Miguel Pascual

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...

Predicting the outcome of competition using experimental data : Maximum likelihood and bayesian approaches

Lotka-Volterra (LV) equations have been used extensively to explore the possible dynamic outcomes of interspecific competition. But while there have been hundreds of papers on the mathematical properties of Lotka-Volterra models, there have been only a handful of papers that explore techniques for fitting these models to actual data, and no papers that explore the interface of experimental design and statistical inference when fitting LV equations to census data. In this paper we present a statistical analysis of Gauses experimental cultures of Paramecium aurelia and P. caudatum, using analytical methods based on maximum likelihood and Bayesian statistics. We compare the effectiveness of these two approaches in addressing several questions about competition from experimental data : Are the mutual effects of competing populations substantial ? Are these competitive effects symmetrical ? Are two populations expected to coexist or to eliminate each other by competition ? We show that even a laboratory-derived data set with minimal variability can entail significant levels of uncertainty about the nature of the competitive interaction. We assess the errors involved in estimating the strength and symmetry of competition, and find that ones conclusions depend critically on assumptions about sources of variability in the data. We also estimate the probabilities of alternative dynamic behaviors for competing species. We use simulations to evaluate how particular experimental designs might improve our power to characterize the dynamic outcome of competition. We show that much more information is gained by running competition experiments at different starting conditions than by replicating the same experiment for a particular starting condition.

Factors Affecting the Homing of Fall Chinook Salmon from Columbia River Hatcheries

Abstract Straying results in an exchange of individuals between wild and hatchery salmon populations and is important because it could affect their genetic differences. Understanding what factors affect straying could help in the development of procedures for controlling the influence of specific stocks on nearby populations. We explore the effects of release date and the transportation of juvenile Chinook salmon Oncorhynchus tshawytscha on straying by adults from two Columbia River hatcheries. Early and late releases from Washougal Hatchery produced much higher straying levels than intermediate release dates, and this pattern was consistent among brood years. Fish reared at Grays River Hatchery and released from Washougal Hatchery strayed significantly more than local (i.e., Washougal) fish of the same brood year and release date. Our results and those from previous studies indicate that the sequence of imprinting events is characterized by the combination of the time at which the fish experience given l...

Conservation of harvested populations in fluctuating environments: the case of the Serengeti wildebeest

1. In this paper we examine the effects of alternative harvesting strategies on the wildebeest (Connochaetes taurinus) population in Serengeti National Park, Tanzania, within a Bayesian decision setting. 2. A wildebeest population dynamics model is constructed where mortality and recruitment are driven by environmental conditions. The applicability of the model is explored by fitting it to historical abundance data. 3. The uncertainty about the true dynamics of the population is represented by different degrees of rainfall-dependence in the recruitment of new individuals to the population. The likelihood of alternative recruitment scenarios is estimated within a Bayesian statistical framework. 4. The implications of different harvesting strategies for conservation, harvest productivity and harvest variability are evaluated using a Monte Carlo simulation of the population dynamics and harvest process. 5. The risk of collapse of the unexploited population is found to be higher for more rainfall-dependent recruitment scenarios. A clear trade-off exists between maximizing average harvest and minimizing the risk of population collapse. Constant harvest rate exploitation regimes produce similar average harvests to constant quota regimes and at the same time significantly reduce the risk of collapse. 6. The fastest way to determine the intensity of rainfall-dependence in the recruitment process is to eliminate all exploitation.

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.

The Patagonian Challenge: Melding Conservation with Development

Patagonia, at the southern tip of South America (Figure 17.1), is a region of over one million km2 shared by Chile and Argentina, endowed with some of the wildest landscapes in the world. Although remote and sparsely populated, Patagonian ecosystems are not pristine—most of them have been significantly disturbed by human activities. As is the case with much of Latin America, Patagonia is experiencing a push for economic development that is imposing ever increasing strains on natural resources.

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.

Analysis of Historic Data for Juvenile and Adult Salmonid Production. Phase 1, Final Report.

Survival of hatchery reared Columbia River chinook (Oncorhynchus tshawytscha) salmon from release to return is highly variable and thought to be related to river flow during juvenile outmigration in the spring. The purpose of this project is to examine the relationship between survival of coded-wire-tagged (CWT) Columbia River salmonids and in-river flow and other freshwater factors. This report covers Phase 1, in which two methods to estimate survival were developed and evaluated, and criteria for data selection were established.