All about sawfish in the Bahamas: tracking movement, breeding and nurseries
Dean’s research is focused on the biology and ecology of the smalltooth sawfish, and he concentrates his efforts around the island of Andros in the Bahamas. As the largest island in the Bahamas, Andros is the least densely populated and its remote west side is nearly pristine. Dean collects blood from smalltooth sawfish to assess reproductive status, muscle samples for food web analyses and fin clips for genetic studies. He tags each sawfish, which is then tracked by satellites and acoustic receivers, to know more about where these animals move, what they do and how best they can be conserved.
Dean Grubbs
I am a fish ecologist with interests in the biology of exploited and poorly studied estuarine and marine taxa. Much of my research addresses specific biological gaps necessary for the management and conservation of coastal and deep-water sharks and rays, including research on endangered smalltooth sawfish. My interest in sharks stems from being raised fishing and exploring Florida’s Gulf coast. I received Bachelor’s degrees in marine science and biology from the University of Miami and a PhD in fisheries science from the College of William & Mary’s Virginia Institute of Marine Science. I was a post-doctoral researcher and faculty member...
All about sawfish in the Bahamas: tracking movement, breeding and nurseries
Our primary goal is to conduct research that supports and promotes the recovery of the Critically Endangered smalltooth sawfish in The Bahamas. Our objectives are to determine the population size and viability of this sawfish population, to assess the probability of recovery and to determine what habitats are critical to its continued survival.
Sawfish are among the most imperilled of all families of sharks and rays. All five species in the group are currently listed as Endangered or Critically Endangered. The Critically Endangered smalltooth sawfish is endemic to the Atlantic basin and its only known viable populations are in the USA and The Bahamas. Our research seeks to address questions and provide data that assist efforts to promote the recovery of this iconic species.
Sawfish include five living species of very large rays and all are listed as Endangered or Critically Endangered according to the IUCN Red List of threatened species. Sawfish have a large toothed rostrum that is used for defence and immobilising prey, but it also makes them vulnerable to fishing nets. The smalltooth sawfish is found only in the Atlantic and the USA supports the most robust population of the species, although it has declined severely due to overfishing, including harvest for the rostra (which are sought as curios), and habitat loss. In 2003, the smalltooth sawfish became the first marine fish listed as Endangered under the US Endangered Species Act. Our research suggests that a reproducing population of smalltooth sawfish exists also in The Bahamas, primarily on the western side of the island of Andros. With SOSF support, in 2016 we were the first to ever witness the birth of baby sawfish, thus confirming that sawfish give birth in Andros. Our tracking data from sawfish tagged in the USA and The Bahamas suggest that these populations are isolated and their recovery may be critical to the recovery of the species. For this reason, the IUCN Shark Specialist Group has designated the US population a ‘Lifeboat’ and The Bahamas’ population a ‘Beacon of Hope’ in its 2018 ‘Saving sawfish: progress and priorities’ update. The western side of Andros is remote and pristine and much of the sawfish habitat lies within Andros West Side National Park. Our data suggest the sawfish population in Andros is much smaller than that of Florida, despite the habitat being comparable. This may be due to differences in protective habitat, available food, density of sharks that compete for food or the number of predators that feed on young sawfish. We seek to unravel these mysteries to assess the likelihood of recovery of The Bahamas’ sawfish population.
Key challenges to sawfish conservation are the ability to estimate and monitor changes in population sizes and to identify habitats critical to survival and recovery. We seek to determine the relative size of the Bahamian smalltooth sawfish population compared to the US population, to define habitats that are critical to survival (such as nursery habitats) and to examine ecological processes that influence changes in The Bahamas’ smalltooth sawfish population. We will use our baited line surveys and records of sawfish sightings to estimate the relative abundance of smalltooth sawfish and coastal sharks that serve as competitors or potential predators to the sawfish. We will examine the overlap between sawfish and sharks in the Andros food web, as a proxy for determining shark species that may compete with sawfish for prey as well as those that may prey on juvenile sawfish. Smalltooth sawfish will be implanted with long-term acoustic transmitters that, along with previously tagged sawfish, are detected by existing SOSF-sponsored acoustic receiver arrays in Andros and Bimini. These data will be used to monitor sawfish residency and long-term movements and migrations as functions of temporal and spatial fluctuations in variables such as tidal cycles and salinity over days, seasons and years. This will also allow us to monitor how often adult females return to known habitats to give birth. We will use blood samples to determine whether females are mature and reproductively active. Genetic material from adult female and young-of-year sawfish will be used to potentially link offspring with their mothers and determine how frequently females return to give birth. In addition, our data will provide baseline information concerning primary sawfish habitat should development take place that affects the habitat negatively.