Carla Riva Rossi

Evaluating Potential Effects of Exotic Freshwater Fish From Incomplete Species Presence–absence Data

Many freshwater ecosystems and biotas around the world are threatened with extinction. Freshwater fishes, for example, are the most endangered vertebrates after amphibians. Exotic fish are widely recognized as a major disturbance agent for native fish. Evaluating the ecological effects of invaders presents many challenges and the problem is greatly augmented in parts of the world where the native fauna is poorly known and where exotic species are commonplace. We use the fish community of Patagonia, a small and distinct native biota dominated by exotic salmonids, as a case study to ask: what can we learn about the effects of exotic fish species from fragmentary or partial data and how do such data point the way to what needs to be learned? We review the available data and literature on the distribution and status of native and introduced fish. We compile a novel regional presence/absence species database, build fish distribution maps, describe distribution patterns of native and exotic species, and identify critical information voids. A comparative review of literature from Patagonia and Australasia, where a similar native and exotic fish fauna is found, helps us to identify research priorities and promising management strategies for the conservation of native fish fauna. We conclude that the main challenge for fish conservation in Patagonia is to identify management strategies that could preserve native species while maintaining the quality of salmonid fisheries.

First Documented Case of Anadromy in a Population of Introduced Rainbow Trout in Patagonia, Argentina

Abstract The examination of population-specific adaptations of introduced salmonids to the wide range of environments found in Patagonia (southern South America) can help unveil some of the genetic and environmental contributions to life history variation. The rainbow trout Oncorhynchus mykiss introduced into Argentina originated from a few parental stocks. Although some of these stocks were anadromous, all of the dozens of established populations described until now have been freshwater resident. In this paper we provide the first documentation of the presence of an anadromous run of rainbow trout in the Santa Cruz River, the second largest river of Argentinean Patagonia. Microsatellite analysis revealed that anadromous and resident fish from the Santa Cruz River are genetically indistinguishable, probably representing alternative life histories within the same population. Both wild types are very different from the fish of Danish origin that were reared in a local hatchery, suggesting that they are desc...

The invasion of an Atlantic Ocean river basin in Patagonia by Chinook salmon: new insights from SNPs

Chinook salmon spawning was first reported in the 1980s in the Caterina River tributary of the Santa Cruz River basin of Patagonia, which drains into the Atlantic Ocean. A naturalized population now persists and its source has been debated. Chinook salmon from California populations was directly released into the Santa Cruz River in the early twentieth century, but ocean ranching experiments on the Pacific coast of Patagonia (Chile) also released Chinook salmon of lower Columbia River origin (University of Washington hatchery stock) in the late twentieth century. We used genetic stock identification with single nucleotide polymorphisms to explore the origin of this Chinook salmon population. The genotypes of salmon that invaded the Santa Cruz River were compared with those derived from 69 known populations from the Northern Hemisphere. Chinook Salmon of the Santa Cruz River were found to be most similar to those from the lower Columbia River. This supports the hypothesis that the Santa Cruz River population was founded from the ocean ranching in southern Chile and the river was invaded by fish straying from Pacific coast basins. Moreover, we find that the life history of these naturalized fish, as inferred from scale analysis, was similar to that of the progenitor stock. We suggest that the successful invasion of the Caterina River in Patagonia by Chinook salmon was aided by pre-adaptations of some of the stocks used in the ocean ranching experiments to conditions in the new environment, rather than a post-colonization adaptation.

A MIOCENE CUSK-EEL (OPHIDIIFORMES: OPHIDIIDAE) FROM PENINSULA VALDES, ARGENTINA

Abstract Genypterus valdesensis, sp. nov. from the Puerto Madryn Formation in Península Valdés, Argentina is the first fossil ophidiid reported from South America and represents the first well preserved record of the genus worldwide. The specimen consists of a nearly complete articulated skull and some disarticulated postcranial elements. A thorough description is given of the osteological features of the species, which can be used to recognize it as a distinct taxon. The fossil species is characterized by the presence of a foramen on infraorbital 3 and by the square-shape of infraorbital 4. An array of morphological features taken in combination contribute to further differentiate G. valdesensis from the Recent species. This specimen also provides unequivocal evidence of the presence of the Ophidiiformes in the southwestern Atlantic Ocean 14 MA.

Disentangling the contributions of ocean ranching and net-pen aquaculture in the successful establishment of Chinook salmon in a Patagonian basin

The presence of Chinook salmon in Patagonia is an example of a successful invasion by a Pacific salmon species. The combination of historical records and genetic data can help to determine the origin of invasive / introduced species and allow the identification of the sources and dispersal process. We analyzed the genetic structure of Chinook salmon in the Futaleufú River (Pacific slope basin of Patagonia) using single nucleotide polymorphism genotypes and a recently described baseline dataset of native North American Chinook salmon populations. Our results revealed that Chinook salmon established in the Futaleufú River have high levels of within-population genetic diversity compared with populations from across the native range. Based on genetic similarity and historical reports, our results indicate that the Futaleufú population was first established by colonizing fish derived from the Lower Columbia River Basin, imported into Chile for ocean ranching purposes during the 1970s and 1980s, and afterward it was strongly supplemented by escaped fish from net pen aquaculture that used broodstock imported during the 1990s from various sources, including the California Central Valley (via New Zealand), the Middle Oregon Coast, and Vancouver Island. The higher incidence of fish derived from the most recent introductions in our sample suggest that the contribution of escaped salmon from these posterior stockings on establishment success must have been particularly strong because included different sources. Subsequent admixture and hybridization among these multiple independent source stocks is likely responsible for the high level of standing genetic variation, which may be facilitating local adaptation and augmenting the opportunity for successful invasion and further colonization.

Shifts in d15N signature following the onset of exogenous feeding in fishes: Importance of combining length and age data

The δ(15) N isotopic change of recently emerged rainbow trout Oncorhynchus mykiss due to diet shift from yolk sac to exogenous feeding was evaluated in a field study. The fit of a general model including both fish length and age in days as co-variables indicates that the specific δ(15) N of individual fish at any given time along the ontogeny is determined by its growth trajectory. The results suggest that estimations based on fish size alone could bias data interpretation and maternal origin determinations in partially migratory salmonids.