Abstract
To assess the feeding habits of Rhinobatos glaucostigma (speckled guitarfish), the stomach contents of 176 individuals were examined. Specimens were obtained from the artisanal gillnet fisheries operating off Nayarit, Mexico, in the southeastern region of the Gulf of California, during January–August 2008 and January–May 2009. Relative measures of prey quantities and nonparametric multivariate methods were used to analyze diet differences between sex and maturity stages. The trophic relationship and feeding strategy were determined using Levin’s niche amplitude index, the Costello method modified by Amundsen, and Pianka’s diet overlap index. The overall diet was dominated by crustaceans, primarily decapods, brachyurans, and cumaceans. Diets were similar between sexes and maturity stages, except between mature females and males where only slight differences were found. Mature females and immature specimens of both sexes showed specialized diets, while mature males had a generalist diet. A significant overlap between sexes and maturity stage diets was found. Diet compositions allowed us to estimate a standardized trophic level of 3.57 for R. glaucostigma. The diet compositions between sexes and maturity stages suggest that all individuals consume similar prey items and have similar trophic roles in the benthic community of the southeastern region of the Gulf of California, where R. glaucostigma should be considered a secondary consumer.
Highlights
At the most basic level, the ecological role of a species is defined by its position in the food web
The number of stomachs examined was sufficient to describe the diet of R. glaucostigma and examine differences between sexes and maturity stages
The results of this study show that the main prey in the diet composition of R. glaucostigma were crustaceans, primarily decapods, brachyurans, and cumaceans, indicating
Summary
At the most basic level, the ecological role of a species is defined by its position in the food web. It is predicted that batoids play a critical role in the dynamics of marine ecosystems as predator species at intermediate levels (Ritchie and Johnson 2009), where they are a significant link in food webs in the demersal marine communities Se predice que los batoideos tienen un papel crítico en la dinámica de los ecosistemas marinos como especies depredadoras a niveles intermedios (Ritchie y Johnson 2009), donde son una liga importante en las redes tróficas de las Ciencias Marinas, Vol 39, No 3, 2013 et al 2008) and an important component of the community structure (Braccini and Perez 2005, Bizzarro et al 2007, Heithaus et al 2008). Quantitative studies of their diet and trophic ecology may contribute towards a better understanding of their ecological role in marine ecosystems, and may facilitate the development of ecosystem-based management approaches (Heithaus et al 2008, Espinoza et al 2013)
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