Shellfish and Habitat Mapping: Coromandel Estuaries

The Waikato Regional Council has conducted shellfish and benthic habitat mapping in the Otahu, Tairua and Wharekawa estuaries. The Department of Conservation has previously conducted similar surveys in Kawhia and Aotea Harbours. The methodologies used by the Waikato Regional Council are adapted from these Department of Conservation surveys. The primary objective of this project was to quantify the distribution and abundance of three species of bivalve (Austrovenus stutchburyi; the New Zealand cockle, Paphies australis; the pipi and Macomona liliana; the wedge shell) and three gastropod taxa (Diloma spp., Zeacumantus spp., Cominella spp.) that are abundant in many Waikato estuaries. A secondary objective was to conduct broad scale habitat mapping to determine the distribution of different types of surface sediment within the estuaries. Purpose: This project aimed to gather baseline information on the distribution and abundance of three species of shellfish in Tairua, Wharekawa and Otahu Estuaries: the cockle (Austrovenus stutchburyi), the pipi (Paphies australis) and the wedge shell (Macomona liliana). The distributions of estuary sediment types, estuarine vegetation and sediment trace elements and organic compounds were also mapped (Felsing & Giles, 2011).

Samples were collected from 275 sites in Tairua Estuary. 82 sites in Otahu Estuary and 160 sites at Wharekawa Estuary. Shellfish were counted and categorised into size classes. Some classification of sediment characteristics and vegetation type is also recorded. Grain size analysis was undertaken at approximately half of the sites. Trace elements and organic compounds are also analysed.

Wharekawa, Tairua and Otahu Estuaries

Wharekawa: February-March 2010 Tairua: November 2009 and March 2010 Otahu Estuary between January and June 2009

The Wharekawa and Tairua surveys sampled over an imaginary 150 m grid throughout the estuaries. The Otahu survey sampled (55 sites) at 20 m intervals on transects at 100 m spacing (perpendicular to the shoreline). Benthic sampling was conducted at a further 29 sites (June 2009) spaced irregularly throughout the upper estuary. In all estuaries, information at each sampling site recorded, including: surface sediment characteristics (subjective substrate categories), counts and size class classification of Austrovenus, Paphies, and Macomona, counts of epifaunal organisms, fringing and intertidal vegetation, including macro and micro-algae, the approximate depth of redox potential discontinuity (RPD) layer (RPD depth is an indication of sediment oxygenation). Sediment samples were collected at random sites for grain size analysis. At each sampling location the surface sediment was described using the qualitative substrate classification of Robertson & Peters (2006)Sediment grain size samples analysed with Malvern 2000 mastersizer. In Tairua, a selection of sediment samples were also examined for the presence of contaminants. Of the 275 samples collected in the estuary, 65 were selected and composited into 22 samples for analysis (Figure 2). Seven additional sites in the upper estuary and Tairua River were sampled in August 2010. Sampling sites and composite samples were chosen to represent areas of special interest or public concern and provide a good spread throughout the estuary. Sediment samples were analysed by Hill Laboratories, Hamilton, for total organic carbon (TOC), thirteen trace elements (antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, thallium, zinc), organochlorine pesticides (organochlorines), pentachlorophenol, tributyl tin and polycyclic aromatic hydrocarbons (PAHs). Frequency of collection: One-off

Some modifications to the sampling could be done to ensure maximum value for effort. These include improvements of the substrate classification system, sampling the edges of subtidal channels and determining shellfish biomass.

Data recorded within written reports and held by the Regional Council. Reports available from Regional Council.

No confidentiality issues. Data available from the Waikato Regional Council. Sensitivity/Confidentiality: None

Data collection complete.