An interdisciplinary team of fifteen men and women scientists, led by specialists from the CONICET, developed a chemical method that will make it possible to accurately define the origin and migratory trajectories of Chinook salmon (Oncorhynchus tshawytscha) in Patagonia. This salmon is native to the North Pacific Ocean and has an invasive behavior in Patagonian waters. Today it is present in tributaries of most of the most important southern hydrographic basins of Argentine and Chilean Patagonia, and catches began to be recorded in other areas, including the Paraná River and the Uruguayan coast. The tool and its validation are described in the journal Total Environmental Science.
Chinook salmon, popularly known as the “king salmon” for weighing, in some cases, 57 kilograms, was raised with commercial fines in marine cages in southern Chile and several specimens that escaped reached southern Argentina. “Most Chinook salmon return to where they were born to breed, but a small percentage colonize new places. This is how they first entered Tierra del Fuego, then Santa Cruz and Chubut and last year specimens were found in the Río de La Plata and the Río Paraná”, explains Esteban Avigliano, leader of the development, CONICET researcher at the Animal Production Research Institute (INPA, CONICET-UBA) and first author of the article, which describes a method that, through the analysis of Chinook salmon otoliths, makes it possible to establish the origin and trajectory of these fish, as well as the chronology of their displacements, in salty and fresh waters of Argentina.
“Knowing the natal origin and the rate of return (or diversion) to the tributaries where they were born and are going to reproduce, added to other aspects of their life cycle, are key tools to understand the dispersal mechanisms and develop management plans in the environments that are being colonized, especially when the use of the habitat in these habitual environments is not well understood. Our method will be useful in this sense”, affirms Alejandra Volpedo, a CONICET researcher, INPA director and one of the authors of the work that has documented that, in their migratory processes and invasions, Chinook salmon can severely impact ecosystems by altering the distribution of nutrients and pollutants, disseminating microorganisms and diseases and thus modifying trophic structures (the relationships between species within ecosystems) and, in this way, negatively affect the diversity and populations of native fish and even favor populations. from other species in vasoras.
A “black box” inside the “king salmon”
To leave offspring, salmonids are governed by what is known as natal homing or “philopatry”, that is, they return to the natal site (they start their life in rivers, go to the sea and return to die after procreating) to reproduce. However, when it comes to an invasive species such as Chinook salmon, a smaller part of the population strays and reproduces in non-natal areas and colonizes new watersheds. Avigliano and colleagues showed that, like the “black box” of an airplane, otoliths, structures inside the vestibular apparatus (inner ear) of Chinook salmon, store information about their origin (place of birth) and the path of the watersheds they traverse throughout their lives. As part of the study, CONICET specialists and professionals from other scientific organizations took water samples from fourteen basins in the Pacific, the Atlantic in Argentina and Chile. “According to our isotopic analyses, we verified that in each section of the hydrological basins (and also depending on the season of the year) the water sample expressed a specific chemical signature established by the relationship between two isotopes (same chemical element but their nuclei have different masses) of strontium (Sr) of geological origin, specifically 86Sr and 87Sr. In this way, we developed a map of the bodies of water where each site corresponds to a value or relationship between those isotopes”, explains Avigliano.
Likewise, the researchers fished 108 specimens of Chinook salmon in different basins and verified that the otoliths of these fish keep a historical record of isotopic signals based on the environments experienced throughout life and migrations. This isotopic relationship found in the otolith is identical to the mass of water in each river. “Like a tree, otoliths have year rings. By relating the values of the isotopic ratios of the different basins and in each growth ring of the salmon otoliths, we can infer the area of birth and the approximate dates of their geographic location throughout their lives. In this way, we were able to validate the effectiveness of our tool”, highlights Avigliano. “Otoliths keep a chronological record of the geochemical signatures experienced by fish from each place they inhabited. For example, if the river beds contain rocks of different types or ages, the geochemical composition changes and the isotopic ratios or isotopic signatures will also be different. This information about the environment is registered in that internal structure of the fish ear”, explains Volpedo.
Likewise, Avigliano and Volpedo emphasize that this methodology will contribute to understanding the dispersal mechanisms of Chinook salmon and other fish species, and will provide elements to develop management plans in rivers in Patagonia. “Our tool will contribute to generating discriminatory models that will make it possible to infer the natal origin of not only Chinook salmon, but also other invasive salmonid species, including discriminating whether they come from aquaculture or wild populations,” concluded Volpedo.