Diet overlap among non‐native trout species and native cutthroat Trout (Oncorhynchus clarkii) in two U.S. ecoregions

The invasion of freshwater ecosystems by non‐native species can constitute a significant threat to native species and ecosystem health. Non‐native trouts have long been stocked in areas where native trouts occur and have negatively impacted native trouts through predation, competition, and hybridization. This study encompassed two seasons of sampling efforts across two ecoregions of the western United States: The Great Basin in summer 2016 and the Yellowstone River Basin in summer 2017. We found significant dietary overlaps among native and non‐native trouts within the Great Basin and Yellowstone River Basin ecoregions. Three orders of invertebrates (Ephemeroptera, Trichoptera, and Diptera) composed the majority of stomach contents and were responsible for driving the observed patterns. Great Basin trout had higher body conditions (k), and non‐native Great Basin trout had higher gut fullness values than Yellowstone River Basin trout, indicating a possible limitation of food in the Yellowstone River Basin. Native fishes were the least abundant and had the lowest body condition in each ecoregion. These findings may indicate a negative impact on native trouts by non‐native trouts. We recommend additional monitoring of native and non‐native trout diets, regular invertebrate surveys to identify the availability of diet items, and reconsidering stocking efforts that can result in overlap of non‐native fishes with native cutthroat trout.     

Trophic relationship between the Patinga hybrid (Piaractus mesopotamicus x Piaractus brachypomus) and Echinorhynchus gomesi Machado Filho, 1948 in fish farms

A total of 122 Patinga specimens were collected from fish farms (P1, P2 and P3), and only those from fish farm P1 were shown to be infected with Echinorhynchus gomesi. In addition, fish in this study were shown to have diets that consisted of 21 different food items, and Notodiaptomus sp. (Copepoda: Calanoida) was identified as a potential intermediate host for E. gomesi.     

Foraging ecology and niche overlap in pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales from waters of the U.S. mid‐Atlantic coast

A complementary approach of stomach content and stable isotope analyses was used to characterize the foraging ecology and evaluate niche overlap between pygmy (Kogia breviceps) and dwarf (K. sima) sperm whales stranded on the U.S. mid‐Atlantic coast between 1998 and 2011. Food habits analysis demonstrated both species were primarily teuthophagous, with 35 species of cephalopods, and 2 species of mesopelagic fishes represented in their overall diets. Pianka's Index of niche overlap suggested high overlap between whale diets (O_n = 0.92), with squids from the families Histioteuthidae, Cranchidae, and Ommastrephidae serving as primary prey. Pygmy sperm whales consumed slightly larger prey sizes (mean mantle length [ML] = 10.8 cm) than dwarf sperm whales (mean ML = 7.8 cm). Mean prey sizes consumed by pygmy sperm whales increased with growth, but showed no trend in dwarf sperm whales. Significant differences were not detected in δ¹⁵N and δ¹³C values of muscle tissues from pygmy (10.8‰ ± 0.5‰, ?17.1‰ ± 0.6‰), and dwarf sperm whales (10.7‰ ± 0.5‰, ?17.0‰ ± 0.4‰), respectively. Isotopic niche widths also did not differ significantly and dietary overlap was high between the two species. Results suggest the feeding ecologies of the pygmy and dwarf sperm whales are similar and both species occupy equivalent trophic niches in the region.