Biology

CITATIONS 72 READS 97 7 authors, including: Some of the authors of this publication are also working on these related projects: La cuenca del río Limay superior: una aproximación a la gestión de su ictiofauna desde un enfoque ecosistémico. Proyecto financiado por la Universidad Nacional del Comahue View project Phylogeography and landscape genetics of aquatic fauna in Patagonia View project

The present paper analyses predation patterns, of Percichthys trucha and salmonid fish upon Galaxias maculatus in five lakes of northern Patagonia with differing community and environmental characteristics. Tank experiments were performed to evaluate relative efficiency of native and exotic predators of G. maculatus under treatments with and without cover (aquatic vegetation). Important differences were found between predators with regards to distribution and consumption of G. maculatus. Salmonids are more efficient than P. trucha in consuming G. maculatus in deep environments with scarcely vegetation; in contrast to native species they frequently use the pelagic environment. Although pelagic habitat might have served in the past as a refuge from native predators in the past, G maculatus now experiences intense predation in the pelagic zone by exotic salmonids. It is suggested that the widespread distribution of G. maculatus in Patagonian lakes may have facilitated the success of salmonids throughout Patagonia.

CITATIONS 10 READS 26 3 authors, including: Some of the authors of this publication are also working on these related projects: La cuenca del río Limay superior: una aproximación a la gestión de su ictiofauna desde un enfoque ecosistémico. Proyecto financiado por la Universidad Nacional del Comahue View project Phylogeography and landscape genetics of aquatic fauna in Patagonia View project

To date a total of 34 alien taxa have been detected in Argentine freshwater systems. Knowledge about these organisms in terms of their actual spread and invasive status is scarce. Despite the existence of some laws regulating the import of foreign organisms, the issue if acknowledged by researchers does not occupy a prime position in research or official agendas. This is mostly due to a lack of awareness of the implications of alien aquatic invaders by policy makers, and the economic instability of the country, which has diverted funds into other areas considered more important. This paper focuses on generating a first assessment of the problem and designing a system that would allow for low-cost gathering of information regarding alien aquatic invaders, and making it readily available for researchers throughout Argentina.

Early in the 20th century, the fish fauna of Patagonia consisted of 20 native fish species. In 1904, exotic species, mostly salmonids from North America and Europe, were introduced, giving rise to an extensive sport fishery. Scientific literature, stocking and catch logbooks, and registries of organizations in charge of enforcing management practices were searched in relation to effects of probable policy goals upon actual fish assemblage structure of two major river basins of northern Patagonia. Policy goal history in this region can be divided into three periods. Between 1904 and 1910, goals were focused on increasing diversity and sport fishery opportunities through salmonid introductions. From 1910 to 1970, goals shifted towards development of both commercial and sport fisheries, increasing diversity by introducing and restocking salmonids and native fish species and preserving both through fishing regulations. In these two periods, policies were centralized under the federal government. From 1970 on, policy has been characterized by decentralization in relation to provincial and national park jurisdictions. The former fosters the development of sport fisheries, while the latter focuses on the protection of native fish species and opposes new introductions. However, Patagonia's isolated environments, lack of road infrastructure, particular management circumstances, biological capacities of released species, and great dispersion capacity of salmonids were fundamental factors that shaped the artificial and natural dispersion in both the Negro and Manso River drainages.

Exotic rainbow trout Oncorhynchus mykiss support an economically valuable recreational fishery in Patagonia but also create concern for impacts on native organisms. These concerns are intensified by the possibility of hatchery release programs in this region. We estimated losses of different prey from predation by rainbow trout in Lake Moreno, Río Negro Province, Argentina, using a bioenergetics model combined with input data from directed sampling on growth, seasonal diet, distribution, and thermal experience. The fish community was sampled seasonally using gill nets, hydroacoustics, and ichthyoplankton [Article] nets. Pelagic galaxiid larvae and benthic juvenile and adult small puyen Galaxias maculatus were the most important components of the diet. Bioenergetics simulations showed that over a 6-year life span in the lake (ages 1-7), rainbow trout attained a body mass of 2.3 kg and consumed 74.7 kg of food, of which 20% consisted of galaxiid larvae and 16% consisted of adult small puyen. Based on an estimated abundance of 29,000 rainbow trout of ages 1-7, this predator exerted significant but sustainable mortality on the native prey populations, consuming 44 metric tons or an estimated 23% of the annual larval galaxiid production and 35 metric tons of adult small puyen, which represented an unknown fraction of the postlarval population. Galaxiids supported the estimated predation demand under current conditions. However, simulations of stocking strategies normally proposed for this region showed that consumption demands on prey would increase to unsustainable levels, reducing native fish populations and likely reducing growth of rainbow trout. It is also probable that the fish community composition would shift further in response to the increased demand for prey by stocked predators. This implies that in some cases, stocking could jeopardize sport fisheries; stocking strategies should be evaluated on a case-by-case basis to be consistent with specific objectives for native fish conservation and sustainable food web interactions. 1406 VIGLIANO ET AL. 1408 VIGLIANO ET AL. 1416 VIGLIANO ET AL.

Knowledge of lake fish communities of Argentine Patagonia has grown in the past 20 years thanks to the use of gill nets. However, National Park officials and Fisher organizations dislike their use and would prefer the use of recreational fisher catch data. The present paper addresses advantages and disadvantages of using gill nets as compared to fishers. This was accomplished by analysis of gill net and fisher catch data from Lake Guillelmo, Parque Nacional Nahuel Huapi for the period 1997-1999. Both sets of data revealed the presence of only two salmonids, brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss). However, relative abundances of each species differed between fishing techniques, rainbow trout being dominant according to fisher catches and brook trout according to gill net catches. In addition, differences in size, age and spatial distribution brought about by the highly selective nature of fisher catches were clearly observed. This shows that fisher catch data can only be used to assess existing recreational Patagonian lake fisheries in terms of current or historical trends in catch composition, structure and fishing pressure. Studies of community composition, structure and processes leading to conservation or recreational fishery management should rely on gill net sampling designs tailored to different ecological and management questions, which can be complemented by fisher catch data.

CITATIONS 21 READS 45 5 authors, including: Some of the authors of this publication are also working on these related projects: La cuenca del río Limay superior: una aproximación a la gestión de su ictiofauna desde un enfoque ecosistémico. Proyecto financiado por la Universidad Nacional del Comahue View project Phylogeography and landscape genetics of aquatic fauna in Patagonia View project

The Northeast, Central, Western and Northwestern, and Patagonia and Tierra del Fuego regions dominate Argentina inland recreational fishing. Being each unique in terms of environmental context, fish fauna and fishery types. High species diversity, extractive fishing and highly priced fly-fishing catch and release fisheries characterizes the Northeast. The Central Western and Northwestern fisheries are extractive, targeting few species. Patagonia and Tierra del Fuego have extractive and catch and release salmonid fisheries on the Andes. There are extractive fisheries of native species on Atlantic drainages of northern Patagonia, and anadromous rainbow and brown trout fisheries on southern Patagonia and Tierra del Fuego.

CITATIONS 6 READS 117 4 authors: Some of the authors of this publication are also working on these related projects: Phylogeography and landscape genetics of aquatic fauna in Patagonia View project La cuenca del río Limay superior: una aproximación a la gestión de su ictiofauna desde un enfoque ecosistémico. Proyecto financiado por la Universidad Nacional del Comahue View project Romina Juncos