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Sea turtle bycatch in the Chilean pelagic longline fishery in the southeasternPacific: Opportunities for conservation
Miguel Donoso a, Peter H. Dutton b,*
a Pacifico Lad, Freire 1364, Quilpu, Chileb Protected Resources Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration,
3333 North Torrey Pines Court, La Jolla, CA 92037, USA
a r t i c l e i n f o
Article history:
Received 14 November 2009
Received in revised form 9 June 2010
Accepted 11 July 2010
Available online xxxx
Keywords:
Sea turtles
Marine conservation
Bycatch
Longlines
Incidental take
Fisheries
a b s t r a c t
Data are presented on sea turtles caught in the Chilean longline fishery targeting swordfish, Xiphias gla-
dius, in international waters off Chile. A total of 10,604,059 hooks from 7976 sets were observed, repre-
senting 94% of the total number of hooks fished between 2001 and 2005. Leatherbacks, Dermochelys
coriacea, (n = 284) and loggerheads, Caretta caretta, (n = 59) were the most common species captured.
Leatherbacks were caught in less than 4% of the sets, with an overall mean of 0.0268 turtles per 1000
hooks. Loggerheads were caught in less than 1% of the sets with a mean catch rate of 0.0056 turtles
per 1000 hooks. Most leatherbacks (97.5% of total) were caught between 24 S and 38S, while logger-
heads were caught primarily in the northern portion of the area fished, between 24 190S and 25310S.
All loggerheads were dehooked where appropriate and released alive. A total of two leatherbacks were
found dead. Despite the lowcatchrate of leatherbacks, thepotential impact of this fishery on theseverely
depleted nesting populations in the eastern Pacific could be significant when combined with other fish-
eries and threats in the region. The very low mortality of bycaught sea turtles observed in our study is
encouraging and suggests that there are opportunities for further reducing harmful effects of swordfish
longline fishing on sea turtles. Results of spatial analysis of loggerhead bycatch relative to fishing effort
show that closure of the northernmost fishing area would eliminate the majority of the loggerheadbycatch.
Published by Elsevier Ltd.
1. Introduction
There is great concern over declining populations of sea turtles
in the Pacific and the extent to which fishing activities contribute
to these continued declines (Sarti et al., 1996; Eckert, 1997; Spotila
et al., 2000; Lewison et al., 2004; Kaplan, 2005; Peckham et al.,
2007). The four species of sea turtles that inhabit in the South East
Pacific Ocean (loggerhead, Caretta caretta, leatherback, Dermochelys
coriacea, green, Chelonia mydas and olive ridley, Lepidochelys oliva-
cea) are listed as endangered or critically endangered species on
the 2009 IUCN Red List of Threatened Species (IUCN1). Leatherback
populations are at risk of extirpation in the Pacific because of over
harvest of eggs, commercial and residential development on nesting
beaches, and incidental bycatch in fisheries (Spotila et al., 2000).
Declines have been documented at nesting beaches in the eastern
Pacific and throughout the Indo-Pacific region, with a complete loss
of the Malaysian nesting population (Chan and Liew, 1996), severe
declines at nesting beaches in Costa Rica and Mexico (Sarti et al.,
1996, 2007; Spotila et al., 2000), and lesser declines at western Paci-
fic nesting beaches (Dutton et al., 2007; Hitipieuw et al., 2007).
Pacific loggerheads generally consist of two distinct breeding
stocks; a North Pacific stock originating from nesting sites in Japan
(Kamezaki et al., 2003), and a South Pacific stock nesting in Austra-
lia and NewCaledonia. Both stocks have declined dramatically over
the last few decades (Chaloupka, 2003; Kamezaki et al., 2003; FAO,
2004). The North Pacific stock inhabits foraging and developmental
areas in coastal neritic and oceanic habitat all the way to the north-
east Pacific off the coast of the Baja California Peninsula, and is ex-
posed to threats from pelagic and coastal fisheries (Bowen et al.,
1995; Kamezaki and Matsui, 1997; Koch et al., 2006; Peckham
et al., 2007). The Australian stock has undergone population de-
clines as a result of nest predation and incidental capture in coastal
and pelagic fisheries in the southwest Pacific (Chaloupka and
Limpus, 2001; Chaloupka, 2003).
In contrast, key Eastern Pacific olive ridley and green turtle
nesting populations have increased significantly in recent years
0006-3207/$ - see front matter Published by Elsevier Ltd.doi:10.1016/j.biocon.2010.07.011
* Corresponding author. Tel.: +1 858 546 5636; fax: +1 858 546 7003.
E-mail address: [email protected] (P.H. Dutton).1 IUCN (International Union for Conservation of Nature), 2009. Species Survival
Commission. Red List Database 2009. Website: http://www.iucnredlist.org/ (accessed
on 19 December 2009).
Biological Conservation xxx (2010) xxxxxx
Contents lists available at ScienceDirect
Biological Conservation
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c o n
Please cite this article in press as: Donoso, M., Dutton, P.H. Sea turtle bycatch in the Chilean pelagic longline fishery in the southeastern Pacific: Oppor-
tunities for conservation. Biol. Conserv. (2010), doi:10.1016/j.biocon.2010.07.011
http://dx.doi.org/10.1016/j.biocon.2010.07.011mailto:[email protected]://www.iucnredlist.org/http://dx.doi.org/10.1016/j.biocon.2010.07.011http://www.sciencedirect.com/science/journal/00063207http://www.elsevier.com/locate/bioconhttp://dx.doi.org/10.1016/j.biocon.2010.07.011http://dx.doi.org/10.1016/j.biocon.2010.07.011http://www.elsevier.com/locate/bioconhttp://www.sciencedirect.com/science/journal/00063207http://dx.doi.org/10.1016/j.biocon.2010.07.011http://www.iucnredlist.org/mailto:[email protected]://dx.doi.org/10.1016/j.biocon.2010.07.011 -
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(Chaloupka et al., 2004). Olive ridleys are the most abundant spe-
cies encountered at sea in the Eastern Tropical Pacific (Eguchi et al.,
2007; Swimmer et al., 2010).
There is a growing effort to quantify the bycatch of sea turtles in
order to enable risk assessment and develop mitigation measures
for different fisheries (Carretta et al., 2005; Watson et al., 2005;
Lewison and Crowder, 2007; Cox et al., 2007; Gilman et al., 2007,
2010; Brazner and McMillan, 2008; Oceanic Fisheries Programme,
2001; Swimmer et al., 2010). Bycatch rates and species composi-
tion vary by fishery type and geographic region (Wallace et al.,
2010). The level of threat posed by individual fisheries to sea tur-
tles depends on status of the affected population(s), the level of in-
jury or mortality caused by the gear, the life stages of the bycaught
turtles, and the level of fishery effort (Soykan et al., 2008; Lewison
et al., 2009; Moore et al., 2009; Wallace et al., 2008, 2010).
Several studies have examined sea turtle bycatch in pelagic
longline fisheries in the Atlantic (Witzell, 1998; Domingo et al.,
2006; Kotas et al., 2004; Lpez-Mendilaharsu et al., 2007;
Marcovaldi et al., 2006; Pons et al., 2010), Mediterranean (Aguilar
et al., 1995; Camias, 2005; Alessandro and Antonello, 2009) the
North Pacific (Kleiber, 1998; McCracken, 2000; Yokota et al.,
2009) and the Eastern Tropical Pacific (Swimmer et al., 2010).
However there is a paucity of high quality information on bycatch
rates in comparable pelagic fisheries operating in the Southeastern
Pacific (Lewison et al., 2004; Lewison and Crowder, 2007; Wallace
et al., 2010). Furthermore, the data that are available in many cases
consist of estimates extrapolated from observer data collected
from a small (220%) portion of the fleets. These estimates typi-
cally have large errors associated due to the relatively low encoun-
ter rates between pelagic longline fishing gear and sea turtles in
the Pacific (Kleiber, 1998; McCracken, 2004). High bycatch rates
have also been shown to be associated with low observed effort
in a given region (Sims et al., 2008) and Wallace et al., 2010 point
out the importance of comprehensive and stratified observer cov-
erage to improving the accuracy of bycatch assessments.
Telemetry and tagging studies have shown that the coastal and
oceanic habitats in the southeastern Pacific are vital foraging desti-nations and migratory pathways for the depleted eastern Pacific
leatherback populations (Eckert, 1997; Shillinger et al., 2008). Mor-
tality resulting from bycatch in small-scale coastal fisheries off Peru
and Chile is believed to have contributed to the decline of eastern
Pacific leatherback nesting populations (Frazier and Brito-Montero,
1990; Eckert, 1997; Alfaro-Shigueto et al., 2007), however the ex-
tent to which leatherbacks and loggerheads interact with high seas
fisheries operating in international waters in thesoutheast Pacific is
unclear. Foraging and developmental habitat for the South Pacific
loggerhead breeding stock is nowknownto extend across theSouth
Pacific to include coastal areasoff Peru, South America (Alfaro-Shig-
ueto et al., 2004; Boyle et al., 2009), further highlighting the need to
assess theadditional threatsposed to loggerheads by fisheries oper-
ating in the southeastern Pacific (Alfaro-Shigueto et al., 2008).In Chile a commercial fishery was established in 2001 that per-
mitted shallow-set longlining for swordfish ( Xiphias gladius) with
the requirement that vessels took an observer at all times to collect
information on the swordfish catch and that all vessels carried a
Vessel Monitoring System (VMS) to track their position in real time
over the Marynsis-based satellite system (Ley 19521, 19972). The
restrictions on swordfish catch include a minimum allowable size
of 184 cm Lower Jaw Fork Length (Decreto Supremo No. 406,
19973) with no discarded fish allowed. Fishers are allowed to retain
up to 30% of the swordfish below the minimum size, and any excess
is confiscated. At the onset of the fishery in 2001, vessels operating
in the north caught a large proportion of illegal-sized juvenile
swordfish. This area, demarcated by a boundary adjacent to the Cor-
dillera de Nazca (20S, 83300W; 20S, 78000W and 24S, 83300W)
was closed to fishing beginning in April 2001 to protect the sword-
fish nursery area.4 Furthermore, as a result of growing concern over
potential impacts of fishing on declining leatherback populations,
the Chilean swordfish observers were trained to collect informationstarting in 2001 on incidental take of sea turtles as part of a joint
program carried out under a bilateral Fisheries Cooperation Agree-
ment between the US National Oceanic and Atmospheric Adminis-
tration (NOAA) Fisheries Service and the Chilean National Fisheries
Service (SERNAPESCA).
Here we present information on incidental capture of sea turtles
by the commercial longline fishery targeting swordfish off the
coast of Chile (in Zone 87 FAO), based on 94% trip coverage by
observers over a 5-year period (20012005). We present seasonal
distribution and abundance of sea turtle bycatch relative to fishing
effort, present catch-per-unit-effort (CPUE) data, and discuss po-
tential measures to reduce bycatch.
2. Materials and methods
2.1. Fishery observations
Information was collected by a trained observer placed on fish-
ing vessels registered as part of the Chilean pelagic longline fleet
for the entire fishing season (FebruaryDecember) each year be-
tween 2001 and 2005 (Appendix A). Observers were on board for
the entire trip, which averaged 35 days for all trips except those
carried out by two of the vessels that were equipped with freezers,
which averaged 60 days at sea. This fleet comprised boats 1742 m
in length operating in international waters off the Chilean EEZ, be-
tween 70180W and 1739S. This area encompasses deep (ca.
20003000 m) abyssal waters.
All the observed vessels targeted swordfish and retained makoshark (Isurus oxirhynchus) and blue shark (Prionace glauca) as by-
catch (as well as other less important species). They used the
American monofilament longline system, as described in Vega
and Licandeo (2009) with non-offset J hooks (Mustad 9/0) baited
with Argentinean shortfin squid (Ilex argentinus), or occasionally
jack mackerel (Scomber japonicus). A yellow or pink chemical
light-stick was hung above each hook. Two vessels used the Span-
ish-style gear configuration where the gangions consist of poly-
ethelene multifilament nylon containing a 5.5 m stainless steel
leader (1.5 mm dia) attaching the hook, and are set closer together
than the American system, with approx 1012 gangions along each
350400 meter section (Barria et al., 2006; Vega and Licandeo,
2009). Vessels using the Spanish system set an average of 2000
hooks on 45 nautical miles (nm) of longline compared with an
average of 1300 hooks on 3555 nmof longline set by vessels using
the American system. Vessels fishing with the American configura-
tion generally began setting gear at dusk (18001900 h) with sets
lasting a total of 18 h including 4 h to set, 8 h soak time, and 6 h
haulback time. Vessels fishing with the Spanish configuration be-
gan setting gear around 18002000 h with sets lasting approxi-
mately 20 h including 5 h set time, 7 h soak time and 8 h haulback.
2.2. Bycatch observations
Observers collected data on sea turtle interactions, location, and
fishing effort (soak time, number of sets, and for each set the date,2 Ley No. 19521. Diario Oficial de la Repblica de Chile, Santiago, Chile, 30 de
Octubre de 1997.
3 Decreto Supremo No. 406. Diario Oficial de la Repblica de Chile, Santiago, Chile,2 de Abril de 1997.
4 Resolucin No. 157 & No. 641 de la Subsecretara de Pesca del 29 de Enero & del12 de Abril de 2001.
2 M. Donoso, P.H. Dutton/ Biological Conservation xxx (2010) xxxxxx
Please cite this article in press as: Donoso, M., Dutton, P.H. Sea turtle bycatch in the Chilean pelagic longline fishery in the southeastern Pacific: Oppor-
tunities for conservation. Biol. Conserv. (2010), doi:10.1016/j.biocon.2010.07.011
http://-/?-http://dx.doi.org/10.1016/j.biocon.2010.07.011http://dx.doi.org/10.1016/j.biocon.2010.07.011http://-/?- -
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time, location, number of hooks, and bait type). Sea surface water
temperature (SST) was recorded during the entirety of the set, and
observers noted temperatures whenever a turtle was encountered.
Sea turtles were identified by species, and where possible were
brought on board, measured, photographed, and a small skin sam-
ple collected for future genetic analysis (Dutton and Balazs, 1995)
to confirm species and determine stock origin (Dutton, 1996). The
curved carapace length (CCL) of turtles brought on board was mea-
sured (Bolten, 1999), and the turtles were tagged (inconel tags
style 681, National band and Tag Co., Newport, KY) following stan-
dard methods described in Balazs (1999). Hooks were removed
where possible and line disentangled prior to releasing turtles. In
cases where leatherbacks could not be brought on board, fishing
operations were suspended to bring the turtles close to the boat,
and crew or observers used line cutters (http://www.dehoo-
ker4arc.com) to release the turtle. Sizes were estimated in these
cases. Estimates were made of the CCL to the nearest 5 cm, in some
cases using a meter stick held alongside the turtle in the water for
reference. Skin samples were obtained from the carapace of
leatherbacks in the water using custom biopsy poles. When a hard-
shell turtle was not brought on board and species identity could
not be confirmed from photographs or genetic analysis, the turtle
was considered an unidentified hardshell species. We classified
loggerheads as juveniles, sub-adults and adults based on CCLs of
85 cm, respectively (Limpus and Limpus,
2003).
2.3. Data analysis
The locations (latitude and longitude) of sets as well as the loca-
tions of sea turtle encounters were mapped in order to visualize
the spatial distribution of sea turtle take relative to fishing effort
for each year using MAPTOOL (2002). Catch-per-unit-effort (CPUE)
was calculated as number of captured turtles/1000 hooks for each
species for each set and summarized by quarter for each year.
We used a simple general linearized model (GLM) to test for
seasonal and inter-annual differences in our observed bycatch
rates of leatherbacks and loggerheads, as follows: first, we deter-
mined the proportion of sets with turtle interactions as the ratio
between the number of sets with turtle interactions and the total
Table 1
Number of vessels, trips, sets and hooks of the Chilean longline fishery between 2001 and 2005.
Year No. vessels Total With observers
No. trips No. sets No. hooks No. trips No. sets No. hooks
2001 12 86 1985 2,689,914 86 1985 2,689,914
2002 13 82 1850 2,336,048 81 1835 2,316,248
2003 13 85 1773 2,243,495 85 1773 2,243,495
2004 10 58 1319 1,804,780 51 1185 1,632,120
2005 10 58 1465 2,161,482 43 1198 1,722,282
20012005 58 369 8392 11,235,719 346 7976 10,604,059
Table 2
Number of observed sets, hooks, captures and CPUE by year and quarter of the Chilean longline fishery between 20012005.
Year Quarter Number of sets Number of hooks Leatherback Loggerhead Green Unidentified
Captures CPUE Captures CPUE Captures CPUE Captures CPUE
2001 1 167 214,348 6 0.0280 26 0.1213 1 0.0047 0 0.0000
2001 2 602 831,822 19 0.0228 5 0.0060 0 0.0000 0 0.0000
2001 3 655 880,632 26 0.0295 2 0.0023 1 0.0011 0 0.0000
2001 4 561 763,112 12 0.0157 2 0.0026 0 0.0000 0 0.0000
2001 Total 1985 2,689,914 63 0.0234 35 0.0130 2 0.0007 0 0.0000
2002 1 194 245,965 9 0.0366 0 0.0000 0 0.0000 0 0.0000
2002 2 562 724,340 46 0.0635 2 0.0028 0 0.0000 0 0.0000
2002 3 620 763,452 52 0.0680 4 0.0052 0 0.0000 0 0.0000
2002 4 459 582,491 28 0.0481 2 0.0034 1 0.0017 0 0.0000
2002 Total 1835 2,316,248 135 0.0583 8 0.0034 1 0.0004 0 0.0000
2003 1 218 296,359 6 0.0202 0 0.0000 0 0.0000 1 0.0034
2003 2 661 863,266 10 0.0116 1 0.0012 1 0.0014 2 0.0023
2003 3 510 613,875 3 0.0049 0 0.0000 0 0.0000 2 0.0033
2003 4 384 469,995 17 0.0362 6 0.0128 1 0.0051 2 0.0043
2003 Total 1773 2,243,495 36 0.0160 7 0.0031 2 0.0020 7 0.0031
2004 1 67 74,366 2 0.0269 0 0.0000 0 0.0000 0 0.0000
2004 2 435 589,505 17 0.0288 1 0.0017 0 0.0000 1 0.0017
2004 3 422 586,930 2 0.0034 0 0.0000 0 0.0000 0 0.0000
2004 4 261 381,319 0 0.0000 1 0.0026 0 0.0000 1 0.0026
2004 Total 1185 1,632,120 21 0.0129 2 0.0012 0 0.0000 2 0.0012
2005 1 90 118,588 2 0.0169 0 0.0000 0 0.0000 4 0.0337
2005 2 383 564,037 12 0.0213 5 0.0089 0 0.0000 0 0.0000
2005 3 468 638,752 12 0.0188 2 0.0031 0 0.0000 0 0.0000
2005 4 257 400,905 3 0.0075 0 0.0000 0 0.0000 2 0.0050
2005 Total 1198 1,722,282 29 0.0168 7 0.0041 0 0.0000 6 0.0035
20012005 1 736 949,626 25 0.0263 26 0.0274 1 0.0011 5 0.0053
20012005 2 2643 3,572,970 104 0.0291 14 0.0039 1 0.0003 3 0.0008
20012005 3 2675 3,483,641 95 0.0273 8 0.0023 1 0.0003 2 0.0006
20012005 4 1922 2,597,822 60 0.0231 11 0.0042 2 0.0008 5 0.0019
20012005 Total 7976 10,604,059 284 0.0268 59 0.0056 5 0.0005 15 0.0014
M. Donoso, P.H. Dutton/ Biological Conservation xxx (2010) xxxxxx 3
Please cite this article in press as: Donoso, M., Dutton, P.H. Sea turtle bycatch in the Chilean pelagic longline fishery in the southeastern Pacific: Oppor-
tunities for conservation. Biol. Conserv. (2010), doi:10.1016/j.biocon.2010.07.011
http://www.dehooker4arc.com/http://www.dehooker4arc.com/http://dx.doi.org/10.1016/j.biocon.2010.07.011http://dx.doi.org/10.1016/j.biocon.2010.07.011http://www.dehooker4arc.com/http://www.dehooker4arc.com/ -
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sets within each quarter and year respectively. We then estimated
the standard error of the proportion in each case using the
expression
r^p
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi^p1 ^p
n 1
r1
We then fitted a GLM with turtle interactions (presence/ab-
sence) as the response variable and year and quarter as predictors.
This model assumes the response variable has a Bernoulli probabil-
ity mass function, and a logit link function was used to relate the
expected value of the response and the linear predictor (Dobson,
2002). The probability of finding a turtle can be modeled by
px egx
1 egx2
where g(x) is the linear predictor:
gx X5i1
aiD1i X4j1
bjD2j 3
where ai is the parameter associated with the year effect, bj are theparameters of the quarter effect, and D are dummy variables. We
applied this analysis separately for leatherbacks and loggerheads.
3. Results
3.1. Fishing effort
The number of longline vessels fishing each year ranged from 10
to 13 (Appendix A). A total of 10,604,059 hooks from 7976 sets
were observed, representing 94% of the total number of hooks
fished between 2001 and 2005 (Table 1). Fishing effort decreasedslightly each year from 1985 sets in 2001 to 1319 sets in 2004
and 1465 sets in 2005 (Table 1). In general, effort was relatively
low during the first quarter each year, since the fishing season usu-
ally starts during March. Most of the fishing effort occurred in the
second (AprilJune) and third (JulySeptember) quarters, and ef-
fort decreased in the fourth quarter (OctoberDecember) (Table 2).
The spatial distribution of the fishing effort also varied from year to
year (Fig. 1).
3.2. Sea turtle bycatch
Leatherbacks (n = 284) and loggerheads (n = 59) were the most
common species captured over the 5-year period of this study (Ta-
ble 2). In addition a total of five green turtles were identified (two
Fig. 1. (AE)Distribution of sea turtle bycatch by species (red circles = loggerheads, blue diamonds= leatherbacks, green squares = green turtles, grey triangles = unidentified
hardshell turtles) relative to fishing effort (sets, black points) by year for the Chilean longline fishery 20012005 (For interpretation of the references to colour in this figurelegend, the reader is referred to the web version of this article.).
4 M. Donoso, P.H. Dutton/ Biological Conservation xxx (2010) xxxxxx
Please cite this article in press as: Donoso, M., Dutton, P.H. Sea turtle bycatch in the Chilean pelagic longline fishery in the southeastern Pacific: Oppor-
tunities for conservation. Biol. Conserv. (2010), doi:10.1016/j.biocon.2010.07.011
http://-/?-http://dx.doi.org/10.1016/j.biocon.2010.07.011http://dx.doi.org/10.1016/j.biocon.2010.07.011http://-/?- -
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in 2001, one in 2002 and two in 2003) and 15 unidentified turtles
were caught in the years 2003 (7), 2004 (2) and 2005 (6) (Table 2).
A total of 14 leatherback, 39 loggerhead and five green sea turtles
were brought on board, where they were tagged, measured andthen released after removing the entangled fishing line.
3.3. Loggerhead bycatch
The majority (n = 35) of the 59 observed loggerheads were
caught in 2001 (Table 2). Loggerhead encounters were rare in the
other 4 years. Of the loggerheads caught in 2001, 26 were captured
during the first quarter in March (Table 2), between 24190S and
25310S and 76580W and 84220W, predominantly by four vessels
fishing in that area 1131 March (Fig. 1). Quarterly CPUE for log-gerheads ranged from 0 to 0.1213/1000 hooks, with an overall
average of 0.0056/1000 hooks (Table 2). The loggerheads occurred
in waters with temperatures ranging from 16.8C to22.1 C,with a
bimodal frequency distribution with peaks at 21 C and 18C
(Fig. 2). The mean length of the 39 measured loggerheads was
63.5 cm CCL (range = 4784 cm, SD = 8.9) (Fig. 3a). The majority
0
5
10
15
20
25
30
35
40
13 14 15 16 17 18 19 20 21 22 23 24 25 26
Percent
Temperature (oC)
Fig. 2. Frequency of loggerhead (dashed line) and leatherback (solid line) bycatch relative to SST in the Chilean longline fishery between 2001 and 2005.
0
2
4
6
8
10
12
14
16
18
41-50 51-60 61-70 71-80 81-90
Numberoftu
rtles
CCL (cm)
0
2
4
6
8
10
12
14
16
61-70 81-90 101-110 121-130 141-150 161-170 181-190
Numberofturtles
CCL (cm)
A
B
Fig. 3. Curved carapace lengths (CCL) of sea turtles caught in Chilean longline fishery between 2001 and 2005. The lengths measured for loggerhead (white bars) and green
turtles (grey bars) are shown in (A). Lengths of 14 leatherbacks measured on board (black bars) as well as estimated lengths for 73 leatherbacks that were not brought onboard (white bars) are shown in (B).
M. Donoso, P.H. Dutton/ Biological Conservation xxx (2010) xxxxxx 5
Please cite this article in press as: Donoso, M., Dutton, P.H. Sea turtle bycatch in the Chilean pelagic longline fishery in the southeastern Pacific: Oppor-
tunities for conservation. Biol. Conserv. (2010), doi:10.1016/j.biocon.2010.07.011
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(82%) was in the juvenile size class range (
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4. Discussion
4.1. Loggerheads
Loggerheads arecommonly encounteredin pelagic longline fish-
eries in theAtlantic,Mediterraneanand North Pacific (Witzell, 1984,
1998; Kotas et al., 2004; Lewison et al., 2004; Watson et al., 2005;
Lpez-Mendilaharsu et al., 2007; Marcovaldi et al., 2006; Ponset al., 2010). This species is known to forage in the northeastern Pa-
cificoff theBajaCaliforniaPeninsula(Peckhamet al.,2007), however
the presence of loggerheads in the southeastern Pacific has only re-
cently been reported from studies in Peru (Alfaro-Shigueto et al.,
2004, 2008; Boyleet al., 2009). Ourresultsconfirmthat loggerheads
foragein waters as far south as 32S off the Chilean coast, and taken
together with results ofAlfaro-Shigueto et al. (2008), indicate that
loggerheads are more commonin the southeastern Pacific than pre-
viously thought, with foraging aggregations concentrated between
15 and 25S off southern Peru and northern Chile. The sizes of the
loggerheads caught in the Chilean longline fishery are consistent
with sizes reported for loggerheads in high-seas longline fisheries
in general (see Lewison and Crowder, 2007) and comprise mostly
large juveniles and sub-adults (Bjorndal et al., 2001; Limpus and
Limpus, 2003). The loggerheads we report for the Chilean longline
fisheryare generally larger than those caughtby theartisanal fishers
inPeru (Alfaro-Shigueto et al., 2004, 2008), with 18% in the subadult
and adults size ranges (>70 cm CCL), as opposed to only 8.4% re-
portedby Alfaro-Shigueto et al. (2008) forthis sizerangein Peruvian
artisanal gillnet and longline bycatch.There were also a greaterpro-
portionof small juveniles(
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(
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4.5. Regional impacts of longline fisheries
Our results provide the first extensive data on sea turtle bycatch
in pelagic longline fisheries operating in the southeastern Pacific,
and the take of leatherbacks in particular is of concern given the
critically endangered status of this species in the Pacific. These
finding should be considered in a broader regional context to bet-
ter understand the extent of the threat of fisheries to the recovery
of the depleted Pacific leatherback populations. Likewise, it is
important to consider the landscape of threats from trawl, net
and other longline fisheries that impact the southern loggerheadstock in order to assess the relative impact of the Chilean longline
fishery on loggerheads.
While our data represent near 95% observed coverage of the
Chilean longline fishing effort, the bycatch data should be consid-
ered as a conservative indication of bycatch in thepelagic swordfish
fisheries operating in the region. There is a small Chilean artisanal
longline fleet, comprising two to six vessels (
-
8/8/2019 Do No So Dutton
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and early 1990s were implicated in the decline of eastern Pacific
leatherbacks during that same time period (Eckert, 1997). The Chil-
ean gillnet fishery for swordfish collapsed in the 1990s and has
been almost non-existent in the last decade or so. However, there
has been a resurgence of this gillnet fishery in Chile in recent years
(Donoso, unpublished data), and this most likely poses a greater
threat to leatherbacks than the current declining Chilean longline
fishery.
The low number of loggerhead interactions and absence of mor-
tality observed in ourstudysuggeststhat thethreat fromtheChilean
longline fisheryon thesouthernloggerhead stock by itself cannotbe
considered significant. Furthermore, the nesting populations, while
declining, have not collapsed to the extent that eastern Pacific
leatherbacks have (Chaloupka et al., 2004). Wide-scale and sus-
tained predation of eggs by foxes is believed to have been a major
causal factorin thehistoric declineof theAustralian loggerhead pop-
ulation(Chaloupka,2003). This threathas been largelyeliminatedin
recent years, and mortality of adults and large juveniles in coastal
trawl, gillnet and crab trap fisheries off Australia and around the
westernPacific is nowbelieved to pose themost seriousthreat, since
these fisheries drownanimals of high reproductivevalue to thepop-
ulation (Poiner & Harris, 1996; Chaloupka, 2003; Limpus and
Limpus, 2003). Nevertheless, concern over the threat from bycatch
of oceanicjuvenilesin distantwaters longline fisheries is warranted.
Modelingof competingrisk factorsindicate that viability of theeast-
ern Australian loggerhead stock is negatively impacted by take of
juveniles in high seas fisheries (Heppell et al., 1996; Chaloupka,
2003). Our study adds to a growing body of literature highlighting
theneed to assess thecontributionfrom cumulative impactsof from
small-scaleartisanal and industrial fisheries in theeastern Pacific to
the continuing decline of the southern Pacific stocks of loggerheads
(Alfaro-Shigueto et al., 2008, 2010).
4.6. Potential bycatch reduction
Our findings, taken together with those ofAlfaro-Shigueto et al.,
2008 suggest that the northern Chilean swordfish fishing area clo-sure put in place in 2001 has most likely helped reduce loggerhead
bycatch. This closed area features a body of consistently warmer
water (>21 C SST) and is within the broader loggerhead hotspot
stretching between 15 and 25S off southern Peru and northern
Chile, evident from our findings combined with other studies
(see Alfaro-Shigueto et al., 2008). The Chilean vessels are moni-
tored in real-time with a satellite-based VMS by SERNAPESCA,
which provides an effective tool for enforcing the closure. Penalties
include fines and impoundment of vessels. This closure is only in
effect for Chilean-flagged vessels and there are foreign fleets that
remain unmonitored but are known to fish in the area adjacent
to Chiles EEZ, including the area closed to Chilean vessels (CPPS,
2004; Herv and Fuentes, 2004). It is notable that two of our ob-
served longline sets (19150
S, 81500
W and 22080
S, 81480
W) oc-curred just within the western-most boundary of this closed area
and that both sets caught loggerheads (Fig. 1), suggesting a high
probability of loggerhead encounters in this area. Our findings sug-
gest that the likelihood of loggerhead bycatch could be signifi-
cantly reduced by further extending the closed area south to 25S.
Further work to develop models that predict likelihood of log-
gerhead presence based on oceanographic parameters could allow
more adaptive real-time fisheries management (Howell et al.,
2008). The NOAA Fisheries Services Turtlewatch program (http://
www.pifsc.noaa.gov/eod/turtlewatch.php) provides tools that have
been developed to help Hawaii-based fishers avoid potential inter-
action with loggerheads in the North Pacific, and a similar ap-
proach could be developed for the southeastern Pacific based on
the further analysis of the findings from our study, given that thesouthernmost range of loggerhead distribution appears to be asso-
ciated with dynamic features associated with the 21 and to a les-
ser extent, 18 isotherms. This along with a suite of other
mitigation measures, including turtle take limits and gear modifi-
cations, have successfully reduced sea turtle bycatch in the Ha-
waii-based longline fishery (Gilman et al., 2007). Developing
similar approaches to avoid leatherback interactions is more chal-
lenging, since they occur throughout the area of operations of the
Chilean longline fleet. Until the fine scale differences in habitat
use by leatherbacks and swordfish adjacent to oceanic convergence
zones are better understood, modification in gear and fishing tech-
niques offer the best potential for reduction in sea turtle bycatch.
Use of circle hooks and mackerel type bait instead of the traditional
J hooks and squid bait has been shown to significantly reduce by-
catch of sea turtles in swordfish and tuna longline fisheries
(Watson et al., 2005; Gilman et al., 2007; Read, 2007). Experiments
have been initiated to test circle hooks and mackerel bait in the
Chilean longline fishery, and there is growing interest in participa-
tion by Chilean fishers (Donoso, unpublished data).
5. Conclusions and conservation recommendations
The extensive observer data collected for the Chilean swordfish
longline fishery in our study provides valuable new information on
the extent of sea turtle interactions with pelagic fisheries, as well as
insights into the biology of loggerheads, leatherbacks and green
turtles in the southeastern Pacific Ocean, including extension of
the documented southern range for these species in the region.
We show that loggerheads are restricted to the northernmost area
fished by the Chilean longline fleet, and that there are opportunities
for applying area closures to avoid loggerhead bycatch that are
compatible with measures designed to improve the sustainability
of the regional swordfish stock. Area closure does not appear to
be a viable approach for reducing leatherback interactions in the
Chilean swordfish fishery, however, given the extent of leatherback
bycatch observed in our study, we recommend the adoption and
further development of fishing techniques that have been shown
to reduce leatherback and loggerhead bycatch, such as use of circle
hooks and mackerel type bait (Watson et al., 2005; Gilman et al.,
2007; Yokota et al., 2009). Our finding that almost all the sea turtles
were caught and released alive suggests that training of crew and
observers in safe handling procedures to disentangle lineand hooks
with dehookers and line cutters, and to resuscitate comatose sea
turtles, has further potential to reduce injury from longlines. We
urge other countries with pelagic fleets that fish in the same inter-
national waters as the Chilean fishery to implement observer pro-
grams similar to the one reported in our study in order to obtain
a more comprehensive understanding of the spatial distribution
of fishing effort and corresponding sea turtle interactions in the re-
gion, and to facilitate the adoption of recommended guidelines to
reduce the mortality of sea turtles that are caught incidentally in
longline fisheries (FAO, 2005). Reduction of bycatch should be partof a holistic conservation strategy for sea turtles that addresses the
multiplerisk factors posedby different coastal and high seas fisher-
ies and anthropogenic threats on nesting beaches (Dutton and
Squires, 2008; Wallace et al., 2010).
Acknowledgements
This study was carried out as part of the USChile Fisheries
Cooperation Agreement between NOAA Fisheries Service and SER-
NAPESCA, with funding from NOAA Fisheries Service and the Insti-
tuto de Fomento Pesquero (IFOP). We thank the IFOP scientific
observers, as well as the captains and crew of the participating
fishing vessels. Carlos Montenegro assisted with statistical analy-
sis. We thank William Perrin, Kelly Stewart, James Carretta andtwo anonymous reviewers for helpful comments and suggestions.
10 M. Donoso, P.H. Dutton/ Biological Conservation xxx (2010) xxxxxx
Please cite this article in press as: Donoso, M., Dutton, P.H. Sea turtle bycatch in the Chilean pelagic longline fishery in the southeastern Pacific: Oppor-
tunities for conservation. Biol. Conserv. (2010), doi:10.1016/j.biocon.2010.07.011
http://www.pifsc.noaa.gov/eod/turtlewatch.phphttp://www.pifsc.noaa.gov/eod/turtlewatch.phphttp://dx.doi.org/10.1016/j.biocon.2010.07.011http://dx.doi.org/10.1016/j.biocon.2010.07.011http://www.pifsc.noaa.gov/eod/turtlewatch.phphttp://www.pifsc.noaa.gov/eod/turtlewatch.php -
8/8/2019 Do No So Dutton
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2005
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Coquimbo Lucia 2001200220032004
2005
26.8 6.6 3.1 1967 103 660 Steel
Coquimbo Canadelo 2001200220032004
2005
28.8 6.5 3.8 1963 140 660 Steel
Coquimbo Las Nieves 2002200320042005 33.5 6.7 3.8 1961 130 660 Steel
Valparaso Pacific Sea 2001200220032004
2005
21.3 5.5 2.5 1949 40 300 Steel
Coquimbo Tami S. 2001200220032004
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42.2 8.5 3.6 1980 374 1300 Steel
Coquimbo Portugal II 2001200220032004
2005
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Coquimbo Elena S. 2001200220032004
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16.6 6.6 3.2 1989 47 350 Steel
Coquimbo Christina S. 2001200220032004
2005
16.6 6.6 3.2 1989 47 350 Steel
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