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Exploring biases in estimating survival probability of marine resources from mark-recapture analyses : a case study with the southern rock lobster Jasus edwardsii

Kordjazi, Z (2015) Exploring biases in estimating survival probability of marine resources from mark-recapture analyses : a case study with the southern rock lobster Jasus edwardsii. PhD thesis, University of Tasmania.

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Capture-mark-recapture (CMR) modelling is commonly used for direct estimation of demographic
parameters in the wild. Whilst it is well known that the precision of estimated parameters in CMR
studies increases with sample size, duration of study and the number of recapture events there are
few studies that explore the design of CMR projects to achieve optimal outcomes. Research funding
and time allocation are two constraints that place restrictions on the research design. This study
addresses this challenge and seeks to demonstrate issues that need to be addressed and ways to
design CMR that minimise costs while still providing the precision and accuracy required for
assessment of marine resources.
A twelve year tagging data set for Jasus edwardsii at a non-fishing site (Crayfish Point Scientific
Reserve, Tasmania, Australia) was used in the study. Cormack-Jolly-Seber (CJS) modelling was
used to compare estimates of survival probability with increasing numbers of surveys from 3 to 12
for both equal (annual) and unequal survey intervals.
The study found that more surveys were required to obtain precise estimates of survival probability
in females than in males, and the number of surveys required increased when intervals between
surveys were unequal. For annual surveys, stable estimates of survival probability generally
required at least five years, which is often beyond the three-year duration commonly used in
scientific studies.
Five annual surveys were used to determine the effect of sample size and fishing effort (the number
of traps set per day and days fished) on the precision of estimated survival probability. Larger
sample sizes (>=500) and more sampling effort were required to determine sex specific survival
probability estimates.
Tag induced mortality (TIM) and tag loss reduce the number of tagged lobsters in the population
and result in an under-estimation of survival probability. TIM is often investigated in aquaria
studies with small sample sizes and over short time periods. In this study, a model based on three
annual-surveys was used to provide in-situ estimates of TIM proportion. Estimates of TIM
proportion were high and varied being on average between 25% and 40%. Capturing sufficient
lobsters during the third survey that were tagged in the first survey and also seen in the second
survey was a major limitation in using this method.
Tag loss is usually estimated by double tagging in the wild. This study investigated the fate of new
tags and existing ( old) tags applied to lobsters. Estimated tag loss rate was different between males
and females and the annual rate of tag loss was similar between years during the two year study
indicating that tag loss is chronic and needs to be accounted for throughout the entire period of
mark-recapture programs. In general, older tags were lost at a slightly higher rate than new tags.
The design of mark-recapture programs will be dependent on the species under study and although
these results are specific for J edwardsii, the issues considered and methods used in this thesis
should assist researchers in the design of tagging surveys. Importantly, both tag loss and tag
induced mortality can be of a magnitude that impacts estimates from mark recapture studies and the
thesis demonstrates issues to be considered in designing a tagging program that meets the objectives
of the study and also enables estimation of issues such as tag loss rate and TIM proportion which
can bias survival probability and population estimates.

Item Type: Thesis (PhD)
Keywords: Capture-mark-recapture (CMR), Cormack-Jolly-Seber (CJS) model, annual survival probability, sample size, Effort, tag induced mortality, tag loss, lobster
Copyright Information:

Copyright 2015 the Author

Date Deposited: 21 Nov 2016 23:06
Last Modified: 21 Nov 2016 23:18
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