The IUCN/SSC Shark Specialist Group
Shark News 14: March 2002
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Historic Trends in Catches of the Brazilian Longline Fishery in the Southwestern Equatorial Atlantic Ocean
Fábio H. V. Hazin1, Matt K. Broadhurst2, Humberto G. Hazin1 and Paulo Travassos1
1Universidade Federal Rural de Pernambuco, Brazil
2Cronulla Fisheries Centre, Australia
Introduction
The pelagic longline fishery off northeastern Brazil began in 1956 with
several Japanese longliners (leased by a Brazilian company) primarily
targeting tunas (Thunnus spp.). This fleet consisted of 12 boats in
1959 (Paiva and Le Gall 1975) and although the fishery was quite
successful, fishing operations were suspended in 1964 due to economic
and political reasons. Between 1976 and 1977, the fishery experienced
a brief revival through the leasing of two Korean longliners. However,
there was no significant effort until 1983, when a Brazilian company
began to operate from Natal (northeast Brazil), using relatively small
vessels to target tunas, billfishes and sharks (mainly the blue shark,
Prionace glauca and other Carcharhinus species). The longline fleet
expanded throughout the following 17 years and by 2000 it consisted
of 18 boats, ranging in size from approximately 16 to 26 m.
Catch data from this fishery have routinely been collected and used
in studies examining biological characteristics of the principle species
caught, including their relative distributions and abundances (Hazin et
al. 1990; 1994a, Travassos et al. 1999), reproductive biology (Hazin et
al. 1994b), and feeding habits (Hazin et al. 1994c). More recently,
Hazin et al. (1998), analysed catch data from some vessels and
provided a brief overview of temporal and spatial variations in catch
compositions. The identification of such factors has proved essential
for the effective management of this fishery. In the present paper, we
have expanded the overview presented by Hazin et al. (1998) and
included yearly catch data until 2000.
Material and Methods
This study used data collected from the log-sheets of longliners
operating off northeast Brazil, between 1983 to 2000. Prior to 1996, all
vessels used Japanese-style multifilament longlines (for details see
Shapiro 1950, Suzuki et al. 1977) baited with Brazilian sardine,
Sardinella brasiliensis. In 1997, all vessels began using monofilament
longlines rigged with light-sticks and baited with squid, Illex argentinus.
Relative abundance of species was evaluated as nominal catch per unit
of effort (CPUE), defined as the number of fish caught per 100 hooks per
year. Catch records included identification of species, with the exception
of sharks, which were collectively grouped up to 1986. After that year,
sharks began to be recorded by species. However, because of difficulties
in distinguishing some of the species of the genus Carcharhinus, for the
purposes of this study, they were grouped under the category "gray
sharks".
Results and Discussion
The data presented in Figure 1 show quite large temporal fluctuations
of total yearly CPUE of most groups of species examined. Many of these
temporal variations can be explained by the changes in overall fishing
strategy over the past 17 years, summarized in 5 distinct periods:
- Period 1 (July 1983 - June 1986): tunas (mainly yellowfin tuna) and
billfish (swordfish Xiphias gladius, sailfish Istiophorus albicans, white
marlin Tetrapturus albidus, and blue marlin Makaira nigricans) were
the main target groups whilst sharks were avoided.
- Period 2 (July 1986 - December 1987): along with tunas and billfishes,
sharks (mainly blue sharks) became a target group.
- Period 3 (January 1988 - June 1991): yellowfin tuna fishing grounds
were discovered off the Archipelago of St. Peter and St. Paul, resulting
in a shift of effort towards this species.
- Period 4 (July 1991 - June 1996): fishing effort was concentrated over
shallow seamounts, where gray sharks species were abundant.
- Period 5 (July 1996 - Dec 2000): although gray sharks were still the
dominant group, the CPUE of swordfish rose sharply owing to a
concentrated effort involving the use of light sticks and squid as bait.
The initial shift in effort towards sharks (period 2)
occurred mainly because of an increased awareness of
their abundance and availability. Unlike nearly all
international longline fisheries, which tend to remove
shark fins and discard the carcass at sea, all shark carcasses
caught off northeastern Brazil were landed and sold
locally. However, because of the low price of their meat,
prior to June 1986, the return paid to fishers was half that
for tunas and billfishes. In July 1986, the fishing company
standardized the return for all species caught following
the realization that although sharks were worth less than
other species, their abundance meant that production
could be more than doubled. The existence of an
established local market for shark products (e.g. frozen
fillets), which had developed from the steady production
of shark meat during the first three years of the fishery,
facilitated this shift in effort.
In January 1988, and during the first quarter of each
consecutive year (period 3), vessels began to operate in
the vicinity of the Archipelago of St. Peter and St. Paul to
target yellowfin tuna that aggregate there in large numbers to feed on
dense schools of spawning flying fish. As a result, the CPUE of this
species more than tripled in the first two years after the new fishing
grounds were discovered. This contributed to an overall rise in the
CPUE of total tunas (Figure 1), and a slight drop in the CPUE of sharks
(1988-90) due to a shift in effort away from areas of their maximum
abundance (i.e. seamounts of the North Brazilian Chain and Fernando
de Noronha Chain).
After 1992 (during period 4), vessels concentrated around the
many seamounts, located mainly in Fernando de Noronha and North
Brazilian Chains, to target gray sharks (Figures 1 and 2). The discovery
of large abundances of this species in the vicinity of these seamounts,
as well an increase in the international price of shark fins, contributed
to this shift in effort.
Figure 1. Yearly mean CPUE of tunas, sharks, billfishes and others fishes caught by Brazilian longliners off northeast Brazil, from July 1983 to December 2000.
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Figure 2. Yearly mean CPUE of blue shark and gray shark caught by Brazilian longliners off northeast Brazil, from July 1983 to December 2000.
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During period 5, catches of billfishes increased as vessels began to
adopt monofilament gear, rigged with lightsticks and squid as bait. The
main species targeted was swordfish, although catches of other billfish
also increased. The use of monofilament in areas not predominantly
dominated by sharks meant that their CPUE subsequently dropped and
is currently comparable to levels observed during period 3.
It is apparent that numerous factors have contributed to changes in
fishing strategies during the past 17 years. Many of the shifts in effort
are either market orientated, reflecting variation in consumer demand
for various species, or as a result of the discovery of new fishing
grounds and stocks. Very few of the changes observed in the first 13
years are gear related, however, given some of the more recent
developments (e.g. use of monofilament), and that most of the fishing
areas have been fully explored, these sorts of changes are likely to
affect CPUE in the future. Ongoing monitoring of the fishing strategy
and any changes in fishing gear are therefore essential for the effective
management of this fishery.
References
Hazin, F. H. V., A. A Couto, K. Kihara, K. Otsuka and M. Ishino. 1990.
Distribution and abundance of pelagic sharks in the south-western
equatorial Atlantic. J. Tokyo Univ. Fish. 77(1):51-64.
Hazin, F. H. V., C. E. Boeckman, E. C. Leal, R. P. T. Lessa, K. Kihara, and
K. Otsuka. 1994a. Distribution and relative abundance of the blue
shark, Prionace glauca, in the southwestern equatorial Atlantic Ocean.
Fish. Bull. 92:474-480.
Hazin, F. H. V., K. Kihara, K. Otsuka, C. E. Boeckman and E. C. Leal.
1994b. Reproduction of the blue shark Prionace glauca in the
south-western equatorial Atlantic Ocean. Fish. Sci. 60(5):487-491.
Hazin, F. H. V., R. Lessa and M. Chammas. 1994c. First observation on
stomach contents of the blue shark, Prionace glauca, from
southwestern equatorial Atlantic. Rev. Brasil. Biol. 154(2):195-
198.
Hazin, F. H. V., J. R. Zagaglia, M. K. Broadhurst, P. E. P. Travassos and
T. R. Q. Bezerra. 1998. Review of a small-scale pelagic longline
fishery off northeastern Brazil. Marine Fisheries Review 60(3):1-8.
Paiva, M. P. and J. Y. Le Gall. 1975. Catches of tunas and tuna like
fishes in the longline fishery area off the coast of Brazil. Arq. Ciênc.
Mar. 15(1):1-18.
Rogers, D. D. 1994. The biology of seamounts. Adv. Mar. Biol. 30:
305-350.
Shapiro, G. D. 1950. The Japanese longline fishery for tunas. Commer.
Fish. Rev. 12(4):1-26.
Suzuki, Z., Y. Warashima and M. Kishida. 1977. The comparison of
catches by regular and deep tuna longline gear in the western and
central equatorial Pacific. Bull. Far Seas Fish. Res. Lab. 15:51-89.
Travassos, P., F. H. V. Hazin, J. R. Zagaglia, R. A. Rocha and J. Schober.
1999. Thermocline structure around seamounts and islands of
Northeast Brazil. Arch. Fish. Mar. Res. 47 (2/3):211-222.
Fábio H. V. Hazin
Universidade Federal Rural de Pernambuco
Avenida Dom Manoel de Medeiros, s/n, Dois
Irmãos,Recife,Pernambuco, Brazil
CEP: 52171-030
Fax: 55 081 33021512
Email: fhvhazin@terra.com.br
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