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Distribution and site fidelity of four endemic catshark species in Walker Bay, South Africa
Abstract
Catsharks (family Scyliorhinidae) and the recently reclassified deepwater catsharks (family Pentanchidae) are two
of the largest families of elasmobranchs and include species that function as important mesopredators in almost
all marine ecosystems. This study focuses on four species endemic to the coast of southern Africa: the puffadder
shyshark Haploblepharus edwardsii, dark shyshark H. pictus, leopard catshark Poroderma pantherinum and pyjama
catshark P. africanum. Similar to most catsharks, these four species are underrepresented in chondrichthyan
research. Our investigation aimed to gain insight into the distribution and site fidelity of the focal species through
mark-recapture efforts in Walker Bay on the southwest coast. The use of 95% minimum convex polygons indicated
large overlaps in distribution among the species as well as between sexes, except for H. edwardsii. Site fidelity was
universally low (0.005) at three key sample sites, although travel distances between sites averaged 3–5.5 km across
all species. The results suggest that sexual segregation is not present for the studied catshark species, with the
possible exception of H. edwardsii, which had a low capture rate. The low levels of site fidelity and movement also
indicated significant levels of site interconnectivity between the three commonly sampled sites as they fell within
the same 5-km2 region of the bay. From the present findings, Walker Bay could be considered an area of interest
for conservation with respect to the four species, allowing for further study of their population dynamics and the
influence of the local marine protected area.
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The bull shark (Carcharhinus leucas Valenciennes, 1839) is a large, primarily coastally distributed shark famous for its ability to penetrate far into freshwater bodies in tropical, subtropical, and warm-temperate climates. It is a cosmopolitan species with a geographical range that includes the coastlines of all major ocean basins (Atlantic Ocean, Indian Ocean, Pacific Ocean). As a consequence, freshwater occurrences of C. leucas are possible everywhere inside its geographic range. Carcharhinus leucas is a fully euryhaline, amphidromous species and possibly the widest-ranging of all freshwater tolerating elasmobranchs. This species is found not only in river systems with sea access that are not interrupted by human impediments but in hypersaline lakes as well. Rivers and estuaries are believed to be important nursery grounds for C. leucas, as suggested by observations of pregnant females in estuaries and neonates with umbilical scars in rivers and river mouths. Due to the physical capability of this species to enter riverine systems, the documentation of its occurrence in fresh and brackish water is essential for future conservation plans, fishery inspections, and scientific studies that focus on the link between low salinity habitats, shark nurseries, and feeding areas. The author’s review of the available literature on C. leucas revealed the absence of a comprehensive overview of fresh and brackish water localities (rivers and associated lakes, estuaries) with C. leucas
records. The purpose of this literature review is to provide a global list of rivers, river systems, lakes, estuaries, and lagoons with records and reports of this species, including a link to the used references as a base for regional, national, and international conservation strategies. Therefore, the objective of this work is to present lists of fresh and brackish water habitats with records of C. leucas as the result of an extensive literature review and analysis of databases. This survey also took into account estuaries and lagoons, regarding their function as important nursery grounds for C. leucas. The analysis of references included is not only from the scientific literature, but also includes semi-scientific references and the common press if reliable. The result of 415 global fresh and brackish water localities with evidence of C. leucas highlights the importance of these habitats for the reproduction of this species. Moreover, gaps in available distribution maps are critically discussed as well as interpretations and conclusions made regarding possible reasons for the distribution range of C. leucas, which can be interpreted as the result of geographic circumstances, but also as a result of the current state of knowledge about the distribution of this species. The results of the examination of available references were used to build a reliable and updated distribution map for C. leucas, which is also presented here.
Kelp forests are associated with high biodiversity as they provide habitat and food source for many species. Redspotted catshark Schroederichthys chilensis is a coastal shark species associated with kelp forests of southern South America dominated by Lessonia trabeculata. Despite its common occurrence redspotted catshark the knowledge on its trophic ecology is rudimentary. This study aimed to assess the effects of presence/absence of kelp L. trabeculata on the isotopic niche of redspotted catshark through comparison of δ¹³C and δ¹⁵N in its blood and fin tissues (non-lethal samples). We found that males were characterized by higher trophic position and enriched carbon sources compared to females in locations where kelp was present. In contrast, males and females were characterized by similar isotopic niche in absence of kelp. These differences are most probably an effect of higher prey diversity associated with microhabitats generated by kelp forests that allow sexual segregation of isotopic niche. Therefore, extensive kelp harvest may cause significant effects in isotopic niche and nutritional status of adult redspotted catshark and may negatively affect its populations.
Threatened chondrichthyan diversity is high in developing countries where scarce resources, limited data, and minimal stakeholder support often render conservation efforts challenging. As such, data on many species, including many evolutionarily distinct endemics, is poor in these countries and their conservation status and habitat needs remain uncertain. Here, we used baited remote underwater videos (BRUVs; n = 419) conducted at 167 sites over two years to assess the frequency of occurrence (FO), relative abundance, diversity, and structure of chondrichthyan assemblages in one of the world’s chondrichthyan biodiversity and endemism hotspots, South Africa. We compared chondrichthyan assemblages across three habitat types, and between unprotected and protected areas (a small marine protected area [MPA] and a larger, seasonal whale sanctuary). Although in total we observed 18 chondrichthyan species (11 families), over half of all observations were of just two species from the same family of mesopredatory endemic catsharks; only 8.8% were larger shark species. These mesopredatory species do not appear to be threatened, but some skates and larger shark species, including some endemics, were much rarer. Overall chondrichthyan FO was high (81% of all BRUVs); FO was higher in kelp (100% of BRUVS) and reef (93%) sites than at sites in sandy habitat (63%), which had a distinct chondrichthyan community. Independent of habitat, the chondrichthyan community did not relate strongly to protection. Because sites with kelp and reef habitat were rare in the whale sanctuary, this protected area had a lower chondrichthyan FO (67% of BRUVs) than either unprotected sites (81%) or those in the small MPA (98%), as well as having lower chondrichthyan relative abundance and species richness. Our study provides evidence of the importance of distinct habitat types to different chondrichthyan species, and suggests that even small MPAs can protect critical habitats, such that they may provide safe refuge for endemic species as anthropogenic pressures increase.
Most of the deep-water sharks presented a K-selected life-history strategy, this biological characteristic made them one of the most vulnerable groups to bottom trawls fisheries. The North East Atlantic has the highest proportion of threatened species, moreover, half of the total species of deep-water sharks that habits Porcupine Bank, are under serious threatened status (Clarke et al., 2016).
Understanding the patterns of deep-water shark populations is the key of an effective management deep-sea fishery. This study reflects a sexual segregation by size and maturity occurring by depths in Galeus melastomus, one of the most abundant species in Porcupine Bank. The phenomenon of sexual segregation of deep-sea sharks into schools of same sex and sizes is a kind of pattern distribution follow by most of deep-sea sharks, recording this kind of animal behaviour is important to predict population process and dynamics with the aim to stablish successful conservation fisheries policies (Wearmouth & Sims, 2008).
Galeus melastomus is a small bottom-dwelling shark widely distribute from Faroe Islands to Senegal, including the Mediterranean basin. It is an oviparous specie, considered an opportunistic with a broad generalist niche (Olaso et al., 2005).
White sharks, Carcharodon carcharias, are often described as elusive, with little information available due to the logistical difficulties of studying large marine predators that make long-distance migrations across ocean basins. Increased understanding of aggregation patterns, combined with recent advances in technology have, however, facilitated a new breadth of studies revealing fresh insights into the biology and ecology of white sharks. Although we may no longer be able to refer to the white shark as a little-known, elusive species, there remain numerous key questions that warrant investigation and research focus. Although white sharks have separate populations, they seemingly share similar biological and ecological traits across their global distribution. Yet, white shark’s behavior and migratory patterns can widely differ, which makes formalizing similarities across its distribution challenging. Prioritization of research questions is important to maximize limited resources because white sharks are naturally low in abundance and play important regulatory roles in the ecosystem. Here, we consulted 43 white shark experts to identify these issues. The questions listed and developed here provide a global road map for future research on white sharks to advance progress toward key goals that are informed by the needs of the research community and resource managers.
Predators have considerable impacts on ecosystems and biodiversity, with many recent studies highlighting their strong top-down effects that influence ecosystem structure and function. The majority of these insights come from studies on a handful of large charismatic predators (i.e. lions Panthera leo: referred to as apex predators when these large predators dominate the food chain) (Roemer, Gompper
& Valkengurgh, 2009; Ripple et al., 2014). The removal of these apex predators has a disproportionately disruptive influence on ecosystem structure and function (Ripple et al., 2014). However, most predators
are neither large nor charismatic and consequently have received relatively little research attention compared with the small group of apex predators upon which much research time and funding are
focused (Roemer et al., 2009). These small- to medium-sized predators, collectively called mesopredators (Prugh et al., 2009), are often capable of living close to humans and can attain population densities considerably greater than that of apex predators (DeLong & Vasseur, 2012). Through their combined influence, mesopredators have the capacity to influence ecosystems (Roemer et al., 2009; Williams et al., 2017). Despite this, we know very little about their ecological roles and how fluctuations in their abundance influence biodiversity.
Hammerhead sharks are among the most intriguing yet imperiled groups of large sharks globally. Until recently, our understanding of their biology, movements, diet, and life histories was challenged by a lack of studies. In recent years there has been a surge of published studies on this group of sharks, incorporating new information on age and growth, behavior, and the threats they face. Here we summarize and compare what is known on the biology and conservation of the three largest species of hammerhead sharks: the great hammerhead (Sphyrna mokarran), the scalloped hammerhead (Sphyrna lewini), and the smooth hammerhead (Sphyrna zygaena). We chose these species since they are the most well-studied of the hammerheads, and also because they are commonly captured in target and non-target fisheries worldwide. Thus, we also discuss population trends and the vulnerabilities of each species, and make recommendations for future studies on these fascinating and complex elasmobranch fishes.
Background
Site fidelity is considered as an animal’s tendency to return to a previously occupied place; this is a component of animal behaviour that allows us to understand movement patterns and aspects related to the animal’s life history. Although there are many site fidelity metrics, the lack of standardisation presents a considerable challenge in terms of comparability among studies.
Methods
This investigation focused on the theoretical development of a standardised composite site fidelity index and its statistical distribution in order to obtain reliable population-level site fidelity comparisons. The arithmetic and harmonic means were used as mathematical structures in order to create different indexes by combining the most commonly used indicators for site fidelity such as Occurrence, Permanence and Periodicity. The index performance was then evaluated in simulated populations and one real population of Commerson’s dolphins ( Cephalorhynchus commersonii (Lacépède 1804)). In the first case, the indexes were evaluated based on how they were affected by different probability values such as the occurrence of the individual within the study area (φ) and capture probability ( p ). As a precision measure for the comparison of the indexes, the Wald confidence interval (CI) and the mean square error were applied. Given that there was no previous data concerning the distribution parameters of this population, bootstrap CIs were applied for the study case.
Results
Eight alternative indexes were developed. The indexes with an arithmetic mean structure, in general, had a consistently inferior performance than those with a harmonic mean structure. The index IH4, in particular, achieved the best results in all of the scenarios and in the study case. Additionally, this index presented a normal distribution. As such, it was proposed as a standardised measure for site fidelity (Standardised Site Fidelity Index—SSFI).
Discussion
The SSFI is the first standardised metric that quantifies site fidelity at a populational level. It is an estimator that varies between zero and one and works in situations where detection is not perfect and effort can be constant or not. Moreover, it has an associated CI that allows users to make comparisons.
Habitat loss, overexploitation, and numerous other stressors have caused global declines in apex predators. This “trophic downgrading” has generated widespread concern because of the fundamental role that apex predators can play in ecosystem functioning, disease regulation, and biodiversity maintenance. In attempts to combat declines, managers have conducted reintroductions, imposed stricter harvest regulations, and implemented protected areas. We suggest that full recovery of viable apex predator populations is currently the exception rather than the rule. We argue that, in addition to well-known considerations, such as continued exploitation and slow life histories, there are several underappreciated factors that complicate predator recoveries. These factors include three challenges. First, a priori identification of the suite of trophic interactions, such as resource limitation and competition that will influence recovery can be difficult. Second, defining and accomplishing predator recovery in the context of a dynamic ecosystem requires an appreciation of the timing of recovery, which can determine the relative density of apex predators and other predators and therefore affect competitive outcomes. Third, successful recovery programs require designing adaptive sequences of management strategies that embrace key environmental and species interactions as they emerge. Consideration of recent research on food web modules, alternative stable states, and community assembly offer important insights for predator recovery efforts and restoration ecology more generally. Foremost among these is the importance of a social-ecological perspective in facilitating a long-lasting predator restoration while avoiding unintended consequences.
Chondrichthyans (sharks, skates, rays and chimaeras) are captured in many marine fisheries. Management and research efforts directed at chondrichthyan fishing are often neglected because of low product value, taxonomic uncertainty, low capture rates, and harvesting by multiple fisheries. In South Africa's diverse fishery sectors, which include artisanal as well as highly industrialised fisheries, 99 (49%) of 204 chondrichthyan species that occur in southern Africa are targeted regularly or taken as bycatch. Total reported dressed catch for 2010, 2011 and 2012 was estimated to be 3 375 t, 3 241 t and 2 527 t, respectively. Two‑thirds of the reported catch was bycatch. Regulations aimed at limiting chondrichthyan catches, coupled with species‑specific permit conditions, currently exist in the following fisheries: demersal shark longline, pelagic longline, recreational line, and beach‑seine and gillnet. Limited management measures are currently in place for chondrichthyans captured in other South African fisheries. Catch and effort dataseries suitable for stock assessments exist for fewer than 10 species. Stock assessments have been attempted for five shark species: soupfin Galeorhinus galeus, smoothhound Mustelus mustelus, white Carcharodon carcharias, spotted ragged‑tooth Carcharias taurus, and spotted gully Triakis megalopterus. Fishery‑independent surveys and fishery observer data, which can be used as a measure of relative abundance, exist for 67 species. Compared with most developing countries, South African shark fishing is relatively well controlled and managed. As elsewhere, incidental capture and bycatch remain challenges to the appropriate management of shark species. In 2013, South Africa's National Plan of Action for the Conservation and Management of Sharks (NPOA‑Sharks) was published. Implementation of the NPOA‑Sharks should help to improve chondrichthyan management in the near future.
The Oceanographic Research Institute's (ORI) Cooperative Fish Tagging Project was initiated in 1984 and is one of the most enduring and successful environmental projects of its kind in South Africa. By the end of 2011, 5 130 anglers had joined the project, of whom 3 457 had tagged one or more fish. In the project's 27-year history (1984–2011), over 251 900 fish from 368 different species have been tagged and released, of which approximately 13 192 (5.2%) have been recaptured. The five most commonly tagged species to date are galjoen Dichistius capensis, dusky kob Argyrosomus japonicus, dusky shark Carcharhinus obscurus, garrick/leervis Lichia amia and spotted grunter Pomadasys commersonnii. Information from the Tagging Project has been extensively used in numerous research projects, scientific publications, popular articles and postgraduate theses. The results generated by this project have also contributed to policy development and decision-making on linefish management in South Africa. Furthermore, the project has had a positive impact on improving angler awareness and knowledge about linefish resources. The concept of tag and release has partly been responsible for changing the ethics of the recreational fishing community, many of whom now release their catch, thereby contributing to a more sustainable fishing future. This paper critically assesses the contribution that the ORI Tagging Project has made as a conservation achievement in general and to linefish management in particular, and reflects on future directions for the project.
ABSTRACT: Elucidating predator-prey relationships is an important part of understanding and assessing the structure and function of ecosystems. Sharks are believed to play a significant role in marine ecosystems, although their specific trophic ecology is largely unexplored. Stable isotopes of nitrogen (δ15N) and carbon (δ13C) are a widely applied tool in food-web studies, but there is a need to quantify stable isotope dynamics in animals, particularly sharks. In this study, diet-tissue discrimination factors (DTDF = stable isotope in consumer tissue - stable isotope in diet) and turnover rates (time for the isotope to be assimilated into the consumer’s tissue) of stable isotopes were estimated in blood, fin, and muscle tissue for the shark species Scyliorhinus stellaris fed 2 diets with different isotope values. Subsequently, these diet- and tissue-specific DTDFs were used in isotopic mixing models to quantify the diet of Scyliorhinus canicula caught in the North Sea and were compared with stomach content data. DTDFs for δ15N (Δ15N) and δ13C (Δ13C) ranged from -1.95 to 3.49‰ and from 0.52 to 5.14‰, respectively, and varied with tissue and diet type. Isotope turnover rates in plasma and red blood cells, expressed as half-lives, ranged from 39 to 135 d. Most of the variability in DTDFs reported in this and other studies with sharks can be explained by linear relationships between DTDF and dietary isotopic values. From these relationships, we propose a method for isotope mixing models using diet-specific DTDFs, which improves diet reconstruction estimates for animals, particularly mesopredator sharks that consume a large range of prey types.
No data exist regarding the linkage between the dispersion of critical resources and the spatial distribution of eastern coyotes (Canis latrans). From February 2000 to January 2002, we investigated landscape-level correlates of fragmentation with coyote spacing patterns and interaction in west-central Indiana to determine whether habitat fragmentation may influence spatiotemporal home-range overlap. Eleven pairs of coyotes (four malefemale, four malemale, three femalefemale) displayed spatial overlap in portions of their home-range utilization distributions; seven pairs interacted temporally. Percent home-range overlap of space-sharing pairs averaged 55%. Area of forested habitat within the overlap zone, pair type, and mean squared difference of nearest-neighbor distances between forested patches explained substantial amounts of variation in percent home-range overlap (R2 = 0.83, P < 0.001). Extent of temporal interaction differed by pair type, as malemale pairs interacted substantially more than malefemale and femalefemale pairs. Five (two malemale, three malefemale) of seven temporally interacting pairs exhibited simultaneous attraction to the overlap zone. The complex combination of environmental pressures present in human-dominated landscapes may facilitate spatiotemporal home-range overlap in coyotes.
Attwood, C. G., Petersen, S. L., and Kerwath, S. E. 2011. Bycatch in South Africa's inshore trawl fishery as determined from observer records. – ICES Journal of Marine Science, 68: 2163–2174.
Ship-based observer data were analysed to describe the volume, composition, utilization, and size structure of catches made by South Africa's inshore trawlers. The sampling rate was 3.5% of all trawls, including unsorted and discard samples. In all, 137 nominal species were recorded. Analysis of species composition separated the trawling grounds into seven areas, providing a framework for stratifying the ground for catch estimation and for selection of representative areas for conservation. The target species, Merluccius capensis and Austroglossus pectoralis, made up 58% of the pre-discard catch. Trachurus trachurus, Pterogymnus laniarius, Raja spp., and Chelidonichthys spp. constituted another 23%. Pre-discard catch volumes of the entire fleet were estimated. The average annual pre-discard catch of M. capensis and A. pectoralis was 9653 and 504 t, respectively, closely matching landing statistics. Argyrosomus inodorus, Rhabdosargus globiceps, Argyrozona argyrozona, and Atractoscion aequidens averaged 294, 230, 107, and 83 t annually, respectively, indicating significant overlap with the handline fishery for A. inodorus and A. argyrozona. A comparison of species composition in unsorted and discard samples revealed the species being preferentially retained. Argyrosomus inodorus and A. aequidens were trawled mainly below their size at maturity. Management needs to consider other species when determining catch or effort limits and area restrictions.
Within-species sexual segregation is a widespread phenomenon among vertebrates, but its causes remain a topic of much debate. Female avoidance of male coercive mating attempts has the potential to influence the social structure of animal populations, yet it has been largely overlooked as a driver of sexual separation. Indeed, its potential role in long-term structuring of natural populations has not been studied. Here we use a comparative approach to examine the suitability of multiple hypotheses forwarded to account for sexual segregation (i.e., activity budget, predation risk, thermal niche–fecundity, and social factors) as drivers underlying sex-specific habitat use in a monomorphic model vertebrate, the small-spotted catshark, Scyliorhinus canicula. Using this hypothesis-driven approach, we show that year-round sexual habitat segregation in S. canicula can be accounted for directly by female avoidance of male sexual harassment. Long-term electronic tracking reveals that sperm-storing female catsharks form daytime refuging aggregations in shallow-water caves (;3.2 m water depth) and undertake nocturnal foraging excursions into deeper water (;25 m) on most nights. In contrast, males occupy deeper, cooler habitat (;18 m) by day and exploit a range of depths nocturnally (1–23 m). Males frequent the locations of shallow-water female refuges, apparently intercepting females for mating when they emerge from, and return to, refuges on foraging excursions. Females partly compensate for higher metabolic costs incurred when refuging in warmer habitat by remaining inactive; however, egg production rates decline in the warmest months, but refuging behavior is not abandoned. Thermal choice experiments confirm that individual females are willing to ''pay'' in energy terms to avoid aggressive males and unsolicited male mating attempts. Long-term evasion of sexual harassment influences both the social structure and fecundity of the study population, with females trading off potential injury and unsolicited matings with longer-term fitness. This identifies sexual harassment as a persistent cost to females that can mediate vertebrate population dynamics.
1. Determining how animals move within their environment is a fundamental knowledge that contributes to effective management and conservation. Continuous ‘round‐the‐clock’ animal movement data are frequently gathered using biotelemetry technology, providing discrete data packages on the presence–absence of animals at known locations through time. Current analyses of such data do not generally account for the interconnectivity of locations as animals move between them and consequently do not integrate graphically or statistically a temporal component to spatial changes.
2. Here, we describe the novel application of network analyses to electronic tag data whereby nodes represent locations and edges the movements of individuals. We demonstrate some of the descriptive and quantitative approaches for determining how an animal’s movement interconnects home range habitats. Telemetry data from arrays of recorders provide movement data of individual animals, and as examples of the method proposed, we examine the movements of two distinct shark species, the small‐spotted catshark ( Scyliorhinus canicula ) and the Caribbean reef shark ( Carcharhinus perezi ). In doing so, we consider both local and global network properties from an animal movement perspective and simulate the effects of node disruption as a proxy for habitat disturbance.
3. Comparative visual representations of two catshark movement networks suggest, for example, potential differences in space use. Multiple regression quadratic assignment procedure shows that habitat is a significant predictor of movement behaviour.
4. Null modelling of C. perezi movement data, corrected for the spatial restriction of static nodes, demonstrated a significant, non‐random distribution of directed movements among sites. Additionally, the connectivity of this animal’s movement network is significantly reduced through targeted disruption of a site of high centrality but not through disruption of a randomly selected site.
5. Network theory is a well‐established theoretical framework and its integration into the fast developing field of animal movement and telemetry might improve significantly how we interpret animal space use from electronically recorded data. This technique has potentially wide application in animal behaviour but may also inform the management of habitat harbouring threatened or endangered species via the simulation, modelling and intuitive visualisation of animal movement interactions.
Holohalaelurus regani was caught in 38% of the 3314 bottom trawls conducted during routine demersal surveys o. the South African west and south coasts from 1986 to 1999. An index of biomass for H. regani has increased on the west coast, from 1606 t in 1986–1993 to 3012 t in 1994–1999, despite c. 130 t being taken annually as by–catch in the demersal fishery. On the south coast, there has also been an increase over the same period, from 793 to 1350 t. Females and juveniles were generally found in shallower water (<300 m) than males, suggesting an inshore nursery area. Male H. regani become mature at 450–500 mm LT, whereas females become mature at 400–450 mm LT. There is reproductive activity throughout the year and fecundity appears to be high. This species is a generalist feeder, with the diet comprising teleosts, crustaceans and cephalopods. H. regani also scavenges offal opportunistically. Its high fecundity, the relative protection of females and juveniles in shallow water that is rarely trawled, its opportunistic diet and its robust nature that may allow it to survive after it has been discarded, have enabled H. regani to increase in numbers, despite indirect fishing pressure.
Many conclusions about mammalian ranging behaviour have been drawn based on minimum convex polygon (MCP) estimates of home
range size, although several studies have revealed its unpredictable nature compared to that of the kernel density estimator.
We investigated to what extent the choice of home range estimator affected the biological interpretation in comparative studies.
We found no discrepancy when the question asked covered a wide range of taxa, as real and very large differences in range
size were likely to have masked smaller differences due to the choice of home range estimator. However, when the question
asked concerned within-species characteristics, the choice of home range estimator explained as much of the variation in range
size as did the ecological variable in question. The implications for macro-ecological and intraspecific studies are discussed.
Movements and habitat selection of male and female dogfish, Scyliorhinus canicula, in a tidal sea lough in south-west Ireland were determined over two temporal scales. Continuous acoustic tracking of four individuals (two males, two females) for 6 days was used to monitor fine-scale changes in behaviour patterns and extent of home ranges. Mark-recapture by number-tagging dogfish captured at sampling stations during August-September in consecutive years was used to reveal long-term philopatric behaviour. Transmitter-tagged male dogfish showed very similar behavioural patterns of low activity during the day in deep water (12-24 m depth) followed by more rapid movements into shallow areas (<4 m) at dusk to feed, before returning to the core space in deep water at dawn. Home ranges occupied by males overlapped almost entirely and were centred in an area where tidal currents form gyres and large crab prey are found. Female S. canicula exhibited a different behavioural strategy. They refuged in caves in shallow water (0.5-1.5 m) during the day and during the 6-day tracking period were nocturnally active two or three times, primarily in deep water. Activity areas of females did not overlap with those of males. Acoustic telemetry, netting, underwater surveys and tag returns revealed males and females were apparently segregated by sex in the lough. Mark-recapture data showed males and females were recaptured from the locations where they were originally caught between 359 and 371 days earlier suggesting at least seasonal segregation in consecutive years. Because female dogfish store sperm enabling temporal separation of the energetically demanding act of copulation with the process of egg-laying, we suggest that this apparent spatial segregation by sex could be driven by the need for females to conserve energy by limiting multiple matings during a time when mating coincides with a peak in egg production and laying.
The practical analysis of space use and habitat selection by animals is often a problem due to the lack of well-designed programs. I present here the “adehabitat” package for the R software, which offers basic GIS (Geographic Information System) functions, methods to analyze radio-tracking data and habitat selection by wildlife, and interfaces with other R packages. These tools can be downloaded freely on the internet. Because the functions of this package can be combined with other functions of R, “adehabitat” provides a powerful environment for the analysis of the space and habitat use.
Apex predators have experienced catastrophic declines throughout the world as a result of human persecution and habitat loss. These collapses in top predator populations are commonly associated with dramatic increases in the abundance of smaller predators. Known as "mesopredator release," this trophic interaction has been recorded across a range of communities and ecosystems. Mesopredator outbreaks often lead to declining prey populations, sometimes destabilizing communities and driving local extinctions. We present an overview of mesopredator release and illustrate how its underlying concepts can be used to improve predator management in an increasingly fragmented world. We also examine shifts in North American carnivore ranges during the past 200 years and show that 60% of mesopredator ranges have expanded, whereas all apex predator ranges have contracted. The need to understand how best to predict and manage mesopredator release is urgentmesopredator outbreaks are causing high ecological, economic, and social costs around the world.
Stable isotopes (δ13C and δ15N) were analysed in vertebrae of Scyliorhinus canicula (n=40; 13 males, 27 females) from the central Tyrrhenian Sea to explore a potential trophic shift in relation to sex and maturity condition. Isotopic values were obtained from the centre and the periphery of the vertebra of each individual to test for the effect of maturity condition. The values of δ13C and δ15N showed significant differences between the immature and mature state of the individuals analysed (U’=1392, P<0.0001 for δ13C; U’=1385, P<0.0001 for δ15N). Differences in values of δ15N demonstrated a trophic shift during maturation progress of S. canicula. The peripheral vertebral part, corresponding to the mature state of each individual, showed higher values of δ15N (mean 5.41‰ SD±1.29‰), compared with the lower values of δ15N (mean 2.78‰ SD±1.52‰) observed in the central vertebral part related to the immature state. In contrast, the isotopic signature of δ13C was lower in the vertebral centra, and thus related to areas less enriched in C13 (mean -22.56‰ SD±1.26‰) in comparison with the vertebral periphery (mean -20.03‰ SD±1.34‰) linked to more productive environments. No significant differences in δ13C or for δ15N values were observed between sexes.
The quantification of capture-related physiological stress is an important factor when assessing the potential for
post-release survival in sharks that are incidentally captured. In the absence of these biological data and when
the post-release fate is unknown, effective management plans cannot be formulated and may lead to highly
susceptible shark populations being overfished. Here, we measured the levels of lactate, glucose, alanine amino
transferase (ALT), aspartate amino transferase (AST), Ca2+, Na+ K+,Cl – Mg 2+ and Pi in the plasma of mature and
immature lesser spotted dogfish (Scyliorhinus canicula, herein dogfish) which were incidentally captured at two
depths (shallow: 50-200 m, and deep: 201-500 m) by bottom trawl off the coast of southern Sicily. These values
were used as biomarkers and physiological indicators of the secondary stress response associated with capture.
This study found that dogfish captured in deeper waters (below 200 m) had elevated levels of glucose, Na+,
Ca2+ and K+ compared to those inhabiting depths less than <200 m. We hypothesize that the elevated levels of
physiological stress in dogfish captured at greater depths may be related to the prolonged duration of the interactions
with the fishing gear in the area off southern Sicily. Our findings provide new data on the capturerelated
stress in dogfish and increase the understanding of the potential for post-release survival in sharks
captured at two depths by bottom trawl, information that is important for improving the general management
plans for the fishery. However, our PC Analysis results revealed that Maturity have a positive contribution from
the sample weight, sample length, ALT, AST and a negative contribution from Pi.
An annotated checklist of chondrichthyan fishes (sharks, batoids, and chimaeras) occurring in South African waters is presented. The checklist is the result of decades of research and on-going systematic revisions of the regional fauna. The chondrichthyan fauna of South Africa is one of the richest in the world with 191 species, comprising 50 families and 103 genera. It consists of 30 families, 64 genera, and 111 species of sharks; 17 families, 36 genera, and 72 species of batoids; and, 3 families, 5 genera, and 8 species of chimaeras. The most species-rich shark families are the whaler sharks Carcharhinidae with 20 species followed by the deepwater catsharks Pentanchidae with 13 species. The most species-rich batoid families are the hardnose stakes Rajidae with at least 21 species followed by the stingrays Dasyatidae with 13 species. This monograph represents the first detailed annotated checklist of chondrichthyans from South Africa in over 30 years.
Patterns of egg deposition and rates of egg development were examined for two endemic South African scyliorhinid shark species: Poroderma pantherinum, the leopard catshark, and Haploblepharus pictus, the dark shy shark. P. pantherinum laid their eggs at an average depth of 18.95 m (min: 7.4 m; max: : 26.8 m) preferentially attaching their eggs singly onto sea fans Leptogorgia palma, Eunicella papillosa and Eunicella tricoronata. H. pictus laid their eggs at an average depth 3m(min: 1m; max: 30.7 m) and attached their eggs, predominantly in pairs, to the seaweed Bifurcariopis capensis. The average temperature at which eggs were found were similar (15°C) and eggs were laid year-round. Embryo development was observed in the laboratory under constant controlled environmental conditions of 14 and 17°C. Embryo length-age relationships were linear for both species and there were significant differences in growth rate at the two temperatures. For P. pantherinum average growth rate was 0.37 mm/day at 14°C and 0.79 mm/day at 17°C. The average incubation period was 266 days at 14°C and 125 days at 17°C. Embryos thus grew two times faster and development time was 53% shorter when the temperature was raised by only 3°C. For H. pictus, the average growth rate was 0.49 mm/day at 14°C and 0.78 mm/day at 17°C. The incubation period was 242 days at 14°C and 190 days at 17°C. The embryos thus grew 1.6 times faster and incubation time was 21.5% shorter when temperature was raised by only 3°C.
In spatial statistics the ability to visualize data and models superimposed with their basic social landmarks and geographic context is invaluable. ggmap is a new tool which enables such visualization by combining the spatial information of static maps from Google Maps, OpenStreetMap, Stamen Maps or CloudMade Maps with the layered grammar of graphics implementation of ggplot2. In addition, several new utility functions are introduced which allow the user to access the Google Geocoding, Distance Matrix, and Directions APIs. The result is an easy, consistent and modular framework for spatial graphics with several convenient tools for spatial data analysis.
Aim
Identifying the main factors affecting the spatial distribution of marine predators is essential in order to evaluate their distribution patterns, predict the potential impact of human activities on their populations and design accurate management actions. This information is also valuable from a more general management perspective, as marine predators are often considered indicators of habitat quality. In this context, we aimed to determine the degree to which environmental features, prey availability and human activities interact and influence spatial distribution of two marine mesopredator elasmobranchs, the small‐spotted catshark ( Scyliorhinus canicula ) and the Mediterranean starry ray ( Raja asterias ), living in a highly human‐exploited environment.
Location
Mediterranean Sea.
Methods
With information obtained from an extended experimental survey, we investigated the relative importance of environmental variables, prey availability and human activities on the spatial distribution of the abundance, biomass and occurrence rate of these marine mesopredators using deviance partitioning analyses.
Results
Our results revealed that environmental variables were the most important factors explaining the spatial distribution of Mediterranean starry ray, whereas small‐spotted catshark distribution was also influenced by prey availability and human factors. From a management point of view, these findings suggest that Mediterranean starry ray could be a good candidate as an indicator species of demersal environmental quality. On the other hand, the distribution of the small‐spotted catshark, which responds in an interactive and complex way to environment, prey availability and particular human activities, may be misleading as an environmental indicator.
Main conclusions
The spatial distribution of elasmobranchs in highly human‐impacted marine areas can reflect the interactive and combined effects of multiple factors. To avoid misunderstandings, attention should be paid to statistical procedures allowing the separation of pure and joint contribution of the factors driving the observed spatial patterns.
Marine and terrestrial environments differ fundamentally in space-time scales of both physical and ecological processes. These differences will have an impact on the animals inhabiting each domain, particularly with respect to their spatial ecology. The behavioural strategies that underpin observed distributions of marine species are therefore important to consider. Comparatively little is known, however, about how wild fishes actually respond to gradients in food supply and temperature, and to potential mates. This paper describes how behavioural theory is being used to elucidate the strategies and tactics of free-ranging sharks in three specific areas of study, namely, foraging on zooplankton, behavioural energetics and sexual segregation. The studies discussed are novel because shark movements were tracked in the wild using electronic tags in relation to simultaneous measurements of prey densities and thermal resources. The results show that filter-feeding (basking shark, Cetorhinus maximus) and predatory (dogfish, Scyliorhinus canicula) sharks have relatively complex behaviour patterns integrally linked to maximizing surplus power, often through making short and longer term ‘trade-off’ decisions between optimal foraging and thermal habitats. Interestingly, female S. canicula exhibit alternative behavioural strategies compared to males, a difference resulting in spatial segregation by habitat. Sexual segregation in this species occurs primarily as a consequence of male avoidance by females. Studies on free-ranging sharks provide a useful model system for examining how a predator's strategy is shaped by its environment. More theory-based studies of the behavioural processes of sharks are required however, before critical comparisons with other vertebrate predators are possible. Suggestions for further research to address this knowledge gap are given.
A revised interpretation of the mode of action of the heterocercal tail in sharks shows that the upturned tail axis tends to produce a thrust directed downwards behind the centre of balance of the fish and thus gives a moment turning the head upwards. This is countered in two ways—by the rotation of the tail along its longitudinal axis during each lateral beat, and through the action of the ventral hypochordal lobe. The shape of the tail and the mode of action of the tail in all sharks so far considered reflects a balance between these three factors, in all of them the net effect being the production of a forward thrust from the tail that passes directly through the centre of balance of the fiish. There is normally therefore no tendency for the fish to turn around the centre of balance in a sagittal plane but there is a net sinking effect that is countered by the planning effect of the pectoral fins and the ventral surface of the head.
A study of 56 species of sharks shows that the tail is constructed according to a remarkably consistent common plan, the extremes being the high angled rather symmetrical tail of pelagic sharks such as hums, Lamna and Rhincodon and the straight tails of benthic sharks such as Ginglymostoma in which a ventral hypochordal lobe is absent. When the general body shape of sharks, including the position of insertion of the median and paired fins and the pattern of growth of fin surface areas is considered, the uniformity of the shark body plan and locomolor function is further emphasised.
Four patterns of body form in sharks are recognised: 1) The fast swimming pelagic sharks and the whale sharks have a tail with a high aspect ratio, a conical head, a lateral fluke on the caudal peduncle. 2) The generalised sharks typified by the Carcharhinidae, have lower heterocercal angles, a flattened ventral surface on the head and lack the caudal fluke. 3) The demersal sharks typified by the catsharks (Scyliorhinidae) have a very low, almost straight tail. The ventral hypochordal lobe is absent and the first dorsal fin is posterior in position. 4) The squalomorph sharks are distinct in the absence of the anal fin, presence of a marked epicaudal lobe in the tail and often an elevated insertion of the pectorals.
The anal and second dorsal fins are always the smallest fins and the pectorals grow at the fastest rate. In general there is an inverse relationship between size and rale of growth of all fins and the ventral surface of the head. In hammerheads the growth data confirms that the head has a significant planing action in swimming. The pectoral, second dorsal and anal fins show an extreme constancy of position of insertion in all sharks studied. The locomotor mechanism of sharks is adapted for an efficient cruising swimming but at the same time, the potential instability in the sagittal plan allows for the production of turning moments that are used in attack and feeding.
Sexual segregation occurs when members of a species separate such that the sexes live apart, either singly or in single‐sex groups. It can be broadly categorised into two types: habitat segregation and social segregation. Sexual segregation is a behavioural phenomenon that is widespread in the animal kingdom yet the underlying causes remain poorly understood. Sexual segregation has been widely studied among terrestrial mammals such as ungulates, but it has been less well documented in the marine environment. This chapter clarifies terms and concepts which have emerged from the investigation of sexual segregation in terrestrial ecology and examines how a similar methodological approach may be complicated by differences of marine species. Here we discuss the behavioural patterns of sexual segregation among marine fish, reptile, bird and mammal species. Five hypotheses have been forwarded to account for sexual segregation, largely emerging from investigation of sexual segregation in terrestrial ungulates: the predation risk, forage selection, activity budget, thermal niche–fecundity and social factors hypotheses. These mechanisms are reviewed following careful assessment of their applicability to marine vertebrate species and case studies of marine vertebrates which support each mechanism recounted. Rigorous testing of all hypotheses is lacking from both the terrestrial and marine vertebrate literature and those analyses which have been attempted are often confounded by factors such as sexual body‐size dimorphism. In this context, we indicate the value of studying model species which are monomorphic with respect to body size and discuss possible underlying causes for sexual segregation in this species. We also discuss why it is important to understand sexual segregation, for example, by illustrating how differential exploitation of the sexes by humans can lead to population decline.
Minimum convex polygons (convex hulls) are an internationally accepted, standard method for estimating species' ranges, particularly in circumstances in which presence-only data are the only kind of spatially explicit data available. One of their main strengths is their simplicity. They are used to make area statements and to assess trends in occupied habitat, and are an important part of the assessment of the conservation status of species. We show by simulation that these estimates are biased. The bias increases with sample size, and is affected by the underlying shape of the species habitat, the magnitude of errors in locations, and the spatial and temporal distribution of sampling effort. The errors affect both area statements and estimates of trends. Some of these errors may be reduced through the application of alpha-hulls, which are generalizations of convex hulls, but they cannot be eliminated entirely. alpha-hulls provide an explicit means for excluding discontinuities within a species range. Strengths and weaknesses of alternatives including kernel estimators were examined. Convex hulls exhibit larger bias than a-hulls when used to quantify habitat extent and to detect changes in range, and when subject to differences in the spatial and temporal distribution of sampling effort and spatial accuracy. a-hulls should be preferred for estimating the extent of and trends in species' ranges.
Sexual segregation occurs when members of a species separate such that the sexes live apart, either singly or in single-sex groups. It can be broadly categorised into two types: habitat segregation and social segregation. Sexual segregation is a behavioural phenomenon that is widespread in the animal kingdom yet the underlying causes remain poorly understood. Sexual segregation has been widely studied among terrestrial mammals such as ungulates, but it has been less well documented in the marine environment. This chapter clarifies terms and concepts which have emerged from the investigation of sexual segregation in terrestrial ecology and examines how a similar methodological approach may be complicated by differences of marine species. Here we discuss the behavioural patterns of sexual segregation among marine fish, reptile, bird and mammal species. Five hypotheses have been forwarded to account for sexual segregation, largely emerging from investigation of sexual segregation in terrestrial ungulates: the predation risk, forage selection, activity budget, thermal niche-fecundity and social factors hypotheses. These mechanisms are reviewed following careful assessment of their applicability to marine vertebrate species and case studies of marine vertebrates which support each mechanism recounted. Rigorous testing of all hypotheses is lacking from both the terrestrial and marine vertebrate literature and those analyses which have been attempted are often confounded by factors such as sexual body-size dimorphism. In this context, we indicate the value of studying model species which are monomorphic with respect to body size and discuss possible underlying causes for sexual segregation in this species. We also discuss why it is important to understand sexual segregation, for example, by illustrating how differential exploitation of the sexes by humans can lead to population decline.
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