Assessing depth specific distribution and relative abundance of gold clam and kākahi at Lakes Maraetai and Karaapiro.
Survey sites
The survey was conducted from 5 to 15 May 2025. Multiple sites were surveyed in Lakes Maraetai and Karaapiro as part of the programme aim to assess changes in population structure and spatial spread over time.
SCUBA dive surveys were conducted at six standard depths using quadrats to measure and collect data. Gold clam (Corbicula fluminea), kaakahi (Echyridella menziesii), and native pea clam (Sphaeriidae) within quadrats were measured, counted, and collected.
- Population Counts: Total counts for clams were recorded for Lake Maraetai and Lake Karaapiro.
- Trends: Preliminary trends in total count and depth distribution were assessed.
Preliminary results – May 2025
Lake Maraetai total counts by site
Corbicula were widespread and dominant at most Maraetai sites, especially at the Boat Ramp and at the most upstream site. Kaakahi populations were patchy but very abundant at the upstream site.
Lake Karaapiro total counts by site (does not include Moana roa and Waipuke park)
Corbicula was dominant at Horahora and Bobs Landing, while Kaakahi are more evenly spread but at lower densities. Little Waipa stands out with very low invasive clam presence but still a moderate kaakahi population. Bobs Landing had much lower total counts than anticipated.
Preliminary depth distribution
Note differences in total counts between clams and kaakahi. Corbicula populations were associated with deeper waters, with high numbers and greater spread at 12–15 m. The consistent pattern of higher density and variability at greater depths, likely due to habitat preference or environmental stability in deeper water. Kaakahi were distributed across the depth range, with higher counts at mid to deep depths. However, the peak at 12 m was driven largely by a single outlier: the upstream site in Lake Maraetai, which had 134 individuals at 12 m—the highest Kaakahi count recorded in the entire 2025 survey.
This survey will be repeated in 2026 and 2027 to understand how the abundance of clams and kaakahi at these different sites changes over time.
Field team
NIWA Research team: Michele Melchior, Dave Bremner, Aleki Taumoepeau, Constantin Dransman, Svenja David, Ollie El-Gamel, Rachel Burbach, Elizabeth Graham, Mashanta Monsin, Joepette Hermosilla, Karen Thompson, Maddy Brennan.
Raukawa: Mark Ruka, Charlie Tiare.
Ngaati Koroki Kahukura: Poto Davies, Merekara Warrington.
Project contact: Michele Melchoir.
