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Catching and tracking the world's largest Zambezi (bull) shark Carcharhinus leucas in the Breede Estuary, South Africa: The first 43 hours

  • CPAWS-BC (Canadian Parks and Wilderness Society - British Columbia)
  • Department of Forestry Fisheries & Environment, South Africa

Abstract and Figures

The Zambezi or bull shark Carcharhinus leucas is a large, predatory shark that occurs in warm-temperate, tropical and subtropical coastal and estuarine systems worldwide. To confirm reports of Zambezi sharks in the Breede Estuary on the south-west coast of South Africa, a survey was undertaken during 20-26 January 2009. On 24 January, a large female Zambezi shark was caught on rod and reel. Measuring 400 cm total length and 320 cm precaudal length, it is the largest recorded Zambezi shark. Furthermore, its occurrence in the Breede Estuary is the southernmost record of the species, extending its previously documented range by 366 km. The shark was tagged with a continuous acoustic tag and tracked for 43 consecutive hours. During that period, it swam as far as 20 km upstream, but it also briefly exited the estuary and travelled 2 km out to sea. Most of the time (24%) was spent 11-13 km upstream, where it actively inspected boats and shore-anglers, a behaviour considered to be an opportunistic foraging strategy. Estuaries appear to represent critical habitats in the life history of Zambezi sharks.
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African Journal of Marine Science 2009, 31(1): 107–111
Printed in South Africa — All rights reserved
Copyright © NISC (Pty) Ltd
ISSN 1814–232X EISSN 1814–2338
doi: 10.2989/AJMS.2009.
Short Communication
Catching and tracking the world’s largest Zambezi (bull) shark Carcharhinus
leucas in the Breede Estuary, South Africa: the first 43 hours
ME McCord1* and SJ Lamberth2,3
1 South African Shark Conservancy, Old Harbour Museum, Hermanus 7200, South Africa
2 Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Rogge Bay 8012,
South Africa
3 South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Grahamstown 6140, South Africa
* Corresponding author, e-mail:
Manuscript received February 2009; accepted March 2009
The Zambezi or bull shark Carcharhinus leucas is a large, predatory shark that occurs in warm-
temperate, tropical and subtropical coastal and estuarine systems worldwide. To confirm reports of
Zambezi sharks in the Breede Estuary on the south-west coast of South Africa, a survey was undertaken
during 20–26 January 2009. On 24 January, a large female Zambezi shark was caught on rod and reel.
Measuring 400 cm total length and 320 cm precaudal length, it is the largest recorded Zambezi shark.
Furthermore, its occurrence in the Breede Estuary is the southernmost record of the species, extending
its previously documented range by 366 km. The shark was tagged with a continuous acoustic tag and
tracked for 43 consecutive hours. During that period, it swam as far as 20 km upstream, but it also briefly
exited the estuary and travelled 2 km out to sea. Most of the time (24%) was spent 11–13 km upstream,
where it actively inspected boats and shore-anglers, a behaviour considered to be an opportunistic
foraging strategy. Estuaries appear to represent critical habitats in the life history of Zambezi sharks.
Keywords: acoustic tracking, Carcharhinus leucas, estuary, freshwater, largest size recorded, nursery
Zambezi (bull) sharks Carcharhinus leucas are large
carcharhinid sharks that commonly occur in the turbid
waters of lagoons, river mouths and shallow coastal
waters in tropical and subtropical seas (Sadowsky 1971,
Snelson et al. 1984, Compagno et al. 2005, Simpfendorfer
et al. 2005). Spending much of their time in estuaries, it
is the only shark species that readily occurs in both salt-
and freshwater. Zambezi sharks can breed in freshwater,
although most breeding likely occurs in the high reaches
of warm-water estuaries and rivers (Montoya and Thorson
1982, Cliff and Dudley 1991, Compagno et al. 2005, Pillans
In South Africa, distribution records indicate that the
species occurs from the Moçambican border to Cape St
Francis in the Eastern Cape (Compagno et al. 1989).
Recently, however, increased anecdotal reports of Zambezi
sharks in both the southern Eastern Cape and the Western
Cape provinces, particularly in the Breede Estuary, suggest
a possible southward shift in their distribution and/or a
re-establishment of populations that existed beyond collec-
tive memory.
According to Whitfield (1996, 1998), the Zambezi shark
is partially estuarine-dependent, using estuaries as pupping
and nursery grounds. As such, they would be particularly
susceptible to habitat degradation, alteration and environ-
mental change, and that ever-increasing human utilisation
and concurrent degradation of estuaries will likely result in
population declines. Zambezi sharks are currently targeted or
taken as bycatch in several South African fisheries, including
the drum-line fisheries, pelagic and demersal longline
fisheries, the recreational shark fishery and the handline
fishery, and they are commonly caught in shark-protection
nets off KwaZulu-Natal (Dudley 2000).
Listed as Near-Threatened on the IUCN Red List (IUCN
2008), Zambezi sharks are considered a species of global
conservation concern. The systematic removal of these
predators from either a coastal or estuarine system will
undoubtedly have negative cascade effects on the health
and integrity of these systems (Baum et al. 2003, Myers and
Worm 2003). Thus, it is imperative that further research into
the ecology and life history of this species, and the role of
estuaries in sustaining populations, be conducted.
McCord and Lamberth
To determine whether reports of Zambezi sharks in the
Breede Estuary could be confirmed, a research expedition
was undertaken, with a secondary objective of acoustically
tagging an individual to examine its movement patterns in
the estuary.
Materials and methods
Study area
The Breede River is 322 km long with a draining catchment
area of 12 600 km2. It enters the Indian Ocean in Sebastian
Bay and falls within the warm-temperate Agulhas biogeo-
graphical region (Figure 1) (Emmanuel et al. 1992). The
total surface area of the estuary is approximately 455 ha and
extends 50 km upstream to a series of rocky sills where tidal
influence ceases (Taljaard et al. 2001). The estuary falls
within the winter/bimodal rainfall transition zone, but most of
the catchment falls in the winter rainfall area and flows are
strongly seasonal with high flows and floods during winter.
However, the combination of the two rainfall zones adds
to physical variability, ultimately accounting for multiple
behavioural signals and the high diversity of the ichthyo-
fauna in the estuary (Harrison 1999, Lamberth et al. 2008).
The Breede Estuary is permanently open, has a mean depth
of 4.6 m, and high flows and strong currents are able to
completely flush and reset the system within a single tidal
cycle (Taljaard et al. 2001).
Shark capture and tracking
Attempts to capture a Zambezi shark in the Breede Estuary
were conducted during 20–26 January 2009. Fishing
methods included handline and rod-and-reel using live
spotted grunter Pomadasys commersonnii and dusky kob
Argyrosomus japonicus as bait. Post-capture stress was
minimised by using tow straps around the torso and caudal
areas to reduce pressure on the spinal column and body
cavities. Body measurements taken were total length (TL,
cm), precaudal length (PCL, cm) and interdorsal length
(IDL, cm). Genetic samples were taken and stored in
alcohol for later processing. Sex and stage of maturity were
also recorded. The shark was injected with oxytetracycline
for age validation purposes.
Three types of tags were used; a conventional plastic dart
tag of 14 cm long, which was inserted with a 4 mm outside
diameter applicator needle (Hallprint), a VEMCO-coded
acoustic transmitter (69 kHz R69K), and a VEMCO contin-
uous acoustic transmitter (V16 54 kHz), anchored with
umbrella darts (VEMCO — Division of AMIRIX Systems Inc.,
Halifax, Nova Scotia). All tags were inserted into the dorsal
muscle of the first dorsal fin. An antibiotic (propolis) was used
to wash each tag insertion to prevent possible infection.
Three tracking teams working in 4 h shifts continuously
tracked the Zambezi shark using a VEMCO VR100 acoustic
receiver, beginning at 15:30 on 24 January and ending at
10:00 on 26 January. Positions at the start and end of each
tracking shift were marked on a Garmin handheld GPS. To
ensure integrity of the track, GPS positions were manually
logged every 5–10 min on the VR100. Changes in shark
behaviour near boats, around fishing activities and at tidal
changes were noted throughout the 43 h tracking period.
Temperature, salinity, turbidity and oxygen data were
collected at 18 sites along the length of the estuary, from the
mouth to 35 km upstream, using a YSI 6600 Multi-parameter
Environmental Monitoring System. The ‘salinity run’ started
an hour before high tide on 25 January 2009 in order to
obtain a measure of maximum salinity penetration into the
system. The run was completed once water column salinity
stabilised at 1.0.
The catch
The Zambezi shark (Figure 2) was hooked 5.2 km upriver
at 13:30 on 24 January using rod and reel with live spotted
grunter as bait. It was landed 7.7 km upriver at around 14:50.
The shark measured 400 cm TL and 320 cm PCL with an IDL
of 85 cm. The weight was estimated to be in excess of 600 kg,
using a length–weight relationship provided by Wintner et al.
(2002). However, given the large size of the shark, this derived
weight fell well outside the upper range of the curve and thus
is considered a rough estimate. The shark was female and
appeared pregnant due to the distension of its abdomen.
The capture of a Zambezi shark in the Breede Estuary
represents a range extension south-westwards of 366 km
from Cape St Francis in the Eastern Cape, where it was
previously documented (Compagno et al. 2005). However,
anecdotal and photographic evidence shows that the
presence of this species in the Breede Estuary dates back to
at least the 1960s.
A total of 205 GPS positions were manually logged on
the VR100 receiver when signal strength indicated the
presence of the shark close to the observation boat. During
the first five hours of tracking (15:00–20:00), the shark
appeared to be resting against the edge of a mudbank
drop-off, spending most of its time within 500 m of where
it was released (Figure 3). From 22:00, it started to move
Cape St Francis
34° S
32° S
20° E 24° E 28° E 32° E
St Lucia
Western Cape
Eastern Cape
Figure 1: Map of South Africa showing the Breede Estuary and
other localities mentioned in the text
African Journal of Marine Science 2009, 31(1): 107–111 109
Figure 2: The Zambezi shark that was caught, tagged and released with acoustic tags in the Breede Estuary on 24 January 2009 (photo:
Alison Towner)
Figure 3: Google Earth image of the Breede River showing the track of the tagged Zambezi shark over a 43 h period during 24–26 January
2009. The positions shown (white dots) are those logged at 15 min intervals. Date, time and direction of major movements are indicated by
grey arrows. The hooked and landed positions are shown
St Sebastian
McCord and Lamberth
slowly downstream, inspecting some fishing boats on the
way. At 3:00 the following morning (25 January), it exited
the mouth and swam approximately 2 km out to sea —
it was then 15 km from its release position. At 06:00, the
shark returned to the estuary and spent the next 4 h resting
just inside the surf-zone adjacent to the entrance channel.
From 09:00 to 10:00, it inspected a group of shore-anglers
and cast-netters at the mouth of the estuary, after which it
made a 5 km burst upstream. From there, it swam slowly
farther upstream and spent most of the next 24 h moving
among boats and shore-anglers, possibly in anticipation of
easy prey. The shark spent 24% of its time between 11 km
and 13 km upstream (Figure 3).
The estuary was well mixed at the time of the study, with
barely discernible vertical stratification. Saltwater intrusion
extended 35 km upstream at high tide, but throughout the
tracking period the shark remained within the 15–35 salinity
ranges in the lower 20 km of the estuary. Water tempera-
tures were fairly high, ranging from 20 °C at the mouth to
24 °C upstream. Turbidity at the mouth was low at 5 NTU
but increased to >20 NTU in the upper reaches. The shark
remained within the 10–15 NTU range throughout most of
the daylight hours and forays into the clearer, lower reaches
of the estuary were almost exclusively confined to the night
and early morning. The water column was well oxygenated
throughout the estuary. All physico-chemical parameters
measured were typical of the Breede system at the time of
sampling (Lamberth et al. 2008).
Behavioural notes
Although the shark’s behaviour was not quantified during
this exploratory survey, descriptive notes on its behaviour
near boats and around fishing activities were recorded
during the night when such activities peaked.
On 24 January, boat-based night fishing was concen-
trated between 11 km and 13 km upstream, where the shark
appeared to spend the majority of its time. From 19:40 to
21:00, the shark swam between three boats that were fishing
for grunter and kob. It explored an area beneath each vessel
for several minutes before moving to another boat.
During the final tracking shift (06:00–10:00 on 26 January),
the shark moved from 11 km to 15 km upriver, following
boat-based fishing activities. It moved between seven
boats, all with fishing lines in the water, spending several
minutes near each one before moving away. At 07:23, the
shark moved toward a boat while it pulled anchor and began
following the boat when it trolled downstream with four
rapalla fishing lures in the water. The shark spent approxi-
mately 35 min following the trolling boat.
At 08:00 on 26 January, as tidal flow slacked (low tide
was at 09:20) and the majority of fishing boats returned
to shore, the shark moved into the shallower bank waters
of the river and appeared to drift downstream (at a rate of
approx. 3.5 km h–1), during which time it inspected shore-
and boat-anglers for a few minutes at a time, and frequently
entering shallow waters <1.5 m deep.
Zambezi sharks commonly occur in shallow coastal waters
and estuaries of tropical and subtropical seas throughout the
world (Compagno et al. 2005, Pillans 2006). In South Africa,
they are found in several estuaries and coastal waters from
KwaZulu-Natal to Cape St Francis in the Eastern Cape
(Compagno et al. 1989). This study is the first confirmed
record of Zambezi sharks in the Breede Estuary and
represents the southernmost occurrence for the species,
extending its previously known range by 366 km.
Anecdotal reports and photographs indicate that Zambezi
sharks inhabited the Breede Estuary in the 1960s and 1970s.
A notable reduction in anecdotal reports from the late 1970s
to early 2000s suggests that direct hunting of these sharks
during earlier years (as documented in the photographs)
may have decimated the population of these sharks in
that estuary. Increased reports of Zambezi sharks in the
Breede Estuary since 2003 may mark their local reappear-
ance. Possible reasons for this could be the degradation
and closure of other estuaries — and possible nursery and
breeding grounds — along the South African coastline (Cliff
and Dudley 1991, Turpie et al. 2002).
Previously thought to reach a maximum total length
of 340–350 cm (Bass et al. 1973, Cliff and Dudley 1991,
Dudley 2000, Compagno et al. 2005), the Zambezi shark
under study represents a 50–60 cm increase in the
maximum known size of the species.
The shark spent most of its time between 5 km and
11 km upstream, where boat-based fishing activities were
most concentrated. This may represent conditioning to
these activities, which could result in lower levels of energy
expenditure while foraging. The shark appeared to move with
the tidal flow, swimming down the estuary on slack and low
tide and up the estuary during high tide. Similar movements
have been shown for estuarine fish, whereby they follow
the tidal cycle to minimise energetic output (Ackerman et al.
2000, Heupel et al. 2006, Collins et al. 2007, Childs et al.
2008). Alternatively, the shark may have been following prey
such as grunter and kob, which exhibit synchronised tidal
movements (Cowley et al. 2008). This behavioural adapta-
tion may also allow the shark to opportunistically prey on fish
by either moving on or off the shallow intertidal areas during
the flood and ebb tides. Further tracking studies on this
Zambezi shark will examine its fine-scale movement patterns
and behaviour in the estuary.
As a partially estuarine-dependent elasmobranch species,
Zambezi sharks use estuaries as pupping and nursery
grounds (Whitfield 1998, Pillans 2006). The shark under
study appeared to be pregnant at the time of capture,
suggesting that the Breede Estuary may serve as a nursery
ground for this species. The species was previously thought
to pup only farther north, in the St Lucia Estuary in KwaZulu-
Natal (Bass et al. 1973, Cliff and Dudley 1991). Exploratory
surveys similarly to this study indicate that the Umzimvubu
Estuary, some 800 km north of the Breede Estuary (Figure 1),
may also be a (previously undocumented) nursery ground
for Zambezi sharks; juveniles bearing distinct umbilical scars
were captured in that estuary in February 2008 (S Wintner,
Natal Sharks Board, pers. comm.).
It is uncertain whether this record of a Zambezi shark
in the Breede Estuary represents a single or a population
range extension for the species. The Breede River has ideal
nursery conditions for Zambezi sharks: a permanently open
warm-temperate estuarine system, is highly productive, has
African Journal of Marine Science 2009, 31(1): 107–111 111
few potential predators, favourable salinity and temperature
gradients, and the estuary is relatively large (Whitfield 1996,
Pillans 2006, Wiley and Simpfendorfer 2007, Lamberth et
al. 2008).
Although the residency and abundance of these sharks in
the Breede Estuary is yet to be determined, the discovery
of the largest recorded Zambezi shark there indicates that
the estuary provides favourable habitat for a species listed
globally as Near Threatened (IUCN 2008). Future studies
should focus on the role of these vulnerable predators in the
Breede Estuary, including abundance, residency, population
dynamics and habitat utilisation.
Acknowledgements — We thank those who made the expedition
possible: Hennie Papenfuss and the Big Fish Safari team, Alison
Towner (Marine Dynamics), Stiaan Conradie, Nick Scholtz and Rupert
Bellairs (Lower Breede River Conservancy), Corne Erasmus, Ricardo
Williamson, Mike Meyer and Sarika Singh (Marine and Coastal
Management [MCM]), Warren Swanapoel and Steve Smuts (South
African Shark Conservancy), Alison Kock (Save Our Seas Shark
Centre), Lucy Scott (Agulhas Large Marine Ecosystem), Jean Duplessis
and Enrico Menezies (Cape Nature), Dave McCord and Mike Gray. Lara
van Niekerk (CSIR), Sven Kerwath and Rob Tarr (MCM) are thanked for
their contribution towards the data plots and illustrations. We acknowl-
edge the generous donations and sponsorship from White Shark
Projects, Dyer Island Conservation Trust, Gateway Fruit and Veg. City,
Van Blommestein Slaghuis, Quest Seafood Distributors, Hennie Visser,
BS Diver’s, and Hilary Smith and Tim Arnett (Mudlark Guestlodge). Paul
Cowley and Dave Ebert are thanked for their constructive reviews of the
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... Overall, it is suspected that the Bull Shark has undergone a population reduction of 30-49% over the past three generation lengths (55-80 years) due to declines in habitat quality and levels of exploitation, and it is assessed as Vulnerable A2bcd. The Bull Shark has a circumglobal distribution (McCord and Lamberth 2009, Ebert et al. 2013, Nevill et al. 2014, SEAFDEC 2016, Arunrugstichai et al. 2018, Arai and Azri 2019, Deng 2019, Iqbal et al. 2019, Psomadakis et al. 2019, Soria et al. 2019, M. Dicken unpubl. data 2021. ...
... In Panama, Pacific Ocean, the abundance of Bull Shark was noted by artisanal fishers as scarce in 2009-2011(Rodríguez-Arriati 2011 (Pauly et al. 2020). Although landings data are not a direct measure of abundance, these can be used to calculate population reduction where landings have decreased while fishing effort has remained stable or increased. ...
... Adults are known to use a wide range of coastal habitats with a high dependence on coral reefs (Daly et al. 2014, Espinoza et al. 2016. It reaches a maximum size of 400 cm total length (TL) (McCord andLamberth 2009, Werry 2010), but is mostly reported to be 340-366 cm total maximum length (Ebert et al. 2013, Weigmann 2016. Males mature at 157-226 cm TL and females mature at 180-230 cm TL (Moore et al. 2012, Ebert et al. 2013, Jabado et al. 2016. ...
... Within months, a single adult individual can use habitats as divergent as the open ocean beyond continental shelves, coastal waters, and estuaries (Carlson et al. 2010;Lea et al. 2015;Niella et al. 2017). The largest individual ever recorded (a 400-cm TL female) was acoustically tracked over a 43-hour period in the Breede Estuary, South Africa, and over that period was found to move as far as 20 km upstream and 2 km offshore (McCord and Lamberth 2009). ...
... Like many wide-ranging sharks, there is geographic variation in the biological parameters for this species. However, in summary, this shark is large (400 and ~280 cm TL in the Indo-Pacifc and Atlantic, respectively) (McCord and Lamberth 2009;Springer 1960), slow growing (Branstetter and Stiles 1987;Thorson and Lacy 1982), and long lived (estimated to reach >50 years) (Wintner et al. 2002). Reproduction is placental viviparous, with a gestation period of 10 to 11 months and a reproductive periodicity of 2 years (e.g., Cliff and Dudley 1991;Cruz-Martínez et al. 2004). ...
... Additionally, their ability to traverse vast stretches of open ocean provides further evidence for their potential presence in geographically isolated regions such as the Maldivian archipelago (Lea et al., 2015). The bull shark is a large, slow-growing species with a total length that usually ranges between 257 and 314 cm, with a maximum length reported of 400 cm (McCord & Lamberth, 2009) and a sexual dimorphism where females grow slightly larger than males (Cruz-Martinez et al., 2005;Wintner et al., 2002). ...
Full-text available
Verified records of the bull shark Carcharhinus leucas are lacking in the Maldives. This study provides the first confirmed evidence of 23 sightings observed from 2013 to 2023 in the central and southern atolls of this archipelago. Most of the sightings occurred in close proximity of inhabited areas, where food waste is often discarded into the water, or in several dive sites, suggesting the presence of this species in different location around Central and Southern Atolls. Although further research is required to fully investigate the C. leucas population in the Maldives, this report documents and confirms its presence in this region. This article is protected by copyright. All rights reserved.
... However, this is unlikely in the current study as larger known predators of rays, e.g. bull sharks Carcharhinus leucas, do occur in this estuary (McCord and Lamberth 2009). ...
Many ray species are threatened with extinction, and so understanding their movement and habitat use is vital for developing effective management and conservation efforts. Globally, rays are known to rely on estuarine habitats, but estuary use by rays has not yet been investigated in South Africa. Thirty-three diamond rays Gymnura natalensis and 25 bull rays Aetomylaeus bovinus, both species anecdotally recorded to occur in estuaries, were acoustically tagged. Individuals were tracked using a nation-wide network of receivers in South Africa, the Acoustic Tracking Array Platform (ATAP), that has acoustic receivers in both marine and estuarine environments. Only six rays (4 diamond and 2 bull rays) were recorded using estuaries, but they displayed seasonal philopatry, returning to specific estuaries during spring to autumn months (September to May) for up to 6 consecutive years. Due to a number of rays entering the Breede Estuary, the fine-scale habitat use in this ecosystem was investigated. Marine-estuarine connectivity was significantly influenced by marine temperatures. Additionally, presence in the upper parts of the Breede Estuary (up to 17 km from the mouth) was influenced by temperature, tides and time of day. Findings suggest estuaries are an important, and previously overlooked, habitat type for a portion of the diamond and bull ray populations on the south coast of South Africa, which has management and conservation implications.
... Distribution du requin-bouledogue (Carcharhinus leucas) ©UICN Le requin-bouledogue a une aire de répartition très étendue comprenant les eaux chaudes tropicales, subtropicales, et tempérées à la fois côtières et offshore (Figure 25) (Arai & Azri, 2019; Arunrugstichai et Deng et al., 2019; Iqbal et al., 2019;McCord & Lamberth, 2009;Nevill et al., 2013; Soria et al., 2019; Weigmann, 2016). C'est une espèce démersale et semi-pélagique : le requin-bouledogue est présent dans les eaux peu profondes jusqu'à 30 mètres de profondeur, 164 mètres étant le maximum enregistré ...
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La rapide expansion des activités anthropiques, les changement globaux, la pollution associée à la destruction des habitats et la surpêche menacent la biodiversité marine. Les élasmobranches n’échappent pas à ce constat : aujourd’hui, près de 37.5% des raies et des requins sont menacés d’extinction et la liste ne cesse de s’allonger. L’archipel des Mascareignes (La Réunion, Maurice, Rodrigues) constitue le principal hotspot de biodiversité de l’Océan Indien, et pourtant, les espèces d’élasmobranches évoluant dans ces eaux restent peu connues. Il est impératif de pallier le manque de connaissance de cette biodiversité afin de mettre en œuvre des actions pour la conservation et la gestion des élasmobranches de l’archipel des Mascareignes. De par la combinaison de plusieurs méthodes d'échantillonnage non-invasives (UVC, BRUV, ADNe), cette étude a permis de recueillir des informations préliminaires sur la biodiversité et la distribution des élasmobranches de La Réunion et de l’île Maurice (les données de l’île de Rodrigues n’ont pu être analysées). Entre janvier 2021 et juillet 2022, 19 espèces d’élasmobranches ont été recensées : 348 observations ont été réalisées et 749 individus ont été inventoriés. La raie-fouet rose (Pateobatis fai), la raie aigle ocellée (Aetobatus ocellatus), la raie pastenague à taches noires (Taeniura meyeni) et le requin gris de récif (Carcharhinus amblyrhynchos) sont les espèces les plus abondantes et les plus observées sur la côte Ouest de l’île de La Réunion et sur la côte Nord et Ouest de l’île Maurice. Les modèles additifs généralisés mettent en évidence une corrélation entre la présence de l’espèce de raie A. ocellatus et l’abondance en chlorophylle a. Quant au cycle lunaire et à la luminosité, ils joueraient un rôle sur la dynamique comportementale de l’espèce de raie T. meyeni.
... Depredation tends to be higher in locations where fishing pressure is highest, suggesting sharks are either attracted to the consistent cues associated with fishing activity (smell of fish blood, boat engine noise, etc.) and/or learn to stay in these locations via conditioning. Acoustic tracking of bull sharks (Carcharhinus leucas) in South Africa showed that they spent considerable time close to fishing boats and made clear movements towards fishing boats in response to engine noise and hauling the anchor chain (McCord and Lamberth 2009). These anecdotal lines of evidence suggest that sharks can associate artificial sounds with food rewards. ...
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450 million years of evolution have given chondrichthyans (sharks, rays and allies) ample time to adapt perfectly to their respective everyday life challenges and cognitive abilities have played an important part in that process. The diversity of niches that sharks and rays occupy corresponds to matching diversity in brains and behaviour, but we have only scratched the surface in terms of investigating cognition in this important group of animals. The handful of species that have been cognitively assessed in some detail over the last decade have provided enough data to safely conclude that sharks and rays are cognitively on par with most other vertebrates, including mammals and birds. Experiments in the lab as well as in the wild pose their own unique challenges, mainly due to the handling and maintenance of these animals as well as controlling environmental conditions and elimination of confounding factors. Nonetheless, significant advancements have been obtained in the fields of spatial and social cognition, discrimination learning, memory retention as well as several others. Most studies have focused on behaviour and the underlying neural substrates involved in cognitive information processing are still largely unknown. Our understanding of shark cognition has multiple practical benefits for welfare and conservation management but there are obvious gaps in our knowledge. Like most marine animals, sharks and rays face multiple threats. The effects of climate change, pollution and resulting ecosystem changes on the cognitive abilities of sharks and stingrays remain poorly investigated and we can only speculate what the likely impacts might be based on research on bony fishes. Lastly, sharks still suffer from their bad reputation as mindless killers and are heavily targeted by commercial fishing operations for their fins. This public relations issue clouds people's expectations of shark intelligence and is a serious impediment to their conservation. In the light of the fascinating results presented here, it seems obvious that the general perception of sharks and rays as well as their status as sentient, cognitive animals, needs to be urgently revisited.
... and C. leucas, can be considered truly euryhaline. In the Indo-Pacific region, bull sharks are born at 60 to 75 cm total length (TL), both males and females reaching maturity at ∼ 10-20 years and 180 to 230 cm TL and reaching a maximum recorded size of 400 cm TL (Wintner et al. 2002;Last and Stevens 2009;McCord and Lamberth 2009 Carcharhinus leucas is currently recognized from Sumatra in available distribution maps (Ebert et al. 2021;Gausmann 2021;Rigby et al. 2021). Only few verified inland records of juveniles and subadults from Sumatran freshwater environments had been previously reported (Batang Hari River Basin: Tan and Lim 1998; Musi River: Iqbal et al. 2019). ...
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Six new records of the bull shark Carcharhinus leucas from five different river basins of Sumatra, Indonesia, were reported as a result of captures by artisanal and recreational fishers, including records from rivers of northern and western Sumatra for the first time. These findings may highlight the importance of Sumatran river basins for the reproduction of this threatened species in Indonesian waters. Inland records of C. leucas in Southeast Asia and in particular Indonesia are scarce but important for nature conservation purposes and sustainable future fishery management.
... Both body flex and tail grab are thought to be related with the escape response of fishes and, therefore, steady increases in both indicators with increased air exposure may suggest increased vulnerability of A. japonicus to post-release predation, particularly within predator-rich environments. For example, bull sharks Carcharhinus leucas have been observed orientating themselves around angling activity in certain South African estuaries where they likely opportunistically feed on released fishes (McCord and Lamberth, 2009). ...
Argyrosomus japonicus is arguably South Africa’s most important estuarine recreational and small-scale fishery species. Although juvenile A. japonicus predominate in estuarine environments, where catch-and-release angling is common, limited C&R studies have taken place. The aim of this study was to use angler-behaviour to robustly examine the physiological stress response, reflex impairment and short-term (12–36-hour) survival of A. japonicus following C&R angling. Observations of estuarine recreational angling informed three air exposure treatments based on minimum (10 s), mean (75 s) and maximum (240 s) observed times, for use in a controlled angling experiment. Based on a prior laboratory study, blood sampling was delayed 30–40 min post-capture to allow for peak accumulations of lactate and glucose. Long air exposure (240 s) predicted significantly higher blood glucose concentrations (ANOVA, p = 0.03) than short (10 s) exposure. Similarly, both long (p = 0.01) and moderate (75 s; p = 0.01) air exposure significantly predicted elevated blood lactate concentrations, when compared with short exposure. In terms of physical impairment, long air exposure (240 s) had a significant negative influence on the reflex response (cumulative link model, p = 0.01) of A. japonicus. An observed short-term mortality of 7.7% was primarily attributed to hooking injury. To reduce significant physiological and physical stress, it is proposed that anglers should aim to reduce air exposure times to below the observed mean of 75 s, and ideally to 10 s. For relevant and meaningful future C&R studies, we propound the incorporation of angler behavioural assessments, and the investigation of physiological stress responses, prior to designing field studies.
Coastal elasmobranchs tend to be upper-level predators, which may exert top-down impacts on the systems they inhabit; but there remains much to learn about their trophic ecology. In this chapter, we update our knowledge on the trophic interactions of coastal elasmobranchs as prey, predators, and competitors. We also explore factors that affect these relationships and elasmobranch interactions within key coastal habitats.
The Add-my-Pet (AmP) collection of data on energetics and Dynamic Energy Budget (DEB) parameters currently contains 200 out of over 1100 extant species of chondrichthyans. This milestone in the compilation of data for this group led us to investigate: (1) do the characteristics that we reported in 2014 for 20 chondrichthyan species, relative to other fish, still hold (2) are novel patterns in properties revealed given the additional data and (3) do the four chondrichthyan subgroups (galean, squaleans, rays and chimaeras) differ in properties? We argue that a better understanding of these properties is key to sustainable management of the rapidly dwindling populations worldwide. Most of the inter-specific scatter in ultimate reproduction rate as function of ultimate body weight stems from differences in the mass of neonates as fraction of that of the mother, which is very high in chondrichthyans. The ultimate neonate mass production is found to be proportional to the ultimate respiration rate, with proportionality factor of 10 g/mol. The lifespan is found to be inversely proportional to weight-specific respiration, with a proportionality factor of 0.1 mol/g. The ultimate weight equals the life-time cumulated neonate mass production. These relationships also apply, with more scatter, to all 3000 animal species in the AmP collection. Sharks and rays were found to be more demand-species, contrary to ray-finned fish and chimaeras, which are supply species. Chimaeras also have that smallest weight at birth and precociality coefficient, compared to sharks and rays. Galeans grow much slower than squaleans and rays, but the chimaeras grow even slower. The lifespan equals 25 times the incubation time for chondrichthyans, but they are rather unique in this respect. Last but not least, we discuss the odd implications of recently published data on the energetics of the Greenland shark.
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Ninety one young specimens and 3 adult females of BulI shark ("cação cabeça chata") caught in the lagoon region of Cananéia were examined, their tooth formula being 27/25 and the number of pre-caudal vertebrae ranging from 109 to 115. The proportion between the 1st and 2nd dorsal fins were found to be 2.3 and 2.8 for the young,and 2.9 to 3.1 for the adults. These data confirm that the studied form belongs to C. leuoas. Young occur regularly but in limited numbers.As regards the adults, however, females only appear during the short parturition period, i.e., from November to February. The number of embryos in the litters were from 7 to 9, their sizes ranging between 768-812 mm. The length of the smallest free young found was 697 mm, but young presumably 9 to 12 months old had 98 to 112 cm; between 21 and 24 months they were reaching 124 to 128 cm, that is, the same size they have when they start migrating to the open sea. The feeding inhibition phenomenon during the period of parturition was not observed in the female specimens caught in the lagoon. The more abundant species found in the stomach contents were: Arius spixii; Chloroscombrus chrysurus; A. grandicassus; A. barbus; Felichtys marinus; Genidens genidens; Chanophorus tajacica and Carcharhinus porosus.
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Three objective criteria for assessing sites being considered as marine nature reserves are developed and applied to a region of the west coast of South Africa, between the Groen and the Spoeg rivers, that has been mooted as a possible nature reserve. On a national and regional macroscale, zoogeographic analyses of 2 000 species of invertebrates were used to reappraise accepted marine biogeographic provinces. On a mesoscale and local scale, the intertidal community composition of rocky shores was examined and related to the physiographic habitat diversity. Five major zoogeographic regions are identified around the southern African coast, including a distinct Namaqua province. The Groen-Spoeg area, which receives no adequate conservation, is representative of both the major zoogeographic province that it falls in and the Northern Namaqua sub-province. A long period of limited human access as a result of diamond-mining has kept the shore near-pristine. On a global scale, the region is unique in the extent to which the system is dominated by dense assemblages of limpets. The species-composition of intertidal rocky-shore communities varies greatly according to the degree of wave exposure, and this small-scale variation, reflecting physiographic heterogeneity of the shore, can exceed large-scale zoogeographic variations. Therefore, in order to be representative, a reserve will need to incorporate small-scale variations in physical conditions and biotic composition, as well as large-scale geographic representativeness. The approaches used demonstrate that the Groen-Spoeg has a high priority for conservation; they are also generally applicable to the objective assessment of potential reserves, although they need to be coupled with other criteria, including socio-economic issues.
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Growth rings (GR) were counted in vertebrae of 69 female (56–221 cm precaudal length; 3–238 kg) and 54 male (57–216 cm; 3–180 kg) C. leucas. Annual GR deposition could not be confirmed by centrum edge analyses but was assumed on the basis of ‘mark–recapture’ analysis of 10 sharks held captive for between 2.2 and 20 years in an aquarium. GR counts indicated that the largest female and male were 32 years (221 cm) and 29 years (216 cm), respectively and the smallest mature female and male were 14 years (197 cm) and 25 years (196 cm). Length at 50% maturity was 193 cm (21 years) and 190 cm (20 years) for females and males, respectively. Maximum age is >50 years, and the two specimens (216, 217 cm) that have been held in the aquarium for 20 years are both estimated to be >29 years. Von Bertalanffy parameters for the combined sexes were L∞ = 230 cm, k = 0.071 year–1, t0 = –5.12 years, and Gompertz parameters were w0 = 24 kg, G = 2.86, g = 0.046 year–1.
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The distribution and abundance of teleosts found in southern African estuaries are determined by both biotic and abiotic variables. Factors which have already been shown to have an influence on estuarine-associated fishes are latitude, seasonality, catchment size, estuary size, axial salinity gradients, habitat diversity, estuary type, mouth depth and degree of marine influence, timing of the open phase, the ability of species to adjust to salinity and temperature fluctuations, dissolved oxygen levels, turbidity, available food resources, the Occurrence and severity of floods, trapping of organic material by impoundments, nearshore marine conditions, physical constrictions within estuarine systems, predation, competition, parasite loads, reproductive condition, juvenile cohort abundance, and habitat degradation as a result of pollution or dredging. The influence of several of the above variables on ichthyofaunal diversity and abundance are reviewed, with particular emphasis on salinity fluctuations as a primary factor affecting fish communities. A summary diagram of the biotic and abiotic variables affecting fishes, as well as a conceptual model on the influence of high turbidity on the foraging strategies of selected teleosts, is presented.
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This study compares the fish assemblages of the permanently open cool-temperate Olifants and warm-temperate Breede estuaries on the west and south coasts of South Africa respectively, and their responses to altered freshwater flows. Both estuaries have experienced a >35% reduction in mean annual runoff (MAR) from a historical reference condition to the present day with a >60% reduction possible under future flow scenarios. With the exception of species that have both marine and estuarine breeding populations, the Olifants Estuary fish assemblage has experienced an overall 20% decrease in abundance from reference (pristine state) to the present day and will gradually decline to 55% of reference with a predicted future 60% reduction in MAR. Consequently, future reductions in flow are likely to result in the Olifants Estuary progressing towards a low biomass, low diversity, marine-dominated system. In contrast, reduced freshwater flows in the Breede Estuary are likely to experience an overall reduction in the abundance of species that breed only in estuaries, and in freshwater and catadromous species. Collectively, entirely estuarine-dependent fish will increase in abundance, but considered individually some important exploited species such as Argyrosomus japonicus and Pomadasys commersonnii will collapse to 50% of historical numbers once there has been a 64% reduction in MAR. Overall, fish abundance in the estuary has increased by 6% from reference to the present day and is likely to increase to 115% of reference with future reductions in flow. Some species with a preference for fresh and brackish water will be all but lost from the system, but overall diversity is likely to increase with the range expansion of warm-temperate and subtropical marine species westward. In all, the fish assemblage of the Breede Estuary will experience a gradual change from a relatively high-diversity, low-abundance, freshwater rich system under historical flow conditions to a high diversity, high-abundance, marine-dominated system with future reductions in flow.
Ninety one young specimens and 3 adult females of BulI shark ("cação cabeça chata") caught in the lagoon region of Cananéia were examined, their tooth formula being 27/25 and the number of pre-caudal vertebrae ranging from 109 to 115. The proportion between the 1st and 2nd dorsal fins were found to be 2.3 and 2.8 for the young,and 2.9 to 3.1 for the adults. These data confirm that the studied form belongs to C. leuoas. Young occur regularly but in limited numbers.As regards the adults, however, females only appear during the short parturition period, i.e., from November to February. The number of embryos in the litters were from 7 to 9, their sizes ranging between 768-812 mm. The length of the smallest free young found was 697 mm, but young presumably 9 to 12 months old had 98 to 112 cm; between 21 and 24 months they were reaching 124 to 128 cm, that is, the same size they have when they start migrating to the open sea. The feeding inhibition phenomenon during the period of parturition was not observed in the female specimens caught in the lagoon. The more abundant species found in the stomach contents were: Arius spixii; Chloroscombrus chrysurus; A. grandicassus; A. barbus; Felichtys marinus; Genidens genidens; Chanophorus tajacica and Carcharhinus porosus.Noventa e um espécimes jovens e 3 fêmeas adultas de "cação cabeça chata" capturados na região lagunar de Cananeia foram examinados, constatando-se a fórmula dental 27/25 e número de vértebras pré-caudais entre 109 e 115.Verificouse que as proporções entre a la. nadadeira dorsal e a 2a. foram de 2.3 e 2.8 para os jovens e de 2.9 até 3.1 para os adultos.Ficou assim confirmado que a forma es tudada pertence a C. leuaas. É comum a ocorrência de jovens dentro da região estudada~ no entanto,quanto aos adultos,as fêmeas só são encontradas durante o período de parição, i.é, de novembro a fevereiro. Constatou-se que o número de embriões nas ninhadas foi de 7 a 9 e seus tamanhos oscilaram ent re 768-812 mm. O comprimento do menor jovem livre encontrado foi de 697 mm, sendo que jovens de presumivelmente 9 a 12 meses têm de 98 a 112 cm; entre 21 e 24 meses alcançam 124 a 128 cm, ou seja, os tamanhos que apresentam quando emigram para mar aberto. Não ficou confirmado o fenômeno da inibição alimentar nas fêmeas capturadas, já observado em genetrizes da mesma espécie durante o período de parição no delta do Mississippi. O conteúdo estomacal apresentou, por ordem decrescente de abundância: Arius spixii (13); Chloroscombrus chrysurus (7); A. grandicassus (6); A. barbus (4); Felichtys marinus (3); Genidens genide ns (2); Chanophorus tajacica (2); Carcharhinus porosus (2); Conodon nobilis, Caranx crysos, scomberomorus maculatus, Sphyrna tiburo, Rhinoptera brasiliensis, Dasyatis americana, Diapterus rhombeus (1), além de cerca de 25/30 exemplares de Callinectes sp.