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Novel methods for quantifying movement behavior of free-ranging fish from telemetry data


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Stehfest, KM 2013 , 'Novel methods for quantifying movement behavior of free-ranging fish from telemetry data', PhD thesis, University of Tasmania.

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In recent decades, technological progress in the field of biotelemetry has allowed the collection
of vast amounts of data on the movement of free-ranging marine animals and recently there
have been great advances in analysing data from tags that allow the observation of complete
animal tracks. One of the most common and low-cost tools for tracking marine animals,
however, are automated acoustic arrays, which often do not record complete tracks but
provide presence/absence data for tagged animals at fixed locations. The development of
quantitative methods for analysing these data has lagged behind the technological advances in
the field.
This thesis applies novel methods for quantifying the movement behaviour of highly mobile
free-ranging teleosts and elamsobranchs using automated acoustic tracking data and answers
ecological questions of management relevance for tropical tuna (Yellowfin tuna Thunnus
albacares) and a temperate shark species (Broadnose sevengill shark Notorynchus cepedianus).
Additionally, pop-up satellite archival tag (PSAT) data are analysed for the temperate shark
species, to put the findings of the acoustic tracking data analysis into the context of the
animals’ large-scale movement behaviour.
The two acoustic datasets represent two different types of common receiver array designs: For
the tuna study, individual receivers were deployed at ecologically significant locations (fish
aggregating devices, FADs) to determine the residency at and movement between these locations. For the shark study, receivers were deployed as multiple curtains between opposite
shorelines to detect passes of animals through the curtains and determine general movement
patterns within a coastal area.
Network analysis methods were applied to both datasets to quantify the co-occurrence of
individuals at a given location and to determine the relative importance of each location to the
animals. For the former, we adapted association indices from social network analysis to
quantify temporally explicit joint occurrences of individuals. For the latter we treated the
number of transitions between locations as a measure of the connectivity between them. The
network analysis approach to the acoustic tracking data was well suited to the type of array
used in the tuna study and was a considerable improvement over traditional measures of cooccurrence
which often only include either the spatial or the temporal dimension, not both. It
provided new insight into the temporal dynamics of tuna aggregations at FADs and how they
may be linked to between-FAD movement. We observed large interannual variation in
movement rates of tuna between FADs, and corresponding interannual variability in the mean
number of spatio-temporal associates for each individual as well as the temporal stability of
associations. When movement rates were high, associations within FAD aggregations decayed
to randomness three times faster than when movement rates were lower. This raises the
possibility that if FADs are sufficiently close for fish to perform frequent between-FAD
movements, school mixing may be increased and cohesion reduced. For the shark data, we compared results from the network analysis to a Markovian movement
model estimated from counts of observed transitions. Specifically, we tested the suitability of
the two methods for determining whether the differences in large-scale movement behaviour
between males and females we established from the PSAT data are mirrored in their space-use
during their coastal summer residency. Both spatial network analysis and Markov chain analysis
showed differences in space-use between male and female broadnose sevengill sharks,
however, rankings of the relative importance of geographic areas differed between the two
approaches. This indicated that not only transitions but also residency periods, which are not
accounted for by spatial network analysis, were important for identifying priority areas for the
Determining how animals interact and move within their environment has been a relatively
understudied area, lacking in quantitative analytical methods. This thesis has applied various
novel approaches which quantify both how individuals interact and use space, deepening our
understanding of the two and the link between them.

Item Type: Thesis - PhD
Authors/Creators:Stehfest, KM
Keywords: movement, acoustic tracking, shark, tuna
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