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Modelling the population dynamics of a benthic octopus species: exploring the potential impact of environment variation and climate change

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André, J (2009) Modelling the population dynamics of a benthic octopus species: exploring the potential impact of environment variation and climate change. PhD thesis, University of Tasmania.

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Abstract

Cephalopods are increasingly targeted by fisheries, yet their population
dynamics are generally poorly understood due to their intrinsically complex
nature and their great sensitivity to environmental factors. As a consequence,
population structure and biomass can change rapidly over short time-scales,
with currently no means of predicting future recruitment or the consequences
of climate change on these species. The aim of this study was therefore to
develop a mechanistic model to predict the population dynamics and the
potential impact of environmental variability and climate change on a
cephalopod species.
The benthic octopus Octopus pallidus was the main focus of this research and
laboratory rearing of juveniles allowed the relationships between early
growth and the significant factors affecting growth to be examined (i.e. food
intake, food conversion and fluctuating environmental temperatures). Results
indicated high intra- and inter-individual variability in feeding rates,
conversion rates and growth rates, with no indication of periodicity for any of
the variables. Based on the concept that growth is bi-phasic (a rapid
exponential growth phase followed by a second slower growth phase) and
using results from captive studies on O. pallidus and Octopus ocellatus, a
temperature-dependent bioenergetic model describing growth in octopus
was developed. Model projections were consistent with laboratory data and
sensitivity analyses suggested that metabolic rate has the greatest influence on the growth threshold at which the switch from fast to slower growth
occurs. In order to simulate juvenile growth trajectories in the wild, the
bioenergetic model was further developed to include dynamic seasonal
temperatures and individual variability in growth and hatching size. Results
indicated that hatching size was secondary to inherent variation in growth
rates in explaining size-at-age-differences, and that size-at-age distributions
in some cohorts tended to become bimodal under certain food intake levels.
Predictions from the individual-based bioenergetic models were integrated
into a matrix population model, which was used to project the population
under the predicted temperature conditions generated by the
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
from the emission scenarios of the Intergovernmental Panel for Climate
Change (IPCC). Simulations suggested that increasing water temperatures
might not be as beneficial to octopus as previously thought. Survivorship and
incubation time were found to drive the population dynamics and while O.
pallidus has the potential to survive under climate change conditions, the
population structure and dynamics are likely to change substantially with a
potential decrease in average generation time, a streamlining of the life cycle,
and a possible loss of resilience to catastrophic events.
Mechanistic models relating cephalopod biology to the environment, like
the one presented in this thesis, constitute a valuable way forward to
elucidate population dynamics in these highly plastic animals.

Item Type: Thesis (PhD)
Additional Information:

© 2009 the author

Date Deposited: 04 Aug 2010 04:39
Last Modified: 11 Mar 2016 05:53
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