Territory Stories

The Darwin Dolphin Monitoring Program : Abundance, Apparent Survival, Movements and Habitat Use of Humpback, Bottlenose and Snubfin Dolphins in the Darwin Area.

Details:

Title

The Darwin Dolphin Monitoring Program : Abundance, Apparent Survival, Movements and Habitat Use of Humpback, Bottlenose and Snubfin Dolphins in the Darwin Area.

Creator

Brooks, Lyndon; Pollock, Kenneth; Northern Territory. Department of Land Resource Management

Collection

E-Publications; E-Books; PublicationNT

Date

2015-10-28

Description

This report presents the results of a coastal dolphin monitoring program for the Ichthys LNG Project (the Project) in Darwin Harbour. The monitoring program comprised a capture-recapture study and a spatial habitat use study on humpback, bottlenose and snubfin dolphins in Darwin Harbour and two adjacent sites, Bynoe Harbour to the west and Shoal Bay to the east (the sample area). Data were collected over a period of three and a half years (October 2011 to April 2015) in a systematic and intensive sampling program consisting of eight twice-yearly sampling sessions (dry and wet season samples), each of approximately three weeks duration (primary samples). The capture-recapture study, based on photographic identification of individuals, yielded estimates of abundance, apparent survival and movements by site and over time. The spatial habitat use study, based on group detections, yielded estimates of variation in use of the sample area in terms of locations and over time.

Notes

Made available via the Publications (Legal Deposit) Act 2004 (NT)

Language

English

Subject

Dolphins -- Northern Territory -- Ecology; Biodiversity conservation -- Northern Territory

Publisher name

Northern Territory Government

Place of publication

Palmerston

Format

iv, 51 pages : colour map ; 30 cm.

File type

application/pdf

ISBN

9781743501023

Use

Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government

License

https://creativecommons.org/licenses/by/4.0/

Parent handle

https://hdl.handle.net/10070/262099

Citation address

https://hdl.handle.net/10070/484684

Page content

The Darwin Dolphin Monitoring Program 23 RESULTS SUMMARY The seasonal patterns differed among the sites, with greater apparent survival following wet than dry seasons in Darwin Harbour and Shoal Bay but the opposite pattern in Bynoe Harbour with greater apparent survival there following dry than wet seasons. The wet to dry season estimate in Shoal Bay was very high with a very small standard error which often indicates a confounded estimate. There is no apparent reason however why this estimate should be confounded. All humpback dolphins captured in Shoal Bay in the wet season primary samples two and four and all but one of 18 captured in wet season primary sample six were subsequently recaptured there indicating that the estimate of close to 100% apparent survival is reasonable. Overall, the apparent survival estimates were on average greater in Darwin Harbour than the other two sites, with the seasonal contrast being strongest in Shoal Bay. The apparent survival estimate for wet to dry seasons in Darwin Harbour was 0.98, at the upper limit of what biological survival might be expected to be and indicating no permanent emigration of humpback dolphins from Darwin Harbour of dolphins present there in a wet season. If an annual biological survival rate of 0.98 is assumed to be constant, approximately 15% of humpback dolphins that were present in Darwin Harbour during a dry season were estimated to permanently emigrate prior to the following wet season. Applying this estimate of biological survival to Bynoe Harbour and Shoal Bay, approximately 18% of humpback dolphins present in Bynoe Harbour during a dry season and 30% of those present during a wet season are estimated to emigrate permanently, while approximately 53% of dolphins present in Shoal Bay in a dry season are estimated to emigrate permanently. While about 9% were estimated to have moved in both directions between Bynoe Harbour and Darwin Harbour in a typical interval between primary samples, the estimated rates of movement to and from Shoal Bay were very small (at most 1% per interval). These are relatively small populations and the confidence intervals around the apparent survival (S) and transition parameters () were quite wide, indicating caution against over-interpretation. The estimated number of humpback dolphins present on the three sites during the eight primary samples is plotted in Figure 4.


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