Images(4)

Plankton Indicator

Datepost 1945

Object number00056041

NameLarval sampler

MediumMetal

DimensionsOverall: 350 × 120 × 145 mm, 1740 g

ClassificationsTools and equipment

Credit LineAustralian National Maritime Museum Collection Gift from CSIRO, Oceans and Atmosphere

Terms

DescriptionThis plankton indicator is donated to the museum by CSIRO, along with a CPR body (of earlier vintage) and a CPR cassette (of more recent vintage). This plankton indicator is a variant of the Mark III plankton indicator developed after WWII for the East Anglian Fishery. The tailplane is the give-away. The forward depressor has been omitted (or removed) on this model in favour of a tail flap. Not a bad idea because the flap angle could be easily adjusted. The method was to deploy the plankton indicator and tow it for one mile, after which it was recovered and the internal disc changed. The plankton on the recovered discs was transferred to numbered tubes containing formalin for later laboratory analysis. Ship positions were recorded for the first and last haul of the series and the intervening positions (regularly spaced) were then extrapolated mile by mile.SignificancePlankton indicators are more or less a precursor to the plankton recorders- and were designed so researchers could collect data from fishing fleets without affecting their normal fishing operations. It was crucial in determining concentrations of phytoplankton and zooplankton, without requiring a constant underway tow, as is required for the Continuous Plankton Recorder (CPR). While the CPR is more accurate, and recovers a greater number of sampling material, the plankton indicator served its purpose as ‘indicating’ average populations of plankton located within normal operating areas for fishing fleets.

Its detailed use in Australian waters is as yet to be determined. Further research into historic plankton surveys immediately post WWII is required to accurately project its full significance. However, it is not represented in any other Australian museum collection (as known) and is therefore significant as a representative of early- to-mid twentieth century offshore microbial sampling.