Global patterns and trends of tuna isotopes

Stable carbon and nitrogen isotope analysis is a common tool to estimate trophic position and examine habitat patterns of a range of coastal and marine predators, but due to the extensive oceanic habitat and logistics required to conduct wide-scale sampling, global comparisons have been limited to date. The CLIOTOP 2016-01 ‘Tuna Isotopes’ Task Team recently convened two workshops in Hobart, Australia to draft two scientific papers. 

At each workshop, key results were interpreted and selected based on a global isotope analysis of a dataset of 4281 tuna isotope values previously compiled by the task team (formerly WG3; Young et al. 2015). Generalized Additive Mixed Models were used to explore the influence of spatial, biological and environmental variables on the tuna isotope values. Model predictions were then overlaid on a world map to show the global spatial distribution of isotope values of tuna (Figure 1). Additional approaches were applied to examine differences between regional isotope gradients of tuna to model-derived baseline isoscapes. These differences were used to identify regions of high and low movement. Complementary time-series analyses were also performed to explore potential temporal trends in the dataset.

Figure 1. Global isoscapes of model predicted stable (a) carbon and (b) nitrogen isotope values in tunas.

High impact publications are anticipated in the near future as a result of these workshops, which were also attended by other local CLIOTOP scientists (Jock Young, Alistair Hobday, Clothilde Langlais and Karen Evans) and provided useful input. This workshop recognized the value of international collaboration to bring disparate datasets together to look at large-scale ecological patterns that are relevant to fisheries and ecosystem based management, especially in times of a changing climate. We thank IMBER and CSIRO for sponsoring these writing workshops.

Reference: Young, J.W., R.J. Olson, F. Menard, P.M. Kuhnert, L.M. Duffy, V. Allain, J.M. Logan, A. Lorrain, C.J. Somes, B. Graham, N. Goni, H. Pethybridge, M. Simier, M. Potier, E. Romanov, D. Pagendam, C. Hannides, C.A. Choy (2014). Setting the stage for a global-scale trophic analysis of marine top predators: a multi-workshop review. Rev. Fish Biol. Fisheries. DOI 10.1007/s11160-014-9368-4