Conservation biology of the Smalltooth Sawfish: science to help save the USA's first endangered elasmobranch

pp. 131-13

Female philopatry in smalltooth sawfish Pristis pectinata: conservation and management implications

Populations are more effectively managed with information on breeding and dispersal behavior, making the evaluation of these characteristics essential for effective conservation of a species. In the USA, 2 critical habitat units were designated in 2009 for the federally endangered smalltooth sawfish Pristis pectinata. Previous research in the Charlotte Harbor Estuary Unit (CHEU) of critical habitat shows that female smalltooth sawfish are polyandrous and highly philopatric to nursery grounds. However, these characteristics have not yet been examined in a larger area of designated critical habitat: the Ten Thousand Islands/Everglades Unit (TTIEU). We used microsatellite genotypes from 214 juvenile smalltooth sawfish to examine mating and dispersal behavior via sibship analyses and reconstruction of parental genotypes with the program COLONY. Parental reconstruction yielded 71 female and 117 male genotypes. Many females returned to the same region within TTIEU for parturition on a biennial cycle; however, at least 1 female switched parturition sites within TTIEU and at least 2 females produced litters in both TTIEU and CHEU over the study period. The maximum number of pups genetically assigned to 1 female was 12, a number that is consistent with that found for CHEU (8 pups), and within the litter size range reported (7 to 14) for the species. Confirmation of these mating behaviors and reproductive characteristics is important for understanding how the present population uses these protected habitats at different life stages, and for determining future habitat protection and population expansion strategies to restore smalltooth sawfish to previously occupied areas of their range

Using public encounter data to direct recovery efforts for the endangered smalltooth sawfish Pristis pectinata

Conservation planning for difficult-to-survey endangered species can be challenging because information on distribution, abundance, and habitat associations is hard to gather. We used data provided by the public for an easily identified rare marine species, the endangered smalltooth sawfish Pristis pectinata, to provide information to direct recovery efforts in US waters. Data from public encounters from 1998 to 2008 occurring between Texas and Georgia were analyzed. Most records (99.7%) were from Florida waters. Although all size classes were reported, the majority were sawfish ≤200 cm estimated total length. There was an inverse relationship between sawfish size and extent of northern distribution, with ≤200 cm animals having a wider latitudinal distribution and occurring farthest north, and >200 cm animals reported mostly in southern Florida. Most encounters occurred in estuarine and nearshore habitats, and their locations were not randomly distributed, having positive association with inshore mangrove and seagrass habitats. While sawfish were reported in depths up to 73 m, there was a significant relationship between size and depth, with smaller animals occurring in shallower waters. Although historically common from Texas to North Carolina, this study shows that the core range of smalltooth sawfish is now the area in Florida from the Caloosahatchee River south through the Ten Thousand Islands and Everglades National Park to Florida Bay. These results provide resource managers with information to direct recovery efforts, including the current range, areas where recovery may be expected to occur, and the habitat needs of various size classes

The ecology of elasmobranchs occurring in the Everglades National Park, Florida: implications for conservation and management

The elasmobranch fauna of Everglades National Park was studied using longline, gillnet, and rod and reel surveys. Thirteen species of elasmobranchs were identified including three species not previously reported in the park. Species richness was highest in the areas with the greatest influence of marine waters from the Gulf of Mexico and lower in estuarine areas and those subject to periods of hypersalinity. Most elasmobranch species were recorded as juveniles, with at least three species occurring as neonates, and there were few adults of any species. Electivity indices for salinity, temperature, and depth were calculated for Carcharhinus leucas (Valenciennes, 1841), Carcharhinus limbatus (Valenciennes, 1841), Ginglymostoma cirratum (Bonnaterre, 1788), and Negaprion brevirostris (Poey, 1868), and indicated possible habitat partitioning based on these environmental characteristics. Tag-recapture data suggested that N. brevirostris may have a high level of residency and probably remains inside the park for long periods, while all other species showed movements into and out of the park on a regular basis. Results demonstrate the utility of the park for the conservation and management of elasmobranch species and the need to consider how future changes to the environment will affect this important group of predators

Improving conservation planning for an endangered sawfish using data from acoustic telemetry

Understanding the movement and habitat use patterns of threatened species is essential to effective conservation\ud planning. Modern tracking techniques such as active tracking and passive acoustic monitoring can be useful tools in elucidating this information for aquatic species. To aid in the development of conservation strategies for juvenile critically endangered smalltooth sawfish (Pristis pectinata) their fine scale movements and habitat use in southwest Florida were studied using a combination of these techniques. Between 2002 and 2006 a total of 12 individuals were actively tracked for periods of up to 24 h to provide\ud detailed habitat use and movement parameters (distance moved, speed, and linearity). Smaller individuals\ud (<100 cm stretched total length (STL)) had the smallest home ranges, low linearity of movement and had a preference for very shallow mud banks. Juveniles >100 cm STL demonstrated larger home ranges, preference for shallow mud or and sand banks, and remained close to mangrove shorelines. Tide was found to be the main factor influencing movement on short time scales. Sawfish <150 cm STL spend the majority of their time in water <50 cm, while larger juveniles spend most of their time in water 50–100 cm deep. From 2003 to 2007 a total of 22 individuals were fitted with acoustic tags for long-term monitoring. Juveniles >130 cm had high levels of site fidelity for specific nursery areas for periods up to almost 3 months, but the smaller juveniles had relatively short site fidelity to specific locations. The use of a combination of tracking and monitoring techniques provided an expanded range of information by generating both short and long term data on habitat use. The data demonstrated that the conservation of shallow mud and sand banks, and mangrove shorelines will benefit the recovery of these endangered elasmobranchs

Distribution and habitat partitioning of immature bull sharks (Carcharhinus leucas) in a southwest Florida estuary

The distribution and salinity preference of immature bull sharks (Carcharhinus leucas) were examined based on the results of longline surveys in three adjacent estuarine habitats in southwest Florida: the Caloosahatchee River, San Carlos Bay, and Pine Island Sound. Mean sizes were significantly different between each of these areas\ud indicating the occurrence of size-based habitat partitioning. Neonate and young-of-the-year animals occurred in the Caloosahatchee River and juveniles older than 1 year occurred in the adjacent embayments. Habitat partitioning may reduce intraspecific predation risk and increase survival of young animals. Classification tree analysis showed that both temperature and salinity were important factors in determining the occurrence and catch per unit effort (CPUE) of immature C. leucas. The CPUE of ,1 year old C. leucas was highest at temperatures over 29 degrees C and in areas with salinities between 7‰ and 17.5‰. Although they are able to osmoregulate in salinities from fresh to fully marine, young C. leucas may have a salinity preference. Reasons for this preference are unknown, but need to be further investigated

Range, sexual dimorphism and bilateral asymmetry of rostral tooth counts in the smalltooth sawfish Pristis pectinata Latham (Chondrichthyes: Pristidae) of the southeastern United States

Rostral tooth counts of Pristis pectinata specimens from museum collections, research surveys, and fisheries activities were examined to provide information on sexual dimorphism, bilateral asymmetry, and to aid in the resolution of the taxonomic uncertainty that surrounds the Pristidae. Counts were taken from 105 smalltooth sawfish captured in Florida and Georgia, USA, from 1834 to 2007. The number of rostral teeth present was 22 to 29 per side and 45 to 56 in total. These counts were more constrained, and mean values lower, than historically reported for this species in the literature. Pristis pectinata rostral tooth counts exhibited sexual dimorphism, with males on average having more rostral teeth than females. Bilateral asymmetry in rostral tooth counts was displayed in 73% of individuals, with no consistent side on which the greatest count occurred. No significant difference between left and right side rostral tooth counts was found

Abiotic affinities and spatiotemporal distribution of the endangered smalltooth sawfish, Pristis pectinata, in a south-western Florida nursery

Understanding how endangered marine species rely on coastal habitats is vital for population recovery planning. The smalltooth sawfish (Pristis pectinata) is one of several critically endangered sawfishes worldwide known to use estuaries and rivers during their early life history. In a Florida estuary designated as critical habitat by the USA government, juveniles were monitored to characterise seasonality, recruitment, and habitat use. Stretched total length ranged from 671 to 2172 mm (n = 137, mean = 1248 mm). Sawfish were captured year round. Captures of neonates with embryonic rostral sheaths allowed refinement of the size at birth (671–812 mm) and confirmed a protracted timing of parturition (November–July), which peaked between April and May. Although sampling occurred throughout the estuary, five locations had the greatest catch rates. Most juvenile sawfish had an affinity for water 30°C, dissolved oxygen >6 mg L–1, and salinity between 18 and 30. Greater catch rates for sawfish >1 year old were associated with shoreline habitats with overhanging vegetation such as mangroves. These results detail habitat use within a recognised nursery that can be used for conservation of the first endangered marine fish species in the USA

Tracking public interest and perceptions about smalltooth sawfish conservation in the USA using Instagram

The population of smalltooth sawfish (Pristis pectinata) in the USA was listed as endangered under the US Endangered Species Act in 2003. Based on objectives identified in the Smalltooth Sawfish Recovery Plan, an interdisciplinary team developed a variety of outreach efforts and products to educate the public and promote sawfish conservation. These include safe viewing, handling, release, and reporting guidelines for boaters, divers, and anglers that may interact with the species. The usefulness of monitoring social media to track public interest and perceptions of smalltooth sawfish was investigated via Instagram posts mentioning sawfish encounters in the USA. We aimed to identify how current outreach efforts and messaging can be improved and expanded to better inform the public and promote positive change in their behaviour to further protect smalltooth sawfish. All encounters occurred in Florida waters and the trend of sawfish‐related Instagram posts increased congruently with traditionally reported sawfish encounters from 2012 to 2019. The number of Instagram users who indicated that they reported their encounter or that any sawfish encounter should be reported has increased, suggesting outreach efforts have gained traction and that some members of the public are actively promoting sawfish conservation through encounter reporting. The overall tone, and thereby public perception of and attitude towards sawfish, was largely positive. Though social media can be used to guide outreach initiatives and provides a platform for researchers to engage large public audiences, future research efforts should include electronic surveys within the recreational, commercial, diving, and angling communities. Additionally, social media posts should be compared with traditionally reported encounters, and media professionals working with scientists should focus on increasing the utility of social media as a way to collect encounter reports and create engaging educational content to be included with continued outreach efforts throughout the south‐eastern USA