An Interview with PhD Student Andres Olivos


This last week I had the unique opportuntiy to work alongside Oregon State University’s PhD student Andres Olivos. In my last post I talked about what I learned and some of what we did during the week. In this post I will share an interview I had with Andres about his research. Enjoy!

Gloria: First would you please explain what your research consists of and the mission of the research? What do you hope to find?

Andres: My doctoral research is about non-native salmon and their relationship with freshwater habitat. I'm particularly interested in the landscape's potential to provide high-quality habitat for salmon spawning and rearing, in relation to the distribution of events and magnitude of introductions -- a concept known as propagule pressure*. With the spatial distribution of habitat characteristics and propagule pressure, I hope to better understand the present distribution of non-native salmonids. 

*From Wikipedia I found: “Propagule pressure (also termed introduction effort) is a composite measure of the number of individuals of a species released into a region to which they are not native.”

Gloria: Why did you decide to do this research in Chile?

Andres: Chile is probably the place with the highest salmonid propagule pressure in the world. Over a century ago, people started seeding rivers and lakes with trout and salmon looking to establish commercial and recreational fisheries. In the late 80s, salmon aquaculture began in southern Chile and today is the second largest farmed salmon industry after Norway. One of the issues of net-pens is that escapes are persistent and hardly avoidable. Salmonid invasion patterns, the differential success between species, and the impacts of these processes are still poorly understood, making research urgent in the region.


Gloria: Why are you collecting parts of the salmon and trout (stomach, muscle, liver, axillary process of pelvic fin, and otoliths)?

Andres: From every salmon or trout we catch, we take measurements and samples that can help us understand their origin, life histories, and health of the individuals. The samples are going to different labs working collaboratively to answer questions about invasive salmonids in Chile. For example, the stomach content is essential information on the short-term diet of the fish (hours), while doing stable isotopes analysis from muscle tissue can help us infer long-term diet composition and even about the regions where they had lived (months to years). Otoliths - the ear-bones - are also an excellent tool for studying life histories as they grow in layers with time, storing chemical and morphological signals about every life stage. Muscles and liver are also useful indicators of body condition and can be used to study heavy metals accumulation. Lastly, the axillary process of the pelvic fin (connecting tissue between body and base of the fin) is rich in DNA and easy to obtain, so our collaborators use it by a protocol for population genetics studies.


Gloria: How many salmon were let out of a salmon farm in the Puget Sound? How many salmon are let out of salmon farms in Chile each year? What do you make of this?

Andres: In August of 2017, from one of the five salmon farms in the Puget Sound, approximately 200,000 Atlantic Salmon escaped from a net-pen due to currents and poor maintenance. The case was well documented, and the concern of the public led to a salmon farm ban in Washington starting in 2025. In Chile, the scenario is contrasting. From official reports of mass releases and persistent "leaks" in daily operations, we estimate a total escape of 1 million fish per year in Patagonian waters. Regardless, several hundred net-pens keep operating as they had become structural in the region's economy and regulation remains light. 

Gloria: Can you explain why you take notes on depth and width, terrain and canopy, and GPS coordinates of all the streams? What will you do with this information?

Andres: Salmonids are very dependent on hydrological conditions for selecting habitat. That is why we generate geomorphology models to describe channel conditions related to salmon habitat-use. Since Digital Elevation Models available for the region are space-borne and with low resolution, we rely on regressions using drainage areas and precipitation for calculating variables such as channel width and depth. In the field, I measure these variables to validate and calibrate the regressions for this area of the world and perform other calculations to estimate habitat suitability. 


Gloria: What streams' characteristics can help figure salmon presence in a river?

Andres: First of all, the habitat connectivity to the ocean is essential for salmon to occupy a stream (excepting for landlocked populations). Once identified the barriers to anadromy in the stream network, we characterize reaches by flow, gradient, and valley-constraint(a ratio between channel width and valley width). These three variables are crucial to studying the presentation of high-quality habitat, a model known as the Intrinsic Potential (IP) of salmon habitat, developed in the Pacific Northwest and widely applied for salmon research and management.

Gloria: What is the importance to the environment of this research? Can you explain how your research is related to salmon farms and what salmon farm impact is on the environment?

Andres: Biological invasions are an important cause of extinction, and freshwater systems are especially sensitive. Salmonids are within the most harmful families of invaders, and two of them are included in the 100 World's Worst Invasive Alien Species (IUCN); the brown trout and the rainbow trout, both very successful in Chile. Salmon net-pens - which also raises trout - are concerning as they are the only current source of propagule. The escapes have impacts related to the predation, competition and disease transmission to native species. However, salmon aquaculture can also have other effects on the ecosystem as estuarine eutrophication*, benthic hypoxia*, pharmaceutical effluents*, pathogen amplification*, between others.

*From Wikipedia I found:Estuarine eutrophication: When an estuary becomes overly enriched with minerals and nutrients that induce excessive growth of plants and algae.

*From speaking more with Andres I found: Benthic hypoxia: When uneaten fish food and feces accumulate on the sea floor the breakdown process becomes anaerobic and produces harmful substances.

*From speaking more with Andres I found: Pharmaceutical effluents: is an outflowing of water contaminated by antibiotics and antiparasitics (used on the farmed fish) into the ocean.

*From speaking more with Andres I found: Pathogen amplification: When infectious diseases and parasites affect net-pens of fish and the pathogens increase in the environment. This is serious because many of those agents can also infect native fish.

Gloria: What will you do with the environmental DNA we extracted from the rivers?

Andres: With the filters we used and stored, I'm going to do a DNA extraction - meaning I'll generate cell lysis and take out the genetic material. Afterward, with PCR equipment and species-specific primers, I'll try to amplify salmonid genes looking for their presence/absence in streams.

A big thanks to Andres Olivos for having me and letting me take part in his research. It is good to see people doing important work in the world.

Gloria Goni-McAteer1 Comment