Josh Stewart

Who I am

I grew up as a city kid from New York, far from the tropical oceans where I now work. My escape was the American Museum of Natural History, where I would spend hours in the Hall of Ocean Life staring at frozen tiger sharks chasing sea turtles or lying on the floor examining a life-size blue whale suspended from the ceiling. As a teenager, I took every available opportunity to volunteer for research and conservation projects and went swimming, diving, sailing, kayaking – anything that would get me into the water. When I started college, I enrolled in classes on fish biology and scientific diving and volunteered for every field project I could find. The programme I was part of focused heavily on underwater archaeology, so in between surveying fish biomass or coral recruitment, I was helping to excavate 17th-century shipwrecks. I’m not sure how many hours I spent underwater over those four years, but it’s safe to say that salt water was coursing through my veins as I set out to start my career.

In my first year out of college I received a Rolex Scholarship that enabled me to travel around the world learning about marine conservation priorities and the many different approaches that dedicated experts are taking to improve the outlook of marine ecosystems. Of all the systems and species I worked with, I was especially taken with manta and mobula rays. These charismatic species are threatened globally by targeted fisheries and being taken as by-catch, and yet at the time we knew so little about their basic biology and ecology. Shortly after my first experience working with manta rays in the Maldives, I helped found the Manta Trust and since then I have been working to improve our understanding of the ecology and conservation status of manta and mobula rays.

In 2018 I completed my PhD at Scripps Institution of Oceanography, which was focused on the movements, stock structure, and foraging behavior of mobulid rays.

Where I work

The Tropical Eastern Pacific is an incredibly rich marine environment supported by high productivity. Massive schools of jacks and grouper thrive in protected areas along the coast and the region is famous for its large pelagic species. Equatorial upwelling regions and the Costa Rica Dome support some of the world’s largest fisheries – both commercial and artisanal – and attract top predators such as sharks, billfishes and tunas. These productive habitats are also home to some of the most famous populations of manta and mobula rays in the world. I collaborate on projects that investigate the ecology and conservation of mobulid rays from the lush green coast of Jalisco, Mexico, to the arid beaches of northern Peru, and many locations in between. Every region has different species and populations of mobulid rays, with their own unique ecological questions and conservation issues. Across this broad geographic range, science and conservation interact with a variety of cultural and economic scenarios, each of which presents its own set of challenges and opportunities. Without question, one constant across regions is the importance of collaborating with local stakeholders in order to achieve research and conservation outcomes that benefit both marine ecosystems and the communities that rely on them.

What I do

My research in general focuses on developing better methods for managing large marine species. In some cases, this means filling knowledge gaps about basic ecology and biology, such as movements and foraging behaviour. This helps us determine how populations are connected, what drives the spatial patterns in abundance and distribution that we observe, and how we can design conservation and management strategies to be more effective based on this information. In other cases, my work focuses on identifying population trajectories, estimating population abundance and identifying management strategies that would result in better outcomes for threatened populations.

In Pacific Mexico, our programme focuses on understanding what drives mantas to seasonally visit specific regions where they are most vulnerable to human-related impacts such as ship strikes and entanglement in fishing gear. We work closely with local undergraduate students and fishing communities to conduct field research such as satellite and acoustic tagging, abundance surveys, zooplankton collections and environmental monitoring. A major aspect of our programme is providing technical skills training and research experience to young scientists and exposing children in local primary and secondary schools to marine science. We train undergraduate students in field data-collection methods, provide them with logistical support for individual research projects and help place them in research- and conservation-related jobs or graduate study programmes.

In a separate SOSF-funded project, we are working with the Inter-American Tropical Tuna Commission (IATTC) to reduce by-catch mortality of mobulid rays in industrial tuna fisheries. By IATTC mandate, mobulid rays may not be retained by fishing vessels and must be released using handling methods that are not harmful. However, mortality rates of released mobulid rays are not known. Fishing vessels are currently experimenting with different release methods that should improve the chances of survival of mobulid rays (such as using a cargo net or a stretcher to move and release the animal). We are working with the IATTC observer programme to deploy survivor satellite tags on these released mobulids. This information will tell us not only what proportion of individuals survive, but which handling and release methods maximise survival. This in turn will aid in the development of handling guidelines that will minimise the impact of these fisheries on mobulid populations throughout the Eastern Pacific. This project is possible thanks to the close collaboration of fishing vessel crews and IATTC observers.