Abstract
Dissolved oxygen (DO) content of the global ocean is declining (ocean deoxygenation) due to sea temperature warming, increased stratification, and most importantly climate change and ocean acidification (Keeling et al., 2010; Vedor et al., 2021). A major consequence of climate change that has gained attention only recently is a decrease in the dissolved oxygen content of the world’s oceans which is exacerbated by stressors of global climate change (Keeling et al., 2010; Levin, 2018). Anthropogenic climate change leads to ocean warming, acidification, deoxygenation, reductions in near-surface nutrients, and changes to primary production, all of which are expected to affect marine ecosystems (Kwiatkowski et al., 2020). Significant deoxygenation has occurred over the past 50 years and human pressure on earth is increasing and the scale of their impacts continue to expand, suggesting larger changes are approaching (Keeling et al., 2010; Limburg et al., 2020). Ocean acidification (OA) and ocean warming caused by global climate change are leading to declines in dissolved oxygen in the ocean with implications for ocean productivity and marine habitats and species (Keeling et al., 2010). The first response by animals to changes is alterations in behaviors such as migration, dispersal, reproduction, and foraging behaviors (Carlson & Parsons 2003). Among marine life impacted by deoxygenation, elasmobranchs (sharks and rays) are directly threatened due to their biological characteristics of slow growth late sexual maturity, and low fecundity (Simpfendorfer et al., 2011). Sharks have comparatively high physiological demands for oxygen making them vulnerable to changes in seawater chemistry (Vedor et al., 2021). To investigate this, the relationship between dissolved oxygen levels and shark space use were evaluated. This project explored sharks spatial use over three different years and evaluated if they avoid low oxygen areas. Water samples from several locations around the Gulf of Mexico were collected and dissolved oxygen levels were measured for 2021. Oxygen data from 2012 and 2017 were obtained and shark migration data was obtained from satellite tracking data collected by OCEARCH and the Center for Sportfish Science and Conservation at Texas A&M University. Geographic Information Systems (GIS) was used to analyze how dissolved oxygen, along with other parameters, relate to sharks space use and investigate if sharks are avoiding low oxygen areas. Results suggest dissolved oxygen may play a role in sharks spatial use, with little overlap between shark positions and areas of low dissolved oxygen, indicative of potential avoidance. Shark showed a high percentage of occurrences in a mid to high dissolved oxygen range of 190 – 200 umol/kg. The results of this project allow for an improved understanding of how changes in ocean chemistry affect top mobile predators, as well understanding changes in dissolved oxygen in the Gulf of Mexico.