These losses dealt a major blow to a species that has already suffered one of the most severe range contractions of any Atlantic marine fish, now persisting only in limited areas of the southeastern United States and The Bahamas.
Listed as the first marine fish under the U.S. Endangered Species Act since 2003, smalltooth sawfish were once abundant in Florida’s Indian River Lagoon (IRL) but vanished by the 1970s, largely due to fishery bycatch, especially gill nets. Recovery now depends on the protection of shallow, mangrove-lined nursery habitats, where young sawfish find food and refuge during their most vulnerable years.
Against the backdrop of recent mortality events, new research is offering a rare note of optimism. A study by Florida Atlantic University’s Harbor Branch Oceanographic Institute, in collaboration with the Florida Fish and Wildlife Conservation Commission (FWC), provides evidence that a historical nursery area within the IRL may once again be supporting juvenile smalltooth sawfish.
Using acoustic tagging technology, researchers tagged seven small juveniles and tracked their movements for up to two years, integrating multiple independent data sources and analytical approaches. The study combined long-term acoustic monitoring with verified reports from the U.S. Sawfish Recovery Hotline. Acoustic receivers deployed throughout the southern IRL and along the Saint Lucie River allowed scientists to document fine-scale movements, seasonal residency, and habitat use across multiple years.
The research was guided by established criteria for identifying elasmobranch nursery habitats and focused on spatial use, site fidelity and environmental factors shaping juvenile distribution within a historically important portion of the species’ range along Florida’s East coast. Movement data were evaluated alongside environmental conditions such as salinity, temperature, dissolved oxygen and freshwater inflows, placing sawfish habitat use within a broader estuarine and water-management context.
Together, these complementary lines of evidence created a robust framework for evaluating nursery function and informing future conservation planning in southeast Florida.
Results of the study, published in the journal Fishery Bulletin, revealed that juvenile smalltooth sawfish showed strong site fidelity in the South Fork of the Saint Lucie River, spending as much as 87 percent of their detected days within an area of just 0.4 square kilometers. Juveniles were most often associated with water temperatures between 75 and 84 degrees and salinities of 15 to 30 (ocean water is 35), which are indicative of moderate freshwater inflows.
“These findings provide the first evidence that the Indian River Lagoon is once again functioning as a nursery for this endangered species,” said Sarah Torre, first author and a Ph.D. candidate at FAU Harbor Branch. “High-use areas within the broader nursery, such as the upper Saint Lucie River, are essential for the early survival of smalltooth sawfish and underscore the importance of protecting specific habitats to support their recovery. While other coastal species, like juvenile bull sharks, also use broad estuarine nurseries, the strong fidelity of smalltooth sawfish to relatively small sections of the nursery during their first two years is unique.”
Seasonal changes in freshwater inflows influenced how juveniles used the system. Stable salinity conditions in the South Fork supported extended residency, while periods of extreme temperature or very low salinity prompted some individuals to temporarily move downstream. The findings suggest that long-term alterations to freshwater management could disrupt these patterns, potentially increasing stress and predation risk for young sawfish during critical developmental periods.
“Even though the Indian River Lagoon is not currently designated as critical habitat for juvenile smalltooth sawfish, our acoustic data and reports from the Sawfish Recovery Hotline confirm that multiple cohorts repeatedly use the Saint Lucie River across seasons and years, meeting established nursery criteria,” said Matt Ajemian, Ph.D., an associate research professor and director of the Fisheries Ecology and Conservation Lab (FEC) at FAU Harbor Branch, who serves as Torre’s advisor and co-authored the study. “These findings highlight the ecological importance of this region, the need to preserve red mangroves and maintain healthy water quality, and the value of targeted conservation efforts to help smalltooth sawfish reestablish in their historical range.”
Findings from the study point to a narrow window of opportunity for recovery. While the repeated use of the Saint Lucie River suggests that suitable nursery conditions still exist within the IRL, the small spatial footprint of these high-use areas also makes them especially vulnerable to changes in water quality, shoreline modification, and altered freshwater management. Because young sawfish concentrate their activity in such limited portions of the system during their earliest years, even localized disturbances could have outsized consequences for survival, recruitment and the long-term stability of the population.
“After the significant losses we’ve seen in recent years, identifying places where juvenile sawfish are successfully surviving is crucial for the species’ future,” said Gregg R. Poulakis, Ph.D., senior author and a research scientist at the FWC. “This research gives managers something tangible to work with – specific locations and environmental conditions that are clearly supporting young sawfish. Protecting these areas and managing surrounding waterways with the needs of early life stages in mind could make the difference between continued decline and a slow but meaningful recovery for the species.”
Other study co-authors are Andrew K. Wooley, Lukas B. Heath and Dylan M. Yakich, all with FWC; Liberty L. Boyd, Ph.D., post-doctoral researcher at FAU Harbor Branch, and Michael P. McCallister, a Ph.D. student and research coordinator with the FEC lab at FAU Harbor Branch.
This research was funded by the National Marine Fisheries Service under Section 6 (Cooperation with States) of the Endangered Species Act awarded to the FWC.
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About Harbor Branch Oceanographic Institute:
Founded in 1971, Harbor Branch Oceanographic Institute at Florida Atlantic University is a research community of marine scientists, engineers, educators, and other professionals focused on Ocean Science for a Better World. The institute drives innovation in ocean engineering, at-sea operations, drug discovery and biotechnology from the oceans, coastal ecology and conservation, marine mammal research and conservation, aquaculture, ocean observing systems and marine education. For more information, visit www.fau.edu/hboi.
About Florida Atlantic University:
Florida Atlantic University serves more than 32,000 undergraduate and graduate students across six campuses along Florida’s Southeast coast. Recognized as one of only 13 institutions nationwide to achieve three Carnegie Foundation designations - R1: Very High Research Spending and Doctorate Production,” “Opportunity College and University,” and Carnegie Community Engagement Classification - FAU stands at the intersection of academic excellence and social mobility. Ranked among the Top 100 Public Universities by U.S. News & World Report, FAU is also nationally recognized as a Top 25 Best-In-Class College and cited by Washington Monthly as “one of the country’s most effective engines of upward mobility.” To learn more, visit www.fau.edu.
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