Trace Elements in Tissues of Whale Sharks (Rhincodon typus) Stranded in the Gulf of California, Mexico.

Concentration of essential (Se, Zn and Cu) and non-essential (As, Cd, Hg and Pb) trace elements were measured in selected tissues of two dead whale sharks (Rhincodon typus) stranded in the Gulf of California (GC) in 2017 and 2018. Concentrations of Cd and Pb in the skeletal muscle of the whale shark from La Paz Bay, GC were higher compared to a previous study on whale shark from China. The shark from La Paz Bay also presented higher concentration of Pb in the epidermis, compared to the same tissue of the other whale shark stranded in Punta Bufeo, GC. The Hg in all analysed tissues was lower than those documented in carnivorous sharks. Molar ratio Se:Hg shows an excess of Se over Hg in all the tissues sampled in both sharks.

Spatial and trophic preferences of jumbo squid Dosidicus gigas (D'Orbigny, 1835) in the central Gulf of California: ecological inferences using stable isotopes.

RATIONALE: The jumbo squid Dosidicus gigas is a fishery resource of considerable economic and ecological importance in the Mexican Pacific. Studies on its habitat preferences are needed to understand recent fluctuations in the abundance and availability of the species. Stable isotope analysis allows us to infer ecological aspects such as spatial distribution and trophic preferences. METHODS: We used an isotope ratio mass spectrometer, automated for carbonate analysis, and coupled to an elemental analyzer, to determine the isotopic composition of statoliths (δ18 O and δ13 C values) and beaks (δ13 C and δ15 N values) from 219 individuals caught over two fishing seasons (2007 and 2009) off the coast of Santa Rosalía, in the central Gulf of California. We used these isotopic ratios to assess variation in spatial and trophic preferences by sex, size, and fishing season. RESULTS: In the 2009 group, we observed significant differences in statolith δ13 C values and beak δ13 C and δ15 N values between males and females. Between size groups, we observed significant differences in statolith δ18 O and δ13 C values in 2007 and in beak δ13 C and δ15 N values during both seasons. Both seasons were characterized by high overlap in δ18 O and δ13 C values between sexes and in 2009 between size groups. We observed low trophic overlap between sexes in 2009 and between size groups during both seasons. CONCLUSIONS: The isotopic ratios from statoliths and beaks indicate that D. gigas has changed its spatial and trophic preferences, a shift that is probably related to changes in the species' diet. This intraspecific variation in preferences could be related to characteristics such as size, which may influence squid distribution preferences.

Reproductive parameters of the Pacific angel shark Squatina californica (Selachii: Squatinidae).

Reproductive characteristics of the Pacific angel shark, Squatina californica, were evaluated from 420 specimens obtained from the artisanal fishery in La Paz Bay, Gulf of California, Mexico. Females (99 cm, 6000 g) were larger than males (95 cm, 5000 g) in terms of both total length (L(T)) and body mass (M(T)). The overall sex ratio was significantly different from the expected 1:1, suggesting sexual segregation of mature individuals in La Paz Bay. Males had developed reproductive organs and calcified claspers from 72 cm L(T); the median size at maturity (LT50 ) was 75.6 cm. In females, only the left ovary was functional and mature ovarian follicles were present from 77 cm L(T); the estimated LT50 was 77.7 cm. For the 10 gravid females sampled, uterine fecundity was between two and 10 embryos. Mature, non-gravid females with small and large ovarian follicles appeared simultaneously with gravid females with follicles that did not exceed 1.9 cm diameter.

Population and individual foraging patterns of two hammerhead sharks using carbon and nitrogen stable isotopes.

RATIONALE: Individual foraging behavior is an important variable of predators commonly studied at the population level. Some hammerhead shark species play a significant role in the marine ecosystem as top consumers. In this context, stable isotope analysis allows us to infer some ecological metrics and patterns that cannot usually be obtained using traditional methods. METHODS: We determined the isotopic composition (δ(13)C and δ(15)N values) of dorsal muscle and vertebrae of Sphyrna lewini and Sphyrna zygaena using a continuous-flow system consisting of an elemental analyzer combined with a Delta Plus XL mass spectrometer. Foraging variability by sex and by individual was inferred from the isotopic values. RESULTS: There were no significant differences in the isotopic values of muscle samples between sexes, but there were differences between species. The trophic niche breadth of the two species was similar and overlap was low. A low niche overlap was observed between S. lewini individual vertebrae. We found differences in the δ(15)N values of S. zygaena vertebrae, with lower values in the first group of samples. CONCLUSIONS: Despite these hammerhead shark species inhabiting the same area, there was low trophic niche overlap between species and individuals, due to different individual foraging strategies, according to the carbon and nitrogen isotopic profiles obtained. The use of tissues that retain lifetime isotopic information is useful to complement studies on trophic ecology.

Bioaccumulation and biomagnification of total mercury in four exploited shark species in the Baja California Peninsula, Mexico.

The present study determined the average mercury bioaccumulation in the muscle tissue of four shark species (Carcharhinus falciformis, Prionace glauca, Sphyrna zygaena and Isurus oxyrinchus) captured in the Baja California Peninsula. We also evaluated biomagnification of some prey consumed by sharks. All sharks' species had mercury levels over the limit specified by the Mexican government for human consumption. Blue shark (P. glauca) presented highest mercury values (1.96 ± 1.48 µg/g Hg d.w.) and it was the unique specie that showed a negative correlation with mercury content (Rs = -0.035, p = 0.91). Scomber japonicus was the prey with high content of mercury (0.57 ± 0.02 µg/g).

Mercury and selenium bioaccumulation in the smooth hammerhead shark, Sphyrna zygaena Linnaeus, from the Mexican Pacific Ocean.

We analyzed total mercury and selenium bioaccumulation in muscle tissue and cartilage fibers (fins) from smooth hammerhead shark, Sphyrna zygaena, caught off Baja California Sur, Mexico. In muscle tissue, the mercury concentration ranged from 0.005 to 1.93 microg g(-1) ww (wet weight), which falls within the safety limits for food set by international agencies (Hg > 1.0 microg g(-1) ww). Only one specimen showed a mercury value that exceeded this limit. In fins, the mercury bioaccumulation was lower (<0.05). Selenium in muscle ranged from 0.11 to 1.63 microg g(-1) ww, while in fins it ranged from 0.13 to 0.56 microg g(-1) ww.

[Ichthyofauna of the Navidad Bay, Jalisco, México]. / Ictiofauna de la Bahía de Navidad, Jalisco, México.

A check-list and the relative abundance of the ichthyofauna from Bahia de Navidad, Jalisco, Mexico is presented. This poorly known area of the eastern Tropical Pacific ocean is characterized by its great fish diversity. A total of 245 fish species (163 genera, 72 families) were collected during the 1994-1995 annual cycle. Vouchers were deposited in Centro de Ecologia Costera, Universidad de Guadalajara. The most important families in number of species were Carangidae (20 species), Haemulidae (20), Serranidae (17), Sciaenidae (13) and Lutjanidae (8); 20 species represented 85% and 80% of relative abundance and biomass respectively. Microlepidotus brevipinnis, Caranx caninus, Caranx caballus, Kiphosus analogus and Caranx sexfasciatus, were the dominant species. Most fish species collected in Bahia de Navidad have zoogeographical affinity with the Panamic Province (65%), and in lesser proportion with the Eastern Pacific Ocean (19%), Circumtropical (7%), Mexican Province (5%), Indo-Pacific Ocean (3%) and Gulf of California (0.4%). The great ichthyological affinity between the study area and the southern Gulf of California suggests an extension of the of Gulf southern limit.