The IUCN/SSC Shark Specialist Group
Shark News 14: March 2002
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The artisanal ray fishery in the Gulf of California: development, fisheries research and management issues
J. Fernando Márquez-Farias, Instituto Nacional de la Pesca, México
Introduction
Fishing for rays in the Mexican Pacific developed with the introduction
of bottom gillnets in the Upper Gulf of California, where local fishers
target flounder, grouper, and many other finfish resources. The boats
used for fishing rays are typical "pangas" 22-25ft in length, using
outboard motors and operated by 1-3 fishers. Fishing trips are from 1-
3 days in duration, and the operation depth varies with the target group
of species. The number of boats used in the ray fishery is currently
unknown but is assumed to be high.
Fishers tend to switch to ray fisheries
depending on the availability of other
resources, for example during seasons
when more valued resources such as
blue crab, shrimps and sierra are
restricted due to regulatory regimes.
The catch is processed on the beach
and stored in ice trucks.
The distribution is mostly regional
and includes fresh fillets or salt dried
meat. The quality is judged primarily
on the colour of the meat (i.e. darker
colour = less value). In general, as
with other artisanal fisheries in
México, the ray fishery is
characterized by limited infrastructure
for processing, low technology,
limited fishing ratio, income supplies
and marketing controlled by few
companies or middlemen, and an
unarticulated role with respect to
regional economies.
Figure 1. Average proportion of rays production by Mexican Pacific states. Dark shaded states represent the Gulf of California region.
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The fishery for rays extends along the Gulf of California on
both sides of Peninsula de Baja California to the Southern
Mexican Pacific Coast. The importance of the ray fishery in terms
of production decreases from North to South (Figure 1).
Compared to the shark fishery that dates back to the late 1930's, the
catch of rays in México is a fairly new activity. The documentation of
production began officially in 1986, assuming previously unregistered
catches. The peak catch of rays was 1996 with 6,666t, and in 2000 the
catch had decreased to 4,944t. The average catch for all Mexican
Pacific states during the period from 1990 to 2000 was 5,514t, showing
a relative stable trend. Catch production of the Gulf of California
surrounding states represented 93% of the Pacific Coast total production
during the same period (Figure 2).
Figure 2. Annual catches of rays in the Pacific Ocean.
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Species composition
Despite the development of the ray
fishery, very few specific studies have
been conducted in the Gulf of
California region. Most have been
carried out along the South West Coast
of Baja California, Bahía Almejas and
provide limited information. This,
however, represents the only
information produced regarding some
commercially important rays in the
region (R. productus, R. steindachneri,
G. marmorata, N. entemedor, among
others), which, unfortunately is mostly
published in low impact journals.
Undoubtedly the most valuable
survey on rays and sharks in the Gulf
of California was carried out in a twoyear
multi institutional research
project conducted during 1998-99,
lead by Dr. Robert Hueter from CSR/
MML (Status of the shark and ray fishery resources in the Gulf of
California: Applied Research to Improve Management and
Conservation. Email: rhueter@mote.org).
A multispecies complex structure and a wide spectrum of life
history strategies of the elasmobranchs studied were elucidated as a
result of the biological examination of the catch in this survey.
Species registered in Sonora state alone show the high diversity and
relative importance in the catches (Table 1). The first five species
represent almost 90% of the catches. Species composition varied
depending mainly on the gillnet mesh size used and the season.
Table 1. Relative proportion of rays in Sonora.
Species
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%
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Rhinobatus productus
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37.98
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Dasyatis brevis
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18.95
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Rhinoptera steindachneri
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14.45
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Gymnura marmorata
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10.94
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Narcine entemedor
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5.00
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Rhinobatus glaucostigma
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4.40
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Gymnura crebripuncata
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2.74
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Myliobatis californica
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2.21
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Zapterix exasperata
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1.61
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Raja velezi
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1.24
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Urobatis maculatus |
0.18
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Dasyatis longus
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0.07
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Mobula munkiana
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0.06
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Urotrygon chilensis
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0.05
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Mobula japanica
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0.04
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Myliobatis longirostris
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0.03
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Urotrygon rogersi
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0.02
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Urobatis halleri
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0.01
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Bycatch
Rays have been caught traditionally as bycatch in well-developed
fisheries such as: blue crab (Callinectes bellicosus), sierra
(Scomberomorus sierra and S. concolor), and shrimp (Litopenaeus
spp., and Farfantepenaeus spp.). A gross calculation of the level of
bycatch in the shrimp fishery using a 1:10 bycatch ratio (1 kg/
shrimp:10 kg/bycatch biomass) (Garcia-Caudillo et al. 2000),
indicated the excessive biomass of rays that have been caught in
the Gulf of California during the last 60 years. This prompted us to
speculate that ray mortality level from bycatch exceeds the mortality
level from the directed ray fishery in the Gulf of California. Parallel
commercial activity has developed as a consequence of the large
amounts of rays caught in the shrimp trawlers. This informal
activity, consisting of middlemen buying the bycatch from the
shrimp trawlers, is resulting in disadvantageous competition for the
authentic fishermen, mainly because the price of the product from
the trawlers is low due to the low operational costs. In addition,
rays are frequently caught in traps used in the blue crab fishery and
in gillnets used for sierra.
The research
From almost no knowledge about the ray catches in the Gulf of
California in 1998, basic information on the fishery, biology and life
history styles of several commercially important rays is now recognized.
Specifically, the research priorities of Instituto Nacional de la Pesca
(INP) and preliminary results are:
- Fishing gear selectivity. Because the fishing gears are constructed
based on the fishers' experience, their characteristics and dimensions
inevitably vary. Panels of different mesh size can be used and various
types of net. Catch performance of gillnets in terms of selectivity is
currently being examined. As expected, preliminary results have
indicated different impacts on the population depending on the size
selectivity properties of gillnets.
- Embryonic growth. Monitoring pregnant females in the catch is
used to estimate the season of parturition and the relative area of
pupping grounds in Sonora state. Synchronization between embryonic
growth of several species of rays and average surface temperature of
the Gulf of California has been found.
- Fecundity. The number of pups produced by species
demonstrates the wide range of litter sizes. Some species are
recognized as highly productive such as Rhinobatos spp. (3-10
pups), and Gymnura marmorata (2-15 pups). Contrarily, species
such as Rhinoptera steindachneri (1 pup) and Mobula (1 pup) have an
extraordinary low fecundity.
- Maturity. Macroscopic sexual organs and histological surveys of
shell glands and testes for several species are examined from specimens
to investigate the possibility of sperm storage as a reproductive strategy,
and for validation of the size at maturity. The maturity stages of the
species are being compared to the selectivity of gillnets in order to
estimate the trend of the gear to retain juveniles.
Regulation and management issues
Shark management in México is still in the process of implementation
due to radical opposition by the recreational sector demanding the
inclusion of allowable proportions of billfishes as bycatch by longliners
and drift gillnet vessels. A summary of regulation guidelines for the
shark fishery was described by Castillo et al. (1998). Regulation of the
shark fishery also includes measures for rays. Unfortunately, the main
causes retarding the implementation of the regulations for sharks are of
political order going beyond the facilities of the INP, and currently, the
commercial ray fishery is not regulated.
However, through the INP, a new instrument for fisheries
management has been developed, the Carta Nacional Pesquera,
CNP (National Fisheries Chart). The CNP has legal and obligatory
status and brings encouraging possibilities to incorporate the
scientific findings of a particular fishery resource (either a single
species or a group of species) identified as a Fishing Management
Unit (FMU). This management tool will allow INP to build a record
summarizing the state of knowledge of a specific FMU which could
be implemented and updated annually. Anyone who is able to
contribute to the knowledge of a certain resource can incorporate
information via the Internet (http://inp.semarnap.gob.mx/
convocatoria/). This information is then reviewed and refereed by
a panel of experts. In this way, information on ray resources has
already been submitted and is currently undergoing the review
process. Ironically, regulation of rays in the Gulf of California could
be implemented faster than the Federal Management Plan for
sharks (which includes ray-like species), which has been in the
planning and development stages for at least seven years.
Legally protected elasmobranch species in Mexico
Manta rays Manta birostris, Mobula japanica and Mobula lucasana
have been protected since March 25, 1994 in the 12 miles perimeter
surrounding the Revillagigedo archipelago (Isla San Benedicto, I. Clarion,
Roca partida, I. Socorro and I. Guadalupe) in the Mexican Pacific.
Commercial fishing is legal in other areas (Camhi et al., in prep).
References
Camhi, M. et al. Global Status of Sharks. In preparation. Occasional
Paper of the IUCN Species Survival Commission. IUCN/SSC Shark
Specialist Group. IUCN, Gland, Switzerland.
Castillo-Geniz, J. L., J. F. Márquez-Farias, M. C. Rodríguez de la Cruz,
E. Cortés and A. Cid del Prado. 1998. The Mexican artisanal shark
fishery in the Gulf of Mexico: towards a regulated fishery. Mar.
Freshwater Res. 49:611-20.
Garcia-Caudillo, J. M., M. A. Cisneros-Mata and A. Balmori. 2000.
Performance of a bycatch reduction device in the shrimp fishery of
the Gulf of California, Mexico. Biological Conservation 92:199-205.
J.Fernando Márquez-Farias
Instituto Nacional de la Pesca. Programa Tiburón.
Centro Regional de Investigación Pesquera, Calle 20 Sur,
605. CP 85400 Guaymas, Sonora, México.
Fax: (622) 22- 2-59-25
Email: fmarquez@tetakawi.net.mx
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