Preprint volume - SIBM

Pre-print Volume –Posters
Topic 4: THE ELASMOBRANCHS
N. HUMPHRIES, D.W. SIMS
Marine Biological Association of the United Kingdom, The laboratory, Citadel Hill Plymouth PL1 2PB, England.
nicmph@mba.ac.uk
HUNTING FOR PREY IN THE OPEN OCEAN:
SEARCH PATTERNS OF MARINE PREDATORS
LA CACCIA DELLA PREDA NELL'OCEANO APERTO:
I MODELLI DI RICERCA DEI PREDATORI MARINI
Abstract – An optimal search theory known as the Lévy flight foraging hypothesis predicts predators should
adopt search strategies known as Lévy flights where prey is sparse and distributed unpredictably.
Empirical studies have generated controversy because less accurate methods have been used to identify
Lévy behaviour; consequently whether foragers exhibit Lévy flights in the wild remains unclear. We present
results from a study using robust statistical methods to test for Lévy flight behaviour from the largest
dataset of animal movements assembled for this purpose from 19 species of open-ocean predator.
Key-words: Lévy flight, searching, marine predators.
Introduction – When searching for sparsely and unpredictably located prey a
specialised random walk known as a Lévy flight has been shown in theoretical studies
to be the most efficient movement pattern (Viswanathan et al., 2008). A Lévy flight
has move step lengths drawn from a power law distribution where the probability of a
step of length l is defined by P(l)~l -μ , with 113 million move steps. Animals were
tagged in the NE Atlantic and N Pacific in a range of coastal and off-shore habitats.
Time series of vertical move displacements were analysed by using rank-frequency
plots to test goodness of fit and maximum likelihood estimation (Clauset et al., 2009)
to derive exponents. Movement patterns with Lévy characteristics have exponents (μ)
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
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