Claudio Baigún

Distribution patterns of native freshwater fishes in Patagonia (Argentina)

Summary The Patagonian ichthyofauna comprises a total of 29 species. This low species richness contrasts with other cold-temperate regions of the southern hemisphere. The fauna includes only 15 species native to the Patagonian Province and seven to the Brazilian Province. Knowledge of native fish fauna diversity patterns is still fragmentary. Based on extensive sampling during the IBOY initiative and also reviewing seminal and review literature, we provide an updated perspective of native freshwater fishes in Patagonia by describing and analyzing their distribution and occurrence across basins. The results show that species richness varies along latitude, with a maximum at the 38°–40° interval, principally due to the presence of Brazilian species inhabiting northern Patagonia. However, species numbers remained constant south of 48° latitude. We report extended distribution ranges for several species such as Diplomystes mesembrinus, Hatcheria macraei, Trichomycterus areolatus, and Odontesthes hatcheri, and also the new discovery of a Brazilian species (Corydoras paleatus) in the north of Patagonia. Cluster analysis based on presence-absence information revealed co-occurrence patterns at the level of basins, showing that only few species (Percichtys trucha, Odontesthes hatcheri, Hatcheria macraei, Galaxias platei, and G. maculatus) are ubiquitous. Restricted distribution and even endemism for the remaining species could be attributed to river drainage systems which influence dispersion ability, to the influence of past glaciation events, and impact by introduced salmonids in the last century. Future research therefore should be focused on distribution patterns of introduced species since they are an important component of present Patagonian fish assemblages. Also, efforts should be devoted to understanding how diversity patterns of freshwater fish communities vary across scales and how community changes are relevant for native species conservation.

Shallow lakes from the Central Plains of Argentina: an overview and worldwide comparative analysis of their basic limnological features

The Central Plains of Argentina is a heterogeneous environment, but the lakes there share some fundamental features: they are all shallow and polymictic as being well exposed to wind. First, we provide a synthesis of the climate, geology, and hydrological network. We also discussed shallow lakes origin and their limnological and biological salient features. Second, we focus on Pampean shallow lakes from a global perspective, comparing the limnological variables: total phosphorus concentration (TP), total nitrogen concentration (TN), chlorophyll a (Chl a) concentrations, and Secchi disk reading (SD) from a compiled database. No significant differences in the Chl a vs. TP relationship were found between Pampean and other shallow lakes. Otherwise, the chlorophyll yield per unit of phosphorus of Pampean lakes is similar to the world shallow lakes average. Moreover, the relationship SD vs. Chl a differed significantly between Pampean and the remaining world lakes, about 50–60%. When confronted against other lakes worldwide, Pampean shallow lakes depart from most of them as having higher TP, TN, and Chl a concentrations and much lower SD transparency, and therefore they stand as extremes of the trophic-state continuum. Despite their highly turbid state, these lakes provide valuable ecosystem services that are highly appreciated and mobilize important economic resources.

Assessment of condition in pejerrey Odontesthes bonariensis (Atheriniformes: Atherinopsidae) populations: which index works best?

The pejerrey Odontesthes bonariensis is the most important target species in temperate freshwater fisheries of Argentina, and assessment of condition has been a regular practice and common diagnostic tool. Most pejerrey fishery studies have used Fultons (K) index, without testing whether underlying assumptions or requirements were met. We analyzed and contrasted the applicability of K, Kn and Wr indices to assess condition status in several pejerrey populations inhabiting Pampean lakes. Our results showed that whereas Wr and Kn displayed significant condition changes across length at some study lakes, Kn portrayed a small range of variation. We also noted that pejerrey maximum length and size structure strongly varied among populations probably due to the characteristics of trophic niche changes through lifespan, depending on lake limnological characteristics and zooplankton availability. We conclude that the K index should be disregarded in those cases where populations show allometric growth and size ranges strongly vary. In turn, the Kn index appears to be only appropriate for regular within population assessment, being difficult to apply when comparisons between populations are needed and when they exhibit different weight-length relationship slopes. Finally, the Wr index should be strongly preferred if the objective is to perform comparisons between pejerrey populations, particularly when population structure is not well known, stocking has been used for population recovery, lakes are strongly supported by limnological changes, data are limited to only one or few samplings and metaphoetesis is suspected in pejerrey populations.

Biological traits and growth patterns of pejerrey Odontesthes argentinensis

This study assesses for the first time the relationship between annual cycles of different biological indices with growth patterns of a marine pejerrey Odontesthes argentinensis population near its southern-distribution boundary in North Patagonia. The reproductive period is between September and November evidenced by an increase in the gonado-somatic index with a peak in October corresponding to spawning. The reproductive cycle was also coupled with metabolic processes related to energy allocation as shown by changes in the hepato-somatic index and body condition. Total length (L(T) ) at maturity was 270 for females and 282 mm for males, whereas fecundity was estimated at mean ±s.d. = 9380 ± 1797 mature oocytes. Based on the marginal increment analysis, most of the scales showed a maximum value during summer, with a sharp decline thereafter during autumn and winter, indicating that scale rings are formed during the latter period and only once a year. Growth fitted by the von Bertalanffy model for both males and females did not show significant differences and showed a rapid growth during the first 2 years. The shorter reproductive period compared with that of the northern O. argentinensis populations inhabiting tropical and subtropical areas was interpreted as an adjustment to temperate environmental conditions. The larger maximum L(T) and L(T) at first maturity are in agreement with the counter-gradient hypothesis and could be related to the selective effects of low temperature and a shorter growing season. This latitude dependency argues strongly against the application of the same fishing regulations for different O. argentinensis populations as a whole and reinforces the need to assess basic biological features at a population scale to promote local sustainable fisheries management.

Fish assemblage of a Pampean shallow lake, a story of instability

Abstract Pampean lakes are characterised by the alternation of flood and drought periods, but little is known about its effects on fish assemblage in an extended temporal scale. This study analyses the temporal variability of the fish assemblage in Chascomús Lake, and discusses the role of temperature and precipitation as potential drivers of fish composition shifts. Data acquisition was based on experimental fishing performed from 1999 to 2013 and from historical fishing records. Two alternative fish assemblage configurations were identified by cluster analysis. Odontesthes bonariensis, Parapimelodus valenciennis and Cyphocharax voga were the dominant species, which accounted for 70–80% of the relative abundance. The species O. bonariensis showed temporal fluctuations in its representativeness, changing from dominant to almost absent, whereas C. voga and P. valenciennis changed their abundance following a similar pattern along time. When historical data were considered, Platanichthys platana appeared as the fourth most relevant species. Precipitation, critical temperatures and fish mortalities were identified as the main drivers of species abundance shifts. This study highlights the importance of long-term assessments to understand the influence of climatic factors and the need to maintain or restore natural ecological processes as the basis to support dynamic sustainable fisheries in Pampean shallow lakes.

Structural Indices for Stock Assessment of and Management Recommendations for Pejerrey Odonthestes bonariensis in Argentina

Abstract Stock assessments based on catch per unit effort (CPUE), relative weight (Wr ), and proportional stock density (PSD) were conducted on 18 populations of pejerrey in pampean lakes ofeastern Argentina. The CPUE ofgill nets ranged from 2.9 to 435.2 kg/net-night and was correlated with zooplankton biomass (r = 0.68; P < 0.01). The average Wr (the ratio of empirical weight to a “standard” weight for a fish of the same size, expressed as a whole number) of designated size-groups ranged from 68 to 119. Low Wr was apparent in all size-groups in two lakes with high inorganic turbidity and in one hypertrophic lake with a chlorophyll-a concentration higher than 400 μg/L. Among all the lakes, the PSD (the proportion of fish of “quality” size in a stock, expressed as a percentage) ranged from 0 to 90 and was not related to Wr of any size-group. The indices of CPUE and PSD provided useful criteria to define five types of pejerrey populations and propose minimum size or slot length limit regulations for harvest...

Assessment of sábalo (Prochilodus lineatus) fisheries in the lower Paraná River basin (Argentina) based on hydrological, biological, and fishery indicators

This study assesses the change in fish exploitation patterns of the sabalo fisheries of the lower Parana River basin based on hydrological, biological, and fishery indicators. From historical catch records, we recorded a shift from a lightly and moderate exploited status before 2001 to a heavily exploited one, as a result of the development of sabalo exports from 2001 onwards. Channel and floodplain connectivity indices demonstrated that the Parana exhibited highly favorable hydrological conditions between 1972 and 1999 but more adverse conditions from 1999 to 2009, as a consequence of flood pulses reduction coincident with a fishing mortality increment. A total catch of 15,000 tons, including local consumption, regional market, informal sales, and exportation volumes, was estimated as the maximum sustainable catch. That level was instead exceeded 3 fold in 2004, in parallel with a decrease in the mean fish length from 48 to 42 cm, along with a reduction in both the mesh size from 16 to 12 cm and megaspawner proportion, and an increase of fishing mortality. Although growth overfishing was not noted, an analysis of the spawning potential ratio trend indicated that recruitment overfishing took place during 2005, since the fishing mortality rate was 4 times greater than the natural mortality rate. These observations suggest that less favorable hydrological conditions after 1999 coupled with a coincident high fishing pressure could have impacted the sabalo population biomass. Management of sabalo fisheries requires to set aside a single economic vision of the resource use moving to an ecosystem-oriented approach that incorporate, among others components, the hydrological regime, species life history traits, fishing impacts on other species, and main stakeholders socioeconomic requirements as key elements for the preservation of fishery sustainability.

Freshwater fishes of Patagonia: conservation and fisheries

The absence of much literature on the Patagonian fish fauna in comparison with that of the neotropics, has previously been blamed on its poor species diversity. Knowledge of the fishes of Patagonia, however, rose sharply at the beginning of the present century, allowing for an understanding of the complex biogeographical history that has led to the present diversity and distribution patterns. There are several new and potential threats to biodiversity and conservation of Patagonian fishes, such as the introduction of exotic species, damming, climate change and changes geared to safeguard economic interests, often acting synergistically. A great amount of new information is now available and the aim of the present review is to articulate this knowledge in a comprehensive way in order to aid in the development of tools to face the increasing challenges posed by environmental change and human activity. Knowledge about fishes of Patagonia has grown at the same time as human actions, and presence.

Characteristics of Deep Pools Used by Adult Summer Steelhead in Steamboat Creek, Oregon

Abstract This study examined environmental factors that affect deep-pool use by adult summer steelhead Oncorhynchus mykiss in Steamboat Creek, Umpqua River basin, Oregon. Deep pools (>0.8 m depth) represented only 4% of the available habitat area, and 39% of these pools had a mean bottom temperature not exceeding 19°C. Fish and habitat surveys were conducted in August and the first half of September of 1991 and 1992. The presence of adult summer steelhead in pools was determined by snorkeling and visual inspection, and the physical, chemical, and geomorphic characteristics were measured. Differences in deep-pool use by summer steelhead and their relationship to environmental characteristics were assessed by descriptive canonical discriminant analysis. The canonical function explained 69% of the variation in deep-pool use and defined a gradient from long, shaded deep pools with a coarse substrate and colder bottoms (which fish used) to shorter, shallower, sunny pools with fine particulate substrate, homoge...

Assessment of Social and Economic Factors For Management of Summer Pejerrey Recreational Fisheries in Pampean Lakes (Argentina)

ABSTRACT This study illustrates the importance of assessing social and economic variables for management of recreational pejerrey fisheries in Pampean lakes. We conclude that summer pejerrey anglers differed by lakes in their motivations, preferences, and economic valuation of their fisheries and that most of the differences were attributed to travel distance, facilities, and quality of the fishery. We surveyed four fisheries located in different geographical areas, assessing preference and motivation by interviewing boat anglers at access points and then applying the contingent value method to assess economic values under current and different management conditions, (greater catch or larger size). Results indicated that anglers considered factors other than catching fish to be important, and a continuum of preferences and motivations was observed on a regional basis. Economic analysis yielding expenditures for study lakes averaged US