After decades of absence, endangered sawfish are raising their young in Florida's Indian River Lagoon again

Can an endangered species come back to a place it vanished from half a century ago? For the smalltooth sawfish in Florida's Indian River Lagoon, the answer appears to be yes - tentatively, and in a very small area.

Smalltooth sawfish (Pristis pectinata) were once abundant along Florida's Atlantic coast, including the Indian River Lagoon (IRL), the largest estuary on the state's eastern seaboard. By the 1970s, they had vanished from the lagoon entirely, victims of gill net bycatch that decimated their numbers. Listed as the first marine fish under the US Endangered Species Act in 2003, the species now persists only in limited areas of southeastern Florida and the Bahamas. And in the winters of 2024 and 2025, mysterious mass mortality events in the Florida Keys - fish swimming in tight circles, losing balance, and dying, likely from neurotoxins or environmental stressors - killed hundreds of large juveniles and adults across more than 80 marine fish species, including an unknown number of sawfish.

Against that grim backdrop, new research from Florida Atlantic University's Harbor Branch Oceanographic Institute and the Florida Fish and Wildlife Conservation Commission offers a note of genuine optimism.

Seven tagged juveniles, two years of data

The study, published in Fishery Bulletin, used acoustic tagging technology to track seven small juvenile sawfish in the southern IRL and along the Saint Lucie River over periods of up to two years. Acoustic receivers deployed throughout the system recorded the fish's movements, allowing researchers to document fine-scale habitat use, seasonal residency patterns, and environmental preferences.

The data were evaluated alongside environmental conditions - salinity, temperature, dissolved oxygen, and freshwater inflows - to understand what makes certain areas suitable for juvenile sawfish. The research team also integrated verified reports from the US Sawfish Recovery Hotline, adding an independent data source that confirmed sawfish presence in the study area across multiple years and cohorts.

A tiny patch of river, 87% of the time

The results revealed remarkably strong site fidelity. Juvenile sawfish spent as much as 87% of their detected days within an area of just 0.4 square kilometers in the South Fork of the Saint Lucie River. They showed preference for water temperatures between 75 and 84 degrees Fahrenheit and salinities of 15 to 30 parts per thousand (ocean water is 35), indicating moderate freshwater inflows.

This degree of concentration in a tiny area during the first two years of life is unusual even by the standards of estuarine nursery species. Lead author Sarah Torre, a PhD candidate at FAU Harbor Branch, noted that while other coastal species like juvenile bull sharks use broad estuarine nurseries, the sawfish's fidelity to such a small section of habitat during their most vulnerable developmental period is distinctive and has direct conservation implications.

Meeting the nursery criteria

The study applied established criteria for identifying elasmobranch nursery habitats - a formal framework used by fisheries scientists to determine whether a particular location genuinely functions as a nursery rather than merely being a place where juveniles sometimes occur. The IRL met the criteria. Multiple cohorts used the Saint Lucie River across seasons and years, with consistent patterns of high residency and habitat selection that indicate sustained nursery function.

This is significant because the Indian River Lagoon is not currently designated as critical habitat for juvenile smalltooth sawfish under federal regulations. The study's findings argue that this designation should be reconsidered.

Vulnerability in a narrow window

The same site fidelity that makes the Saint Lucie River a productive nursery also makes the sawfish population there acutely vulnerable. When juvenile fish concentrate 87% of their activity in less than half a square kilometer, even localized disturbances - a pollution event, shoreline development, or changes in freshwater management - could affect the entire cohort.

Seasonal patterns added nuance to the vulnerability picture. Stable salinity conditions in the South Fork supported extended residency, but periods of extreme temperature or very low salinity prompted some individuals to temporarily move downstream. Long-term alterations to freshwater management upstream could disrupt these patterns, potentially increasing stress and predation risk during critical developmental windows.

The preservation of red mangroves along the shoreline and the maintenance of healthy water quality emerged as key factors supporting nursery function. Mangroves provide the shallow, complex habitat structure that juvenile sawfish rely on for shelter and foraging. Their removal or degradation would directly undermine the conditions that make the nursery viable.

A narrow path to recovery

Senior author Gregg R. Poulakis, a research scientist at the FWC, framed the findings in terms of actionable conservation. After the significant losses in recent years, identifying specific locations where juvenile sawfish are successfully surviving gives managers concrete targets for protection. The study provides the kind of spatially explicit, environmentally contextualized data that conservation planning requires - not just where sawfish are, but what conditions they need and how sensitive those conditions are to human activity.

Whether the Indian River Lagoon's renewed nursery function represents the beginning of a genuine recovery or a fragile anomaly depends on what happens next. The habitat is there. The fish are using it. The question is whether the surrounding human infrastructure - water management, land use, pollution control - will allow it to persist.