Sergio Madrigal Mora
Who I am
Although I was born in a city and have lived there most of my life, I am lucky it happened to be San José, Costa Rica. The great thing about this city is that it takes only a short drive up the mountains to be surrounded by lush tropical forest, or a couple hours down the coast to reach beautiful beaches. When I was a child my family took me to all these places, so from very early on I knew I wanted to be a biologist. As soon as I was done with high school, I did not hesitate to start my Bachelor’s in biology at the University of Costa Rica. I was interested in many different fields, like entomology and herpetology, but it was diving for the university’s reef-monitoring project that helped me decide I was most passionate about marine biology, and fish in particular. After graduating in 2020, I got the chance to go to California State University Long Beach (CSULB) for my Master’s, thanks to the Fulbright Foreign Student Program. With Dr Christopher Lowe as my thesis adviser and alongside Dr Mario Espinoza, who had been my undergraduate adviser at University of Costa Rica, we started a thesis project where I could get shark research training at CSULB and return to Costa Rica to apply it on Pacific nurse sharks.
Where I work
My research is located in Santa Elena Bay, an embayment of only seven square kilometres (2.7 square miles) surrounded by the dry tropical forest of the Santa Rosa National Park, in northern Costa Rica on the Pacific side. In 2018 Santa Elena Bay was declared a marine management area, where fishing within the bay is restricted to low-impact methods (handline, spear fishing, sport fishing). This bay was recently identified as an Important Shark and Ray Area as it provides various habitats that are essential for elasmobranchs, such as mangrove forest, rocky and coral reefs and sandy sea floor. The habitats are frequented by elasmobranch species that include eagle ray, Pacific whiptail stingray, lemon shark and, of course, our focus species: the Pacific nurse shark. Santa Elena and its adjacent waters are also special in their oceanography, as this region is influenced by a strong seasonal upwelling from late December to early April, when water temperatures decrease as much as 10 °C. Because of this seasonal upwelling, the bay functions like a giant laboratory for us, one that allows us to study how changes in water temperature can affect sharks’ movements as they seek thermal refuge from the colder waters.
What I do
I am studying the movements and aggregations of Pacific nurse sharks using acoustic telemetry, drone surveys and longline fishing surveys. For a day of field work, we are usually on the boat by 7 am and on the way to Santa Elena Bay, which is 25–30 minutes from Cuajiniquil, the town where we stay during field trips. Once we are in Santa Elena, we start the day with drone surveys to look for nurse sharks and observe if they are forming aggregations. On fishing survey days, we deploy two or three longlines throughout the day. If we capture sharks we tag them, measure their body lengths, annotate their sex, collect DNA samples and attach an acoustic transmitter for tracking, if we have any available. Other days we dedicate mostly to data offloading from our telemetry equipment in the water. We dive for our acoustic receivers and temperature loggers and bring them up to the boat to download their most recent data and replace batteries before redeploying them.
When I am back in San José, I either go into the lab at University of Costa Rica or work from home. On days like these, work consists mostly of data management from our previous field trips, analysis of all the data we’ve acquired so far or writing grant proposals that will help us secure more funding. Alternatively, we may be writing up results that we’ll soon turn into scientific papers. Although field work in the beautiful Santa Elena Bay is without doubt a privilege, I think the computer work is my favourite part of the job – though my peers tend to disagree with me on this!