Stable isotope profiles of partially migratory salmonid populations in Atlantic rivers of Patagonia

Abstract

In the present study, profiles of stable isotope composition were characterized for two species with partially migratory populations in rivers along the latitudinal gradient of Patagonia, brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss. The effects of factors (e.g. ontogeny of fishes, location, species and fasting) that may influence the stable isotope analysis (SIA) were evaluated, as was SIA evaluated as a tool to assign individual fish to their corresponding ecotype. Anadromous fishes exhibited enriched d 15 N (15Á2 AE 1Á0%; mean AE S.D.) and d 13 C (À19Á2 AE 1Á3%) relative to resident fishes' d 15 N (8Á8 AE 1Á1%) and d 13 C (À23Á2 AE 2Á5%). For both species, the difference in d 15 N was larger between resident (range 6Á8-10Á7%) and anadromous (range 14Á3-17Á8%) fishes than that in d 13 C. Values of d 13 C, while not as dramatically contrasting in rainbow trout, provided a powerful anadromy marker for brown trout in the region. Increases were found in both d 15 N and d 13 C during the spawning migration of anadromous rainbow trout, most likely due to fasting. Differences in stable isotopes between location, size and species were found, suggesting different stable isotopes base levels in freshwater environments and different trophic levels and feeding location of anadromous populations. The SIA was demonstrated as a powerful tool for ecotype discrimination in Patagonian Rivers, overriding any effect of sampling location, size or species.

Chinook salmon (Oncorhynchus tshawytscha, Walbaum 1792) in the Beagle Channel, Tierra del Fuego: the onset of an invasion

“…Anadromous salmon are typically enriched with d 15 N and d 13 C relative to the other sources of N and C in watersheds (Rubenstein & Hobson 2004), revealing ocean migrations in individuals sampled in freshwater. C signatures also correlate with the use of different ocean domains by different populations (Ciancio et al 2008). Stable isotope analysis of Ovando-Lapataia Chinook population indicates general patterns consistent with those of other populations in the region, but characteristically enriched levels of C indicates a distinct ocean feeding location as compared to Atlantic populations in the Santa Cruz River.…”

“…Accordingly, exotic Chinook salmon in New Zealand (James and Unwin 1996) and in Argentina (Ciancio et al, 2008) prey on native fish and squid. Potential prey for Chinook salmon in the Beagle Channel are several fish species, like the Notothenioids (Eleginops maclovinus, Patagonotothen tessellata, P. cornucola, P. sima, Paranotothenia magellanica, Harpagifer bispinis), the Zoarcidae Austrolychus depressiceps, the galaxiid Galaxias maculatus, that inhabit the Ovando and Lapataia rivers, the Atherinidae Odonthestes smitti and O. nigricans, and the fuegian spratt Sprattus fuegensis, that migrate into the Beagle Channel every summer.…”

The use of stable isotopes to trace small-scale movements by small fish species

“…Movement or dispersal ability is an important trait in understanding species coexistence at the regional scale (Kneitel & Chase, 2004). Examples of movement of biological significance that have been described in the literature include those for reproductive habitat (Hobson & Wassenaar, 1997), for feeding (Ciancio et al, 2008), and for over-wintering (Wocher & Rosch, 2006). In aquatic ecosystems in particular, movement by salmonid species is well represented in the literature, whereas those made by cyprinids are not (Lucas & Baras, 2001).…”

Discrimination between farmed and free-living invasive salmonids in Chilean Patagonia using stable isotope analysis

“…The isotopic signatures of small juveniles will not generally be affected by anadromy or piscivory, but large anadromous salmonids returning from the sea to spawn in Atlantic Patagonia (Ciancio et al 2008a, b) have shown enriched d 15 N SIS similar to values found amongst farmed fish in our study. In this case, scale analysis or Sr:Ca profiles (Ciancio et al 2008b) may be required to identify anadromous individuals, which may not be readily separated from aquaculture escapees by SIA alone. Cessation of feeding can also result in d 15 N enrichment due to mobilisation, reorganisation and catabolism of tissue (Doucett et al 1999), but fasting is only likely to affect SIS of salmonids during spawning (Ciancio et al 2008b), and perhaps also during the first few days following a escape event, when escapees may have empty stomachs while they learn to forage on natural prey (Munakata et al 2000).…”

“…In this case, scale analysis or Sr:Ca profiles (Ciancio et al 2008b) may be required to identify anadromous individuals, which may not be readily separated from aquaculture escapees by SIA alone. Cessation of feeding can also result in d 15 N enrichment due to mobilisation, reorganisation and catabolism of tissue (Doucett et al 1999), but fasting is only likely to affect SIS of salmonids during spawning (Ciancio et al 2008b), and perhaps also during the first few days following a escape event, when escapees may have empty stomachs while they learn to forage on natural prey (Munakata et al 2000). The latter will tend to delay the time of isotopic incorporation, and therefore extend the length of time aquaculture escapees can be detected.…”