This post is one of a series on projects supported by the Anderson Cabot Center’s Marine Conservation Action Fund (MCAF). Through MCAF, the Aquarium supports researchers, conservationists, and grassroots organizations around the world as they work to address the most challenging problems facing the oceans.
Today’s post is about Dr. Ramón Bonfil, who works with a team of scientists from Océanos Vivientes AC searching for critically endangered sawfishes in Mexico.
Last June 14–July 5, a team of scientists from Océanos Vivientes AC finished its fourth field expedition to search for critically endangered sawfishes in Mexico. The smalltooth sawfish (Pristis pectinata) and the largetooth sawfish (Pristis pristis) used to be widespread and abundant in Mexican waters of the Gulf of Mexico and Caribbean 50 years ago, but the growth of coastal fisheries and human coastal development since the 1970s brought their local populations to the brink of local extinction.
Since 2015, Dr. Ramón Bonfil, Executive Director of Océanos Vivientes AC, and his team of scientists have been busy trying to find out the fate of these two species in Mexican waters. With the help of the Marine Conservation Action Fund, the Mexican Government (CONANP), and the Save Our Seas Foundation, they are searching for the last living sawfishes in places where they used to be abundant as well as in areas where there is still relatively untouched sawfish habitat. The team of scientists uses fishing nets and fishing lines to try to catch the sawfishes, as well as drones to try to locate them from the air in areas where the water is transparent enough (such as in the Caribbean coast in Quintana Roo). But the main hope for finding these elusive and unusual creatures is a cutting-edge technique known as environmental DNA, or eDNA for short.
All living creatures constantly lose cells and tissue to the environment; simply by showering, we are shedding cells. Fish shed cells into the water column via skin loss, mucus, urine, feces, sperm, and eggs. By taking water samples from an estuary or bay, we can determine what species live there and sometimes their relative abundances, by matching the DNA that remains in the water with that known for the target species.
The team carried out three field trips in 2015, surveying the estuary of Tecolutla in Veracruz, Bahía de Chetumal, and Bahía de la Ascensión in Quintana Roo, and the course of the Usumacinta River and the coastal lagoons of the state of Tabasco. Their most recent field trip covered two large Marine Protected Areas in the coast of Campeche, Terminus Lagoon, and the Biosphere Reserve of Los Petenes.
So far, none of the fishing gear or the flights with the drones has produced evidence of live sawfishes. However, during surveys in Bahia de la Ascension, they were able to locate spotted eagle rays (Aetobatus narinari), Caribbean whiptail stingrays (Styracura schmardae), and lemon sharks (Negaprion brevirostris), thus validating the use of drones for locating elasmobranchs in clear shallow waters. However, the results from the eDNA in Tecolutla, the first surveyed site, have shown that sawfishes were in the area in the recent past! This is exciting news and gives the team hope that when all the eDNA samples taken in the four field trips are finally analyzed, more evidence about the existence of the last sawfishes in Mexico will be unveiled.
The field trips are intense and tiring, as they usually mean spending three weeks working nonstop for an average of 9 hours per day in a boat setting and recovering the fishing gear, performing the aerial transects with the drones, and taking as many water samples as possible. During 2016, the field trips also involved filtering the water samples every night for 3 to 4 hours in a hotel room, only to get up early the next day to continue the surveys. Fortunately during this last trip, the methodology was streamlined, and the team does not need to filter the water samples every night.