Development and application of DNA techniques for validating and improving pinniped diet estimates

Polymerase chain reaction techniques were developed and applied to identify DNA from .40 species of prey contained in fecal (scat) soft-part matrix collected at terrestrial sites used by Steller sea lions (Eumetopias jubatus) in British Columbia and the eastern Aleutian Islands, Alaska. Sixty percent more fish and cephalopod prey were identified by morphological analyses of hard parts compared with DNA analysis of soft parts (hard parts identified higher relative proportions of Ammodytes sp., Cottidae, and certain Gadidae). DNA identified 213 prey occurrences, of which 75 (35%) were undetected by hard parts (mainly Salmonidae, Pleuronectidae, Elasmobranchii, and Cephalopoda), and thereby increased species occurrences by 22% overall and species richness in 44% of cases (when comparing 110 scats that amplified prey DNA). Prey composition was identical within only 20% of scats. Overall, diet composition derived from both identification techniques combined did not differ significantly from hard-part identification alone, suggesting that past scat-based diet studies have not missed major dietary components. However, significant differences in relative diet contributions across scats (as identified using the two techniques separately) reflect passage rate differences between hard and soft digesta material and highlight certain hypothesized limitations in conventional morphological-based methods (e.g., differences in resistance to digestion, hard part regurgitation, partial and secondary prey consumption), as well as potential technical issues (e.g., resolution of primer efficiency and sensitivity and scat subsampling protocols). DNA analysis of salmon occurrence (from scat soft-part matrix and 238 archived salmon hard parts) provided species-level taxonomic resolution that could not be obtained by morphological identification and showed that Steller sea lions were primarily consuming pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. Notably, DNA from Atlantic salmon (Salmo salar) that likely originated from a distant fish farm was also detected in two scats from one site in the eastern Aleutian Islands. Overall, molecular techniques are valuable for identifying prey in the fecal remains of marine predators. Combining DNA and hard-part identification will effectively alleviate certain predicted biases and will ultimately enhance measures of diet richness, fisheries interactions (especially salmon-related ones), and the ecological role of pinnipeds and other marine predators, to the benefit of marine wildlife conservationists and fisheries managers.

Avian Piscivores as Vectors for Myxobolus cerebralis in the Greater Yellowstone Ecosystem

Myxobolus cerebralis, the cause of whirling disease in salmonids, has dispersed to waters in 25 states within the USA, often by an unknown vector. Its incidence in Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri within the highly protected environment of Yellowstone Lake, Yellowstone National Park, is a prime example. Given the local abundances of piscivorous birds, we sought to clarify their potential role in the dissemination of M. cerebralis. Six individuals from each of three bird species (American white pelican Pelecanus erythrorhynchos, double-crested cormorant Phalacrocorax auritus, and great blue heron Ardea herodias) were fed known-infected or uninfected rainbow trout O. mykiss. Fecal material produced during 10-d periods before and after feeding was collected to determine whether M. cerebralis could be detected and, if so, whether it remained viable after passage through the gastrointestinal tract of these birds. For all (100%) of the nine birds fed known-infected fish, fecal samples collected during days 1–4 after feeding tested positive for M. cerebralis by polymerase chain reaction. In addition, tubificid worms Tubifex tubifex that were fed fecal material from known-infected great blue herons produced triactinomyxons in laboratory cultures, confirming the persistent viability of the parasite. No triactinomyxons were produced from T. tubifex fed fecal material from known-infected American white pelicans or double-crested cormorants, indicating a potential loss of parasite viability in these species. Great blue herons have the ability to concentrate and release viable myxospores into shallow-water habitats that are highly suitable for T. tubifex, thereby supporting a positive feedback loop in which the proliferation of M. cerebralis is enhanced. The presence of avian piscivores as an important component of aquatic ecosystems should continue to be supported. However, given the distances traveled by great blue herons between rookeries and foraging areas in just days, any practices that unnaturally attract them may heighten the probability of M. cerebralis dispersal and proliferation within the Greater Yellowstone Ecosystem.