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 19 Figure 3 Humpback dolphin: Estimated total number of dolphins present in each primary sample with 95% confidence interval (CRD model all sites combined) RESULTS SUMMARY The estimates for apparent survival display a mixture of seasonal and fully time-varying patterns. If biological survival is assumed to be constant, humpback dolphins present in a dry season are more likely to permanently emigrate than those present in a wet season. The mean seasonal estimates are 0.70 for dry to wet season intervals and 0.92 for wet to dry season intervals. If a biological survival rate of 0.975 is assumed, while there is very little permanent emigration for humpback dolphins present in a wet season (about 6%), the rate of permanent emigration for dolphins present in a dry season is substantial (about 30%). Perhaps the main driver of the fully time-varying pattern was the higher rate of apparent survival (lower rate of permanent emigration) in the dry to wet season interval between primary samples five and six. In contrast to the apparent survival pattern, humpback dolphins present in a dry season were less likely to emigrate temporarily during the following wet season than dolphins present in a wet season were to temporarily emigrate during the following dry season. Humpback dolphins temporarily absent in a wet season were more likely to stay away in the following dry season than dolphins absent in a dry season were to stay away in the following wet season. Taken together, the estimates for temporary emigrating and of staying away indicate that a higher proportion of humpback dolphins were temporarily absent from the sampling area in dry than wet seasons. Overall however, the confidence intervals on the temporary emigration parameters were quite wide and, although the seasonal pattern was well established by the AICc weights, the true sizes of the estimates are uncertain. 60 70 80 90 100 110 120 P1 P2 P3 P4 P5 P6 P7 P8 U95%CI L95%CI Estimate


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