An individual-based model of skipjack tuna (Katsuwonus pelamis) movement in the tropical Pacific ocean

Joe Scutt Phillips, Alex Sen Gupta, Inna Senina, Erik van Sebille, Michael Lange, Patrick Lehodey, John Hampton, Simon Nicol

    Research output: Contribution to journalArticle

    Abstract

    The distribution of marine species is often modeled using Eulerian approaches, in which changes to population density or abundance are calculated at fixed locations in space. Conversely, Lagrangian, or individual-based, models simulate the movement of individual particles moving in continuous space, with broader-scale patterns such as distribution being an emergent property of many, potentially adaptive, individuals. These models offer advantages in examining dynamics across spatiotemporal scales and making comparisons with observations from individual-scale data. Here, we introduce and describe such a model, the Individual-based Kinesis, Advection and Movement of Ocean ANimAls model (Ikamoana), which we use to replicate the movement processes of an existing Eulerian model for marine predators (the Spatial Ecosystem and Population Dynamics Model, SEAPODYM). Ikamoana simulates the movement of either individual or groups of animals by physical ocean currents, habitat-dependent stochastic movements (kinesis), and taxis movements representing active searching behaviours. Applying our model to Pacific skipjack tuna (Katsuwonus pelamis), we show that it accurately replicates the evolution of density distribution simulated by SEAPODYM with low time-mean error and a spatial correlation of density that exceeds 0.96 at all times. We demonstrate how the Lagrangian approach permits easy tracking of individuals’ trajectories for examining connectivity between different regions, and show how the model can provide independent estimates of transfer rates between commonly used assessment regions. In particular, we find that retention rates in most assessment regions are considerably smaller (up to a factor of 2) than those estimated by this population of skipjack's primary assessment model. Moreover, these rates are sensitive to ocean state (e.g. El Nino vs La Nina) and so assuming fixed transfer rates between regions may lead to spurious stock estimates. A novel feature of the Lagrangian approach is that individual schools can be tracked through time, and we demonstrate that movement between two assessment regions at broad temporal scales includes extended transits through other regions at finer-scales. Finally, we discuss the utility of this modeling framework for the management of marine reserves, designing effective monitoring programmes, and exploring hypotheses regarding the behaviour of hard-to-observe oceanic animals.

    LanguageEnglish
    Pages63-74
    Number of pages12
    JournalProgress in Oceanography
    Volume164
    DOIs
    StatePublished - 1 May 2018

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    Katsuwonus pelamis
    individual-based model
    Pacific Ocean
    ocean
    oceans
    ecosystem dynamics
    animal
    dynamic models
    population dynamics
    animal models
    advection
    searching behavior
    La Nina
    Eulerian analysis
    water currents
    ecosystems
    taxis
    El Nino
    marine park
    trajectories

    Cite this

    Scutt Phillips, J., Sen Gupta, A., Senina, I., van Sebille, E., Lange, M., Lehodey, P., ... Nicol, S. (2018). An individual-based model of skipjack tuna (Katsuwonus pelamis) movement in the tropical Pacific ocean. Progress in Oceanography, 164, 63-74. DOI: 10.1016/j.pocean.2018.04.007
    Scutt Phillips, Joe ; Sen Gupta, Alex ; Senina, Inna ; van Sebille, Erik ; Lange, Michael ; Lehodey, Patrick ; Hampton, John ; Nicol, Simon. / An individual-based model of skipjack tuna (Katsuwonus pelamis) movement in the tropical Pacific ocean. In: Progress in Oceanography. 2018 ; Vol. 164. pp. 63-74
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    abstract = "The distribution of marine species is often modeled using Eulerian approaches, in which changes to population density or abundance are calculated at fixed locations in space. Conversely, Lagrangian, or individual-based, models simulate the movement of individual particles moving in continuous space, with broader-scale patterns such as distribution being an emergent property of many, potentially adaptive, individuals. These models offer advantages in examining dynamics across spatiotemporal scales and making comparisons with observations from individual-scale data. Here, we introduce and describe such a model, the Individual-based Kinesis, Advection and Movement of Ocean ANimAls model (Ikamoana), which we use to replicate the movement processes of an existing Eulerian model for marine predators (the Spatial Ecosystem and Population Dynamics Model, SEAPODYM). Ikamoana simulates the movement of either individual or groups of animals by physical ocean currents, habitat-dependent stochastic movements (kinesis), and taxis movements representing active searching behaviours. Applying our model to Pacific skipjack tuna (Katsuwonus pelamis), we show that it accurately replicates the evolution of density distribution simulated by SEAPODYM with low time-mean error and a spatial correlation of density that exceeds 0.96 at all times. We demonstrate how the Lagrangian approach permits easy tracking of individuals’ trajectories for examining connectivity between different regions, and show how the model can provide independent estimates of transfer rates between commonly used assessment regions. In particular, we find that retention rates in most assessment regions are considerably smaller (up to a factor of 2) than those estimated by this population of skipjack's primary assessment model. Moreover, these rates are sensitive to ocean state (e.g. El Nino vs La Nina) and so assuming fixed transfer rates between regions may lead to spurious stock estimates. A novel feature of the Lagrangian approach is that individual schools can be tracked through time, and we demonstrate that movement between two assessment regions at broad temporal scales includes extended transits through other regions at finer-scales. Finally, we discuss the utility of this modeling framework for the management of marine reserves, designing effective monitoring programmes, and exploring hypotheses regarding the behaviour of hard-to-observe oceanic animals.",
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    Scutt Phillips, J, Sen Gupta, A, Senina, I, van Sebille, E, Lange, M, Lehodey, P, Hampton, J & Nicol, S 2018, 'An individual-based model of skipjack tuna (Katsuwonus pelamis) movement in the tropical Pacific ocean' Progress in Oceanography, vol. 164, pp. 63-74. DOI: 10.1016/j.pocean.2018.04.007

    An individual-based model of skipjack tuna (Katsuwonus pelamis) movement in the tropical Pacific ocean. / Scutt Phillips, Joe; Sen Gupta, Alex; Senina, Inna; van Sebille, Erik; Lange, Michael; Lehodey, Patrick; Hampton, John; Nicol, Simon.

    In: Progress in Oceanography, Vol. 164, 01.05.2018, p. 63-74.

    Research output: Contribution to journalArticle

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    AU - Scutt Phillips,Joe

    AU - Sen Gupta,Alex

    AU - Senina,Inna

    AU - van Sebille,Erik

    AU - Lange,Michael

    AU - Lehodey,Patrick

    AU - Hampton,John

    AU - Nicol,Simon

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    Scutt Phillips J, Sen Gupta A, Senina I, van Sebille E, Lange M, Lehodey P et al. An individual-based model of skipjack tuna (Katsuwonus pelamis) movement in the tropical Pacific ocean. Progress in Oceanography. 2018 May 1;164:63-74. Available from, DOI: 10.1016/j.pocean.2018.04.007