Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Chondrichthyes Rajiformes Myliobatidae

Scientific Name: Myliobatis californicus
Species Authority: Gill, 1865
Common Name(s):
English Bat Ray
Spanish Poncho Gris, Raya Murciélago, Tecolote
Myliobatis californica Gill, 1865
Taxonomic Notes: Myliobatis californica Gill, 1865 was a misspelling of this species.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor(s): Cailliet, G.M. & Smith, W.D.
Reviewer(s): Kyne, P.M., Fowler, S.L. & Compagno, L.J.V. (Shark Red List Authority)
The Bat Ray was assessed as Least Concern on the 2000 Red List. It is updated here due to new and better information available and remains Least Concern globally but is assessed as Data Deficient in México.

This abundant eastern Pacific coastal ray is relatively fast-growing, reaching maturity at around 2 to 3 years for males and five years for females. It produces up to 12 pups per year although smaller litter sizes are more common. It is not a main target of any major fishery, being taken in the US primarily by recreational anglers and only secondarily by commercial fishermen. In México, it is taken in directed elasmobranch fisheries and as bycatch in other fisheries. There are no reliable population estimates, catch data are unreliable with some catches unreported or generically reported as "ray", and catch per unit effort data do not exist. However, it does not appear that the commercial or recreational catches pose any threat to this population in US waters, which represent a sizeable portion of its range and the main centre of distribution for this species. Myliobatis californicus is considered to be a species of Least Concern at the time of this assessment. Improved recording and monitoring of landings in Mexican artisanal and industrial fisheries are needed and the species is assessed as Data Deficient in the Mexican Pacific.
Previously published Red List assessments:
2000 Lower Risk/least concern (LR/lc)

Geographic Range [top]

Range Description: The bat ray occurs from Oregon, USA to Baja California, México (including the Gulf of California) in the eastern Pacific Ocean.
Countries occurrence:
Mexico (Baja California, Baja California Sur); United States (California, Oregon)
FAO Marine Fishing Areas:
Pacific – eastern central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The Pacific coast and Gulf of California stocks may be disjunct subpopulations, since there are few taken in the southern Gulf of California (C. Villavicencio-Garayzar pers. comm.). No information on the population size or subpopulations is available.

Centres of abundance in US Pacific coast estuaries appear to be Elkhorn Slough and San Francisco, Tomales, Humboldt, Morro, Santa Monica, and San Pedro Bays in California (Talent 1985, Gray et al. 1997, Ebert 2003). Other California bays such as Drakes Estero in northern California, and Alamitos, Anaheim, Newport, Mission, and San Diego Bays in southern California are also frequented by this species (Monaco et al. 1990). In México, these rays are uncommonly reported in the southern Gulf of California but are often observed or captured in the Pacific coast of Baja and the northern Gulf of California.
Current Population Trend: Unknown
Additional data:

Habitat and Ecology [top]

Habitat and Ecology: Bat rays are commonly found in shallow bays and have been reported from intertidal zones to 108 m but are more common in shallower waters (Morris et al. 1996). In southern California, it occurs along the open coast and around islands where it frequents kelp beds and sandy bottoms near rocky reefs and sandy beaches.

The reproductive mode of bat rays is aplacental viviparity. Females produce up to 12 offspring (more commonly smaller litter sizes) in an annual reproductive cycle, with gestation lasting about one year (Baxter 1980, Martin and Cailliet 1988a). The pups are born at ~20 cm DW (Martin and Cailliet 1988a). Females reach a larger size and age and have a growth coefficient (k) in the von Bertalanffy growth equation of 0.0995 (Martin and Cailliet 1988b), reaching its asymptotic size (~159 cm DW) in approximately 25 years. Age at maturity for females has been observed by Martin and Cailliet (1988a) to be ~5 years, at ~88 cm DW. Males reportedly mature at ~60 cm DW and an age of ~2 to 3 years. Ageing by means of counting rings in the vertebral centra of this species has not been validated, either by tagging or by vertebral marginal increment or centrum edge analyses. In southern Baja California, México, these rays apparently mature at smaller size than reported from California with males attaining maturity between 40 and 50 cm DW and females <70 cm DW have been found to be immature (Villavicencio-Garayzar 1995, 1996), however limited biological information on the species from this region is available.

In San Francisco Bay and Elkhorn Slough in Monterey County California, parturition appears to occur from March through June, with a peak in April and May. It also reportedly occurs at approximately the same time in other bays (Humboldt, Tomales, Morro, Santa Monica and San Pedro Bay) in California (Talent 1985, Martin and Cailliet 1988a). Bays and sloughs appear to be important nursery areas. Females are also thought to release their pups along more open coastal areas in southern California, and have been observed giving birth to young in water 1m in depth over a shallow flat in Catalina Harbor. Newly born pups are reportedly found in northern California sloughs in April and May; also in the shallow surf zone in more southerly areas such as Santa Monica Bay in southern California around late May and June (Talent 1985, Martin and Cailliet 1988a, Monaco et al. 1990). In Estero de Punta Banda along the northern portion of the Baja California peninsula, M. californicus abundance increases from October to a maximum in January and become uncommon in the spring and summer months (Beltrán-Félix et al. 1986). Peak abundance of bat rays in Bahía Almejas, México along the southern portion of the Pacific Baja California peninsula occurs in March and consists primarily of adults (Villavicencio-Garayzar 1995, 1996). Both locations appear to serve as pupping and reproductive grounds for the bat ray.

This ray is an opportunistic benthic feeder, consuming numerous types of bottom-dwelling invertebrates, including the eggs of some fish species such as herring, topsmelt, jacksmelt, and midshipman (Talent 1982). Pups caught in places like Elkhorn Slough consume crustaceans and molluscs (Barry et al. 1996). Bat rays are preyed upon by larger sharks such as the sevengill, Notorynchus cepedianus, and white, Carcharodon carcharias, (Ebert 1989) as well as pinnipeds. However, man is probably the most important predator. The bat ray occasionally occurs in epipelagic schools (Walford 1935, Roedel and Ripley 1950). Movement patterns may be associated with thermal tolerance or preference (Matern et al. 2000). Although it possesses a spine, this ray is not considered dangerous. Groups kept in aquaria have been observed to interact with each other and with visitors (G. and V. Dykhuizen, pers. comm).

Life history parameters
Age at maturity: 50% maturity: 5 years (Martin and Cailliet 1988b) (female); First maturity: 2 to 3 years (Martin and Cailliet 1988b) (male).
Size at maturity (disc width): 50% maturity: 88.1 cm DW (Martin and Cailliet 1988a) (female); Maturity: 45 to 62.2 cm DW (Martin and Cailliet 1988a), first maturity (Bahía Almejas): 50 cm DW, 100% maturity: 60 cm DW (Villavicencio-Garayzar 1996) (male).
Longevity: At least 24 years (females) (Martin and Cailliet 1988b).
Maximum size (disc width): 180 cm DW (Eschmeyer et al. 1983).
Size at birth: 22 to 35.6 cm DW (Baxter 1980, Martin and Cailliet 1988b).
Average reproductive age (years): Unknown.
Gestation time: 9 to 12 months (Martin and Cailliet 1988a).
Reproductive periodicity: Annual.
Average annual fecundity or litter size: 2 to 12 pups (Baxter 1980; Martin and Cailliet 1988a).
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Systems: Marine

Threats [top]

Major Threat(s): Directed artisanal elasmobranch fisheries (in México).

Recreational fisheries (in U.S.).

Indirect landings by demersal trawls, longlines, and gillnets (in U.S. and México).

Bat rays are not directly targeted but are landed in multi-species artisanal elasmobranch fisheries in México. Fishery surveys conducted in the Gulf of California (Notarbartolo di Sciara 1987, Hueter et al. unpublished data) and Bahía Magdalena lagoon complex (Villavicencio-Garyazar 1995, Bizzarro and Smith unpublished data) indicate that this species is not a common component of artisanal landings. No information is available on the species' contribution to bycatch in other artisanal or trawl fisheries, but they are taken in shrimp trawls.

In Humboldt Bay, California, bat rays were persecuted because of perceived predation on commercial oyster beds. This activity was undertaken under permit by the oyster company and an average of over 1,100 individuals (minimum in one year, two; maximum, 9,197) were removed from 1956, with a total reported catch of 42,996 rays from 1956 to 1992 (Gray 1994, Gray et al. 1997). Bat rays were captured by trawl, longline and trap, however, information on fishing effort is not available. Furthermore, there are no details of population size that would allow the detection of changes in density as a result of this removal policy, and so the localized affect of this practice is unknown. Gray (1994) demonstrated that predation by bat rays in oyster beds was in fact rare which later prompted a change in the oyster company permit and extermination effectively ceased. Ironically, bat rays fed extensively on red rock crabs, a major oyster predator (Gray 1994, Gray et al. 1997).

Conservation Actions [top]

Conservation Actions: The Bat Ray is presently one of the many species considered, but not yet actively regulated, under the Pacific Fishery Management Council's Groundfish Management Plan for the U.S. eastern Pacific. Additionally, the state has general restrictions on usage of certain types of commercial gear in the nearshore zone, which offers a good degree of protection for Bat Rays and Angel Sharks Squatina californica (Leet et al. 2001). Thus, despite the fact that there are no current conservation measures the demand for bat ray has been relatively low allowing for some protection for this species, at least within the centre of its U.S. distribution at the present time. More needs to be learned about the status of critical reproductive and nursery habitat. Possible future fishing mortality increases within regulatory constraints could be a concern if mature females become an increasingly important component of the catch, or if inshore fisheries develop that are efficient at targeting this species. Considering its localised and limited distribution, it is unknown how much additional fishing pressure might be necessary to exceed its intrinsic compensatory limits and subject it to recruitment overfishing. In addition, a re-assessment of the combined sport and commercial harvest is recommended.

In México, a moratorium on the issue of elasmobranch fishing permits was enacted in 1993, but no formal management plan has been implemented for M. californicus specifically or for most other chondrichthyans. However, legislation is currently being developed in México to establish national elasmobranch fishery management. Elasmobranch landings in México are poorly monitored and lack species specific details. All batoids are generally broadly termed "manta raya" in catch records. Although easily identified, these rays are rarely documented on a species-specific basis in México. Improved clarity in catch records would provide an essential basis for detecting fishery trends and are needed throughout the species' range. Expanded monitoring of directed elasmobranch catches and bycatch in México is necessary to provide valuable information on the biology and population status of these rays.

In addition to species-specific landings and bycatch details, life history information including age, growth, longevity, movement patterns, habitat use, and further reproductive studies throughout its range are needed from the southern portion of the species' range. Fishery-independent surveys of this and other demersal elasmobranchs are necessary to provide estimates of abundance and biomass. Tagging, tracking, and genetic studies are essential for determining the population structure, movement patterns, and possible subpopulations of this ray.

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 USA and Mexico. At the time of writing, the USA has developed a National Plan of Action (NPOA), while Mexico had developed a NPOA but implementation has been blocked by industry (Anon. 2004).

Citation: Cailliet, G.M. & Smith, W.D. 2006. Myliobatis californicus. The IUCN Red List of Threatened Species 2006: e.T39416A10232894. . Downloaded on 09 October 2015.
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