New Zealand Journal of Marine and Freshwater Research abstracts
Identification of fish responsible for five layers of echoes recorded by high-frequency (200 kHz) echosounding in Lake Rotoiti, North Island, New Zealand
DAVID K. ROWE
National Institute for Water and Atmospheric
Research Ltd Private Bag 3123 Hamilton, New Zealand
Abstract
Layers of echoes, segregated by depth, were recorded by high-frequency (200 kHz) echosounding in several lakes near Rotorua, New Zealand. The fish species responsible for the echo layers in Lake Rotoiti are identified. Schools of 1
+-year-old smelt
(Retropinna retropinna) produced a band of spike-like echoes between 2 and 10 m depth. Below this layer, larval bullies
(Gobiomorphus cotidianus) produced a second, scattering-type layer. A third layer of echoes, below the scattering layer, was produced by 2
+-year-old smelt. Smaller fish were responsible for a deeper, fourth layer of echoes, apparent only in Lake Rotoiti, but the actual species or life history stage was not identified. Echoes within 5 m of the lake bottom at depths over 40 m comprised a fifth layer and were caused mainly by adult koaro
(Galaxias brevipinnis). Echoes from trout
(Oncorhynchus mykiss), from schools of smelt in Layers 1 and 3, and from adult koaro were of a similar amplitude. As acoustic surveys of trout density will depend on identification of trout from the size of their echoes, such surveys should be carried out at times when smelt are not schooling and when adult koaro are scarce.
Keywords Oncorhynchus mykiss; rainbow trout; Retropinna retropinna; smelt; Gobiomorphus cotidianus; common bully; Galaxias brevipinnis; koaro; high-frequency echosounding; echo identification; Lake Rotoiti; acoustic surveys; scattering layers; fish distribution
M92031
Received 11 June 1992; accepted 3 December 1992
New Zealand Journal of Marine and Freshwater Research, 1993: Vol. 27: The Royal Society of New Zealand 1993
Received 11 June 1992; accepted 3 December 1992
PDF file of entire paper: medium quality (4220K); (scanned from paper original: notes about this process)
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