By Lauren Benoit Romeiro, Marine Scientist. B.S. in Marine Biology and a master’s in Oceanography from University of Rhode Island and a well-respected photographer/cinematographer focusing on the conservation of sharks in the Northwest Atlantic.
Background
The Mako shark, Isurus oxyrinchus, is a large mackerel shark. They are highly migratory and one of five endothermic species meaning they have a specialized blood vessel structure called a countercurrent exchange that allows them to maintain a higher body temperature than the surrounding water. This allows them to be efficient hunters in any environment. Also the fastest shark in the ocean; fearless and intelligent there are few that can compete with the Mako as predators. Unfortunately these qualities have made this animal a high target for fisheries. In order to help better manage and protect this species we need to understand their behavior and habitat use.
The Goal
To investigate (a) habitat use on and off the continental shelf and (b) analyze socialization, hunting and mating/reproductive behavior.
Where
This study (now til 2026), will focus on endothermic and pelagic sharks from Maine to Long Island from the coast all the way out to the canyons.
Why
The Mako shark is listed as endangered according to the IUCN red list and has a high risk of extinction. It is a highly migratory species that is vulnerable to commercial and recreational fishing everywhere it goes. It is also listed under Appendix II of CITIES (Convention on International Trade in Endangered Species), meaning they can’t be traded unless it can be shown that fishing won’t threaten their chances for survival.
The Western North Atlantic is a marine predator biodiversity hot spot, and it represents a critical portion of the migratory pathways for over a dozen large species of sharks, many of which are threatened due to overfishing. This region is also a climatically dynamic area, with parts of the U.S. Northeast continental shelf warming faster than 99.9% of rates observed across the global ocean. The Mako shark calls the North Atlantic home during the summer months and it is theorized that they use this area as a feeding and mating ground. It is important that we understand how this animal is using the area so we can create management plans to help protect it and its habitat.
Methods
- Deep-sea BRUVS (baited remote underwater video systems) – These camera rigs sit on the ocean floor anywhere from a few ft to 1000m to evaluate habitat use and capture never before seen behaviors and species.
- eDNA – Sequencing of water to characterize the vertical distribution of shark biodiversity. Establish a baseline measure for marine predators in a rapidly warming oceanic region.
- Fin Cameras – Analyze socialization, hunting and mating behavior through high definition video.
- Psat Tags – Deployed on free swimming animals such as female blue sharks and very large makos we can narrow where the nursery ground is in New England.
- Stable Isotope Analysis – Obtained by taking a biopsy on free swimming animals. A powerful tool for assessing habitat usage, migration patterns and trophic ecology. Given the high variability in habitat use exhibited by elasmobranchs, there are likely to be large differences in isotope signatures of distinct food webs in which they are feeding, making elasmobranchs ideal candidates for isotope migration studies to identify critical habitats. As an animal forages it obtains an isotopic composition of that environment which can be used as a natural “tag” to track movements through isotopically distinct habitats.
- Reproductive Hormones – Obtained by taking a biopsy on free swimming animals. We are able to evaluate the reproductive status of Blue & Mako sharks in the North Atlantic Ocean through hormone concentrations found in muscle tissue. This is a powerful tool to confirm that these animals are using this area as a mating/nursery ground.
Discussion
Previous studies on sharks use tagging as the primary method for research, which requires catching and restraining the animal resulting in significant consequences for survival and behavior. Large predatory sharks are difficult to study because their life cycles occur solely or partially outside of the observable realm, leaving the data largely open for interpretation. This study focuses on using non-invasive techniques that give us the ability to observe behaviors and occurrences in difficult to study areas and species. Broad-scale movements determined by acoustic and satellite tracking reveal migratory pathways, environmental preferences and patterns in habitat use and residency. Fine-scale movements recorded by advanced biologging tags allow the quantification of patterns in activity, feeding and energetics and provide behavior and physiological context to other studies of broad scale movements. Data collected from this project will advance scientific discovery of sharks and create meaningful conservation evidence to augment adaptive management plans for species and ecosystems in the area.