ArticlePDF Available

Collapse and Conservation of Shark Populations in the Northwest Atlantic


Abstract and Figures

Overexploitation threatens the future of many large vertebrates. In the ocean, tunas and sea turtles are current conservation concerns because of this intense pressure. The status of most shark species, in contrast, remains uncertain. Using the largest data set in the Northwest Atlantic, we show rapid large declines in large coastal and oceanic shark populations. Scalloped hammerhead, white, and thresher sharks are each estimated to have declined by over 75% in the past 15 years. Closed-area models highlight priority areas for shark conservation, and the need to consider effort reallocation and site selection if marine reserves are to benefit multiple threatened species.
Content may be subject to copyright.
DOI: 10.1126/science.1079777
, 389 (2003);299 Science
, et al.Julia K. Baum
Collapse and Conservation of Shark Populations in the Northwest
This copy is for your personal, non-commercial use only.
clicking here.colleagues, clients, or customers by
, you can order high-quality copies for yourIf you wish to distribute this article to others
here.following the guidelines
can be obtained byPermission to republish or repurpose articles or portions of articles
): December 29, 2010 (this infomation is current as of
The following resources related to this article are available online at
version of this article at:
including high-resolution figures, can be found in the onlineUpdated information and services,
can be found at: Supporting Online Material
, 5 of which can be accessed free:cites 13 articlesThis article
247 article(s) on the ISI Web of Sciencecited by This article has been
34 articles hosted by HighWire Press; see:cited by This article has been
subject collections:This article appears in the following
registered trademark of AAAS.
is aScience2003 by the American Association for the Advancement of Science; all rights reserved. The title
CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005.
(print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience
on December 29, 2010www.sciencemag.orgDownloaded from
Collapse and Conservation of
Shark Populations in the
Northwest Atlantic
Julia K. Baum,* Ransom A. Myers, Daniel G. Kehler,
Boris Worm, Shelton J. Harley, Penny A. Doherty
Overexploitation threatens the future of many large vertebrates. In the ocean,
tunas and sea turtles are current conservation concerns because of this intense
pressure. The status of most shark species, in contrast, remains uncertain. Using
the largest data set in the Northwest Atlantic, we show rapid large declines in
large coastal and oceanic shark populations. Scalloped hammerhead, white, and
thresher sharks are each estimated to have declined by over 75% in the past
15 years. Closed-area models highlight priority areas for shark conservation,
and the need to consider effort reallocation and site selection if marine reserves
are to benefit multiple threatened species.
Human exploitation has propagated across
land, coastal areas, and the ocean, transform-
ing ecosystems through the elimination of
many species, particularly large vertebrates
(1, 2). Only in the past half century, as fishing
fleets expanded rapidly in the open ocean,
have large marine predators been subject to
this intense exploitation. Many species, in-
cluding tuna, billfishes (3), and sea turtles
(4), are of immediate conservation concern as
a result. Among the species impacted by
these fisheries, sharks should be of particular
concern. Despite their known vulnerability to
overfishing (5, 6), sharks have been increas-
ingly exploited in recent decades, both as
bycatch in pelagic longline fisheries from the
1960s onward (7) and as targets in directed
fisheries that expanded rapidly in the 1980s
(8). The vast geographic scale of pelagic
marine ecosystems constrains our ability to
monitor shark populations adequately. Thus,
the effect of exploitation on sharks has, for
most populations, remained unknown (9).
Shark management and conservation have
been hindered by the lack of knowledge on
their status or even the direction of the pop-
ulation trends.
We present an analysis of logbook data
for the U.S. pelagic longline fleets targeting
swordfish and tunas in the Northwest Atlantic
(Fig. 1). Pelagic longlines are the most wide-
spread fishing gear used in the open ocean.
The data set presented is the largest available
for this region (214,234 sets between 1986
and 2000 with a mean of 550 hooks per
longline set) and includes one of the longest
time series for sharks. Six species or species
groups were recorded from 1986 onward, and
eight species from 1992 onward (Table 1).
For most shark species examined, this is the
only data set from which reliable abundance
trends can be estimated for the Northwest
Atlantic (10). It is also one of the only avail-
able sources worldwide from which the ef-
fects of exploitation on sharks in the open
ocean can be investigated. However, consid-
erable unreporting may occur in logbook
data, and missing values cannot be distin-
guished from true zeros (11). To address this
problem, we developed a method to model
the positive catches using generalized linear
models (GLMs) with a zero-truncated nega-
tive binomial distribution (12, 13). Our meth-
od assumes only that if a positive number of
sharks is recorded for a set, then it is approx-
imately correct. We standardized catch per
unit effort (CPUE) time series for area, sea-
son, fishery variables, and year to obtain
indices of abundance. We then performed
extensive checks on the robustness of our
results and tested the validity of alternative
explanations to the observed trends in abun-
dance (13). For each species, the observed
direction of the trend was the same in all
analyses, and although the magnitude of the
declines fluctuated slightly among models,
our conclusions are the same irrespective of
the model used.
We estimate that all recorded shark spe-
cies, with the exception of makos, have
declined by more than 50% in the past 8 to
15 years (Figs. 2 and 3). Although we
expect declines when populations are ini-
tially exploited, the shark populations ana-
lyzed here had been exploited to varying
degrees since the 1960s (14, 15). Because
sharks have low maximum intrinsic rates of
increase, compensatory responses to ex-
Department of Biology, Dalhousie University, Halifax,
NS, Canada B3H 4J1.
*To whom correspondence should be addressed. E-
Fig. 1. Map of the Northwest Atlantic showing the distribution of effort in the U.S. pelagic longline
fishery between 1986 and 2000, categorized by number of sets (0 to 800
), within the nine areas
assessed: 1, Caribbean; 2, Gulf of Mexico; 3, Florida East Coast; 4, South Atlantic Bight; 5, Mid
Atlantic Bight; 6, Northeast Coastal; 7, Northeast Distant; 8, Sargasso/North Central Atlantic; 9,
Tuna North/Tuna South. Areas were modified from the U.S. National Marine Fisheries Service
classification for longline fisheries. The 1000-m coastal isobath (dotted line) is given for reference.
on December 29, 2010www.sciencemag.orgDownloaded from
ploitation are limited and recovery is ex-
pected to be slow (6 ).
The trend in abundance is most striking
for hammerhead sharks; we estimate a de-
cline of 89% since 1986 [95% confidence
interval (CI): 86 to 91%] (Figs. 2A and 3A).
This group is primarily composed of scal-
loped hammerheads (Sphyrna lewini)(16).
The trend for white sharks was an estimated
79% decline (95% CI: 59 to 89%) (Fig. 2B).
Catch rates declined in three areas that com-
prise 80% of its catch (Areas 2 to 4) (Fig.
3B). Since the early 1990s, no white sharks
have been reported in Areas 6 and 7, and very
few from Areas 5 and 8 (17). The rarity of
this species (18) resulted in less precise trend
estimates than for the other shark species.
Life-history traits have indicated that scal-
loped hammerhead and white sharks would
be among the sharks most vulnerable to over-
exploitation (19, 20).
Tiger shark catch rates declined by an esti-
mated 65% since 1986 (95% CI: 58 to 72%)
(Figs. 2C and 3C), while the coastal species
recorded from 1992 declined by an estimated
61% (95% CI: 55 to 66%) (Figs. 2D and 3D).
The latter species, members of the genus Car-
charhinus, were grouped because they are dif-
ficult to distinguish. Individual analysis, how-
ever, showed declines for each species (ranging
from 49 to 83%). Management of these species
has been a contentious issue because of uncer-
tainty in their status (21). We provide strong
quantitative evidence to support the argument
that these species have declined substantially in
the past decade.
The trends for oceanic sharks have also
shown decline. We estimate that thresher
sharks—a group composed of the common
thresher (Alopias vulpinus) and bigeye
thresher (A. superciliousus)— have declined
by 80% (95% CI: 76 to 86%) (Figs. 2E and
3E). Unlike the area examined for other oce-
anic sharks, the area examined for thresher
sharks encompasses the known distribution
of their Northwest Atlantic populations (18).
Observed declines suggest that these popula-
tions have collapsed. The interpretation of
trends in abundance for other oceanic sharks
is complex because their ranges extend across
the North Atlantic. Blue sharks declined by
an estimated 60% (95% CI: 58 to 63%) (Fig.
2F). Conflicting patterns between the areas of
highest catches (Areas 5 to 7: 90% catches)
(Fig. 3F) could indicate density-dependent
habitat selection, with blue sharks moving
into preferential habitat (Area 7) as the pop-
ulation declined. Abundance of mako sharks
(mostly shortfin mako, Isurus oxyrinchus)
declined moderately (Figs. 2G and 3G). The
oceanic whitetip shark declined by an esti-
mated 70% (95% CI: 62 to 75%) (Figs. 2H
and 3H). From our data, we cannot infer
reliable trends for oceanics across the entire
North Atlantic Ocean. However, because oth-
er longline fleets exert intense fishing effort
across the North Atlantic (7), this pattern
could well be representative of the entire
Our results show that overfishing is
threatening large coastal and oceanic sharks
in the Northwest Atlantic. The large and rapid
declines we document are in addition to sub-
stantial historical reductions (2, 22). Overex-
ploitation of elasmobranchs (sharks, skates,
and rays) is known to have already nearly
eliminated two skate species from much of
their ranges (23, 24). The magnitude of the
declines estimated here suggests that several
sharks may also now be at risk of large-scale
Marine reserves have been shown to be
effective in rebuilding depleted fish popula-
tions (25). In the open ocean this could be
different, because animals move across large
areas (26 ), as do fishing fleets (27 ). We used
simple models to analyze the implications of
large-scale marine reserves for shark conser-
vation (13). Models were based on empirical
data (distribution of fishing effort from log-
book data, catch rates per species from sci-
entific observer data) and run under two sce-
narios that represent the extremes of likely
outcomes: (i) after the closure, fishing effort
is displaced and changes such that the same
total swordfish quota is caught (“constant-
quota scenario”); or (ii) fishing effort is dis-
Fig. 2. Declines in estimated relative abundance for coastal shark species: (A) hammerhead, (B)
white, (C) tiger, and (D) coastal shark species identified from 1992 onward; and oceanic shark
species: (E) thresher, (F) blue, (G) mako, and (H) oceanic whitetip. For each species, the overall
trend (solid line) and individual year estimates ( 95% CI) are shown. Relative abundance is
initially set to 1, to allow comparisons among species.
Fig. 3. The estimated annual rate of change, in each area (F 95% CI) and in all areas combined
(E 95% CI), for coastal shark species: (A) hammerhead, (B) white, (C) tiger, and (D) coastal shark
species identified from 1992 onward; and oceanic shark species: (E) thresher, (F) blue, (G) mako,
and (H) oceanic whitetip. Areas with fewer than 40 observations are excluded.
17 JANUARY 2003 VOL 299 SCIENCE www.sciencemag.org390
on December 29, 2010www.sciencemag.orgDownloaded from
placed but remains constant overall (con-
stant-effort scenario). Area 7 has been
closed since July 2001 to reduce bycatch of
endangered sea turtles (28). We examined the
effects of closing this area and each of the
remaining areas (Fig. 1) in turn on catches of
13 examined shark species, and on 2 turtle
and 10 finfish species of concern (2931).
Model results show that marine reserves
can indirectly cause harm if fishing effort is
merely displaced. For example, the closure of
Area 7 meets its objective in reducing sea
turtle bycatch and also protects sharks of
lower conservation concern: blue and mako
sharks. However, this closure increases catch
of almost every other species (Fig. 4), be-
cause effort is redistributed to areas of higher
species diversity. In contrast, closure of Area
3 would afford protection to most coastal
shark species, including the hammerheads,
but catch rates of oceanic sharks and sea
turtles would increase (Fig. 4). Closure of
Area 5 would be needed to protect thresher
sharks (Fig. 4). Clearly, if marine reserves are
to be effective, their placement is of critical
importance, and conservation initiatives must
explicitly consider impacts on the whole
community of species. Emphasis on single-
species conservation, without controlling ef-
fort, simply shifts pressure from one threat-
ened species to another and may actually
jeopardize biodiversity.
We have presented strong quantitative
evidence showing large declines in many
coastal and oceanic shark species over a
short period. Our results indicate that they
should be given conservation attention
equal to that given other threatened large
marine predators. Given that in all oceans,
longline and other pelagic fisheries are in-
tense and catch many of the same shark
species (7 ), serious declining trends in
Northwest Atlantic shark abundances may
be reflective of a common global phenom-
enon. Because consumers exert important
controls on food web structure, diversity,
and ecosystem functioning (32, 33), perva-
sive overfishing of these species may initi-
ate major ecological changes. However, our
analysis shows that marine reserves are not
a panacea for overexploitation. Instead, we
suggest that carefully designed marine re-
serves in concert with reductions in fishing
effort (34) could hold promise for safe-
guarding sharks and other large pelagic
predators from further declines and ecolog-
ical extinction.
References and Notes
1. J. Alroy, Science 292, 1893 (2001).
2. J. B. C. Jackson, Proc. Natl. Acad. Sci. U.S.A. 98, 5411
3. C. Safina, Song for the Blue Ocean (Holt, New York,
4. J. R. Spotila, R. D. Reina, A. C. Steyermark, P. T. Plotkin,
F. V. Paladino, Nature 405, 529 (2000).
5. The low fecundity and late age at maturity of elas-
mobranchs (sharks, skates, rays) render these fishes
more vulnerable to overexploitation than most te-
leost fishes, as evidenced by the history of collapsed
shark fisheries (6).
6. J. A. Musick, G. Burgess, G. Cailliet, M. Camhi, S.
Fordham, Fisheries 25, 9 (2000).
7. R. Bonfil, Overview of World Elasmobranch Fisheries
(FAO, Fisheries Technical Paper 341, Rome, 1994).
8. D. Rose, An Overview of World Trade in Sharks and
Other Cartilaginous Fishes (TRAFFIC Network, Cam-
bridge, UK, 1996).
9. J. I. Castro, C. M. Woodley, R. L. Brudek, A Preliminary
Evaluation of the Status of Shark Species (FAO, Fish-
eries Technical Paper 380, Rome, 1999).
10. We examined all available scientific observer and
logbook data for the pelagic longline fleets target-
ing swordfish and tunas in the Northwest Atlantic:
(i) U.S. observers on Japanese boats (1978 to
1988); (ii) U.S. observers on U.S. boats (1985 to
2000); (iii) Canadian observers on Japanese boats
(1979 to 1984, 1986 to 2000); (iv) Canadian ob-
servers on Canadian boats (1979 to 2000); and (v)
logbook data from U.S. boats (1986 to 2000). For
each of these data sets, we standardized catch per
unit effort (CPUE) time series using GLMs to obtain
unbiased indices of abundance. Reliable trends
could only be estimated from (v). Estimated trends
from (i) to (iv) were extremely uncertain and con-
tained much wider year-to-year fluctuations than
are realistic according to shark life histories. This is
likely the result of limited and/or nonrandom fleet
Table 1. Examined shark species, categorized as large coastal or oceanic according to the U.S. Fishery
Management Plan (FMP) for Sharks of the Atlantic Ocean (35). These species are also caught in U.S.
commercial and/or recreational shark fisheries.
Species Latin name
Year first
Total number
Large coastal species
Hammerhead spp. Sphyrna lewini, S. mokarran, S. zygaena 1986 60,402
White Carcharodon carcharias 1986 6,087
Tiger Galeocerdo cuvieri 1986 16,030
Coastal spp. Carcharhinus altimus, C. brevipinna,
C. falciformis,* C. limbatus,
C. obscurus, C. signatus
1992 80,480
Oceanic species
Thresher spp. Alopias superciliousus, A. vulpinus 1986 23,071
Blue Prionace glauca 1986 1,044,788
Mako spp. Isurus oxyrinchus, I. paucus 1986 65,795
Oceanic whitetip Carcharhinus longimanus 1992 8,526
Porbeagle Lamna nasus 1992 829
*The silky shark (C. falciformis) is biologically an oceanic species, but is classified in the FMP as a large coastal.
Fig. 4. Results from closed-area model showing
predicted changes in catch as caused by year-
round longline closure of Areas 3, 5, and 7.
Remaining areas are shown in fig. S2. Results
for the constant-quota (above and fig. S2) and
constant-effort (fig. S3) scenarios were similar.
Negative values refer to reductions in catch.
Error bars are 95% bootstrap confidence inter-
vals, accounting for the uncertainty in the ob-
server estimates of species composition. Black
bars represent sharks (SPL, scalloped hammer-
head; GHH, great hammerhead; TIG, tiger; SBG,
bignose; FAL, silky; SBK, blacktip; DUS, dusky;
SNI, night; PTH, common thresher; BTH, bigeye
thresher; BSH, blue; SMA, shortfin mako; OCS,
oceanic whitetip), dark gray bars represent sea
turtles ( TTL, loggerhead; TLB, leatherback), and
light gray bars represent finfish ( WHM, white
marlin; BUM, blue marlin; BFT, bluefin tuna;
BET, bigeye tuna; ALB, albacore tuna; DOL,
common dolphinfish; WAH, wahoo; OIL, oilfish;
SAI, Atlantic sailfish). See table S2 for scientific
names and conservation status.
on December 29, 2010www.sciencemag.orgDownloaded from
coverage (5%), or the limited temporal and spa-
tial overlap among data sets.
11. If the reporting rate has changed over time, then the
ratio of missing values to true zeros will change, and
using the assumed zeros to infer trends may lead to
biased results.
12. J. Grogger, R. Carson, J. Appl. Econ. 6, 225 (1991).
13. Methods and robustness analysis details are available
as supporting online material on Science Online.
14. H. Nakano, A Review of the Japanese Fishery and
Research on Sharks in the Atlantic Ocean (Interna-
tional Commission for the Conservation of Atlantic
Tunas, Madrid, SCRS/92/145, 1993).
15. D. Au, Species Composition in the Japanese Long-line
Fishery off Southern and Eastern United States (Inter-
national Commission for the Conservation of Atlantic
Tunas, Madrid, SCRS/84/75, 1985).
16. L. J. V. Compagno, FAO Species Catalogue, vol. 4,
parts 1 and 2, Sharks of the World: An Annotated and
Illustrated Catalogue of Shark Species Known to Date
(FAO, Rome, Fish. Synop. 125, 1984).
17. No white sharks have been caught in the 4200 sets
monitored since 1990 by the U.S. observer programs
for pelagic longline fleets in this region. Before this
time, observers had recorded 142 white sharks.
18. L. J. V. Compagno, FAO Species Catalogue for Fishery
Purposes, no. 1, vol. 2, Sharks of the World: An
Annotated and Illustrated Catalogue of Shark Species
Known to Date (FAO, Rome, 2001).
19. S. E. Smith, D. W. Au, C. Show, Mar. Freshw. Res. 49,
663 (1998).
20. NMFS, United States National Plan of Action for the
Conservation and Management of Sharks (National
Marine Fisheries Service, Silver Spring, MD, 2001).
21. Controversy over 1997 large coastal shark quota cuts
resulted in lawsuits between the fishing industry and
the U.S. National Marine Fisheries Service (NMFS). In
2002, a lawsuit protesting NMFS’s failure to protect
these species was also launched.
22. G. F. de Oviedo, Historia General y Natural de las
Indias (1535–1557) (Atlas, Madrid, reprinted 1959).
23. K. Brander, Nature 290, 48 (1981).
24. J. M. Casey, R. A. Myers, Science 281, 690 (1998).
25. B. S. Halpern, R. S. Warner, Ecol. Lett. 5, 361 (2002).
26. B. A. Block et al., Science 293, 1310 (2001).
27. L. W. Botsford, J. C. Castilla, C. H. Peterson, Science
277, 509 (1997).
28. U.S. Federal Register, vol. 66, p. 36711. This closure
remains enforced to date (U.S. Federal Register, vol.
67, p. 45393).
29. We included sea turtle and finfish species listed by
the International Union for the Conservation of Na-
ture (IUCN) and/or NMFS as severely overfished,
with further overfishing occurring, threatened, or en-
dangered (see table S2 for details). Common dolphin-
fish, wahoo, and oilfish were included because they
are caught in large numbers, but very little is known
about their stock status and sensitivity to overfishing.
All species were caught in at least two areas with a
minimum sample size of 25 individuals.
30. IUCN, 2002 IUCN Red List of Threatened Species
(IUCN, Gland, Switzerland, and Cambridge, UK, 2002)
31. NMFS, Stock Assessment and Fishery Evaluation for
Atlantic Highly Migratory Species 2002 (National Ma-
rine Fisheries Service, Highly Migratory Species Man-
agement Division, Silver Spring, MD, 2002).
32. T. Essington, D. Schindler, R. Olson, J. Kitchell, C.
Boggs, Ecol. Appl. 12, 724 (2002).
33. B. Worm, H. K. Lotze, H. Hillebrand, U. Sommer,
Nature 417, 848 (2002).
34. NMFS has reduced directed shark fishery quotas and
has also closed areas within the Gulf of Mexico and
along the U.S. east coast in 2000 and 2001, respec-
tively, with the aim of reducing incidental catch (of
species other than sharks) (31). No analysis has been
undertaken to test their effectiveness.
35. NMFS Final Fishery Management Plan for Atlantic
Tuna, Swordfish, and Sharks (National Marine Fisher-
ies Service, Highly Migratory Species Management
Division, Silver Spring, MD, 1999).
36. We thank NOAA-NMFS for data; J. Cramer, L. R.
Beerkircher, and J. Musick for advice; W. Blanchard,
L. Gerber, and M. Ortiz for technical assistance; H.
Keith for initial closed-area model implementation;
and H. K. Lotze and H. Whitehead for comments on
the manuscript. Many thanks to the longline fishers
who provided their logbooks to NMFS. This re-
search is part of a larger project on pelagic longlin-
ing initiated and supported by a Pew Charitable
Trusts grant to L.B. Crowder and R.A.M., with ad-
ditional support by Natural Sciences and Engineer-
ing Research Council of Canada scholarships to
J.K.B. and D.G.K.
Supporting Online Material
Figures S1 to S3
Tables S1 and S2
25 October 2002; accepted 20 November 2002
Selective Trafficking of
Non–Cell-Autonomous Proteins
Mediated by NtNCAPP1
Jung-Youn Lee,
Byung-Chun Yoo,
Maria R. Rojas,
Natalia Gomez-Ospina,
L. Andrew Staehelin,
William J. Lucas
In plants, cell-to-cell communication is mediated by plasmodesmata and in-
volves the trafficking of non–cell-autonomous proteins (NCAPs). A component
in this pathway, Nicotiana tabacum NON-CELL-AUTONOMOUS PATHWAY
PROTEIN1 (NtNCAPP1), was affinity purified and cloned. Protein overlay assays
and in vivo studies showed that NtNCAPP1 is located on the endoplasmic
reticulum at the cell periphery and displays specificity in its interaction with
NCAPs. Deletion of the NtNCAPP1 amino-terminal transmembrane domain
produced a dominant-negative mutant that blocked the trafficking of specific
NCAPs. Transgenic tobacco plants expressing this mutant form of NtNCAPP1
and plants in which the NtNCAPP1 gene was silenced were compromised in their
ability to regulate leaf and floral development. These results support a model
in which NCAP delivery to plasmodesmata is both selective and regulated.
In plants, the trafficking of NCAPs that are
involved in the regulation of plant development
is thought to occur through plasmodesmata (1
6). However, little information is available con-
cerning the manner in which such NCAPs enter
this cell-to-cell translocation pathway (5, 6). To
identify potential components in this pathway,
we used the NCAP CmPP16 (7) as bait for the
affinity purification of interaction partners con-
tained within a plasmodesmal-enriched cell
wall protein (PECP) fraction (810) prepared
with tobacco BY-2 cells [fig. S1, A and B (11)].
A resultant highly enriched 40-kD protein was
identified (Fig. 1, fig. S1C), cloned, and named
NtNCAPP1 (GenBank accession number
AF307094; hereafter called NCAPP1) [fig. S2
The specificity of the interaction between
NCAPP1 and CmPP16 was tested using a
protein overlay approach (11). Native
NCAPP1 (contained within the PECP prepa-
ration) interacted with only a very small sub-
set of the proteins present in the PECP frac-
tion (Fig. 2A). Furthermore, fractions en-
riched for cytoplasmic proteins exhibited
only minimal interaction with NCAPP1 (Fig.
2B). A reciprocal experiment in which the
PECP fractions were probed with the
CmPP16 bait confirmed the specificity of the
interaction between native NCAPP1 and
CmPP16 (Fig. 2C). As the CmPP16 is an
endogenous NCAP located within the phloem
sap (7 ), we next used fractionated phloem sap
(11) in an overlay with PECP and, as antici-
pated, detected a strong signal in the region
corresponding to the CmPP16 (Fig. 2D). A
range of other phloem proteins also interacted
positively with NCAPP1, consistent with ob-
servations that various phloem components
can traffic through plasmodesmata (12).
These results confirmed that the NCAPP1
enrichment achieved in our affinity chroma-
tography experiments (Fig. 1) was due to its
specific interaction with the CmPP16 bait.
The presence of a range of NCAPP1-interact-
ing proteins in the phloem sap suggests that
NCAPP1 (and other isoforms) may be central
to NCAP trafficking in general.
Subcellular localization of NCAPP1 was
examined by expression of fluorescently
tagged NCAPP1 in BY-2 cells (Fig. 3). In
contrast to the fluorescence pattern observed
with free EGFP (enhanced green fluorescent
protein) (Fig. 3A), NCAPP1-EGFP accumu-
lated at the cell periphery (Fig. 3B). Similar-
ly, fluorescence associated with CmPP16-
RFP was highest at the periphery of BY-2
cells (Fig. 3C). A role for the predicted NH
Section of Plant Biology, Division of Biological Sci-
ences, University of California, 1 Shields Avenue,
Davis, CA 95616, USA.
Molecular, Cellular, and De-
velopmental Biology, University of Colorado, Boulder,
CO 80309 0347, USA.
*To whom correspondence should be addressed. E-
17 JANUARY 2003 VOL 299 SCIENCE www.sciencemag.org392
on December 29, 2010www.sciencemag.orgDownloaded from
... The overall CPUE has decreased significantly [11]. Many studies have reported the collapse of fisheries resources worldwide [12][13][14][15]. Due to the interference of human activities such as overfishing and industrial construction, the habitats of offshore fishery resources in the South China Sea have been destroyed, fishery resources have declined, and the community structure has been altered [16][17][18]. ...
Full-text available
The universal laws of thermodynamics in the process of ecosystem development have long been the common research focus of ecology and biophysics. Eco-exergy from thermodynamics is a popular theory in the study of ecosystem self-organization that has been widely used in the study of wetlands and aquatic ecosystems. This study is based on the data of bottom trawl fishery resources in the Northern South China Sea in 1964–1965, 1997–1999, 2006–2007, and 2017. Based on the eco-exergy theory, the exergy contribution rate (PC) of the nekton community and the exergy contribution rate (PL) of different organismic populations were constructed. The eco-exergy (EX) and specific eco-exergy (EXsp) of the nekton in the northeastern South China Sea were analyzed. The results show that, from 1964 to 2017, the EX and EXsp of the nekton community decreased 13.28-fold and 1.42-fold, respectively. Fish populations remained the major contributors to the EX and EXsp of the nekton community; however, compared to crustaceans and cephalopods, their role in maintaining the stability and complexity of the community structure was gradually weakened, and the genetic information per unit of biomass decreased. Meanwhile, compared to fish, the proportion of the EX of crustaceans and cephalopods in the nekton community showed an upward trend. The proportion of crustaceans increased from 2.76% in 1997–1999 to 14.84% in 2017, while that of cephalopods increased from 3.55% to 16.67%. Based on the findings, we speculate that crustaceans and cephalopods play an increasing role in the stability and complexity of the fishery resource structure in the Northern South China Sea. The species replacement in the nekton was obvious, and the dominant species of the Nekton community gradually changed from k-type species to r-type species in the Northern South China Sea.
... The Blue shark (Prionace glauca) is the most abundant and widely distributed pelagic shark species [12] . It is the most exploited by-catch in tuna longline fisheries and has a high prevalence in the fin trade [13][14][15] resulting in observed population declines [16][17][18][19][20][21][22] . Effective management of blue sharks requires a global approach defining spatio-temporal patterns in behavior and habitat use [10,23] . ...
Full-text available
The relationship between habitat and behaviour provides important information for species management. For large, free roaming, marine animals satellite tags provide high resolution information on movement, but such datasets are restricted due to cost. Extracting additional biologically important information from these data would increase utilisation and value. Several modelling approaches have been developed to identify behavioural states in tracking data. The objective of this study was to evaluate a behavioural state prediction model for blue shark (Prionace glauca) ARGOS surface location-only data. The novel nature of the six SPLASH satellite tags used enabled behavioural events to be identified in blue shark dive data and accurately mapped spatio-temporally along respective surface location-only tracks. Behavioural states modelled along the six surface location-only tracks were then tested against observed behavioural events to evaluate the model's accuracy. Results showed that the Behavioural Change Point Analysis (BCPA) model augmented with K means clustering analysis performed well for predicting foraging behaviour (correct 86% of the time). Prediction accuracy was lower for searching (52%) and travelling (63%) behaviour, likely related to the numerical dominance of foraging events in dive data. The model's validation for predicting foraging behaviour justified its application to nine additional surface location-only (SPOT tag) tracks, substantially increasing the utilisation of expensive and rare data. Results enabled the critical behavioural state of foraging, to be mapped throughout the entire home range of blue sharks, allowing drivers of critical habitat to be investigated. This validation strengthens the use of such modelling to interpret historic and future datasets, for blue sharks but also other species, contributing to conservational management.
... Desgraciadamente, en la actualidad, el recurso hidrobiológico del tiburón en sus diferentes especies es objeto de una gran explotación pesquera que perjudica su existencia en todo el mundo. Situación que ha generado que la mayoría de las poblaciones de especies grandes y se encuentran en estado de reproducción hayan sido perjudicadas drásticamente, disminuyendo en los últimos años (Baum et al., 2003;Myers et al., 2007). Más del 17% del total de recursos acuáticos de tiburones del mundo están amenazados o en peligro (Stevens et al., 2000;IUCN, 2010). ...
Full-text available
El comercio ilegal de vida silvestre es una de las cuatro actividades ilegales más rentables del mundo. Su perjuicio alcanza a la fauna marina, compuesta por grupos de animales que a nivel global albergan algunos grupos considerados como recursos hidrobiológicos, entre ellos, los peces. Estos recursos hidrobiológicos sustentan la oferta alimenticia en la población humana. Sin embargo, esta explotación ha llevado a la reducción significativa de las poblaciones de algunas especies claves en el ecosistema marino, sobre todo al grupo de los condrictios. Los tiburones, que pertenecen a este grupo, son sobreexplotados principalmente por sus aletas para satisfacer la demanda asiática. La práctica del aleteo (que consiste en quitarle al tiburón sus aletas y luego desechar el resto del cuerpo) ha llevado a que muchas especies de tiburones se encuentren en categoría de desaparecer y ha incrementado el número de grupos de crimen organizado trasnacionales (DOT) que tienen incluso injerencia en las instituciones administrativas del Estado peruano, las cuales brindan facilidades para que se consolide el ilícito negocio. Es importante aumentar los esfuerzos de fiscalización, complementar el marco legal y fortalecer el trabajo articulado entre las autoridades correspondientes.
... These dramatic declines are mainly a result of by-catch from tuna (Thunnus sp.) and/or billfish (e.g. swordfish Xiphias gladius) longline fisheries [6,18], where a spatial and temporal overlap exists between the vertical niche of blue sharks and expanding fishing effortsparticularly in the North Atlantic [50]. Despite being globally assessed as 'Near Threatened' on The International Union for Conservation of Nature (IUCN) Red List of Threatened Species [51], the most recent stock assessment of blue sharks in the North Atlantic conducted by The International Commission of the Conservation of Atlantic Tunas (ICCAT) in 2015 proposed their likely status to be 'Endangered' [51]. ...
... Globally, there is growing concern regarding population declines of chondrichthyan fishes (sharks, rays, and chimaeras, herein "sharks and rays"). These declines are primarily caused by overexploitation from direct and indirect fishing activities (Baum et al., 2003;Dulvy et al., 2021;Pacoureau et al., 2021). Reported global shark and ray catch has declined by approximately 20% since 2003 , with an estimated 70% decrease in abundance of oceanic sharks and rays since 1970 . ...
Full-text available
Global catch rates of sharks and rays from artisanal fisheries are underre-ported, leading to a lack of data on population status. This forms a major barrier to developing effective management plans, such is the case in Central and West Africa. Over 3 years, we undertook the first systematic quantitative assessment of sharks and rays landed by an artisanal fishery in the Republic of the Congo. During 507 sampling days (mean 14 surveys per month), we recorded 73,268 individuals. These comprised 42 species, of which 81% are considered at an elevated risk of extinction. Landings were dominated by immature individuals, especially for species of conservation concern. Presence of species thought to have largely disappeared from the region such as the African wedgefish (Rhynchobatus luebberti) and smoothback angelshark (Squatina oculata) suggest Congolese waters are a potential stronghold for these species-warranting increased protection. We identified seasonality of catch within years, but not across years. Both inter-and intra-annual trends varied by species, signifying annual fluctuations in catch of each species but consistent catch of all species year-on-year. Analysis showed increased catch between the short-wet and the long-wet, and the long-dry seasons (January-February and August-September). Lowest catch was shown to occur during the short-wet and the short-dry seasons (October-December), which may provide an opportunity for seasonal closures or gear restrictions.
... Incidental take, i.e., the bycatch of marine megafauna, occurs in nearly all fishing fleets and is of growing global concern (Baum et al., 2003;Lewison et al., 2004;Lewison and Crowder, 2007;Peckham et al., 2007;Rees et al., 2016). Recent research reveals that marine migratory megafauna, including cetaceans (Brownell et al., 2019), elasmobranchs (Temple et al., 2018) and sea turtles (Wallace et al., 2013a), frequent coastal areas within the range of small-scale fisheries, potentially increasing the likelihood of producing high levels of bycatch (Block et al., 2005;James et al., 2005) and/or depredation, i.e., the predation of fish trapped by fishing gear while the gear is still in the water (Fader et al., 2021). ...
Full-text available
Bycatch is a major global threat to marine megafauna and occurs in nearly all fishing fleets, including small-scale fisheries that use gillnets. Gillnets represent a threat to endangered air-breathing megafauna, who incidentally entangle in bottom-set gillnets and suffocate after being attracted by bait that is secured on fishing gear. We here provide the first evidence that hawksbill turtles feed on trapped fish in gillnets, suggesting that potential prey items trapped in gillnets may act as additional bait, attracting carnivorous sea turtles towards this threat. This overlooked depredating behaviour potentially explains and increases the likelihood of critically endangered hawksbill turtle bycatch in gillnet fisheries, calling for technological and management solutions.
... As an important component of the ecosystem, sharks influence the structure and the functionality of marine communities (Camhi et al., 2008). Major populations of oceanic predators, such as large sharks, are impacted by anthropogenic threats due to their low fecundity, low growth rates, late sexual maturation, and reproductive aggregations (Baum et al., 2003;Hammerschlag and Sulikowski, 2011;Worm et al., 2013;Barreto et al., 2017). Furthermore, there are limitations and challenges in data availability to investigate population decays, extinction threats, and potential consequences for marine ecosystems (Worm et al., 2013; Ward-Paige and Corrêa et al. ...
... Understanding the ecology of populations is critical for their effective conservation and management. Over the past decade shark conservation has become a global priority (Ormond et al., 2017;Daly et al., 2018;Birkmanis et al., 2020) due to the substantial decline in some shark populations (Graham et al., 2010;Worm et al., 2013;Dulvy et al., 2014;Roff et al., 2018;Pacoureau et al., 2021), including specifically in the Atlantic Ocean and Caribbean Sea (Ward-Paige et al., 2010;Dwyer et al., 2020;MacNeil et al., 2020) as the result of intense overexploitation and other human activities, such as habitat degradation (Baum et al., 2003;Pikitch et al., 2006;Jennings et al., 2008;Heupel et al., 2009;Guzman et al., 2020). In response many nations have implemented measures such as fishing bans, quotas and Marine Protected Areas (MPAs) in order to reduce the impact of fishing on local reef shark populations (Gallagher et al., 2017;Ward-Paige, 2017;Guzman et al., 2020). ...
Full-text available
The assessment of parameters population size and individual home range is important for effective conservation management of sharks. This study uses the novel application of photo identification (photo-ID) to BRUVS footage as a non-invasive alternative to tagging in order to generate individual capture histories. These were used in mark-recapture models to estimate effective population sizes and to determine home ranges. In the Cayman Islands a total of 499 shark sightings of six coastal shark species were recorded on BRUVS from 2015-2018, but re-sighting rates were only sufficient for the determination of population parameters for two species-Caribbean reef shark (Carcharhinus perezi) and nurse shark (Ginglymostoma cirratum). The calculated super-population sizes for Caribbean reef shark (180 ± 37 SE) and nurse shark (336 ± 61 SE) were greater than the estimates for each species based on a closed-population model (Caribbean reef shark: 128 ± 40 SE, nurse shark: 249 ± 48 SE), though both measures indicated that there were about twice as many nurse sharks (1.3-1.8 sharks/km 2) as Caribbean reef sharks (0.7-1 shark/km 2) within the study area. The demographic compositions included numerous immature individuals, indicating that breeding of both species takes place within the study area of 188 km 2. Most recognizable individuals of both species showed linear home ranges of <20 km, but a few individuals were observed to have moved longer distances (Caribbean reef shark: 125.37 km, nurse shark: 156.07 km). The data indicate that the home ranges and long-distance movements of individual sharks observed within the islands' marine protected areas (MPAs) often extend to areas beyond the MPA's boundary, potentially exposing them to fishing activities. This study provides the first estimates of population size for Caribbean reef and nurse sharks in the Cayman Islands and the first estimate of a Caribbean reef shark population globally.
Full-text available
The harvest of the edible sea urchin Paracentrotus lividus is intensively practiced in some regions of the Western Mediterranean Sea. The removal of the largest individuals can determine an overall reduction in population size and a size class truncation that can lead to a drastic drop the self-sustenance. The aim of this study is to evaluate the variability of the population reproductive potential across 5 years in one of the main harvest hotspots of Sardinia (Western Mediterranean Sea). The breeding stock consists of commercial and under-commercial size individuals which were sampled on a monthly basis to estimate their GonadoSomatic Index (GSI) and the Individual Gamete Output (IGO). In addition, the reproductive potential of the population-Total Gamete Output (TGO)-was calculated across the 5-year period in relation with the variation of the density of the breeding stock. During the last year, the reproductive potential was also estimated in a well-conserved population of a nearby Marine Protected Area. No significant variability in GSI and IGO was found over the 5 years nor when compared with the ones of protected population in the last year. However, the intensive harvest drastically rescaled the population body-size: although density of the commercial size class remained low, density of the under-commercial size-class halved from the beginning to the end of the study. Accordingly, the proportional decrease of their gamete output contribution led to a 40% loss of the reproductive potential of the whole population in the 5-year period. Interestingly, despite the loss of reproductive potential due to the decrease of the breeding stock density, the average values of IGO slightly increased across the years leading to the highest Annual Gamete Output (AGO) during the fourth year of sampling. This positive pattern could suggest a mechanism of reproductive investments of the survivors in terms of gonad production rate or increase in spawning intensity. This work provides evidence of the direct effect of size-selective harvesting on the rapid loss of population self-sustenance. Furthermore, it lays new prospective for future research of the indirect effects of the rescaling population body-size in functional traits of the sea urchin.
Full-text available
A demographic technique is used to compare the intrinsic rates of population increase of 26 shark species hypothetically exposed to fishing mortality. These rates (r2M) are used as a measure of the relative ability of different sharks to recover from fishing pressure. The method incorporates concepts of density dependence from standard population modelling and uses female age at maturity, maximum reproductive age, and average fecundity. A compensatory response to population reduction is assumed in pre-adult survival to the extent possible given the constraints of the life-history parameters. ‘Rebound’ productivity was strongly affected by age at maturity and little affected by maximum age. Species with lowest values (r2M < 0.04) tended to be late-maturing medium- to large-sized coastal sharks, whereas those with the highest (> 0.08) were small coastal, early-maturing species. Sharks with mid-range values (r2M = 0.04–0.07) were mostly large (> 250 cm maximum size) pelagic species, relatively fast growing and early maturing. Possible selection pressures for these three shark groups, management implications, practical applications for the derived parameter r2M, and recommended areas of research are discussed.
Full-text available
The American Fisheries Society (AFS) recommends that regulatory agencies give shark and ray management high priority because of the naturally slow population growth inherent to most sharks and rays, and their resulting vulnerability to overfishing and stock collapse. Fisheries managers should be particularly sensitive to the vulnerability of less productive species of sharks and rays taken as a bycatch in mixed-species fisheries. The AFS encourages the development and implementation of management plans for sharks and rays in North America. Management practices including regulations, international agreements and treaties should err on the side of the health of the resource rather than short-term economic gain. The AFS encourages the release of sharks and rays taken as bycatch in a survivable condition. Regulatory agencies should mandate full utilization of shark carcasses and prohibit the wasteful practice of finning. Multilateral agreements among fishing nations, or management through regional fisheries management organizations are sorely needed for effective management of wide ranging shark stocks. The AFS encourages its members to become involved by providing technical information needed for protection of sharks and rays to international, federal, state, and provincial policy makers so decisions are made on a scientific, rather than emotional or political, basis.
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.
Full-text available
Records show that the common skate, Raia batis, has declined in abundance in the Irish Sea since the early years of the twentieth century, and is now very rare. As I report here, it is possible to calculate the highest mortality which the species will withstand without collapsing. It is likely that the mortality due to fishing has exceeded this level for some time and that the species will not recover while fishing continues. This represents the first clear case of a fish brought to the brink of extinction by commercial fishing.
The global marine fish catch is approaching its upper limit. The number of overfished populations, as well as the indirect effects of fisheries on marine ecosystems, indicate that management has failed to achieve a principal goal, sustainability. This failure is primarily due to continually increasing harvest rates in response to incessant sociopolitical pressure for greater harvests and the intrinsic uncertainty in predicting the harvest that will cause population collapse. A more holistic approach incorporating interspecific interactions and physical environmental influences would contribute to greater sustainability by reducing the uncertainty in predictions. However, transforming the management process to reduce the influence of pressure for greater harvest holds more immediate promise.