Myliobatis californicus 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Chondrichthyes Myliobatiformes Myliobatidae

Scientific Name: Myliobatis californicus
Species Authority: Gill, 1865
Common Name(s):
English Bat Ray
Spanish Raya Murciélago, Poncho Gris, Tecolote
Myliobatis californica Gill, 1865
Taxonomic Source(s): White, W.T. and Naylor, G.J.P. 2016. Resurrection of the family Aetobatidae (Myliobatiformes) for the pelagic eagle rays, genus Aetobatus. Zootaxa 4139(3): 435-438.
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: 2015
Date Assessed: 2014-09-13
Assessor(s): van Hees, K., Pien, C., Ebert, D.A., Cailliet, G.M. & Smith, W.D.
Reviewer(s): Machura, B. & Lawson, J.
Facilitator/Compiler(s): Walls, R.H.L. & Dulvy, N.K.
Bat Ray (Myliobatis californicus) occurs from Oregon, United States, to Baja California, México (including the Gulf of California) in the eastern Pacific Ocean. This eastern Pacific coastal ray is relatively fast-growing, reaching maturity at around 2-3 years for males and five years for females. It produces up to 12 pups per year although smaller litter sizes are more common.

Bat Ray is caught in artisanal multi-species elasmobranch fisheries in México, is obtained as bycatch in demersal trawls, longlines, and gillnets in the United States and México, is caught in recreational fisheries in the United States, and was historically targeted in the United States. There are no reliable population estimates, however this species has been recorded in artisanal elasmobranch fishery surveys in the Gulf of Mexico and in species-specific landings in California. In artisanal elasmobranch fisheries, this species was relatively common in catches along the mainland coast of Mexico (Sorona), and much less common in catches from the Baja peninsula. Commercial bycatch landings of this species have generally increased from 2001-2014, and recreational fishing surveys suggested that population abundance increased from the 1950s to the 1990s, which has been reinforced by recent fisheries-independent surveys from 2013 to 2014. Additionally, fisheries in California that historically targeted this species as a nuisance, ceased in 1994.

Given the fast growth and early maturity of this species, as well as patterns that suggest an increase in abundance in Californian waters, and commonality in catches along the mainland coast of Mexico, this species is considered to be Least Concern. However, it is unknown if the rarity of this species in the Baja peninsula suggest natural low abundance or is a result of overfishing, so overall population trend remains unknown. Improved recording and monitoring of landings in Mexican artisanal and industrial fisheries are needed.
Previously published Red List assessments:

Geographic Range [top]

Range Description:Bat Ray occurs from Oregon, United States, 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
Additional data:
Lower depth limit (metres):180
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:No information on the population size or subpopulations is available for this species. However, the Pacific coast and Gulf of California stocks may be disjunct subpopulations as there are few taken in the southern Gulf of California (C. Villavicencio-Garayzar pers. comm.). The highest abundances in estuaries along the Pacific coast 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 often observed and captured on the Pacific coast of Baja and the northern Gulf of California, but are uncommon in the southern Gulf of California.

A survey of artisanal fishers targeting elasmobranchs in the Gulf of California covered landing sites in both Baja California and the Mexican mainland (Sonora). This survey found that Bat Ray comprised 5.6% of the chondrichthyan landings in 1998-1999, and was considered one of the five most prominent taxa found in landings in 1999 (accounting for 3.0%). Only three species accounted for >5% of the catch in either year, so these landings are significant. Bat Ray specimens that were examined were mostly immature, females comprised the largest size classes and were of larger mean sizes than males, and the overall landed sex ratio was male-biased (Bizzarro et al. 2007). When broken down by region, Bat Ray was one of five taxa that accounted for the greatest proportion of the ray landings along Sonora, Mexico (1.2% of the total catch; Bizzarro et al. 2009a), and comprised a much smaller proportion of the total chondrichthyan catch on Baja California (only 0.3% of the total catch, and were only encountered in autumn and winter; Bizzarro et al. 2009). On the Pacific side of Baja California, fishery surveys in the 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 other information is available on the species' contribution to bycatch in other artisanal or trawl fisheries, but they are known to be taken in shrimp trawls.

Commercial bycatch of skates and rays in California reference Bat Ray as one of the four most common taxa in these landings, although not all caught skates and rays are identified to species (Leet et al. 2001). A report on the status of skate and ray populations in California, noted that while landings underwent an increase from 103 metric tons (mt) in 1989 to 868 mt in 1999, this does not necessarily reflect an increase in abundance (Leet et al. 2001). In species-specific commercial landings data in California, Bat Ray landings increased between 2001 (0.09 mt) and 2012 (6.93 mt). The past two years (2012 and 2013) recorded much lower landings of 2.84 and 3.38 mt, respectively (California Department of Fish and Wildlife).

In Humboldt Bay, California, Bat Ray were persecuted because of perceived predation on commercial oyster beds. This activity was taken under permit by the oyster company and an annual average of over 1,100 individuals were caught, with a total reported catch of 42,996 rays from 1956 to 1992 (Gray 1994, Gray et al. 1997). Bat Ray 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 Ray fed extensively on red rock crabs, a major oyster predator (Gray 1994, Gray et al. 1997).

Carlisle et al. (2008) analysed recreational fishing derby data from 1951 to 1995 in Elkhorn Slough, California. Derbies were held in the summer, in an attempt to control shark and ray populations that were suspected of reducing shellfish and finfish populations in the slough. Of the total catch of all the derbies analysed, Bat Ray were the most abundant species, with a total of 3,310 (55.6%) individuals caught.  Although fishing effort in these derbies increased through the decades, the average number of bat rays landed per derby decreased slightly from 63 in the 1950s to 50 in the 1990s. However, the relative abundance of bat rays steadily increased from 47% in the 1950’s to 68% in the 1990s. As the other species in the slough saw declines in relative abundance, these data suggest that Bat Ray may not be as susceptible to fishing pressure. Additionally, Bat Ray age, size and sex structure remained stable throughout the derbies, indicating fishing pressure did not dramatically impact the population. The derbies concluded in 1995, and fishing pressure on this species was greatly reduced in this area. Gill net fishing for sharks and rays in Elkhorn Slough was conducted from 2013–2014 by a student at Moss Landing Marine Laboratories. Although fishing was conducted with a different gear type at a different location in the slough, Bat Ray, especially immature individuals, were the most abundant comprising 62.3% of the catch (van Hees, 2014, unpublished data).
Current Population Trend:Unknown
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:Bat Ray is 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, this species occurs along the open coast and around islands where it frequents kelp beds and sandy bottoms near rocky reefs and sandy beaches.

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 Harbour. 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, Bat Ray 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 Bay Ray 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 this ray.

The reproductive mode of Bay Ray is histotrophy (Hamlett 2005). Females produce up to 12 offspring (more commonly smaller litter sizes) in an annual reproductive cycle, with gestation lasting nine to twelve months (Baxter 1980, Martin and Cailliet 1988a). The pups are born at 22-35.6 cm disc width (DW) (Baxter 1980, 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, reaching asymptotic size (159 cm DW) in 24 years (Martin and Cailliet 1988b). Age at 50% maturity for females has been observed by Martin and Cailliet (1988a) to be 5 years, at 88.1 cm DW. Males reportedly first mature at around 2-3 years of age, and size at 50% maturity occurs between 45 and 62.2 cm DW (Martin and Cailliet 1998a,b). 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. Maximum size is 180 cm DW (Eschmeyer et al. 1983).
Generation Length (years):14.5

Use and Trade [top]

Use and Trade: Bat Rays are valued for their meat.

Threats [top]

Major Threat(s): Bat Ray is caught in artisanal multi-species elasmobranch fisheries in México, is also obtained as bycatch in demersal trawls, longlines, and gillnets in the United States and México, is caught in recreational fisheries in the United States, and was historically targeted in the United States.

Conservation Actions [top]

Conservation Actions: 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. 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 Ray and Pacific Angel Shark (Squatina californica; Leet et al. 2001). Despite the fact that there are no formal conservation measures, the demand for Bat Ray has been relatively low allowing for some protection for this species, at least within the centre of the known United States distribution. More needs to be learned about the status of critical reproductive and nursery habitat. If fishing mortality increases within regulatory constraints, could be problematic or this species, although it is unknown how much fishing pressure this species can withstand. 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: van Hees, K., Pien, C., Ebert, D.A., Cailliet, G.M. & Smith, W.D. 2015. Myliobatis californicus. The IUCN Red List of Threatened Species 2015: e.T39416A80677869. . Downloaded on 24 January 2017.
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