ABSTRACT Trace elements were determined in three areas of the right (RL) and left (LL) lobe of the liver obtained from a whale shark (Rhincodon typus) stranded in Mexico. Mean ± standard error concentrations in μg g-1 wet weight were for zinc (Zn) RL: 22.5 ± 2.1; LL: 26.5 ± 7.1, arsenic (As) RL: 33.0 ± 1.6; LL: 20.0 ± 9.9 and cadmium (Cd) RL: 15.5 ± 0.9; LL: 11.3 ± 3.7; copper (Cu) RL: 3.2 ± 0.3; LL: 2.2 ± 0.8, selenium (Se) RL: 0.5 ± 0.1; LL: 1.2 ± 0.6, mercury (Hg) RL: 0.06 ± 0.02; LL: 0.05 ± 0.004 and lead (Pb) RL: 0.05 ± 0.02; LL: 0.05 ± 0.01. Concentrations showed significant (P < 0.05) differences within the same lobe but not between lobes. The trace element levels found in this whale shark represent the baseline levels of the trophic base's health status in the study area.

ABSTRACT Background: Bahía de la Paz, Mexico have seasonal blooms of planktonic prey that support a range of marine species including whale sharks (Rhincodon typus). Goals: This study includes the first sampling cycle that covers all climatic seasons, to know changes in the abundance and composition of zooplankton in the coastal waters off the El Mogote Sandbar, in Bahía de La Paz, BCS, Mexico. Methods: A total of 96 plankton samples were collected at predetermined field stations, spanning the entire length of the El Mogote from June 2016 to May 2017. Results: Total biomass was significantly different between seasons (Kruskal-Wallis chi-squared = 29.993, p = 0.000001385), with the lowest biomass recorded in spring (176.28 ml 100 m-3, 10.1%); and highest observed for winter (703.04 ml 100 m-3, 40.4%). Zooplankton composition was largely comprised of two main taxonomic groups: Copepoda (396,234 organisms100 m-3, 43.1%) and Chaetognatha (196,986 organisms100 m-3, 21.4%). The total number of individuals (sum of all taxonomic groups) per season showed significant differences (Kruskal-Wallis chi-squared = 29.78, p = 0.000001533) with the highest concentrations recorded in winter (292,429 organisms100 m-3, 31.8%) and lowest in spring (162,995 organisms100 m-3; 17.7%). Conclusions: This information provides the first work focused solely in the El Mogote area as a main foraging site for whale sharks, with clear changes in plankton communities with respect to shifting climatic seasons, and the importance of certain taxonomic groups to the diet of whale sharks.

RESUMEN Antecedentes: En la Bahía de la Paz, México se presentan proliferaciones de plancton estacionales que son presas potenciales de varias especies marinas incluyendo tiburón ballena (Rhincodon typus). Objetivos: En este estudio se presenta el primer ciclo de muestreo que cubre todas las temporadas climáticas, para conocer cambios en la abundancia y composición de zooplancton en aguas costeras de la barra de arena El Mogote en Bahía de La Paz, BCS, Mexico. Metodología: De junio 2016 a mayo 2017 se recolectaron 96 muestras de plancton en estaciones predeterminadas que cubren todo el largo de El Mogote. Resultados: La biomasa de zooplancton fue significativamente diferente entre temporadas (Kruskal-Wallis chi-cuadrada = 29.993, p = 0.000001385), la biomasa más baja se registró en primavera (176.28 ml 100 m-3, 10.1%) y la más alta en invierno (703.04 ml 100 m-3, 40.4%). El zooplancton estuvo compuesto principalmente por dos grupos taxonómicos: Copépodos (396,234 organismos100 m-3, 43.1%) y Quetognatos (196,986 organismos100 m-3, 21.4%). El número total de individuos (suma de todos los grupos taxonómicos) entre temporadas fue significativamente diferente (Kruskal-Wallis chi-cuadrada = 29.78, p = 0.000001533), las concentraciones más altas se registraron en invierno (292,429 organismos100 m-3, 31.8%) y las más bajas en primavera (162,995 organismos100 m-3; 17.7%). Conclusiones: Este es el primer trabajo enfocado exclusivamente al área de El Mogote como principal sitio de alimentación del tiburón ballena, con cambios estacionales claros en las comunidades de plancton y la importancia de ciertos grupos taxonómicos en la dieta del tiburón ballena.

Abstract The whale shark is the world’s largest filter feeding shark and holds international protection as an endangered species. It is known to form seasonal aggregations linked to blooms of zooplanktonic organisms. The aim of this study was to investigate whether whale shark foraging behaviors are related to the density and/or concentration of available prey items. Zooplankton samples were obtained between October-2016 and March-2017 from Bahia de La Paz in the absence (n =3 2) and presence (n = 12) of foraging whale sharks. Results indicated that zooplankton biomass was 1.6 times significantly greater (t = -3.21, p < 0.05) when sharks were observed feeding and the mean number of zooplankton individuals of all taxonomic groups in the presence of feeding whale sharks was 2.5 times greater than in the absence of feeding, although it was not significantly different (t = -1.70, p > 0.05). The dominant taxonomic groups were copepods and chaetognaths with no significant differences found in the mean number of copepods (t = -1.81, p > 0.05), chaetognaths (t = -1.70, p > 0.05), euphausiids (t = -0.12, p > 0.05) and decapods (t = -1.80, p > 0.05), between the presence and absence of feeding whale sharks. In conclusion, whale sharks feeding behaviors occur during higher concentrations of zooplankton biomass and the species may potentially target dense patches of both copepods and chaetognaths.

Resumen El tiburón ballena es el tiburón filtrador más grande del mundo y tiene protección internacional como especie en peligro de extinción. Forman agregaciones estacionales vinculadas a floraciones de organismos zooplanctónicos. El objetivo de este estudio fue investigar si el comportamiento de alimentación del tiburón ballena está relacionado con la densidad o concentración de presas disponibles. Las muestras de zooplancton fueron obtenidas entre octubre-2016 y marzo-2017 en Bahía de La Paz en la ausencia (n = 32) y presencia (n = 12) de tiburones ballena alimentándose. Los resultados indicaron que la biomasa de zooplancton fue 1.6 veces significativamente mayor (t = -3.21, p < 0.05) y el número de individuos promedio de todos los grupos taxonómicos fue 2.5 veces mayor, aunque sin diferencias significativas (t = -1.70, p > 0.05) en presencia de tiburones ballena alimentándose. Los grupos taxonómicos dominantes fueron copépodos y quetognatos, sin diferencias significativas en el número promedio de copépodos (t = -1.81, p > 0.05), quetognatos (t = -1.70, p > 0.05), eufáusidos (t = -0.12, p > 0.05) y decápodos (t = -1.80, p > 0.05), entre la presencia y ausencia de tiburones ballena alimentándose. En conclusión, el comportamiento de alimentación del tiburón ballena se produce durante las concentraciones más altas de biomasa de zooplancton y las especies potencialmente pueden dirigirse a parches densos tanto de copépodos como de quetognatos.

ABSTRACT The shortbill spearfish Tetrapturus angustirostris Tanaka, 1915 is a widespread tropical and temperate species but is relatively rare, with very few published or cataloged records in museums and fish collections. We reported for the first time a specimen of T. angustirostris from the Pacific coast of Mexico, including meristic, morphometric and molecular data, which was caught in the vicinity of Los Cabos, Baja California Sur, Mexico, in November 2015.

As part of a continuing microalgae monitoring program, phytoplankton samples were collected from 19 August 2014 to 25 February 2015 at a fixed sampling site in the southern part of the Bahía de La Paz, Mexico. The armored dinoflagellate Oxytoxum caudatum was observed mainly in net samples of phytoplankton. Study of live specimens did not show great variation in cell size or shape. Cells were 24-38 µm long and 12-16 µm wide (n= 30). This is the first record of O. caudatum in the Gulf of California.

Analysis of wild phyllosoma of Panulirus inflatus (Bouvier, 1895) and P. gracilis Streets, 1871 determined the morphological structures having taxonomic value for differentiation of the two species, in addition to the structures described previously. Of 54 phyllosoma, species identity was confirmed by PCR-restriction fragment length polymorphism (RFLP) on 42 P. inflatus and 4 P. gracilis, for which morphology and morphometric measurements were taken. Morphological analysis found subexopodal spines, spines at the base of pereopods 1 and 2, and the mandibles are structures of taxonomic value for differentiating the two species. Morphometric data did not allow differentiation.

This paper analyzes the seasonal variability on larval fish assemblage structure and the relationships to hydrographic conditions during 4 seasonal surveys in the northern Gulf of California. Two periods were identified according to thermohaline properties and associated fauna: a cold period, when temperature drops and the coastal current flows equatorward in winter and spring (anticyclonic circulation), dominated by species of temperate and subtropical affinity (e.g., Engraulis mordax and Merluccius productus); and a warm period, characterized by poleward intrusion of Tropical Surface Water in summer and autumn (cyclonic circulation), with a high diversity of tropical-subtropical species (e.g., Benthosema panamense and Anchoa spp.). Cluster analysis defined 2 groups of stations and associated taxa: a Northern Group, located in the Delfín Basin, including mainly demersal taxa; and a Mainland-Insular group, of species with various affinities (demersal, coastal-pelagic, mesopelagic). Seasonal variability is identified as the main element in the structuring of larval fish assemblages. However, hydrodynamic changes influence the aggregation patterns and the prevalence of the coastal pelagic, demersal and mesopelagic biota throughout the year.

Se analiza la variabilidad estacional de los ensambles de larvas de peces en relación con las condiciones hidrográficas, durante 4 cruceros en la región norte del Golfo de California (GC). De acuerdo a las propiedades termohalinas y fauna asociada se identificaron 2 periodos: un periodo frío, cuando la temperatura disminuye y la corriente costera fluye en dirección al ecuador en invierno y primavera (circulación anticiclónica), dominado por especies de afinidad templada y subtropical (e.g., Engraulis mordax y Merluccius productus); y un periodo cálido, caracterizado por la intrusión de agua tropical superficial en verano y otoño (circulación ciclónica), con alta diversidad de especies de afinidad subtropical-tropical (e.g., Benthosema panamense y Anchoa spp.). La variabilidad estacional se identifica como el elemento principal en la estructuración de los ensambles de larvas de peces. Sin embargo, la hidrodinámica incide en los patrones de agregación y el predominio de la biota pelágico costera, demersal y mesopelágica a lo largo del año.

Larval fish community structure in El Bajo Espíritu Santo seamount from the southern part of the Gulf of California was studied. Fish larvae were identified and grouped in 48 families, 84 genera and 76 species. Their biological richness constitutes about 30% of the actual Gulf of California fishes. Numerically dominant taxa were represented by individuals whose adults belong to the mesopelagic, reef and coastal pelagic habitat (Vinciguerria lucetia, Mugil cephalus, Harengula thrissina, Benthosema panamense, Scomber japonicus, Mulloidichthys dentatus, Hyporamphus rosae, Abudefduf troschelii, Eucinostomus argenteus, Triphoturus mexicanus and Gobiidae). Large pelagic species from oceanic origin were also found in the samples, although they were scarce (Tetrapturus audax, Coryphaena hippurus). A high diversity (H') was found between late spring and autumn (2.0-2.8), it was determined in coincidence with an increment and maximum values of sea surface temperature (21-30 °C). Larval fish community structure was related with reproductive periods and mesoscale events of the ocean dynamics.

Se determinaron los cambios en la estructura de la comunidad de larvas de peces en una montaña submarina conocida como El Bajo del Espíritu Santo (EBES) situada al sur del Golfo de California. Las larvas de peces fueron identificadas y agrupadas en 48 familias, 84 géneros y 76 especies. La riqueza de especies fue notable por que representa cerca del 30% del total de las especies de peces del Golfo de California. Los taxa numéricamente dominantes están representados por individuos cuyos adultos pertenecen al hábitat mesopelágico, arrecifal y pelágico costero (Vinciguerria lucetia, Mugil cephalus, Harengula thrissina, Benthosema panamense, Scomber japonicus, Mulloidichthys dentatus, Hyporhamphus rosae, Abudefduf troschelii, Eucinostomus argenteus, Triphoturus mexicanus y Gobiidae). Especies de pelágicos mayores de origen oceánico también estuvieron presentes aunque fueron escasas (Tetrapturus audax, Coryphaena hippurus). Se determinó una alta diversidad (H') desde finales de primavera hasta el otoño (2.0-2.8) en coincidencia con el incremento y máxima temperatura superficial del mar (21-30 °C). La estructura de la comunidad y su variación en el tiempo estuvieron relacionadas con la alternancia en los periodos reproductivos y eventos de mesoescala de la dinámica oceánica del Golfo de California.