PPO2012-08 Pitt Island Shag foraging ecology MIKE BELL Wildlife Management International Limited, PO Box 607, Blenheim 7240, New Zealand mike@wmil.co.nz Presentation of draft final results to the Department of Conservation CSP Technical Working Group 1 August 2013
POP2012-08 Pitt Is. shag foraging ecology Specific Objectives Draft final results. Overall Objective To describe the foraging ecology of Pitt Island shags. Specific Objectives 1. To describe the spatial distribution and dive profiling of Pitt Island shag foraging behaviour at the Chatham Islands. 2. To describe the diet of Pitt Island shags at the Chatham Islands.
POP2012-08 Pitt Is. shag foraging ecology Pitt Island shag • Endemic to the Chatham Islands • Nationally endangered • High – Moderate risk from fishing • Significant population decline in last 15 years - 729 pairs in 1997, down to 434 in 2011 • Little known about ecology and breeding biology
POP2012-08 Pitt Is. shag foraging ecology Methods • GPS tracking • GPS devices attached to central back of birds • Time depth recorders (TDR’s) • TDR’s attached to plastic leg band • Birds captured at nest • Duel deployment (both GPS and TDR attached to each bird) • Birds need to be recaptured to recover devices and download data
POP2012-08 Pitt Is. shag foraging ecology Results • 27 birds caught and devices deployed • 17 birds re-caught and devices recovered • Birds not recovered due to nest failure, and hence birds no longer occupying nest sites- 9/10 Predation 1/10 chick death at hatching
POP2012-08 Pitt Is. shag foraging ecology Results – foraging behaviour • Foraging area data from 15 of the 17 GPS devices recovered • 79 individual foraging trips • Mean foraging distance 5.2km (range 0.4-18.2km) • No difference between NE and Waitangi birds • Observed difference between sexes, but unlikely to be a real difference as influenced by behaviour of one male
POP2012-08 Pitt Is. shag foraging ecology Results – foraging range Pt Munning and Te Whakuru
POP2012-08 Pitt Is. shag foraging ecology Results – foraging range Waitangi
POP2012-08 Pitt Is. shag foraging ecology Results – foraging behaviour • High forging site fidelity • Individual birds returning to the same areas to forage- 60% of birds feeding in one location only 33% in two locations 7% (one bird) in three locations
POP2012-08 Pitt Is. shag foraging ecology Results – diving behaviour • Dive data from 10 of the 17 TDR devices recovered • 39 full foraging trips, 4 partial trips • 6709 dives
POP2012-08 Pitt Is. shag foraging ecology Results – data recovered A12, Female breeding at Point Munning Foraging trip to Okawa Point 18 16 14 12 10 8 6 4 2 0 16:58 30 Sep 2013 18:04
10 12 14 16 18 0 2 4 6 8 Results – data recovered 16:58 POP2012-08 Pitt Is. shag foraging ecology 10 12 14 16 0 2 4 6 8 16:58:19 16:58:29 16:58:39 16:58:49 16:58:59 16:59:09 30 Sep 2013 16:59:19 16:59:29 16:59:39 16:59:49 16:59:59 17:00:09 17:00:19 17:00:29 17:00:39 17:00:49 17:00:59 17:01:09 17:01:19 17:01:29 17:01:39 17:01:49 17:01:59 17:02:09 17:02:19 17:02:29 17:02:39 17:02:49 17:02:59 18:04 17:03:09 17:03:19 17:03:29 17:03:39 17:03:49
Results – data recovered 10 12 14 16 0 2 4 6 8 16:58:19 16:58:29 POP2012-08 Pitt Is. shag foraging ecology 16:58:39 16:58:49 16:58:59 16:59:09 16:59:19 16:59:29 16:59:39 16:59:49 16:59:59 17:00:09 17:00:19 17:00:29 17:00:39 Rest period 17:00:49 17:00:59 17:01:09 17:01:19 17:01:29 17:01:39 17:01:49 17:01:59 Dive duration 17:02:09 17:02:19 17:02:29 17:02:39 17:02:49 17:02:59 17:03:09 17:03:19 17:03:29 17:03:39 17:03:49 Dive depth
POP2012-08 Pitt Is. shag foraging ecology Results – dive depth • Mean dive depth 6.6m; max 24.4m; 90% of dives <13m • No difference between the sexes 20.0 18.0 16.0 14.0 Frequency (%) 12.0 10.0 8.0 6.0 4.0 2.0 0.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Dive depth (m)
POP2012-08 Pitt Is. shag foraging ecology Results – dive duration • Mean dive duration 22s, max 69s, most dives <40s • No difference between the sexes 16.0 14.0 12.0 Frequency (%) 10.0 8.0 6.0 4.0 2.0 0.0 <5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60 61-65 66-70 Dive duration (s)
POP2012-08 Pitt Is. shag foraging ecology Results – dive duration and depth • Strong relationship between dive duration and depth 25 20 Dive depth (m) 15 10 5 0 0 10 20 30 40 50 60 70 Dive duration (s)
POP2012-08 Pitt Is. shag foraging ecology Results – rest period • Mean rest period 19s, no difference between the sexes • weak relationship between dive duration and rest period 60 50 40 Rest period (s) 30 20 10 0 0 10 20 30 40 50 60 70 Dive duration (s)
POP2012-08 Pitt Is. shag foraging ecology Results – Daily foraging timing • All dives during daylight, with no clear daily pattern 18.0 16.0 14.0 12.0 Frequency (%) 10.0 8.0 6.0 4.0 2.0 0.0 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 Dive start time
POP2012-08 Pitt Is. shag foraging ecology Results – Foraging efficiency • Birds spent an average of 50% of foraging time underwater per trip (41-70%) • No regional or sex difference 40 35 30 Frequency (%) 25 20 15 10 5 0 <10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 Time underwater (%)
POP2012-08 Pitt Is. shag foraging ecology Results – Foraging area comparison • Linked GPS and TDR data – 39 foraging trips • Some difference in foraging parameters from different areas Mean dive Mean Mean Mean Foraging trip dives/ duration Mean rest depth % trips duration trip (s) period (s) (m) underwater Okawa Point 19 01:07:14 83 27.5 24.2 9.4 53.4 Te Whakuru I. 3 0:33:25 92 9.0 20.0 2.7 31.7 Waitangi 9 0:53:17 85 22.7 20.3 6.4 51.5 South Coast 3 1:26:03 115 26.3 23.0 8.0 54.1 Port Hutt Bays 5 01:44:52 133 25.2 21.8 6.7 54.7
POP2012-08 Pitt Is. shag foraging ecology Results – Estimating species foraging range Use foraging parameters to estimate foraging range • Foraging range 18km • Max dive 25m Possible to determine overlap with commercial rock lobster fishery
POP2012-08 Pitt Is. shag foraging ecology
POP2012-08 Pitt Is. shag foraging ecology Results – Overlap with commercial rock lobster fishery • Foraging range covers all coastal waters of the Chatham Islands. • However as 90% of dives <13m, most significant bycatch risk during January and February when pots set close to shore
POP2012-08 Pitt Is. shag foraging ecology Recommendations • Undertake further foraging studies – • Investigate regional differences in foraging behaviour and efficiency • Investigate foraging behaviour and efficiency during other stages of breeding (i.e. chick rearing) • Determine drivers in variable timing of breeding at different colonies
POP2012-08 Pitt Is. shag foraging ecology Recommendations • Undertake a ecological studies • Breeding biology • Breeding success and causes of failure • Focusing on possible causes of population decline
POP2012-08 Pitt Is. shag foraging ecology Acknowledgements Thanks to landowners in the Chatham Islands who allowed access across their property for us to undertake this research; in particular Bruce Tuanui, Jack Daymond, Jim Murrison, and Abe Neilson. WMIL staff Mark Fraser assisted in the field, and Kelvin Floyd produced the maps. This project was funded by the Department of Conservation’s Conservation Services Programme (www.doc.govt.nz/mcs ) project POP2012-08 (100% Crown funded). Additional funding was provided by Forest & Bird following a grant from The Mohamed bin Zayed Species Conservation Fund and we are grateful for this support.
Recommend
More recommend
