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Globally, sawfishes are threatened with extinction because they occur in coastal habitats, which are disproportionally affected by human activities. In particular, sawfishes are susceptible to myriad fisheries that operate in the same regions. Unfortunately, these well-documented threats can be only partly mitigated because of ongoing human resource needs. However, the outlook for sawfishes is optimistic if we build on 5 successful research and conservation approaches developed over the past 2 decades: (1) local ecological knowledge, (2) identification of nurseries, (3) state-of-the-art techniques, (4) tagging studies, and (5) threat mitigation. If appreciation of healthy ecosystems that contain top predators like sawfishes can be fostered by healthy human populations where sawfishes occur (e.g. ecosystem management, promotion of sustainable livelihoods), and if local knowledge can be used to influence scientific studies that inform customized management decisions, this group of iconic species will have a chance to recover. In addition, promoting sample collection, sample archiving, and collaboration, especially in instances of sawfish mortality, will maximize the knowledge gained, despite often limited funding and limited samples. The first 2 decades of the 21st century have seen the first steps taken toward sawfish recovery, but there is more to do. Ultimately, translation of research results into conservation actions that include enforcement and fisher behavior change will be the key to sustained recovery. This Overview provides a context for the papers in the Theme Section ‘Biology and ecology of sawfishes’, and we incorporate them as part of a mini-review of research on this threatened group to provide a future outlook.

The smalltooth sawfish Pristis pectinata is threatened with extinction throughout its range and has been designated as Critically Endangered by the IUCN. In the USA, the species historically ranged from Texas to North Carolina, but mortality in fisheries and habitat loss have reduced the range to primarily southwest Florida. The US population was listed as endangered under the US Endangered Species Act in 2003. At that time, data on the biology and ecology of the species were limited. Research and outreach efforts have since expanded, and the quality and quantity of information has increased such that the US population is now one of the most well-studied sawfish populations worldwide. Smalltooth sawfish are born in litters of 7-14 individuals at lengths of 64-81 cm stretched total length (STL), reach maturity in 7-11 yr at approximately 340 cm STL for males and 370 cm STL for females, grow to a maximum size of about 500 cm STL, and live an estimated 30 yr in the wild. Smalltooth sawfish are piscivorous and shift from shallow estuarine waters as small juveniles to a broader array of coastal habitats as large juveniles and adults. The species is physiologically resilient to anthropogenic stressors, but preserving habitat and reducing fishing effects remain priorities. Data synthesized in this review have advanced our understanding of smalltooth sawfish life history and habitat needs, as well as the threats that continue to affect the population. Cumulatively, these data support optimism for recovery of the smalltooth sawfish in the USA and potentially beyond, though recovery will still require decades.

Similar to other elasmobranchs, the smalltooth sawfish Pristis pectinata is slow growing, matures late in life, and produces relatively few young, all factors that have contributed to its sensitivity to dramatic population declines from overfishing and habitat loss. Currently, the physiological stress response of these fish to capture or to other physiological challenges such as habitat loss, climatic changes, or pollution is unknown. In the absence of these data, conservation plans may be less effective, making populations susceptible to further declines. We examined basic stress physiology over ontogeny and as a function of capture using different fishing gears. We also examined stress parameters to test whether degraded habitat and water quality from altered habitats may have resulted in chronic stress in juveniles. Results suggested that the stress response to capture by all methods was low, particularly for blood lactate, compared to other elasmobranchs examined to date. Metabolic stress was found to change over ontogeny, with young of the year (YOY) eliciting the highest responses. Glucose, pCO2, bicarbonate, potassium, and hematocrit indicated that gillnet capture induced greater stress responses than longline capture. Significantly higher metabolic stress was observed in YOY and juveniles captured in the 2 nurseries most influenced by anthropogenic activities, the Peace and Caloosahatchee rivers, than in the 2 relatively pristine nurseries in Everglades National Park. Overall, the low physiological stress responses to all capture methods investigated in this study suggest that this species is resilient, which should promote optimism for recovery of the population.

Compared with that of other charismatic elasmobranchs, the component community of metazoan parasites infecting endangered smalltooth sawfish Pristis pectinata is exceedingly poorly characterized: adults of Dermophthirioides pristidis and Neoheterocotyle inpristi (ectoparasitic flatworms of skin and gill, respectively) were the only confirmed parasites prior to the description, based on specimens reported herein, of Mycteronastes caalusi. Our opportune and directed parasitological examinations of 290 smalltooth sawfish (277 live inspections; 13 necropsies; 671 to 2640 mm stretch total length) in south Florida coastal waters revealed at least 8 species of Platyhelminthes, 9 of Arthropoda, 4 of Annelida, and 1 of Nematoda. This collection includes representatives of an undescribed species of Aporocotylidae (Digenea) and myriad new host records, considerably updating and advancing our understanding of smalltooth sawfish symbionts. We also confirm that D. pristidis and N. inpristi are extant and propose D. pristidis as a reliable biological tag. Some of these parasites are evidently highly host-specific and so vulnerable to extinction.

Smalltooth sawfish Pristis pectinata use southwest Florida nurseries during at least their first 2 to 3 yr, and understanding region-specific habitat use patterns is important for effective management. Research occurred in 2 nurseries within the Charlotte Harbor estuarine system: the Caloosahatchee River, a highly human-altered nursery, and a more natural nursery, the Peace River. Between 2010 and 2013, a total of 148 juveniles ranging from 70.8 to 218.7 cm stretch total length were caught in gill nets, and 133 were acoustically tagged. The probability of encountering a sawfish during sampling was most influenced by season in both nurseries (highest during spring and summer), followed by dissolved oxygen in the Caloosahatchee River, and salinity and temperature in the Peace River. Temperature had lasting, atypical effects on movements when severe cold events occurred during the study. Outside of these disturbances, sawfish used all habitats available to them in both nurseries, but tended to reside in perennial high-use areas called nursery hotspots. Acoustic monitoring showed that juveniles gradually moved between 4 hotspots along a 20 river kilometer stretch of the Caloosahatchee River with seasonal changes in freshwater inflows or sometimes suddenly in response to large flow events. In contrast, sawfish in the Peace River remained associated with one nursery hotspot year-round. Reasons for these inter-nursery variations are attributed to differences in geomorphology and freshwater inflow regimes. This study illustrates that a full understanding of the life history of a species and the development of a conceptual model requires investigation of the species on a broad spatial scale. This consideration is important to avoid overgeneralization of habitat use patterns between nurseries.

Sawfishes (Family Pristidae) constitute one of the most threatened families of marine fish, and substantial management efforts are required to stabilize and recover their populations worldwide. Philopatry is common in marine animals, including sharks and rays, and can be a key driver of population structure, which in turn determines the most appropriate scale required for effective population assessment and management. We examined philopatry at 2 known smalltooth sawfish Pristis pectinata nursery sites in the Charlotte Harbor estuarine system, Florida (i.e. Caloosahatchee and Peace rivers) by reconstructing parental genotypes based on composite genotypes from dorsal fin clippings of offspring captured within the nurseries between 2004 and 2015. Of 55 reconstructed females, 45 clearly exhibited philopatry to these nursery sites, most on a biennial cycle. Thirty-four females gave birth in the Caloosahatchee River, 19 gave birth in the Peace River, and 2 females used both nurseries for parturition. Nine females have been giving birth at these sites for a decade or more. Two females produced offspring with the same male over consecutive breeding seasons and one other pair of parents was identified at a 6 yr interval, suggesting that females store sperm, use an unknown mating aggregation site, or both. Male genotypes (n = 192) were rarely seen more than once at these nurseries (n = 7). However, some males mated in consecutive years, and successfully with multiple females within years. Evidence of parturition site fidelity by smalltooth sawfish in Florida likely extends the time before range expansion would be expected.

Habitat use and movements of juvenile (

Growing concerns about the conservation of elasmobranchs have prompted a surge in research, because scientific studies that can support management actions are needed. Sawfishes are among the most threatened fishes worldwide and epitomize the challenge of conserving widely distributed, large-bodied marine fishes. We used a comparative approach to provide data on the trophic ecology of the smalltooth sawfish Pristis pectinata in the western Atlantic coastal waters of southwest Florida, USA. Specifically, we applied (1) stable isotope techniques to fin tissues of smalltooth sawfish and 2 sympatric elasmobranch species that have well-documented diets (i.e. bull shark Carcharhinus leucas and cownose ray Rhinoptera bonasus), and muscle tissue from a variety of known and potential prey species; and (2) an 18S rRNA gene sequencing technique to identify prey taxa in sawfish fecal samples. These analyses provided evidence that the smalltooth sawfish feeds primarily on teleost and elasmobranch fishes at all life stages even though sawfish move from estuarine to coastal habitats during their ontogeny. Although both sawfish and bull sharks occupy estuarine waters as juveniles and are piscivorous, the results also indicate that these species partition habitat. The cownose ray has been thought of as migratory throughout its range, but these data indicate that non-migratory, estuarine populations exist at lower latitudes. Collectively, these results will aid in the development of management decisions regarding these species and in improving long-term recovery planning for the smalltooth sawfish.

Although conservation efforts have reduced threats, the endangered smalltooth sawfish, Pristis pectinata, is still at risk from anthropogenic effects such as entanglement in recreational and commercial fishing gear. From 2017 to 2021, data from field research and the public in Florida documented 176 individuals that were entangled, injured, or killed by debris or human interactions. While entanglements in fishing gear (e.g., trawls, fishing tackle) remain the most frequent threat, interactions with household items have increased. Since 2017, 30 sawfish were reported with encircling debris (e.g., monofilament loops, rubber bands, ball bungee cords) around anterior parts of their bodies. Ball bungee cords have emerged as a problem, likely related to the popularity of their use in securing boat lift canopy covers. Collectively, encircling items have interfered with eye, spiracle, gill, and mouth function. Continued outreach is a priority to address these pollutants, their sources (e.g., manufacturers), and their effects on recovery., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Gregg Poulakis reports financial support was provided by the National Marine Fisheries Service. The other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Sawfishes (Pristidae) are large, highly threatened rays named for their tooth-studded rostrum, which is used for prey sensing and capture. Of all five species, the smalltooth sawfish, Pristis pectinata , has experienced the greatest decline in range, currently found in only ~20% of its historic range. To better understand the genetic underpinnings of these taxonomically and morphologically unique animals, we collected transcriptomic data from several tissue types, mapped them to the recently completed reference genome, and contrasted the patterns observed with comparable data from other elasmobranchs. Evidence of positive selection was detected in 79 genes in P. pectinata , several of which are involved in growth factor/receptor tyrosine kinase signaling and body symmetry and may be related to the unique morphology of sawfishes. Changes in these genes may impact cellular responses to environmental conditions such as temperature, dissolved oxygen, and salinity. Data acquired also allow for examination of the molecular components of P. pectinata electrosensory systems, which are highly developed in sawfishes and have likely been influential in their evolutionary success., Competing Interests: The authors declare no conflicts of interest., (© 2024 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

We report 24 new records of the Brazilian cownose ray Rhinoptera brasiliensis outside its accepted geographic range. Sequencing of a 442-base pair portion of the mitochondrial NADH dehydrogenase subunit 2 gene for 282 Rhinoptera samples revealed eight records off the east coast of the USA and 16 from the eastern Gulf of Mexico. Both sexes of all life stages were documented in all seasons over multiple years in the Indian River and Lake Worth lagoons, Florida, indicating that their range extends further in the western North Atlantic than previously described., (© 2020 Fisheries Society of the British Isles.)

Achorovermis testisinuosus gen. et sp. n. (Digenea: Aporocotylidae) infects the heart of the smalltooth sawfish, Pristis pectinata Latham (Rhinopristiformes: Pristidae), in the eastern Gulf of Mexico. Specimens of the new genus, along with the other blood flukes that infect batoids are similar by having an inverse U-shaped intestine and a curving testis as well as by lacking tegumental spines. The new genus differs from all of the other blood flukes infecting batoids by having an elongate body (>50 × longer than wide), a testis having >100 curves, and an ovary wholly anterior to the uterus. It differs from Ogawaia glaucostegi Cutmore, Cribb et Yong, 2018, the only other blood fluke infecting a rhinopristiform, by having a body that is >50 × (vs <30 ×) longer than wide, a testis that is >75 × (vs <40 ×) longer than wide and has >100 (vs <70) curves, an ovary wholly anterior to (vs lateral and dorsal to) the seminal vesicle, a uterus wholly posterior to (vs overlapping and lateral to both) the testis and ovary, and a sinuous (vs convoluted) uterus. The new species joins a small group of chondrichthyan blood flukes that lack tegumental spines: O. glaucostegi, Orchispirium heterovitellatum Madhavi et Rao, 1970, Myliobaticola richardheardi Bullard et Jensen, 2008, Electrovermis zappum Warren et Bullard, 2019. Blood flukes infecting batoids are further unique by having a curving testis. That is, the blood flukes infecting species within Selachii are morphologically distinct from those infecting species within the Batoidea (excluding Gymnurahemecus bulbosus Warren et Bullard, 2019). Based on the morphological similarity, we suspect that the new species shares a recent common ancestor with O. glaucostegi. The discovery of the new species brings the total number of chondrichthyan blood flukes to 11 species assigned to nine genera.

The foundation of food web analysis is a solid understanding of predator-prey associations. Traditional dietary studies of fishes have been by stomach content analysis. However, these methods are not applicable to Critically Endangered species such as the smalltooth sawfish (Pristis pectinata). Previous research using the combination of stable isotope signatures from fin clips and 18S rRNA gene sequencing of fecal samples identified the smalltooth sawfish as piscivorous at low taxonomic resolution. Here, we present a high taxonomic resolution molecular technique for identification of prey using opportunistically acquired fecal samples. To assess potential biases, primer sets of two mitochondrial genes, 12S and 16S rRNA, were used alongside 18S rRNA, which targets a wider spectrum of taxa. In total, 19 fish taxa from 7 orders and 11 families native to the Gulf of Mexico were successfully identified. The sawfish prey comprised diverse taxa, indicating that this species is a generalist piscivore. These findings and the molecular approach used will aid recovery planning for the smalltooth sawfish and have the potential to reveal previously unknown predator-prey associations from a wide range of taxa, especially rare and hard to sample species.

Temperature is one of the most influential drivers of physiological performance and behaviour in ectotherms, determining how these animals relate to their ecosystems and their ability to succeed in particular habitats. Here, we analysed the largest set of acceleration data compiled to date for elasmobranchs to examine the relationship between volitional activity and temperature in 252 individuals from 8 species. We calculated activation energies for the thermal performance response in each species and estimated optimum temperatures using an Arrhenius breakpoint analysis, subsequently fitting thermal performance curves to the activity data. Juveniles living in confined nursery habitats not only spent substantially more time above their optimum temperature and at the upper limits of their performance breadths compared to larger, less site-restricted animals, but also showed lower activation energies and broader performance curves. Species or life stages occupying confined habitats featured more generalist behavioural responses to temperature change, whereas wider ranging elasmobranchs were characterised by more specialist behavioural responses. The relationships between the estimated performance regimes and environmental temperature limits suggest that animals in confined habitats, including many juvenile elasmobranchs within nursery habitats, are likely to experience a reduction of performance under a warming climate, although their flatter thermal response will likely dampen this impact. The effect of warming on less site-restricted species is difficult to forecast since three of four species studied here did not reach their optimum temperature in the wild, although their specialist performance characteristics may indicate a more rapid decline should optimum temperatures be exceeded.

Mycteronastes Kearn and Beverley-Burton, 1990 (Monogenoidea: Monocotylidae: Merizocotylinae) was resurrected from subjective synonymy with Merizocotyle Cerfontaine, 1894 , and its diagnosis was emended to include monocotylids with a haptor lacking a central loculus and having 5 peripheral (2 bilateral pairs and an unpaired anteromedial loculus), 1 interhamular, and 17 marginal loculi. The 3 species of Mycteronastes accepted herein are parasitic within the olfactory sacs of rays and sawfishes: Mycteronastes icopae ( Beverley-Burton and Williams, 1989 ) Kearn and Beverley-Burton, 1990 (type species) from the giant shovelnose ray, Glaucostegus typus (Anonymous (Bennett)) (Glaucostegidae), in the southwestern Pacific Ocean; Mycteronastes undulatae Kearn and Beverley-Burton, 1990 from the undulate ray, Raja undulata Lacepède (Rajidae), in the northeastern Atlantic Ocean; and Mycteronastes caalusi n. sp. from the smalltooth sawfish, Pristis pectinata Latham (Pristidae), in the Gulf of Mexico. Mycteronastes caalusi is most easily differentiated from its congeners by the combination of having 2 median cephalic papillae, an oval haptor that is wider than the body proper and lacks a deeply scalloped margin, a comparatively large anteromedial peripheral loculus, an unsclerotized male copulatory organ that is wholly anterior to the vaginal pores, a relatively small distal portion of the uterus (ootype chamber) that is mostly anterior to the vaginae, and a delicate uterus. The present study is the first report of a monocotylid from the olfactory sacs of P. pectinata and the first record of a species of Mycteronastes from the Gulf of Mexico. Notes on the taxonomy and systematics of some species assigned to Calicotyle Diesing, 1850 (Monocotylidae: Calicotylinae) are included.

Endangered smalltooth sawfish (Pristis pectinata) were opportunistically sampled in south Florida and aged by counting opaque bands in sectioned vertebrae (n=15). Small sample size precluded traditional age verification, but fish collected in spring and summer had translucent vertebrae margins, while fish collected in winter had opaque margins. Trends in Sr:Ca measured across vertebrae with laser ablation-inductively coupled plasma-mass spectrometry corresponded well to annual salinity trends observed in sawfish estuarine nursery habitats in south Florida, thus serve as a chemical marker verifying annual formation of opaque bands. Based on that finding and assumptions about mean birth date and timing of opaque band formation, estimated age ranged from 0.4 y for a 0.60 m total length (TL) male to 14.0 y for a 4.35 m TL female. Von Bertalanffy growth parameters computed from size at age data were 4.48 m for L(∞), 0.219 y(-1)for k, and -0.81 y for t(0). Results of this study have important implications for sawfish conservation as well as for inferring habitat residency of euryhaline elasmobranchs via chemical analysis of vertebrae.

Sawfish (family Pristidae) are among the most critically endangered marine fish in the world, yet very little is known about how genetic bottlenecks, genetic drift, and inbreeding depression may be affecting these elasmobranchs. In the US Atlantic, the smalltooth sawfish (Pristis pectinata) has declined to 1-5% of its abundance in the 1900s, and its core distribution has contracted to southwest Florida. We used 8 polymorphic microsatellite markers to show that this remnant population still exhibits high genetic diversity in terms of average allelic richness (18.23), average alleles per locus (18.75, standard deviation [SD] 6.6) and observed heterozygosity (0.43-0.98). Inbreeding is rare (mean individual internal relatedness = -0.02, SD 0.14; F(IS) = -0.011, 95% confidence interval [CI] = -0.039 to 0.011), even though the estimated effective population size (N(e)) is modest (250-350, 95% CI = 142-955). Simulations suggest that the remnant smalltooth sawfish population will probably retain >90% of its current genetic diversity over the next century even at the lower estimate of N(e). There is no evidence of a genetic bottleneck accompanying last century's demographic bottleneck, and we discuss hypotheses that could explain this. We also discuss features of elasmobranch life history and population biology that could make them less vulnerable than other large marine vertebrates to genetic change associated with reduced population size.

Stable isotopes of neonatal vertebrates reflect those of their mother's diet and foraging location. Evaluating feeding strategies and habitat use of neonates is consequently complicated by the maternal isotopic signal and its subsequent elimination with growth. Thus, methods that measure the loss of the maternal signal, i.e. when the isotopic signal of a neonate reflects its own diet, are needed. Values of δ(13)C and δ(15)N were measured in liver and muscle tissues of <1 year old bull (Carcharhinus leucas) and Atlantic sharpnose (Rhizoprionodon terraenovae) sharks and related to age using, total length, date sampled and umbilical scar stage (USS). We observed a decline in δ(13)C and δ(15)N values with age that was different among species, similar among isotopes, and greater in liver than in muscle; highlighting that retention of the maternal signal is dependent on species-specific life history and tissue characteristics. USS was most effective for assessing the loss of the maternal isotopic signal in the faster growing Atlantic sharpnose shark, but was less effective for the slower growing bull shark. Total length and date sampled were overall less effective and may be more informative for slower growing species when coupled with USS, as variable size at birth and misclassification of animals >1 year old, which remain in nursery habitats, increase the variability of the isotopic values. Consideration of the maternal signal and measuring its loss are thus necessary when analyzing the stable isotopes of young animals, as there is potential to misinterpret feeding strategies, over-estimate trophic position and incorrectly assign carbon source., (Copyright © 2011 John Wiley & Sons, Ltd.)

To aid recovery efforts of smalltooth sawfish (Pristis pectinata) populations in U.S. waters a research project was developed to assess how changes in environmental conditions within estuarine areas affected the presence, movements, and activity space of this endangered species. Forty juvenile P. pectinata were fitted with acoustic tags and monitored within the lower 27 km of the Caloosahatchee River estuary, Florida, between 2005 and 2007. Sawfish were monitored within the study site from 1 to 473 days, and the number of consecutive days present ranged from 1 to 125. Residency index values for individuals varied considerably, with annual means highest in 2005 (0.95) and lowest in 2007 (0.73) when several P. pectinata moved upriver beyond detection range during drier conditions. Mean daily activity space was 1.42 km of river distance. The distance between 30-minute centers of activity was typically <0.1 km, suggesting limited movement over short time scales. Salinity electivity analysis demonstrated an affinity for salinities between 18 and at least 24 psu, suggesting movements are likely made in part, to remain within this range. Thus, freshwater flow from Lake Okeechobee (and its effect on salinity) affects the location of individuals within the estuary, although it remains unclear whether or not these movements are threatening recovery.

Bycatch mortality in net fisheries was the major reason for the decline of the endangered smalltooth sawfish, Pristis pectinata, in the United States. These fisheries have been reduced or eliminated in some states including Florida--where most smalltooth sawfish are currently found in the United States. To determine whether other factors are still affecting this species, we obtained non-net fishery entanglement, injury, and mortality data by soliciting information from anyone who may have encountered this species. Smalltooth sawfish were damaged by marine pollution (e.g., polyvinyl chloride pipe, monofilament line, non-monofilament line) and injured by humans. Examples of injuries caused directly by humans include removal of rostra, shooting an individual with a powerhead, and shooting another with arrows. Many people are aware that the smalltooth sawfish is protected by state and federal laws, but some are still not aware of (or willing to accept) this status. The impacts of marine pollution and injuries directly caused by humans on this endangered species can be ameliorated by incorporating fisher education into the conservation and management processes.