Batoid Species Research Articles

THE MESOPTERYGIAL VEIN: A RELIABLE VENIPUNCTURE SITE FOR INTRAVASCULAR ACCESS IN BATOIDS.

Intravascular access in batoid species is commonly achieved using the ventral coccygeal or radial wing vessels. However, these approaches can be difficult because of the presence of cartilage, lack of specific landmarks, species variation, and small vessel size in many species. This study used postmortem contrast radiography and gross dissection to develop landmarks for a new, dependable vascular access in three Myliobatiform species commonly maintained in captivity: Atlantic stingray (Hypanus sabinus), cownose ray (Rhinoptera bonasus), and smooth butterfly ray (Gymnura micrura). The mesopterygial vein provides quick vascular access and is suitable for administration of large fluid volumes and intravascular drugs. It is located immediately ventrolateral to the metapterygium cartilage, which sits adjacent to the coelomic cavity and supports the caudal half of the pectoral fin. Using the pectoral girdle and cranial third of the metapterygium cartilage as landmarks, vascular access can be achieved by directing a needle medially at approximately a 30° (adult cownose rays) or 45° angle (Atlantic stingrays, juvenile cownose rays, smooth butterfly rays) toward the metapterygium cartilage. Differences in the degree of needle direction are due to species and age-specific shapes of the metapterygium cartilage. The mesopterygial vein is an alternate site of quick and reliable venous access in batoid species.

DNA Barcode Reveals the Bycatch of Endangered Batoids Species in the Southwest Atlantic: Implications for Sustainable Fisheries Management and Conservation Efforts.

Today, elasmobranchs are one the most threatened vertebrate groups worldwide. In fact, at least 90% of elasmobranch species are listed in the International Union for Conservation of Nature (IUCN) Red List, while more than 40% are data-deficient. Although these vertebrates are mainly affected by unsustainable fishery activities, bycatch is also one of the major threats to sharks and batoids worldwide, and represents a challenge for both sustainable fishery management and for biodiversity and conservational efforts. Thus, in this study, DNA barcode methodology was used to identify the bycatch composition of batoid species from small-scale industrial fisheries in the southwest Atlantic and artisanal fisheries from southeast Brazil. A total of 228 individuals belonging to four Chondrichthyes orders, seven families, and at least 17 distinct batoid species were sequenced; among these individuals, 131 belonged to species protected in Brazil, 101 to globally threatened species, and some to species with trade restrictions provided by Appendix II of the Convention on International Trade in Endangered Species (CITES). These results highlight the impacts on marine biodiversity of bycatch by small-scale industrial and unmanaged artisanal fisheries from the southwest Atlantic, and support the implementation of DNA-based methodologies for species-specific identification in data-poor fisheries as a powerful tool for improving the quality of fisheries’ catch statistics and for keeping precise bycatch records.

Reproduction and embryonic development of the red stingray Hemitrygon akajei from Ariake Bay, Japan

The reproductive system of the red stingray Hemitrygon akajei was described from 1,418 specimens, 682 males and 736 females, sampled year-round (2003–2014) from Ariake Bay to provide reproductive life history information for conservation and management of the species. Females reach sexual maturity at a larger size than males with the size at 50% sexual maturity 522.2 mm disc width (DW) and 321.5 mm DW, respectively. Male stingrays had semen in the seminal vesicles year-round. Dental sexual dimorphism was aseasonal. The mating period is protracted, spanning 7 consecutive months October–April but ovulation occurred during May. This suggests female sperm storage, which has not been described for dasyatid stingrays. Females have a single functional ovary and uterus (left) and reproduce via aplacental viviparity with lipid histotrophy. Gestation required 3 months with parturition during late July and early August. Uterine eggs without macroscopic embryos were observed during the first half of gestation suggesting a short period of arrested development or diapause. Developmental cohorts based on morphological features were described for embryos and can be used to characterize embryo growth and development for other stingray species. Observations of foetal mortality (1.25%) and morphologically abnormal embryos (0.72%) were uncommon. Pregnancy rate was 90% and reproduction was annual and synchronous. Hemitrygon akajei fecundity ranged from 7 to 25 and increased with female size. Although H. akajei is a medium-sized dasyatid ray, it has the highest fecundity reported for any batoid species. Elasmobranchs life histories usually are associated with a low degree of productivity that results in rapid population decline with increased fishing pressure. Producing high numbers of small young is a successful reproductive strategy for H. akajei that may be partly responsible for their resilience to fishing pressure and continued abundance in Ariake Bay. This study is the first to describe reproduction of H. akajei, an economically important top predator inhabiting coastal ecosystems throughout Asia.

Population structure and male-biased dispersal in the short-tail stingray Bathytoshia brevicaudata (Myliobatoidei: Dasyatidae)

Selective pressures driving dispersal in vagile species often differ between males and females, resulting in sex-biased dispersal. Male-biased dispersal is common in mammals, where there is greater reproductive investment by females, and there is emerging evidence for a similar pattern in elasmobranchs. We examine the population structure of the short-tail stingray (Bathytoshia brevicaudata), a large, viviparous coastal species common in southern hemisphere waters. Using 11 nuclear (nDNA) microsatellite markers from 202 individuals in comparison to mitochondrial (mtDNA) data reported by Le Port and Lavery (J Hered 103:174–185, 2012), we elucidate patterns of dispersal at both southern hemisphere and New Zealand scales. At a global scale, estimates of population differentiation were comparable across marker types (microsatellite FST = 0.148, p 0.05) than for mtDNA (ϕST = 0.054, p < 0.05). Female-only data displayed a greater degree of population differentiation from both nDNA and mtDNA compared to male-only data, and population assignment tests indicated that males were significantly more likely to be immigrants to the population from which they were sampled. We estimate that within New Zealand, male-mediated gene flow is at least fivefold greater than female-mediated gene flow. This molecular evidence for sex-biased dispersal in a batoid species adds further support to male-biased dispersal as a recurrent pattern in viviparous elasmobranchs. Many elasmobranch species are vulnerable to extinction, and understanding movement patterns is crucial to management of threatened populations.

Deep-sea elasmobranch fauna with the first descriptions of genera Arynchobatis and Pseudoraja from the Miocene Yatsuo group in Toyama, central Japan

ABSTRACT Herein, we describe 22 deep-sea elasmobranch species of the early to middle Miocene Yatsuo Group found in central Japan. The deep-sea elasmobranch fauna of the Yatsuo Group comprises various Squaliformes species together with a few scyliorhinid members and batoids species. This study represents the first fossil record of the occurrence of Arhynchobatis and Pseudoraja. The Yatsuo fauna is divided into three assemblages: Kurosedani Formation, lower Higashibessho Formation, and upper Higashibessho Formation assemblages. The Kurosedani Formation and upper Higashibessho Formation assemblages include many Squalus but only few Squaliolus species, and scyliorhinids. The lower Higashibessho Formation assemblage comprises many Squaliolus species, but only few Squalus species. Squalus species inhabit in shallower deep sea, unlike other genera occurring in the Yatsuo Group, and also it is more frequent in the horizon deposited in the shallower deep-sea than in the other horizons. The frequency of demersal scyliorhinids decreases in the dysoxic environment at the bottom layer. Occurrence of the tropical-subtropical batoid species of Pseudoraja and Benthobatis indicates subtropical palaeoenvironments in central Japan during the early to middle Miocene. At present, species of these two genera are not distributed in areas surrounding Japan.

Preliminary analysis of the feeding habits of batoids from the genera &lt;i&gt;Mobula&lt;/i&gt; and &lt;i&gt;Myliobatis&lt;/i&gt; in Northern Peru

Abstract.- This study provides baseline information on the feeding habits of five batoid species from the genera Mobula and Myliobatis sampled from the small-scale driftnet fishery in northern Peru. The diets of Mobula mobular, Mobula munkiana and Mobula thurstoni consisted mainly of euphausiids. Dietary niche breadth indicated a pelagic feeding behaviour of a specialist and a trophic level of a secondary predator for both M. mobular and M. munkiana. In contrast, Myliobatis chilensis and Myliobatis peruvianus consumed mostly gastropods and crustaceans. Dietary niche breadth indicated a feeding behaviour of a benthic specialist and a trophic level of a secondary predator for Myliobatis chilensis.

Langhian rays (Chondrichthyes, Batomorphii) from Brielas, Lower Tagus Basin, Portugal.

The Langhian Vc unit of Brielas section (Caparica road, Almada), in the marine Miocene of the Lower Tagus Basin (West Portugal), is rich in batoid species. In this study, batoids are represented by 149 isolated fossil teeth and a single fossil dental plate collected from a bulk sample of washed and sorted sediment. A total of 12 species belonging to the orders Rhinopristiformes, Rajiformes, Torpediniformes and Myliobatiformes were identified. All genera and some species are known to have extant representatives. Aetobatus cappettai Antunes and Balbino, 2006, is described now from Langhian material which suggests it is older than previously supposed. The biogeographic ranges, environmental constraints and behaviour of the species described in this study point out to an infralittoral environment characterized by the dominance of warm water conditions, where episodic upwelling contributed to the occurrence of different types of batoids coexisting in the same habitat.

Elasmobranch diversity with preliminary description of four species from territorial waters of Bangladesh

There is a significant lack of data regarding the biodiversity of elasmobranchs in the territorial waters of Bangladesh, since that sharks and rays are not targeted by commercial fishing industry, but rather encountered as a bycatch. This paper updated the diversity of elasmobranchs in the territorial waters of Bangladesh. The study was carried out to identify two coastal areas of Patharghata, Barguna and Cox's Bazar between October, 2015 and September, 2016. Using fish landing station survey techniques, total 20 species of elasmobranch were encountered, including eight species of sharks and 12 species of batoids, under 14 genera, ten families. This is the most expended field based records of elasmobranch fishes of Bangladesh.&#x0D; Bangladesh J. Zool. 46(2): 185-195, 2018

Effect of body length, trophic position and habitat use on mercury concentrations of sharks from contrasted ecosystems in the southwestern Indian Ocean

The non-essential metal mercury (Hg) can have deleterious effects on health of organisms, and tends to bioaccumulate with age in long-lived organisms and to biomagnify along food webs. Because elasmobranchs are fished for human consumption and their Hg levels are frequently above the maximum Hg concentration recommended for fish consumption, understanding the drivers of Hg concentration is of considerable interest. Total Hg concentrations were analysed in muscle tissues of 14 shark and 2 batoid species (n = 339 individuals) sampled across multiple habitats (coastal, open ocean and bathyal) in the southwestern Indian Ocean. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were analysed to assess whether relative trophic position and foraging habitats affected Hg concentrations. Hg concentrations increased with δ15N and body length, highlighting the mechanisms of bioaccumulation and biomagnification in relation with the trophic position and size of the individuals. Habitats where elasmobranchs were collected also affected their Hg concentrations. Bathyal sharks had high Hg concentrations that were almost similar to those of oceanic species, despite their lower relative trophic position. Higher bioavailability of Hg due to its enhanced methylation in deeper waters was considered as the most likely explanation for this result. These results highlight that multiple factors contribute to mercury accumulation in elasmobranchs.

The valves of the cardiac outflow tract of the starry ray, Raja asterias (Chondrichthyes; Rajiformes): Anatomical, histological and evolutionary aspects.

The cardiac outflow tract of chondrichthyans is composed of the myocardial conus arteriosus, equipped with valves at its luminal side, and the bulbus arteriosus devoid of myocardium. Knowledge of the histomorphology of the conal valves is scarce despite their importance in preventing blood backflow to the heart. Current information on the subject refers to a single shark species. The present report is the first to describe the structure of the conal valves of a batoid species, namely, Raja asterias. Hearts from seven starry rays were examined using scanning electron microscopy and histochemical techniques for light microscopy. In all hearts, the conus showed four transverse rows of three pocket-like valves each. Each valve was composed of a leaflet and its supporting sinus. The leaflet had a stout central body, rich in glycosaminoglycans, which contained fibroblasts, collagen and elastin. The central body was surrounded by two thin fibrous layers, outer and inner, formed mainly by collagen. The valves of the anterior row, which were the largest of the valvular system, were attached proximally to the conus arteriosus and distally to the bulbus arteriosus, and not to the ventral aorta as previously reported for chondrichthyans. The arrangement of the anterior valves in the starry ray is an anatomical pattern that apparently has been preserved throughout the evolution of vertebrates.

Advances in understanding the roles and benefits of nursery areas for elasmobranch populations

Nursery areas are critical to the survival of many marine species, and it is widely accepted that elasmobranch species use nursery areas where they improve species fitness. A 2007 review proposed an approach to identify elasmobranch nursery areas to help clarify their location and use. Here we examine progress towards defining elasmobranch nurseries in the intervening ≥10 years. Many studies have used these criteria, and some have tested their effectiveness, but it is apparent that there is still much to learn. Our current understanding of elasmobranch nurseries is biased towards tropical coastal shark species with few studies of temperate, pelagic, deep-water or batoid species. Recent research has used the criteria to more accurately identify nursery areas, determine that some species may not use them and, at times, improve conservation and management. Results are also revealing that some areas considered to be nurseries do not meet the criteria. Although we have learned a great deal about the location and use of elasmobranch nurseries, there are still several questions to be answered and species to be considered. Continued application of nursery criteria and improved knowledge of nursery areas will lead to improved conservation and management systems.

Reproductive strategy of the Pacific cownose ray Rhinoptera steindachneri in the southern Gulf of California

Rhinoptera steindachneri is one of the most common batoid species in the artisanal gill net fishery of the Gulf of California. In this study we investigated its reproductive biology based on 317 specimens caught in Bahía de la Paz, Mexico. Females measured up to 94.2-cm disc width (DW) and males reached 82.5cm DW; there were no significant differences in size or weight between sexes. The median size at maturity was estimated at 68.5cm DW for males and 71.8cm DW for females, and the median size at pregnancy was 84.3cm DW. Only the left ovary and uterus were functional; a maximum of six preovulatory vitellogenic follicles per female was recorded, although uterine fecundity was one embryo per female. Ovulation and birth occurred in May, June and July, with birth sizes ranging from 38.1 to 42cm DW. R. steindachneri in Bahía de la Paz exhibited low fecundity, large size at maturity and birth and a continuous and synchronous annual reproductive cycle.

Descripción morfológica del aparato bucal de adultos de Urotrygon nana y U. rogersi (Urotrygonidae): diferencias intraespecíficas e interespecíficas

Background. Teeth can change significantly in shape and size depending on their position in the jaw, age and sex of the organism. Sometimes due to the loss of these teeth, an incomplete description of the dental morphology exists for several batoid species, which makes it difficult to evaluate intraspecific and interspecific differences. Goals. Describe the differences in tooth morphology as well as the arrangement of teeth in adults of two species of batoids (Urotrygon nana and U. rogersi) distributed over soft bottoms of the continental shelf of the Mexican tropical Pacific. Methods. After collecting the jaws of ten adult individuals of U. nana and U. rogersi we counted the number of rows and series of the first functional row, and described the shape of the cartilage and teeth. In addition, we identified the type of heterodonty. Results. Similarities between the cartilage and teeth of both species were observed. In both sexes of U. nana monognatic heterodonty was observed, with three dental morphotypes in Palatocuadrado and two in Meckel’s cartilage. U. rogersi has sexual heterodonty with just one morph. Conclusions. We believe it is necessary to expand the number of samples (taking into account the different stages of life), and generate additional ethological studies that provide information on the reproductive behavior of the species.

Batoid nurseries: definition, use and importance

Nursery areas are crucial for many elasmobranch species, providing benefits that increase fitness and survival. Shark nurseries are well studied and our knowledge of their function and importance has expanded over the past few decades. However, little attention has been given to batoid nurseries, with studies covering less than 6% of the 663 currently described species. Threats of extinction faced by batoids reinforce the importance of defining these critical habitats. This review synthesises current knowledge of batoid nursery areas to provide a better understanding of their ecological roles and importance. Historically, different criteria have been used to define viviparous and oviparous batoid nurseries, causing confusion that could lead to failure of conservation and management strategies by under-or overestimating the importance of areas and delaying effective action. We suggest the criteria used to identify shark nurseries be applied to juvenile batoids, standardizing this nursery definition for all elasmobranchs, but we also advocate for a second set of criteria that identifies egg case nurseries. Batoids are thought to play 3 main ecological roles in nursery areas: energetic links, bioturbators and mesopredators. Biotic and abiotic features affect abundance and distribution of batoids within nurseries and likely play a key role in their habitat use. However, analysis of batoid ecological roles in nursery areas is limited by the lack of research on their early life history stages. Thus, identification of areas that support sensitive life stages and an improved understanding of early life history are crucial for the efficient management and conservation of batoid species and their nurseries.

Species composition of the international shark fin trade assessed through a retail-market survey in Hong Kong.

The shark fin trade is a major driver of shark exploitation in fisheries all over the world, most of which are not managed on a species-specific basis. Species-specific trade information highlights taxa of particular concern and can be used to assess the efficacy of management measures and anticipate emerging threats. The species composition of the Hong Kong Special Administrative Region of China, one of the world's largest fin trading hubs, was partially assessed in 1999-2001. We randomly selected and genetically identified fin trimmings (n = 4800), produced during fin processing, from the retail market of Hong Kong in 2014-2015 to assess contemporary species composition of the fin trade. We used nonparametric species estimators to determine that at least 76 species of sharks, batoids, and chimaeras supplied the fin trade and a Bayesian model to determine their relative proportion in the market. The diversity of traded species suggests species substitution could mask depletion of vulnerable species; one-third of identified species are threatened with extinction. The Bayesian model suggested that 8 species each comprised >1% of the fin trimmings (34.1-64.2% for blue [Prionace glauca], 0.2-1.2% for bull [Carcharhinus leucas] and shortfin mako [Isurus oxyrinchus]); thus, trade was skewed to a few globally distributed species. Several other coastal sharks, batoids, and chimaeras are in the trade but poorly managed. Fewer than 10 of the species we modeled have sustainably managed fisheries anywhere in their range, and the most common species in trade, the blue shark, was not among them. Our study and approach serve as a baseline to track changes in composition of species in the fin trade over time to better understand patterns of exploitation and assess the effects of emerging management actions for these animals.

Large batoid fishes frequently consume stingrays despite skeletal damage.

The shapes of vertebrate teeth are often used as hallmarks of diet. Here, however, we demonstrate evidence of frequent piscivory by cartilaginous fishes with pebble-like teeth that are typically associated with durophagy, the eating of hard-shelled prey. High-resolution micro-computed tomography observation of a jaw specimen from one batoid species and visual investigation of those of two additional species reveal large numbers of embedded stingray spines, arguing that stingray predation of a scale rivalling that of the largest carnivorous sharks may not be uncommon for large, predatory batoids with rounded, non-cutting dentition. Our observations demonstrate that tooth morphology is not always a reliable indicator of diet and that stingray spines are not as potent a deterrent to predation as normally believed. In addition, we show that several spines in close contact with the jaw skeleton of a wedgefish (Rhynchobatus) have become encased in a disorganized mineralized tissue with a distinctive ultrastructure, the first natural and unequivocal evidence of a callus-building response in the tessellated cartilage unique to elasmobranch skeletons. Our findings reveal sampling and analysis biases in vertebrate ecology, especially with regard to the role of large, predatory species, while also illustrating that large body size may provide an escape from anatomical constraints on diet (e.g. gape size, specialist dentition). Our observations inform our concepts of skeletal biology and evolution in showing that tessellated cartilage—an ancient alternative to bone—is incapable of foreign tissue resorption or of restoring damaged skeletal tissue to its original state, and attest to the value of museum and skeletal specimens as records of important aspects of animal life history.

Genetic identity of eutetrarhynchids from the Persian Gulf, with intraindividual and intraspecific variability of Prochristianella butlerae Beveridge, 1990

The examination of the two batoid species, Pastinachus sephen (Forsskål) and Himantura gerrardi (Gray), resulted in a morphologic identification of the five eutetrarhynchid species, namely Parachristianella indonesiensis Palm, 2004 reported for the first time from Himantura gerrardi, Pa. monomegacantha Kruse, 1959, Prochristianella clarkeae Beveridge, 1990, Pr. butlerae Beveridge, 1990 and Dollfusiella spinulifera (Beveridge et Jones, 2000). By sequencing the partial 28S rDNA and calculating the genetic distances between the morphologically identified specimens from the Persian Gulf and their allopatric morphological conspecifics as well as using a phylogeny, the specimens of the Persian Gulf were considered as the allopatric conspecifics of Parachristianella indonesiensis, Pa. monomegacantha and Prochristianella clarkeae. Since the specimens of Dollfusiella from the Persian Gulf and D. spinulifera from Australia had a high genetic distance and placed in two separate clades, the Iranian specimens of Dollfusiella were treated as the cryptic species of D. spinulifera. Following the treatment of Prochristianella macracantha Palm, 2004 as the synonym of Pr. butlerae Beveridge, 1990, it was also expressed that although Pr. butlerae appeared to be a variable species in terms of its metric data, there was an identical oncotaxy in all the conspecifics. A detail examination of the specimens from the Persian Gulf as well as Australian voucher specimens revealed a great intraindividual and intraspecific variability in this species. Since, the sequence information is only available for the Iranian specimens and there is no possibility to evaluate the genetic distance and their monophyly, we consider these two allopatric populations as one species.

The Late Jurassic ray Kimmerobatis etchesi gen. et sp. nov. and the Jurassic radiation of the Batoidea

The laminated marine mudstones of the Late Jurassic of Kimmeridge, southern England, yield two exceptionally well-preserved partial skeletons of a previously unrecognised species of early batoid. These are described as a new genus and species, Kimmerobatis etchesi gen. et sp. nov. which has a general “guitarfish” bauplan as in all other batoids known from the Jurassic. This species possesses a combination of primitive characters such as centra present within the majority of the synarcual and antorbital cartilages that fail to reach the pectoral skeleton along with more derived characters, such as the lack of fin spines. Until now, little study has been carried out on the affinities of Jurassic batoids, despite their key role in understanding batoid evolution. Results from parsimony and likelihood phylogenetic reconstruction indicates that the whole-bodied Jurassic batoids Spathobatis, Belemnobatis, and Kimmerobatis gen. nov. form their own clade, Spathobatidae, and do not lend support to a monophyletic “Rhinobatidae”. Among Jurassic batoids, Kimmerobatis gen. nov. is most derived, but with derived characters being independently acquired compared to modern batoids (e.g. presence of a postpelvic process). The inclusion of whole bodied Jurassic fossils have generated a more resolved hypothesis of batoid evolution throughout the Cretaceous and into the Cenozoic.

Trophic ecology of the blotched stingray, Urotrygon chilensis (Elasmobranchii: Myliobatiformes: Urotrygonidae), in three areas of the Mexican Pacific

Background. There is a current global consensus that to achieve a sustainable use of fisheries resources, management of every organism subject to exploitation is required rather than only those targeted directly by the fisheries. Further understanding the feeding habits of the species in the ecosystem as well as the predator&ndash;prey relationships and their trophic levels is crucial. Batoids occupy an important ecological niche as benthic predators in estuaries and bays. There is no directed fishery for the blotched stingray, Urotrygon chilensis (G&uuml;nther, 1872), but it is commonly caught incidentally by trawl and bottom gillnets fisheries subsequently diminishing its population. Recently, artisanal fisheries in Mexico have become focused on batoid species due to the depletion of shark catches, although there are few studies on its biology and ecology. Materials and methods. We analysed the trophic ecology of the blotched stingray in two main areas from the Mexican Central Pacific to understand the species&rsquo; diet and detect possible differences throughout fishing areas using stomach content analysis. We analysed the overlap in diets between areas and the trophic level at each area. Results. We analysed 423 specimens and found 15 prey groups. Representatives of the two crustacean higher taxa&mdash;Cladocera and Peracarida were the most important food items in the north area, while the crustacean family Penaeidae was the most important in the south area, having no significant overlap between areas (C&lambda; = 0.33). The estimated trophic position for the blotched stingray was 3.51&ndash;3.56 in both areas, and according to the Levin&rsquo;s index, the range of the trophic niche breadth for the blotched stingray was 0.059 and 0.039, which indicates that it is a specialist predator. Conclusion. The blotched stingray is a specialist predator that can adapt to different prey depending on which organisms are present in the ecosystem. It is necessary to continue with these types of studies for the other species inhabiting the area, in addition to monitoring fisheries landings, fishing effort, and variations in biotic and abiotic factors in the area over a long period. However, this study outlines an approach for reaching the ultimate goal of sustainable exploitation of marine resources on an ecosystem level.

Size-weight relationships of batoids captured by artisanal fishery in the southern Gulf of California, Mexico

This study reports the size–weight relationships (SWR) for nine batoid species that are frequently fished by the artisanal fisheries in the southern Gulf of California. Analysis included a total of 2,012 specimens, caught from October 2013 to July 2016. The slope values (b) oscillated from 2.80 to 3.56. Growth was isometric for five species and positively allometric for four. There were differences in SWR between sexes for three species being in all cases the female greater and heavier than males. This is the first analysis of SWR for the batoid species studied in the Gulf of California.