Narcine bancroftii is a shallow water species found on soft substrates from the intertidal zone to a depth of 35 m. Both oviducts appear to be synchronous in adult females. A 47 cm TL female caught in Maranhão, Brazil, contained embryos which were aborted on landing on the vessel. Oviducts are very thin-walled, transparent and puncture easily. The smallest female containing embryos (aborted) was 36.0 cm TL (Carvalho 1999).

Red List Category

Red List Criteria

Version

2007

Carvalho, M.R. de, McCord, M.E. & Myers, R.A.

Fowler, S.L. & Kyne, P.M. (Shark Red List Authority)

Narcine bancroftii is a shallow water species found on soft substrates from the intertidal zone to a depth of 35 m. The species has a wide range in the Western Atlantic from North Carolina, through the Gulf of Mexico, the Caribbean, the Lesser and Greater Antilles and the north coast of South America to at least Maranhão in northern Brazil. The southern extent of its range is uncertain due to previous records representing the Southwest Atlantic endemic, N. brasiliensis. The species reaches ~60 cm TL, females are reported to have a fecundity up to ~20 pups, and the species is characterized by a very low age at maturity in females of two years. The species is captured as bycatch by inshore shrimp trawl and other fisheries. It does not appear to be utilized and is discarded at sea, but survivorship rates are thought to be very low. Furthermore, abortion of embryos by captured gravid females is of concern. While specific catch data are lacking over most of the species' range, declines to 2% (95% confidence intervals 0.5 to 5%) of its baseline abundance in 1972 have been demonstrated in the Northern Gulf of Mexico. Shrimp trawl fishing is intense in that area and while the implementation of Turtle Exclusion Devices and Bycatch Reduction Devices has lowed overall bycatch rates, these mitigation measures are thought to be ineffective for this species due to it size and sluggish swimming ability. Given the species' very low age at maturity it would take a very intense fishery to locally eliminate this species; however, this has been demonstrated in the Northern Gulf of Mexico. Further data showing declines of a similar magnitude are available from the US east coast and Florida. While specific data are lacking, fishing activities, both artisanal and commercial in nature are generally intense and most often unregulated in shallow inshore waters of the remainder of the species' range. Given that large declines have been documented in US waters where data are available, there is no reason to suspect that similar declines have not also occurred elsewhere across the species' range. The species is therefore globally assessed as Critically Endangered, based on observed declines in US waters and inferred declines throughout the rest of the species' range. Information from outside US waters is a priority.

Although this species exhibits an extensive distribution, taxonomic revision may result in subdivision of the species in the future, thereby restricting its range (Carvalho 1999a). This will lead to a subsequent decrease in population size.

Unknown

Electric rays are sluggish swimmers, with small home ranges, highly localized within an area and concentrating in surf zones adjacent to barrier beaches and on offshore sand bars in warm months and moving offshore in winter (Rudloe 1989), making them susceptible to localized population depletion. The species is captured as bycatch by inshore shrimp trawl seining net fisheries. It does not appear to be utilized and is discarded, but survivorship rates are thought to be very low. Furthermore, gravid females of the species have been observed to abort embryos upon capture and so even if discarded individuals survive, reproductive output is reduced. While specific catch data are lacking over most of the species range, declines to 2% (95% confidence intervals 0.5 to 5%) of its baseline abundance in 1972 have been demonstrated in the Northern Gulf of Mexico, most probably caused by shrimp trawling (Shepherd and Myers 2005). Shrimp trawl fishing is intense in that area, particularly in shallow waters (thus coinciding with the bathymetric range of N. bancroftii), with 4 to 5 million trawl hours annually (Shepherd and Myers 2005). While data in Shepherd and Myers (2005) compared the time period 1972 to 2002, the actual severity of declines may have been underestimated as shrimp trawling began in the region during 1912 to 1915 (Shepherd and Myers 2005). Similar high rates of decline are seen in the US coastal areas between Cape Canaveral (Florida) and Cape Hatterus (North Carolina) in US trawl surveys between 1989 and 2001 (a decline to 5% during this period). Furthermore, similar rates of decline are seen between 1994 and 2004 from diver surveys (data from Reef Environmental Educational Foundation) in eastern Florida and the Florida Keys. These declines may not be representative of the entire range, but these are the only regions with reliable survey data, and should be representative of regions with similar fishing impact. While specific data are lacking, fishing activities, both artisanal and commercial in nature are generally intense and most often unregulated in shallow inshore waters of the remainder of the species' range. See Fowler et al. (2005) for regional and country overviews. Given that large declines have been documented in US waters where data are available, there is no reason to suspect that similar declines have not also occurred elsewhere across the species' range where fishing activities are intense and unregulated. Pollution and oil exploration may also adversely affect the habitat of N. bancroftii, although no specific information is available.

There are no conservation measures directed at this species. While the implementation of Turtle Exclusion Devices and Bycatch Reduction Devices in shrimp trawl fisheries in the Northern Gulf of Mexico has lowed overall bycatch rates (for example see Steele et al. (2002), these mitigation measures are thought to be ineffective for this species due to it size and sluggish swimming ability. Details of bycatch in coastal fisheries throughout the rest of the species' range (i.e., outside of US waters) is required to determine the impact of fishing activities and allow for a more robust global assessment.