Residency Of Sharks Research Articles

Environmental stress reduces shark residency to coral reefs

Coral reef ecosystems are highly threatened and can be extremely sensitive to the effects of climate change. Multiple shark species rely on coral reefs as important habitat and, as such, play a number of significant ecological roles in these ecosystems. How environmental stress impacts routine, site-attached reef shark behavior, remains relatively unexplored. Here, we combine 8 years of acoustic tracking data (2013-2020) from grey reef sharks resident to the remote coral reefs of the Chagos Archipelago in the Central Indian Ocean, with a satellite-based index of coral reef environmental stress exposure. We show that on average across the region, increased stress on the reefs significantly reduces grey reef shark residency, promoting more diffuse space use and increasing time away from shallow forereefs. Importantly, this impact has a lagged effect for up to 16 months. This may have important physiological and conservation consequences for reef sharks, as well as broader implications for reef ecosystem functioning. As climate change is predicted to increase environmental stress on coral reef ecosystems, understanding how site-attached predators respond to stress will be crucial for forecasting the functional significance of altering predator behavior and the potential impacts on conservation for both reef sharks and coral reefs themselves.

Multi-year effects of wildlife tourism on shark residency and implications for management

Wildlife tourism can assist species conservation through community-involvement and education, while contributing to regional economies. In the last decade, shark diving has become increasingly popular among wildlife tourists worldwide, including cage-diving with white sharks (Carcharodon carcharias). In Australia, birthplace of the white shark diving industry, an adaptive management framework has been developed to minimise potentially detrimental effects on white sharks. We monitored the residency of 135 white sharks using acoustic tracking over eight years (2013–2021) at the Neptune Islands Group Marine Park to assess the efficacy of management regulations put in place in 2012, which limited the number of operating boats to three and a maximum of five weekly days of activity. A sensitivity analysis was conducted to investigate possible differences in shark residency as a function of number of acoustic receivers used and their corresponding distances to long-term monitoring stations. Similar residency patterns were observed independently of the number of receivers used or their deployment locations, suggesting that the monitoring design was adequate to monitor shark residency. White shark yearly residency decreased following the implementation of new regulations in 2012 and returned to baseline levels by 2013–2014. Our results highlight that white shark residency can recover from tourism-related changes and showcase how adequately-developed and -implemented regulations can enable the successful management and long-term sustainability of one of the oldest shark tourism industries. This adaptative framework (problem identification, development and implementation of policies, efficacy monitoring and performance evaluation) is broadly applicable to management of other tourism industries.

Are sharks attracted to caged fish and associated infrastructure?

There are increasing concerns over the possible effects of aquaculture pens on the local abundance and residency of sharks, and its associated risk for shark bites at nearby beaches and surf breaks. We used acoustic tracking and a before–during–after–control–impact design to assess the residency and local abundance of 117 bronze whalers and 843 white sharks around a 45-m-diameter aquaculture pen installed in South Australia for tourism purposes. Only 14 bronze whalers (12.0% of individuals tagged) and nine white sharks (1.1% of individuals tagged) were detected throughout the 5-year monitoring period and there was no evidence of the pen affecting these sharks, in either the number of sharks detected or number of detections (proxy for length of time detected). The low amount of interactions with the pen was likely to be due to a combination of low fish biomass, pen installed in a shallow location, local shark species being migratory species, and good husbandry practices. Adequate planning and management, and good husbandry practices, such as removal of dead fish from pens and avoiding over-feeding to ensure the feed is entirely consumed, are key to reducing shark interactions with cage fish and associated infrastructure.

Short-term response of research activities on white shark behaviour

Context Researchers studying animals need to ensure that sampling procedures and the methods they use are as harmless and non-disruptive as possible, particularly when their focal species are threatened or protected. White sharks (Carcharodon carcharias) are Vulnerable under the IUCN Red List, protected globally, and are frequently studied by marine ecologists. Aims To assess white shark responses to research activities (i.e. tagging and biopsy procedures, and electric deterrent trials) conducted at the Neptune Islands Group Marine Park (South Australia, Australia). Methods Trends in shark residency following research activities were assessed by comparing shark abundance (number of sharks detected by acoustic receivers and sighted by cage-diving operators) before, during, and after scientific expeditions, and to natural fluctuations in the absence of research activities using 8 years (2013–2021) of acoustic tracking and daily sighting reports from a wildlife tourism industry. Key results Number of white sharks and residency decreased after sampling. However, changes observed following research activities were similar to natural fluctuations, suggesting that these changes reflected natural variations rather than being due to sharks responding negatively to the research activities. Conclusions Our study showed that external tagging, biopsies, or deterrent trials do not affect short- and long-term residency or abundance of white sharks, probably owing to the research activities being minimally intrusive and to sharks having efficient immune systems and remarkable ability to heal from injuries. Implications Re-evaluating study methods forms part of the researcher’s responsibilities to ensure best practice and to abide by national and international codes for the care and use of animals for scientific purposes.

Urban sharks: residency patterns of marine top predators in relation to a coastal metropolis

Understanding and ultimately predicting how marine organisms will respond to urbanization is central for effective wildlife conservation and management in the Anthropocene. Sharks are upper trophic level predators in virtually all marine environments, but if and how their behaviors are influenced by coastal urbanization remains understudied. Here, we examined space use and residency patterns of 14 great hammerheads Sphyrna mokarran, 13 bull sharks Carcharhinus leucas, and 25 nurse sharks Ginglymostoma cirratum in proximity to the coastal metropolis of Miami, Florida, using passive acoustic telemetry. Based on the terrestrial urban carnivore literature, we predicted sharks would exhibit avoidance behaviors of areas close to Miami, with residency patterns in these urban areas increasing during periods of lower human activity, such as during nocturnal hours and weekdays, and that dietary specialists (great hammerhead) would exhibit comparatively lower affinity towards highly urbanized areas relative to dietary generalists (bull and nurse shark). However, we did not find empirical support for these predictions. Space use patterns of tracked sharks were consistent with that of ‘urban adapters’ (species that exhibit partial use of urban areas). Modeling also revealed that an unmeasured spatial variable was driving considerable shark residency in areas exposed to high urbanization. We propose several hypotheses that could explain our findings, including food provisioning from shore-based activities that could be attracting sharks to urban areas. Ultimately, the lack of avoidance of urban areas by sharks documented here, as compared to terrestrial carnivores, should motivate future research in the growing field of urban ecology.

Space use patterns of sharks in relation to boat activity in an urbanized coastal waterway

Aquatic ecosystems face numerous anthropogenic threats associated with coastal urbanization, with boat activity being among the most prevalent. The present study aimed to evaluate a potential relationship between boat activity and shark space use in Biscayne Bay, Florida (USA), a coastal waterway exposed to high levels of boating. Spatiotemporal patterns in boat density and traffic were determined from aerial surveys and underwater acoustic recorders, respectively. These data were then compared with residency patterns of bull (Carcharhinus leucas), nurse (Ginglymostoma cirratum) and great hammerhead (Sphyrna mokarran) sharks quantified through passive acoustic telemetry. Results were mixed, with no detectable relationship between boat density and shark residency for any of the species. Hourly presence of G. cirratum decreased with increasing boat traffic, a relationship not seen in the other two species. Explanations for these results include habituation of sharks to the high levels of chronic boat activity in the study area and interspecific differences in hearing sensitivity.

The power of national acoustic tracking networks to assess the impacts of human activity on marine organisms during the COVID-19 pandemic

COVID-19 restrictions have led to an unprecedented global hiatus in anthropogenic activities, providing a unique opportunity to assess human impact on biological systems. Here, we describe how a national network of acoustic tracking receivers can be leveraged to assess the effects of human activity on animal movement and space use during such global disruptions. We outline variation in restrictions on human activity across Australian states and describe four mechanisms affecting human interactions with the marine environment: 1) reduction in economy and trade changing shipping traffic; 2) changes in export markets affecting commercial fisheries; 3) alterations in recreational activities; and 4) decline in tourism. We develop a roadmap for the analysis of acoustic tracking data across various scales using Australia's national Integrated Marine Observing System (IMOS) Animal Tracking Facility as a case study. We illustrate the benefit of sustained observing systems and monitoring programs by assessing how a 51-day break in white shark (Carcharodon carcharias) cage-diving tourism due to COVID-19 restrictions affected the behaviour and space use of two resident species. This cessation of tourism activities represents the longest break since cage-diving vessels started day trips in this area in 2007. Long-term monitoring of the local environment reveals that the activity space of yellowtail kingfish (Seriola lalandi) was reduced when cage-diving boats were absent compared to periods following standard tourism operations. However, white shark residency and movements were not affected. Our roadmap is globally applicable and will assist researchers in designing studies to assess how anthropogenic activities can impact animal movement and distributions during regional, short-term through to major, unexpected disruptions like the COVID-19 pandemic.

Long-Term Acoustic Monitoring Reveals Site Fidelity, Reproductive Migrations, and Sex Specific Differences in Habitat Use and Migratory Timing in a Large Coastal Shark (Negaprion acutidens)

Knowledge of the movement patterns of the lemon shark Negaprion acutidens is poor in contrast to the allopatric N. brevirostis. Using acoustic telemetry, we investigated daily (diel and tidal) and seasonal patterns in residency, fidelity, home range, habitat preference, and migratory patterns along the Ningaloo coast, Australia. Thirty eight adult N. acutidens were monitored for up 6.1 years (mean 2.5 y) with 19 animals detected for more than 3 years and 5 for more than 5 y. Approximately 50% of the tagged animals remained within 10 km of their tagging location for more than 12 months (average core home range of 1.7 km2). Surprisingly, residency of adults was greater than juveniles in this known nursery area. Adults showed a strong preference for lagoon habitats and moved into shallow nearshore habitats at high tide and at night. During winter months, female sharks shifted their core home range 0.45 km further offshore into deeper lagoon areas, a shift which is likely due to behavioral thermoregulation. Space use by males and females within core areas was asynchronous indicating sexual segregation by resident sharks. Both resident and non-resident sharks were detected up to 140 km away. These highly directional (southerly) and rapid movements (140 km in 2 days) were largely correlated with the parturition and mating periods with males departing 1–2 months earlier than females. In females, periodicity of migrations was variable with evidence of annual and biannual patterns. Negaprion acutidens are highly susceptible to over-fishing and movement data are essential to quantify spatio-temporal overlap with fisheries and assist with developing spatially explicit stock assessment models.

The impact of injury on apparent survival of whale sharks (Rhincodon typus) in South Ari Atoll Marine Protected Area, Maldives

The whale shark (Rhincodon typus) is an endangered species with a declining global population. The South Ari Atoll Marine Protected Area (SAMPA), Maldives, is one of few locations globally where year-long residency of individuals occurs. This SAMPA aggregation appears to consist almost exclusively of immature males. Due to its year-round residency, this local aggregation is subjected to a high degree of tourism pressure. This ecotourism contributes to the high level of interest and protection offered to whale sharks by the local community. Unfortunately, if regulations are not followed or enforced, tourism can bring with it major stressors, such as accidental injuries. We used POPAN capture-mark-recapture models and lagged identification rate analysis to assess the effect of major injuries on whale shark residency within SAMPA. Injuries may be obtained outside SAMPA. We found individuals with major injuries had a higher apparent survival in the area than those without. Lagged identification rates also demonstrated that sharks with major injuries are more likely to return to the area. We suggest that major injuries result in sharks prolonging their time in the developmental habitat. These findings have implications for individual fitness and the population viability of this endangered species. We propose targeted conservation strategies be considered to protect sharks from further injury. Based on the presented spatio-temporal distributions of sharks, and current local knowledge of sighting patterns, speed limit zones and propeller-exclusion zones should be implemented and enforced. If carried out alongside tourist education, these measures will contribute to the protection of whale sharks within SAMPA and beyond. Furthermore, our results can aid research direction, alongside regulation and enforcement development, at similar sites worldwide.

Scarring patterns of whale sharks, Rhincodon typus, at a provisioning site in the Philippines

Abstract Shark‐based tourism continues to be a rapidly growing industry, and thus understanding the impacts of such activities is essential to mitigate the potential negative effects on the target species. The consequences of provisioning on whale sharks (Rhincodon typus) are not fully understood, although changes to the local environment, ecology, behaviour, and site visitation patterns have been highlighted. Here, the scarring patterns of whale sharks were investigated at a provisioning site in Oslob, Cebu, Philippines, as an indicator of the physical impacts of tourism activities on individual sharks. Photographic identification was used to attribute scars to individual animals (n = 152) between March 31, 2012 and January 31, 2015. Scars were categorized by type and body location, and were compared with non‐provisioned aggregations in Australia, Mozambique, and Seychelles. Oslob whale sharks were more scarred than other studied populations, with 94.7% (n = 144) having at least one scar, and with 90.8% (n = 138) having more than one scar. Scarring incidence was found to be significantly higher in sharks that regularly visited the provisioning site, and analysis of scarring over time in highly resident sharks showed that all individuals gained scars through periods of consistent re‐sightings. A significantly higher incidence of minor scar types was found, most commonly on the dorsal side of the animal, probably resulting from sustained proximity to boats and ropes throughout the provisioning activities. The consequences of interactions with propeller boats were observed, despite a ban on their use in the provisioning site, highlighting the risk to the species beyond the study site. We recommend the strict enforcement of a minimum distance between boats and sharks, a zero‐contact policy during interactions, the expansion of the provisioning site, and the implementation of a no‐boat‐access zone around the perimeter of the provisioning site to mitigate potential collisions.

Sex-based differences in movement and space use of the blacktip reef shark, Carcharhinus melanopterus.

Information on the spatial ecology of reef sharks is critical to understanding life-history patterns, yet gaps remain in our knowledge of how these species move and occupy space. Previous studies have focused on offshore reefs and atolls with little information available on the movement and space use of sharks utilising reef habitats closer to shore. Cross-shelf differences in physical and biological properties of reefs can alter regional ecosystem processes resulting in different movement patterns for resident sharks. Passive acoustic telemetry was used to examine residency, space use and depth use of 40 blacktip reef sharks, Carcharhinus melanopterus, on an inshore reef in Queensland, Australia, and assess temporal or biological influences. All sharks showed strong site-attachment to inshore reefs with residency highest among adult females. Sharks exhibited a sex-based, seasonal pattern in space use where males moved more, occupied more space and explored new areas during the reproductive season, while females utilised the same amount of space throughout the year, but shifted the location of the space used. A positive relationship was also observed between space use and size. There was evidence of seasonal site fidelity and long-distance movement with the coordinated, annual migration of two adult males to the study site during the mating season. Depth use was segregated with some small sharks occupying shallower depths than adults throughout the day and year, most likely as refuge from predation. Results highlight the importance of inshore reef habitats to blacktip reef sharks and provide evidence of connectivity with offshore reefs, at least for adult males.

Trophic resources and mercury exposure of two silvertip shark populations in the Northeast Pacific Ocean

Worldwide shark populations have experienced rapid declines over the last decades, mainly due to overfishing. Marine protected areas (MPAs) have thus become an indispensable tool for the protection of these marine predators. Two recently-created MPAs in the Northeast Pacific Ocean, the Revillagigedo National Park and Clipperton Atoll, are characterized by different trophic structures potentially influencing the trophic niche and contaminant exposure of resident sharks in these two sites. In this context, we used carbon (δ13C) and nitrogen (δ15N) stable isotope analyzes as well as total mercury concentrations ([THg]) to assess the effect of foraging site on the trophic niche and Hg levels of juvenile silvertip (ST) sharks Carcharhinus albimarginatus. Analyzing fin clip samples from Revillagigedo and Clipperton, we found that shark δ15N varied spatially in relation to δ15N baselines, suggesting similar trophic position in both MPAs. Moreover, δ13C values indicated that ST sharks from Revillagigedo would feed on different food webs (i.e. both benthic and pelagic) while individuals from Clipperton would only rely on benthic food webs. These differences between MPAs led to a weak overlap of isotopic niches between the two populations, highlighting the site residency of juvenile ST sharks. Within each population, [THg] was not correlated with trophic tracers (δ15N and δ13C) and was also similar between populations. This study revealed no influence of site or food web in [THg] and raises the question of the origin of Hg exposure for reef shark populations in the Northeast Pacific Ocean.

Multi-tissue stable isotope analysis reveals resource partitioning and trophic relationships of large reef-associated predators

Defining the role of reef predators is particularly important given the rapid rate at which some species are declining, yet knowledge of trophic relationships is often lacking, particularly for large wide-ranging species that may use coral reefs seasonally or opportunistically. We used a multi-tissue stable isotope approach to investigate the trophic ecology of common reef predators in the central Great Barrier Reef of Australia. Our study revealed significant trophic separation among reef predators, especially when considering isotopic data from muscle, a slower turnover tissue. Based on muscle data, the bull shark Carcharhinus leucas, a large wide-ranging coastal species, occupied a higher trophic position and had a larger isotopic niche breadth (19.12) relative to smaller predators, including resident sharks (4.5 ± 0.72) and large-bodied teleosts (4.4 ± 1.82). Spanish mackerel Scomberomorus commerson and bull sharks had the largest unique total areas of isotopic niche space (expressed as a percentage) that did not overlap with any other species, 95% and 69.4%, respectively, which means they had lower isotopic overlap. In general, faster turnover tissues such as whole blood and plasma showed higher isotopic overlap and smaller niche breadth for all reef predators. These results suggest that bull sharks use similar prey resources to large and small resident predators, at least during short periods. Our findings highlight the importance of investigating dietary changes in faster-turnover tissues of reef predators, particularly large wide-ranging species, which may have key roles in coral reef food webs through direct predation and competition.

Residency and long-distance movements of sevengill sharks (Notorhynchus cepedianus) tagged in San Francisco Bay

BackgroundSevengill sharks are common inhabitants of estuaries and coastal areas and particularly abundant in San Francisco Bay (SFB). There is limited knowledge about the level of residency and migratory movements of this species. We describe the degree of residence of sevengill sharks in SFB and nearby locations, using ultrasonic tags and automated listening stations.ResultsSevengills showed a high degree of residency in SFB, particularly to the Golden Gate (GG) area where they have a strong site preference, both seasonally and inter-annually. Site fidelity was also the highest at the GG. In sharks with deployment times longer than 300 days, we found that > 80% of visits of all mature males were at GG, 80% of visits of a single mature female occurred there, > 85% of visits of most juvenile males, and > 70% of visits of most juvenile females. At GG, sharks moved into the range of the receiver day and night without a strong preference for a particular time of the day, which implies movements up and down the area day and night. At most other locations within the bay, sharks were present during daytime hours, while at Point Reyes during nighttime hours. Sharks moved into SFB during early spring and summer, and moved out of SFB to Point Reyes during late spring and fall. Three sevengill sharks migrated roughly 800 km southeastward along the coastline from SFO, one making three trips back and forth between the sites.ConclusionsThere was strong evidence of residency of sharks within SFB, and sharks repeatedly returned to the same region of the bay with some sharks making long-distance movements.

Feeding the world's largest fish: highly variable whale shark residency patterns at a provisioning site in the Philippines.

Provisioning wildlife for tourism is a controversial yet widespread practice. We analysed the residency patterns of juvenile whale sharks (Rhincodon typus) in Oslob, Philippines, where provisioning has facilitated a large shark-watching operation since 2011. We identified 208 individual sharks over three years, with an average of 18.6 (s.d. = 7.8, range = 6–43) individuals sighted per week. Weekly shark abundance varied seasonally and peak-season abundance (approx. May–November) increased across years. Whale sharks displayed diverse individual site visitation patterns ranging from a single visit to sporadic visits, seasonal residency and year-round residency. Nine individuals became year-round residents, which represents a clear response to provisioning. The timing of the seasonal peak at Oslob did not align with known non-provisioned seasonal aggregations elsewhere in the Philippines, which could suggest that seasonal residents at Oslob exploit this food source when prey availability at alternative sites is low. Since prolonged residency equates to less time foraging naturally, provisioning could influence foraging success, alter distributions and lead to dependency in later life stages. Such impacts must be carefully weighed against the benefits of provisioning (i.e. tourism revenue in a remote community) to facilitate informed management decisions.

No persistent behavioural effects of SCUBA diving on reef sharks

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 567:173-184 (2017) - DOI: https://doi.org/10.3354/meps12053 No persistent behavioural effects of SCUBA diving on reef sharks Darcy Bradley1,*, Yannis P. Papastamatiou2, Jennifer E. Caselle3 1Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, CA 93106, USA 2Department of Biological Sciences, Florida International University, North Miami, FL 33181, USA 3Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA 93106, USA *Corresponding author: darcybradley@ucsb.edu ABSTRACT: Despite rapid growth in the marine tourism sector, the impacts of recreation on the marine environment are generally not well understood. Most existing studies of marine recreation ecology have focused on behavioural changes resulting from direct interactions between humans and wildlife including provisioning. However, non-consumptive, non-provisioning human impacts may also result in persistent behavioural impacts to shark populations. In this study, we examined differences in residency, abundance, and behaviour of reef sharks at Palmyra Atoll in response to long-term SCUBA diving activity, using a combination of survey techniques including baited remote underwater video systems and multi-year passive acoustic monitoring. In most locations with recreational diving operations, some level of human impact is pervasive, but on Palmyra, extractive fishing is prohibited, and scientific diving activities are concentrated on just a few sites that house long-term monitoring projects. These sites experience relatively intensive diving, while the majority of the island is entirely undived. Evidence from elsewhere has shown that sharks behaviourally respond to people in the water over short time scales, but our results indicate that this response may not persist. We did not detect differences in reef shark abundance or behaviour between heavily dived and undived locations, nor were there differences in shark residency patterns at dived and undived sites in a year with substantial diving activity and a year without any diving. Our results suggest that humans can interact with reef sharks without persistent behavioural impacts, and that well-regulated shark diving tourism can be accomplished without undermining conservation goals. KEY WORDS: Shark · Tourism · Predator · Residency · Abundance · Behavioural activity Full text in pdf format Supplementary material PreviousNextCite this article as: Bradley D, Papastamatiou YP, Caselle JE (2017) No persistent behavioural effects of SCUBA diving on reef sharks. Mar Ecol Prog Ser 567:173-184. https://doi.org/10.3354/meps12053 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 567. Online publication date: March 13, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Extreme Inverted Trophic Pyramid of Reef Sharks Supported by Spawning Groupers

The extent of the global human footprint [1] limits ourunderstanding of what is natural in the marine environment. Remote, near-pristine areas provide some baseline expectations for biomass [2, 3] and suggest that predators dominate, producing an inverted biomass pyramid. The southern pass of Fakarava atoll-a biosphere reserve in French Polynesia-hosts an average of 600 reef sharks, two to three times the biomass per hectare documented for any other reef shark aggregations [4]. This huge biomass of predators makes the trophic pyramid inverted. Bioenergetics models indicate that the sharks require ∼90 tons of fish per year, whereas the total fish production in the pass is ∼17 tons per year. Energetic theory shows that such trophic structure is maintained through subsidies [5-9], and empirical evidence suggests that sharks must engage in wide-ranging foraging excursions to meet energy needs [9, 10]. We used underwater surveys and acoustic telemetry to assess shark residency in the pass and feeding behavior and used bioenergetics models to understand energy flow. Contrary to previous findings, our results highlight that sharks may overcome low local energy availability by feeding on fish spawning aggregations, which concentrate energy from other local trophic pyramids. Fish spawning aggregations are known to betargeted by sharks, but they were previously believed to play a minor role representing occasional opportunistic supplements. This research demonstrates that fish spawning aggregations can play a significant role in the maintenance of local inverted pyramids in pristine marine areas. Conservation of fish spawning aggregations can help conserve shark populations, especially if combined with shark fishing bans.

Three decades of longlining in Bimini, Bahamas, reveals long-term trends in lemon shark Negaprion brevirostris (Carcharhinidae) catch per unit effort.

In Bimini, Bahamas, the consistent employment of longlines, beginning in 1982, provided a rare opportunity to explore population trends for large resident sharks. This study assessed three shallow water longline survey periods at this location; 1982-1989, 1992-2002 and 2003-2014, with the aim of determining trends in annual catch per unit effort (CPUE) for an IUCN listed near-threatened species, the lemon shark Negaprion brevirostris. A general additive model (GAM) was used to analyse the non-linear annual CPUE values over the entire 32-year research period. The GAM displayed high variability of annual CPUE, with a peak value of 0·026 N. brevirostris per hook day (hooks day(-1) ) in 2000. The temporal pattern of CPUE indicated an abundance trend with a complete cycle, from trough to trough, occurring over a period of approximately 18 years. The 1982-1989 survey period saw the highest proportion of mature individuals (19·8%) and the smallest average pre-caudal length (LPC ; 124·8 cm). The 1992-2002 survey period had the highest average annual CPUE (0·018 hooks day(-1) ), while the 2003-2014 research period saw largest average LPC size (134·8 cm) and the lowest average CPUE values (0·009 hooks day(-1) ) of the entire research period. The long-term trend identified in this study provides a baseline for future assessment.

Poblaciones de tiburones en las bahías Chatham y Wafer del Parque Nacional Isla del Coco, Costa Rica

<p><strong> </strong>At least fourteen species of sharks live in the Marine Protected Area of Isla del Coco National Park (ICNP), some are resident species such as the whitetip reef shark (<em>Triaenodon obesus</em>); others are migratory and visit the National Park throughout the year, e.g. the scalloped hammerhead shark (<em>Sphyrna lewini</em>) and the whale shark (<em>Rhincodon typus</em>). Between March 2010 and August 2012 six expeditions out to the ICNP were carried, during this period 25 night trips (from 18:00 to 22:00 hr) for shark tagging were conducted in the Wafer and Chatham bays. During those trips, 185 sharks were analyzed: 81.1 % were whitetip reef sharks (<em>T. obesus</em>), 16.7 % were blacktip sharks (<em>Carcharhinus limbatus</em>), 1.1 % were blacktip reef sharks (<em>Carcharhinus melanopterus</em>) and 1.1% were silvertip sharks (<em>Carcharhinus albimarginatus</em>). The most common species in Bahía Chatham was <em>T. obesus</em>, while the most common one in Bahía Wafer was <em>C. limbatus</em>, which represented 80.9 % and 80.5 % of the total sharks caught, respectively. Regarding <em>T. obesus</em>, a sex ratio of 1.2 males per female was estimated (X<sup>2</sup>=0.09; p=0.17); in turn a sex ratio of 1.01 males per female was observed (X<sup>2</sup>=0.04; p=0.79) for <em>C. limbatus</em>. The average total length for <em>T. obesus </em>and <em>C. limbatus</em> was 103.66±13.91 cm and 76.58±14.56 cm respectively; suggesting that black tip sharks use those bays during immature stages. The results show an interspecific spatial segregation of the most common resident sharks at ICNP, apparently the clear waters and the coral cover of Chatham Bay are preferred by <em>T. obesus</em>; while the turbid waters of the Genio River mouth are preferred by <em>C. limbatus</em></p>

CORRELATIONS OF CAPTURE, TRANSPORT, AND NUTRITION WITH SPINAL DEFORMITIES IN SANDTIGER SHARKS,CARCHARIAS TAURUS, IN PUBLIC AQUARIA

A number of captive sandtiger sharks (Carcharias taurus) in public aquaria have developed spinal deformities over the past decade, ranging in severity from mild curvature to spinal fracture and severe subluxation. To determine the frequency and etiologic basis of this disease, U.S. public aquaria participated in a two-stage epidemiologic study of resident sharks: 1) a history and husbandry survey and 2) hematology, clinical chemistry, and radiography conducted during health exams. Eighteen aquaria submitted data, samples, or both from 73 specimens, including 19 affected sharks (26%). Sharks caught off the Rhode Island coast or by pound net were smaller at capture and demonstrated a higher prevalence of deformity than did larger sharks caught from other areas via hook and line. Relative to healthy sharks, affected sharks were deficient in zinc, potassium, and vitamins C and E. Capture and transport results lead to two likely etiologic hypotheses: 1) that the pound-net capture process induces spinal trauma that becomes exacerbated over time in aquarium environments or 2) that small (and presumably young) sharks caught by pound net are exposed to disease-promoting conditions (including diet or habitat deficiencies) in aquaria during the critical growth phase of their life history. The last hypothesis is further supported by nutrient deficiencies among affected sharks documented in this study; potassium, zinc, and vitamin C play critical roles in proper cartilage-collagen development and maintenance. These correlative findings indicate that public aquaria give careful consideration to choice of collection methods and size at capture and supplement diets to provide nutrients required for proper development and maintenance of cartilaginous tissue.