ppo2012-08 pitt island shag foraging ecology · 2018-05-25 · pop2012-08 pitt is. shag foraging...

MIKE BELL

Wildlife Management International Limited, PO Box 607, Blenheim 7240, New Zealand

[email protected]

PPO2012-08 Pitt Island Shag foraging ecology

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.


• 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

Pitt Island shag


• 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

Methods


• 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

Results


• 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

Results – foraging behaviour


Results – foraging range Pt Munning and Te Whakuru


Results – foraging range Waitangi


• 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

Results – foraging behaviour


• Dive data from 10 of the 17 TDR devices recovered

• 39 full foraging trips, 4 partial trips

• 6709 dives

Results – diving behaviour


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Results – data recovered

16:58 30 Sep 2013 18:04

A12, Female breeding at Point Munning Foraging trip to Okawa Point


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16:58 30 Sep 2013 18:04

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Dive duration

Rest period

Dive depth


Results – dive depth

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Fre

qu

en

cy (

%)

Dive depth (m)

• Mean dive depth 6.6m; max 24.4m; 90% of dives <13m

• No difference between the sexes


Results – dive duration

• Mean dive duration 22s, max 69s, most dives <40s

• No difference between the sexes

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<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

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qu

en

cy (

%)

Dive duration (s)


Results – dive duration and depth

• Strong relationship between dive duration and depth

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25

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Div

e d

ep

th (

m)

Dive duration (s)


Results – rest period

• Mean rest period 19s, no difference between the sexes

• weak relationship between dive duration and rest period

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Rest

peri

od

(s)

Dive duration (s)


Results – Daily foraging timing

• All dives during daylight, with no clear daily pattern

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Dive start time


Results – Foraging efficiency

• Birds spent an average of 50% of foraging time underwater per trip (41-70%)

• No regional or sex difference

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<10 11-20 21-30 31-40 41-50 51-60 61-70 71-80

Fre

qu

en

cy (

%)

Time underwater (%)


Foraging

trips

Mean

trip

duration

Mean

dives/

trip

Mean

dive

duration

(s)

Mean rest

period (s)

Mean

depth

(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

Results – Foraging area comparison

• Linked GPS and TDR data – 39 foraging trips

• Some difference in foraging parameters from different areas


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


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


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


Recommendations

• Undertake a ecological studies

• Breeding biology

• Breeding success and causes of failure

• Focusing on possible causes of population decline


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.

Acknowledgements

ppo2012-08 pitt island shag foraging ecology · 2018-05-25 · pop2012-08 pitt is. shag foraging...

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