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 15 sample, secondary sample or both. In particular, capture probability varied interactively by primary and secondary sample or by primary sample only. Temporal variation for apparent survival and temporary emigration refers to the intervals between consecutive primary samples, while temporal variation in capture probability refers to the occasion. Consecutive seasonal intervals alternated between dry to wet and wet to dry seasons. MSCRD models included the above for each site with additional parameters for movement between sites. As for temporary emigration, these varied by primary sample, by season or constant over time. Movements between sites can only be estimated when movements were observed. For movements by primary sample, this means that estimates can be made only between the sites and for the intervals when movements were observed. Having not observed a movement does not mean that no movement occurred: these are small populations and an animal must have been captured in both sites in consecutive primary samples for its movement to have been observed. For movements by season, if a movement between a pair of sites was observed for one dry to wet or one wet to dry interval, estimates for all dry to wet or wet to dry intervals may be estimated by assuming they are the same for corresponding seasons: i.e., if movement was observed between a pair of sites for at least one seasonal interval, estimates may be made for all corresponding intervals. Similarly, for constant movement models, at least one movement between the pair of sites must have been observed. Movements between pairs of sites might also be assumed to be symmetric, with the same rate of flow in both directions. In that case, movements need to be observed only in one direction for the rate in both directions to be estimated. Consequently, it is possible to estimate symmetric flow between Shoal Bay and the other sites although no movements from Shoal Bay were observed. Where there were no observed movements to support estimates, the affected parameters were fixed to zero. It is unlikely that models with complex structures on movement parameters will be found to fit well as relatively few movements were observed. For the MSCRD models, capture probability varied by site, primary sample, secondary sample or combinations of these. In particular, models were fitted for capture probability varying interactively by site, primary sample and secondary sample or varying interactively by site and primary sample. With apparent survival, movement, temporary emigration, capture probability and abundance parameters on three sites over eight primary samples each with nine secondary samples there are a very large number of parameters to be estimated, even in reduced parameter models (i.e., not fully time varying on all parameters). Attempts to fit MSCRD models to the complete data caused catastrophic estimation problems with more complex models and generated estimates after up to 10 million iterations that were accompanied by warnings that numeric convergence was suspect. The complexity of the problem was greatly reduced by collapsing over the nine secondary samples on


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