Pteroplatytrygon violacea

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES DASYATIDAE

Scientific Name: Pteroplatytrygon violacea
Species Authority: (Bonaparte, 1832)
Common Name(s):
English Pelagic Stingray, Blue Stingray
French Pastenague Violette
Spanish Raya Negra
Synonym(s):
Trygon violacea Bonaparte, 1832
Taxonomic Notes: Originally described and named Trygon violacea by Bonaparte in 1832. Subsequent workers on Dasyatidae phylogenetic relationships suggested other generic affinities for Bonaparte's species. These include Dasyatis violacea and most recently Pteroplatytrygon violacea, the current valid name.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2009
Date Assessed: 2007-02-16
Assessor(s): Baum, J., Bianchi, I., Domingo, A., Ebert, D.A., Grubbs, R.D., Mancusi, C., Piercy, A., Serena, F. & Snelson, F.F.
Reviewer(s): Musick, J.A., Kyne, P.M., Cavanagh, R.D., Valenti, S.V. & IUCN SSG Pelagic Shark Red List Workshop participants (Shark Red List Authority)
Justification:
The pelagic stingray is widespread, with an almost circum-global distribution, throughout tropical and subtropical areas of the Pacific, Atlantic and Indian Oceans. It is perhaps the only species of stingray that occurs in pelagic, oceanic waters. The species is taken as bycatch in pelagic longline fisheries around the world. It is caught frequently by tuna and swordfish longliners and mostly discarded, but is retained and utilised in some areas (for example Indonesia). Post-discard survival rates are thought to be low in some areas because the fish are often discarded with serious mouth and jaw damage. Analyses of research surveys conducted with pelagic longlines in the 1950s and recent (1990s) observer data from commercial pelagic longline fisheries suggest increases in CPUE in the tropical Pacific Ocean and Northwest Atlantic. Although there is some debate as to consistency of reporting of pelagic stingrays in fisheries statistics and data are lacking from several areas of the species? range, there are no data to suggest that significant declines have occurred in this species. Increasing fishing effort in pelagic fisheries, owing to decreasing abundance of target species (swordfish and tunas) will result in an increase in catches of this species and associated high discard mortality in some areas. Careful monitoring is therefore required, however, given increasing trends observed in some regions, this species? widespread distribution, and in the absence of evidence to suggest significant declines it is currently assessed as Least Concern globally.

Geographic Range [top]

Range Description:This stingray is widespread, with an almost circumglobal distribution, throughout tropical and subtropical areas of the Pacific, Atlantic and Indian Oceans, between 52°N-50°S and 167°W and 180°E (Mollet 2002).
Countries:
Native:
Algeria; Antigua and Barbuda; Australia; Barbados; Benin; Brazil; Cameroon; Canada; Chile; Costa Rica; Côte d'Ivoire; Dominica; Ecuador; El Salvador; Equatorial Guinea; France; Gabon; Ghana; Grenada; Guatemala; Honduras; Indonesia; Ireland; Italy; Japan; Liberia; Libya; Madagascar; Mexico; Mozambique; New Zealand; Nicaragua; Nigeria; Panama; Paraguay; Peru; Saint Lucia; Sierra Leone; South Africa; Spain; Taiwan, Province of China; Togo; United States; Uruguay
FAO Marine Fishing Areas:
Native:
Atlantic – western central; Atlantic – northeast; Atlantic – eastern central; Atlantic – southwest; Atlantic – southeast; Atlantic – northwest; Indian Ocean – western; Indian Ocean – eastern; Mediterranean and Black Sea; Pacific – southeast; Pacific – northeast; Pacific – northwest; Pacific – eastern central; Pacific – western central; Pacific – southwest
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: The population structure, migratory patterns and reproduction cycles are not well known throughout most of this species' range.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: This is perhaps the only species of stingray that occurs in pelagic, oceanic waters (Last et al. 1994). It is usually found from the surface to 100 m depth over deep water (Mollet 2002), but has been reported to 238 m (Bester et al. 2007). It is a relatively small ray, attaining a maximum size of 80 cm disc width (DW) (Mollet et al. 2002). Females reach maturity at 39-50 cm DW (Wilson and Beckett 1970, Mollet et al. 2002, Neer 2008, Forselledo et al. 2007), and males at 37-50 cm DW (Wilson and Beckett 1970, Mollet et al. 2002, Neer 2008). Females mature at 3 years, males mature at 2 years and longevity is about 10 years (Wilson and Beckett 1970, Mollet et al. 2002, Neer 2008).

Reproduction is viviparous with histotrophy and the gestation period is less than 2-4 months (Ranzi and Zezza 1936, Tortonese 1956, Wilson and Beckett 2002, Forselledo et al. 2007). Copulation takes place in spring and females move inshore during summer to give birth (Whitehead et al. 1984, Tortonese 1956, Forselledo et al. 2007.). Females give birth to 4-13 pups per litter (average 6) (Ebert, 2003, Neer 2008, Tortonese, 1956, Fisher et al. 1987), and newborn stingrays measure approximately 14.3-24.1 cm DW (mean range) (Mollet et al. 2002, Mollet 2002).

In the northeast and eastern central Pacific there appears to be two discrete populations of this stingray, one migrating from eastern Pacific equatorial waters to off the California coast, and a second central Pacific population that migrates northwards, sometimes as far as Japanese and British Columbia waters (Ebert 2003). This suggests that these stingrays may have a fairly complicated population structure, but unfortunately virtually nothing is known about this or the abundance of this ray at this time. Females in the eastern Pacific population are thought to give birth in winter in warmer water off the coast of Central America, before migrating to higher latitudes nearer the coast including the Southern California Bight (Mollet 2002). Information from the western and central Pacific also suggests that females give birth in November-March in warmer water near the equator (Mollet 2002). In the Mediterranean Sea, the migration pattern appears to be different from that in the eastern Pacific, with females giving birth in the Bay of Naples before the rays migrate to warmer water (Lo Bianco 1909, Ranzi 1933, Mollet 2002). Rays in the Bay of Naples appeared to migrate as the water became colder. In the Southwest Atlantic, the population existing off Brazil possibly carries out its reproductive cycle in water southeast of Brazil and Uruguay on the slope and in oceanic waters, migrating towards the tropical zone to give birth (Forselledo et al. 2007).

Data from pelagic longline fisheries in the Southwest Atlantic show that the proportion of males in the captures is greater than females (ratio of 1.8:1 (n=1317)). Conversely, other data available for the eastern Pacific and western Atlantic Oceans indicate that there is a significantly higher ratio of females to males observed. Females outnumbered males 2:1 to 7:1 in the eastern Pacific samples and at a ratio greater than 3:1 for the western Atlantic (Wilson and Beckett 1970, D.B. Holts, unpublished data, Neer 2008).
Systems: Marine

Threats [top]

Major Threat(s): The major threats to pelagic stingray populations are pelagic longline fisheries for tunas, billfishes, and other pelagic shark species (Neer 2008). This species is caught frequently by tuna and swordfish longliners and mostly discarded, but is retained and utilised in some areas (for example Indonesia) (Domingo et al. 2005, Mollet 2002, Vaske 2002, A. Amorim pers. comm., Forselledo et al. 2007, White et al. 2006). The magnitude of regional and indeed global catch is currently unknown.

There is evidence for skewed sex ratios in this species (see Habitat and Ecology above). Whether these ratios are obtained in actual fisheries bycatch is unknown, however if so, an asymmetric take of this species could potentially impact the long-term stability of pelagic stingray populations (Neer 2008).

South Atlantic
Of 2.054 pelagic stingrays captured between 2001-2005 by the Uruguayan longline fleet in the South Atlantic Ocean, 35% were dead when discarded, 50% were discarded alive and the state of 15% could not be determined. However, these stingrays are often smashed against the side of fishing boats to remove the hooks as the fishermen are afraid of being stung. As a result most pelagic stingrays are discarded with serious mouth and/or jaw damage and therefore there is concern that survival is ultimately low, even in the group discarded alive above (Domingo et al. 2005, Forselledo et al. 2007.).

Annual CPUE data for the Uruguayan longline fleet, operating in the Southwest Atlantic, between 2000-2006, varied between 0.27 (2001) to 1.2 (2005) individuals per 1,000 hooks (0.76 in 2006), with no significant trend (Forselledo et al. 2007). Large aggregations are captured in some areas, resulting in very variable CPUEs and large numbers taken on fewer hooks (78.2 individuals/1000 hooks in the South Atlantic) (Forselledo et al. 2007).

Eastern Pacific
This stingray appears to be very common in the eastern Pacific, although catch data for this species is very uneven. There is some debate as to consistency of reporting of pelagic stingrays. Observers on pelagic shark research cruises and tuna longliners reportedly do not record catch records of these species in a consistent manner and discussions with observers in the North Pacific suggest that stingrays, most likely referable to P. violacea, are not being recorded on a regular basis (L. Jordan pers. comm. August 2004, D.A. Ebert pers. obs. 2004).

A study in the tropical Pacific Ocean comparing research surveys conducted with pelagic longlines in the 1950s with recent (1990s) observer data from the commercial pelagic longline fishery suggests that pelagic stingrays have increased in the region (Ward and Myers 2005). Surveys in the 1950s caught no pelagic stingrays, and interviews with scientists who conducted the surveys confirmed that they neither caught nor saw any pelagic stingrays, but certainly would have recorded them if they had (Ward pers. comm.).

Pelagic stingrays are also discarded with serious mouth/jaw injuries off South America in the eastern Pacific and probably low chance of survival (Jimmy Martinez pers. comm.).

Northwest Atlantic
In the Gulf of Mexico, an analysis similar to that in the tropical Pacific Ocean, which compares 1950s research survey data with 1990s observer data from pelagic longlines suggests that there may have been a similar increase in pelagic stingrays in this region (R. Myers and J. Baum unpublished data).

Indian Ocean
This species was believed to be rare in the Southwest Indian Ocean, until it was revealed that these stingrays are actually quite commonly caught as bycatch of the longline fleet, but generally unreported (Forselledo et al. 2007.). Interviews with commercial longliners in this region have revealed that the fishermen were quite familiar with it, but that scientists were not (D.A. Ebert and P.D. Cowley unpubl. data). This species is scattered throughout Indonesia in open ocean areas, and is caught occasionally by pelagic gillnet and longline fisheries, whre it is retained for human consumption (White et al. 2006).

Mediterranean
This species is captured by pelagic longline fisheries operating in the Mediterranean Sea. This bycatch is almost certainly mostly discarded, with a low discard survival rate due to damage to jaws and/or mouth as a result of treatment on board fishing vessels. Again the magnitude of Mediterranean-wide catches is unknown. Reports of common stingrays Dasyatis pastinaca in pelagic fisheries catches in the Mediterranean may refer to pelagic stingrays Pteroplatytrygon violacea. In Italian seas pelagic stingrays are the most commonly caught elasmobranch species in the Albacore long line fisheries and the second most common elasmobranch catch in swordfish long line fisheries (Filanti et al. 1986, di Natale et al. 1995, Orsi Relini et al. 1999). Total bycatch of P. violacea in the swordfish fishery in the Ligurian Sea was estimated at ~2,000 (up to 20 per boat) in 1995, although the catch was smaller and more variable in 1996) (Mollet 2002). Rey and Alot (1984) reported the results of a swordfish longline surveys in Mediterranean Spanish waters, and recorded only two pelagic stingrays in 11 fishing operations (<0.001). The pelagic stingray is also occasionally taken by recreational fisheries (Fischer et al. 1987), which presumably does not have a significant impact on population numbers.

Conservation Actions [top]

Conservation Actions: No specific conservation measures in place. Further efforts should be made to gather data from longline fishing vessels and other commercial fishing operations that may encounter this species. Continued research efforts aimed at careful monitoring of populations of this species is required.

Bibliography [top]

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Citation: Baum, J., Bianchi, I., Domingo, A., Ebert, D.A., Grubbs, R.D., Mancusi, C., Piercy, A., Serena, F. & Snelson, F.F. 2009. Pteroplatytrygon violacea. In: The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 28 November 2014.
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