Data from a long-term native fish monitoring project in Waitakere, Auckland, illustrates the benefits of longterm monitoring and the limitations of one-off sampling.
Our ecologists have been undertaking annual state-of the-environment monitoring of fish communities in Waitakere waterways since 2002. This data keeps the Auckland Council well informed on environmental health and allows effects on streams of development or restoration to be evaluated.
Freshwater ecologist Eddie Sides says some fish populations fluctuate from year to year without any clear trend whilst others change slowly over long periods.
The data for inanga (whitebait) in the graph (right), for instance, shows that if sampling had been carried out in 2002 only, inanga would have been found at just 5% of sites, yet just two years later in 2004 would have been found at 40% of sites. Both results are ’snap shots’ and are not representative of normal values. Furthermore, single-year sampling could give rise to misleadin.conclusions: that, in 2002 and 2007, inanga populations were flatlining (or dying out) or, in 2002 and 2004, that they were rocketing!
“Once we have enough data to plot population cycles and other patterns we have a powerful predictive tool for ecological management,” Eddie says. “Our data provides Auckland Council with the information it needs to make decisions that help sustain native freshwater fish populations in Waitakere.” Stream health indicator Eddie says the biodiversity of fish communities is a good indicator of stream health. “Freshwater ecosystems are incredibly productive - it is not uncommon to find fish at a density of one per square metre.”
Factors affecting fish communities include water quality, habitat characteristics and barriers to fish movement such as hanging culverts.
Surveys of fish communities can also reveal the whereabouts of pest species and endangered native species. “We have over 50 native fish species, of which about two-thirds are classified as threatened or at-risk,” Eddie points out. “Some species which are still common, such as longfin eel and inanga, have been in decline for decades due to fishing and impacts on their habitats.
“At some point we need to get serious about turning these trends around if we value these species.”
1 November 2012