Juvenile Scalloped Hammerhead Sharks Research Articles

Characteristics and species composition of a small-scale shark fishery in Puerto Rico: Jurisdictional issues enable legal landings of prohibited and endangered species

Shark fishing is increasingly regulated in the Caribbean region. We present new information on the characteristics, landings, species composition, and size composition of the shark fishery of Puerto Rico, a U.S. Caribbean territory, and discuss current regulatory issues. Sharks are mainly landed in a small-scale targeted fishery operating in territory jurisdiction (coast to 17 km) that supplies local demand for inexpensive fish. There are at least 16 species caught: a small number of large Tiger (Galeocerdo cuvier) and Blacktip (Carcharhinus limbatus) sharks and many small but adult Sharpnose sharks (Rhizopriodon spp.) accounted for >80% of landed weight. The catch of Sharpnose sharks was significantly skewed to males. Juvenile Scalloped Hammerhead sharks (Sphyrna lewini) were the second-most caught species but accounted for a small proportion of the landed weight and value given their small size. Differences between territory and U.S. federal regulations (17 km-370 km jurisdiction) leads to legal territory landings of federally prohibited species, especially Scalloped Hammerhead sharks, which might undermine the conservation potential of federal regulations. Scalloped Hammerhead sharks are also listed under the U.S. Endangered Species Act (ESA) making ongoing catches more problematic from a legal perspective. Scalloped Hammerhead shark catch reduction could have minimal livelihood impacts because of their low value, which presents an opportunity for stakeholders to engage on catch reduction measures. This study provides new details on how and why different shark species are caught in Puerto Rico, which could facilitate better management that protects threatened species and maintains livelihoods for people.

Bioaccumulation and biomagnification in elasmobranchs: A concurrent assessment of trophic transfer of trace elements in 12 species from the Indian Ocean

We provided the first multi-species study investigating the presence and organotropism of trace elements in three tissues of 12 elasmobranch species. Shark species showed comparable TE loads, although milk sharks and juvenile scalloped hammerhead sharks exhibited the highest Cd and Hg levels, respectively. Fins accumulated higher levels of Pb, Co, and Cr; muscles higher V, As, and Hg; livers higher Se and Cd levels. The organotropism of TEs calls for cautious when choosing a tissue to be sampled since certain tissues, like fin clips, do not provide reliable surrogate for the internal loads of some TEs. Strong correlations between essential and toxic TEs indicated detoxification mechanisms, while the TMF provided evidence for Hg, As and Se biomagnification along the food-web.Considering the difficulties in assessing elasmobranchs contamination from different areas, the proposed multi-species approach represents a valuable way to estimate the species-specific accumulation and transfer of pollutants in sharks.

DNA Analysis of Juvenile Scalloped Hammerhead Sharks Sphyrna lewini (Griffith, 1834) Reveals Multiple Breeding Populations and Signs of Adaptive Divergence in the South Pacific

Shark species have undergone drastic population declines in recent decades due to overfishing and habitat destruction; thus, establishing connectivity among the populations of various shark species is important to determine the appropriate units and spatial scale for conservation and management, particularly as this group is long-lived with late age of maturation. Consequently, we used DNA variation at 1,317 putatively neutral and 25 potentially adaptive single nucleotide polymorphisms (SNPs) to analyze population genetic structure among 174 unrelated individuals of scalloped hammerhead sharks (Sphyrna lewini) from the Rewa Delta and the Ba Estuary, where documented aggregations of neonates and young-of-the-year occur in the island of Viti Levu, Republic of Fiji. Results of the pairwise FST analysis for the neutral loci revealed a small but significant genetic differentiation (FST: 0.004; P-value = 0.0009). Furthermore, the 25 potentially adaptive loci (i.e., under putative selection) revealed a magnitude of differentiation four times bigger than the estimate obtained using neutral genetic diversity (FST: 0.017; P-value = 0.0009). Interestingly, population assignment tests, using the neutral SNP data set and two different software packages, Admixture and assignPOP, provided evidence for the existence of up to four genetically differentiated populations among our samples. Assignment probabilities ranged from 0.98 ± 0.01 to 0.81 ± 0.03. Admixture and assignPOP assigned the same individuals to the same putative populations for all sampled neonates. Thus, our results provide unequivocal evidence that adult females from multiple genetically differentiated breeding populations contribute to these juvenile aggregation sites.

Periodicity of the growth-band formation in vertebrae of juvenile scalloped hammerhead shark Sphyrna lewini from the Mexican Pacific Ocean.

The age of 296 juvenile scalloped hammerhead sharks Sphyrna lewini caught by several fisheries in the Mexican Pacific Ocean from March 2007 to September 2017 were estimated from growth band counts in thin-sectioned vertebrae. Marginal-increment analysis (MIA) and centrum-edge analysis (CEA) were used to verify the periodicity of formation of the growth bands, whereas elemental profiles obtained from LA-ICP-MS transect scans in vertebrae of 15 juveniles were used as an alternative approach to verify the age of the species for the first time. Age estimates ranged from 0 to 10+ years (42-158.7 cm total length; LT ). The index of average percentage error (IAPE 3.6%), CV (5.2%), bias plots and Bowker's tests of symmetry showed precise and low-biased age estimation. Both MIA and CEA indicated that in the vertebrae of juveniles of S. lewini a single translucent growth band was formed during winter (November-March) and an opaque band during summer (July-September), a period of faster growth, apparently correlated with a higher sea surface temperature. Peaks in vertebral P and Mn content spatially corresponded with the annual banding pattern in most of the samples, displaying 1.19 and 0.88 peaks per opaque band, respectively, which closely matched the annual deposition rate observed in this study. Although the periodicity of growth band formation needs to be verified for all sizes and ages representing the population of the species in the region, this demonstration of the annual formation of the growth bands in the vertebrae of juveniles should lead to a re-estimation of the growth parameters and productivity of the population to ensure that it is harvested at sustainable levels.

Community profiling of the intestinal microbial community of juvenile Hammerhead Sharks (Sphyrna lewini) from the Rewa Delta, Fiji

Fourteen juvenile scalloped hammerhead sharks (Sphyrna lewini; SHS) were captured between November and December 2014 in the Rewa Delta in Fiji, and assessed for intestinal microflora characterisation using 16S rRNA amplicon sequencing by Illumina Miseq. The microbial population revealed a fluctuating dominance between the Enterobacteriaceae and Vibrionaceae families, namely Citrobacter and Photobacterium spp. Other related marine operational taxonomic units were closely related to Afipia felis, Chloroflexus aggregans, Psychrobacter oceani, Pontibacter actiniarum and Shigella sonnei. Two sharks had distinctive profiles that were dominated by known pathogens, namely Aeromonas salmonicida and Klebsiella pneumonia. The presence of a Methanosaeta species, and of Shigella and Psychrobacter, would suggest sewage contamination because of a spill that occurred on the 6th of December 2014. This study successfully establishes a baseline for future research.

THE FEEDING HABITS OF JUVENILE SCALLOPED HAMMERHEAD SHARKS (SPHYRNA LEWINI) CAUGHT IN THE GULF OF NICOYA, COSTA RICA

Sharks present strong intraspecific changes in feeding habits, which may vary according to size, geographic location and season. This study analyzed the stomach contents of 52 juvenile scalloped hammerhead sharks (25 females and 27 males) caught by artisanal vessels in the Gulf of Nicoya. Regarding the organisms found in the stomachs, 41.07 % were teleost fish, 30.36 % mollusks and 28.57 % crustaceans. Mollusks presented the highest Relative Importance Index (RII) (43.05 %), followed by teleost fish (41.37 %) and crustaceans (15.58 %). Squids (Loliginidae) were the items with the greatest RII (32.57 %). By means of the Pianka index, a relatively low overlap between sexes was identified, suggesting a spatial sexual segregation and, in consequence, an ecological niche separation between male and female hammerhead sharks.

Ontogenetic migration of a female scalloped hammerhead shark Sphyrna lewini in the Gulf of California

Little information exists on the vertical and horizontal movements of juvenile scalloped hammerhead sharks (Sphyrna lewini). Measurements of the sizes of juveniles caught in nets close to shore and those swimming in schools at seamounts and islands in the southwestern Gulf of California, Mexico indicate that at least part of the population undergoes a migration during their life cycle at a length of approximately 115 cm total length (TL) from coastal to offshore waters. Three juvenile hammerhead sharks were outfitted with archival tags in Mazatlan and La Paz Bay (LPB), Mexico during February 2006 and January 2007, respectively. A single juvenile female measuring 95 cm TL tagged in LPB was recaptured. It traveled a distance of approximately 3,350 km during a 10.5-month period from LPB northward to the central Gulf of California and returning to LPB, 11.7 km north of the location it was tagged. During this migration, the hammerhead increasingly moved from shallow coastal waters to deeper waters to possibly maximize its foraging success. After moving offshore, the shark remained in shallow and warm waters of less than 30 m depth and as high as 32°C during the day, and made repeated dives to deeper and colder waters of 250 m depth and 11°C, at night. Our study documents a female scalloped hammerhead shark changing life history phases from a nursery-inhabiting juvenile inshore to a migratory sub-adult offshore. We also infer that this shark swam within a school of conspecifics at an offshore island or seamount during the day, and migrated away at night, diving to greater depths to feed on mesopelagic prey. We show that this female shark carried out her complete biological cycle in both coastal and offshore areas of the central and southwestern Gulf of California, suggesting maximization of foraging opportunities and continued growth. In this study, we provide evidence for the first time of an ontogenetic migration of a juvenile scalloped hammerhead shark in the Gulf of California, which could be of great significance for the regional management and conservation of sharks in the Gulf of California.

Feeding grounds of juvenile scalloped hammerhead sharks (Sphyrna lewini) in the south-eastern Gulf of California

The aim of this study was to determine whether juvenile scalloped hammerhead sharks (Sphyrna lewini) use the south-eastern Gulf of California as a nursery and feeding area. This information could help lay the groundwork required for the conservation of this endangered species. To address this, we carried out stable isotope (δ15N and δ13C) and stomach content analyses of sharks caught between 2000 and 2004 in Mazatlan, Mexico. Stomach contents and δ13C values indicated that S. lewini is a predator that feeds on benthic prey near the coast. Differences in δ15N average values between sizes classes ( 100 cm) suggest that there was an ontogenetic change in this shark’s feeding habits and also in their living environment (from benthic areas to pelagic areas). The trophic position indicated that S. lewini is a tertiary consumer, but with a high degree of trophic plasticity, and thus, different trophic roles, highlighting the importance of this predator as a regulator of prey populations. Finally, the linear isotopic relationship between S. lewini and its prey indicates a long residency within the Mazatlan area. Our results demonstrate that the south-eastern Gulf of California is a nursery area that offers abundant food for juvenile scalloped hammerhead sharks.

A Comparison of the Foraging Ecology and Bioenergetics of the Early Life-Stages of Two Sympatric Hammerhead Sharks

Juvenile scalloped hammerhead sharks, Sphyrna lewini (Griffith and Smith, 1834), were collected in northwest Florida to examine foraging ecology, bioenergetics, and trophic level [30-60 cm fork length (FL); mean FL= 41.5 cm; N = 196]. Diet analysis was performed using single and compound measures of prey quantity, as well as seven broad diet categories. Diet composition and estimated daily ration were compared to previously published information on bonnethead sharks, Sphyrna tiburo (Linnaeus, 1758). Diet overlap was low between species. Juvenile S. lewini feed on relatively small (85% of prey items < 5% shark length) teleosts (mostly bothids and sciaenids) and shrimps, whereas juvenile S. tiburo has been documented to feed mostly on crustaceans and plant material. Plant material contributed little to the diet of S. lewini. Estimated daily ration was significantly lower for S. lewini than for S. tiburo, regardless of whether plant material was included in the model. Trophic level was calculated at 4.0 for S. lewini and 2.6 for S. tiburo. stable isotope analysis showed S. lewini had significantly higher (delta)15N values and significantly lower (delta)13C values than S. tiburo, consistent with the difference observed in calculated trophic level. These results provide evidence that juvenile hammerhead species coexist in coastal northwest Florida by feeding at separate trophic levels.

Nursery habitat use and foraging ecology of the brown stingray Dasyatis lata determined from stomach contents, bulk and amino acid stable isotopes

Identification of nursery habitats and knowledge of the trophic ecology and habitat use of juvenile fishes within these habitats are fundamental in developing sound management and con- servation strategies. The brown stingray Dasyatis lata is a large benthic predator that inhabits the coastal waters of Hawai'i. Although abundant in these ecosystems, little is known about its basic eco - logy. Stomach content, bulk and amino acid stable isotope analyses were used to assess diet and habitat use of juvenile brown stingrays and to examine the possibility of competitive interactions with juvenile scalloped hammerhead sharks Sphyrna lewini that are sympatric with brown stingrays in K¯ ane'ohe Bay, Oahu. Based on stomach contents, brown stingrays fed almost exclusively on crus- taceans. An ontogenetic shift in stingray diet and an increase in relative trophic position (TP) were apparent from stomach content and stable isotope analysis. Stingray bulk δ 13 C and δ 15 N values indi- cated long-term foraging fidelity to subregions of the bay. Use of K¯ ane'ohe Bay as a nursery habitat was supported by nitrogen isotopic analysis of individual amino acids from stingray muscle samples. Our results clearly demonstrated that stingrays foraged within the bay for the majority of their juve- nile lives then shifted to offshore habitats with the onset of sexual maturity. Trophic enrichment fac- tors used to estimate TPs from amino acid analysis in previous studies may underestimate TPs in elas- mobranchs owing to urea retention for osmoregulation. Potential prey resources were partitioned between stingrays and juvenile scalloped hammerhead sharks, and TP estimates from each analyti- cal method indicated that juvenile scalloped hammerhead sharks forage on higher TP prey than do juvenile brown stingrays. These results show that the study of foraging ecology and habitat use of marine animals can greatly benefit from integrating traditional stomach content and bulk stable isotopic analyses with nitrogen isotopic analyses of individual amino acids.

Estimation of daily energetic requirements in young scalloped hammerhead sharks, Sphyrna lewini

Juvenile scalloped hammerhead sharks, Sphyrna lewini, are apex predators within their nursery ground in Kāne‘ohe Bay, Ō‘ahu, Hawai‘i. Understanding daily maintenance requirements of a top-level predator is an important step toward understanding its ecological impact within a nursery ecosystem. Juvenile S. lewini were fed a range of daily ration levels to examine the effect of feeding rate on growth and gross conversion efficiency. The von Bertalanffy growth model yielded the best fit to the data, predicting a maintenance ration of 115 kJ kg−1 day−1 (3.4% body weight (BW) day−1) and a maximum growth rate of 38 kJ kg−1 day−1. This finding is in agreement with the previous prediction of high energetic requirements for S. lewini. In combination with the hypothesized food limitation within Kāne‘ohe Bay, this result may explain the observed high mortality rates of S. lewini. Gross conversion efficiency, K 1, ranged from −36% to 34%, with maximum efficiency at feeding levels of 5.1% BW day−1. The growth conversion efficiency of S.␣lewini is similar to that of lemon sharks and teleost fishes. Growth rates of juvenile S. lewini are possibly restricted by their high metabolic rate, limited food availability and foraging inexperience. By directly examining the effect of ration size on growth and food conversion, it was possible to resolve discrepancies between earlier studies, which used respiratory metabolism and gut content analyses.

Hammerhead Shark Research Immersion Program: Experiential Learning Leads to Lasting Educational Benefits

High school students (n=45) participated in a 5-day research immersion study on juvenile scalloped hammerhead sharks in Kaneohe Bay, Oahu, Hawaii. Self-surveys were used to evaluate scientific concepts and skills taught during the program. There was a significant shift in students' perceived level of understanding for all categories of concepts and skills. A month following the immersion, a subset of participants (n=9) was given the opportunity to communicate what they had learned to a small group of professional science teachers. A second set of surveys were used to evaluate whether the students had retained knowledge from the 5-day immersion well enough to communicate information to others. During this follow-up, students were able to recall knowledge and demonstrate skills even without a review session. Students reported that they had a good understanding of what they were teaching and were able to teach effectively 79% of the time. Independently, the teachers also rated the students' effectiveness at 79%. The similarity between the teacher and student responses is evidence that the high school students were capable of accurate self-evaluations, validating the positive shift in concepts and skills documented by self-surveys. The lasting impact of the 5-day immersion provides support for experiential and constructivist teaching.

Diet and Diel Feeding Periodicity of Juvenile Scalloped Hammerhead Sharks, Sphyrna lewini, in Kāne'ohe Bay, Ō'ahu, Hawai'i

I studied diet and feeding habits in juvenile scalloped hammerhead sharks in Kāne'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 Kāne'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.

Diel movement patterns of the Hawaiian stingray, Dasyatis lata: implications for ecological interactions between sympatric elasmobranch species

The Hawaiian stingray, Dasyatis lata, is a common benthic elasmobranch in nearshore Hawaiian waters. Acoustic telemetry was used to track the movements of seven rays in Kaneohe Bay, Oahu, Hawaii. Rays were tracked continuously over 31–74 h periods. Geographical movements were analyzed to determine space utilization and rate of movement. Rays were found to utilize significantly larger activity spaces at night (0.83±0.70 km2) (mean±SD) than during the day (0.12±0.15 km2). Mean total activity space for rays tracked was 1.32±0.75 km2. Rates of movement were also significantly higher at night (0.34±0.30 km h-1) than during the day (0.15±0.22 km h-1). Average straight-line swimming speed was 0.64±0.16 km h-1, with a maximum observed swimming speed of 1.9 km h-1. Tidal stage had no effect on rate of movement. Comparison with previously published data on juvenile scalloped hammerhead sharks, Sphyrna lewini, in Kaneohe Bay revealed a high degree of overlap in habitat use and time of activity, suggesting possible ecological interactions between these two species.

Exposure to solar radiation may increase ocular UV-filtering in the juvenile scalloped hammerhead shark, Sphyrna lewini

Light energy is necessary for vision, but ocular tissues are subject to photodamage, and many vertebrates sequester UV-absorbant pigments in their pre-retinal ocular tissues, in part to minimize such damage. In this study (21 May–1 July 2001), juvenile scalloped hammerhead sharks, Sphyrnalewini (Griffith and Smith, 1834), were exposed to higher levels of solar radiation than they had previously experienced in the source habitat in the turbid waters of Kane'ohe Bay, Hawai'i, USA. Light transmission through the ocular media was measured in two individuals shortly after capture and in other individuals after 7, 14, 20, 27, and 41 days exposure to high light levels in a shallow, outdoor pen. Sharks from their usual habitat filtered a small proportion of the UV spectrum, but sharks exposed to greater solar radiation showed increased UV blocking in their corneal tissues, particularly at wavelengths below 310 nm. The proportion of UV blocked was relative to the duration of exposure. There were no changes attributable to exposure duration in transmission through the whole eye or lens, nor was there any clear pattern to variation in transmission through dorsal, ventral, anterior, and posterior quadrants of the cornea. Further experiments will be needed to confirm that this apparently rapid corneal adaptation to high light was due to the increased UV exposure.

Food limitation in a nursery area: estimates of daily ration in juvenile scalloped hammerheads, Sphyrna lewini (Griffith and Smith, 1834) in Kāne'ohe Bay, Ō'ahu, Hawai'i

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.

Bioenergetics of free-ranging juvenile scalloped hammerhead sharks ( Sphyrna lewini) in Kāne'ohe Bay, Ō'ahu, HI

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 (V̇o 2). 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.

Metabolic rates of juvenile scalloped hammerhead sharks (Sphyrna lewini)

Oxygen consumption of juvenile scalloped hammerhead sharks, Sphyrna lewini, was measured in a Brett-type flume (volume=635 l) to quantify metabolic rates over a range of aerobic swimming speeds and water temperatures. Oxygen consumption (log transformed) increased at a linear rate with increases in tailbeat frequency and swimming speed. Estimates of standard metabolic rate ranged between 161 mg O2 kg–1 h–1 at 21°C and 203 mg O2 kg–1 h–1 at 29°C (mean±SD: 189±15 mg O2 kg–1 h–1 at 26°C). Total metabolic rates ranged from 275 mg O2 kg–1 h–1 at swimming speeds of 0.5 body lengths per second (L s–1) to a maximum aerobic metabolic rate of 501 mg O2 kg–1 h–1 at 1.4 L s–1. Net cost of transport was highest at slower swimming speeds (0.5–0.6 L s–1) and was lowest between 0.75 and 0.9 L s–1. Therefore, these sharks are most energy efficient at swimming speeds between 0.75 and 0.9 L s–1. These data indicate that tailbeat frequency and swimming speed can be used as predictors of metabolic rate of free-swimming juvenile hammerhead sharks.

A new acoustic tailbeat transmitter for fishes

A new acoustic transmitter for monitoring the tailbeat frequency of free-swimming fishes and sharks is described. The transmitter is externally mounted on the fish's caudal peduncle and produces an acoustic pulse with every lateral movement of the tail. Field tests on obligate-swimming juvenile scalloped hammerhead sharks ( Sphyrna lewini) show these transmitters accurately telemeter tailbeat deflections from free-swimming sharks. Tests in a flume show sharks with transmitters work harder and swim slower than sharks without transmitters, but these laboratory data can be used to correct for instrument artifacts on free-swimming sharks. A shark tracked with a tailbeat-sensing transmitter exhibited similar movement and activity patterns to shark pups tracked with smaller, orally inserted internal transmitters. The similarity of tracks indicate that the shark equipped with the tailbeat transmitter behaved normally. Thus, this new transmitter design offers a cost-effective, minimally intrusive method for accurately measuring activity rate and energy consumption of active fishes and sharks in the field.

Kinematics and critical swimming speed of juvenile scalloped hammerhead sharks

Kinematics and critical swimming speed (Ucrit) of juvenile scalloped hammerhead sharks Sphyrna lewini were measured in a Brett-type flume (635 l). Kinematic parameters were also measured in sharks swimming in a large pond for comparison with those of sharks swimming in the flume. Sharks in the flume exhibited a mean Ucrit of 65&plusmn;11 cm s-1 (&plusmn; s.d.) or 1.17&plusmn;0.21 body lengths per second (L s-1), which are similar to values for other species of sharks. In both the flume and pond, tailbeat frequency (TBF) and stride length (LS) increased linearly with increases in relative swimming speed (Urel=body lengths traveled per second). In the flume, tailbeat amplitude (TBA) decreased with increasing speed whereas TBA did not change with speed in the pond. Differences in TBF and LS between sharks swimming in the flume and the pond decreased with increases in Urel. Sharks swimming at slow speeds (e.g. 0.55 L s-1) in the pond had LS 19 % longer and TBF 21 % lower than sharks in the flume at the same Urel. This implies that sharks in the flume expended more energy while swimming at comparable velocities. Comparative measurements of swimming kinematics from sharks in the pond can be used to correct for effects of the flume on shark swimming kinematics and energetics.