Ontogenetic partial migration is associated with environmental drivers and influences fisheries interactions in a marine predator

James S E Lea,Lara L Sousa,Nicolas E Humphries,Bradley M Wetherbee,Choy Aming,Nuno Queiroz,Neil Burnie,Guy M Harvey,Mahmood S Shivji,David W Sims,James Watson

doi:10.1093/icesjms/fsx238

Abstract

Abstract The ability to predict animal movement based on environmental change is essential for understanding the dynamic nature of their spatial ecology, and in turn the effectiveness of conservation strategies. We used a large marine predator that displays partial migration (the tiger shark Galeocerdo cuvier) as a model to test the role of oceanic conditions in predicting the space-use of different size classes. By using generalized additive mixed models (GAMMs), we revealed that environmental variables (sea surface temperature, primary productivity, thermal fronts, and bathymetry) had much greater predictive power for the movements of large, migratory tiger sharks than for small, resident individuals. We also found that coverage of tiger shark movements within “shark sanctuaries” (protected areas specifically for sharks) in the northwest Atlantic could be increased from 12 to 52% through inclusion of Bermuda’s waters. However, as large tiger sharks are migratory, over 80% of potential longline fisheries interactions would still occur outside the boundaries of even the expanded protected areas. This emphasises that management of highly migratory species needs to be dynamic and account for changing interactions with fisheries over time, which in a changing climate may rely on predicting movements based on oceanic conditions to be effective.

Highlights

Long-distance migrations that span hemispheres or ocean basins cause significant variation in population distribution and structure, often connecting disparate ecosystems and facilitating transfer of energy between them (Gonzalez-Solıs et al, 2007; Block et al, 2011)
The ability to predict animal movements based on environmental variation, including characteristics of partial migration, is valuable both for understanding their basic ecology and helping management initiatives aimed at promoting population sustainability
Given observations of partial migrations appearing to be associated with shark size, and the seasonal trends in large-scale migrations of adult sharks (Lea et al, 2015), we examined movements of the small and large sized sharks in relation to water temperatures by overlaying the latitude of all tiger shark locations on monthly averages of sea surface temperature (SST) at a resolution of 0.25 for the duration of the study (Figure 2)

Summary

Introduction

Long-distance migrations that span hemispheres or ocean basins cause significant variation in population distribution and structure, often connecting disparate ecosystems and facilitating transfer of energy between them (Gonzalez-Solıs et al, 2007; Block et al, 2011). Constrain, migration, and influence the paths taken often remain elusive, for marine species (Hays et al, 2016). Evaluation of such factors can help predict animal movements based on changing environmental conditions, in turn revealing how they interact with both their ecological communities and human activities, such as fishing (Hazen et al, 2013; Queiroz et al, 2016). The ability to predict animal movements based on environmental variation (e.g. temperature gradients, prey availability), including characteristics of partial migration, is valuable both for understanding their basic ecology and helping management initiatives aimed at promoting population sustainability

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