Monitoring
Snapper in Te-Whanganui-A-Hei
Marine Reserve
An annual monitoring programme is undertaken in accordance with the management plan for the area.
Fish
Formal fish monitoring has occurred since 1997, using baited underwater video and underwater visual census. Species targeted by fishers have responded positively to protection.
In 2006, baited underwater video results inside the reserve show the number of snapper and size distribution of individual snapper are similar to results of past surveys in 2003 and 2004. However, in 2006 there was a substantial increase in the numbers of legal sized snapper (> 270 mm fork length) outside the reserve. This resulted in the lowest reserve:non-reserve ratio of legal sized snapper recorded to date at Te Whanganui-A-Hei (only 3.5 times more abundant inside the reserve than outside, compared with 7.0-18.3 times more abundant in the previous six surveys).
Underwater visual censuses continue to indicate that marine reserve protection has at most a weak effect on the majority of other fish species at Hahei. In 2006, no significant effect of reserve status was detected for the reef fish assemblage as a whole, which appears to be responding much more strongly to the environmental gradient running through the reserve and adjacent reference areas.
Rock lobster
Lobster (Jasus edwardsii) monitoring was established in 1996.
In 2007, lobster abundance (22 lobsters per 500 m2 ± 4.9 SE) was 1.8 times higher than 2006 levels and 6 times higher relative to the non-reserve area surveyed. As such, the present levels of lobster within the reserve are equivalent to 57 km2 of fished rocky-reef coastline.
The increase in abundance was largely attributable to on-growth of sub-legal lobsters between 2006 and 2007. Lobster abundance in non-reserve areas also increased between 2006 and 2007 primarily due to an increase in juvenile lobsters. However, as for previous surveys, legal lobsters occurred at very low densities in non-reserve areas (<0.5 lobsters per 500 m2), indicative of fishing-related effects.
The high abundance of, and increase in, legal-sized lobsters in 2007 relative to 2006 suggests that the steady on-growth of sub-legal lobsters within the reserve population has now materialised to higher levels of legal lobsters, i.e., the dominant size-class in the reserve population in 2006 was between 70-90 mm CL, whereas the dominant size class in 2007 was between 100-120 mm CL.
Benthic
In 2006 benthic habitats were typical of those found within north-eastern New Zealand coastal areas, with algal assemblages more abundant and diverse within the reserve.
Reserve sites were generally dominated by mixed algal stands in shallow water < 8 m depth, with the laminarian alga Ecklonia radiate abundant at depths > 10 m depth. Two sites of special interest surveyed within the reserve had the highest diversity typified by Ecklonia radiate forest with diverse understoreys of sponge, ascidian and bryozoan assemblages.
Non-reserve sites were dominated by shallow Carpophyllum habitat and urchin barrens < 8 m depth and Ecklonia radiate forest > 10 m depth. The non-reserve site with the highest diversity was comprised of patches of Ecklonia radiate with a diverse understorey of encrusting sponges and ascidians.
Barrens habitat, associated with high urchin (Evechinus chloroticus) densities had the lowest diversity of all habitats surveyed. At several sites within the reserve typified by high lobster abundance, densities of the urchin Evechinus chloroticus were low, with the opposite being apparent at several non-reserve sites.
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