The hawksbill sea turtle Eretmochelys imbricata is categorized as Critically Endangered on the IUCN Red List and its population has declined by over 80% in the last century. The Eastern Pacific population is one of the most threatened hawksbill populations globally. Western Mexico is the northern distribution limit for hawksbill sea turtles in the Eastern Pacific and recent research indicates that the Mexican Pacific portion of the population is a separate management unit because of the restricted movements of these turtles. Here we use the most complete database of sighting records in the north-west Pacific of Mexico to identify sites where hawksbill turtles are present. We also develop a conservation index to determine the conservation status of hawksbill turtle sites. Our results demonstrate the importance of this region for juveniles and the relevance of rocky reefs and mangrove estuaries as habitats for hawksbill turtles. We identified 52 sites with records of hawksbill turtles. Most of these sites (71%) are not protected; however, sites with high conservation value included islands and coastal sites along the Baja California peninsula that are established as marine protected areas. Reefs and mangrove estuaries relevant for hawksbill turtles are probably also significant fish nursery areas that are important for local fishing communities, creating opportunities for conservation strategies that combine science, local engagement and policy to benefit both local fishing communities and hawksbill sea turtle conservation.

Spatial variations of polychaetes along the Baja California Peninsula continental shelf were analysed in two ways: (1) by evaluating the species richness and defining the faunal assemblages from local sampling, and (2) by characterizing the latitudinal variation of beta-diversity based on the distribution of all polychaetes reported up to now. Twenty-seven stations from three oceanographic expeditions were sampled, and 2858 individuals from 38 families and 231 species were identified. Polychaetes were abundant (mean = 37.5 ind 0.1 m−2) and diversified (mean = 15 species station−1). Differences in species composition defined seven faunal assemblages, but their number of species did not show significant latitudinal changes. The beta-diversity analysis was based on distribution data of 730 species from 47 families. The presence of a group of islands in the middle Gulf could have a negative effect on the species distribution, since the lowest values of β T-diversity (0.39) were found in the northern Gulf, but their species were different from those recorded in the central region. The wide variation in β T-diversity (0.5–0.87) showed latitudinal changes in the species composition, mainly in the Gulf mouth (0.86–0.87), which indicated that the fauna inside the Gulf was different from that inhabiting the Pacific coasts. The ICE and Chao2 estimators showed that the polychaetes in the study area are relatively well known (>80%), and that most species (415) have small distribution ranges. The effects of these infrequent species were similar at each latitudinal band, which suggested that the observed β T-diversity pattern could represent a suitable estimation.

Ecologists examine diet composition in order to assess the spatial and temporal variations in interactions between species, the impact of different species traits on the ecological network structure, and the long-term effects of the removal of different species by small-scale fisheries. In this study, our goal was to compare the diets of silky sharks (Carcharhinus falciformis) and scalloped hammerhead sharks (Sphyrna lewini) off the south-west coast of Mexico in order to infer their diet preferences and spatial distributions. We sampled 164 S. lewini (96 stomachs had food, 68 were empty) and 183 C. falciformis (30 stomachs had food, 153 were empty) in Puerto Madero, Chiapas in 2011. The large number of empty stomachs may be the result of using longline fishing gear, which causes high stress resulting in regurgitation. Based on the index of relative importance (%IRI), the fish Chloroscombrus orqueta (IIR = 27.7%) was the most important species in the diet of S. lewini, while the squid Dosidicus gigas (IIR = 34%) was the primary prey of C. falciformis. Levin's index (Bi) and Shannon's index (H′) confirm that both sharks are generalists, as in other regions. The trophic levels of S. lewini (TL = 4.1) and C. falciformis (TL = 4.2) are characteristic of tertiary consumers; meanwhile, the Morisita–Horn index indicates low interspecific overlap between all categories. These results confirm that these two sharks have different foraging preferences or movement patterns; thus, there is no trophic overlap between species as they play unique roles in the ecological network off the south-west coast of Mexico.

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 predator's 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 δ15N (16.48 ± 0.94‰) and δ13C (−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.

A total of 75 specimens belonging to four species of thalassinoids were collected in the intertidal and estuarine zones of two localities along the Pacific coast of Mexico. Callianassa tabogensis is recorded for the first time in Mexico, and is transferred to the genus Neotrypaea. Material of Callichirus is assigned to Callichirus seilacheri with some doubts due to taxonomic problems related to this genus in the eastern Pacific. Neocallichirus cf. grandimana, an amphi-American species described for the western Atlantic and previously reported in Ecuador and along the Pacific coast of Panama and Colombia, is reported for the first time in Mexico. Upogebia dawsoni is recorded for the second time from the coast of Jalisco. An updated list of Axiidea and Gebiidea known from the Mexican Pacific is provided, including 35 species.

A total of 101 denticled roundray Urotrygon cimar were caught in a large area of the Gulf of Tehuantepec. Sizes ranged from 102 to 282 mm total length. Rays were caught at depths between 17 and 62 m. These records confirm the presence of the denticled roundray off the southern coast of the Mexican Pacific.

Numerous specimens of Ophistognathus panamaensis were observed along the coast of Oaxaca in western Mexico and one specimen was collected by Hawaiian sling in the coral reef zones of Huatulco, Mexico in November 2012. Therefore, this paper reports for the first time the occurrence of O. panamaensis in Mexico and extends its previous distribution by 1245 km north of the Eastern Pacific equatorial zone.

The sailfish Istiophorus platypterus is one of the most common billfish species in the Mexican Pacific. Information about its feeding habits in the coastal region of Acapulco, Guerrero is extremely limited. In the present study we quantified the diet of sailfish, based on captures made from March 2008 to December 2009 by the sport fishing fleet of Acapulco. We analysed a total of 561 stomachs, of which 254 contained food (45%). The size interval of examined specimens was between 101 and 212 cm postorbital length and between 15 and 47 kg total weight. In general, teleosts were the most important prey, followed by cephalopods. According to index of relative importance, the most important species in the diet were the fish Auxis thazard (63.04%) and Fistularia commersonii (6.62%), followed by the cephalopod Octopus spp. (4.58%). There were no significant differences in the diet by sex (males and females), sexual maturity (immature and mature), or by season (warm and cold seasons). In all cases the most important prey species was A. thazard. We conclude that the sailfish I. platypterus off Acapulco behaves as a specialist predator because, despite the consumption of a high number of prey items, it feeds preferentially on a reduced number of prey species that form schools, and are available and abundant in the ocean.

The small, monogeneric family of polychaetes known as Trochochaetidae has been exclusively collected in the northern hemisphere, mainly in temperate–cold environments. Nine species have been described so far including Trochochaeta mexicana sp. nov. described herein, while one species remains unnamed. Only two species had previously been recorded in the eastern Pacific, so T. mexicana sp. nov. is the first record for the family in the tropical Mexican Biogeographic Province. The new species is characterized by having a pair of eyes, acicular neurochaetae on chaetigers 2 and 3, a small knob-like antenna and a nuchal crest projecting through chaetiger 1. Trochochaeta mexicana sp. nov., together with Trochochaeta kirkegaardi, Trochochaeta diverapoda and Trochochaeta cirrifera are the only trochochaetids that have been found exclusively in warm environments.

A checklist of 53 soft-bottom species of polychaetes from the coastal lagoon Estero de Urías is presented here. Depth, sediment temperature, salinity, grain size, organic matter content, and dissolved oxygen ranges where polychaete species were found are provided. Twenty-six species are reported for the first time for the Estero de Urías coastal lagoon. This is the first report of the sabellid Amphicorina gracilis, the spionid Marenzelleria viridis, and the syllid Exogone (Parexogone) molesta for the Pacific coast of Mexico.

Dasybranchetus pacifica, collected in Concepcion Bay, Baja California Sur, Gulf of California, is described as a new species. In addition, the type species of the genus, Dasybranchetus fauveli Monro, 1931, is redescribed based on type material. The new species differs from D. fauveli in the absence of branchiae, the begining of the mid-dorsal lobe from chaetiger 2 instead of chaetiger 9, abdominal segments with well-developed neuropodial lobes, and hooded hooks with a main fang and three rows of subapical teeth in the following arrangement: 4 teeth in the basal line, 3 in the middle line, and 2 in the apical line.

The aim of this study is to analyse the Nephtyidae from the Gulf of California. Previous studies about the family Nephtyidae from the continental shelf of the Gulf include 21 species of which seven have been synonymized by several authors, so that at present only 14 species are recognized. In this study, 1763 specimens of Nephtyidae from the continental shelf of the Gulf of California were examined. Eight species were identified, from which Aglaophamus longicirrata sp. nov. and Aglaophamus foliosa sp. nov. are newly described. Aglaophamus longicirrata sp. nov. is characterized by the presence of very long dorsal cirri in median parapodia and by having 16 rows of subterminal papillae with 3–7 papillae per row, and a pair of middorsal papillae on the proboscis. Aglaophamus foliosa sp. nov. is characterized by foliaceous long dorsal cirri; the proboscis bears 16 rows of subterminal papillae and an irregular number of papillae per row, from 5 to 15. A taxonomic key is presented for the species of Nephtyidae recorded from the continental shelf of the Gulf of California, including the two new species of Aglaophamus.

Despite a recent revision of the dinoflagellates of the order Dinophysiales on Mexican coasts and a checklist of dinoflagellates from the Mexican Pacific, many records still need to be confirmed, for there are very few reliable illustrations and/or descriptions. In this paper, species composition and distribution of dinoflagellates belonging to the Dinophysiales, the product of the analysis of net phytoplankton material collected from coasts of the tropical Mexican Pacific (Jalisco to Chiapas) are presented. The material has been studied using light microscopy, although a few species were also studied by scanning electron microscopy (SEM). Forty-one species from five genera were identified, with two new records annotated for the Mexican Pacific: Amphisolenia thrinax and Metaphalacroma skogsbergii, and two new species of the genus Amphisolenia, Amphisolenia fusiformis sp. nov. and Amphisolenia michoacana sp. nov. Illustrations, dimensions and distribution data are provided for each species, and descriptions of the new species are also given. Amphisolenia palmata, A. rectangulata, A. truncata, Dinophysis apicata, D. hindmarchii, Histioneis biremis, H. crateriformis, H. pulchra, Ornithocercus cristatus, O. heteroporoides and O. orbiculatus are illustrated for the first time in the waters of the Mexican Pacific. The number of species found in this study is relatively low. The species Dinophysis norvegica and D. sacculus, reported in previous papers, do not seem to occur in Mexican waters, as their distribution is rather limited to the Mediterranean Sea and the North Atlantic, respectively. Finally, the identity of certain species of Dinophysis and the nature of the new species described here are discussed.