Ofelia Escobar-Sánchez

Embryonic bicephaly in the blue shark, Prionace glauca , from the Mexican Pacific Ocean

A case of bicephaly in embryos of the blue shark Prionace glauca in the Mexican Pacific Ocean is described. Malformed female shark embryos were found in pregnant females caught in the Gulf of California (Punta Arenas) and off the western coast of Baja California Sur, Mexico (San Lazaro). Abnormal sharks showed a symmetric bicephaly that could be caused by the high number of embryos found in the uterus of the blue shark, which is the most fecund species of shark in the world. The abnormality probably began during the embryonic development.

Trophic ecology of the blue shark ( Prionace glauca ) based on stable isotopes (δ 13 C and δ 15 N) and stomach content

Occupying the upper levels of trophic webs and thus regulating prey at lower levels, sharks play an important role in the trophic structure and energy dynamics of marine ecosystems. In recent years, the removal of these individuals from upper trophic levels as a result of overfishing has negatively affected ecosystems. We analysed the diet of blue sharks ( Prionace glauca ) caught off the west coast of Baja California Sur, Mexico, during the months of February–June in 2001, 2005 and 2006. We employed both stomach content and stable isotope analyses as each method provides distinct yet important information regarding the role of blue sharks in marine food webs, allowing us to estimate the relative contribution of different prey items to this predators diet. Of the 368 stomachs analysed, 210 contained food (57%) and 158 (43%) were empty. Based on stomach contents and the index of relative importance (IRI), the pelagic red crab ( Pleuroncodes planipes ) was the most important prey, followed by the squids Gonatus californiensis (34.1%) and Ancistrocheirus lesueurii (10.4%). The mean (±SD) values for δ 15 N (16.48 ± 0.94‰) and δ 13 C (−18.48 ± 0.63‰) suggest that blue sharks prefer feeding in oceanic waters. The trophic level based on stomach content analysis was 4.05, while that based on the stable isotope analysis was 3.8, making blue sharks top consumers in the marine ecosystem of Baja California Sur, Mexico.

First case of synophthalmia and albinism in the Pacific angel shark Squatina califórnica

The first record in Mexican waters of albinism and synophthalmia (partial cyclopia) in the Pacific angel shark, Squatina californica is presented. Albinism is not lethal, but synophthalmia may cause the death of the individual immediately after birth.

Diet of the cortez damselfish Stegastes rectifraenum (teleostei:Pomacentridae) from the rocky reef at Los Frailes, Baja California Sur, Mexico

The stomach contents of 50 Cortez damselfish Stegastes rectifraenum captured at Los Frailes, Baja California Sur, Mexico were analysed to describe their diet. According to our results, S. rectifraenum is an omnivorous species with a preferente for certain prey; invertebrates (benthic copepods) and algae (Bryopsis spp. and Ectocarpus spp.). Other animal components (Cerithium spp. and Olivella spp.) can also be found in their diet. No differences were observed between genders (analysis of similarity (ANOSIM), R 1⁄4 0.002, P 1⁄4 0.001) or among seasons (ANOSIM, R 1⁄4 0.046, P 1⁄4 0.001), therefore their food can be available all year at the rocky reef at Los Frailes.

Incidence of xanthism in the leopard grouper Mycteroperca rosacea (Perciformes: Serranidae) in the Gulf of California

Five leopard grouper Mycteroperca rosacea specimens were captured in the Gulf of California, two of which presented a rare orange pigmentation on both sides of the body. The remaining individuals presented changes to the normal pigmentation pattern on the left or right flanks. The possible causes of these phenomena are discussed.

Mercury in Fish, Crustaceans and Mollusks from Estuarine Areas in the Pacific Ocean and Gulf of Mexico Under Varying Human Impact

Mercury (Hg) is the most dangerous trace element present in the edible parts of fishes and invertebrates. With the aim of having a general view on Hg occurrence in commercially exploited biota (fish and invertebrates) from selected estuarine systems of Mexico, we compiled information related to Hg levels in fish (elasmobranchs and teleosts), shrimps, clams, mussels and oysters from impacted estuarine areas and other coastal ecosystems in the Pacific Ocean and the Gulf of Mexico. Levels of Hg in the Asiatic clam Corbicula fluminea (a freshwater species) were relatively low (< 0.32 µg g−1) in comparison to individuals collected in moderate or severely impacted sites. In the case of marine mollusks ( Crassostrea corteziensis and Mytella strigata) Hg concentrations were comparable to those from low or moderately contaminated sites. In shrimps, Hg values were low (< 0.72 µg g−1) and consistently higher in hepatopancreas tissue than in muscle. Rays had lower Hg levels ( < 0.4 µg g−1 wet weight) than sharks (< 2.0 µg g−1 wet weight). Teleost fish have been studied more thoroughly than other groups; Hg levels in muscle tissue varied by two orders of magnitude (from 0.02 to 1.58 µg g−1 dry weight). Among studied organisms, fish are known as the main pathway of Hg entrance to humans. It is necessary to generate information of the rates of consumption of fish, especially of predator species. Considering legal limits of Hg and methyl Hg (1.0 and 0.5 µg g−1 wet weight, respectively) in edible portion of fish in Mexico, at present there is risk to the human population for the consumption of the scalloped hammerhead shark Sphyrna lewini.