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The ability to detect species at low densities, greatly improves the success of management action on alien invasive species and decreases their possible impact on ecosystems. In the last two decades, exotic Chinook salmon (Oncorhynchus tshawytscha) have established populations in both Pacific and Atlantic river basins of Patagonia. The last established populations have been reported in the extreme south of Patagonia, on the island of Tierra del Fuego (TDF). The relatively recent appearance of Chinook salmon in TDF and the great phenotypic plasticity of this species, make it necessary to study their distribution and expansion as soon as possible, since they have the potential to negatively impact on native ecosystems. With the objective of knowing the current distribution status of exotic Chinook salmon in TDF, we optimized and implemented a detection method based on environmental DNA (eDNA). First, we designed Chinook salmon-specific primers, with no cross-amplification, using DNA from other species that are living at the same environment. Second, we validated the primers in situ by detecting Chinook salmon DNA from natural environments at the same time that we performed a conventional survey using an electrofishing survey method. Finally, we collected water samples from 10 river basins and one estuary within TDF and one river basin from Isla de los Estados (IE) and performed single-species real-time PCR assays. We were able to detect Chinook salmon DNA from 5 basins and from the estuary in TDF. These eDNA-based results allowed us to confirm the expansion of exotic Chinook salmon since they were first reported in TDF.

SUMMARY: Subantarctic notothenioids are exposed to wider variations in temperature than those encountered in the Antarctic Ocean, the ancestral environment of the group. In this study the influence of temperature on the routine metabolic rate of Subantarctic teleosts was described and the results were compared with routine metabolic rates of species with different geographical distributions, exploring the concept of Metabolic Cold Adaptation (MCA). Oxygen consumption (VO 2R ) was determined as an estimate of the routine metabolic rate for the following Subantarctic notothenioids: Paranotothenia magellanica, Patagonotothen sima, Eleginops maclovinus, Harpagifer bispinis and the eelpout Austrolycus depressiceps. In all studied species and tested temperatures, body mass and VO 2R showed a positive correlation. A drop in the temperature from 10 to 2ºC produced a significant reduction of VO 2R values with a Q 10 (10-2) varying between 4.69 and 9.54. VO 2R values were related to species habitat: pelagic species reached the highest values of VO 2R , while sluggish species had the lowest ones. We can conclude that the metabolic rates of these species of Subantarctic fish do not show MCA at the investigated temperatures.

The energy density (ED) of nine species of sub-Antarctic fishes was estimated by calorimetry. The fish, seven notothenioids, one atherinopsid and one galaxiid, represents some of the more abundant species in the ichthyofauna of the Beagle Channel. Principal-components analysis (PCA) of the ED of the different organs/tissues indicated that PC(1) and PC(2) accounted for 87% of the variability. Separation along PC(1) corresponded to differences in muscle and liver energy densities whereas separation along PC(2) corresponded to differences in the ED of the gonads. Differences between species were significant except for P. sima. Inclusion of the gonadosomatic index (GSI) as an explanatory variable enabled us to establish the existence of energy transfer from muscle and liver to the gonads in ripe P. tessellata females. Total ED values varied between 4.21 and 6.26 kJ g(-1), the pelagic Odontesthes sp. being the species with the highest ED. A significant relationship between ED and muscle dry weight (DW(M)) was found for all the species except P. tessellata. These data are the first direct estimates of ED of fishes from the Beagle Channel.

The Patagonian blennie Eleginops maclovinus is a coastal and estuarine species, important in recreational and commercial fisheries, and with aquaculture potential. This study assessed the effect of temperature on feeding and the allocation of energy in growth and swimming in a sub-Antarctic population. For growth experiments, two groups of 8 juveniles were reared at 4 and 10 °C (corresponding to winter and summer habitat temperatures, respectively) for 3 months. Swimming experiments were conducted at 5 and 10 °C, measuring the oxygen consumption before and after forced swimming for 1 min at a speed of 10 total lengths (TL)/s. Temperature affects growth. TL increased 0.09 cm at 4 °C versus 0.30 cm at 10 °C. Body mass grew 0.49 g at 4 °C versus 1.65 g at 10 °C, whereas the Fulton's condition factor increased 0.021 at 4 °C versus 0.080 at 10 °C. The ingested food was more than twofold higher at 10 than at 4 °C, while the feces produced at 4 °C was about twofold higher. The scope between baseline and peak oxygen consumption after forced swimming was affected by temperature, being 4.51 at 5 °C and 3.03 at 10 °C. The percentage energy expenditure until the return of baseline oxygen consumption values showed a marked temperature effect, being higher at 5 °C. We propose the existence of a tradeoff in the allocation of energy between swimming activity and growth, with proportionally more energy being consumed at low temperatures for swimming than for other physiological functions like growth.