Geographic and ontogenetic variation in the diet of two commonly exploited batoids (Chilean eagle ray and Pacific guitarfish) off Peru: evidence of trophic plasticity

This study provides information about the diet across geographic areas and throughout ontogeny and sex of two coastal and commercial batoid species in Peru (Chilean eagle ray Myliobatis chilensis and Pacific guitarfish Pseudobatos planiceps). Data was collected in the central coast (13°30′S to 14°30′S; Pisco district, Lima) and in the northern coast (13°12′S to 13°49′S; San Jose district, Lambayeque) off Peru during the second semester of the years 2015 and 2016 (i.e., winter and spring) in an El Niño event. A total of 357 stomach contents were analyzed in northern and central Peru with different oceanographic and ecological conditions. In the central coast, M. chilensis showed a high trophic position (tertiary consumer) due to its high consumption of Peruvian anchoveta (Engraulis ringens), while P. planiceps had a lower trophic position (secondary consumer) and a less specialized diet of benthic invertebrates (i.e., crustaceans and mollusks) and pelagic fish (e.g., E. ringens). In the northern coast, both species preyed mainly upon benthic invertebrates and to a lesser degree on fish; therefore, their trophic position was lower. Dietary variation was influenced by species, geographic location, and ontogeny. The diet variability between geographic locations shows insights of these batoids’ trophic plasticity and opportunistic feeding behavior in response to differences in the local prey availability, an effect that may be amplified during the El Niño–Southern Oscillation (ENSO). The spatial variation in this species diet may indicate that they play different ecological roles in distinct environments. This study contributes to the scarce literature about batoids’ ecology in the southeast Pacific Ocean and presents novel information on habitat-specific diet composition.

     

First assessment of the diet composition and trophic level of an assemblage of poorly known chondrichthyans off the central coast of Peru

Although chondrichthyans are conspicuously present in shallow waters, many ecological aspects of neritic species in the Humboldt Current System remain unknown. This study provides a first assessment of the diet of seven commercially exploited and understudied sympatric chondrichthyans inhabiting nearshore habitats off the central coast of Peru: four stingrays (Hypanus dipterurus, Myliobatis peruvianus, M. chilensis, and Urotrygon chilensis), a guitarfish (Pseudobatos planiceps), a smooth-hound shark (Mustelus mento), and a chimaera (Callorhinchus callorynchus). A total of 166 stomachs were examined between 2012 and 2015 and prey items were pooled for the total of years for analysis. Although our analysis did not account for inter seasons variability, our results suggest diet partitioning among species, except for the stingrays’ group. A diet based on soft-bottom polychaetes and fish was shared by H. dipterurus, M. peruvianus, and M. chilensis, while soft-bottom polychaetes and crabs were more important in U. chilensis. The smooth-hound shark and guitarfish exhibited a diet dominated by crabs, and the chimaera consumed mainly hard-bottom mollusks. Foraging habitat estimations distinguished two main habitats of association: Benthic, including the stingray U. chilensis, the chimaera, and the smooth-hound shark; and benthic-demersal, including the guitarfish, and the rest of stingrays. A pattern of feeding specialization was observed for H. dipterurus, P. planiceps, and C. callorynchus. Preliminary trophic level estimations based on diet composition placed these species as secondary consumers. Intraspecific dietary variation was assessed for P. planiceps and H. dipterurus as their sampled sizes allowed meaningful comparisons. The diet of P. planiceps varied from small to large sizes but not for H. dipterurus. No differences were detected on diet composition between males and females in either species. Despite the limited temporal resolution, this study provides the first insights of chondrichthyans predatory activity, suggesting diet partitioning among the species of this assemblage in a nearshore habitat of the central coast of Peru. Enhancing the temporal resolution of this type of studies would improve our knowledge on trophic functioning in the Humboldt Current ecosystem.