Of Fin and Feather

“We looked out over the water and reasoned that because most of the life there exists below the surface, out of sight, the ocean remained at the same mythical levels of abundance. But those of us who searched our memories could look back and realize that baitfish had disappeared from the estuaries in the early summer; that the schools of bluefish were smaller; that cod and pollock and mackerel were harder and harder to find. Only when we began to put these facts together did we suspect what had been lost.

But what were we to do about it? What is any one of us to do in the face of changes of this magnitude - changes taking place not in a single region or among a small population but moving like tidal waves across nations and continents, through oceans?

The one thing we cannot do is sit and simply watch these changes happen.”

Matt Rigney | In Pursuit of Giants: One Man’s Global Search for the Last of the Great Fish

Several large, ring-shaped structures lie scattered atop the water off the small islands that cling to the Baja California coast. Within them, the water churns with movement from the hundred pound behemoths swimming just beneath the surface. Thousands of birds dive in and around, a chaotic symphony of fins and feathers, signaling none other than the most important moment of the day – feeding time. 

Though they appear relatively nondescript, bobbing up and down with the rising swell, these pens serve an important purpose. Known by many names, aqua farms, fish farms, aquaculture facilities, they maintain a function similar to that of their land dwelling counterparts – to raise and grow fish.

Some might wonder, “Why is a fish farm even necessary, when fish can grow on their own in the open sea?”

Unfortunately, statistics over the past three decades provide a poignant answer. Fisheries worldwide have declined, and continue to decline, at a rampant pace. Harvests are at, if not greatly surpassed by, their sustainable limits for many critical species – including the Pacific bluefin tuna raised in these pens. Overharvesting presents an imminent threat to ocean ecology and food security for millions of people. Aquaculture provides one tangible, albeit challenging, solution.

Mexican fish ranchers have operated the facilities off these islands, Las Islas Coronados, since 2001.* While fish farms can reduce the global demand for wild-caught tuna and other species, there is debate about their impacts on surrounding ecosystems.

For example, fish farms provide food for people and reduce the environmental impacts of importing fish from other countries. However, they can also be a source for disease vectors, non-native species, and nutrient loads. The debate is complicated because impact studies are often based on small-scale operations.

The Las Islas Coronados fish farms provided the foundation for a case study to investigate an active, full-scale aquaculture operation.

“There are just seabirds everywhere. The islands are covered in birds, nests, and nutrients - fish carcasses and bird droppings. And rattlesnakes. It’s not like Indiana Jones-style, crawling with snakes, but after talking with snake experts who have studied these islands, it’s true. Definitely more rattlesnakes than other places.”

Dr. Jeremy Long | Principle Investigator, San Diego State University

Mexican and US scientists have been collaborating to investigate various ecological inquiries on the Coronados for years. For example, Dr. Jesús Sigala-Rodríguez (Universidad Autónoma de Aguascalientes) and Dr. Rulon Clark (San Diego State University) studied the behavior and ecology of the unique subspecies of Southern Pacific Rattlesnake (Crotalus oreganus caliginis) that flourishes, in unusually large quantities, across the islands.

During each research trip, their boats would cruise past the tuna farms while commuting to the islands. The feeding frenzy of birds and fish, a frequent observation. Life on the islands thrived. Not only with the rattlesnakes, but also an abundance of Western Gulls (Larus occidentalis) and California Brown Pelicans (Pelecanus occidentalis californicus) - far more than the collaborators had ever witnessed in similar environments.

Back at San Diego State University, a graduate student in the Clark Lab shared these observations and piqued the curiosity of community ecologist and fellow SDSU professor, Dr. Jeremy Long. Together, the three professors returned to the islands to investigate further.

Connecting the dots between the snakes, the birds, and the fish pens, the three scientists formulated a compelling question they hadn’t yet considered -

What if the fish farms were affecting the island ecosystem?  

To investigate this overarching question, the team set out to explore three lines of inquiry that might reveal evidence of this land-sea connection:

1. Comparing animal and plant tissues from the islands now to ones in historical collections from the same place - Are there nutrient differences detected in other levels of the food web here versus in areas without fish pens?
2. Reviewing historical records alongside modern observations - Did bird densities on the islands increase as tuna pens became more abundant?
3. And lastly, would changes in bird densities and nutrient levels shift in areas located farther from the fish farms?

“The ultimate goal is to understand what impacts one ecosystem might have on another through the transition of nutrients in various ways. And to further understand the effects of those nutrients on the component species and the way they interact with each other. Fundamentally, it’s an examination of human decisions about resources having cascading effects into surrounding ecosystems. Thinking more carefully about the costs and benefits of aquaculture is important for not just ecology, but policy and management. If it’s done well it could be one of many solutions we implement to try and minimize our overall impact on biodiversity while still meeting the needs of our fellow humans. But if it’s not done well, it can have a lot of unintended impacts on natural systems. That’s what we are here to explore on this ecosystem-level scale.”

Dr. Rulon Clark | Co-Principle Investigator, San Diego State University

These data can provide a better understanding of the true impact of fish farms on their surrounding environment and inform where they might best be placed in the future. Though inquiries of this nature, ones that span the boundary between land and sea, are seldom easy to embark upon - they are possible.

With a collaboration that spanned not only ecosystems - but countries, disciplines, techniques, and time - the investigation began.

To begin to decode whether or not the fish farms are having an impact on the islands - the research team needed to establish a baseline. What did the islands look like prior to the farm's existence? Did bird abundances change since their implementation? What would this mean for the nutrient subsidies (external inputs) on the islands? 

Without ready access to a time machine, the team turned to an alternate method of time travel in the form of a collaboration with the San Diego Natural History Museum. Founded in 1874, the institution holds a vast collection of over 8 million specimens collected with a focus across Southern California and Baja - fortuitously including the Coronados Islands.

“Data from long-term monitoring efforts and historical collections both play a critical role in providing present day scientists and managers with a reference or baseline against which we can evaluate our observations of existing systems. Historic conditions are often considered our conservation target as they represent a time in which humans had a lesser impact on how systems would naturally operate. With this in mind, we can compare present day observations to what was documented in the past, allowing us to determine how far we may be from that reference condition. Without these types of references, questions of this nature would be near to impossible to answer.”

Dr. Keith Lombardo | Director of the Southern California Research Learning Center, National Park Service

Through these questions, specimens preserved for over 150 years come alive. Their delicate tissues - skin, feathers, scales - provide critical insight into the past through the use of isotopic analysis. Isotopes are different forms of the same element and are present everywhere in different ratios. Think Carbon, Nitrogen, and Oxygen. Certain isotopes, known as stable isotopes, are utilized as markers to understand a variety of ecological parameters such as diet, geographic location, food web dynamics, and more. Once incorporated into tissues, stable isotopes in preserved specimens don’t change with time. Thus, stable isotopes paint a picture, both past and present, of how ecosystems are structured.

With meticulous care, the team collects small tissue samples from historical specimens of plants, beetles, lizards, mice, and rattlesnakes. These are then compared with recently collected samples from similar species collected across the island and a nearby “control site.” 

The control site, Cabrillo National Monument, lies just north of the islands on the US side of the border.  This small, but mighty, unit of the National Park Service has been protected for over 100 years and thus represents an almost identical habitat and species composition to that of the Coronados, minus the adjacent fish pens and the abundance of nesting seabirds. When viewed together, these three sets of samples - the historical samples from the Natural History Museum, the modern day control samples from the National Park, and the modern day samples from the Coronados - will help the team better understand if and how the pens influence nutrient flow to the islands.

Back on the islands, and in the present, the research team sets out on an ambitious expedition. With a group of individuals spanning multiple disciplines and specialities, they aim to collect the assorted tissue samples for isotopic comparison and more clues as to the modern influence of the sea pens on the island. 

One way this is accomplished is through an extensive array of bird surveys. Equipped with bird-spotting scopes, binoculars, and small hand-held counters - the team has several study locations throughout the small cluster of islands that comprise the chain. Over the last few years they have frequently revisited these locations, completing exhaustive collections of bird abundance and diversity. Having survey locations on different islands that vary in distance from the fish pens, allows the researchers to understand how far the impacts of the pens extend.

These modern day surveys are compared with historical observations from several sources - primary literature, dissertations, government reports, grey literature, and perhaps one of the most important - local accounts and knowledge. Researchers from  Groupo de Ecología y Conservación de Islas  (GECI) - a Mexican NGO focused on conserving and studying the islands - have been key collaborators in understanding how bird densities have changed through time.

“There are multiple institutions and countries involved, and there are plenty of advantages to this. Several minds with different focuses can provide better results because you’re not restricted by a specific methodological focus, or by the practices of a single discipline. You are able to take advantage of the specific knowledge from everyone’s line of work. The fact that it is a bi-national project is also important because both countries are interested in the results of this research. Each country will probably use the information for different purposes, but at the end of the day, this study will be utilized to the max. This project being multi-institutional is beneficial because each institution might have the ability to access different things, but with the combined efforts you can have better methods, analyses, and results. Finally, interdisciplinarity is amazing because everyone’s knowledge and experience is brought to the table and then combined. I think this is the best way to do science: not using a single focus, but a bi-national, multi-institutional, and cross-disciplinary one.”

Dr. Jesús Sigala-Rodríguez | Co-Principal Investigator, Universidad Autónoma de Aguascalientes

Taking a step back and viewing all of the pieces together, the question remains, are the adjacent fish farms impacting this island ecosystem? 

Since 2019, the team has visited the islands four times and surveyed seabirds, observed the fish pens, and collected hundreds of tissue samples for isotopic analysis. Additionally, they have sampled historic specimens from the Natural History Museum. Preliminary observations suggest that the islands have changed in many ways including increases in nesting seabirds and their use of the fish farms for feeding. If fish farms are affecting the islands via seabirds, there should be differences in the isotopes present in organisms on the islands when compared with the control site at Cabrillo. Indeed, preliminary isotopic observations suggest that seabirds currently play a much larger role on the islands. To identify the role of the fish farms in this pattern, Dr. Long and colleagues are comparing isotope levels in tissues collected from these locations before and after the deployment of the fish farms.

“What we often find as biologists, is the more time we spend in an environment - the more we learn and the more questions we have. 

This work is ongoing and we are excited to uncover more about the compelling cross-ecosystem interactions playing out on these islands. Our team continues to actively process and analyze the tissue samples from these trips. With each trip comes the discovery of new patterns that are inspiring further investigations. For example, even though the islands and Cabrillo are only a short distance apart, we see intriguing differences. These differences, despite the proximity of these sites and similar climates, hint at the possibility that such variations may indeed be a result of the fish farms. Our curiosity drives us to uncover deeper questions  and – though we aren’t there yet - a better understanding of the ecosystem and our role in it. ”

Dr. Jeremy Long | Principle Investigator, San Diego State University

The ongoing dialogue around aquaculture is complex. Rightfully so, there are many considerations when understanding the impacts of these facilities and deciding where they should be placed. If fish farms positively impact seabird populations and their subsidies to islands and other adjacent ecosystems, this research might provide evidence as to the benefits of aquaculture beyond that of a food source.

Historically, many island ecosystems have been devastated by introduced species for ranching and other purposes. Although several of those  species have since been eradicated, the islands struggle to return to some semblance of their previous state. Fish farms may provide a useful restoration tool for island managers by expediting the recovery of seabirds that nest on these islands. Regardless of the outcome, asking questions such as these is important to make informed decisions about the preservation and longevity of our natural resources.

Importantly, the implications of this work stem beyond policy and management outcomes. Public understanding and engagement of science as it relates to sustainable practices is a top priority. With the bi-national nature of this project, it was critical to the research team that public outreach and engagement was diverse, multi-faceted, and boundary spanning.

“Being able to work on this project is special. I am Mexican and was raised in Mexico. I knew I wanted to be a biologist, but I didn’t really know I was going to be able to give back to Mexico. It is such a feeling of accomplishment and life purpose to be able to research on the Coronados Islands. There is a special feeling to go back to where I grew up, my roots, and give back in this way.”

Ana Gómez Ramírez | Lead Graduate Researcher, San Diego State University

One of the exciting ways the results of this research has extended beyond the scientific community is through a partnership with a local education non-profit - the  Ocean Discovery Institute . In order to inspire the next generation of science leaders, Ocean Discovery Institute creates learning experiences for young people traditionally excluded from science due to race, income status, and educational opportunity. Over half of the students in this program are from Mexican, Hispanic, and Latino backgrounds, but may not have interacted with scientists that look like them or that have conducted research in Mexico.

Through this platform, hundreds of students have connected with the research team through multiple livestream lectures and field trip experiences. Fifteen youth leaders visited the study control site and national park, Cabrillo National Monument. Despite living only a few miles away, for many, this was their first visit to a national park and even to the coast. During this experience, the youths worked directly with the research team to learn about the project, participate in survey techniques, and collect preliminary data for use in the study. From the park you can view Las Islas Coronados clearly on the horizon - a perfect backdrop for engaging the next generation of young, curious science explorers in scientific inquiry in real and meaningful ways.   

As with all projects of this nature, it takes a community of dedicated partners and practitioners working together to drive our collective knowledge forward. First and foremost, we would like to acknowledge the local ranchers who maintain the Baja fish pens and local knowledge holders who offered their historical observations for comparison - without their efforts, none of this would be possible. For their professional expertise, friendship, and good will, thank you to all of our collaborators on both sides of the US - Mexican Border. To San Diego State University graduate student, Ana Gómez Ramírez, who not only contributed scientific expertise, but completed the Spanish translation of this document and supported communications between partners - thank you for making science more inclusive and accessible for our collective community. 

Funding Acknowledgement: Support for this work was provided by California Sea Grant (Grant #NA180AR4170073).

*Disclosure: Tended to and overseen by Mexican fish ranchers, the tuna ranches were established adjacent to Las Islas Coronados in 2001 by the Australian company, Baja Aqua Farms (Muñoz 2007).