MCSPOP Chatham Island and Pitt Island shag census 2011

Transcription

1 MCSPOP10-02 Chatham Island and Pitt Island shag census 11 Igor Debski 1, Mike Bell 2 & Dan Palmer 1 1. Science & Technical, Department of Conservation 2. Wildlife Management International Limited

2 Objectives (a) conduct a complete recensus of Chatham Island and Pitt Island shags in such a way as to maximise comparability with earlier counts in order to determine any trend in population size; and (b) investigate the effects of timing and methodology on colony counts, and make recommendations for future monitoring of the populations of Chatham Island and Pitt Island shags.

3 Chatham Island shag Pitt Island shag

4 Methods Followed the methods of Bell & Bell (00) as closely as feasible in order to maximise the comparability with 1997/98 Counted breeding pairs Timed counts at incubation when maximum counts would be made Extensive survey of all coast line suitable for shag nesting sites was conducted on 11 consecutive days, from 1 to 11 October 11 (except 3 outlying islands) Additional counts at sites where temporal variation known to be important On foot and by boat Also report results from a series of visits to breeding sites around main Chatham Island

5 Map of Chatham Islands showing census search effort

6 Example GPS plot of on foot search

7 Example GPS plot of boat search

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11 Results Chatham Island shag breeding colonies

12 Pitt Island shag breeding areas

13 Chatham Island shag Cape Fournier Cape Pattisson Incidentals Matarakau Motuhinahina Island Ngatikitiki Rocks Number of nests Okawa Point Okawa Point b Okawa Point a Okawa Point c Okawa Point d Point Weeding Point Weeding b Wharekauri Island JanFebMar AprMayJun Jul AugSepOct NovDec JanFebMarAprMayJun Jul AugSepOctNovDec Month Monthly counts for Chatham Island shags

14 Pitt Island shag Cape Fournier Cape Pattisson Incidentals Little Awatotara Creek Matarakau Motuhinahina Island Number of nests Okawa Point Okawa Point b Okawa Point 4 Okawa Point c Okawa Point d Point Weeding Point Weeding b Wharekauri Island Jan Mar AprMay Jun Jul Aug Sep Oct NovDec Jan Mar AprMay Jun Jul AugSep Oct NovDec Month Monthly counts for Pitt Island shags

15 Colony Number of nests Overall change 1997/98 03/04 11 Matarakau Kaingaroa Okawa Point Cape Fournier The Pinnacles Ke Orea Point Waitangi Cape Pattison Ngatikitiki Cape Young Motuhinahina Chatham Island total % decline Motutapu Point Kokepa Rock Rabbit Island North-eastern Reef Star Keys Pitt Island and surrounding islands total % decline Total % decline Chatham Island shag census results

16 Comparative breeding area Number of nests Overall change 1997/98 03/04 11 Matarakau Kaingaroa to Te Wakaru Island Okawa Point Owenga-Ko Orea Point SW Coast Waitangi Red Bluff Port Hutt Bays Port Hutt Point Somes South Point Somes North Ngatikitiki Rocks Cape Young Motuhinahina Chatham Island total % decline Pitt Island North Pitt Island East Pitt Island South Pitt Island West Pitt Island total % decline Rabbit Island Mangere incl. Little Mangere Castle Rangatira Star Keys Pitt Island and surrounding islands total % decline 1997/98-11 comparative subtotal % decline Fourty Fours Sisters Western Reef Total Pitt Island shag census results

17 Conclusions Results represent a real declines in the populations, with no information to suggest such substantial numbers of breeding pairs may have been missed in 11. Greatest declines in population for both species at Pitt Island and offlying islands, including protected, predatorfree sites. Declines likely to be driven by at-sea factors, but lack of information on causal mechanisms.

18 Recommendations Future survey methods: Counts should be timed to coincide with incubation at all colonies/breeding areas, recognising temporal variability. Boat/on foot methods should be standardised for any one area. Aerial photography is likely to be well suited for Chatham Island shags and should be trialled alongside ground counts.

19 Understanding causal factors: Describe the nature and extent of direct fishing impacts (see INT11-02). Quantify demographic parameters and identify which are leading to the decline. Describe the at-sea foraging habits (see proposed POP12-08). Quantify diet (see proposed POP12-08). Compare studies of the elements listed above between sites where colony trends differ (e.g. Motuhinahina vs Pitt Island area)