Size spectrum models are representations of ecological communities of individuals which grow and change trophic levels. They provide a powerful tool for predicting abundance and biomass for marine ecosystems, and are particularly useful in data-poor situations, as they draw upon well-established theory regarding how individual processes scale with body size. A key emergent feature of such a representation by size and trophic levels is a decreasing trend in abundance, i.e., the size spectrum. Dynamic size spectrum models can be implemented either under the form of community model, where individuals are only characterized by their size; the trait-based model, where individuals are further characterized by their asymptotic size; and the multispecies model where additional trait differences are resolved.  Multispecies and multi-fleet fisheries scenarios can be explicitly represented and model outputs can be used to estimate standard fisheries and conservation reference points and indicators [Blanchard et al. 2014].

conceptual diagram showing the goal of modeling the size spectrum from zooplankton to marine mammals (Univ. Tasmania)

Implementations of size spectrum models are being developed for East Antarctica. Specifically, northern and southern models are being implemented for the Kerguelen Axis (Prydz Bay and southern Kerguelen Plateau). The Kerguelen Axis region is the most important location for primary production in East Antarctica, supports high value toothfish and icefish fisheries (on the northern Kerguelen Plateau), and is an important foraging area for marine mammals and birds.

The East Antarctic implementations of size spectrum models are being developed including 20 fish and 3 squid groups that encompass the key mesopelagic taxa in the region, and models explicitly representing higher and lower trophic levels (seabirds and marine mammals, and zooplankton respectively) are also under development. Migratory behaviour of mesopelagic taxa is being represented through an interaction matrix that constrains predator-prey interactions based on the degree of spatio-temporal overlap between groups. Models will also include explicit representation of toothfish fisheries.

The models’ domain for this region is congruent with the Atlantis and an Ecopath with Ecosim model also under development by MESOPP partners, which will allow model intercomparison to address model uncertainty.

More on size spectrum modeling:

  • Blanchard, J. L., Andersen, K. H., Scott, F., Hintzen, N. T., Piet, G., & Jennings, S. (2014). Evaluating targets and trade‐offs among fisheries and conservation objectives using a multispecies size spectrum model. Journal of Applied Ecology, 51(3), 612–622.
  • Blanchard, J. L., Heneghan, R. F., Everett, J. D., Trebilco, R., & Richardson, A. J. (2017). From Bacteria to Whales: Using Functional Size Spectra to Model Marine Ecosystems. Trends in Ecology & Evolution.
  • Scott, F., Blanchard, J. L., & Andersen, K. H. (2014). mizer: an R package for multispecies, trait-based and community size spectrum ecological modelling. Methods in Ecology and Evolution, 5(10), 1121–1125.