapace Length refers to the measurement of koura, which is from behind the eyes to the end of the carapace.
Dr Kusabs says to have a sustainable and regulated market, researchers still need more information about the state of the kōura fishery.
"We need to know the abundance, biomass, size, sex ratio, breeding time, fecundity, size at breeding. We found out their breeding season was April to November and at a 28mm minimum OCL size, 50% of breeding females would have the chance to breed before growing large enough to be harvested."
That information would help develop rules for the fishery. Currently kōura are restricted to 50 per person per day and commercial sales are banned.
Proposed regulations include tau kōura being the only allowable means of deep water harvest, a continued ban on commercial sales, retain the 50 per day limit with a 28mm minimum size, restrict the harvest to 1 December-31 March to avoid breeding season, and ban the taking of females with eggs.
Dr Kusabs used tau kōura on eight Rotorua lakes and found three – Rotorua, Rotoma and Rotoiti - had kōura in large enough numbers to consider harvesting. Further work will be carried out on the other seven lakes in the region.
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