Malcolm J. Smale

Ultrasonic telemetry, tracking and automated monitoring technology for sharks

Sharks were among the first marine animals to carry telemetry systems because of their size and the need to understand their interactions with humans. Modern telemetry systems can gather many kinds of data (limited only by imagination, funding and sensor types), indicating which animals are near telemetry receivers and what they are doing. Receivers now range from simple autonomous detector units for deployment in mid-water in large-scale grids, to sophisticated automated benthic recorders, to triangulating radio-linked buoy systems (RAP), to ship-borne transponders. In addition, archival tags can now gather and store data even while the shark is away, to be downloaded later. Older types had to be recovered, but popup tags release from sharks automatically, surface and transfer data to satellites, while CHAT tags download whenever queried by a nearby transponding acoustic receiver. Sophisticated animal-borne tags dramatically increase the information gathered about sharks and their environment. The examples provided show the parallel progression of shark biology and acoustic biotelemetry illustrating that telemetry systems are tools for gathering data, which can often be honed to facilitate biological experiments. Future visions include sensors that directly measure shark swimming power and cardiac output, compressing the data so that it can be delivered to RAP systems tracking multiple animals with meter resolution in near real time. CHAT tags as small as 22 mm diameter should be able to return similar data from trips of hundreds of kilometers. Continued communication between biologists and engineers is essential to develop these technologies.

Recent strandings and sightings of whale sharks in South Africa

Available information on whale shark strandings around the coast of South Africa during the period 1984–1995 was collated. Stranded animals ranged in size from 3–11 m TL, most were immature and the sex ratio was even. Aerial observations and sightings by divers indicate that whale sharks are most abundant in South African waters during the austral summer and autumn months.

An Ethogram of Body Patterning Behavior in the Squid Loligo vulgaris reynaudii on Spawning Grounds in South Africa

Squids are capable of a high degree of visual signaling, most of which is expressed through the neurally controlled chromatophore organs in the skin. An accurate catalog (or ethogram) of these signals is an essential prerequisite to quantified behavioral analyses and experimentation. Body patterns such as those described here may also be useful for distinguishing between morphologically identical species or subspecies of commercial importance. The natural behavior of Loligo vulgaris reynaudii on spawning grounds was filmed by divers, and the body patterning repertoire was described in detail; 23 chromatic components, 4 postural components, and 9 locomotor components of body patterning were observed and correlated with different types of behaviors. Most of the chromatic components were expressed during intraspecific behaviors (e.g., agonistic behavior among males, courtship, mating) and, to a lesser extent, during interspecific interactions with fishes. Several of the most basic types of body patterns are described, the most distinctive of which are Lateral Display and White Flashing used between males in agonistic contests. This species is comparable to other Loligo spp. in its complexity of body patterning behavior.

Spatial and seasonal distribution patterns of the ragged-tooth shark Carcharias taurus along the coast of South Africa

Catches from competitive shore-anglers, inshore boat-based anglers and sightings by spearfishers and divers were used to infer the spatial and seasonal movement patterns of young-of-the-year (<1.2m TL), juvenile (1.2–1.8m TL), sub-adult (1.8–2.4m TL) and adult (>2.4m TL) ragged-tooth sharks Carcharias taurus along the coast of South Africa. Adult sharks inhabited the entire coast between Maputaland in the east and St Helena Bay on the West Coast. The geographical range of sharks at earlier life-history stages decreased with size. The vast majority (93.8%) of young-of-the-year sharks recorded from competitive shore-angling club records were between East London and St Francis Bay on the East Coast, suggesting this region to be the primary nursery area for C. taurus. Estuarine systems, although utilised by young-of-the-year and juvenile C. taurus, do not form an important component of their nursery area in South Africa. Catches of pregnant and post partum females taken during the same time of year and in different areas indicated a biennial reproductive cycle. C. taurus appears to display a high degree of affinity for particular reefs. The reason some reefs are chosen over others, despite having similar physical characteristics, remains unclear. A significant increase in the number of C. taurus caught in competitions held by the Border Rock and Surf Angling Association between 1984 and 2004 suggests an increase in the abundance of C. taurus.

Sex-specific and individual preferences for hunting strategies in white sharks

1. Fine-scale predator movements may be driven by many factors including sex, habitat anddistribution of resources. There may also be individual preferences for certain movementstrategies within a population which can be hard to quantify.2. Within top predators, movements are also going to be directly related to the mode of hunting,for example sit-and-wait or actively searching for prey. Although there is mounting evidencethat different hunting modes can cause opposing trophic cascades, there has been littlefocus on the modes used by top predators, especially those in the marine environment.3. Adult white sharks (Carcharhodon carcharias) are well known to forage on marine mammalprey, particularly pinnipeds. Sharks primarily ambush pinnipeds on the surface, but there hasbeen less focus on the strategies they use to encounter prey.4. We applied mixed hidden Markov models to acoustic tracking data of white sharks in acoastal aggregation area in order to quantify changing movement states (area-restricted searching(ARS) vs. patrolling) and the factors that influenced them. Individuals were re-tracked overmultiple days throughout a month to see whether state-switching dynamics varied or if individualspreferred certain movement strategies.5. Sharks were more likely to use ARS movements in the morning and during periods of chummingby ecotourism operators. Furthermore, the proportion of time individuals spent in the two differentstates and the state-switching frequency, differed between the sexes and between individuals.6. Predation attempts/success on pinnipeds were observed for sharks in both ARS and patrollingmovement states and within all random effects groupings. Therefore, white sharks can use both a ‘sitand-wait’ (ARS) and ‘active searching’ (patrolling) movements to ambush pinniped prey on the surface.7. White sharks demonstrate individual preferences for fine-scale movement patterns, whichmay be related to their use of different hunting modes. Marine top predators are generallyassumed to use only one type of hunting mode, but we show that there may be a mix withinpopulations. As such, individual variability should be considered when modelling behaviouraleffects of predators on prey species.

Residency Patterns and Migration Dynamics of Adult Bull Sharks (Carcharhinus leucas) on the East Coast of Southern Africa

Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities. However, little is known about the spatial and temporal scales of their habitat use and associated ecological role. In this study, we employed passive acoustic telemetry to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195–283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months. The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events. Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean  = 533 km) with eight of these sharks returning to the study site. During migration, individuals exhibited rates of movement between 2 and 59 km.d−1 (mean  = 17.58 km.d−1) and were recorded travelling annual distances of between 450 and 3760 km (mean  = 1163 km). Migration towards lower latitudes primarily took place in austral spring and winter and there was a significant negative correlation between residency and mean monthly sea temperature at the study site. This suggested that seasonal change is the primary driver behind migration events but further investigation is required to assess how foraging and reproductive activity may influence residency patterns and migration. Results from this study highlight the need for further understanding of bull shark migration dynamics and suggest that effective conservation strategies for this vulnerable species necessitate the incorporation of congruent trans-boundary policies over large spatial scales.

Shark fishing effort and catch of the ragged-tooth shark Carcharias taurus in the South African competitive shore-angling fishery

An integrated telephone and on-site questionnaire survey was used to estimate total shark fishing effort and specific catch of the ragged-tooth shark Carcharias taurus by coastal club-affiliated shore-anglers, primarily along the east coast of South Africa. Mean total shark fishing effort was estimated to be 37 820 fisher-days year−1 (95% CI = 28 281–47 359 fisher-days year−1) with a mean cpue of 0.073 C. taurus fisher−1 day−1 (95% CI = 0.068–0.078 fisher−1 day−1). Cpue for C. taurus varied significantly along the coast and ranged from a high of 0.260 fisher−1 day−1 in the Eastern Cape to zero fisher−1 day−1 on the West Coast. The total number of C. taurus caught annually by coastal club anglers was estimated at 1 764 fish year−1 (95% CI = 321–3 207 fish year−1). The majority (92.1%) of young-of-the-year sharks (<1.2m total length, TL) were recorded between East London and Jeffreys Bay, suggesting that this may be the primary nursery area for C. taurus. Post-release mortality ranged from 3.8% for young-of-the-year sharks to 18.5% for adult sharks (>2.4m TL). The majority (76.2%) of anglers interviewed stated that they now fished less for sharks since the banning of vehicles on beaches in December 2001. As a result of this ban, almost half (49.2%) of interviewed anglers stated that they now fished more for non-cartilaginous species.

Comparative feeding ecology of bull sharks (Carcharhinus leucas) in the coastal waters of the southwest Indian Ocean inferred from stable isotope analysis.

As apex predators, sharks play an important role shaping their respective marine communities through predation and associated risk effects. Understanding the predatory dynamics of sharks within communities is, therefore, necessary to establish effective ecologically based conservation strategies. We employed non-lethal sampling methods to investigate the feeding ecology of bull sharks (Carcharhinus leucas) using stable isotope analysis within a subtropical marine community in the southwest Indian Ocean. The main objectives of this study were to investigate and compare the predatory role that sub-adult and adult bull sharks play within a top predatory teleost fish community. Bull sharks had significantly broader niche widths compared to top predatory teleost assemblages with a wide and relatively enriched range of δ13C values relative to the local marine community. This suggests that bull sharks forage from a more diverse range of δ13C sources over a wider geographical range than the predatory teleost community. Adult bull sharks appeared to exhibit a shift towards consistently higher trophic level prey from an expanded foraging range compared to sub-adults, possibly due to increased mobility linked with size. Although predatory teleost fish are also capable of substantial migrations, bull sharks may have the ability to exploit a more diverse range of habitats and appeared to prey on a wider diversity of larger prey. This suggests that bull sharks play an important predatory role within their respective marine communities and adult sharks in particular may shape and link ecological processes of a variety of marine communities over a broad range.

Variation in palaeo-shorelines explains contemporary population genetic patterns of rocky shore species

Processes driving and maintaining disjunct genetic populations in marine systems are poorly understood, owing to a lack of evidence of hard barriers that could have shaped patterns of extant population structure. Here, we map two genetically divergent lineages of an obligate rocky shore fish, Clinus cottoides, and model sea-level change during the last 110 000 years to provide the first evidence of a vicariant event along the southern coastline of Africa. Results reveal that lowered sea levels during glacial periods drastically reduced rocky intertidal habitat, which may have isolated populations in two refugia for at least 40 000 years. Contemporary coastal dynamics and oceanography explain secondary contact between lineages. This scenario provides an explanation for the origin of population genetic breaks despite a lack of obvious present-day geographical barriers and highlights the need for including palaeo-oceanography in unravelling extant population patterns.

Environmental influences on the abundance and sexual composition of white sharks Carcharodon carcharias in Gansbaai, South Africa

The seasonal occurrence of white sharks visiting Gansbaai, South Africa was investigated from 2007 to 2011 using sightings from white shark cage diving boats. Generalized linear models were used to investigate the number of great white sharks sighted per trip in relation to sex, month, sea surface temperature and Multivariate El Niño/Southern Oscillation (ENSO) Indices (MEI). Water conditions are more variable in summer than winter due to wind-driven cold water upwelling and thermocline displacement, culminating in colder water temperatures, and shark sightings of both sexes were higher during the autumn and winter months (March–August). MEI, an index to quantify the strength of Southern Oscillation, differed in its effect on the recorded numbers of male and female white sharks, with highly significant interannual trends. This data suggests that water temperature and climatic phenomena influence the abundance of white sharks at this coastal site. In this study, more females were seen in Gansbaai overall in warmer water/positive MEI years. Conversely, the opposite trend was observed for males. In cool water years (2010 to 2011) sightings of male sharks were significantly higher than in previous years. The influence of environmental factors on the physiology of sharks in terms of their size and sex is discussed. The findings of this study could contribute to bather safety programmes because the incorporation of environmental parameters into predictive models may help identify times and localities of higher risk to bathers and help mitigate human-white shark interactions.