|Scientific Name:||Dasyatis longa|
|Species Authority:||(Garman, 1880)|
Dasyatis longus (Garman, 1880)
|Taxonomic Notes:||Garman originally designated the species as Trygon longa in 1880. Garman later referred to the species as "longus" in 1913, however, the species name longa has precedence.
Differentiation between D. longa and D. dipterura can be through examination of the tail folds. Dasyatis longa possess only a short lower tail fold whereas D. dipterura has both an upper and lower caudal folds present. Although D. longa frequently has a tail length that is considerably greater than its body length, the thin whiptails of dasyatids are often damaged and vary considerably among individuals. Tail length alone is not a useful determinant between these species.
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Reviewer(s):||Bizzarro, J.J., Kyne, P.M. & Fowler, S.L. (Shark Red List Authority)|
A large (to 158 cm disc width) batoid distributed in the eastern Pacific from México to Colombia, occurring on the continental shelf to at least 90 m. Extremely limited information is available on Dasyatis longa. Misidentification of the species may confound or further limit clarity of fisheries and biological details due to morphological similarities with its eastern Pacific congener, D. dipterura. The relatively large body size of the species could be associated with slow growth and extended longevity. This potential, coupled with the observed low fecundity of 1 to 5 offspring suggests that the species could be highly vulnerable to fisheries, particularly when females move inshore to give birth. However, it may occupy deeper waters for much of the year than are typically exploited by artisanal fisheries. It represents only a small proportion of the total observed elasmobranch landings in the Gulf of California. Detailed information on landings of D. longa is unavailable outside of México, although it is likely to be taken by inshore fisheries throughout its Central American range. Based on the extremely limited information pertaining to the biology, distribution, and fisheries of this species, it is classified as Data Deficient. However, given its potential vulnerability and the unregulated fishing pressure across its range, research should be directed at better defining its conservation status.
|Range Description:||Reported from the central Pacific coast of Baja California, México to Colombia including the Galapágos Islands, and possibly north to San Diego, California, USA (Nishida and Nakaya 1990, Acero and Franke 1995, Villavicencio-Garyazar 1995). Limited records of the species occurrence are available.|
Native:Colombia; Costa Rica; Ecuador (Galápagos); El Salvador; Guatemala; Honduras; Mexico (Baja California, Baja California Sur, Chiapas, Colima, Guerrero, Jalisco, Michoacán, Nayarit, Oaxaca, Sinaloa, Sonora); Nicaragua; Panama
|FAO Marine Fishing Areas:||
Pacific – eastern central; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||No information is available on the abundance, population structure, or population dynamics of this species.|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||
Dasyatis longa occurs to depths of at least 90 m over sandy bottoms or near reefs (Michael 1993, Acero and Franke 1995). Biological information on the species is sparse. Villavicencio-Garayzar et al. (1994) provided details on the reproductive biology of the species based on 23 female and 28 male specimens from Bahía Alemejas on the Pacific coast of Baja California Sur, México. Males greater than 82 cm disc width (DW) were determined to be mature and females were found to be mature at ~110 cm DW (Villavicencio-Garayazar et al. 1994). As in other myliobatoid rays, females possess a single functional ovary. The number of offspring per litter ranges from one to five and size at birth is approximately 40 cm DW (R. Hueter et al. unpublished data, Villavicencio-Garayazar et al. 1994). Gravid females have been captured containing near term embryos in shallow estuaries and tidal creeks in the Bahía Magdalena lagoon complex during late summer months. It is possible that these areas are used as pupping or nursery grounds with females returning to deeper water following parturition (W. Smith personal observation). Mating may occur in the summer shortly after pupping. The gestation period is estimated 10 to 11 months (Villavicencio-Garayazar et al. 1994). Diet is reported to consist primarily of crustaceans (Beebe and TeeVan 1941). Life history parameters below are taken from Villavicencio-Garayzar et al. (1994).
Life history parameters
Age at maturity (years): Unknown.
Size at maturity (disc width): Female: ~110 cm DW; Male: ~80 cm DW.
Longevity (years): Unknown.
Maximum size (disc width): at least 156 cm DW.
Size at birth (cm): Unknown.
Average reproductive age (years): Unknown.
Gestation time: 10 to 11 months.
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: 1 to 5 pups/litter.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Directed artisanal elasmobranch fisheries and indirect landings by unregulated demersal trawl, longline, and gillnet fisheries throughout the species' range.
The species is highly vulnerable to demersal gillnets. Tail spines are the source of entanglement in netting, making a wide range of mesh sizes effective for capturing juveniles as well as adults.
In addition to landings reported from the Gulf of California and the Mexican Pacific, the species is described as a component of the artisanal fisheries of Isla Gorgona, Colombia (Acero and Franke 1995). It is likely to contribute to artisanal fisheries throughout Central America, but no specific information is available.
In México, a moratorium on the issue of elasmobranch fishing permits was enacted in 1993, but no formal management plan has been implemented for D. longa specifically or most other chondrichthyans in México. Legislation is currently being developed in México to establish national elasmobranch fishery management, but progress has been seriously delayed. Elasmobranch fisheries are unmanaged throughout Central America, and attempts to regulate these fisheries would greatly improve conservation of D. longa and other chondrichthyans.
Elasmobranch landings in México and Central America are poorly monitored and lack species-specific details. Large sharks are typically grouped as "tiburónes" and small sharks as "cazonés" while all batoids are generally broadly termed "manta raya". Mexican federal fisheries agencies began providing slightly more taxonomic resolution of ray landings by recently listing several new categories. Landings of D. longa, however, may still not be determined as they are grouped as "manta raya" which may include dasyatid as well as urotrygonid and mobulid species. Improved clarity in catch records would provide an essential basis for detecting fishery trends. Expanded monitoring of elasmobranch catches in México, Central and South America are necessary to provide valuable species- and sex-specific information and improve our limited knowledge of the extent of these fisheries.
In addition to the much needed species-specific catch details, life history information including age, growth, longevity, movement patterns, habitat use, and further reproductive studies throughout its range. Fishery-independent surveys of this and other demersal elasmobranchs are necessary to provide estimates of abundance and biomass.
The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species in the region. See Anon. (2004) for an update of progress made by nations in the range of D. longa.
|Citation:||Smith, W.D. 2006. Dasyatis longa. The IUCN Red List of Threatened Species 2006: e.T60157A12315125. . Downloaded on 09 February 2016.|
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