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Seabird mortality at trawler warp cables and a proposed mitigation measure: A case of study in Golfo San Jorge, Patagonia, Argentina

Authors:
  • Centro para el Estudio de Sistemas Marinos - CONICET
  • National University of Patagonia San Juan Bosco (UNPSJB)

Abstract

We studied the interaction between seabirds and warp cables in the high-seas Argentine hake Merluccius hubbsi trawl fishery operating in Golfo San Jorge, Argentina, and tested the efficacy of a simple mitigation measure designed to reduce mortality at warp cables. Observations were made onboard hake trawlers during the height of the fishing season, between December 2004 and April 2005. Thirteen seabird species used food made available by fishing operations. The most frequent and abundant seabirds (% occurrence, mean maximum number per haul) were the Kelp gull Larus dominicanus (98.1%, 348.5) and the Black-browed albatross Thalassarche melanophrys (96.1%, 132.2). Contacts with warp cables were recorded for six species in 81.4% of hauls, with a mean number of contacts per haul of 14.4 ± 23.8 (range = 0–127). A total of 53 individuals were killed due to interactions with nets and cables, resulting in a total cable mortality rate of 0.14 birds/haul. Considering the fishery’s fishing effort, the estimated total number of birds killed during the study was 2703 (CV = 0.8), of which 306 (CV = 0.9) were killed due to contacts with warp cables (255 Kelp gulls and 51 Black-browed albatross). The tested device consisted of a plastic cone attached to each warp cable. In hauls with mitigation device, the number of contacts was reduced by 89% and no seabirds were killed. Mean distances between seabirds and cables were significantly larger in hauls with than without mitigation device (2.6 vs 0.9 m). The proposed device could be easily applied in this and other trawl fisheries operating in Argentine waters. Increased effort should be placed in implementing mitigation measures and the monitoring of cable related mortality associated to high-seas trawlers operating in the Argentine Continental Shelf.
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Seabirdmortalityattrawlerwarpcablesanda
proposedmitigationmeasure:Acaseofstudy
inGolfoSanJorge,Patagonia,Argentina
ArticleinBiologicalConservation·April2007
DOI:10.1016/j.biocon.2006.11.008
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Seabird mortality at trawler warp cables and a proposed
mitigation measure: A case of study in Golfo San
Jorge, Patagonia, Argentina
Diego Gonza
´lez-Zevallos
a,
*, Pablo Yorio
a,b
, Guillermo Caille
c
a
Centro Nacional Patago
´nico – (CENPAT) – (CONICET), Biologı´a y Manejo de Recursos Acua
´ticos (BMRA), Bvd. Brown 3500, Puerto
Madryn – CP 9120, Pcia. Chubut, Argentina
b
Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA
c
Fundacio
´n Patagonia Natural, Marcos Zar 760, 9120, Puerto Madryn, Chubut, Argentina
ARTICLE INFO
Article history:
Received 1 September 2006
Received in revised form
31 October 2006
Accepted 13 November 2006
Available online 12 January 2007
Keywords:
Seabirds
Hake trawlers
Mortality
Mitigation measures
ABSTRACT
We studied the interaction between seabirds and warp cables in the high-seas Argentine
hake Merluccius hubbsi trawl fishery operating in Golfo San Jorge, Argentina, and tested
the efficacy of a simple mitigation measure designed to reduce mortality at warp cables.
Observations were made onboard hake trawlers during the height of the fishing season,
between December 2004 and April 2005. Thirteen seabird species used food made available
by fishing operations. The most frequent and abundant seabirds (% occurrence, mean max-
imum number per haul) were the Kelp gull Larus dominicanus (98.1%, 348.5) and the Black-
browed albatross Thalassarche melanophrys (96.1%, 132.2). Contacts with warp cables were
recorded for six species in 81.4% of hauls, with a mean number of contacts per haul of
14.4 ± 23.8 (range = 0–127). A total of 53 individuals were killed due to interactions with nets
and cables, resulting in a total cable mortality rate of 0.14 birds/haul. Considering the fish-
ery’s fishing effort, the estimated total number of birds killed during the study was 2703
(CV = 0.8), of which 306 (CV = 0.9) were killed due to contacts with warp cables (255 Kelp
gulls and 51 Black-browed albatross). The tested device consisted of a plastic cone attached
to each warp cable. In hauls with mitigation device, the number of contacts was reduced by
89% and no seabirds were killed. Mean distances between seabirds and cables were signif-
icantly larger in hauls with than without mitigation device (2.6 vs 0.9 m). The proposed
device could be easily applied in this and other trawl fisheries operating in Argentine
waters. Increased effort should be placed in implementing mitigation measures and the
monitoring of cable related mortality associated to high-seas trawlers operating in the
Argentine Continental Shelf.
2006 Elsevier Ltd. All rights reserved.
1. Introduction
Seabirds are important components in marine ecosystems
which regularly associate to commercial fisheries activities
around the world. This association often leads to negative
effects on their populations (Furness, 2000; Montevecchi,
2002). Several studies have reported high incidental mortality
rates at vessels operating with different fishing gear, such as
gill nets, drift nets, trawl nets, and longlines (e.g. Jones and
DeGange, 1988; Brothers, 1991; Weimerskirch et al., 1997;
0006-3207/$ - see front matter 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biocon.2006.11.008
*Corresponding author: Tel.: +54 2965 451024/450401/451301/451375x215; fax: +54 2965 451543.
E-mail addresses: diegue@cenpat.edu.ar (D. Gonza
´lez-Zevallos), yorio@cenpat.edu.ar (P. Yorio), gcaille2003@yahoo.com.ar (G. Caille).
BIOLOGICAL CONSERVATION 136 (2007) 108116
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/biocon
Author's personal copy
Sullivan and Reid, 2003; Baker and Wise, 2005; Go
´mez-Laich
et al., 2006). Given their life-history traits, seabirds are highly
sensitive to slight changes in adult mortality (Furness and
Monaghan, 1987), and thus incidental mortality may signifi-
cantly affect their populations.
Seabird mortality in trawl vessels, in particular, may occur
while birds attempt to obtain food from the net or due to their
collision with vessel or fishing gear cables (Bartle, 1991; Wei-
merskirch et al., 2000; Baird and Thompson, 2002; Gonza
´lez-
Zevallos and Yorio, 2006; Sullivan et al., 2006a). Recent studies
have highlighted the importance of seabird mortality due to
the birds being dragged under water when struck by the warp
cable while they are taking advantage of fisheries discards be-
hind the vessel (Gonza
´lez-Zevallos and Yorio, 2006; Sullivan
et al., 2006a). The varied causes of trawler mortality require
specifically developed and targeted mitigation measures.
Probably the most critical mitigation measure aimed at reduc-
ing incidental mortality caused by warp cables is the effective
management of offal discharge (e.g. Wienecke and Robertson,
2002). Another option is the development of bird-scaring de-
vices, some of which have been recently tested for their effi-
cacy (Sullivan et al., 2006b).
The Patagonian shelf is an area of global significance for
seabirds, where more than 50 seabird species forage (Favero
and Silva Rodrı´guez, 2005). Sixteen of these also reproduce
along the Patagonian coast (Yorio et al., 1998). Knowledge of
seabird interactions with high-seas trawl fisheries in the
Argentine Continental Shelf is still relatively poor, and little
is known about the effects on seabird mortality due to cables.
A recent study reported that Black-browed albatrosses (Tha-
lassarche melanophrys) and Kelp gulls (Larus dominicanus) were
drowned when their wings were trapped in cables that hold
the net (Gonza
´lez-Zevallos and Yorio, 2006). Although interac-
tions were not quantified, the study suggested the potential
negative impact on seabird populations associated to this
fishery and showed the need for further evaluations. One of
the affected species, the Black-browed albatross, is cata-
logued as endangered according to UICN criteria (Birdlife-
International/UICN, 2001), and thus information on the extent
of mortality is of significant value. In this paper we present
information on seabird mortality due to cables at the high-
seas Argentine hake (Merluccius hubbsi) trawl fishery which
operates in Golfo San Jorge, Argentina. We determined the
species composition and relative abundances of seabirds
attending vessels, quantifying contacts with cables and resul-
tant mortality rates and assess its importance relative to net
related mortality. Finally, we present results of a test on the
efficacy of a simple mitigation measure designed to reduce
mortality at cables. Up to date, no mitigation measure has
been tested or implemented in trawlers operating in waters
under Argentine jurisdiction.
2. Materials and methods
2.1. Study area and characteristics of coastal fisheries
The Golfo San Jorge (Fig. 1) is one of the most important coas-
tal areas in terms of marine biodiversity and one of the prior-
ity seabird areas in Argentina. Thirteen of the 17 Patagonian
breeding seabirds nest on islands of this coastal sector,
including a significant proportion of the total population of
some of such species (Yorio et al., 1998). This area is subject
to several human activities, including commercial fisheries.
About 18 ice trawlers operate from September to May, gener-
ally from 20 to 50 km offshore, although they can occasionally
fish in waters outside Golfo San Jorge to distances over
100 km offshore. These vessels are 26.4 ± 2.4 m long (range =
21.2–30.9), have 458.1 ± 65.0 HP (range = 380–624), and tow
bottom nets (100–120 mm mesh size; 2 and 20 m vertical
and horizontal mouth opening respectively) at three knots.
Trawls last between 2 and 3 h. The target species is the Argen-
tine hake. During the height of the fishing season the trips by
trawlers last between 1 and 5 days (5–7 hauls/day). Fish are
sorted on deck and non-commercial sizes of hake and by-
catch species are discarded overboard. In addition to the ice
trawlers, the waters of Golfo San Jorge are used by about 70
freezer double ring trawl vessels targeting on Argentine red
shrimp (Pleoticus muelleri) and a few small coastal trawlers
also fishing for Argentine hake.
2.2. Seabirds associated with fishing vessels and
interactions with fishing gear
Information was gathered on board three different ice trawl-
ers (17% of the fishing fleet size), for a total of 52 hauls (11
fishing days) from December 2004 to April 2005. In all trips
and only during haulback activities, seabirds associated to
the vessel were identified to species level and counted using
7·35 binoculars. Frequency of occurrence was defined as
the percentage of hauls in which each species was observed.
Black-browed albatross and Kelp gulls were identified into
adult and young birds on the basis of beak coloration and
plumage for the former and plumage characteristics for the
latter.
Information on the incidental capture of seabirds in nets
was also obtained at each of the 52 hauls, recording species
identity and number of birds caught. Interactions with warp
cables were quantified simultaneously at both the starboard
and port warps recording non-fatal contacts (when birds were
struck by a cable and survived) and fatal contacts (when birds
struck by the cable were dragged underwater and drowned).
Only cases when a bird was observed drowned and caught
in the cable were recorded as fatal. Discards are discharged
on both sides of the vessel and flow toward the stern affecting
both cables. Contact and mortality rates at both cables for
each species were quantified in 43 of the 52 hauls, as interac-
tions between seabirds and cables could not be recorded dur-
ing the last haul of the day or the last haul before returning to
port. Observations at each haul were made from the stern of
the vessel during the time period that fish was discarded
(approximately 30 min to 2 h, depending on the size of the
catch).
At the beginning of each haul, information on wind speed
(WS) and ambient temperature (AT) to the nearest Cwas
gathered from the bridge. In addition, for each haul, the num-
ber of fishing vessels operating within sight was recorded.
Distance of each haul to the nearest coastline, either main-
land or island, was measured from digitized maps.
During March 2005, fishing was undertaken during two
days in an area more than 100 km from the nearest coastline
BIOLOGICAL CONSERVATION 136 (2007) 108116 109
Author's personal copy
and outside Golfo San Jorge (Fig. 1). Fishing at such large dis-
tances from the coast is uncommon for vessels in this fishing
fleet, and thus information gathered was not included in the
main analysis. However, given the opportunity, information
was also gathered on seabird interactions with warp cables
for a total of 10 hauls.
2.3. Design of mitigation measure
During the high season of January and February of 2006, a
mitigation device to reduce mortality at cables was specifi-
cally designed and tested on board one of the commercial
fishing vessels. The device consisted of a plastic cone (traffic
cone) attached to each warp cable (Fig. 2). The cone was 1 m
long by 10 and 20 cm minimum and maximum diameter,
respectively, and orange in color. The cone can be opened in
half, allowing its deployment to the cable from the deck,
and is attached to a rope which helps lower the device sliding
it through the cable up to where the warp cable enters the
water. The device was tested under normal operating
conditions.
To assess the effects of the mitigation device on the num-
ber of seabird contacts and behavior, cones were attached to
both warp cables in a total of 12 of 22 hauls during eight fish-
ing days. Cones were set in alternate hauls to allow a compar-
ison between hauls with and without device during similar
sampling conditions. Information was gathered simulta-
neously at both warp cables. At each haul, the number of fatal
and non-fatal contacts was recorded during the entire period
with discarding activities. In addition, the distances to the
cable of the closest three seabird individuals were estimated
every 5 min and an average was obtained for each haul. Re-
cords obtained every five minutes were considered indepen-
dent given the speed of the vessel and the turn-over of birds
at the stern. Given that Black-browed albatross and Kelp gulls
are the most abundant at hake trawlers and show the highest
interaction with warp cables (Gonza
´lez-Zevallos and Yorio,
2006), distances to cables of these two species were also inde-
pendently estimated.
2.4. Statistical analysis
Results are given as mean number and range of individuals
(min, max). The estimated number of birds killed was
calculated adapting for trawlers the methods described by
Klaer and Polacheck (1995) for longliners, where:
68º 00` 65º 00`
Cabo Dos
Bahías
Cabo
Aristizábal
CR
Cabo Tres
Puntas
Chubut
S
0 50 Km
67º 00`
South
America
Argentina
Go
Jor
Atlantic
Ocean
45º 30`
46º 00`
46º 30`
68º 00` 65º 00`
Cabo Dos
Cabo
CR
Cabo Tres
Puntas
S
0 50 Km
67º 00`
South
America
Argentina
Go
Jor
Atlantic
Ocean
68º 00`
Cabo Dos
Cabo
CR
Cabo Tres
Puntas
Santa Cruz
0 50 Km
67º 00`
South
America
Argentina
Golfo San
Jorge
Atlantic
Ocean
45º 30`
46º 00`
46º 30`
Fig. 1 – Map of Golfo San Jorge, Argentina, showing the spatial distribution of the trawl hake fishery. ‘‘d’’: location of hauls
without mitigation measure, ‘‘h’: location of hauls with mitigation measure and CR: city of Comodoro Rivadavia.
1
2
net
vessel
4
3
5
1
2
net
vessel
4
3
5
Fig. 2 – Legend: (1) cones, (2) warp cables, (3) rope, (4) aluminum hook, (5) fastener.
110 BIOLOGICAL CONSERVATION 136 (2007) 108116
Author's personal copy
b
B¼HPc
i¼1Hi
bi
Pc
i¼1Hi
b
B= estimated total birds caught;
b= observed number of birds caught;
H= total number of hauls;
h= number of observed hauls;
bi¼bi
hi= mean number of observed birds caught per haul in
cruise i;
i= cruise number;
c= number of observed cruises.
Coefficients of variation (CV) are given for estimates be-
cause these are more useful than confidence intervals for
comparing relative precision.
The relationship between cable contacts and environmen-
tal conditions was analyzed only for the Kelp gull as low sam-
ple size precluded the analysis for other seabirds present. The
relationship between the number of Kelp gull contacts and
recorded variables (WS, AT and abundance) was analyzed
using a generalized linear model (GLM) with a quasipoisson
structure error. Linear regression was used to assess the
effects of the distance to the coastline on Kelp gull abundance
at vessels. Finally, we used the Friedman non-parametric test
to assess the effectiveness of the mitigation device. Results
are given as mean ± 1 SD.
3. Results
3.1. Species and abundance of seabirds associated with
fishing vessels
A total of 13 seabird species was recorded using food made
available by the hake trawl fishery operating at Golfo San Jorge
during the study period (Tab l e 1). The most frequent and abun-
dant seabirds were the Kelp gull and the Black-browed alba-
tross. The White-chinned petrel (Procellaria aequinoctialis),
Southern giant petrel (Macronectes giganteus), and Imperial cor-
morant (Phalacrocorax atriceps) also showed a relatively high
frequency of occurrence, although they were present in smal-
ler numbers. The rest of the species were observed in low
numbers and in less than 50% of hauls (Tab l e 1).
3.2. Seabird contacts with warp cables
Interactions were observed between seabirds and both nets
and warp cables. Most interactions between seabirds and
warp cables occurred when birds were feeding on discards
from the surface, right behind the vessel, and were struck
by the cable from behind or in the scapular area of the wing.
On occasions, birds collided with the warp cable when flying
low in direction to the vessel. Contacts were recorded in 81.4%
of hauls (n= 43). A total of 6 species showed contacts with
warp cables, with a mean number of species per haul of
1.5 ± 1.2 (range = 0–4) (Ta ble 2). Mean number of contacts per
haul was 14.4 ± 23.8 (range = 0–127). Eighty-one percent of re-
corded cases corresponded to the Kelp gull, 12% to the Black-
browed albatross, 4.6% to the Great shearwater, 1.5% to the
Sooty shearwater, 0.6% to the Imperial cormorant, and 0.3%
to the Magellanic penguin. Of the contacts recorded for Kelp
gulls and Black-browed albatross, 4.4% and 6.8% respectively
corresponded to juvenile individuals.
A stepwise generalized linear model showed that Kelp gull
abundance was the only variable related to the recorded num-
ber of contacts for this species (p= 0.004) (Fig. 3a). Number of
Kelp gulls per haul varied between 0 and 1000 individuals
(mean = 348.5 ± 279.2). Environmental conditions measured
during each haul were variable, with wind speeds ranging be-
tween 0 and 30 km/h (mean = 16.3 ± 7.0) and ambient temper-
atures ranging between 15 and 30 C (mean = 21.2 ± 3.4).
However, wind speed (p> 0.1) (Fig. 3b), and ambient tempera-
ture (p> 0.6) (Fig. 3c) were not significantly related with the
number of contacts. The model explained 29.4% of the devi-
ance in the contact rate. Lineal regression analysis showed
that Kelp gull abundance was negatively related with distance
to the nearest coast (R
2
= 0.26, p< 0.001) (Fig. 4).
Table 1 – Frequency of occurrence (in percentage) and mean number and range of individuals per haul of seabirds
attending high-seas hake trawlers at Golfo San Jorge during the height of the fishing season of 2004–2005; n= 52 hauls
Species Frequency of occurrence Mean (range)
Kelp gull (Larus dominicanus) 98.1 348.5 (0–1000)
Black-browed albatross (Thalassarche melanophrys) 96.1 132.2 (0–500)
White-chinned petrel (Procellaria aequinoctialis) 80.8 12.9 (0–150)
Southern giant petrel (Macronectes giganteus) 75.0 6.8 (0–40)
Imperial cormorant (Phalacrocorax atriceps) 59.6 51.6 (0–400)
Magellanic penguin (Spheniscus magellanicus) 48.1 13.1 (0–100)
Antarctic skua (Catharacta antarctica) 44.2 1.0 (0–6)
Sooty shearwater (Puffinus griseus) 42.3 40.6 (0–500)
Great shearwater (Puffinus gravis) 40.4 43.1 (0–400)
Wilson’s Storm-petrel (Oceanites oceanicus) 17.3 0.4 (0–5)
South American tern (Sterna hirundinacea) 15.4 0.9 (0–8)
Royal albatross (Diomedea epomophora) 9.6 0.2 (0–3)
Cayenne tern (Thalasseus sandvicencis eurygnatha) 3.8 0.2 (0–6)
Mean number of species per haul 6.3 (2–11)
Mean number of birds per haul 651.3 (35–1684)
BIOLOGICAL CONSERVATION 136 (2007) 108116 111
Author's personal copy
3.3. Cable and net related mortality
A total of 53 individuals were killed due to interactions with
fishing gear during the fishing season 2004–2005, of which
11.3% corresponded to cable related mortality. Birds were
struck by the warp cable and drowned when dragged under-
water. Individualswere killed by warp cables in 11.6% of hauls
analyzed (n= 43), resulting in a total mortality rate of
0.14 birds/haul. The two affected species were the Kelp gull
(0.12 birds/haul) and Black-browed albatross (0.02 birds/haul).
The incidental capture of seabirds in nets was recorded in
40.4% of the observed hauls (n= 52). A total of 47 individuals
were caught, resulting in a mean capture rate of 0.9 birds/
haul. Species killed included the Sooty shearwater, Great
shearwater, Magellanic penguin and Imperial cormorant,
reaching a maximum number per haul of 8, 6, 4 and 2 individ-
uals, respectively. These four species were incidentally caught
in nets during haulback. Net related mortality was signifi-
cantly larger than that related to warp cables (Mann–Whitney
U= 785, p= 0.001) (Fig. 5).
A total of 18 high-seas hake ice trawlers operated during
the study period of 2004–2005, adding to a total of 521 fishing
days (Secretarı´a de Pesca de la Provincia de Chubut, Dele-
gacio
´n Zona Sur, unpublished data). Considering that each
vessel conducts a minimum of five hauls per day during
the high fishing season, an estimated total of 2605 hauls were
made during the five month study period. The estimated to-
tal number of birds killed in the study period of 2004–2005
was 2703 (CV = 0.8), of which 306 (CV = 0.9) seabirds were
killed due to contacts with warp cables. These included 255
(CV = 1.0) Kelp gulls and 51 (CV = 2.2) Black-browed albatross
(Tab le 3). Seabirds drowned in nets included four diving spe-
cies, and estimated total number of birds killed varied
between 204 and 1275 depending on species (Table 4). It has
to be stressed that estimates presented are just an indica-
tion of the actual figures of birds killed.
During the two day fishing trip to the area 100 km offshore
in March 2005, both fatal and non-fatal contacts of Black-bro-
wed albatrosses with warp cables were recorded in 87.5% of
hauls (n= 10). Mean number of contacts per haul was
23.6 ± 16.6 (range = 0–42). Number of individuals and contacts
recorded outside Golfo San Jorge were significantly larger
than those recorded within the gulf (number of individuals:
227 ± 102.8 vs. 132.2 ± 135.3, Mann Whitney U= 128, p= 0.011
and number of contacts: 23 ± 16.6 vs. 1.7 ± 3.4, Mann Whitney
U= 34.5, p< 0.001). During the two fishing days, 11 Black-bro-
wed albatrosses were killed by warp cables, resulting in a
mortality rate of 1.1 birds/haul.
3.4. Effectiveness of mitigation measure tested
Significant differences were found in the number of contacts
between hauls with and without mitigation device (Ta b l e 5 ).
0
50
100
150
0 5 10 15 20 25 30 35
0
50
100
150
0 5 10 15 20 25 30 35
0
50
100
150
0 200 400 600 800 1000
a
c
b
Number of contacts (fatal and non fatal) / haul
Fig. 3 – Relationship between number of contacts (fatal and
non-fatal) and: (a) Kelp gull abundance in number of
individuals per haul, (b) wind velocity in km/h and (c)
ambient temperature to the nearest C.
Table 2 – Mean number and range of both fatal and non-
fatal contacts with warp cables per haul of seabirds
attending high-seas hake trawlers at Golfo San Jorge
during the height of the fishing season of 2004–2005;
n= 43 hauls
Species Mean (range)
Kelp gull 11.6 (0–126)
Black-browed albatross 1.7 (0–14)
Great shearwater 0.6 (0–6)
Sooty shearwater 0.2 (0–7)
Imperial cormorant 0.1 (0–2)
Magellanic penguin 0.05 (0–2)
Mean number of species contacts per haul 1.5 (0–4)
Mean number of contacted per haul 14.4 (0–127)
0
5
10
15
20
25
0 200 400 600 800 1000
Di
number of individuals/ haul
Distance to the nearest coastline
Fig. 4 – Kelp gull abundance at hake trawl vessels operating
at Golfo San Jorge, Argentina, in relation to the distance to
the nearest coastline (km).
112 BIOLOGICAL CONSERVATION 136 (2007) 108116
Author's personal copy
In hauls with mitigation device, the number of contacts was
reduced by 89% with respect to hauls without the mitigation
device. Mean number of contacts per haul was 5.4 ± 7.2 and
58.5 ± 43.3 in hauls with and without mitigation device,
respectively. No seabirds were killed due to contacts with
warp cables during the implementation of the device
(n= 12), while 11 individuals (eight Kelp gulls and three
Black-browed albatrosses) were killed in hauls without the
mitigation device (n= 10) (Table 5). This resulted in a mortality
rate of 0.8 birds/haul for Kelp gulls and 0.3 birds/haul for
Black-browed albatross. During the testing of the mitigation
device a total of 15 individuals were also killed in nets
(n= 22) (11 Magellanic penguins, three Imperial cormorants
and one Kelp gull).
Distance of birds from the cone or where the cable entered
the water were significantly different, with birds remaining
further away at cables with the device (Table 5). Kelp gulls
and Black-browed albatrosses were present in all the hauls
when observations were made (n= 22). Distances between
Kelp gulls and cables were significantly larger in hauls with
(2.5 ± 1.17; range = 0.5–8) and without (0.75 ± 0.53;
range = 0.1–3) mitigation device (Mann Whitney U= 43339,
p= 0.006). Similarly, distances between Black-browed alba-
trosses and cables were significantly larger in hauls with
(7.3 ± 3.62; range = 1–15) and without (2.07 ± 1.37; range =
0.2–6) mitigation device (Mann Whitney U= 4414, p< 0.001).
4. Discussion
Our results confirm the occurrence of mortality caused by
strikes with warp cables in the hake trawl fishery operating
at Golfo San Jorge. A previous study conducted in the same
fishery reported that more than 100 Black-browed albatrosses
and 150 Kelp gulls were drowned when struck by cables dur-
ing the height of the fishing season (Gonza
´lez-Zevallos and
Yorio, 2006). However, in such study no continuous observa-
tions were made from the stern of the vessel and thus mortal-
ity was likely underestimated. The present study based on
continuous observations shows that contacts are frequent
and confirms that they may result in mortality for the same
two species, with an estimated 51 Black-browed albatrosses
and 255 Kelp gulls killed during the five month study period.
Although based on a small sample, mortality rate of Black-
browed albatrosses due to cable strikes in the same feeding
area was higher during the testing of the mitigation device
in the height of the fishing season of 2006 and when fishing
took place 100 km offshore in 2005. This variability in mortal-
ity rates suggests that caution is needed when evaluating this
interaction between seabirds and fishing gear. Cable related
mortality was significantly lower than that recorded for net
related mortality, which affected diving species.
Black-browed albatrosses, as well as many Kelp gulls, take
discards from the surface behind the vessel, increasing the
Net
_
+
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
_
+
Cables
_
+
_
+
mean
_
+
95% confid int
Mean number of fatal contacts/ haul
Fig. 5 – Mean number of fatal contacts per haul in nets
(n= 52) and warp cables (n= 43) during the height of the
fishing season of 2004–2005.
Table 3 – Seabirds killed in warp cables and estimated mortality during the height of the fishing season of 2004–2005;
n= 43 hauls
December 2004 January 2005 February 2005 April 2005
Total estimated hauls for the whole fishery 855 805 465 480
Sampled hauls 18 8 11 6
Black-browed albatross
Flock size 20–150 70–500 10–250 15–400
Number of individuals killed 0 1 0 0
Mortality rate (individuals/haul) 0.1
Estimated total mortality 51 (CV = 2.2)
Kelp gull
Flock size 110–1000 330–830 15–250 10–370
Number of individuals killed 2 3 0 0
Mortality rate (individuals/haul) 0.1 0.4
Estimated total mortality 255 (CV = 1.0)
BIOLOGICAL CONSERVATION 136 (2007) 108116 113
Author's personal copy
chances of interactions with warp cables. Contact rate was
found to be related to Kelp gull abundance, similar to what
was observed for the Black-browed albatross at finfish trawl-
ers operating in the Malvinas (Falklands) Island waters (Sulli-
van et al., 2006a). Incidental capture in trawl nets of Great
shearwaters, Imperial cormorants, and Magellanic penguins
also occurred during the months when their highest abun-
dances were recorded (Gonza
´lez-Zevallos and Yorio, 2006).
Discharge level, which can influence seabird abundance
around vessels (Arcos and Oro, 2002; Gonza
´lez-Zevallos and
Yorio, 2006; Sullivan et al., 2006b) is thus an important factor
affecting the likelihood of mortality in fishing gear. Sullivan
et al. (2006a) reported that sea state and both wind speed
and direction can also affect contact rates. In the present
study, environmental variables were not related to the num-
ber of contacts by Kelp gulls. Further research is needed to
understand this relationship through a wider range of envi-
ronmental conditions and for other species in the seabird
assemblage associated to hake trawlers.
Even though the estimated number of seabirds killed by
warp cables in this fishery may seem relatively low, the overall
cable related mortality resulting from offshore trawl fishing
operations in the Argentine Continental Shelf should not be
underestimated. Over 300 high-seas trawlers are currently
operating in the continental shelf under Argentine jurisdic-
tion (Bertolotti et al., 2001). The opportunistic observations
made 100 km offshore during this study suggest that mortality
rates are very likely significantly higher at trawler fleets oper-
ating in the high seas. Information on cable related mortality
in the South-west Atlantic is also available for demersal finfish
trawlers operating in the Malvinas (Falkland) Islands Exclusive
Economic Zone (Sullivan et al., 2006a). These authors esti-
mated that over 1500 seabirds, mostly Black-browed albatross,
were killed during a 12-month period in 2002/2003. The Black-
browed albatross is catalogued as endangered according to
UICN criteria (Birdlife-International/UICN, 2001) and its popu-
lations have shown a significant reduction in numbers (Rob-
ertson and Gales, 1998; Huin, 2001). Incidental mortality in
longline fisheries has been implicated in this decline (Robert-
son and Gales, 1998; Favero et al., 2003; Gandini and Frere,
2006), but cable related mortality at trawl vessels is very likely
contributing to the observed population trends.
The cones tested as a mitigation device proved to be effec-
tive under the operating fishing conditions. Contact rate
with warp cables, which is significantly correlated with bird
mortality (Sullivan et al., 2006a), was significantly reduced
Table 4 – Seabird mortality in nets and estimated mortality during the height of the fishing season of 2004–2005;
n = 52 hauls
December 2004 January 2005 February 2005 April 2005
Total estimated hauls for the whole fishery 855 805 465 480
Sampled hauls 21 10 13 8
Imperial cormorant
Flock size 5–400 30–200 1 5–150
Number of individuals killed 4 0 0 0
Mortality rate (individuals/haul) 0.19
Estimated total mortality 204 (CV = 2.2)
Great shearwater
Flock size 0 1 10–100 6–400
Number of individuals killed 0 0 0 9
Mortality rate (individuals/haul) 1.12
Estimated total mortality 459 (CV = 2.2)
Magellanic penguin
Flock size 2-30 10-100 0 0
Number of individuals killed 15 10 0 0
Mortality rate (individuals/haul) 0.71 1
Estimated total mortality 1275 (CV = 1.3)
Sooty shearwater
Flock size 0 2 4–20 6–500
Number of individuals killed 0 0 0 9
Mortality rate (individuals/haul) 1.12
Estimated total mortality 459 (CV = 2.2)
Table 5 – Fatal and non-fatal contacts and approach distances (meters) at warp cables (mean number and range per haul),
comparing hauls without (n = 10) and with (n = 12) mitigation measure during January and February of 2006
Without mitigation
measure, n=10
With mitigation
measure, n=12
Friedman
T
2
p
Non-fatal contacts 56.4 (22–128) 5.4 (0–21) 14.29 =0.001
Fatal contacts 1.1 (0–4) 0 39.16 <0.001
Approach distance 0.9 (0.1–4) 2.6 (0.5–8) 8.69 =0.003
114 BIOLOGICAL CONSERVATION 136 (2007) 108116
Author's personal copy
in hauls with device and, additionally, no seabirds were killed.
Moreover, distances between seabirds and the warp cables
were significantly larger in hauls with the mitigation device,
indicating that the cones were effective in deterring the birds
from the area where the cable enters the water. The cone’s
size and orange color very likely increase the detection by
scavenging individuals of the forward moving cable. Sullivan
et al. (2006b) suggest that high contrast colors of mitigation
devices make them more effective. In addition, even if the
cone would strike a bird, the interaction would probably lead
to a lower probability for the bird being injured or trapped by
the cable given the protection afforded by the cone. Other
mitigation measures have been suggested as effective means
of reducing seabird mortality caused by warp cables strikes,
such as the elimination or reduction of fishing waste dis-
charge (Wienecke and Robertson, 2002; Sullivan et al.,
2006a) and bird scaring devices (Tori lines, Warp scarer and
Brady Baffler) (Sullivan et al., 2006b).
Cones are simple devices to deploy on-board, and although
they have not yet been produced commercially, they are unli-
kely to be expensive. In addition, only one member of the crew
is required to deploy the device. Moreover, 82% of the 11 inter-
viewed crew members of the vessel where the device was
tested considered that it does not affect fishing practices and
73% of them expressed their willingness to adopt the device.
The proposed device could be easily applied in this and other
trawl fisheries operating in Argentine waters. Current On-
board Observer Programs in Argentine do not include the mon-
itoring of seabird-cable interactions, although a couple of
them recently included protocols for the monitoring of net re-
lated mortality and the composition of seabird assemblages
associated to fishing operations. Given the potential effects
of this interaction on some seabird populations, increased ef-
fort should be placed in the testing of mitigation measures and
the monitoring of cable related mortality associated to high-
seas trawlers operating in the Argentine Continental Shelf.
Acknowledgements
We thank Centro Nacional Patago
´nico (CONICET) for institu-
tional support, Secretarı´a de Pesca de la Provincia de Chubut –
Delegacio
´n Zona Sur for logistical support, Wildlife Conserva-
tion Society and Project ARG/02/G31 implemented by PNUD/
GEF/Fundacio
´n Patagonia Natural for financial support, and
IDEA WILD for the donation of field equipment. Special
thanks to P. Feinsinger and colleagues of Design Course
Salta-2005. Thanks to G. Harris, M.V. Rodriguez, P. Dell’Arcipr-
ete, S. Copello, J. A
´lvarez, R. A
´lvarez, J. Burella, J. Pe
´rez Botel, P.
Quercia and the captains and crews of the hake trawlers for
their help and advice, and to an anonymous referee for
helping improve the final version.
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Incidental mortality of seabirds caused by interactions with the warp wires of trawl vessels in Australia's Commonwealth-managed Southern and Eastern Scalefish and Shark Fishery has been reported by on-board observers. Seabird mortality as a result of fishery interactions is an issue of global conservation concern. This paper describes an industry-led study that developed and tested the effectiveness of 2 experimental mitigation devices for trawl vessels: a baffler and a water sprayer. These were tested against a control which was previously the only prescribed device (a warp deflector called a pinkie). Seabird interactions were observed during 69 shots comparing the sprayer against the control, and 55 shots comparing the baffler against the control. The seabird mitigation device employed alternated between the trial device (either the water sprayer or baffler) and the control device. Both experimental mitigation devices showed significant reductions in heavy interaction rates (interactions per shot) compared with the pinkie (83.7 and 58.9%). On stern trawlers, both new devices are deployed at the start of fishing and retrieved at the end of fishing operations, whereas pinkies need to be deployed and retrieved for each shot. This results in time savings and reduced risks to crew. Based on the findings from this study, the Australian Fisheries Management Authority now allows vessels to meet seabird bycatch mitigation requirements through use of either new device. The outcomes of this research and subsequent uptake of the new mitigation devices will greatly contribute to the reduction of incidental fishing mortality in Australian, and potentially other trawl fisheries.
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Magellanic penguins ( Spheniscus magellanicus ) disperse widely during winter and are a major consumer of marine resources over the Patagonian Shelf. Magellanic penguins were equipped with geolocators at Martillo Island in late February- early March 2017 and recaptured at the beginning of the next breeding season to recover the devices and to collect blood samples for stable carbon (δ ¹³ C) and nitrogen (δ ¹⁵ N) isotope analysis. We evaluated their whole winter dispersal and their trophic niche by sex during the last month of the winter dispersal. Also, we evaluated their spatial overlap with bottom trawl and shrimp fisheries using data from satellite fisheries monitoring. Penguins dispersed northwards up to 42°S and showed latitudinal spatial segregation between sexes during May to August (females were located further north than males). In contrast, during the last month of the winter dispersal females were located more southerly and showed lower trophic position than males. Also, females did not dive as deep as males during winter. We found high overlap between both fisheries and penguin’s spatial use in regions with documented interaction. However, no sex-specific statistical differences with fisheries overlap were found. Our results highlight the importance of understanding the spatial domains of each sex and assessment of their potential conflicts with bottom trawl fishery and shrimp fishery during the winter period.
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Data collected by Australian observers, combined with logbook data supplied by all Japanese vessels fishing in the Australian Fishing Zone were used to estimate the total seabird catch and catch rates (and associated variances) within the Australian Fishing Zone by season and area. The species composition of subsamples of captured seabirds was used in conjunction with the estimates of total by-catch to provide estimates of by-catch by species. The total by-catch of all seabird species by Japanese longline within Australian waters was estimated to be 2,981 (cv 17%) for the 1992 fishing year, 3,590 (cv 15%) in 1993 and 2,817 (cv 19%) in 1994. However, the observed seabird bycatch may underestimate the total number of seabirds killed by 27%. The increase in total seabird by-catch between 1992 and 1993 is partly due to the use of monofilament nylon longline gear by two vessels in 1993, and the decrease from 1993 to 1994 was mainly due to a corresponding reduction in fishing effort. For the three years examined, 78% of the total seabird by-catch was albatrosses, with black-browed albatross (Diomedea melanophrys) and shy albatross (D. cauta) caught in the greatest numbers. Catches of yellow-nosed albatross (D. chlororhynchos), wandering albatross (D. exulans), and grey-headed albatross (D. chrysostoma) were also substantial. The proportions of individual species caught showed considerable inter-annual variability. Most seabirds caught and killed by longline fishing are captured during line setting. Data collected by the observers were also used to determine the influence of various environmental factors and mitigation measures on seabird catch rates. Generalised linear models were used to determine the statistical significance of the effect of each factor on the seabird catch rate. Results show that the environmental factor that has the most influence is whether line setting was carried out at night or during the day. For the data examined, the chance of catching seabirds during day sets was five times greater than for night sets. For v night sets, the chance of catching seabirds during the full half-phase of the moon was five times greater than during the new half-phase. Other environmental factors with significant effects were the area and season fished. Wind, cloud and sea conditions were not found to have a significant influence. Considerable variation in the seabird by-catch rate among vessels was found, which is probably due to differences in their implementation of mitigation measures, as well as the clumped distribution of seabirds by area and time. Interannual variation in the by-catch rate was found to be statistically significant but the differences among years was small in comparison to other factors. An examination of the influence of mitigation measures for sets made during the day in summer in the Tasmanian area showed that the level of bait thawing and unidentified factors related to individual vessels were most significant in determining the seabird by-catch rate, followed by the use of a bait throwing device. It was not possible to examine the influence of the use of bird scaring tori poles and lines as these were used during all sets examined in detail. For this data set, the amount of cloud cover had an influence, while moon phase, sea conditions and wind strength did not.
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The incidental mortality of albatrosses Diomedeidae and petrels Procellariidae by longline fishing vessels, has been assessed and analysed in several areas of the globe. We provide the first direct estimates of incidental mortality rates of albatrosses and petrels along the Argentine Shelf and shelf break. The estimated by-catch rate for the whole period analysed (1999-2001) was 0.04 birds/1,000 hooks, with a maximum of 0.20 birds/1,000 hooks observed in 1999. Annual captures averaged 1,160 birds; however, the large variation observed indicates that annual by-catch may be in the order of thousands, with around 10,000 seabirds being killed by longliners through the study period. Most of the captures were observed along the Patagonian shelf break. At least 12 bird species were incidentally taken, with Black-browed Albatrosses Thalassarchemelanophris and White-chinned Petrels Procellariaaequinoctialis accounting for about 80% of total captures. The information provided in this study allowed the design and future implementation of mitigation measures and new survey methods onboard longliners operating in Atlantic waters on the Argentine shelf.
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We studied discard use and incidental mortality of seabirds attracted to high-sea trawl vessels operating in the Golfo San Jorge, Argentina, during the height of the fishing season in 2003 and 2004. Fourteen seabird species ate food made available by fishing operations. The most frequent and abundant seabirds (percent occurrence, mean number per haul) were the kelp gull Larus dominicanus (98.9%, 207.0), the black-browed albatross Thalassarche melanophrys (98.9%, 94.2) and the white-chinned petrel Procellaria aequinoctialis (91%, 8.4). Flock sizes for the 3 species var- ied from a few to a maximum of 1600 birds. Total seabird abundance varied significantly between stages of the fishing operation, being higher during discarding and haulback than during towing. Incidental capture of seabirds in nets was recorded in 37% of 89 hauls, with a mean capture rate of 1.2 birds per haul. Species incidentally caught were the great shearwater Puffinus gravis, the imper- ial cormorant Phalacrocorax atriceps and the Magellanic penguin Spheniscus magellanicus, with rates that varied between months and years. Considering the fishery's fishing effort, the estimated total numbers of birds killed during the study were 2254 great shearwaters (CV = 1.1), 1233 imperial cormorants (CV = 1.1) and 35 Magellanic penguins (CV = 2.4) in 2003, and 311 imperial cormorants (CV = 1.7) and 1516 Magellanic penguins (CV = 1.1) in 2004. Black-browed albatrosses and kelp gulls were also struck by the warp cable while feeding on discards from the surface, and drowned when they were dragged underwater. The results obtained in this study show that the hake trawl fishery operating in the Golfo San Jorge may have a significant effect on some seabird populations through the provision of fishing discards and incidental mortality.
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A conservative calculation of the number of albatrosses killed annually on Japanese longlines in southern oceans in 44 000. The actual figure could be double and is sufficiently high to substantiate claims that serious declines in albatross populations are due to this fishing activity. Albatrosses have an economic impact on longline fisheries with annual losses to the southern bluefin tuna fishery alone exceeding $A7 million. If all fish species and the total longlining effort were considered, it would be many millions of dollars greater. Apart from a concern for albatrosses, Japan's longline fishermen would also benefit by using the solutions offered. It is suggested that a 70% reduction in the problem is possible and that an overall reduction in excess of 90% could be achieved. Further monitoring is essential.
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The effects of different environmental and operational factors on the incidental capture of Black-browed Albatross (Thalassarche melanophris) in long-line fishing operations were analysed. This is the most commonly captured seabird by Argentine long-line fishing vessels, and significant decreases in its populations have been mainly attributed to long-line fishing practices. The estimated mean rate ± s.d. of by-catch for the analysed period (1999-2003) was 0.03 ± 0.39 birds per 1000 hooks. Black-browed Albatrosses were mainly caught during day settings. Higher capture rates were observed during autumn and winter. The effect of the length of long-lines on the incidental capture of Black-browed Albatrosses was also analysed, showing that higher capture rates occurred when short long-lines were deployed. Seasonal differences in the distribution of captures were observed, being widely distributed to the north of the shelf-break during autumn-winter (i.e. non-breeding season) and mostly concentrated in southernmost latitudes, closer to the presumed breeding area in the Malvinas (Falkland) Islands during spring-summer. Mortalities during winter were mainly associated with the Patagonian Toothfish (Dissostrichus eleginoides) fishery, while those observed during summer were associated with long-liners targeting Kingklip (Genypterus blacodes) on the Patagonian Shelf.