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When the tide finally retreated on Tuesday April 19th, a hardy crew of
parents and children spent the day digging up little plots of mud on a
large grid of points laid out using GPS on Whangapoua estuary. In each
sample they counted and measured the size of the cockles, and noted the
presence of other shellfish, which they had to identify using a set of
pictures. This is part of an on-going monitoring system for shellfish
throughout the Hauraki Gulf. It is under the overall organisation of The
Hauraki Gulf Forum (Auckland Council), but is contributed to by other
organisations, especially the Department of Conservation. The data are
collected by volunteers – mainly school children – but analysed
independently by the Ministry of Fisheries, who report back to the
Forum. The Forum produces an excellent Teachers Resource Kit, both in
book form and as a DVD. The idea is that the day is fun for all, and
that some learning about shellfish ecology and monitoring methods is
achieved. While the number of cockles found might be influenced a bit by
the persistence of the diggers, measuring shell lengths is easy and not
subject to much error. Subsequent classroom follow-ups are designed to
let the children see the collated results of their individual efforts,
and to impart some ideas about possible harvesting impacts, and ‘what
eats what’ out there on the mud. Ideas about the graphical presentation
of numerical data are also introduced. The whole package is designed for
children at the upper primary to intermediate level.
Since 2007, in samples
taken from the same locations (within a few metres), the number of
cockles appears to have increased slightly (Fig 1). While this might
seem good, a worrying trend is for a decrease in average cockle size
(Fig 2); there appears to be a bigger proportion of smaller cockles, and
a smaller proportion of big cockles now than there was in 2007. Cockle
numbers and sizes vary a lot from year to year and place to place, so
these results simply mean we should be wary, and perhaps not always go
for the biggest shellfish when gathering! Over the same period pipi
numbers seem to have declined, and we found only very small ones this
year.
Fig 1. Changes in cockle and pipi density
at Whangapoua
Fig 2. Average Cockle Size
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