Context Establishing the roles that different species play within ecosystems is key to understanding how ecosystems function and determining the feeding relationships among species. Aims This study analysed the stomach contents of finescale triggerfish, Balistes polylepis, at two sites in the southern Gulf of California, in order to describe its diet. Methods The prey-specific index of relative importance (%PSIRIi) was determined, diet width was calculated with Levins’ index and the Costello method, and the trophic position was estimated using the R package dietr. Key results B. polylepis is an omnivorous species with a preference for animal material (TL = 3.1) that feeds on a wide range of prey. It is categorised as a generalist predator (Levins’ index, Bi = 0.99). The most important items in the diet were the colonial ascidian Lissoclinum fragile (%PSIRIi = 13.52) at Las Ánimas, and the Xanthidae family (%PSIRIi = 13.24) at San Juan de la Costa. Implications B. polylepis plays an important role. Because it can exploit a broad variety of resources, it participates in trophic interactions with several other species. It is essential to determine the trophic habits of this species in other areas of its distribution.

La Bahía de La Paz, es una de las bahías más grandes de la zona central del Golfo de California, esta zona se caracteriza por los altos niveles de captura comercial de peces que existen en la zona; sin embargo el número de investigaciones realizadas para conocer su diversidad taxonómica es bajo. Se determinó la variación en la diversidad taxonómica del ensamblaje de peces en ocho localidades de la zona oeste de la Bahía de La Paz, en el periodo de marzo de 2002 a abril de 2003. Se evaluaron los cambios en la diversidad de peces de arrecifes rocosos considerando la distancia taxonómica entre las especies, utilizando los índices de diversidad alfa, alfa promedio, beta y gamma, y los índices de distintividad taxonómica (Δ*), así como la distintividad taxonómica promedio (Δ+).Se realizaron censos visuales en 48 transectos de 100*5 m (500 m2) a una profundidad promedio de 5 m en un horario de 09:00 a 16:00 horas. Se observaron 24,633 organismos pertenecientes a 92 especies de 67 géneros de peces. De acuerdo a los índices de diversidad Alfa Promedio, Beta y Gamma, el mes con mayor diversidad fue agosto (19.5, 40.5 y 60 especies, respectivamente) y el de menor diversidad fue diciembre (20.625, 27.375 y 48 especies, respectivamente). Los índices de distintividad taxonómica (Δ*), y distintividad taxonómica promedio (Δ+), en el análisis espacial no mostraron diferencias (p=>0.05), mientras que en su forma temporal ambos mostraron diferencias (p=<0.05).

No abstract

An analysis of the variation of the density and biomass of the fish communities of the lagoon of La Paz, Mexico was carried out from November 2016 to September 2017. A total of 2763 organisms were collected with a total biomass of 211,422.93 g in an area of 5022 m 2 , a density and biomass of 0.550 lnd/m 2 and 44.091 g/m 2 . The site with the largest biomass was recorded in Zacatecas (11.179 g/m 2 ) located north of the lagoon, while Grand Plaza recorded the lowest biomass (2.732 g/m 2 ). Regarding the density, the maximum value was recorded in the site Yate Hundido, located northwest of the lagoon (0.129 lnd/m 2 ) and the lowest was Las Palmas (0.036 lnd/m 2 ) located north of the lagoon. The most abundant species was Diapterus peruvianus with 683 individuals and a biomass of 37,507.57 g. The physicochemical variables showed two seasons with significant change where we can observe higher temperatures in the summer (average of 27.45˚C) and minimum in winter (average of 22.49˚C). The Shannon-Weaver diversity index showed a difference (p = 0.050) between months, with the highest value recorded in April (H' = 2.133 bits/ind) and the lowest in June (H' = 1.041 bits/ind). The biomass and density values recorded in the lagoon were found to be associated with the spatio-temporal variation of temperature of the lagoon, as well as the resident and transitory species located in the area of study. In addition, the body sizes recorded corresponded to juvenile and young adult individuals.

No abstract