Squatina Californica Research Articles

Four new genera and five new species of lecanicephalideans (Cestoda: Lecanicephalidea) from elasmobranchs in the Gulf of California, Mexico.

A total of 53 spiral intestines from 3 species of rays collected in the Gulf of California, Baja, Mexico, was examined for cestodes of the order Lecanicephalidea. Four new genera and 5 new species were discovered as a result of this study. These are Aberrapex senticosus n. gen., n. sp., from Myliobatis californica, Paraberrapex manifestus n. gen., n. sp., from Squatina californica and Healyum harenamica n. gen., n. sp., Healyum pulvis n. sp. and Quadcuspibothrium francisi n. gen., n. sp., from Mobula japanica. Aberrapex n. gen. and Paraberrapex n. gen. can be distinguished from all other lecanicephalidean genera based on the lack of an apical structure (pars apicalis) on their scolex. Aberrapex n. gen. can be distinguished from Paraberrapex n. gen. based on the presence of an external seminal vesicle, a vagina positioned lateral rather than medial in the proglottid, and an ovary that is tetralobed rather than bilobed in cross section. Healyum n. gen. and Quadcuspibothrium n. gen. are unique among lecanicephalidean genera, including Aberrapex n. gen. and Paraberrapex n. gen., in their possession of a trilobed ovary in cross section. Quadcuspibothrium n. gen. can be distinguished from Healyum n. gen. based on its unique shape of the acetabula, which are diamond-shaped. The 2 species of Healyum n. gen. can be distinguished from one another based on the dimensions and the shape of the scolex, the diameter of the suckerlike acetabula, as well as the shape of the spiniform microtriches on the acetabular rims. Discobothrium arrhynchum is transferred to the genus Aberrapex n. gen. and the original description of this species is emended to include details of the vas deferens and the uterine duct and uterus. The microtrich patterns of the 5 new species and Aberrapex arrhynchum n. comb. are described. These are the first records of tapeworms of the Lecanicephalidea from the Gulf of California. Squatina californica and Mobula japanica represent new host records for lecanicephalidean tapeworms. The ordinal diagnosis of the Lecanicephalidea by Euzet (1994) is emended to include these 4 new genera.

Prey Capture by the Pacific Angel Shark, Squatina californica: Visually Mediated Strikes and Ambush-Site Characteristics

Eleven of 23 sharks tested attacked a fish model from beneath a transparent partition, which was designed to block near-field mechanical cues. Head-on approaches by the model elicited a higher frequency of attacks and shorter attack latencies than caudal approaches (frequency, P = 0.04; latency, P = 0.03). Night attacks may have been facilitated by turbulence-generated bioluminescence. Resting sharks and vacated depressions were usually adjacent to reefs, either facing or aligned parallel to margins of nearby reefs, and oriented toward upslope directions. Four sharks that were identified based on natural pigment patterns returned to the near proximities (< 3 m) of previously occupied ambush sites. Based on our experiments and observations, we suggest that (1) prey movement sensed visually is the most important cue for eliciting daytime attacks, (2) the sharks probably possess an anterodorsally directed field of vision, and (3) ambush sites are selected based on substrata characteristics likely to be associated with prey availability.

Population Structure of the Pacific Angel Shark, Squatina californica (Squatiniformes: Squatinidae), around the California Channel Islands

Starch gel electrophoresis was employed to examine genetic variability in three samples of the Pacific angel shark, Squatina californica, around the California Channel Islands. Gene products of 25 enzyme systems encoded by 29 presumptive loci were examined. Seven loci were polymorphic, with a mean sample heterozygosity of 0.056. F-statistics and contingency chi-square analysis revealed significant genetic divergence between northern samples (Santa Rosa and Santa Cruz Islands) and a southern sample (San Clemente Island). This apparent barrier to gene flow may result from a combination of behavioral characteristics and topography of the sea floor around the California Channel Islands. Significant allele-frequency differences in an elasmobranch species have not been detected previously over such short geographical distances.

Evolutionary Aspects of Gene Expression in the Pacific Angel Shark, Squatina california (Squatiniformes: Squatinidae)

Horizontal starch gel electrophoresis was employed to examine gene expression in the Pacific angel shark, Squatina californica. Forty enzyme systems encoded by 72 presumptive gene loci were examined using 15 buffer systems and were scored for tissue expression in each of 12 tissues. To clarify aspects of enzyme evolution, the patterns of expression are described and compared to what is known for other vertebrates. The patterns of tissue-specific expression in S. californica were similar to those of other vertebrates, but some exceptions were noted. New findings described herein regarding the evolution of enzyme systems in the vertebrates include (1) additional support for the presence of a third creatine kinase locus, possibly Ck-B, in sharks; (2) the discovery of a new fructose-bisphosphatase locus, designated Fbp-C; and (3) the presence of only one supernatant NAD-dependent malate dehydrogenase (sMdh-A) compared to two sMDHs reported in bony fishes. This study has provided the baseline description of elasmobranch gene expression for future comparative studies of other species of sharks and rays.

Growth and demography of the Pacific Angle Shark (Squatina californica), based upon tag returns off California

Knowledge of the age, growth and demography of an organism can be quite useful for managing its fishery. However, for many elasmobranch species, no valid estimates of age, growth and therefore age-specific mortality and natality rates are available. Thus, even though the distribution, abundance, habits and reproduction of a population may be known, no reliable estimates of population growth are possible. As a result, detailed demographic analysis has been completed for only a few shark species (e.g. the California leopard shark, Triakis semlfasciata). All age-determination techniques attempted for the Pacific angel shark (Squatina californica) have met with difficulties. Recently, however, we have accumulated data on 69 tag-recaptures and have used this information to model a von Bertalanffy growth function (VBGF) to predict the growth of this commercially exploited shark species. We performed a demographic analysis of this species, which yielded a net reproductive rate (R0) of 2.25, a generation time (G) of 14.5 years, and an estimate of the instantaneous population growth coefficient (r) of 0.056 year-1, assuming that only natural mortality (M) was occurring, estimated to be 0.2 year-1. When reasonable estimates of fishing mortality (F) are included in the survivorship function, Ro and r are reduced considerably. Presently, Pacific angel sharks first enter the fishery at the same size and age at which they first reproduce. Until accurate estimates of M and Fare available, it would be prudent to set a size limit considerably above the size at first reproduction to protect the Pacific angel shark in California.

Vertebral Growth Zone Deposition in Pacific Angel Sharks

Vertebrae and body size measurements were taken from 334 Pacific angel sharks collected from commercial gill netters off Santa Barbara, California, from Sept. 1979-Nov. 1983. Radiographs of vertebral centra from 247 specimens were studied to delineate calcified bands for age determination. The vertebrae of the smallest newborn sharks (260 mm TL) had 6 or 7 bands while those of the largest (1140 mm TL) had 42 bands. Bands were not deposited annually but were related to somatic growth. This hypothesis is supported by the number of bands in embryos and newborn Pacific angel sharks, growth of girth, and vertebral centrum dimensions, laboratory grow-out studies of tetracycline-injected sharks, and evidence from six tetracycline-injected tag returns.

Three species of Trebius Kr�yer, 1838 (Copepoda: Siphonostomatoida) parasitic on Pacific elasmobranchs

The paratypes of Trebius akajeii Shiino, 1954, originally collected from Dasyatis akajei (Muller & Henle) at Owase, Japan, and the paratypes and newly collected specimens of T. latifurcatus Wilson, 1921, previously collected from Urolophus and Myliobatis at Venice, California, are redescribed. New host records for T. latifurcatus are: Torpedo californica Ayres, Squatina californica Ayres, Rhinobatos productus (Ayres), Platyrhinoides triseriata (Jordan & Gilbert), Raja inornata (Jordan & Gilbert) and Gymnura marmorata (Cooper). A new species, Trebius heterodonti, is described from the horn shark Heterodontus francisci (Girard) collected from southern California waters. These three species of Trebius are apparently closely related to each other. Diagnostic characters of the species are provided along with a discussion on the taxonomic value of selected features.

Reproduction and Development of the Pacific Angel Shark, Squatina californica, off Santa Barbara, California

Specimens of Squatina californica were collected from commercial gill-net boats off Santa Barbara, California, from Jan.-Nov. 1983 for studies of reproduction. Sexual maturity in both males and females began between 900 and 1000 mm TL. Fecundity estimates from egg and embryo numbers ranged between 1 and 11. The number of young did not increase with increasing size of the female after maturity. Reproduction in the angel shark appears to follow an annual cycle. Embryo size from samples of pregnant females taken in eight months increased gradually for the 12 months between Aug. and July. Pupping occurred in spring and each female had an average of six pups. Growth rates ranged from 45 mm TL per month in very young embryos to 10 mm TL per month in those approaching the size at birth and the overall mean growth rate was 23 mm TL per month. Individual developmental morphology is described for five embryos ranging in size from 35.4-175 mm TL.

An intrauterine leech infection: Branchellion lobata Moore, 1952 (Piscicolidae) in the Pacific angel shark (Squatina californica) from California

The leech Branchellion lobata Moore, 1952 (Piscicolidae) was discovered on the ventral surface of two embryo Pacific angel sharks (Squatina californica) from off Santa Barbara, California, in October 1976. These leeches were also found around the cloaca and in the spiracle valves of the pregnant female. This is the first known report of an intrauterine leech infection.

New Records of Marine West Coast Fishes

1. Squatina californica Ayres The angel shark is a rare visitor north of California, but occasionally this species is taken north of its usual range. A specimen was reported (Evermann and Goldsborough, Bull. U. S. Bur. Fish., 26, 1906 (1907): 222 and 228) from southeastern Alaska. Since Squatina californica has not been recorded from Puget Sound, the capture of a female, about 3Y2 feet long, near Seattle, on October 9, 1931, by William Jankus, may be of interest. This specimen is preserved in the Department of Fisheries Collection of Fishes, University of Washington.