Biomass estimation of Artemia at Lake Grassmere, Marlborough, New Zealand

Abstract

During 1980-1982, a sampling program to estimate Artemia biomass was carried out over an annual cycle in the solar salt ponds of Lake Grassmere, Marlborough, New Zealand. Density of Artemia was highest over 238.5 ha of the 1782 ha in 13 ponds, averaging 0.55 m deep, which form the final stages in salt concentration. Artemia and hydrological samples were taken twice a month on 23 occasions from April 1981 to April 1982 inclusive, and on each occasion, 86 sample stations over four ponds were sampled in triplicate. An unbiased estimate of biomass using the arithmetic mean was developed, together with confidence interval estimates based on the bootstrap method giving 95% confidence bound estimates within 25% of the estimated total Artemia biomass in each sampled pond.

Artemia biomass concentrations within 50 m of the pond edges were, on average, 2.5 times those at the pond centre, and the biomass estimation procedure was thus accordingly stratified. Generally, Artemia were contagiously distributed with the edge stratum biomass having a log-normal distribution at each sampling time. Biomass was highest during late spring and summer, and lowest in late autumn through winter. Maximum estimated total biomass over 238.5 ha was 12 000 kg dry weight during January 1982.