The impact of predation by South Island Pied Oystercatchers (Haematopusfinschi) on a protected shellfish, the toheroa (Paphies ventricosa), in northern NewZealand Journal Paper
- Author
- Rynkowski, L.; Bennion, M.; Browne, C.M.; Cockrem, J.F.; Ross, P.
- Year
- 2023
- Journal / Source
- Emu - Australian Ornithology
- Publisher / Organisation
- Taylor & Francis group
- Volume
- 123
- Number
- 2
- Pages
- 118-128
- Summary
- In northern New Zealand, there is speculation that predation by a recovering shorebird, the South Island Pied Oystercatcher (Haematopus finschi), has caused the continuing decline of an endemicsurf clam, the toheroa (Paphies ventricosa). Consequently, there have been requests by the publicfor these protected birds to be culled to protect and restore the toheroa. To better inform management and decision-making for these species we set out to understand the impact of oystercatcher predation on toheroa at Ripiro Beach in New Zealand. A study was conducted to establish the spatiotemporal overlap of toheroa and oystercatcher distributions, determine oystercatcher prey selection, and assess the impacts of oystercatcher predation on toheroa population size structure. Monthly surveys over a 12-month period indicated limited spatial over-lap between the two species, and that most toheroa beds on Ripiro Beach are not subjected to oystercatcher predation. In areas where oystercatchers and toheroa co-occurred, oystercatchers consumed a variety of prey including polychaetes, small and medium-sized toheroa and a non-threatened surf clam (P. subtriangulata). While oystercatchers do feed on toheroa (and may be capable of locally reducing abundance of small toheroa in a population), feeding on larger individuals (>50 mm in length) was not observed. These results suggest that culling of oyster-catchers would be of no benefit for the recovery of toheroa populations. It is likely that less obvious factors are impeding the recovery of toheroa in New Zealand. This study highlights the importance of understanding predator-prey interactions before implementing management actions such as lethal control.