ArticlePDF Available

Transoceanic Migration, Spatial Dynamics, and Population Linkages of White Sharks

Authors:
  • El Colegio de la Frontera Sur – Unidad Chetumal

Abstract and Figures

The large-scale spatial dynamics and population structure of marine top predators are poorly known. We present electronic tag and photographic identification data showing a complex suite of behavioral patterns in white sharks. These include coastal return migrations and the fastest known transoceanic return migration among swimming fauna, which provide direct evidence of a link between widely separated populations in South Africa and Australia. Transoceanic return migration involved a return to the original capture location, dives to depths of 980 meters, and the tolerance of water temperatures as low as 3.4 degrees C. These findings contradict previous ideas that female white sharks do not make transoceanic migrations, and they suggest natal homing behavior.
Content may be subject to copyright.
subtracting each judge’s rating of the typical
American from his or her rating of the typical
compatriot for each NCS item. Assuming that
cultures agree on the typical American, this proce-
dure in effect subtracts the bias plus a constant and
leaves a potentially better estimate of national
character. We standardized the differences as T
scores, using difference score normative values from
the worldwide sample, excluding the United States.
The difference scores were highly correlated with
NCS scores (rs 0 0.65 to 0.91, P G 0.001) and
provided essentially the same results. ICCs between
difference scores and NEO-PI-R observer ratings
ranged from –0.44 for England to 0.48 for Lebanon
(median, 0.03). ICCs between differences scores and
NEO-PI-R self-reports ranged from –0.47 for Russia
to 0.53 for Poland (median, 0.01). For the five
factors, correlati ons with observer ratings across
cultures ranged from 0.08 to 0.23, and those with
self-reports ranged from –0.37 to 0.23. These results
suggest that the lack of correspondence between
NEO-PI-R and NCS profiles is not simply due to
different sta ndards of evalua tion in different
cultures. A different issue concerns the reference-
group effect (28), according to which self-reports
and observer ratings of individuals are implicitly
made by reference to the distribution of scores in the
rater’s culture. Such an effect would tend to make
aggregate personality scores uniform for all cultures,
and the failure to find correlations with NCS factors
would be due to a lack of variation in aggregate
NEO-PI-R means. However, NEO-PI-R means in fact
vary systematically across cultures and show strong
correlations across methods and with other culture-
level variables (12, 14). Thus, the reference-group
effect cannot explain the failure to find correlations
with NCS scales.
28. S. J. Heine, D. R. Lehman, K. P. Peng, J. Greenholtz,
J. Pers. Soc. Psychol. 82, 903 (2002).
29. F. van de Vijver, K. Leung, J. Pers. 69, 1007 (2001).
30. D. L. Hamilton, T. L. Rose, J. Pers. Soc. Psychol. 39,
832 (1980).
31. T. W. Adorno, E. Frenkel-Brunswik, D. J. Levinson, R. N.
Sanford, The Authoritarian Personality [Norton, New
York, 1969 (original work published 1950)].
32. F. H. Allport, The Nature of Prejudice (Houghton
Mifflin, New York, 1954).
33. R.R.M. receive s royalties from the Revised NEO
Personality Inventory. This research was supported
in part by the Intramural Research Program of NIH,
National Institute on Aging. Czech participation was
supported by grant 406/01/1507 from the Grant
Agency of the Czech Republic and is related to
research plan AV AV0Z0250504 of the Institute of
Psychology, Academy of Sciences of the Czech
Republic. S.G.’s participation was supported by the
Turkish Academy of Sciences. Burkinabe
`
and French
Swiss participation was supported by a grant from
the Swiss National Science Foundation to J.R. The
data collection in Hong Kong was supported by
Research Grants Council Direct Allocation Grants
(DAG02/03.HSS14 and DAG03/04.HSS14) awarded
to M.Y. Data collection in Malaysia was supported by
Univesiti Kebangsaan Malaysia Fundamental Re-
search Grant 11JD/015/2003 awarded to K.A.M.
Portions of these data were presented at the 113th
Convention of the American Psychological Association,
August 2005, Washington, DC. For helpful comments
on the manuscript, we thank Y. H. Poortinga; for their
assistance on this project we t hank F. Abal, L. de
Almeida, S. Baumann, H. Biggs, D. Bion, A. Butkovic
´
,
C. Y. Carrasquillo, H. W. Carvalho, S. Catty, C.-S.
Chan,A.Curbelo,P.Duffill,L.Etcheverry,L.Firpo,J.
Gonzalez, A. Gramberg, H. Harrow, H . Imuta, R.
Ismai l, R. Kamis, S. Ka nnan, N. Messoulam, F. Molina,
M. Montarroyos Calegaro, S. Mosquera, J. C. Munene,
V. Najzrova, C. Nathanson, D. Padilla, C. N. Scollon, S. B.
Sigurdardottir, A. da Silva Bez, M. Takayama, T. W.
Teasdale, L. N. Van Heugten, F. Vera, and J. Villamil.
Supporting Online Material
www.sciencemag.org/cgi/content/full/310/5745/96/DC1
Materials and Methods
References
Tables S1 and S2
Appendix S1
11 July 2005; accepted 31 August 2005
10.1126/science.1117199
Transoceanic Migration, Spatial
Dynamics, and Population
Linkages of White Sharks
Ramo
´
n Bonfil,
1
*
Michael Mey
¨
er,
2
Michael C. Scholl,
3
Ryan Johnson,
4
Shannon O’Brien,
1
Herman Oosthuizen,
2
Stephan Swanson,
2
Deon Kotze,
2
Michael Paterson
2
.
The large-scale spatial dynamics and population structure of marine top
predators are poorly known. We present electronic tag and photographic
identification data showing a complex suite of behavioral patterns in white
sharks. These inclu de coastal return migrations and the fastest known
transoceanic return migration among swimming fauna, which provide direct
evidence of a link between widely separated populations in South Africa and
Australia. Transoceanic return migration involved a return to the original capture
location, dives to depths of 980 meters, and the tolerance of water temperatures
as low as 3.4-C. These findings contradict previous ideas that female white sharks
do not make transoceanic migrations, and they suggest natal homing behavior.
Great white sharks (Carcharodon carcharias)
occupy the apex of most marine food webs in
which they occur. Their major centers of abun-
dance are in the coastal waters of California–
Baja California, Australia–New Zealand, South
Africa, and, formerly, the Mediterranean Sea
(1–3). Management and conservation of this
threatened species (4, 5) have been limited,
partly because its space utilization and mi-
grations and the linkages between popula-
tions were poorly understood and difficult to
research until the development of sophisticated
telemetry instruments and high-resolution ge-
netic markers for the species (6–9). Long be-
lieved to primarily be shelf inhabitants, white
sharks are now known to be more pelagic and
to travel from California to Hawaii (6). Males
are assumed to move between distant popula-
tions, whereas females have been assumed to
be nonroving and philopatric (9).
We tagged white sharks off the Western
Cape of South Africa between June 2002 and
November 2003 with pop-up archival satellite-
transmitting (PAT) tags (n 0 25), near-real-time
satellite tags (from here onward, Bsatellite
tags[)(n 0 7), and acoustic tags (n 0 25) in
order to study their spatial dynamics (table S1).
Using high-resolution photographic identifica-
tion techniques, we have recorded the daily
presence or absence of individual white sharks
off Gansbaai (34-39S, 019-24E; Western
Cape) since October 1997 (10).
Electronic tagging and photographic identi-
fication records reveal complex spatial dynam-
ics in white sharks, which we categorized into
four behavioral patterns: rapid transoceanic re-
turn migrations, frequent long-distance coastal
return migrations, smaller-scale patrolling, and
site fidelity. A white shark performed a previ-
ously unknown fast transoceanic return migration
spanning the entire Indian Ocean, swimming
coast-to-coast from South Africa to Australia
and back. This È380-cm total length (TL;
measured as a straight line from the tip of the
snout to the end of the upper caudal lobe)
female shark (number P12), PAT-tagged on 7
November 2003 off Gansbaai, traveled in 99
days to a location 2 km from shore and 37 km
south of the Exmouth Gulf in Western Aus-
tralia (22-0105µS, 113-5313µE; Fig. 1A).
This shark_scourseofÈ11,100 km (11)en-
tailed a counterclockwise displacement of more
than 750 km off the southern tip of Africa,
followed by a remarkably direct path toward
northwestern Australia, indicating that white
sharks do not need oceanic islands as gate-
ways for transocea nic migrations, as previ-
ously hypothesized (12). Shark P12 traveled
at a minimum speed of 4.7 km hour
j1
during
its migration to Australia (13), which is the
fastest sustained long-distance speed known
among sharks (14 –17 ) and comparable to
1
Wildlife Conservation Society, 2300 Southern Boulevard,
Bronx, NY, 10460, USA.
2
Marine and Coastal Manage-
ment Branch, Department of Environmental Affairs and
Tourism, Private Bag X2, Roggebaai 8012, Cape Town,
Western Cape, South Africa.
3
White Shark Trust, Post Of-
fice Box 1258, Strand Street 6, Gansbaai 7220, Western
Cape, South Africa; and Department of Zoology, Univer-
sity of Cape Town, Rondebosch 7700, Western Cape,
South Africa.
4
Department of Zoology and Entomology,
University of Pretoria, Pretoria 0002, South Africa.
*To whom corresponde nce should be ad dressed.
E-mail: rbonfil@wcs.org
.Present address: Sea Technology Services, Ground
Floor, Foretrust House, Martin Hammerschlag Way,
Cape Town, Western Cape, South Africa.
R EPORTS
7 OCTOBER 2005 VOL 310 SCIENCE www.sciencemag.org
100
th at of some of the fastest-swimming tunas
(18, 19). Records obtained through photo-
graphic identification revealed the return of
P12 from Australia back to its original tagging
site on 20 August 2004 (Fig. 2 and fig. S1),
evidencing site fidelity and an outstanding
navigational ability. Shark P12 performed the
fastest transoceanic return migration recorded
among marine fauna (14, 20), taking just
under 9 months to complete a circuit of more
than 20,000 km. Logged records from the
photographic identification study show that
P12 is a seasonal visitor (from June to De-
cember) to the Gansbaai area (table S2). It
has been recorded during 38 different days
spanning 1999–2004, suggesting that it is a
South African shark and that its transoceanic
return migration could be common. A second
PAT-tagged shark (unsexed, È200- to 230-cm
TL; number P3) traveled to an offshore lo-
cation 242 km SE of Port Elizabeth, where its
tag detached on 26 December 2003, in what
might have been the first leg of a migration
toward Australia (Fig. 1A).
Fig. 1. Transoceanic
migration of a white
shark from South Af-
rica to northwestern
Australia and possible
first leg of a second
transoceanic-migrating
shark. (A) Positions of
(dots) and track fol-
lowed by (black line)
shark P12 during coast-
al and transoceanic
movement; geolocation-
estimated positions
were corrected using
SST data to derive
positions shown (11).
The first leg of another
possible transoceanic
migration to Australia
(or an offshore move-
ment toward the north-
east coast of South
Africa) is shown by the
pop-up location of the
PAT tag from shark P3
(blue line and square).
Tagging and pop-up
dateswereasfollows:
for P12, 7 November
2003 and 28 February
2004; for P3, 14 April
2003 and 25 December
2003. SST is an average
composite at 4 km
resol utio n for daily
Moderate Resolution
Imaging Spectro-
radiometer data
from 23 November
2003to28February
2004. Southwest In-
dian Ridge shown as
white depth contours
(100 to 2000 m). The
scale bar represents
5000 km; the white
arrow marks the tag
deployment location.
(B) Differential time-
at-depth patterns dur-
ing the coastal and
oceanic legs of shark
P12’s trip, showing a
bimodal pattern with a
strong preference for
the depths of 0.0 to
0.5 m and 500 to 750 m
during transoceanic
travel. (C) Minimum
(black line and squares)
and maximum (bright
blue line) depths and
minimum temperature
(orange dots) visited during the coastal and oceanic phases of movement; all data are in 6-hour periods.
A
B
C
R EPORTS
www.sciencemag.org SCIENCE VOL 310 7 OCTOBER 2005
101
Transoceanic return migration is previously
unknown in white sharks and only suspected in
other chondrichthyans. Our results provide
direct evidence of a physical link between
two of the most important and widely sepa-
rated white shark populations, and they con-
firm philopatry in white sharks. They also
prove that female white sharks are capable of
transoceanic migrations and indicate that the
sex-biased dispersal of this species (9) is not
necessarily based on differences in the pro-
clivity of either sex to undertake transoceanic
migrations, but is probably attributable to
differences in how these migrants become
reproductively integrated into the Brecipient[
population. In light of our data, the transmis-
sion of nuclear, and not mitochondrial, genetic
material between South Africa and Australia
(9) could be explained if (i) both sexes make
transoceanic migrations, but only males repro-
duce in the recipient population, and/or (ii)
females make transoceanic migrations and
mate with males from the recipient popula-
tion, only to return to their original location to
give birth. Indeed, the migration of P12 from
South Africa to Australia corresponds to what
is thought to be the mating season in this re-
gion (21). An eventual return of this shark to
give birth in South Africa would prove natal
homing in white sharks, as has been sug-
gested for other shark species (22, 23), and
would support recent theories about the simi-
larity of reproductive strategies among a wide
range of marine taxa (24).
The mechanisms used by P12 to navigate to
Australia and back remain unknown; aside
from a few shallow seamounts on the South-
west Indian and Ninety East Ridges, there are
no other topographic features that could be
used for orientation on the route it followed
(Fig. 1A). We analyzed the satellite-transmitted
summary data to reveal the diving pattern of
P12 and found that during eastward trans-
oceanic migration, it made frequent deep dives,
reaching record maximum depths (980 m) (25),
experienced record ambient temperatures of
3.4-C, and spent 18% of the time at depths
of 500 to 750 m (Fig. 1, B and C). This shark
spent considerably more time (61%) just be-
low the surface (0.0 to 0.5 m) while in oceanic
waters than when in coastal waters (23%),
swimming most of the time (66%) above 5 m
during this trip. A strong preference for sur-
face swimming during oceanic travel is a be-
havioral pattern previously unreported in white
sharks (1, 2, 6, 26 ). We speculate that, like
many other vertebrates (14), white sharks could
be using visual stimuli such as celestial cues
as an important navigational mechanism in
addition to, or instead of, following gradients
in Earth_smagneticfieldasiscommonlyac-
cepted behavior for sharks (27).
Great white sharks undertake long-distance
return migrations along the South African coast
with relative frequency, as revealed by the track-
ing of satellite tags and by PAT tag pop-up
locations (Fig. 3 and fig. S2). They travel from
high-abundance sites in the Western Cape
(28, 29) to waters as far as 92000 km away off
kwaZulu-Natal and beyond, using underwater
routes along the continental shelf, then return
to their original tagging sites off the Western
Cape after 4 to 6 months. A 284-cm TL female
(S1) was fitted with a satellite tag in Mossel
Bay (34-08S, 22-07E) on 24 May 2003 and
completed the first tracked long-distance return
migration for a chondrichthyan, moving in
65 days to waters northeast of Delagoa Bay
(Mozambique) and outside the South African
Economic Exclusive Zone, where white sharks
are legally protected (Fig. 3). S1 returned to
Mossel Bay 162 days after being tagged, and
was photographed with its transmitter still at-
tached. Shark S2, a 310-cm TL female double-
tagged with satellite and acoustic tags in Mossel
Bay on 31 May 2003, was tracked for 46
days to the Tugela Bank, then recorded by our
acoustic-tag bottom monitors back in Mossel
Bay 123 days after being tagged (Fig. 3). In
total, 25% of tagged sharks that yielded in-
formation moved from the Western Cape to
kwaZulu-Natal and beyond, and 12.5% showed
return migrations (Fig. 3 and fig. S2). The high
proportion of immature white sharks (table S1,
Fig. 3, and fig. S2) moving to the rich en-
vironment of the Tugela Bank (30, 31) suggests
that these long-distance coastal return migra-
tions might be feeding-related events.
Records obtained from satellite and PAT tags
reflect additional spatial dynamics patterns in
white sharks, including smaller-scale patrolling
behavior and site fidelity (Fig. 3 and figs. S3 and
S4). These patterns and the return migrations
described above suggest a wider and more com-
plex range of behavioral patterns in white sharks
than was previously thought to exist. The dis-
covery of a trans–Indian Ocean return-migrating
white shark after a relatively low tagging effort,
in addition to its periodic absence from Gansbaai
as evidenced through photographic records, im-
plies that the Australian and South African pop-
Fig. 2. Photogr aphic identi fi-
cation records of shark P12 at
tagging (7 November 2003) and
upon return to the tagging loca-
tion at Gansbaai (20 A ugust
2004) after its transoceanic mi-
gration to Western Australia. (A)
Trailing edge of the first dorsal
fin, showing a unique notch
pattern allowing identification;
the white lines connect corre-
sponding notches in both photo-
graphs. (B) Right side of the first
dorsal fin, with magnified details
(left insets) showing a unique
black pigmentation pattern aid-
ing identification.
R EPORTS
7 OCTOBER 2005 VOL 310 SCIENCE www.sciencemag.org
102
ulations maintain a physical link within a single
generation and that this return migration might
be more common than is presently known.
Our studies show that we do not have a full
understanding of the ways in which identified
populations are connected. The movement of a
female to a region of Australia known for the
presence of Australian white sharks and its
return to South Africa, in conjunction with pre-
vious genetic studies, implies that earlier hypothe-
ses about sex-biased dispersal might need to be
modified. Males are currently considered to be
the ones who move between populations (9), but
our data suggest that the connectivity between
populations could be facilitat ed also or exclu-
sively by females. The return of females mating
in Australia to give birth in South Africa would
be consistent with genetic analyses; the finding
of a rare male of South African Borigin[ in
Australia (9) might reflect equally rare birthing
in Australia by South African females.
The discoveries presented here and our lack
of evidence of sex- or size-related patterns of
space utilization in white sharks underscore the
need for additional research. Multidisciplinary
studies integrating population genetic analyses
and electronic tagging, as well as the devel-
opment of improved monitoring instruments,
should be encouraged.
Long-distance and transoceanic migrations
expose great whites to increased risk of mor-
tality as they leave domestically protected
waters in South Africa/Australia and travel into
neighboring or remote countries, sometimes
located across entire ocean basins. An in-
creasing global demand for shark products
(32), coupled with our findings, suggests that
global protective measures, such as the recent
listing of the white shark in CITES Appendix
2 (CITES, Convention on International Trade
in Endangered Species of Wild Fauna and
Flora), are warranted to ensure the effective-
ness of local protective legislation currently in
place in a handful of countries.
References and Notes
1. A. P. Klimley, D. G. Ainley, Eds., Great White Sharks:
The Biology of Carcharodon carcharias (Academic
Press, San Diego, CA, 1996).
2. L. J. V. Compagno, Sharks of the World. An Annotated
and Illustrated Catalogue of Shark Species Known to
Date. Vol. 2. Bullhead, Mackerel and Carpet Sharks
(Heterodontiformes, Lamniformes and Orectolobiformes).
FAO Species Catalogue for Fishery Purposes No. 1 (Food
and Agriculture Organization of the United Nations,
Rome, 2001).
3. A. Soldo, I. Jardas, Periodicum Biologorum 104, 195
(2002).
4. L. J. V. Compagno, M. A. Marks, I. K. Fergusson,
Environ. Biol. Fish 50, 61 (1997).
5. C. Hilton-Taylor, Compiler, 2002 IUCN Red List of
Threatened Species (IUCN, Gland, Switzerland, 2000).
6. A. M. Boustany et al., Nature 415, 35 (2002).
7. B. A. Block, H. Dewar, C. Farwell, E. D. Prince, Proc.
Natl. Acad. Sci. U.S.A. 95, 9384 (1998).
8. R. L. Johnson et al., paper presented at the meeting
on Conservation Research of Great White Sharks,
New York, 20 to 22 January 2004 (Wildlife Conser-
vation Society, New York, 2004).
9. A. T. Pardini et al., Nature 412, 139 (2001).
10. Materials and methods are available as supporting
material on Science Online.
11. The positions estimated from archived light-level data
using geolocation algorithms provided by the manu-
facturer of the tags were corrected using satellite sea
surface temperature (SST) data with the method
described in the supporting online material.
12. G. Cliff, L. J. V. Compagno, M. J. Smale, R. P. Van Der
Elst, S. P. Wintner, S. Afr. J. Sci. 96, 365 (2000).
13. The widely accepted definition of migration is ‘the
act of moving from one spatial unit to another’ (14).
This definition is general enough to be applicable to
all animal taxa, independently of spatiotemporal
scales, and includes at its core individual migration.
14. R. R. Baker, Migration: Paths Through Time and Space
(Hodder and Stoughton, London, 1982).
15. S. A. Eckert, B. S. Stewart, Environ. Biol. Fish 60, 299
(2001).
16. N. E. Kohler, P. A. Turner, Environ. Biol. Fish. 60, 191
(2001).
17. I. G. Priede, Fish. Res. 2, 201 (1984).
18. B. A. Block et al., Science 293, 1310 (2001).
19. T. Itoh, S. Tsuji, A. Nitta, Fish. Bull. (Wash. D.C.) 101,
514 (2003).
20. D. Inagake et al., Bull. Nat. Res. Inst. Far Seas Fish 38,
53 (2001).
21. M. P. Francis, in (1), pp. 157–172.
22. R. E. Hueter, M. R. Huepel, E. J. Heist, D. B. Keeney, J.
Northw. Atl. Fish. Sci. 35, 239 (2005).
23. K. A. Feldheim, S. H. Gruber, M. V. Ashley, Proc. R.
Soc. London Ser. B 269, 1655 (2002).
24. P. Cury, Can. J. Fish. Aquat. Sci. 51, 1664 (1994).
25. Previous reports of record diving depths of 1280 m
for white sharks (2) are based on the capture of one
specimen in a longline set at that depth; however, to
our knowledge, there is no evidence that the shark
was caught at 1280 m as opposed to anywhere else
along the water column.
26. F. G. Carey et al., Copeia 2, 254 (1982).
27. T. P. Quinn, Trends Ecol. Evol. 9, 277 (1994).
28. L. J. V. Compagno, D. A. Ebert, M. J. Smale, Guide to
the Sharks and Rays of Southern Africa (Struik, Cape
Town, South Africa, 1989).
29. R. L. Johnson, thesis, University of Pretoria, South
Africa (2003).
30. S. T. Fennessy, S. Afr. J. Mar. Sci. 14, 263 (1994).
31. S. T. Fennessy, S. Afr. J. Mar. Sci. 14, 287 (1994).
32. S. C. Clarke, thesis, University of London, UK (2003).
33. We thank the Natal Sharks Board and particularly S.
Dudley, G. Cliff, K. Cox, and W. Harrison for valuable
fieldwork assistance and helpful discussions in the
satellite tag study and S. Dudley for assistance in the
design and supervision of the acoustic tag study;
B. Mangold, C. Masterton, S. Parsons, P. Koen, D.
Woodborne, and P. Fre
´
on for the health maintenance
of sharks; R. and J. Portway, L. Staverees, D. Reynolds, T.
Keswick, and M. Rutzen for support and assistance with
fieldwork; L. Drapeau for Geographic Information Sys-
tems assistance; Smit Marine for maintaining bottom
receivers; M. N. Bester for supervision and D. Sadie for
conception of the acoustic tag study; and the Roe Foun-
dation, Wildlife Conservation Society, the South African
Government, International Fund for Animal Welfare,
World Wide Fund for Nature, and Professional Associ-
ation of Diving Instructors–Aware for financial support.
Supporting Online Material
www.sciencemag.org/cgi/content/full/310/5745/100/
DC1
Materials and Methods
SOM Text
Figs. S1 to Fig. S4
Tables S1 and S2
References
16 May 2005; accepted 21 July 2005
10.1126/science.1114898
Fig. 3. Northeastward long-distance return migrations of South African white sharks. The figure
shows the tracks of two satellite-tagged sharks showing long-distance return migrations and
crossing to Mozambique. Shark S1 (black trace) left Mossel Bay after tagging (24 May 2004); moved
rapidly to Bird Island, residing within a limited area (385 km
2
) for 27 days; and continued northeast
along the shelf edge, then in oceanic waters beyond the Agulhas Current, reaching Mozambique 65
days after tagging. Transmissions ceased 11 days later, to resume on Bird Island 62 days later, then
at the original tagging location on 2 November 2003. Shark S2 (white trace), tagged on 31 May 2003
with satellite and acoustic tags, traveled steadily along the coast to the Tugela Bank in 37 days,
where it ceased transmitting 9 days later and was recorded by acoustic bottom receivers back in
Mossel Bay on 1 October 2004. The red star indicates the tagging location; the dashed line indicates
projected movement during long periods without transmissions.
R EPORTS
www.sciencemag.org SCIENCE VOL 310 7 OCTOBER 2005
103
... For analyses we categorised sharks as juveniles (male and female: 175-300 cm TL), sub-adults (male: >300-360 cm TL; females: >300-480 cm TL) and adults (male: >360 cm TL; female: >480 cm TL) . Transmitters were attached to the first dorsal fin using methods described by Bonfil et al. (2005). We coated the tags with Propspeed (Oceanmax Manufacturing, FIGURE 1 | Satellite tracks of 33 white sharks Carcharodon carcharias tagged at five locations along the South African coast in 2012. ...
... These sharks thus crossed several countries' respective EEZs and spent time in Areas Beyond National Jurisdictions (high seas). The extent of their movements was similar to that reported by Bonfil et al. (2005), which identified temporary residency to coastal bays and long-distance coastal migrations along the Southern African coast. These diverse movement strategies have been identified for white sharks in Australia and the United States (Jorgensen et al., 2010;Bradford et al., 2020) and highlight this species' adaptability and their role in connecting a diverse range of habitats and ecosystems. ...
... These diverse movement strategies have been identified for white sharks in Australia and the United States (Jorgensen et al., 2010;Bradford et al., 2020) and highlight this species' adaptability and their role in connecting a diverse range of habitats and ecosystems. However, unlike Bonfil et al. (2005), we recorded no transboundary movement between South Africa and Australia. Our results, coupled with previously published movement and genetic results (Pardini et al., 2000;Bonfil et al., 2005;Andreotti et al., 2016), suggest that transboundary movement between South Africa and Australia is rare. ...
Article
Full-text available
Human activities in the oceans increase the extinction risk of marine megafauna. Interventions require an understanding of movement patterns and the spatiotemporal overlap with threats. We analysed the movement patterns of 33 white sharks ( Carcharodon carcharias ) satellite-tagged in South Africa between 2012 and 2014 to investigate the influence of size, sex and season on movement patterns and the spatial and temporal overlap with longline and gillnet fisheries and marine protected areas (MPAs). We used a hidden Markov model to identify ‘resident’ and ‘transient’ movement states and investigate the effect of covariates on the transition probabilities between states. A model with sex, total length and season had the most support. Tagged sharks were more likely to be in a resident state near the coast and a transient state away from the coast, while the probability of finding a shark in the transient state increased with size. White sharks moved across vast areas of the southwest Indian Ocean, emphasising the need for a regional management plan. White sharks overlapped with longline and gillnet fisheries within 25% of South Africa’s Exclusive Economic Zone and spent 15% of their time exposed to these fisheries during the study period. The demersal shark longline fishery had the highest relative spatial and temporal overlap, followed by the pelagic longline fishery and the KwaZulu-Natal (KZN) shark nets and drumlines. However, the KZN shark nets and drumlines reported the highest white shark catches, emphasising the need to combine shark movement and fishing effort with reliable catch records to assess risks to shark populations accurately. White shark exposure to shark nets and drumlines, by movement state, sex and maturity status, corresponded with the catch composition of the fishery, providing support for a meaningful exposure risk estimate. White sharks spent significantly more time in MPAs than expected by chance, likely due to increased prey abundance or less disturbance, suggesting that MPAs can benefit large, mobile marine megafauna. Conservation of white sharks in Southern Africa can be improved by implementing non-lethal solutions to beach safety, increasing the observer coverage in fisheries, and continued monitoring of movement patterns and existing and emerging threats.
... Moreover, vertical movements of susceptible aquatic animals can reveal regions where likelihood of negative interactions can occur, for example, in depths occupied relative to fishing effort and potential for capture (Coelho et al., 2015;Tolotti et al., 2015;Hutchinson et al., 2019). Vertical movements can also be predictable with species exhibiting specific behaviors during residency vs. migration phases (Bonfil et al., 2005;Francis et al., 2012). Gaining a thorough understanding of a species' ecology therefore requires multi-faceted long-term telemetry datasets from individual animals across and within multiple life stages (Speed et al., 2010;Hussey et al., 2015). ...
... While population structure is not clearly defined within and among all regions, genetically distinct groups exist at the regional level such as in the WNA and southern Africa (O'Leary et al., 2015) and at finer scales such as in southern-western and eastern Australia/New Zealand (Blower et al., 2012;Gubili et al., 2015;Hillary et al., 2018). As a highly migratory species, the white shark has been shown to undertake long-distance movements along continental shelves, forays into pelagic waters, and infrequently across ocean basins (Bonfil et al., 2005;Weng et al., 2007a;Domeier and Nasby-Lucas, 2008;Duffy et al., 2012), with no evidence of trans-equatorial movements (Jorgensen et al., 2010). ...
... Drivers of these movements have been suggested to be abiotic factors including temperature or currents as well as biotic factors such as mating, pupping, prey availability, or predation risk Domeier and Nasby-Lucas, 2013;Hoyos-Padilla et al., 2016;Skomal et al., 2017;Jorgensen et al., 2019). White sharks from multiple ocean basins have been shown to spend considerable time in coastal over-shelf waters with regular offshore, pelagic phases (Bonfil et al., 2005;Jorgensen et al., 2010;Domeier, 2012;Duffy et al., 2012;Bradford et al., 2020). At times, these pelagic phases can coincide in latitude or longitude with a typical population-level seasonal migration pattern (Weng et al., 2007a;Domeier andNasby-Lucas, 2008, 2013) or in contrast to the typical seasonal pattern (Bonfil et al., 2010;Skomal et al., 2017;Bradford et al., 2020;Spaet et al., 2020). ...
Article
Full-text available
Understanding how mobile, marine predators use three-dimensional space over time is central to inform management and conservation actions. Combining tracking technologies can yield powerful datasets over multiple spatio-temporal scales to provide critical information for these purposes. For the white shark ( Carcharodon carcharias ), detailed movement and migration information over ontogeny, including inter- and intra-annual variation in timing of movement phases, is largely unknown in the western North Atlantic (WNA), a relatively understudied area for this species. To address this need, we tracked 48 large juvenile to adult white sharks between 2012 and 2020, using a combination of satellite-linked and acoustic telemetry. Overall, WNA white sharks showed repeatable and predictable patterns in horizontal movements, although there was variation in these movements related to sex and size. While most sharks undertook an annual migratory cycle with the majority of time spent over the continental shelf, some individuals, particularly adult females, made extensive forays into the open ocean as far east as beyond the Mid-Atlantic Ridge. Moreover, increased off-shelf use occurred with body size even though migration and residency phases were conserved. Summer residency areas included coastal Massachusetts and portions of Atlantic Canada, with individuals showing fidelity to specific regions over multiple years. An autumn/winter migration occurred with sharks moving rapidly south to overwintering residency areas in the southeastern United States Atlantic and Gulf of Mexico, where they remained until the following spring/summer. While broad residency and migration periods were consistent, migratory timing varied among years and among individuals within years. White sharks monitored with pop-up satellite-linked archival tags made extensive use of the water column (0–872 m) and experienced a broad range of temperatures (−0.9 – 30.5°C), with evidence for differential vertical use based on migration and residency phases. Overall, results show dynamic inter- and intra-annual three-dimensional patterns of movements conserved within discrete phases. These results demonstrate the value of using multiple tag types to track long-term movements of large mobile species. Our findings expand knowledge of the movements and migration of the WNA white shark population and comprise critically important information to inform sound management strategies for the species.
... Despite the inherent difficulties of navigating in the aquatic realm, numerous fishes routinely complete astonishing long-distance journeys. Among these are (1) the transoceanic migrations of great white sharks (Carcharodon carcharias), which travel some 10,000 km between Australian and South African waters (Bonfil et al. 2005); (2) the homing of Pacific salmon (Oncorhynchus sp.) to their natal rivers from oceanic feeding grounds in the Pacific after a multi-year absence (Quinn 2018); and (3) the seasonal reproductive migrations of bluefin tuna (Thunnus thynnus) between feeding areas in the Atlantic Ocean and spawning grounds, either in the Gulf of Mexico or the Mediterranean Sea (Block 2001;Aranda et al. 2013). ...
... But for animals such as elasmobranchs that are exquisitely sensitive to electrical stimuli, disentangling whether fish are responding to magnetic or electric stimuli in a given situation is often challenging. From an ecological perspective, there are good reasons to suspect that elasmobranchs are magnetically sensitive, inasmuch as many species undertake lengthy and highly oriented migrations across ocean environments where an ability to sense Earth's magnetic field would potentially be useful in navigation (e.g., Carey and Scharold 1990;Bonfil et al. 2005). At present, however, unequivocal demonstrations that elasmobranchs detect and exploit earth-strength magnetic fields in navigation have remained sparse, in part because of the inseparable nature of electric and magnetic fields. ...
Article
Full-text available
As the largest and most diverse vertebrate group on the planet, fishes have evolved an impressive array of sensory abilities to overcome the challenges associated with navigating the aquatic realm. Among these, the ability to detect Earth’s magnetic field, or magnetoreception, is phylogenetically widespread and used by fish to guide movements over a wide range of spatial scales ranging from local movements to transoceanic migrations. A proliferation of recent studies, particularly in salmonids, has revealed that fish can exploit Earth’s magnetic field not only as a source of directional information for maintaining consistent headings, but also as a kind of map for determining location at sea and for returning to natal areas. Despite significant advances, much about magnetoreception in fishes remains enigmatic. How fish detect magnetic fields remains unknown and our understanding of the evolutionary origins of vertebrate magnetoreception would benefit greatly from studies that include a wider array of fish taxa. The rich diversity of life-history characteristics that fishes exhibit, the wide variety of environments they inhabit, and their suitability for manipulative studies, make fishes promising subjects for magnetoreception studies.
... Sharks can move more than 20,000 km (Bonfil et al., 2005), while reef-associated species (e.g. Blacktip ...
Thesis
Full-text available
Globally, elasmobranch populations (sharks and rays) are declining due to increasing anthropogenic and climate pressures. Genetic connectivity between elasmobranch populations is crucial to ensure their persistence and sustain the ecological integrity of ecosystems. Genetic connectivity implies gene flow among discrete populations occurring via the dispersal of individuals outside their population of origin, followed by reproduction — a process that can be biased between sexes (i.e. sex-biased dispersal or SBD). In this thesis, I first examine the current knowledge of population structure and SBD in elasmobranchs, and the tools that are commonly used. Next, this thesis uses novel genomic approaches (kinship, nuclear single nucleotide polymorphisms, and mitochondrial genomes) to provide insights into the patterns of (i) population structure, (ii) sex-chromosome systems, and (iii) SBD in elasmobranchs. My thesis focuses on three shark species that allow the study of dispersal patterns based on life history, local ecology, population size and different seascape features: Northern River Shark, Glyphis garricki; School Shark, Galeorhinus galeus; and Bull Shark, Carcharhinus leucas. Overall, male-biased dispersal (MBD) was observed in 25 of the 50 studied species. Population structure was found at both broad (Bull Shark) and fine (Northern River Shark) spatial scales. I demonstrated that 19 out of the 21 studied elasmobranch species contain X and Y chromosomes using the R function I developed. Combined, the sex-linked markers and kinship data supported the evidence of MBD in the Northern River Shark and the Bull Shark. My final discussion synthesised the observed dispersal patterns and examines the potential ecological and evolutionary drivers for these patterns. I critically compared the genetic and analytical approaches for the detection of population structure and SBD. Finally, potential implications of these quantitative findings for management were highlighted.
... Links between different populations enable the exchange of genetic diversity (Bonfil et al. 2005;Skomal et al. 2009), bolstering the resilience of populations and ecosystems (Oliver et al., 2015;Sgrò, Lowe & Hoffmann, 2011). These processes are likely occurring with adjacent proposed manta ray subpopulations in the Raja Ampat MPA Network, which show limited exchange . ...
Article
Full-text available
Background The reef manta ray ( Mobula alfredi ) is a globally threatened species and an iconic tourist attraction for visitors to Indonesia’s Komodo National Park (NP). In 2013, manta ray fishing was banned in Komodo NP and its surroundings, preceding the nationwide manta ray protection in 2014. Over a decade ago, a previous acoustic telemetry study demonstrated that reef manta rays had high fidelity to sites within the park, while more recent photo-identification data indicated that some individuals move up to 450 km elsewhere. Characterization of manta ray demographics, behavior, and a focused assessment on site use of popular tourism locations within the park is vital to assist the Komodo NP Management Authority formulate appropriate manta ray conservation and management policies. Methods This study uses a long-term library ( MantaMatcher.org ) of photo-identification data collected by researchers and citizen scientists to investigate manta ray demographics and habitat use within the park at four sites frequented by tour operators: Cauldron, Karang Makassar, Mawan, and Manta Alley. Residency and movements of manta rays were investigated with maximum likelihood analyses and Markov movement models. Results A total of 1,085 individual manta rays were identified from photographs dating from 2013 to 2018. In general, individual manta rays displayed a higher affinity to specific sites than others. The highest re-sighting probabilities came from the remote southern site, Manta Alley. Karang Makassar and Mawan are only ~5 km apart; however, manta rays displayed distinct site affinities. Exchange of individuals between Manta Alley and the two central sites (~35.5 km apart) occurred, particularly seasonally. More manta rays were recorded traveling from the south to the central area than vice versa . Female manta rays were more mobile than males. Similar demographic groups used Karang Makassar, Mawan, and Manta Alley for foraging, cleaning, cruising, or courtship activities. Conversely, a higher proportion of immature manta rays used the northern site, Cauldron, where foraging was commonly observed. Fishing gear-related injuries were noted on 56 individuals (~5%), and predatory injuries were present on 32 individuals (~3%). Tourism within the park increased from 2014 to 2017, with 34% more dive boats per survey at Karang Makassar and Mawan. Discussion The Komodo NP contains several distinct critical habitats for manta rays that encompass all demographics and accommodate seasonal manta ray movements. While the present study has not examined population trends, it does provide foundational data for such work. Continued research into manta ray abundance, long-range movements, and identifying and protecting other critical aggregation areas within the region is integral to securing the species’ recovery. We provide management recommendations to limit undue pressure on manta rays and their critical habitats from tourism.
... El Tiburón Blanco (Carcharodon carcharias [Linnaeus, 1758]) es una especie que habita en las regiones subtropicales y templadas de todos los océanos, incluido el Mar Mediterráneo (Moro et al., 2019), y hace algunas incursiones en aguas tropicales (Duffy et al., 2012). Anteriormente se creía que esta especie era esencialmente costera, pero, con la ayuda de marcaje satelital y análisis genéticos, se ha documentado que los Tiburones Blancos realizan movimientos regulares hacia aguas oceánicas e inclusive entre distintos continentes (Pardini et al., 2001;Bonfil et al., 2005Bonfil et al., , 2010. Con base en análisis de secuencias de la región D-loop del ADN mitocondrial, se reconoce que existen seis clados monofiléticos asociados a Australia y Nueva Zelandia, Sudáfrica, Atlántico noroccidental, Mar Mediterráneo, Pacífico Noroeste y Pacífico Noreste (Tanaka et al., 2011), lo que sugiere la existencia de al menos seis subpoblaciones de esta especie a nivel mundial. ...
... El Tiburón Blanco (Carcharodon carcharias [Linnaeus, 1758]) es una especie que habita en las regiones subtropicales y templadas de todos los océanos, incluido el Mar Mediterráneo (Moro et al., 2019), y hace algunas incursiones en aguas tropicales (Duffy et al., 2012). Anteriormente se creía que esta especie era esencialmente costera, pero, con la ayuda de marcaje satelital y análisis genéticos, se ha documentado que los Tiburones Blancos realizan movimientos regulares hacia aguas oceánicas e inclusive entre distintos continentes (Pardini et al., 2001;Bonfil et al., 2005Bonfil et al., , 2010. Con base en análisis de secuencias de la región D-loop del ADN mitocondrial, se reconoce que existen seis clados monofiléticos asociados a Australia y Nueva Zelandia, Sudáfrica, Atlántico noroccidental, Mar Mediterráneo, Pacífico Noroeste y Pacífico Noreste (Tanaka et al., 2011), lo que sugiere la existencia de al menos seis subpoblaciones de esta especie a nivel mundial. ...
Book
El objetivo general del Programa de Acción para la Conservación de la Especie Tiburón Blanco (PACE) consiste en establecer una estrategia integral de investigación, protección y conservación del Tiburón Blanco en aguas mexicanas, que permita incrementar el conocimiento de la especie, robustecer las medidas de manejo para su aprovechamiento no extractivo sustentable y prevenir y mitigar las posibles amenazas para la especie y su hábitat.
... These animals use an extremely sensitive electrosensory organ (the ampullae of Lorenzini) (Kalmijn, 1982;Tricas & Sisneros, 2004) with detection thresholds ranging between 20 and 100 Â 10 3 nVÁcm À1 to localise prey, predators and conspecifics through low-frequency bioelectric field emissions (0-15 Hz). Fish, including elasmobranchs, also detect subtle variations in magnetic field components (i.e., polarity, inclination angle and total intensity), which are assumed to assist large-scale and homeward orientation (Bonfil et al., 2005;Kalmijn, 1978;Weng et al., 2007). For example, the European eel (Anguilla anguilla) displayed orientation shifts in response to very subtle variations in the ambient field (e.g., a 2.4 μT intensity increase and a 2 inclination decrease) (Naisbett-Jones et al., 2017). ...
Article
As part of energy transition, marine renewable energy devices (MRED) are currently expanding in developed countries inducing the deployment of dense networks of submarine power cables. Concern has thus raised about the cable magnetic emissions (direct or alternating current) because of potential interference with the sensorial environment of magneto-sensitive species, such as sharks and rays. This study sought to assess the short-term behavioural responses of juvenile thornback rays (Raja clavata) (n = 15) to direct and alternating (50 Hz) uniform 450-μT artificial magnetic fields using 1 h focal-sampling design based on a detailed ethogram. Careful control of magnetic fields' temporal and spatial scales was obtained in laboratory conditions through a custom-made Helmholtz coil device. Overall, qualitative or quantitative behavioural responses of juvenile rays did not significantly vary between control vs. exposed individuals over the morning period. Nonetheless, rays under direct current magnetic field increased their activity over the midday period. Synchronisation patterns were also observed for individuals receiving alternating current exposure (chronologic and qualitative similarities) coupled with a high inter-individual variance. Further studies should consider larger batches of juveniles to address the effect of long-term exposure and explore the sensitivity range of rays with dose-response designs.
... La conectividad poblacional también puede darse durante la etapa adulta, a través de la migración de los adultos para fines de alimentación o reproducción. Por ejemplo, los atunes, tortugas y mamíferos marinos, conocidos en conjunto como la megafauna pelágica, nadan activamente haciendo migraciones de miles de kilómetros (Bowen et al., 1995;Bonfil et al., 2005); este comportamiento activo puede contribuir a la conectividad poblacional. ...
... White sharks (Carcharodon carcharias), similarly to some marine mammals, have exceptional dispersal potential and environmental tolerance, but their distinct reproductive behaviour limits gene flow in the absence of obvious physical barriers to dispersal (Bonfil et al., 2005;Engelhaupt et al., 2009;Jorgensen et al., 2010;Oñate-González et al., 2015;Rosenbaum et al., 2009;Weng et al., 2007). ...
Article
Full-text available
Background: The interplay of animal dispersal and environmental heterogeneity is fundamental for the distribution of biodiversity on earth. In the ocean, the interaction of physical barriers and dispersal has primarily been examined for organisms with planktonic larvae. Animals that lack a planktonic life stage and depend on active dispersal are however likely to produce distinctive patterns. Methods: We used available literature on population genetics and phylogeography of elasmobranchs (sharks, rays and skates) to examine how marine barriers and dispersal ecology shape genetic connectivity in animals with active dispersal. We provide a global geographical overview of barriers extracted from the literature and synthesize the geographical and hydrological factors, spatial and temporal scales to characterize different types of barriers. The three most studied barriers were used to analyse the effect of elasmobranch dispersal potential and barrier type on genetic connectivity. Results: We characterized nine broad types of marine barriers, with the three most common barriers being related to ocean bathymetry. The maximum depth of occurrence, maximum body size and habitat of each species were used as proxies for dispersal potential, and were important predictors of genetic connectivity with varying effect depending on barrier type. Environmental tolerance and reproductive behaviour may also play a crucial role in population connectivity in animals with active dispersal. However, we find that studies commonly lack appropriate study designs based on a priori hypotheses to test the effect of physical barriers while accounting for animal behaviour. Main conclusions: Our synthesis highlights the relative contribution of different barrier types in shaping elasmobranch populations. We provide a new perspective on how barriers and dispersal ecology interact to rearrange genetic variation of marine animals with active dispersal. We illustrate methodological sources that can bias the detection of barriers and provide potential solutions for future research in the field.
Article
Full-text available
Purpose: Among 29 different species of sharks reported in the Adriatic, the great white shark and the basking shark are included as very rare species. These two species, like other sharks, have life history characteristics, such as slow growth, delayed ages at maturity, low fecundity and long gestation periods, that make them particularly vulnerable to overfishing. A number of studies carried out throughout the world indicate that numbers of these two species decline. Methods: This paper gives collected data of records of these two species in the Eastern Adriatic, based on bibliographical research and collaboration with numerous persons and institutions. Conclusion: Since 19th century 61 records of the great white shark and 27 records of the basking shark have been collected in the Eastern Adriatic. According to obtained results, a proposal of their protection in the same area has been presented.
Article
Full-text available
Evidence of philopatric behavior in diverse species of sharks is accumulating through various sources of data, including studies of shark behavior, genetics and fisheries. If sharks display natural tendencies to return to a home area, birthplace or another adopted locality during portions of their life cycles, as opposed to roaming and dispersing throughout their overall ranges, the impact of fisheries removals and habitat alterations on shark populations and stocks could be profound, and the use of shark catch data to assess stocks could be complicated. We review the accumulating evidence for philopatry in sharks and discuss its implications for fisheries management and conservation of shark species.
Article
Full-text available
Tracking movements of marine animals for extended periods at sea is very expensive and labour intensive. The only method that shows promise for world-wide tracking in long-term studies is satellite tracking.The purpose of this study was to test this technique under operational conditions on basking sharks in the North Atlantic Ocean. These fish feed on plankton near the surface, and the long-term objective is to investigate the foraging and migratory movements in relation to sea surface temperature and plankton distribution patterns.A basking shark equipped with a special UHF radio transmitter was tracked for 17 days off the West Coast of Scotland using the ARGOS satellite data collection and location system. The shark surfaced during warm sunny weather and its movements were rather localised. Swimming speed was estimated as 0.106 body lengths per second between locations on successive satellite orbits. Simultaneous infrared imagery using the NOAA 7 AVHRR indicated the shark's movements relative to sea surface temperature variations.This preliminary experiment clearly demonstrates the feasibility of satellite-based monitoring of movements of marine animals using currently available operational satellite systems.
Article
Full-text available
The deployment of electronic data storage tags that are surgically implanted or satellite-linked provides marine researchers with new ways to examine the movements, environmental preferences, and physiology of pelagic vertebrates. We report the results obtained from tagging of Atlantic bluefin tuna with implantable archival and pop-up satellite archival tags. The electronic tagging data provide insights into the seasonal movements and environmental preferences of this species. Bluefin tuna dive to depths of >1000 meters and maintain a warm body temperature. Western-tagged bluefin tuna make trans-Atlantic migrations and they frequent spawning grounds in the Gulf of Mexico and eastern Mediterranean. These data are critical for the future management and conservation of bluefin tuna in the Atlantic.
Article
Distribution records of white sharks in the tropical southwest Indian Ocean are both sparse and speculative. This paper provides the first confirmed records of white sharks from four localities in the region. A male white shark of about 5 m total length was taken by a fisheries vessel off Le Morne on the island of Mauritius in 1971. A white shark over 4 m long was caught at Matemwe Beach, Zanzibar, in 1993. A female white shark, estimated at 3.8 m, was taken in an artisanal net fishery near Antsiranana, in the Baie de Diego Suarez on the northeastern tip of Madagascar in 1994. A pregnant white shark, reported at 6.4 m, was taken in an artisanal net fishery near Malindi, Kenya, in 1996. At least seven embryos, 1.1 m long and weighing 10-20 kg, were found. White sharks in the tropical Indian Ocean may be predominantly large, possibly mature, specimens. Their occurrence in oceanic island waters may facilitate trans-oceanic movements, which has important consequences for the conservation and management of this species.
Article
Species composition, sizes, trends in occurrence and catch rates of elasmobranchs caught by prawn trawlers on the Tugela Bank of Natal, South Africa, were examined from May 1989 to June 1992. Seven endemic species were recorded, the remainder having Indo-West Pacific or western Indian Ocean distributions. Most sharks were between 0,5 and 1 m long and most of the Myliobatiformes were 0,5 m in disc width. The small sizes of trawl-caught elasmobranchs indicates that the Tugela Bank functions as a nursery area for several species. None of the species examined exhibited diel patterns in frequency of occurrence, but Gymnura natalensis, Himantura gerrardi, Dasyatis chrysonota chrysonota, Sphyrna lewini and the rhinobatids occurred more frequently in warmer months. One species, Halaelurus lineatus, was more frequently taken during cooler months. Himantura gerrardi, Sphyrna lewini, Mustelus mosis and Rhizoprionodon acutus were recorded more frequently in shallower trawls (20–33 m) and G. natalensis and D. c. chrysonota more frequently in deeper trawls (33–45 m). Trawl-induced mortality was shown to be species specific, S. lewini having the highest mortality (98%). Based on catch rates recorded and trawl fleet effort, it is calculated that 44 600 elasmobranchs were caught by Tugela Bank trawlers from 1989 to 1992. About 57% of these were returned to the water alive. These figures are compared to catches made by recreational anglers and the Natal Sharks Board during the same period.
Article
The tagging of sharks using conventional tags has long been recognized as a valuable means for studying various aspects of their life history, migrations and movements, and population structure. Conventional tags are defined as those that can be identified visually without the use of special detection equipment. Tagging studies specifically targeting sharks began in the late 1920's, and today numerous cooperative shark tagging programs exist worldwide. Cooperative programs depend on the joint participation of scientists and public volunteers to accomplish research objectives. Benefits and problems of these programs are discussed using the tagging methodologies, protocols, and results of the National Marine Fisheries Service Cooperative Shark Tagging Program. An additional 63 shark tagging studies and programs of all types are reviewed. Information useful for behavioral, biological, and fishery management studies can be derived from data resulting from these studies, including species and size composition, sex ratios, spatial and temporal distribution, migrations, movement patterns, rates of travel, delineation of pupping grounds, distribution of maturity intervals, indices of relative abundance, and recognition of individuals. Specific tagging experiments can be designed to provide additional data on age and growth, homing and site fidelity, dispersal rate, residence time, movement rates, tag shedding, and population parameters (e.g. size, mortality, recruitment, exploitation, interaction rates, and stock identity). Sources of bias inherent in tagging and recapture data include mortality, variation in tagging effort and fishing pressure, non-recovery and non-reporting of tags, and tag shedding. Recent advances in tagging methodologies that complement and extend conventional tagging studies will further our knowledge on shark movements and migrations, particularly in the areas of resource utilization and management, space utilization, and population dynamics.