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Shark nursery areas: Concepts, definition, characterization and assumptions
Abstract
The concept of elasmobranch species using nursery areas was introduced in the early 1900s and has been an accepted aspect of shark biology and behavior for several decades. Despite several descriptions of how shark species use nursery areas and what types of regions nurseries may be found in, no explicit definition of what constitutes a shark nursery area has been presented. Here we evaluate the assumptions of the current shark nursery paradigm in light of available data. Based on examination of these assumptions and available methods of quantifying and accurately describing shark nursery areas, a new more quantitative definition of shark nursery areas is proposed. This definition requires 3 criteria to be met for an area to be identified as a nursery: (1) sharks are more commonly encountered in the area than other areas; (2) sharks have a tendency to remain or return for extended periods; and (3) the area or habitat is repeatedly used across years. These criteria make the definition of shark nursery areas more compatible with those for other aquatic species. The improved definition of this concept will provide more valuable information for fisheries managers and shark biologists.
... Given that neonates receive no postnatal investment, selection of optimal habitat for their young is presumably as far as breeding females are able to extend their care. Under this scenario, areas with high densities of individuals under the age of 1 year may exist, where multiple females select similar environments to maximise the odds of neonatal survival by providing protection from predators and access to food (Heupel, Carlson and Simpfendorfer 2007). These 'nursery'-like areas may extend across vast areas of open ocean which makes speculation about their spatial dynamics difficult. ...
... These OMZ boundary areas could provide optimal conditions for whale shark neonates, and may, at broad scales, come close to meeting the criteria for a pelagic 'nursery'-like habitat (Heupel, Carlson and Simpfendorfer 2007). In addition, for whale shark young transiting the prey sparse or predator-rich open ocean for ~3 years, the zooplankton aggregating nature of the upper and lower OMZ boundaries may provide optimal conditions for foraging in productive waters whilst allowing individuals to remain in close proximity to 'hypoxic shelter' in the form of physiological refuge from predators. ...
... The observed preference for moderate Chl-a areas also suggests a strategy to maximise foraging and minimise predation compared to high Chl-a areas, where predators will be most abundant. Acting together, these features maximise the odds of neonatal survival by providing protection from predators and access to food (Heupel, Carlson and Simpfendorfer 2007). ...
Neonate whale sharks < 1.5 m in length are rarely encountered, with approximately 35 sightings recorded globally between 1970 and 2020. Although potentially pregnant females seem to frequent certain sites, parturition areas are unknown, and most neonates have been sighted opportunistically in offshore environments, suggesting nursery habitat may occur in remote parts of the ocean. Here, documented accounts of neonate whale sharks with corresponding locations were mapped in relation to oceanography to identify whether there are commonalities in where they occur. Results show that locations of neonate sightings coincide with permanent oxygen minimum zones (OMZs)—with associated high surface chlorophyll‐a (Chl‐a) and low oxygen at depth—more often than would be expected by random chance. Two main hypotheses are proposed to explain this apparent association: (i) adult female whale sharks selectively pup in waters adjacent to low oxygen regions offering a proximate refuge from oceanic predators as well as enhanced foraging opportunities, or that (ii) pupping occurs randomly in the open ocean but that OMZs restrict neonates to shallower surface waters where they are more frequently encountered by humans than elsewhere. Testing both hypotheses requires more data on the relationship between whale shark movement ecology and dissolved oxygen concentrations. As a first step, a model predicts the highest likelihood of neonates occurring in waters above OMZs, focussed around intermediate Chl‐a regions at the boundaries of highly productive upwelling systems. These areas could be the focus of future, more targeted studies. Here, biologging devices measuring in situ oxygen concentrations will be useful for exploring how different life stages interact with OMZs, which are expanding due to climate‐driven deoxygenation. What this might mean for neonate whale shark conservation in future warmer oceans remains an open question.
... Aggregations vary temporally (year-round v. seasonal) and in spatial extent (small patchy reefs vs. continental coastlines vs. at 84.6 m depth at a thermocline (Pelletier et al. 2023), which include mating (Yano et al. 1999;Stevens et al. 2018), social behavior (Perryman et al. 2022), feeding Fonseca-Ponce et al. 2022), predator avoidance (Palacios et al. 2023), cleaning (Barr and Abelson 2019;Perryman et al. 2019), and for thermoregulation after deep diving; up to 711 m and 1246 m for M. alfredi and M. birostris, respectively (Couturier et al. 2018;Fonseca-Ponce et al. 2022;Andrzejaczek et al. 2022). For juveniles, certain aggregation areas function as nurseries (defined for elasmobranchs by Heupel et al. 2007) which for M. alfredi has been confirmed in Raja Ampat, Indonesia (Setyawan et al. 2022a), and suggested to occur in the Eastern Cape, South Africa (Marshall et al. 2022c). ...
... Our results also included the first photographic confirmation of juvenile M. birostris inhabiting South African waters. At Port Ngqura, only the third nursery criteria outlined by Heupel et al. (2007), which states that habitat is used by juveniles across the year, was met. The first M. alfredi nursery that met all three criteria was identified in Wayag Lagoon, Raja Ampat, Indonesia (Setyawan et al. 2022a, b). ...
... The first M. alfredi nursery that met all three criteria was identified in Wayag Lagoon, Raja Ampat, Indonesia (Setyawan et al. 2022a, b). Several possible nursery areas that meet at least one or more of the three criteria (Heupel et al. 2007) include the Maldives (Kitchen-Wheeler et al. 2011), Nusa Penida, Indonesia , for M. alfredi; the Red Sea for M. birostris ; and Flower Garden Banks (Stewart et al. 2018a, b) and Florida (Pate and Marhsall 2020) for M. cf. birostris. ...
Both the reef manta ray, Mobula alfredi and oceanic manta ray M. birostris, are repeatedly observed in South Africa, yet little is known about the distributions of either species. In this study, we collated citizen science observations since 2003 to reveal six areas in the KwaZulu-Natal (KZN) and Eastern Cape provinces, where manta rays have been sighted across multiple years. Using their unique ventral spot patterning, 184 individuals were photo-identified, comprising 139 M. alfredi and 45 M. birostris. Most of the photo-identified M. alfredi individuals were encountered in the iSimangaliso Wetland Park (IWP) in KZN (89%; n = 119) and for M. birostris, Aliwal Shoal (48%; n = 22). We identified 32 new transboundary records of 28 M. alfredi also photographed in the Inhambane Province, Mozambique, demonstrating connectivity, specifically to Závora (n = 27). One M. alfredi individual traveled multiple times between the IWP and Závora, Mozambique, totaling 1305 km, and another individual traveled from the Pondoland MPA to the IWP in South Africa, a distance of over 600 km. Further, we extend the southern range for M. alfredi in Africa by over 500 km from Mdumbi Beach to Port Ngqura, Eastern Cape. These collective findings represent South Africa’s first in-water assessment of manta ray aggregations, showing the IWP in particular to be a critical habitat for M. alfredi. Further, the movements documented here suggest the M. alfredi population in southern Africa to be one of the most mobile globally. We hope the baseline data provided here will drive increased research and transboundary management for M. alfredi and M. birostris along the KZN and Eastern Cape coastlines.
... The presence of nursery areas, small juveniles, and pregnant females is necessary to declare an area as a nursery (Heupel et al., 2007). Heupel et al. (2007) suggested that an area requires three criteria to be identified as a nursery: (1) species are more commonly encountered in the area than other areas (2) species tend to remain or return for extended periods, and (3) the area or habitat is repeatedly used across years. ...
... The presence of nursery areas, small juveniles, and pregnant females is necessary to declare an area as a nursery (Heupel et al., 2007). Heupel et al. (2007) suggested that an area requires three criteria to be identified as a nursery: (1) species are more commonly encountered in the area than other areas (2) species tend to remain or return for extended periods, and (3) the area or habitat is repeatedly used across years. The data obtained in our study and previous studies in the region prove that this region is a breeding area for elasmobranch species (Yağlıoğlu et al., 2015;Başusta et al., 2021;Akyol and Şen, 2022). ...
... In conclusion, our data provide evidence to recognize Iskenderun Bay as a nursery area for longnose spurdog sharks Squalus blainville, meeting all the criteria proposed to identify nursery areas (Castro, 1993;Heupel et al., 2007). These findings constitute the first documented evidence of a longnose spurdog shark nursery area in the Iskenderun Bay in Turkish marine waters. ...
protection and increasing the survival of newborns. This study aims to investigate a potential nursery area for Squalus blainville in the northeastern Mediterranean Sea that has very scarce information in the eastern Mediterranean Sea and contributes to the length-weight relationships. We identified the location of the potential nursery area by interviewing local fishermen. We collected 48 adults and 22 embryos neonates of S. blainville specimens from the entrance of Iskenderun Bay on 03 April 2024. We recorded 48 longnose spurdog sharks in the catches ranging from 68.9 cm to 120.2 cm TL, which corresponded to mature individuals. The length-weight relations (LWR) of combined sexes of S. blainville were observed as W = 0.0005 x L3.0277 (R2 =0.9303). Our data provide evidence to recognize Iskenderun Bay as a possible nursery area for longnose spurdog sharks, meeting all the criteria proposed to identify nursery areas. These findings constitute the first documented evidence of a longnose spurdog shark nursery area in the Iskenderun Bay in Turkish marine waters.
... Broad-scale characterizations of nursery habitat have become more specific and testable for conservation ecology purposes while simultaneously reiterating the importance of abundance sampling within the methodology (Bass, 1978;Beck et al., 2001;Branstetter, 1987Branstetter, , 1990Dahlgren et al., 2006;Heupel et al., 2007;Nagelkerken et al., 2015;Springer, 1967). Consequently, how we circumscribe a nursery area is dependent on the definition employed and the method for which juvenile abundance is sampled (Table 1). ...
... For shark species that utilize these nursery areas, a standardized definition was previously established for classifying a nursery area. It states that in order to identify a nursery area, it must fulfil three criteria: (i) sharks must be found within the area more than others, (ii) sharks either remain in the range or return to the same area over long periods of time, and (iii) the habitat is repeatedly used over multiple years (Heupel et al., 2007). This definition provides easily testable measures to define a habitat and has been employed previously in this area on a small budget and timeframe, but we must also recognize that there remains a non-trivial level of uncertainty and investigator discretion when utilizing even the better-described definitions. ...
... Springer, 1967* Shallow waters segregated from adult population, with ample food sources and free of predation where juvenile sharks remain until maturity Occurrence Bass, 1978 Include primary nurseries, where actual birth of neonate sharks takes places, and secondary nurseries which are inhabited by slightly older but still juvenile sharks Occurrence Branstetter, 1990 Areas ranging from completely protected to very unprotected from adult shark populations where food is unlikely to be limiting Productivity and occurrence Castro and Beach (1993) Shallow waters utilized by multiple species for juvenile rearing. Multiple nursery areas possible based on seasonal migration trends Occurrence Beck et al., 2001 Juveniles in nursery habitats contribute disproportionately more to adult population relative to non-nursery areas through higher density, growth, survival, or population contribution Density, growth rate, survivorship, or contribution Dahlgren et al., 2006 Effective juvenile habitat that contributes a greater proportion of individuals to adult populations Contribution Heupel et al., 2007 Sharks are more commonly encountered in area, sharks remain or return to area for extended periods, area repeatedly used across years Density, residency, and annual use Nagelkerken et al., 2015 Multiple habitats functionally connected in a mosaic with a core area restrained by home range Contribution, home range study, cohort progression, and migration routes Note: All definitions following Springer (1967) are created in conjunction with this original definition. *All following definitions build off Springer, 1967 definition. ...
New approaches to abundance surveying utilizing unoccupied aerial vehicles (UAVs) are proving to be effective tools in marine and terrestrial environments. We explored UAV efficacy for surveys in the Galapagos Marine Reserve (GMR), where relative abundance patterns of juvenile sharks and subsequent classifications of putative nursery areas based on environmental drivers are lacking. The UAV method allowed greater temporal and spatial coverage. We expanded classification of shark nursery habitat through monthly drone surveys and environmental data collection at 14 sites around San Cristobal Island (GMR) from November 2018 to July 2019. In the period of surveying, 56 flights identified 453 juvenile Carcharhinus limbatus (blacktip shark). Classification of nurseries followed three criteria, necessitating higher density, short‐term residency, and annual site fidelity in target locations. We developed preliminary generalized linear models to elucidate potential environmental parameters influencing the perceived abundance and habitat preference of juveniles. Four sites were identified as either potential nurseries or nursery areas for the target species based on previous excursions. An averaged model was subsequently created from the models found to best explain deviance patterns (R² = 0.10–0.44) in perceived shark abundance and habitat preference. Relative variable importance (RVI) values further clarified the parameters most associated with higher juvenile presence. This approach provides a systematic method of abundance surveying while simultaneously beginning the process of defining when and where we expect to find higher abundance through environmental modelling of most influential parameters to perceived abundance in this environment.
... A pesar de los considerables esfuerzos de investigación realizados para identificar y mejorar el conocimiento sobre la importancia que tienen estas áreas de crianza para los tiburones, hasta hace relativamente poco tiempo, aún no se contaba con una definición explícita sobre lo que constituye un área de crianza (Heupel et al. 2007). Dado que no todas las especies de tiburones tienen áreas de crianza, aunado a que la sola presencia de tiburones juveniles en un área específica no garantiza que estas constituyan áreas de crianza, y contribuyan significativamente a la supervivencia y reclutamiento de la población, surge la necesidad de contar con una definición más clara, cuantitativa y estandarizada (Heithaus 2007;Heupel et al. 2007). ...
... A pesar de los considerables esfuerzos de investigación realizados para identificar y mejorar el conocimiento sobre la importancia que tienen estas áreas de crianza para los tiburones, hasta hace relativamente poco tiempo, aún no se contaba con una definición explícita sobre lo que constituye un área de crianza (Heupel et al. 2007). Dado que no todas las especies de tiburones tienen áreas de crianza, aunado a que la sola presencia de tiburones juveniles en un área específica no garantiza que estas constituyan áreas de crianza, y contribuyan significativamente a la supervivencia y reclutamiento de la población, surge la necesidad de contar con una definición más clara, cuantitativa y estandarizada (Heithaus 2007;Heupel et al. 2007). ...
... Fue así como Heupel et al. (2007) propusieron una definición más cuantitativa de las áreas de crianza basada en tres criterios comprobables: ...
Debido a que muchas especies de tiburones cuentan con poblaciones compartidas entre varios países del POT, resulta indispensable contar con programas estandarizados que permitan la comparación de datos en la región y ayuden a establecer políticas de manejo y conservación regionales adecuadas. En este sentido, los programas de marcaje y monitoreo de tiburones tienen el potencial de proporcionar información valiosa sobre la historia de vida y patrones de movimiento de los tiburones, contribuyendo a la toma de decisiones para su protección y manejo sostenible. Sin embargo, su efectividad depende en gran medida del diseño y la aplicación de buenas prácticas. Un programa de marcaje y monitoreo mal diseñado o ejecutado puede llevar a resultados inservibles, sesgados e incluso al daño irreversible de los tiburones marcados.
El presente documento tiene como objetivos: 1) describir los conceptos biológicos y ecológicos básicos de las áreas de crianza de tiburones; 2) describir las metodologías y técnicas utilizadas para el estudio de tiburones neonatos y juveniles; 3) generar un protocolo estandarizado para la caracterización y monitoreo de las potenciales áreas de crianza; y 4) promover las buenas prácticas que garanticen la calidad y comparabilidad de los datos obtenidos así como la supervivencia de los tiburones. Esperamos que este documento sea de utilidad tanto para investigadores como para las personas interesadas en el estudio y la conservación de las áreas de crianza de tiburones.
... Although they are relatively small bodied compared to adults, juvenile sharks are often top predators within estuaries that serve as nurseries (Heithaus, 2007;Matich & Heithaus, 2015). These juvenile sharks are often constrained to shallow habitats to reduce the risk of predation by larger sharks including conspecifics outside of core nursery areas (Guttridge et al., 2012;Heithaus, 2007;Heupel et al., 2007). Juvenile bull sharks (Carcharhinus leucas) can also take advantage of low-salinity waters that most potential predators cannot access (Heupel & Simpfendorfer, 2008;Heupel et al., 2010;Matich & Heithaus, 2015). ...
... While dry season catch rates were similar across all three bays, during the wet season, bull shark catch rates in the bay with the lowest mean salinities (due to artificially enhanced freshwater flow) were more than 2.5 times that of the other two bays. At the broadest spatial scales, juvenile bull sharks appear to be constrained by water temperature-setting the poleward extent of nurseries-and predation risk, which results in the use of shallow nurseries to avoid large sharks (Castro, 2010;Heithaus, 2007;Heupel et al., 2007;Matich & Heithaus, 2015). Bull sharks can survive in lower-salinity waters than other sharks in the Gulf of Mexico and Atlantic Ocean (Hyatt et al., 2018;Pillans et al., 2005; Thorson et al., 1973), allowing them to avoid predators and potential interspecific competitors. ...
The Ten Thousand Islands Estuary of Southwest Florida is the site of ongoing long-term hydrologic restoration. It features gradients of human impacts to freshwater input, from restricted to enhanced flows, including areas with relatively small human effects on water delivery. Thus, it is an excellent location to investigate the biotic and abiotic factors influencing the abundances and size structure of bull shark populations within these estuarine nurseries. We used long-term monitoring data to determine how bull shark abundance varied across three bays differing in human alterations to freshwater flow, which feature spatiotemporal variation in abiotic (salinity, temperature, dissolved oxygen, depth) and biotic (prey abundance and presence of competing species) factors. Boosted Regression Tree analysis revealed that juvenile bull shark abundance was influenced primarily by minimum monthly salinity (relative influence = 42.1). There was also considerable interannual (RI = 29.1%) and monthly (RI = 18%) variation. Minimum temperature (6.6%), average dissolved oxygen (2.1%), and prey abundance (2%) had smaller effects. Spatiotemporal fluctuations in shark abundance relative to abiotic conditions drove seasonally divergent patterns in abundance relative to human water management. While dry season catch rates were similar across all three bays, during the wet season, catches of bull sharks in the bay with the lowest mean salinities due to artificially enhanced freshwater flow were more than 2.5 times that of the other two bays. Overall, our findings suggest that upstream restoration of estuaries will have considerable influence on the suitability of estuarine nurseries for bull sharks, increasing suitability in areas where freshwater flow is enhanced but likely decreasing abundances in areas where inputs are reduced.
... In July-September, YOY records were distributed as follows: 34.6% in Buena Vista, 37.5% in Las Lisas and 24.8% in Sipacate. The data indicate that neonates and YOY are consistently present both seasonally and annually across the three coastal areas, aligning with the criteria established by Heupel et al. (2007). ...
... The present study used fishery-dependent data collected through a Citizen Science programme to analyse the temporal patterns of the early-stage scalloped hammerhead sharks. While Heupel et al. (2007) emphasised the importance of using fishery-independent data to effectively identify nursery habitats, such data with sufficient temporal and spatial coverage are often lacking (Froeschke et al., 2010) ...
The scalloped hammerhead (Sphyrna lewini) is the shark most frequently landed in Guatemalan artisanal fisheries. From 2017 to 2023, fishery‐dependent monitoring recorded 10,000 individuals across three fishing communities. Neonates represented the largest proportion (n = 5860), followed by young of the year (YOY, n = 3929) and significantly fewer juveniles (n = 183) and adults (n = 28). Seasonal patterns were evident, with neonates (84%) and YOY (67.5%) peaking between May and August. The data suggest that neonates and YOY are prevalent seasonally and annually in the three coastal areas.
... Some of these areas may be defined as nurseries (Heupel et al., 2007), which are essential habitats (Heithaus, 2007) and are of great interest to threatened species, like the porbeagle shark (Hyde et al., 2022;Rigby et al., 2019). Therefore, the use of new tools, including the identification of Important Shark and Ray Areas (ISRAs) (Hyde et al., 2022;Kyne et al., 2023), may improve the design and implementation of conservation and management measures, particularly for essential habitats like nurseries (Hyde et al., 2022). ...
... The presence of an important reproductive habitat on the western European shelf is suggested byBiais et al. (2017), supported by captures of juveniles, particularly newborns (break in May 2008. Furthermore, the Spanish longline fleet targeting swordfish has sporadically caught porbeagle sharks as bycatch in the northeast Atlantic(Mejuto et al., 2020), including individuals of 60-95 cm FL, similar to Sharks 2 and 3 documented in this study and those byBiais et al. (2017).According to the criteria established byHeupel et al. (2007), this region is not necessarily classified as a potential nursery area. It remains uncertain whether porbeagle sharks are more commonly encountered in Asturias in comparison to other regions in northern Spain, and there is not clear evidence of a recurring pattern of return across the years. ...
Opportunistic records can provide valuable information on certain species, including the critically endangered porbeagle shark (Lamna nasus). This note documents the occurrence of three juveniles, with approximate 120‐, 88‐, and 85‐cm fork lengths respectively, observed along the coast of Asturias, Spain, in 2024. Given the three distinct scenarios in which these records respectively occurred (incidental capture, washed ashore and stranding), they emphasize the role of citizen science in identifying potential threats to this species, particularly in early stages of life, in a region that may be important and previously overlooked.
... Although these records could reinforce the hypothesis of the presence of a nursery zone in southern Brazilian coastal waters (García-Cortés et al. 2021), specifically in the summer (Vooren et al. 2005), they alone are not sufficient evidence to determine the existence of a nursery area. Heupel et al. (2007) propose three fundamental criteria to establish shark nursery areas, which include higher density, greater site fidelity, and frequent use. Nonetheless, identification of pupping and nursery areas is essential since it may be a potential tool for spatial conservation measures aiming to protect the individuals at their first life stages (Heupel et al. 2007), increasing the probabilities of successful recruitment events (Beck et al. 2001). ...
... Heupel et al. (2007) propose three fundamental criteria to establish shark nursery areas, which include higher density, greater site fidelity, and frequent use. Nonetheless, identification of pupping and nursery areas is essential since it may be a potential tool for spatial conservation measures aiming to protect the individuals at their first life stages (Heupel et al. 2007), increasing the probabilities of successful recruitment events (Beck et al. 2001). Therefore, we encourage further research efforts to identify a possible nursery area in southern Brazil. ...
The shortfin mako shark, Isurusoxyrinchus, plays essential ecological and economic roles in all oceans as a top predator and an important fishery resource. However, knowledge of its reproductive biology is still incomplete on a global basis, mainly due to a lack of sampling of mature females, particularly pregnant ones. In this paper, we studied the reproductive biology of shortfin mako sharks in the southwestern South Atlantic Ocean (SWAO) by describing primary and secondary sexual characteristics (both macroscopic and histologic) and determining the median length at maturity (TL50) using a Bayesian approach. Individuals were collected from pelagic longline fisheries in the SWAO between November 2020 and July 2021. The morphology of the ovaries and their characteristic ovarian pores are described. The histologic analyses showed at least three different follicular development stages for both sexes. The TL50 was found to be 278 cm (95% Cr. I., 257–387) in total length for females and 197 cm (95% Cr. I., 187–207) in total length for males. With these updated parameters, we analyzed the species’ use of the SWAO in different life stages between 2018 and 2023. We found that individuals from different life stages are present in the study area at different times throughout the year and over the years, with, generally, larger individuals in spring and summer. The updated reproductive parameters for the SWAO will support future stock assessments of this species. The evidence of a heterogeneous use of the study area can be seen as an indication of a lack of stock structuring in the region.
... For example, neonates and juveniles may use coastal habitats as nursery areas , which are thought to improve the recruitment of reproducing adults (Beck et al. 2001;Fodrie et al. 2009). Because of the potential significance of shark nursery areas for fitness in shark populations (Heupel et al. 2007;Kinney and Simpfendorfer 2009), there is general interest in identifying such habitats (e.g. Simpfendorfer and Milward 1993;DeAngelis et al. 2008;Froeschke et al. 2010a) and defining drivers of habitat use within those potential nursery areas as population management or conservation tools (e.g. ...
... Channels are typically within 50 m of shore and are thought to limit the distribution of shark neonates (Bouyoucos et al. 2020a). Apaura and Vaiane are nursery areas for N. acutidens (Bouyoucos et al. 2022), meaning that these sites exhibit high shark abundance relative to other sites and persistent use of these habitats by individuals over time (Heupel et al. 2007). Abundance of neonatal C. melanopterus appears to fluctuate between Maharepa and Paorea on an annual basis, suggesting that these sites may serve as nursery areas over longer time scales (Bouyoucos et al. 2022). ...
Context
Coastal habitats function as shark nursery areas; however, coastal habitats can experience extreme variation in abiotic conditions and are susceptible to human disturbances.
Aims
Drivers of abundance were tested within a shark nursery-area system in two populations of reef-associated neonate sharks, namely, blacktip reef sharks (Carcharhinus melanopterus) and sicklefin lemon sharks (Negaprion acutidens).
Methods
Catch data from a fisheries-independent gill-net survey (n = 90 sets from October 2018 to March 2019) at 10 sites around Moorea, French Polynesia, were used to test for associations between shark abundance and abiotic conditions (temperature, oxygen, pH, salinity, lunar phase and depth). Historical levels of fin-fish fishing effort, trampling (i.e. human movement through habitat), and coastal artificialisation (i.e. walls and embankments) estimated for each site were used to test for anthropogenic effects on shark abundance.
Key results
There were no effects of any abiotic or anthropogenic factor on abundance of either species.
Conclusions
Previous work corroborates our findings by demonstrating neonate sharks’ physiological tolerance to extreme abiotic conditions and high survival in response to anthropogenic stressors. Alternatively, populations are already degraded from decades of coastal development.
Implications
These data can aid in predicting the use of coastal habitats as shark nursery areas.
... These shifts in space usage by southern stingrays may be related to both foraging and avoidance of predation (Tilley, 2011;Tilley and Strindberg, 2012 (Hitt et al., 2011;Legare et al., 2018). The juvenile stingrays may also balance the risk of predation and foraging success by using shallow, high complexity habitats (coral hardbottom and patch reefs) at night for safety from larger predators, as has been suggested for elasmobranchs and other species (Franco et al., 2006;Heupel et al., 2007;Legare et al., 2015;Martins et al., 2018). ...
... During our study, we primarily encountered juvenile southern stingrays, and these individuals were resident to Brewers and Perseverance Bays for average of 256 d, confirming one of the three nursery area criteria set forth by Heupel et al. (2007) and Martins et al. (2018). Further research is needed to clarify whether these bays serve as important nursery habitat for southern stingrays. ...
This study provides some of the first evidence of how a common Caribbean fish species that relies on seagrass and sand habitats interacts with an invasive seagrass. The invasive seagrass Halophila stipulacea, first documented in the Caribbean in 2002, has rapidly expanded its range, displacing native seagrasses, and overgrowing bare sand. The southern stingray (Hypanus americanus) uses shallow seagrass and sand habitats for foraging. This paper examined the impacts of the invasive seagrass, H. stipulacea, on southern stingray behavior, foraging and movement patterns using acoustic telemetry and visual observations. From 2015 to 2018, 15 southern stingrays (14 juveniles of unknown sex and 1 female) were tagged with acoustic transmitters and passively monitored within an acoustic array in Brewers and Perseverance Bays, St. Thomas, United States Virgin Islands. The residence time, rates of movement and activity spaces for 50% and 95% utilization distributions (UD) were calculated for day and night periods. Tagged southern stingrays were detected within the array on average for 260 d (range 11–801 d) and residency for all individuals averaged 53% over the monitoring period (1079 d). Mean rates of movement per individual ranged from 40 to 150 m h−1, was lowest during the nighttime and were significantly higher during crepuscular periods. Activity spaces during day and night periods were nearly identical and averaged 0.05 km2 and 0.25 km2 for 50% and 95% UD, respectively. Distances between day and night 50% UD activity spaces was 148 m (range 8–409 m) and mean percent overlap was 38%. In addition to acoustic monitoring, benthic cover of available habitats and visual surveys of stingray behavior and habitat preferences were conducted along fixed transects. Monotypic stands of the invasive H. stipulacea seagrass represented 42% of benthic cover, followed by bare sand (27%), mixed patches of native and invasive seagrasses (23%) and the native Syringodium filiforme (7%). A habitat selection index (HSI) comparing the percent cover of available habitats and habitats occupied by stingrays found a strong preference for the native seagrass S. filiforme (HSI = 2.30) and bare sand (HSI = 1.79) compared to H. stipulacea (HSI = 0.70). Visual surveys also revealed that 50% of foraging stingrays were in S. filiforme, while 28% and 17% were foraging in H. stipulacea and bare sand, respectively. Our results are an important baseline for examining how further expansion of H. stipulacea may affect southern stingray movement patterns and foraging preferences.
... Studies looking into blacktip sharks have found a preference for warmer waters close to tidal inlets that lead into deeper waters (Froeschke et al., 2010). Juvenile blacktip sharks were found to select habitats and exhibit movement patterns that aided in predator avoidance rather than prey distribution (Heupel et al., 2007). Heupel et al. (2007) also found that increased sea surface temperatures correlated with increased growth rates and metabolic rates for blacktip sharks. ...
... Juvenile blacktip sharks were found to select habitats and exhibit movement patterns that aided in predator avoidance rather than prey distribution (Heupel et al., 2007). Heupel et al. (2007) also found that increased sea surface temperatures correlated with increased growth rates and metabolic rates for blacktip sharks. Water temperatures also impact bull shark migratory patterns and seasonal distributions (Matich et al., 2024). ...
... Specifically, juvenile white sharks use coastal habitats more frequently than adults (Kerr et al. 2006, Carlisle et al. 2012, Skomal et al. 2017. These coastal areas are considered to be white shark 'nurseries' if they meet all of these criteria: exhibit a high density of young-of-year (YOY) individuals relative to other areas, relatively high site fidelity of those YOY individuals, and persistence of use across years (Heupel et al. 2007). Areas meeting some or all of these criteria for white sharks have been identified in the Southern California Bight (SCB) (Weng et al. 2007, White et al. 2019, Anderson et al. 2021b (Curtis et al. 2018), and eastern South Africa (Dicken & Booth 2013). ...
... Prey availability is considered to be a defining characteristic of both nursery areas and other essential habitat for sharks (Heithaus 2007, Heupel et al. 2007). Prey availability is related to ontogenetic habitat shifts, because juvenile and adult white sharks, like many other species of shark (Wetherbee & Cortés 2004), have dissimilar diets (French et al. 2018). ...
Ontogenetic habitat shifts are a common feature of many marine species, including sharks, which face conservation threats when their distributions overlap with human resource extraction and habitat modification. White sharks Carcharodon carcharias , for example, exhibit a distinctly coastal phase as juveniles, with a limited distribution compared to the basin-scale range of adults. Using an unoccupied aerial vehicle (UAV), we studied a coastal aggregation site within a Southern California Bight nursery area to determine how fine-scale temporal and oceanographic factors affect white sharks at different developmental stages. White shark density, as measured via UAV, was highly variable across time of day and day of year, with modest variation across years. Typically, more sharks were observed in the late afternoon hours. Sharks, especially those <3 m total length, were observed more often during periods of colder seafloor temperatures, potentially reflecting avoidance of these colder, deeper waters by more cold-intolerant smaller white sharks. Alternate models incorporating sea surface temperature showed a very small but significant association between surface temperatures and <3 m total length white sharks for the months we surveyed, but no such association for larger sharks. There were no or only modest effects of visibility, swell height, chl a levels, sea state, and tidal height on UAV-observed shark density. Understanding how temporal patterns and oceanographic predictors of density change over time as well as how shark ontogeny interacts with these factors can help us to better understand how this species uses coastal habitats and predict when they may be more likely to share marine space with humans.
... Protecting key locations for reproductive activities and the early stages of offspring development is essential for the species' survival (Heupel et al., 2007). Though not the focus of this study, our results showed aggregations of different life stages, which can be used to identify areas with the potential of being nursery areas. ...
... Though not the focus of this study, our results showed aggregations of different life stages, which can be used to identify areas with the potential of being nursery areas. Further research is needed to determine whether these areas meet the 3 criteria for nursery areas: higher density of juveniles than in other sites, presence of juveniles for an extended period, and multiple-year presence of juveniles (Heupel et al., 2007). ...
Growing human use of the marine environment increases the proximity of humans to marine wildlife and thus likely increases human–wildlife interactions. Such interactions influence perceptions of nature and promote or undermine conservation. Despite their importance, human–wildlife interactions are rarely considered in ecosystem‐based marine spatial planning (MSP). Ideally, these interactions should be identified and considered in ecosystem‐based management (EBM), which is often purported to be the basis for MSP. We used Marxan software and data from a citizen science project documenting location, species, age, sex, and activity type to identify regions along Israel's coast with a high probability of encounters between people and 2 species of guitarfish. We considered the geographic distribution of these encounters and the various activities undertaken by the reporting observers. We ran 4 scenarios in Marxan. Two had conservation goals of 30% and 50% guitarfish habitat protection. In the third and fourth scenarios, we added a 50% conservation goal of human leisure activities to each guitarfish conservation goal. We also conducted a gap analysis between our guitarfish conservation goals and the Israel Nature and Parks Authority's master plan for marine protected areas. We found the park authority was close to meeting the 30% goal but was far from meeting the conservation goal of 50% of guitarfish habitat conservation. Different human uses were more likely to interact with different life stages of guitarfish, and different recreational activities occurred in different areas. Identifying areas of specific human use showed which activities should be addressed in conservation management decisions. Our addition of certain recreational uses to the model of habitat conservation showed how enhancing human dimensions in conservation planning can lead to more holistic ecosystem‐based conservation necessary for effective marine planning.
... ISRAs delineated for threatened species (46%) were characterized by key habitats for reproductive or feeding purposes. Information available to identify reproductive areas for sharks and rays has benefited from the recognition of nursery areas as critical habitats through the definition and application of criteria [58][59][60]. This led to ongoing research efforts across the region to identify such areas which in turn increased the information available to apply the ISRA Criteria. ...
Identifying critical habitats is key to the conservation and recovery of threatened species. A third of chondrichthyans (sharks, rays, and chimaeras) are threatened with extinction but robust biological and ecological information to delineate critical habitats for many species remains limited. Here, we investigated (1) research outputs and trends across the Central and South American Pacific region to determine whether sufficient information was available to identify critical habitats; (2) whether regional Important Shark and Ray Areas (ISRAs) were spatially representative; (3) what species and which ecological traits were most commonly used in the delineation of critical habitats; and (4) discuss how ISRAs can inform research priorities and area-based management in support of chondrichthyan conservation. Sixty-five ISRAs were identified for 97 of 190 chondrichthyan species occurring in the region (51%). Across key life-history processes, reproductive areas were most identified (n = 50). Of 821 published studies (2,160 entries), 31.48% (28% entries) primarily focused on fisheries and 48.51% included enough information to inform the ISRA process. Most (58.98%) of these studies originated from Mexico (n = 342, 744 entries) and Ecuador (n = 147, 276 entries). France and Honduras had the least regional research outputs relevant to apply the ISRA Criteria. Significant ecological data gaps were identified in oceanic (including areas beyond national jurisdiction), deepwater (>200 m), and along the southern part of the region (i.e., southern Chile). Deepwater species, chimaeras, and 21% of threatened species had knowledge gaps that did not allow the identification of ISRAs. If area-based management decisions in this region were based on ISRAs, and effectively implemented and enforced, diversity hotspots and at least 97 species could receive protection, including 79% of threatened species and 54% of those considered range-restricted. Increased monitoring and research efforts, with a corresponding increase in funding to fill existing gaps is key to support the identification of important habitats across this region.
... Once the species has been resolved taxonomically, attention can shift to filling key knowledge gaps with respect to their distribution through data collection and research. This step may involve the identification of essential fish habitats (areas that are critical for species viability) such as foraging grounds or egg-laying sites (Heupel et al., 2007). Opportunistic data extracted from unrelated surveys can prove extremely valuable as a starting point; however, the vagaries, likely errors, and low taxonomic certainty of opportunistic data sets can result in a datarich, information-poor (DRIP) scenario (Kosmala et al., 2016;Sulkava et al., 2007;Wilding et al., 2017). ...
Elasmobranchs, specifically skate species (superorder Batoidea), are at risk of extinction, with over one‐third currently listed as Endangered, exacerbated due to their k‐selected life strategy. A regional conservation approach is required to support the collection of rigorous, species‐specific data alongside collaborative efforts across sectors and jurisdictions. Skate species that extend beyond jurisdictional boundaries encounter additional complexities from divergent national legal frameworks, monitoring requirements, and conservation priorities, resulting in inconsistent data collection. Here we present an innovative research “toolbox,” initially devised for the Critically Endangered flapper skate (Dipturus intermedius) in the North‐East Atlantic, but applicable to most demersal elasmobranchs. This toolbox offers a systematic approach (Why, What, Who, Where, and When?) to obtain critical information for the conservation of elasmobranchs, with a focus on standardization and cross‐border collaboration. Recent advancements in understanding flapper skate ecology highlight the potential for regional conservation initiatives, emphasizing the importance of coordinated actions, and serve as an illustrative example within the context of the “toolbox.”
... obs.;2015) and EPO (IATTC unpublished data). Although Silky Sharks use offshore structures as juvenile refuge and/or foraging habitats (Springer 1960;D'Aubrey 1964;Morato et al. 2010;Duffy et al. 2015;Filmalter et al. 2017;Rogers 2018;), it is unknown whether they also use these structures as pupping grounds (i.e., females give birth directly on these structures) and/ or nursery grounds (e.g., juveniles are more abundant around these structures than elsewhere; Heupel et al. 2007). Silky Sharks born offshore likely undergo an ontogenetic shift from primarily structure-associated (e.g., seamounts, floating objects) juveniles to more free-ranging adults (Clavareau et al. 2020;Murray et al. 2023) that often associate with tunas and marine mammals (Anderson and Ahmed 1993;Bonfil 2008;Stevens 2010;Clavareau et al. 2020;Talwar et al. 2024). ...
The Silky Shark (Carcharhinus falciformis) is highly vulnerable to population decline, yet leads shark bycatch in some of the world’s largest tuna fisheries. As such, this species provides an appropriate case study for regional fisheries management organizations—exemplified by the Inter-American Tropical Tuna Commission—to develop conceptual population assessment frameworks that integrate diverse data streams to elucidate population structure and dynamics of assessed species. Using genetic, movement, life history, and small- and large-scale fishery-dependent data from across much of the Silky Shark’s Pacific Ocean range, we found preliminary evidence for a three-stock model—southern, central, and northern—in the eastern Pacific Ocean (EPO). Length distributions of Silky Sharks varied with latitude and across fishery gears and strategies. The predominance of small juveniles, including neonates, caught on or near the continental shelf by small-scale fisheries and offshore by purse seines set on floating objects, including fish aggregating devices, suggested that Silky Sharks use both shelf-edge habitats and offshore areas as pupping and/or nursery areas. Finally, we showed that sex ratios favored females in oceanic and equatorial zones, where most Silky Shark bycatch in large-scale fisheries occurs. Our study serves as a roadmap to comprehensively understand spatial population dynamics of common bycatch species lacking a dispersive larval phase, such as elasmobranchs, by integrating genetic, biological, ecological, and fisheries data. Specifically, our work can inform stock assessments and management measures that may improve Silky Shark conservation in the EPO and elsewhere.
... Regular encounters with neonates/YOY in Handrema Bay in the northeast of the lagoon over the past decade provide preliminary evidence that this is likely to be a nursery habitat. Based on our limited data, this area meets the testable criteria of an elasmobranch nursery: (1) more juveniles are found here than in other areas nearby, (2) individuals tend to remain in the area over time and (3) the habitat is repeatedly used across years (Heupel et al. 2007). The main caveats are that we did not systematically sample the whole lagoon for criteria 1, so neonates may also be present elsewhere, and our detailed survey results support criteria 2 but data are limited at this stage. ...
Reef manta rays Mobula alfredi have fragmented populations across their range and show high site fidelity to certain aggregation sites. The species has been observed around Mayotte, an island in the northern Mozambique Channel with a surrounding barrier reef and a large 1500 km² lagoon. Here, we examined their distribution, movements and population demographics using a combination of citizen science observations and archival satellite tag data. Mayotte’s lagoon and the passes that connect it with the open ocean were important for two life history functions: a bay in the northeast of the island appears to serve as a nursery habitat, and surface feeding is frequently recorded in several areas of the lagoon. All five tracked individuals remained in local waters within ~ 285 km of Mayotte, although estimated track lengths were up to 1579 km over the 4-month tracking duration, highlighting that other regional aggregation sites in Mozambique or the Seychelles are within their potential dispersal range. The four tracked mature individuals spent extensive time outside Mayotte’s lagoon, often diving to mesopelagic depths. Their median swimming depth had a crepuscular signal, being particularly shallow at sunrise and in the early morning (~ 5 m depth), potentially feeding in surface waters, while the median swimming depth was between 30 and 40 m at other times. Considering the small population size and isolation shown here and the low population growth rate of the species, it will be important to identify and minimise threats in the region around Mayotte to improve the conservation of this Vulnerable species.
... Of particular interest, the Argentarola Island site appears to be a potential nursery area. Indeed, a higher number of egg cases was spotted compared to the other sites, and two different adult specimens, probably females, were observed in 2023 and 2024, suggesting that this habitat is repeatedly used across the years (Heupel et al., 2007). Based on definition proposed by Ellis et al. (2012), the finding of juveniles is required to confirm Argentarola Island as a nursery ground. ...
In the circalittoral zone of the Mediterranean Sea, the nursehound Scyliorhinus stellaris lays eggs in spawning areas located at depths between 25 and 50 m in the red gorgonian meadows. Given the evident decline of the nursehound population in the Mediterranean and its high vulnerability, investigating spawning and potential nursery areas is crucial for the conservation of this species. Using non-invasive techniques such as diving activities with the help of R.O.V. ( Remote Operated Vehicle ), spawning areas have been identified along the Tuscany coast in Italy. In addition, B.R.U.V.S. ( Baited Remote Underwater Video System ) was used as an auxiliary method to diving activities in order to record the presence of nursehound individuals. Between 2018 and 2024 (except for 2022), 66 eggs were spotted around Monte Argentario peninsula on the Argentarola Island, Grotta del Corallo, Cala Grande, Capo D’Uomo, Cala della Maddalena and around Giannutri Island in Punta Scaletta. The highest number of eggs was observed around the Argentarola Island, Grotta del Corallo, and Cala Grande, both daily and during the entire study period, which suggests that these three sites represent spawning areas. Furthermore, two adult nursehound individuals have also been sighted near Argentarola Island, suggesting this site could represent a potential nursery area. Further data will be collected in these sites through more in-depth investigation in order to understand spatial distribution patterns, relative abundance, population estimates and behavior of this species along the Tuscany coast.
... A migration of neonates from an offshore area to the study sites in the inner part of the fjord shortly after birth would seem unlikely. Thus, the results obtained in this study could imply that an enclosed environment, such as the Comau Fjord, functions as primary nursery area (see Bass, 1978;Heupel et al., 2007) for S. acanthias. The notion of the fjord serving as a primary nursery area could possibly extend to other shark species. ...
Fjord ecosystems serve as crucial habitats for elasmobranchs, supporting them across all life stages. Chilean Patagonia provides one of the most complex and extensive networks of fjord ecosystems in the world, displaying high marine biodiversity, including elasmobranchs. However, little is known about this ecologically important group of fishes in these ecosystems. This study investigates the biodiversity of elasmobranchs in the Comau Fjord over a period of 6 months by combining morphological and molecular data. In total, 309 specimens within a radius of 7.5 km were recorded, belonging to six families and nine species: Hexanchus griseus (77.5–178 cm L T ), Notorynchus cepedianus (180.6 cm L T ), Schroederichthys bivius (35–65.2 cm L T ), Scymnodon macracanthus (37.3 cm L T ), Centrophorus squamosus (87.4 cm L T ), Deania calceus (58.3–98.6 cm L T ), Squalus acanthias (25.5–101.1 cm L T ), Dipturus chilensis (62.9–152 cm L T ), and Dipturus trachyderma (69.8–194 cm L T ). This included records of three species previously unknown in the fjord and was equivalent to nearly 20% of the elasmobranch richness found in Southern Chile. The results further suggest that the Comau Fjord could be a primary nursery ground for several species of elasmobranchs. This is the first time that a species inventory of elasmobranchs is conducted in a Chilean fjord system. The outcomes of this research provide an elasmobranch species checklist with biological aspects from the Comau Fjord, which are essential data to inform decision makers, conservation managers, and future research.
... In simultaneously sampling several age classes we show not only that young-of-year remain in post-hatching habitats for extended periods, but also that mixing of immature life stages is repeated across years. These are two of three criteria for the classification of shark nurseries (Heupel et al., 2007). Nursery grounds Cook et al. ...
Sharks are increasingly threatened with extinction due to overexploitation. Research priorities to mitigate these trends include identifying ontogenetic variations in spatial and temporal habitat use, as well as critical habitat areas to protect key life stages and processes. Here we demonstrate the regional applicability of laser ablation inductively coupled plasma mass spectrometry with natural tags (barium, magnesium, manganese, strontium) for investigating broad-scale habitat use patterns amongst at risk elasmobranchs in the Northeast Atlantic. We assess vertebral elemental composition in smallspotted catsharks Scyliorhinus canicula as a model species in the Bristol Channel and English Channel, UK, and identify ontogenetic variations throughout the sampling area, with shared habitat use by young-of-year and sub-adults distinct from adult life stages. We find sex segregation only amongst adults, which appears to be driven by male dispersal. Finally, we suggest that distinct adult populations appear to use multiple birthing grounds which therefore are potentially critical habitats for population recruitment, but with differential importance according to usage. Together these findings present an opportunity to integrate precautionary management into current conservation planning in the UK; S. canicula is centrally important to marine food webs, therefore strengthening population robustness against emerging fisheries and environmental perturbations should be a key objective.
... The Bimini Islands enclose an approximately 21-km 2 lagoon that is between 0 and 1.2-m deep at low tide. The relatively shallow water depth limits the abundance of large marine predators, providing a nursery habitat for juvenile lemon sharks (Heupel et al., 2007;Morrissey & Gruber, 1993). Individuals show high site fidelity to their pupping area through at least the first three years of life (Morrissey & Gruber, 1993), after which home range size increases and sharks gradually disperse into deeper and less-protected habitats around the lagoon, with emigration out of the lagoon near sexual maturity (~1.7-m precaudal length, Brown & Gruber, 1988). ...
Home range size and metabolic rate of animals are theorized to scale in relation to body mass with similar exponents. This expectation has only been indirectly tested using lab‐derived estimates of basal metabolic rate as proxies for field energy requirements. Therefore, it is unclear if existing theory aligns with observed patterns of home range scaling since field metabolic rates may scale differently than basal metabolic rates. We conducted the first direct field test of the relationship between home range and metabolic rate allometry. Using acoustic telemetry, we simultaneously measured the home range sizes and field metabolic rates of lemon sharks (Negaprion brevirostris) spanning one order of magnitude in body mass and compared the allometric scaling exponents of these traits. Similarity between allometric scaling exponents confirmed an expected strong association between metabolic rate and home range size. However, a nonsignificant but negative association between standard metabolic rate (SMR) and home range size suggests a complex relationship between metabolism and home range, contrasting previous assumptions of a positive relationship. Nevertheless, an overall positive association between home range size and total metabolic rate persisted, driven by a strong association between active energy expenditure and home range size. These findings underscore the intricate relationship between energetics and home range size, emphasizing the need for additional direct field investigations and the potential for modern tagging technologies to gather relevant data.
... Neonate and young-of-the-year catches are commonly used to identify shark nursery areas, based on criteria from Heupel, Carlson, and Simpfendorfer (2007). However, assessing these criteria is difficult due to variability in coastal habitat use by early life stages (Yates et al. 2012) and limited sampling data with adequate coverage (Froeschke et al. 2010). ...
This study investigates the spatial overlap in habitat use among four key predatory species—school shark ( Galeorhinus galeus ), broadnose sevengill shark ( Notorynchus cepedianus ), copper shark ( Carcharhinus brachyurus ) and sand tiger shark ( Carcharias taurus )—along the Argentine coast to identify important areas for joint management. Leveraging habitat suitability predictions for these predators, we generated annual and seasonal maps to identify significant regions of habitat overlap. Notably, the coastal zone between the Uruguayan and northern Argentine coasts emerged as crucial for developing fishery management and conservation strategies for these four species. Historical catch data also identified important zones for recreational fishing and potential nursery sites, stressing the need for targeted management of the coastal area between Punta Rasa and Mar del Plata (36.3°–38° S). This highlights the necessity of comprehensive fishing regulations with stronger enforcement in the unregulated provincial waters of Chubut and Santa Cruz, as well as the Uruguayan coast. Our findings underscore the importance of integrating species‐specific ecological data in designing marine protected areas and conservation strategies tailored to the unique life history and movement patterns of these sharks. Additionally, the study emphasizes the need for adaptive, multijurisdictional management strategies to accommodate the migratory nature of these species across provincial and national waters. The implications of these findings are discussed within the context of current chondrichthyan policy in Argentina, presenting a foundational basis for informing future management strategies aimed at sustaining shark populations in the Southwest Atlantic.
... In their rush to find food, they will spend much time foraging and trying to capture prey, a vital skill acquired through trial and error (Guttridge et al., 2009). While moving throughout the reef system, small-bodied neonates will also likely encounter larger-bodied predators skilled in hunting, exposing them to high predation pressures early in life (Guttridge et al., 2012;Heupel et al., 2007;Hussey et al., 2017;Trujillo et al., n.d. under review). ...
Elasmobranch fishes (i.e., sharks, skates, and rays) exhibit remarkable wound‐healing capabilities and consistently maintain a high capacity for tissue regeneration throughout their lives. This high capacity for wound healing may be particularly important for neonatal elasmobranchs that are still developing their immune system. However, little is known about the costs associated with wound healing and the potential influence of environmental variables or life history. In this study, we explore (1) the impact of minor, external injuries on the growth and body condition of neonatal blacktip reef (Carcharhinus melanopterus) and sicklefin lemon (Negaprion acutidens) sharks using a long‐term fisheries‐independent dataset from Moorea, French Polynesia, (2) the influence of ambient temperature on healing rates in neonatal blacktip reef sharks at two experimental temperatures (25°C and 29°C), and (3) variations in umbilical wound‐healing rates between blacktip reef and sicklefin lemon sharks using an additional long‐term dataset from St. Joseph Atoll, Seychelles. We found no impact of minor, external injuries on growth and body condition in neonatal blacktip reef and sicklefin lemon sharks, accelerated umbilical wound healing in neonatal blacktip reef sharks exposed to elevated ambient temperatures, and distinct umbilical wound‐healing rates between neonatal blacktip reef and sicklefin lemon sharks. Enhancing our understanding of sharks' healing capabilities and the influence of environmental factors on this process is crucial for informing handling practices aimed at improving post‐release survival rates of captured sharks under current and future oceanic conditions.
... Te high presence of small-sized sharks in the catches is likely due to the coastal nature of artisanal fshing, which may intersect with nursery areas for coastal elasmobranch [21]. Tis observation could highlight ontogenetic segregation, where juveniles and neonates tend to frequent these coastal habitats for reasons of protection or/and food availability [22]. ...
Establishing length–weight relationships (LWRs) is essential for conserving fish populations, especially where gaps hinder efforts, particularly crucial for elasmobranch populations in the Gulf of Guinea. This study presents LWRs established for six species of elasmobranchs landed by artisanal maritime fishing in Mayumba, located in the south of Gabon. The data were collected in May 2022 and between September 2022 and March 2023. This work provides the first LWRs for six elasmobranch species that have not yet been referenced at the regional level. One of these species, Paragaleus pectoralis, lacks referenced data on FishBase.
... The designation of any region as a shark nursery assumes that YOY and juvenile sharks are more commonly encountered in that area relative to other parts of the species' range, juvenile sharks remain in or return to the area for extended periods, and the area is used by juveniles across multiple years (Heupel et al., 2007). Consequently, the observation reported here cannot be used to substantiate the waters of southern New England as a nursery ground for C. brevipinna. ...
A juvenile spinner shark, Carcharhinus brevipinna, was captured and released in the coastal waters of Rhode Island, USA, where range delineations based on historic records of spinner sharks and the species' congener, the blacktip shark, Carcharhinus limbatus, are plagued by misidentification. The shark in question was within the size range of neonates for C. brevipinna and bore a partially healed umbilical wound. This highlights questions concerning the distribution of nursery habitats for the species along the East Coast of North America and how that may be altered by climate change.
... In general, shark nurseries have been characterized by: (i) higher probabilities of encountering juveniles than in adjacent areas, (ii) above average site fidelity; and (iii) repeated use between years 26,29 , in addition to (iv) abundant prey resources and (v) reduced predation risk 30-32 e.g., where smaller sharks are isolated from adults 6,30,33-38 . The current understanding of elasmobranch nurseries is, however, biased towards tropical coastal shark species with few studies on oceanic species 6,26,29,39,40 . Since juvenile mortality is considered one of the most critical factor impacting the sustainability of shark populations 26,39,41 , high fishing effort in nurseries will contribute to faster population declines 3,42-46 . ...
Populations of large pelagic sharks are declining worldwide due to overfishing. Determining the overlap between shark populations and fishing activities is important to inform conservation measures. However, for many threatened sharks the whereabouts of particularly vulnerable life-history stages – such as pregnant females and juveniles – are poorly known. Here, we investigated the spatial distribution of size classes, energy transfer and reproductive states of pregnant females of the endangered shortfin mako, Isurus oxyrinchus, using spatially resolved catch data from a Spanish surface longline vessel (1996 − 2009) in the South-east Pacific Ocean. Our results suggest a general eastward gradient of occurrence of pregnant females of thousands of kilometers from western oceanic feeding grounds towards the eastern Pacific, where we observed an aggregation area of small juveniles. Moreover, the potential nursery likely overlapped a longline fishing hotspot, increasing the vulnerability of juveniles from fisheries. Our results suggest that limiting fishing pressure in this area could reduce mortality of early life stages and contribute to the conservation of this endangered shark species.
... Indeed, in this study, a total of four angling events were of recaptured sharks, with one shark caught three separate times and one caught only one day after it was first captured. It has been well-documented in previous studies that other species of elasmobranchs use shallow, subtidal zones as refuges from predators, and it is likely that juvenile nurse sharks are using these fishing sites around shallow, highly impacted urban areas (e.g., areas near marinas and sea walls) for protection from predation [23,45]. Recaptures in this study suggest they may be site attached with small home ranges, which is supported by existing literature on other species [22,23,25]. ...
Nurse sharks (Ginglymostoma cirratum), especially juveniles, are often encountered by near-shore and shore-based recreational anglers and are suggested to exhibit minimal behavioral and physiological responses to capture, largely based on studies of adults using commercial or scientific fishing methods. To quantify the sub-lethal effects of recreational angling on juvenile nurse sharks, 27 individuals (across 31 angling events) were caught using hook-and-line fishing methods. Over a 30-min period, 4 blood samples were taken with variable time intervals between sampling (i.e., randomized ordering of an interval of 5, 10, and 15 min between each sampling event). Lactate increased by 611% (6.7 ± 2.17 mmol/L) on average over the 30-min fight, and significant relationships were identified between lactate and blood draw number, fight time, and temperature, with large effect sizes. Significant relationships were also detected between blood draw number, glucose, and hematocrit, while osmolality was only affected by fishing site. These results suggest juvenile nurse sharks may exhibit a greater physiological stress response when exposed to recreational angling than adults captured with other fishing methods.
... Thus, for individuals for which the tag remained attached until late October or early November (sharks 12, 14, 15, and 17-19), the pop-up location might be indicative for parturition sites, providing evidence for coastal or even fjord-based parturition sites on the west coast of Norway. Indeed, an area with a disproportionately high abundance of immature spurdogs, albeit at least already young-of-the-year, was identified near the Espevaer and Røvaer islands , in proximity to the southernmost pop-up locations, but more data are needed to confirm whether such area might serve as a spurdog nursery area Heupel et al., 2007). This aligns with findings from the NW Atlantic, ...
The spurdog (Squalus acanthias Linnaeus, 1758) is a globally distributed squaliform shark that has historically been overfished but is now recovering in the northeast Atlantic. Data series on spurdog movement and habitat use have been somewhat limited to research surveys due to challenges associated with electronic tagging. Here, we offer a revised attachment method for externally attached pop‐up satellite archival tags that was successful in long‐term deployments on pregnant females. Twenty‐one spurdogs were tagged in two fjord systems in western Norway for an average of 243 days and provided new details about their behaviour, demonstrating affinity for coastal habitat based on the pop‐up locations and recovery positions of the tags (84% within 40 km from tagging location), and depth–temperature profiles. It is likely that parturition therefore occurs in these coastal waters, making them important to the life cycle of this species. The realized depth niche of tagged individuals suggested that surveys may miss sharks if they do not cover the full water column because the sharks used large parts of the water column and spent much time in shallower waters, albeit with seasonal variations (deeper and shallower in winter and summer, respectively). Adoption of this tagging method and combination with movement data from acoustic transmitters will help to better resolve the behaviour of this species as it transitions from a species at risk to a managed fishery. Such studies will provide a more comprehensive understanding of the species' habitat requirements that will empower better informed protections against a return to the red list of threatened species.
... Their roles in controlling prey populations and facilitating ecosystem stability make them critical to sustaining or restoring marine biodiversity (Heupel et al., 2014;Barrıá et al., 2015;Roff et al., 2016;Shipley et al., 2023). Understanding the behaviour and ecological role of elasmobranchs is critical for their conservation and management, particularly in regions harbouring threatened and data-deficient species such as the Inhambane coastline in southern Mozambique (Heupel et al., 2007;Block et al., 2011;Speed et al., 2011;Pereira, 2021). Despite their ecological significance, numerous elasmobranch species are under threat from anthropogenic pressures Worm et al., 2013;Davidson et al., 2016;O'Malley et al., 2017). ...
Understanding the behaviour and ecological role of elasmobranchs is essential for their conservation, particularly in regions harbouring threatened and data-deficient species like the Inhambane coastline in southern Mozambique, southwestern Indian Ocean. This study employed long-life remote underwater video cameras (LL-RUV) to observe elasmobranch occurrence and behaviour at a rocky reef near Praia do Tofo known for frequent elasmobranch sightings. Between 2021 and 2024, 524 hours of LL-RUV data were collected, revealing the presence of 14 threatened and data-deficient elasmobranch species. Reef manta rays (Mobula alfredi), small eye stingrays (Megatrygon microps), and oceanic manta rays (Mobula birostris) were identified as the primary elasmobranch users of the studied cleaning stations (n = 81, n = 72 and n = 61 respectively), engaging in mutualistic interactions with cleaner fish and spending significant amounts of time at the studied reef. In contrast, spotted eagle rays (Aetobatus ocellatus) and blacktip sharks (Carcharhinus limbatus) were solely observed cruising over the reef without engaging in cleaning interactions (n = 40 and n = 27 respectively). In addition, this study provides evidence of intra- and inter-specific interactions between reef and oceanic manta rays, small eye stingrays and bowmouth guitarfish (Rhina ancylostoma) and co-occurrences of both manta ray species and smalleye stingrays with “hitchhiker” species including cobia (Rachycentron canadum) and remoras (Echeneis spp.). The use of LL-RUV cameras represents a significant advancement in marine research. These cameras enable continuous, non-intrusive, long-term monitoring of marine environments, capturing natural behaviours, while minimising disturbances caused by divers. As a result, more accurate observations of elasmobranch behaviour and cleaning station dynamics can be recorded, which might be missed during short-term surveys. This research highlights the potential of LL-RUV cameras as powerful tools for advancing our understanding of elasmobranch occurrence and behaviour and underscores their value in informing targeted and effective conservation strategies. Beyond elasmobranch research, LL-RUVs hold tremendous potential for studying a wide range of marine species and habitats, offering a versatile tool for ecological monitoring and conservation efforts across diverse marine ecosystems.
... Habitat utilization and movement of marine vertebrates are mainly driven by ontogenetic shifts in their life-history priorities, such as survival, growth, and reproduction (Heupel, Carlson & Simpfendorfer, 2007;Carlisle et al., 2015). This premise, coupled with intraspecific and interspecific interactions, influences marine trophic dynamics, ecosystem structure, and overall biodiversity (Werner & Gilliam, 1984;Baum & Worm, 2009). ...
Background
The morphology and hunting behavior of thresher sharks make them easily distinguishable. These species are distributed across the Tropical Pacific Ocean feeding on squid and small fish. However, ontogenetic changes in their feeding strategies and habitat use are still unknown in this region.
Methods
We examined the δ ¹³ C and δ ¹⁵ N signatures in vertebral collagen from populations of Alopias pelagicus and Alopias superciliosus inhabiting the Galapagos Marine Reserve, focusing on three maturity stages: neonate, juvenile and adult. The vertebrae samples were taken from the seizure of illegal fishing activities carried out by a foreign fleet within the Galapagos archipelago. A total of thirty-three vertebrae from A. pelagicus and twenty-one from A. superciliosus were analyzed.
Results
Both species displayed significant differences in their δ ¹⁵ N values ( p < 0.001), but not in δ ¹³ C ( p = 0.230), suggesting a similar habitat use, but different prey consumption. Throughout their ontogeny, A. pelagicus displayed isotopic differences ( p < 0.001), where neonates showed lower δ ¹³ C values and higher δ ¹⁵ N values compared to juveniles, probably because they still reflect the isotopic signatures of their mothers even after the first year of life. This study highlights trophic differences between both species, accompanied by an ontogenetic variation in A. pelagicus , aspects that allow us to understand the role of these species within the dynamics of the Eastern Tropical Pacific ecosystem.
... For example, nursery areas are used by several shark species (Zanella et al., 2019;TinHan et al., 2020;LaFreniere et al., 2023), including S. canicula (see Cau et al., 2013Cau et al., , 2017. These are areas where neonate or young-of-year sharks are more commonly encountered than in other areas, have a tendency to remain or return for extended periods, and use the area repeatedly across years (Heupel et al., 2007), and are thus candidates for protection to safeguard critical life processes such as parturition and maturation. ...
Global marine biodiversity declines require bold and ambitious plans to safeguard ecosystem services. Overfishing, habitat loss and projected climate impacts have yielded deleterious effects on marine predators, in particular, driving increasing threat of extinction for many shark species with implications for ecosystem health. Identifying and protecting critical habitat areas for sharks is fundamental to their protection, and may allow for species recovery. Here we use baited remote underwater video stations to investigate spatial and temporal patterns of habitat use by sharks in a Special Area of Conservation (SAC) that is centrally important to the regional blue economy in the UK, the Cardigan Bay SAC. Our results show heterogeneous spatial habitat use and temporal trends in habitat sharing between smallspotted catsharks Scyliorhinus canicula and nursehounds S. stellaris. Nearshore reef habitats are substantially more important than non-reef habitats for both species. The relative abundance of each species, however, is roughly inversely seasonally proportional, with S. canicula and S. stellaris relative abundance highest in March and September, respectively. Temporal niche partitioning may be an important mechanism in marine systems, but has not been widely investigated in sympatric shark communities. These findings are directly relevant for ongoing development of the Welsh Marine Evidence Strategy (2019-2025) and the Welsh National Marine Plan, particularly to inform spatial planning to strengthen the role of SAC management design in protecting important shark areas.
... The most common large species in the small fin survey are the scalloped and smooth hammerheads, blacktip, spinner, and bull sharks (Fig. 4B). All these species are tropical, cosmopolitan, threatened, and use coastal areas as nurseries where aggregating juveniles are frequently caught by longline, gillnet, and trawl fisheries (22)(23)(24). ...
Many shark species have been overexploited for international markets, including fins for shark fin soup in Southeast Asia. Previous studies highlighted the value of large, threatened shark species, regulated under CITES Appendix II. However, sampling biases may have overlooked small shark species. Here, we address this by identifying species from ~4000 small shark fins in Hong Kong. These fins included species not recorded in previous surveys, raising the market’s species diversity to 106. Nearly 75% of the small fins came from small shark species and 58.1% of small species were threatened with extinction. We identified an important CITES listing gap: Trade in 19 small, threatened species, especially from the family Triakidae, is unregulated. In addition, a quarter of small fins come from large sharks, indicating that substantial exploitation of juveniles is occurring and may be affecting fisheries sustainability. Enhanced surveillance of small shark fin trade is essential to ensure effective conservation under emerging trade regulations.
... Despite considerable interspecific and intra-specific life-history variation (Last et al. 2016a;Bradley et al. 2017), many sharks and rays exhibit late maturity, low fecundity, long gestation, and slow growth, making them particularly vulnerable to fishing pressure (Cortés 2000). Additionally, their reliance on nurseries (Heupel et al. 2007) and philopatric behaviour (Chapman et al. 2015) increase the risk of local extirpation. Small populations are prone to inbreeding and genetic drift, resulting in a loss of genetic diversity (Rus Hoelzel et al. 2006;Allendorf et al. 2012). ...
Context
The extinction risk of sharks and rays exceeds that of most other vertebrates. Genetic analyses can help identify conservation risks.
Aims
Identification of Fiji’s maskray and testing the null hypothesis of no genetic differentiation within the species over time.
Methods
Mitochondrial DNA cytochrome oxidase subunit 1 (COI) barcoding was used for species identification, and DArT-seq technology to monitor the genetic diversity. Cohort samples were collected in 2015 and 2022. A subset from each cohort was barcoded. The genetic survey was complemented by a size comparison between the two cohorts.
Key results
Barcoding of the COI gene showed a maximum similarity of 97.84% to Kuhl’s maskray (Neotrygon kuhlii) and 96.83% to the Coral Sea maskray (Neotrygon trigonoides), but no higher-level distinct species match to reference sequences in the Barcode of Life Datasystem. Genotyping of 56 individuals in two cohorts yielded 21,293 single nucleotide polymorphisms (SNPs), and 3871 SNPs per individual were retained. The neutral genetic diversity remained stable over time. The 2015 cohort showed positive inbreeding, with one full-sibling pair identified in each cohort. Body size comparisons indicated a significant reduction in disc length and width in the 2022 cohort.
Conclusions
The smaller body size of the 2022 cohort may hint at increased fishing pressure, but genetic diversity has not been affected. Thus, the null hypothesis is accepted.
Implications
These findings provide insights into the genetic diversity of Fiji’s maskray and enable a genetic comparison with current Neotrygon species known in the region. Taxonomy confirmation is needed, but the presence of a cryptic or potentially new maskray in Fiji seems plausible.
... Ontogenetic dietary shifts, which include changes in diet or habitat with increasing size or age, in marine organisms are widely prevalent in nature [1]. These shifts often indicating a transition from a juvenile strategy focused on growth and survival to an adult strategy that includes reproduction [2]. As fish grow, they may develop a variety of feeding-related structures (gill rakers, pyloric ceca, or teeth) and behaviors (filter feeding or particulate feeding), which can markedly enhance their growth rate and improve survival chances [3]. ...
The demersal fish populations constitute a valuable commercial resource in the Beibu Gulf, northern South China. However, our understanding of the ontogenetic dietary shifts of fish, particularly Lagocephalus spadiceus, which is the most widely distributed fish in the northern South China Sea, is lacking. Therefore, we conducted a study using high-throughput sequencing and stable isotope analyses to examine the diet of L. spadiceus. The individuals were collected during 2 bottom trawl surveys in April and August 2022. The length distribution showed that small L. spadiceus was more abundant in shallow water, whereas large fish were generally found in offshore water. High-throughput sequencing indicated that L. spadiceus mainly fed on crustaceans and fish. Ontogenetic changes in diet composition and stable isotope values were also observed. As L. spadiceus grew, they started preying on larger individuals, specifically fish. The ¹⁵N enrichment in large fish supported to small fish supports these findings. The trophic niche indicated a segregation between individuals in shallow waters (mostly small fish) and offshore waters (mostly large fish), which helps in reducing the competition within the species. The L. spadiceus occupied the role of mid-predator (trophic level ~ 3.66) and increased with body length and water depth. Consequently, both high-throughput sequencing and stable isotope analyses provided evidence of intraspecific dietary variation and trophic niche partitioning of L. spadiceus in the Beibu Gulf, South China Sea.
... Only 8 individuals were re-sighted out of approximately 19-23 different specimens, which does not compellingly suggest the presence of site fidelity behavior in this area. The nursery area hypothesis can be defined based on three primary criteria for newborn or young-of-the-year (YOY) individuals (i.e., individuals < 1 year old): (1) sharks are more commonly encountered in the area than in other areas, i.e., density in the area is greater than the mean density over all areas; (2) sharks have a tendency to remain or return for extended periods (weeks or months), i.e., site fidelity is greater than the mean site fidelity for all areas; (3) the area or habitat is repeatedly used across years, whereas others are not [41]. ...
Simple Summary
Between 2012 and 2023, using non-invasive photo-identification techniques, 23 specimens of grey reef sharks were identified in the Mozambique Channel off Nosy Be, in an area called “Mokarran”. Some specimens have been re-sighted in this area for up to 1982 days. A probable aggregation and nursery area for this species may have been identified off the coast of Madagascar and, if confirmed, it will be necessary to provide for its protection.
Abstract
Following preliminary underwater observations of about 1000 h carried out monthly between 2012 and 2023 (except the years 2021 and 2022), 23 specimens of grey reef sharks were spotted and photo-identified off the coast of Nosy Be in Madagascar, on an emerging reef called “Mokarran” at a depth between 15 and 30 m. Over 10 years of observations, eight specimens were re-sighted, identified with a non-invasive photo-identification technique of part of the first dorsal and the caudal fin, and one specimen was re-identified after 1982 days from the first sighting, i.e., after more than 5 years. In addition, six specimens of probably pregnant females were also identified in the same area. The population was entirely made up of females. The aggregation area could represent a new nursery site which, if confirmed after further investigations, will require greater protection.
... Whilst relatively more is understood about nursery areas for sharks than for rays , nursery areas for ray species are increasingly being identified. As is the case for sharks, nursery areas for rays are habitats with proportionally high neonate and juvenile abundance that is stable over time, where young individuals remain for extended periods (Heupel et al., 2007;Martins et al., 2018). Because a large number of ray species lay eggs (Wheeler et al., 2020), nursery areas for rays are also defined as habitats with proportionally high egg abundance, where the habitat is used repeatedly across time and newly hatched rays leave the area (Martins et al., 2018). ...
... Because of their bioecological im-portance in the reproductive success of chondrichthyans, nursery grounds are widely considered to be essential habitats especially for sharks (Heithaus, 2007). From the perspective of utilization by chondricthyan species, this essential habitat requires three criteria to be met for an area to be identified as a nursery: (i) sharks are more commonly encountered in the area than other areas; (ii) sharks have a tendency to remain or return for extended periods; and (iii) the area or habitat is repeatedly used across years (Heupel et al., 2007). Bass (1978) classified shark nursery areas into two types: primary and secondary. ...
The capture of 176 neonate longnose spurdogs Squalus blainville (Risso, 1827), suggests a potential nursery ground in the eastern Marmara Sea (GFCM GSA28). Sampling was performed by means of a scientific bottom trawl hauled at a depth range of 121-126 m on 21 February 2024. Available data show that S. blainville may be captured in demersal fishery within their first year of life. Total length (TL) and total weight (TW) of the examined males ranged from 169 to 279 mm (238.4±20.7 mm) and from 21.4 to 117 g (66.5±19.8 g), respectively. The TL and TW of the examined females ranged from 187 to 292 mm (241.1±25.3 mm) and from 30.1 to 146 g (66.8±29.2 g), respectively. A male neonate (TL=169 mm) examined is believed to be the smallest free-swimming longnose spurdog caught to date. Under current fisheries regulations, S. blainville is a protected shark species in the waters of Türkiye and therefore should be released if caught as bycatch. However, in addition to reducing fishing pressure on the species by prohibiting targeted fishing, area-based conservation actions, which are based on closing areas that are critical for chondrichthyans (e.g., nurseries) to fishing either on a year-round or seasonal basis, should now be included in the conservation plans for S. blainville and other protected species in Turkish waters. Keywords: Squalus, nursery, Marmara Sea, conservation, hypoxia
... Although our study was limited by a small number of pregnant specimens, this finding supports the fact that larger-sized skate species produce larger purses. Some species of elasmobranchs, particularly highly mobile pelagic sharks, are known to occupy separate, usually shallower locations during the early stages of life (i.e., [32][33][34]). A reproductive strategy seemingly less likely for relatively sessile demersal species and one previously not reported for Amblyraja, we found that A. hyperborea < 20 cm (YOY) occupied a largely separate depth range than larger sizes, <900 m, effectively a separate nursery ground. ...
Deepwater survey data and specimens collected from the Grand Banks to Baffin Bay in the Northwest Atlantic were used to examine the distribution, morphometrics, meristics and maturity of two siblings, Amblyraja hyperborea and A. jenseni. Our study confirmed that the two species occupy different locations, their distributions separated by Davis Strait, a biogeographic break separating Atlantic from Arctic waters. A. hyperborea with a smaller maximum size and size at maturity inhabited colder Arctic slope waters in Baffin Bay while larger A. jenseni were located in warmer Atlantic slope waters. Despite their distributional separation and thus reproductive isolation, spine counts and body morphology were almost indistinguishable between species. Only upper jaw teeth row count and difference in the size of spines on the mid-rear wings differentiated the two species. Also, for both species, the proportion of dorsal fins joined, disc shape and relative tail length changed with total length. Secondary reproductive anatomy, clasper length and vas deferens weight, shell gland and uterus weight underwent initial acceleration in growth when the gonads transitioned to stage 2 (adolescent, maturing). Also, YOY A. hyperborea were found to distribute at shallower depths than larger stages, constituting a nursery, which was not observed for A. jenseni.
... Further, individual management practices may be best for LCS species as previous studies have noted significant differences in the population dynamics and life history characteristics (Casey, 2006;Castro, 2010) and differences in habitat utilization may indicate varying interactions between species and their shared habitat that should be assessed on an individual basis (Barker & Schluessel, 2005). Differences in ecological niches between size categories of species that do not utilize nursery areas (Atlantic sharpnose and tiger sharks) could reduce predation and competition (Heithaus, 2001;Heupel et al., 2007). For species exploiting nursery areas (blacktip and sandbar sharks), salinity emerged as important given that movements of larger animals away from nursery habitats correspond with shifts toward higher salinities (Grubbs & Musick, 2007;Heupel & Simpfendorfer, 2002;Santander-Neto et al., 2020). ...
Understanding spatial ecology and predicting animal movements in response to environmental changes, such as anthropogenic climate change and multidecadal variability, is critical for effective conservation strategies. Niche structuring is key to some coastal shark species and size classes coexisting in the US Atlantic and Gulf of Mexico to limit interspecific and intraspecific interaction. Data from four fishery‐independent bottom longline surveys were used to evaluate the abiotic ecological niches of eight species of small and large coastal sharks. Gaussian mixture models separated length composition data into 14 size categories for ecological niche analysis. Generalized additive mixed effect models were fit and coupled with output from dynamic high‐resolution ocean models to predict suitable abiotic habitats, evaluate potential shifts in distribution, and explore the impacts of large‐scale climatological trends on abiotic habitats from 1994 to 2019. The abiotic niche for small coastal sharks generally tended toward warmer, high salinity, shallow bottom waters close to shore. No overarching niche was found for large coastal sharks, but appreciable ontogenetic differences were seen. Most taxa analyzed exhibited declining annual trends in higher quality habitats, particularly during fall months. The analysis provided evidence of shifts north along the Atlantic, to deeper offshore waters in the Atlantic and Gulf of Mexico, and the potential to redistribute in response to multidecadal climate variability for multiple species. The analytical framework described could aid in developing various spatiotemporal management measures, and results provide insight into the habitat characteristics of several species over broad spatiotemporal ranges and through ontogeny.
... Reef shark neonates and juveniles inhabit shallow nursery areas that protect them from predation by larger (adult) sharks (Heithaus 2007;Heupel et al. 2007). However, this also means that the neonatal sharks are to some extent confined to these small areas over the reef flats. ...
Elasmobranch (i.e. sharks, skates, and rays) behaviours have been found to align with moon phases; yet, it is not fully understood how the moon influences elasmobranchs’ foraging habits. In coastal ecosystems, tidal changes are typically seen as the primary influence on the behavioural rhythms of fishes, which are linked to the lunar cycle. Sharks have been documented to synchronise behaviours, such as foraging patterns, with the phases of the moon, but studies have yet to clearly separate and identify the mechanisms by which the lunar phase affects these patterns. The island of Moorea, French Polynesia, serves as a nursery habitat for neonatal blacktip reef and sicklefin lemon sharks within the South Pacific amphidromic system, which experiences minimal tidal ranges (~ 0.2 m). This setting provides a unique opportunity to isolate the lunar cycle’s effects from tidal influences. We compared catch rates of neonates of both shark species and foraging success, through stomach content analysis, of blacktip reef sharks across the lunar cycle. Our findings did not support the hypothesis of lunar-induced entrainment of foraging patterns for these neonatal reef sharks. However, understanding the environmental factors that shape the behavioural patterns and foraging strategies of neonatal reef sharks is becoming increasingly important against the backdrop of human disturbances.
... Compared to sharks in higher latitudes, many sharks in more equatorial waters exhibit year-round residencies in their respective nurseries (e.g. Murchie et al., 2010), which can offer survival advantages (Heupel et al., 2007). The tropicalization of higher latitude estuaries could thus provide sharks with similar benefits if their protective functions and prey availability are not negatively impacted by climate change. ...
Seasonal variability in environmental conditions is a strong determinant of animal migrations, but warming temperatures associated with climate change are anticipated to alter this phenomenon with unknown consequences.
We used a 40‐year fishery‐independent survey to assess how a changing climate has altered the migration timing, duration and first‐year survival of juvenile bull sharks (Carcharhinus leucas).
From 1982 to 2021, estuaries in the western Gulf of Mexico (Texas) experienced a mean increase of 1.55°C in autumn water temperatures, and delays in autumn cold fronts by ca. 0.5 days per year. Bull shark migrations in more northern estuaries concomitantly changed, with departures 25–36 days later in 2021 than in 1982. Later, migrations resulted in reduced overwintering durations by up to 81 days, and the relative abundance of post‐overwintering age 0–1 sharks increased by >50% during the 40‐year study period.
Yet, reductions in prey availability were the most influential factor delaying migrations. Juvenile sharks remained in natal estuaries longer when prey were less abundant. Long‐term declines in prey reportedly occurred due to reduced spawning success associated with climate change based on published reports. Consequently, warming waters likely enabled and indirectly caused the observed changes in shark migratory behaviour.
As water temperatures continue to rise, bull sharks in the north‐western Gulf of Mexico could forgo their winter migrations in the next 50–100 years based on current trends and physiological limits, thereby altering their ecological roles in estuarine ecosystems and recruitment into the adult population. It is unclear if estuarine food webs will be able to support changing residency patterns as climate change affects the spawning success of forage species.
We expect these trends are not unique to the western Gulf of Mexico or bull sharks, and migratory patterns of predators in subtropical latitudes are similarly changing at a global scale.
Aspects of the early life stages of the oceanic manta ray (Mobula birostris), particularly the identification of nursery areas, are either data-deficient or unknown. This study delves into the sighting frequency and habitat use of Mobula birostris in the southwestern Gulf of California, Mexico. Over a period of 9 years, we tracked the movements of manta rays using photo identification and acoustic telemetry in relation to seawater temperature. Our study identified 53 individuals, five of which were tagged with acoustic transmitters. All individuals were immature, with 31 of the 53 being sighted more than once, and three observed in different years. Tagged manta rays displayed a notable preference for La Reina, as their primary daytime habitat, exhibiting a high residency index (0.76) and remaining at the location for up to 55 consecutive days. Based on our observations and acoustic detections, M. birostris has a seasonal occurrence in the southwestern Gulf of California between July and November. These findings validate a potential nursery area for M. birostris in La Reina, serving as a refuge during its early life stage.
This study aimed to identify the most commonly used artisanal fishing gear for capturing elasmobranchs along the coast of Maranhão State, within the Brazilian Amazon Coast. Interviews were conducted with 314 fishers across 17 coastal municipalities using semi-structured questionnaires. These gathered information on vessel characteristics, fishing gear, and elasmobranch species caught in the region. Six types of fishing gear were identified, with gillnets and longlines being the most frequently used. Of the 70 elasmobranch species identified along the Brazilian Amazon Coast, 35 are commonly captured. Among rays, the species most frequently cited by fishers were Hypanus guttatus, Rhinoptera bonasus, Hypanus geijskesi, Aetobatus narinari, Gymnura micrura, Mobula hypostoma, Mobula birostris, and Pseudobatos percellens. For sharks, the most frequently mentioned species included Carcharhinus acronotus, Sphyrna tudes, Carcharhinus leucas, Ginglymostoma cirratum, Galeocerdo cuvier, Rhizoprionodon porosus, and Carcharhinus porosus. Notably, all identified species are susceptible to capture by both gillnets and longlines. To mitigate the impact of these practices on population stocks, particularly for species threatened with extinction, it is essential to develop targeted conservation measures and management plans that address fishing gear, capture areas, and most vulnerable species.
In the 20 years since the IUCN SSC Shark Specialist Group’s first status report (2005), much has changed for
sharks, rays and chimaeras. This report updates our understanding, and the scope of information reflects the scale
of these two decades of change. The breadth of research topics has expanded, mirroring the inclusion of a greater
diversity of species, and attention is being trained on the emerging threats and the accelerating global changes to
aquatic ecosystems. The 2005 report heralded a sea change for sharks, rays and chimaeras, whose historical
obscurity in policy, conservation and fisheries management was a serious concern. In this report, the increased focus that was called for is now apparent
in the scale of work happening across the planet.
In the 20 years since the IUCN SSC Shark Specialist Group’s first status report (2005), much has changed for sharks, rays and chimaeras. This report updates our understanding, and the scope of information reflects the scale of these two decades of change. The breadth of research topics has expanded, mirroring the inclusion of a greater diversity of species, and attention is being trained on the emerging threats and the accelerating global changes to aquatic ecosystems. The 2005 report heralded a sea change for sharks, rays and chimaeras, whose historical obscurity in policy, conservation and fisheries management was a serious concern. In this report, the increased focus that was called for is now apparent in the scale of work happening across the planet. This particular section/file focuses on the Indian Ocean. For the entire report please visit: https://portals.iucn.org/library/node/52102
The co-occurrence of people and sharks within nearshore areas raises concerns about human safety. Unprovoked shark bites are one of the most renowned negative human–wildlife encounters. White sharks (Carcharodon carcharias) are implicated in most fatal unprovoked shark bites globally, but there is limited knowledge of white shark behaviour in the presence of people. We used drone-based methods to analyse human–shark and wildlife–shark interactions. We found a higher probability of a white shark interaction with a nearby person (0.81) in comparison to an animal (0.65). Fishers had the highest, and swimmers had the lowest probability of a white shark interaction. White sharks exhibited investigative behaviour in most interactions, with directional changes towards a nearby person or animal in 85.9% and 94.0% of interactions, respectively. There was a higher probability for white sharks to increase their speed towards animals (0.16) than people (0.01). The likelihood of white sharks altering their speed or direction when people were present depended on human activity. Overall, our study highlighted the value of drone technology in providing insights into white shark behaviour. It also supported the contention that, while people and white sharks coexist within nearshore areas, the probability of a negative human–wildlife encounter remains low.
The sandbar shark, Carcharhinus plumbeus, is commonly captured in the Gulf of Gabès (southern Tunisia). Of 932 specimens collected from January 2001 to May 2004, the smallest mature male was 1545 mm total length and the largest male was 1935 mm. All males above 1600 mm were mature. Adult females ranged 1660-2815 mm, while all females above 1720 mm were mature. The pupping season occurred in spring and early summer, with parturition in July. Gestation was estimated at twelve months, with females appearing to reproduce in alternate years. The diameter of the largest yellow-yolked oocytes ranged 29-32 mm (mean 30.3±1.2) with the mass ranging 9.1-13.3 g (mean 11.9±1.3). Both uteri were compartmentalized into chambers and a single embryo developed in each chamber. Length and weight at birth, based on near-term embryos, were estimated at 450-650 mm and 532-1458 g. The chemical balance of development, based on the mean dry masses of the largest yellow-yolked oocytes and near-term embryos, was 40.3, showing that C. plumbeus is a matrotrophic species. Ovarian fecundity was slightly higher than uterine fecundity. There was a positive relationship between uterine fecundity and total length of females. Litter sizes ranged 4-10 (mean 6.9±1.1). Embryos and free-swimming juvenile and adult females significantly outnumbered males.
Ultrasonic telemetry was used to determine the movements and distribution of juvenile hammerhead sharks (Sphyrna lewini) on their natal grounds in Kaneohe Bay, Oahu, Hawaii. Transmitters were force fed to six pups which were tracked for periods of up to 12 days. All animals showed a high fidelity to a shared daytime core area to which they repeatedly returned after exhibiting wider ranging nocturnal movements. During daytime, the shark pups formed a loose school which moved about within the core area, hovering about 1.5 m off the bay floor. This daytime refuging behavior may serve an antipredation function. Nighttime movements covered the bay floor and bases of patch and fringing reefs and probably represented foraging excursions. Occasional forays away from the core area also occurred during daytime. The small size of the total activity spaces may indicate a healthy forage base for the sharks. Nocturnal swimming speeds were greater than diurnal swimming speeds.
Movement patterns of juvenile sandbar sharks in Delaware Bay were investigated with acoustic telemetry. Thirteen sharks were tracked for between 6-70 h during June-September, 1998. Movements were closely related to tidal currents and most sharks spent the majority of time within 3 km of shore and in water 2-5 m deep. Two sharks ranged further afield and one of these crossed the bay from DE to NJ.
Previous research suggests that nursery areas provide an abundant food source as well as protection from predation for young sharks, and that these benefits are the reasons they use these areas. This study examined the abundance of prey species within a known nursery area, Terra Ceia Bay, Florida, and compared those data with the amount of time blacktip sharks spent within various geographic zones within the nursery. The most abundant prey species within the study site were pinfish, Lagodon rhomboides, pigfish, Orthopristis chrysoptera, spotfin mojarra, Eucinostomus argenteus, and silver perch, Bairdiella chrysoura. Prey species were found to be most abundant in the mid to southern portion of the nursery area, whereas sharks spent the majority of their time within the northern portion of the study site. There was no correlation between the amount of time sharks (as a whole and by individual) spent within a geographic zone and the abundance of prey species within that area. These results suggest that prey abundance is not the main factor directing the movement patterns and habitat choice of juvenile Carcharhinus limbatus within Terra Ceia Bay. Predator avoidance may be more important in the use of the nursery grounds by these young animals than prey abundance.
Evidence of philopatric behavior in diverse species of sharks is accumulating through various sources of data, including studies of shark behavior, genetics and fisheries. If sharks display natural tendencies to return to a home area, birthplace or another adopted locality during portions of their life cycles, as opposed to roaming and dispersing throughout their overall ranges, the impact of fisheries removals and habitat alterations on shark populations and stocks could be profound, and the use of shark catch data to assess stocks could be complicated. We review the accumulating evidence for philopatry in sharks and discuss its implications for fisheries management and conservation of shark species.
In this paper, we address a recent article by Beck et al. (2001, Bioscience 51:633-641), in which it was proposed that the value of a juvenile fish habitat could be most efficiently measured as the production of adults from each juvenile habitat on a per area basis. Based upon retrospective microchemical analysis of otoliths, we calculated this metric (nursery value) for tidal freshwater and brackish littoral habitats of an estuarine fish, white perch Morone americana, in the Patuxent River estuary, Maryland (USA). In dominant year-classes of the population, brackish habitats had the highest nursery value, whereas in all other year-classes, freshwater habitats had the highest nursery value. This result highlights the importance of inter-annual variability in habitat use, and consequently presents a challenging trade-off for applying the nursery-role hypothesis to facilitate habitat conservation and management. Despite this limitation, the nursery-role hypothesis provides an enriched and much needed perspective on population connectivity.
Sharks may have an important role in marine ecosystems in relation to populations of fish and invertebrates at lower trophic levels. Fishery management plans stress the need for an ecosystem approach, but few quantitative studies on the foraging ecology of sharks have been published. Stomach contents and catch data of early life stages of Atlantic sharpnose Rhizoprionodon terraenovae, blacktip Carcharhinus limbatus, finetooth Carcharhinus isodon, and spinner sharks Carcharhinus brevipinna taken from fishery independent surveys in Apalachicola Bay, Florida, USA, were examined to test for overlap in resource use. Young-of-the-year Atlantic sharpnose sharks were found to feed mainly on shrimp, juveniles on sciaenids, and adults on clupeids. Young-of-the-year blacktip sharks were found to feed mainly on sciaenids, whereas juveniles fed on clupeids. The primary prey of young-of-the-year and juvenile finetooth and spinner sharks was clupeids. Eight of 10 prey size-selectivity tests showed neutral selection. Compared to relative prey sizes published for teleost piscivores, Atlantic sharpnose and finetooth sharks consume relatively small-sized prey while blacktip sharks consume relatively large prey. Regardless of maturity state and species, diet overlap was high for species-life stage combinations that are similar in size; however, species-life stages did not show significant habitat overlap. Prey categories shared by similar-sized species may not be limiting, although shark species may have alleviated competition pressure by partitioning the resource of time or space.
There is increasing recognition that habitats should be managed as part of fisheries management. It is generally assumed that amount of suitable habitat is linked to production of demersal species and that maps of bottom type will provide the information needed to conserve essential habitats. In this review, a synthesis of nursery habitat is made for Strombus gigas (queen conch), a large, economically important gastropod in the Caribbean region. Juveniles occur on a variety of bottom types over their geographic range. In the Bahamas, nurseries occur in specific locations within large, beds of seagrass, while obvious characteristics of the benthic environment such as seagrass density, depth and sediment type are not good predictors of suitable habitat. Rather, nurseries persist where competent larvae are concentrated by tidal circulation and where settlement occurs selectively. Nursery locations provide for high juvenile growth resulting from macroalgal production not evident in maps of algal biomass, and they provide for low mortality compared with seemingly similar surroundings. Therefore, critical habitats for queen conch juveniles are determined by the intersection of habitat features and ecological processes that combine to yield high rates of recruitment and survivorship. While maps of bottom type are a good beginning for habitat management, they can be traps without good knowledge of ecological processes. A demersal species can occupy different substrata over its geographic range, different life stages often depend upon different bottom types, and specific locations can be more important than particular habitat forms. Habitat management must be designed to conserve habitat function and not just form. Implicit in the concept of 'essential habitat' is the fact that expendable habitat exists, and we need to prevent losses of working habitat because of inadequate protection, restoration or mitigation. Key nurseries may represent distinctive or even anomalous conditions.
From March 1998 to September 2000, we collected Atlantic Sharpnose Sharks, Rhizoprionodon terraenovae, in the north central Gulf of Mexico between St. Louis Bay,
Mississippi and Perdido Bay, Alabama. Collections were typically made in the
Mississippi Sound over a 4-day period, one site per day, using a gill net fished from
1500 to 2200 h at each site. We collected sharks each month from March to October of
each year of the study. We made a total of 100 collections at approximately 60 different
sites. Rhizoprionodon terraenovae were very common and were distributed over the entire
study area. We collected 1,344 R. terraenovae of all size classes and both sexes; 276 in
1998, 300 in 1999 and 768 in 2000. The unexpectedly low number of adult females in
collections (718 adult males: 9 adult females) suggests that females rarely enter shallow
waters after maturation and both pupping and mating occur outside of the Mississippi
Sound. Sharks begin to appear inshore in the spring when water temperatures
approach 20 to 22 C and begin to move out of the area in fall at 24 to 22 C. In each year
of the study, relative abundance (catch rates as catch per unit effort, CPUE, in sharks/
1000 meters net/hour) of adult male R. terraenovae was highest in spring and fall and
lowest during summer. During summer months, catch rates of adult male R. terraenovae
was significantly and inversely related to temperature. We also found a significant
effect of season on condition factor of adult males, with shark condition lowest during
summer months. These results suggest that the exodus of adult males from inshore
waters may be in response to the high temperature/low oxygen conditions of summer.
However, a reproductively motivated migration from the Mississippi Sound is likewise
a possibility.
Age-length data were derived from counting stained bands on whole vertebral centra obtained from gummy shark, Mustelus antarcticus, captured by gill-nets during 1973-76 in Bass Strait and from gummy shark and school shark, Galeorhinus galeus, captured during 1986-87 in Bass Strait and waters off South Australia. The data were fitted to the von Bertalanffy growth equation after adopting the Francis reparametrization and correcting for sampling bias caused by the selectivity effects of the gill-nets of various mesh sizes used to capture the sharks.
The von Bertalanffy growth curves of male and female gummy shark were significantly different, but the growth curves of male and female school shark were not. The growth curves suggest that growth rates of male and female gummy shark in Bass Strait were lower during 1986-87 than during 1973-76 and that the growth rates of male and female gummy shark and school shark in Bass Strait during 1986-87 were lower than those in South Australia at the same time. These apparent temporal and spatial differences in growth patterns of gummy shark are explained by the 'Phenomenon of Apparent Change in Growth Rate'. It is concluded that the growth curves determined for 1986-87 are distorted by the effects of a long history of high and length-selective fishing mortality and that actual growth patterns of gummy shark are better represented by the von Bertalanffy growth equation determined for shark caught in Bass Strait during 1973-76, when fishing mortality was much lower.
Verification of age estimates was attempted by comparing von Bertalanffy growth curves derived from age-length data with those derived from tag release-recapture length-increment data, but these comparisons highlight the limitations of using tag data for this purpose. Although reasonable agreement was found between such growth curves for gummy shark, it appears that school shark older than 11 years cannot be aged accurately from stained whole or sectioned vertebrae. Sectioned vertebrae from a school shark recaptured 35.7 years after being tagged and released and calculated as having an age exceeding 45 years gave estimates of only 18-20 years of age.
The vast majority of published papers concerning seagrass meadows contain statements to the effect that seagrass beds serve as important nurseries for many species. We reviewed more than 200 papers that were relevant to the nursery role hypothesis. We used both vote counting and meta-analytic techniques to evaluate whether the body of previous studies that report seagrass meadows to be nursery grounds actually contain data that support this proposition. We restricted our analyses to papers that compared seagrass beds to other habitats, and examined data on a variety of well-studied species concerning their density, growth, survival and migration to adult habitat. Within this group of papers, we considered potential factors that could influence the nursery function (e.g. location, or laboratory vs field studies). We also evaluated case histories of well-documented large-scale seagrass losses on the nursery function. Major results were consistent with the expectations that abundance, growth and survival were greater in seagrass than in unstructured habitats. Abundance data also suggested that seagrass beds in the Northern Hemisphere might be more important as nursery areas than those in the Southern Hemisphere. Surprisingly, few significant differences existed in abundance, growth or survival when seagrass meadows were compared to other structured habitats, such as oyster or cobble reefs, or macroalgal beds. Nor were there decreases in harvests of commercially important species that could clearly be attributed to significant seagrass declines in 3 well-studied areas. However, there were decreased abundances of juveniles of commercially important species in these areas, suggesting a strong link between seagrass abundance and those of juvenile finfish and shellfish. One important implication of these results is that structure per se, rather than the type of structure, appears to be an important determinant of nursery value. Clearly, more rigorous studies that test all aspects of the nursery role hypothesis are clearly needed for seagrass meadows as well as other structured habitats. The results of such studies will allow better decisions to be made concerning the conservation and restoration of marine habitats.
Nursery habitat use and growth rates of juvenile scalloped hammerhead sharks Sphyrna lewini were measured in a Hawai'i nursery (Kane'ohe Bay, O ¯ 'ahu) using a 28 mo tag-and- recapture study augmented by experimental determination of the relative age of neonate sharks. An estimated 7700 (±2240 SD) hammerhead sharks are born in Kane'ohe Bay each year. Neonates are born in the summer between May and September and had low retention (from 0.07 to 0.15, as a frac- tion of neonate population size) within the bay from Age 0 to Age 1. A primary cause of low retention appears to be mortality from starvation. Most juvenile sharks recaptured after short periods of time at liberty (
The blacktip shark is a cosmopolitan species found throughout tropical and subtropical waters, It is common along the southeast coast of the United States, where it migrates northward to Georgia and the Carolinas in summer and southward to Florida in winter. The blacktip shark feeds on small bony fishes, primarily menhaden, and small elasmobranchs. Males mature between 1,425 and 1,450 mm TL, and all males over 1450 mm TL are mature. Females mature at about 1,560 mm TL. The reproductive cycle lasts 2 years and includes biennial ovulation with a 1-year gestation period. Mating and ovulation occur in Bulls Bay, South Carolina, from mid-May to early June. Parturition occurs the following year from early May to early June in the shallow coastal waters of the Carolinas. The blacktip shark is a viviparous, placental species. Implantation usually occurs during the 10th and 11th weeks of gestation when the embryos measure 178-194 mm TL. The young are born at about 550-600 mm TL during May and early June in the shallow water, coastal nurseries of Georgia and the Carolinas. The neonate stage lasts about a month. The young remain in the shallow water nurseries until fall.
We conducted a two-year gillnet survey of the relative abundance, species diversity, and reproductive condition of sharks from southeastern North Carolina coastal waters. Sixteen shark species were recorded of which Rhizoprionodon terraenovae (Richardson, 1836) was the most common, representing >80% of the total catch in both years. Large coastal species such as Carcharhinus limbatus (Müller and Henle, 1839) and Carcharhinus plumbeus (Nardo, 1827) were caught infrequently, representing 1% of the total catch. Juvenile, or sub-adult size classes in the total catch were dominated by Carcharhinus brevipinna (Müller and Henle, 1839), Carcharhinus obscurus (LeSueur, 1818), C. plumbeus, and Carcharias taurus Rafinesque, 1810. Sub-adult, or adult size classes in the total catch were dominated by Sphyrna tiburo (Linnaeus, 1758), C. limbatus, Carcharhinus isodon (Müller and Henle, 1839), and Carcharhinus acronotus (Poey, 1860). The smallest mature specimen of R. terraenovae, C. limbatus (female) and C. isodon were smaller than previously documented minimum sizes at maturity. Based on the association of gravid females present in catches with neonates, or small juveniles of the same species, southeastern North Carolina was identified as a primary and/or secondary nursery ground for R. terraenovae , C. brevipinna, C. acronotus and C. obscurus during the months of investigation. Our data also suggest that C. limbatus and Sphyrna lewini (Griffith and Smith, 1834) use southeastern North Carolina as a nursery ground, although more infrequently. Similarly, C. plumbeus uses southeastern North Carolina as an over-wintering ground and neonates are reported infrequently. Almost 100% mature female R. terraenovae and S. tiburo were gravid; most were caught from AugustOctober. Embryos of S. tiburo, based on growth rate extrapolation, were at documented parturition size by September.
Michael W. Beck, Kenneth L. Heck, Jr., Kenneth W. Able, Daniel L. Childers, David B. Eggleston, Bronwyn M. Gillanders, Benjamin Halpern, Cynthia G. Hays, Kaho Hoshino, Thomas J. Minello, Robert J. Orth, Peter F. Sheridan and Michael P. Weinstein
One hundred and thirty Atlantic sharpnose shark Rhizoprionodon terraenovae livers were collected from April 1999 to October 2001 from inshore waters of the Mississippi Sound to investigate seasonal and inter-annual variation in their energetic condition. A decline in the hepato-somatic index (IH) was observed from 1999 to 2001. In addition, IH, liver specific energy content and total energy content were lowest during the summer and highest during the spring and autumn, while liver water content was highest during the summer and lowest during the spring and autumn.
A review of past behavioral ultrasonic telemetry studies of sharks and rays is presented together with previously unpublished material on the behavior of the lemon shark, Negaprion brevirostris, around the Bimini Islands, Bahamas. The review, focusing on movement behaviors of 20 shark and three ray species, reveals that elasmobranchs exhibit a variety of temporal and spatial patterns in terms of rates-of-movement and vertical as well as horizontal migrations. The lack of an apparent pattern in a few species is probably attributable to the scarcity of tracking data. Movements are probably governed by several factors, some still not studied, but data show that food, water temperature, bottom type, and magnetic gradient play major roles in a shark's decision of where and when to swim. A few species exhibit differences in behavior between groups of sharks within the same geographical area. This interesting finding warrants further research to evaluate the causes of these apparent differences and whether these groups constitute different subpopulations of the same species. The lack of telemetry data on batoids and some orders of sharks must be addressed before we can gain a more comprehensive understanding of the behavior of elasmobranch fishes. Previously unpublished data from 47 smaller and 38 larger juvenile lemon sharks, collected over the decade 1988–1998, provide new results on movement patterns, habitat selection, activity rhythms, swimming speed, rate-of-movement, and homing behavior. From these results we conclude that the lemon shark is an active predator with a strong, apparently innate homing mechanism. This species shows ontogenetic differences in habitat selection and behavior, as well as differences in movements between groups of individuals within the same area. We suggest three hypotheses for future research on related topics that will help to understand the enigmatic behavior of sharks.
We investigated short-term movements of neonate and juvenile sandbar sharks, Carcharhinus plumbeus, on their nursery grounds in Delaware Bay. The majority of sharks tracked limited their movements to water less than 5m deep, remained within 5km of the coastline, and occupied oblong activity spaces along the coast. In addition to site-attached coastal movements observed, several sharks moved entirely across Delaware Bay or spent considerable time in deeper portions of the central bay. Sharks tracked on the New Jersey side of the bay tended to spend more time in deeper water, farther from shore than sharks tracked on the Delaware side. Observation-area curves estimated that optimal tracking time for sandbar sharks in Delaware Bay was 41h. Indices of site attachment showed that movement patterns of tracked sandbar sharks varied from nomadic to home ranging. There was no significant difference in rate of movement for day/night, crepuscular periods, or between juveniles and neonates. In general, young sandbar sharks patrolled the coast and appeared to be site attached to some extent, but were capable of making longer excursions, including movement entirely across Delaware Bay.
We surgically implanted ultrasonic transmitters in 38 lemon sharks,Negaprion brevirostris, and manually tracked the sharks for 1–153 days. This yielded 2281 positional fixes recorded at 15-min intervals. We used these positional data with availability data of four environmental variables (water depth, temperature, salinity, and bottom type), sampled at 213 stations along 15 transects, to examine usage of habitat. All sharks used contours of water depth, water temperature, and bottom type disproportionately to the availability of these variables in the study site. Specifically, juvenile lemon sharks selected shallower, warmer water with an underlying rocky or sandy substrate, perhaps for predator avoidance. This is the first report on habitat selection by any elasmobranch.
During the spring and summer months of 1995, 1996 and 1997, gillnet and longline surveys were conducted in conjunction with tag and recapture experiments to outline spatial and seasonal distribution of young sandbar sharks, Carcharhinus plumbeus, in Delaware Bay for essential fish habitat mapping, to assess abundance of young sandbar sharks, and to quantify growth during the summer nursery season. Sandbar sharks (n = 943) ranging from 40 to 120cm fork length (48 to 130cm total length) were captured; yearly totals were 199, 314 and 430 in 1995, 1996 and 1997, respectively. Individuals were captured between June and October in water temperatures ranging from 15.4 to 28.5C and salinities ranging from 22.8 to 30.3 ppt. Presence of neonates and catch per unit effort data indicate that pupping begins in late June near the southwestern coast of the Bay. Juveniles were present from early June through September and their spatial distribution in the Bay appeared uniform. Of 782 sandbar sharks tagged and released during the three years, 50 were recaptured. Mean distance from tag to recapture location and mean days-at-liberty of sandbar sharks recaptured in Delaware Bay during the year of tagging were 10km and 18 days, respectively. Some sharks were recaptured as far as 957km from the release location. Length distributions show young-of-the-year sandbar sharks grow about 2–3cm in length during the nursery season.
Shark nurseries, or nursery areas, are geographically discrete parts of a species range where the gravid females of most species of coastal sharks deliver their young or deposit their eggs, and where their young spend their first weeks, months, or years. These areas are usually located in shallow, energy rich coastal areas where the young find abundant food and have little predation by larger sharks. Nurseries are characterized by the presence of both gravid females and free swimming neonates. Neonates are young bearing fresh, unhealed umbilical scars in the case of placental species, or those at or near the birth size in aplacental species. Bulls Bay, South Carolina, is a nursery for the blacknose, spinner, finetooth, blacktip, sandbar, dusky, Atlantic sharpnose, scalloped hammerhead, and smooth dogfish sharks. The lemon shark has its nursery in shallow waters of south Florida and the Bahamas. The bull shark has its nursery in the lagoons of the east coast of central Florida.
We carried out the first experimental study testing an elasmobranchs ability to return home. We displaced juvenile lemon sharks,Negaprion brevirostris, 4–16 km from their observed home ranges at Bimini Islands, Bahamas during daylight and at night. We tracked all sharks except one back to the Bimini Islands and most returned to their home ranges observed before displacement. Even sharks displaced to a site closer to another island with suitable habitat for young lemon sharks returned to their home ranges at Bimini Islands. Sharks displayed a preferred compass direction (PCD) toward the east as their first swimming direction after release, suggesting an innate sense of direction. This bearing was followed shortly afterwards by a home-oriented direction. Swimming speeds prior to reaching shore were approximately twice as fast than the usual cruising speed reported for juvenile lemon sharks. The return of young (0–2 years), inexperienced sharks to their original home range indicate high site fidelity and an ability to home.
We examined a population of blacktip sharks, Carcharhinus limbatus, within a coastal nursery area to define how individuals use the nursery habitat throughout the summer. We used a series of acoustic hydrophones to passively monitor the movement patterns of sharks for periods up to 167 days. We used passive monitoring data to calculate home range estimates using minimum convex polygon (MCP) and fixed kernel estimators. MCP calculated the extent of an individual's range. Kernel estimates provided information regarding the utilization of space within the home range including core area (50% kernel) and larger excursions outside the core area (95% kernel). Individuals within the nursery area typically used a consistently small core area. All sharks monitored in the study site underwent a home range expansion during the month of July, suggesting a synchronous population-level change in habitat use. This change in habitat use was reflected in all home range calculations. Passive monitoring revealed that young sharks remain within the nursery area for up to 6 months. The long-term use of this nursery area reflects its critical importance to young blacktip sharks.
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 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 immatureC. leucas. The CPUE of <1 year oldC. leucas was highest at temperatures over 29°C and in areas with salinities between 7‰ and 17.5‰ Although they are able to osmoregulate
in salinities from fresh to fully marine, youngC. leucas may have a salinity preference. Reasons for this preference are unknown, but need to be further investigated.
The sandbar shark, Carcharhinus plumbeus, is a wide-ranging coastal species in tropical and temperate regions, and it is the most common species of shark in Hawaii, as in many locations where it occurs. Information on the diet and feeding habits of this species in the Pacific Ocean are extremely limited. For this study we quantified the diet of sandbar sharks in Hawaii based on records collected during the Hawaii Cooperative Shark Research and Control Program from 1967 to 1969. During this program a total of 565 stomachs were examined, of which 265 contained food. Sharks ranged in size from 59 to 190cm total length. Teleosts were the most common prey group, but both cephalopods and crustaceans also occurred frequently. Ontogenetic changes in diet of sandbar sharks were apparent, with crustaceans forming a greater proportion of the diet of smaller sharks. Both cephalopods and elasmobranchs increased in importance with increasing shark size. Prey diversity also increased with size, with large, mobile, and reef prey species found more commonly in the diet of larger sharks. Mature male and female sharks appeared to segregate by depth, though major differences in the diet between the sexes were not apparent. However, there was some evidence of dietary differences between sharks caught in different depths and seasons. The results of this study suggest that sandbar sharks in Hawaii and throughout the world, are primarily piscivores, but also consume a variety of invertebrate prey, and that their diet varies with geographical location and stage of development.
Genetic population structure of the blacktip shark, Carcharhinus limbatus, a commercially and recreationally important species in the southeast U.S. shark fishery, was investigated using mitochondrial DNA control region sequences. Neonate blacktip sharks were sampled from three nurseries, Pine Island Sound, Terra Ceia Bay, and Yankeetown, along the Gulf of Mexico coast of Florida (Gulf) and one nursery, Bulls Bay, on the Atlantic Ocean coast of South Carolina (Atlantic). Sequencing of the complete mitochondrial control region of 169 neonates revealed 10 polymorphic sites and 13 haplotypes. Overall haplotype diversity and percent nucleotide diversity were 0.710 and 0.106%, respectively. Haplotype frequencies were compared among nurseries to determine if the high mobility and seasonal migrations of adult blacktip sharks have maintained genetic homogeneity among nurseries in the Atlantic and Gulf. Chi-square analysis and AMOVA did not detect significant structuring of haplotypes among the three Gulf nurseries, P(2)=0.294, ST=–0.005 to –0.002. All pairwise AMOVA between Gulf nurseries and the Atlantic nursery detected significant partitioning of haplotypes between the Gulf and Atlantic (ST=0.087–0.129, P<0.008), as did comparison between grouped Florida Gulf nurseries and the Atlantic, CT=0.090, P<0.001. Based upon the dispersal abilities and seasonal migrations of blacktip sharks, these results support the presence of philopatry for nursery areas among female blacktip sharks. Our data also support the treatment of Atlantic and Gulf blacktip shark nursery areas as separate management units.
Introduction Despite the ecological significance of elasmobranchs as top-level predators in most marine ecosystems (Cortés, 1999), information on their energetics and metabolism is meager. Metabolism is an important component of an organism’s daily energy budget and may account for its greatest, yet most variable proportion (Lowe, 2001). It was hypothesized that sharks had lower metabolic rates than comparable teleosts because most of the original work on the metabolic rate of sharks focused on relatively inactive, cooler-water sharks such as spotted dogfish, Scyliorhinus canicula (Piiper and Schumann, 1967; Metcalf and Butler, 1984) and spiny dogfish, Squalus acanthias (Brett and Blackburn, 1978). Over time, better techniques have evolved that allow study of more active elasmobranch species that were typically considered difficult to work with in captivity. These advances in technology have expanded our knowledge of ecology, activity level, morphology, cellular physiology, and kinematics of elasmobranchs that exhibit a wide range of lifestyles, indicating that elasmobranchs have metabolic rates comparable to teleost fishes of similar size and lifestyle.
A fishery-independent assessment of juvenile coastal shark populations in U.S. waters of the northeast Gulf of Mexico was conducted using two methods: gillnets and longlines. Surveys were conducted monthly during April-October in two fixed sampling areas from 1996 to 1998. The Atlantic sharp-nose shark, Rhizoprionodon terraenovae, and the blacktip shark, Carcharhinus limbatus, were the most common species captured with either longlines or gillnets. An additional 14 shark species were captured, and juvenile indices of abundance were developed for 8 species with gillnets and 6 species of sharks with longlines. Trends in catch-per-unit-effort were found to vary depending on species. Length-frequency information revealed that the majority of sharks captured were juveniles. Given the direct relationship between stock and recruitment for sharks, continued monitoring of juvenile abundance will aid in determining the strength of the parental stock size and for predicting future population strength.
Since the early 1960s, certain sheltered bays and estuaries around Tasmania have been
designated shark nursery areas, where the taking of either the school shark (Galeorhinus galeus)
or the gummy shark (Mustelus antarcticus) has been prohibited. Recent assessments of
Australian stocks of school and gummy sharks indicate that they are close to collapse,
and the management of the fishery has come under review. With respect to shark nursery areas,
concern has focused on the potential rate of incidental mortality of sharks caused by recreational
gill-net fishing and poaching. In 1990, a study was begun in Frederick Henry Bay and Norfolk Bay,
the largest proclaimed shark nursery areas in Tasmania, to estimate recreational net-fishing effort
and incidental captures of sharks. School sharks were caught in waters deeper than 5 m; gummy
sharks and dogfish were caught at all depths. The diversity and relative abundance of shark species
increased with depth, whereas the diversity of teleosts decreased with depth. Most captured school
and gummy sharks were between 1+ and 3+ years of age.
Preliminary estimates of potential incidental mortality demonstrate that gill-netting in depths greater
than 5 m may be a significant source of mortality for both species.
In south-eastern Australian waters, 5835 school sharks have been tagged since 1947. The two techniques used and the effects of some of the tags on the fins and body walls are described. It was found that the percentage return from experiments using both internal and fin tags was three times that from experiments using only fin tags. No significant difference was found in the numbers of white and grey Petersen disc fin tags returned. No deterioration has been detected in these tags and the silver tagging wires have not shown any appreciable signs of wear. Under natural conditions the incision made in the body wall for this insertion of the internal tag has been found to have healed completely within 2 months. Often there is no sign of the scar after 12 months.
Using tethered floats on 20 sharks and ultrasonic telemetry on 3 others, the short-term movements of young Carcharhinus plumbeus were investigated in the area of Chincoteague, Virginia. The general pattern of movement was predominately in the direction of tidal current flow at a horizontal rate approximately equal to current speed. Movement not in the direction of tidal flow occurred rarely and was associated with slow current speed and the proximity of large schools of menhaden, Brevoortia tyrannus. Rate and magnitude of change in swimming direction increased during slack water periods and upon movement into areas with negligible current flow. No day-night, flood current-ebb current, sex, or size effects were found for locomotor activity. Results suggest that tidal current flow is a major factor influencing the movements of young sandbar sharks in this area.
A population of young blacktip sharks (Carcharhinus limbatus) was monitored over three years to determine their mortality rates using a series of acoustic listening stations. Based on these data it was possible to use several mortality estimators, including indirect life history based methods and direct methods such as the Kaplan-Meier and SURVIV methods, to estimate natural, fishing, and total mortality. Kaplan-Meier (6191%) and SURVIV (6292%) methods provided nearly identical total mortality rates during the first six months of life. This agreement suggests that these estimates are accurate for this population. All natural and fishing mortality occurred within the first 15 weeks of the study. This suggests that young sharks are most vulnerable to all types of mortality during this period. Sharks that survived beyond the first 15 weeks successfully left the nursery and were presumed to have migrated southward during fall months. These results provide critical information concerning the early life history of sharks and the importance of nursery areas to the survival of young animals.
Atlantic sharpnose shark Rhizoprionodon terraenovae (Richardson, 1836) diet is described from Crooked Island Sound, an embayment of the northeast Gulf of Mexico. Diet was assessed by life-stage and quantified using six indices: percent by number, percent by weight, frequency of occurrence, the index of relative importance (IRI), IRI expressed on a percent basis (%IRI), and %IRI based on prey category (%IRIPC). Young-of-the-year (YOY) sharks (n = 56 examined, 37 non-empty stomachs) fed on a mix of teleosts (mostly clupeids, 44.6 %IRIPC) and invertebrates (combined, 25.1 %IRIPC), juveniles (n = 185 examined, 118 non-empty stomachs) on sciaenids (40.7 %IRIPC) and clupeids (37.8 %IRIPC), and mature sharks (n = 105 examined, 67 non-empty stomachs) on sciaenids (71.4 %IRIPC). Differences in diet by site and ontogeny were tested by comparing the diet from Crooked Island Sound with previous published data from areas off St. Vincent Island in Apalachicola Bay, an adjacent estuary. Stomach contents were also used to expand on published prey size-predator size information. Spearman correlation analysis, Pianka's overlap values, null-model simulations, and simple correspondence analysis showed that life stage diet differed within and between sites. Three of four size-selectivity tests showed negative size selection. Absolute prey size and the range in absolute prey size increased with increasing shark size. Atlantic sharpnose shark diet was dominated by prey that were < 40% of shark length; however, 69% of prey items were 21%-40% of shark length while 26% were ≤ 20% of shark length. Variations in diet composition within and between the two sites are likely due to differences in shark size, overall habitat structure, and availability of potential prey species. © 2006 Rosenstiel School of Marine and Atmospheric Science of the University of Miami.
I explored the effect of uncertainty in demographic traits on demographic analyses of sharks, an approach not used before for this taxon. I used age-structured life tables and Leslie matrices based on a prebreeding survey and a yearly time step applied only to females to model the demography of 41 populations from 38 species of sharks representing four orders and nine families. I used Monte Carlo simulation to reflect uncertainty in the estimates of demographic traits and to calculate population statistics and elasticities for these populations; I used correlation analysis to identify the demographic traits that explained most of the variation in population growth rates ( λ ). The populations I examined fell along a continuum of life-history characteristics that can be linked to elasticity patterns. Sharks characterized by early age at maturity, short lifespan, and large litter size had high λ values and short generation times, whereas sharks that mature late and have long lifespans and small litters have low λ values and long generation times. Sharks at the “fast” end of the spectrum tended to have comparable adult and juvenile survival elasticities, whereas sharks at the “slow” end of the continuum had high juvenile survival elasticity and low age–zero survival ( or fertility ) elasticity. Ratios of adult survival to fertility elasticities and juvenile survival to fertility elasticities suggest that many of the populations studied do not possess the biological attributes necessary to restore λ to its original level after moderate levels of exploitation. Elasticity analysis suggests that changes in juvenile survival would have the greatest effect on λ, and correlation analysis indicates that variation in juvenile survival, age at maturity, and reproduction account for most of the variation in λ. In general, combined results from elasticity and correlation analyses suggest that research, conservation, and management efforts should focus on these demographic traits.
Aggregation patterns of a population of juvenile blacktip sharks (Carcharhinus limbatus) within a summer nursery area were examined over a period of 3years using an array of acoustic monitors. Individually coded
acoustic tags were surgically implanted into 33–40 neonate sharks each year from 2000 to 2002 and their presence monitored
continuously by the acoustic array. Data from the acoustic monitors was processed to estimate the center of activity location
of each tagged shark every 30min. Nearest neighbor analysis of shark locations revealed that sharks aggregated within the
nursery in all years of the study. Sharks were aggregated most commonly during the early and late summer months (June, October
and November) and became less common through the middle of the study period each year (July–September). Temporal periodicity
within the data revealed a strong diel pattern with sharks aggregating during the day and dispersing at night, except in June
when aggregations often persisted through the night. Aggregations were generally restricted to the mid and northern sections
of the study site. Reasons for aggregations may include predator avoidance or improved feeding efficiency.
I studied diet and feeding habits in juvenile scalloped hammerhead sharks in Kne'ohe Bay, Hawai'i, from August 1995 to May 1998. The most common prey items were a single species of alpheid shrimp and two species of goby. Benthic surveys indicated that the shrimp and gobies are the most abundant benthic megafauna in Kne'ohe Bay. Sharks had small amounts of food in their stomachs (median = 0.22% of body weight), and sharks with open umbilical scars were more likely to have an empty stomach than sharks with healed umbilical scars. There was a significant diel change in the amount of food in the stomach. Analysis of stage of digestion data and the frequency of occurrence of empty stomachs also indicated that sharks fed more at night than during the day. A number of other factors that might influence diet and feeding were also investigated, including the effect of area, sex, year, season, and proximity to the patch reefs. Season and year had significant effects on the amount of food in sharks' stomachs, but sex and proximity to the patch reef did not.
At least eight species of sharks of the families Carcharhinidae and Sphyrnidae use Cleveland Bay in northern Australia as a communal nursery area.Carcharhinus dussumieri, C. fitzroyensis, C. limbatus andC. tilstoni use the bay as a seasonal primary nursery, with juveniles occurring in it for only a few months each year immediately after birth. Alternatively,Carcharhinus sorrah, Rhizoprionodon acutus andR. taylori use the bay as a year-round primary and secondary nursery, with juveniles remaining in it up to the size at maturity. AdultR. taylori also persist in the bay, a behavioural pattern possibly explained by their small maximum size. While present immediately after birth the type of utilisation pattern displayed bySphyrna lewini could not be clarified in this study. Although diets of these species in the bay are similar, there is probably little direct competition for food due to the highly productive habitats in the bay supporting an abundance of food resources. The highest numbers of juveniles occur when prey species are the most abundant, and when temporal separation of some seasonally-occurring species of sharks in effect.
Fifteen species of elasmobranchs, eight sharks and seven rays, have been recorded with reasonable certainty from the Indian
River lagoon system on the central east coast of Florida. We collected four shark and six ray species during a three and one-half
year study of the northern portion of the lagoon system. Five of these appear to be year-round residents, and the remainder
utilize the area only at restricted times of the year or as a nursery ground. The most abundant resident species areDasyatis sayi, D. sabina, andCarcharhinus leucas. Pristis pectinata, once a common resident species, has been extirpated from the lagoons. The distribution of ocean inlets and salinity appear
to be major factors affecting diversity and numbers of elasmobranchs in the Indian River system.
Metabolic and activity rates determined from free-ranging juvenile scalloped hammerhead shark pups (Sphyrna lewini) in Kāne'ohe Bay, Ō'ahu, HI, were used to develop a simplified energy budget for this population. Five shark pups were tracked using a specially designed acoustic tail beat transmitter. Previous laboratory experiments determined that tail beat frequency (TBF) and water temperature could be used as predictors of instantaneous swimming speed (U) and oxygen consumption rates (V̇o2). Sharks carrying transmitters had higher cost of transport than uninstrumented sharks, but because the difference was quantifiable, appropriate corrections could be made for transmitter effects on energy consumption of instrumented sharks. Sharks tracked in Kāne'ohe Bay had an overall average TBF of 70±10 beats min−1 and a U of 0.81±0.1 body lengths s−1, but swam significantly faster at night than during the day. These sharks also exhibited high average metabolic rates (MR) (96±15 kJ kg−1 day−1) compared with other species of sharks previously studied. Sharks tracked during warmer summer months swam slightly faster and exhibited higher MR than one tracked in December. The high MR measured for sharks in the bay indicate that these sharks require a high daily ration. The relatively low caloric value of the most common prey (snapping shrimp, Alpheus malabaricus) suggests that high numbers must be consumed to meet the sharks' daily requirements. Low and/or negative growth rates of shark pups in the field and declining population size over the summer season suggests that a significant percentage of pups in Kāne'ohe Bay may starve as the result of their high MR requirements. Although availability of A. malabaricus may not be limiting in Kāne'ohe Bay, foraging skills of some neonates may be inadequate to enable them to meet their daily energetic needs. However, sharks that are successful in surviving through the winter may actually grow faster in the colder months due to the temperature dependent decrease of their MR and a reduction in conspecific competition as the result of high summer seasonal attrition due to starvation and emigration.
Gastric evacuation and daily ration were studied in juvenile scalloped hammerhead sharks in Kāne'ohe Bay in order to better understand their ecology and role as apex predators in the marine environment. Three major variables known to affect the rate of gastric evacuation were manipulated: meal size, prey species, and temperature. Rates of gastric evacuation were faster than have previously been measured for sharks. The time for 80% of the meal weight (dry) to be evacuated ranged from 5.4 to 22.1 h. Daily ration was estimated using two different methods based on gastric evacuation rates and stomach content data. Estimates ranged from 2.12% to 3.54% of the body weight, which is relatively high compared to other elasmobranchs, but lower than estimates of maintenance ration for juvenile scalloped hammerheads. Data available for diet and growth of juvenile scalloped hammerhead sharks in Kāne'ohe Bay as well as data for their prey species suggest that these sharks may be surviving much of the time at consumption levels below maintenance ration.