On a warm September afternoon in a quiet inlet of Quincy Bay, research scientist Ryan Knotek cuts up frozen Atlantic menhaden, secures them to circle hooks, and casts them into the shallow water. He is waiting for juvenile sand tiger sharks, a species that was once fished to the brink of extinction globally but has quietly staged a remarkable return to the waters of Boston Harbor over the past decade.
Once condemned as the dirtiest harbor in America due to the hundreds of millions of gallons of raw sewage and industrial waste dumped into its waters daily for over a century, Boston Harbor has undergone a dramatic transformation. Following a lawsuit, decades of extensive labor, and a $4.5 billion cleanup effort, the harbor has evolved into a flourishing ecosystem. Researchers note that alongside sand tigers, species such as smooth dogfish, striped bass, bluefish, and winter flounder now frequent the area in increasing numbers. Scientists attribute the return of the sharks to warming ocean temperatures, abundant prey, and natural protection from predators, which encourage the animals to utilize the harbor as a seasonal nursery.
The sharks make an annual migration, traveling north from their wintering and birthplace grounds in Florida and the Carolinas each spring to arrive in Boston Harbor around mid-July. As autumn approaches, they journey back south. Researchers at the New England Aquarium have been tracking and tagging the animals since 2016. Although the fieldwork experienced disruptions during the COVID-19 pandemic in 2020, it was formally relaunched with expanded efforts in 2023 under Dr. Knotek and his colleague Emily Jones, both scientists at the aquarium’s Anderson Cabot Center for Ocean Life. Over the past ten years, the team has successfully caught and tagged 39 juvenile sand tigers.
Despite their intimidating appearance—featuring protruding, jagged teeth and light brown or gray bodies dusted with freckles and black-edged fins—sand tiger sharks are a placid species that pose no threat to humans. Globally, the International Union for Conservation of Nature lists sand tigers as critically endangered, largely because they were intensely overfished by commercial and recreational fisheries between the 1970s and 1990s, decimating between 70% and 90% of their population. Furthermore, the species possesses one of the lowest reproductive rates among sharks, with females typically producing only one or two pups every few years.
Population recovery has been aided significantly by strict legal protections. In 1997, the National Oceanic and Atmospheric Administration enacted federal regulations making it illegal to catch, sell, or purchase sand tiger sharks in U.S. Atlantic waters, with Massachusetts implementing state-level protections in 2009. While these measures have allowed populations to rebound in the northeastern United States, recovery remains slow at an estimated rate of 1% to 2% per year due to the species’ unique biology. Additionally, juveniles are still occasionally caught in gill nets and trawls, presenting ongoing challenges.
Fieldwork in Quincy Bay aims to better understand these summering populations. Data indicates that the sharks spend 70% of their time in this specific corner of the harbor, sheltered by local marshes and historical landmarks. Some individual sharks exhibit high site fidelity, returning to the exact same location year after year. When a shark takes the bait, researchers bring it aboard, place it in a large seawater-filled cooler, flip it onto its back, and attach a black acoustic transmitter. The entire process takes less than 10 minutes before the shark is released. The transmitters allow scientists to track the animals for five years via underwater receivers placed across the harbor and along the Eastern Seaboard.
The ultimate objective of the research is to accumulate sufficient data to petition NOAA for the designation of Boston Harbor as an essential fish habitat, formally recognizing the area as a vital nursery ground for the species.
