Month: January 2020

Toxins in Marine Mammals: a Story

By: Alexa Kownacki, Ph.D. Student, OSU Department of Fisheries and Wildlife, Geospatial Ecology of Marine Megafauna Lab

As technology has developed over the past ten years, toxins in marine mammals have become an emerging issue. Environmental toxins are anything that can pose a risk to the health of plants or animals at a dosage. They can be natural or synthetic with varying levels of toxicity based on the organism and its physiology. Most prior research on the impacts toxins before the 2000s was conducted on land or in streams because of human proximity to these environments. However. with advancements in sampling methods, increasing precision in laboratory testing, and additional focus from researchers, marine mammals are being assessed for toxin loads more regularly.

A dolphin swims through a diesel slick caused by a small oil spill in a port. (Image Source: The Ocean Update Blog)

Marine mammals live most of their lives in the ocean or other aquatic systems, which requires additional insulation for protection from both cold temperatures and water exposure. This added insulation can take the form of lipid rich blubber, or fur and hair. Many organic toxins are lipid soluble and therefore are more readily found and stored in fatty tissues. When an organic toxin like a polychlorinated biphenyl (PCB) is released into the environment from an old electrical transformer, it persists in sediments. As these sediments travel down rivers and into the ocean, these toxic substances slowly degrade in the environment and are lipophilic (attracted to fat). Small marine critters eat the sediment with small quantities of toxins, then larger critters eat those small critters and ingest larger quantities of toxins. This process is called biomagnification. By the time a dolphin consumes large contaminated fishes, the chemical levels may have reached a toxic level.

The process by which PCBs accumulate in marine mammals from small particles up to high concentrations in lipid layers. (Image Source: World Ocean Review)

Marine mammal scientists are teaming with biochemists and ecotoxicologists to better understand which toxins are more lethal and have more severe long-term effects on marine mammals, such as decreased reproduction rates, lowered immune systems, and neurocognitive delays. Studies have already shown that higher contaminant loads in dolphins cause all three of these negative effects (Trego et al. 2019). As a component of my thesis work on bottlenose dolphins I will be measuring contaminant levels of different toxins in blubber.  Unfortunately, this research is costly and time-consuming. Many studies regarding the effects of toxins on marine mammals are funded through the US government, and this is where the public can have a voice in scientific research.

Rachel Carson examines a specimen from a stream collection site in the 1950s. (Image Source: Alfred Eisenstaedt/ The LIFE picture collection/ Getty Images.)

Prior to the 1960s, there were no laws regarding the discharge of toxic substances into our environment. When Rachel Carson published “Silent Spring” and catalogued the effects of pesticides on birds, the American public began to understand the importance of environmental regulation. Once World War II was over and people did not worry about imminent death due to wartime activities, a large portion of American society focused on what they were seeing in their towns: discharges from chemical plants, effluents from paper mills, taconite mines in the Great Lakes, and many more.

Discharge from a metallic sulfide mine collects in streams in northern Wisconsin. (Image Source: Sierra Club)

However, it was a very different book regarding pollutants in the environment that caught my attention – and that of a different generation and part of society – even more than “Silent Spring”. A book called “The Lorax”.  In this 1972 children’s illustrated book by Dr. Seuss, a character called the Lorax “speaks for the trees”. The Lorax touches upon critical environmental issues such as water pollution, air pollution, terrestrial contamination, habitat loss, and ends with the poignant message, “Unless someone like you cared a whole awful lot, nothing is going to get better. It’s not.”

The original book cover for “The Lorax” by Dr. Seuss. (Image source: Amazon.com)

Within a decade, the US Environmental Protection Agency (EPA) was formed and multiple acts of congress were put in place, such as the National Environmental Policy Act, Clean Air Act, Clean Water Act, and Toxic Substances Control Act, with a mission to “protect human health and the environment.” The public had successfully prioritized protecting the environment and the government responded. Before this, rivers would catch fire from oil slicks, children would be banned from entering the water in fear of death, and fish would die by the thousands. The resulting legislation cleaned up our air, rivers, and lakes so that people could swim, fish, and live without fear of toxic substance exposures.

The Cuyahoga River on fire in June 1969 after oil slicked debris ignited. (Image Source: Ohio Central History).

Fast forward to 2018 and times have changed yet again due to fear. According to a Pew Research poll, terrorism is the number one issue that US citizens prioritize, and Congress and the President should address. The environment was listed as the seventh highest priority, below Medicare (“Majorities Favor Increased Spending for Education, Veterans, Infrastructure, Other Govt. Programs.”). With this societal shift in priorities, research on toxins in marine mammals may no longer grace the covers of the National Geographic, Science, or Nature, not for lack of importance, but because of the allocation of taxpayer funds and political agendas. Meanwhile, long-lived marine mammals will still be accumulating toxins in their blubber layers and we, the people, will need to care a whole lot, to save the animals, the plants, and ultimately, our planet.

The Lorax telling the reader how to save the planet. (Image Source: “The Lorax” by Dr. Seuss via the Plastic Bank)

Citations:

“Majorities Favor Increased Spending for Education, Veterans, Infrastructure, Other Govt. Programs.” Pew Research Center for the People and the Press, Pew Research Center, 11 Apr. 2019, www.people-press.org/2019/04/11/little-public-support-for-reductions-in-federal-spending/pp_2019-04-11_federal-spending_0-01-2/.

Marisa L. Trego, Eunha Hoh, Andrew Whitehead, Nicholas M. Kellar, Morgane Lauf, Dana O. Datuin, and Rebecca L. Lewison. Environmental Science & Technology 2019 53 (7), 3811-3822. DOI: 10.1021/acs.est.8b06487

PhD life: Pushing it to the extreme, and its wonders

By Leila S. Lemos, PhD candidate in Wildlife Sciences, Fisheries and Wildlife Department

I already started my countdown: 57 days until my PhD defense date! Being so close to this date brings me a lot of excitement about sharing with the community the results of the project I’ve been working on the past 4.5 years, and that I am really proud of. It also brings me lots of excitement when thinking about the new things that will come in my next phase of life. But even though I am excited, I’ve also been stressed, anxious and under depression. There is a mix of feelings rushing inside of me right now.

For those who don’t know me, I am originally from Rio de Janeiro, Brazil. I’ve been spending the last years far from my family, friends, language and culture. My favorite hobby always was to go to the beach and swim in the warm ocean. I would do that at least twice a week. Brazil is a tropical place and we can go to the beach all year round.

Me and my nephew in one of my favorite places in Brazil: Buzios, Rio de Janeiro.

Being in Oregon is really different. Oregon is gorgeous and I love it here, especially during the summer. However, the fall season brings the rain. Lots of rain, and it only stops around March. The absence of sun (and vitamin D) also contributes to depression. Even during the summer, I cannot swim in the ocean as the water is still really cold.

In addition to all of these factors, a PhD comes with classes, exams, fieldwork, research project, lots of reading and learning, manuscript writing, deadlines and great responsibilities. When you don’t have a scholarship or when it runs out (in my case), you also need to find a way to fund yourself until it finishes. Since last September I have been a teaching assistant for the university to cover my tuition and health insurance costs, and to earn a monthly stipend. The work never ends, and you always have more and more things to do.

Source: Costanza (2015).

A PhD is a full-time job, even if you are still technically a student. Actually, a PhD is a 24-hour job. Even if you are not working, you are thinking about your experiments and/or deadlines. Even if you are not awake, you are dreaming about it. You feel guilty all the time if you are doing things that are not related to your work.

But, it turns out I am not alone. The more I talk to people about the struggles, disappointments, anxiety, impostor syndrome, insomnia, depression, exhaustion of graduate school, the more I find that it is more common than I first thought.  I have several friends facing the same problems right now.

I searched for some stats on this topic and I found a relatively recent study (Levecque et al. 2017) that evaluated the mental health of a sample of PhD students (N = 3659) from five different research discipline categories: sciences, biomedical sciences, applied sciences, humanities, and social sciences. PhD students were compared to other three groups: (1) highly educated individuals in the general population (N = 769), (2) highly educated employees (N = 592), and (3) higher education students (i.e., academic Bachelor, Master or Doctoral degree; N = 333). Research participants answered the web-based questionnaire that follows:

Table 1: Prevalence of common mental health problems in PhD students compared to three comparison groups.

Legend: RR: risk ratio adjusted for age and gender; CI: 95% confidence interval; GHQ2+: experienced at least two symptoms; GHQ3+: experienced at least three symptoms; GHQ4+: experienced at least four symptoms.
Source: Levecque et al. (2017)

It was alarming to me to see some of these results. Here are some of them:

  • A GHQ2+ score indicated psychological distress, and the prevalence was about twice as high in PhD students compared to the highly educated general population. PhD students were consistently more affected when compared to all of the other groups.
  • They found a significant relationship between psychological distress and the risk of having or developing a common psychiatric disorder (GHQ4+).
  • The odds of experiencing at least two psychological symptoms were 34% higher for female PhD students than for males.
  • No differences between scientific disciplines were found.

And here’s the funny thing: My PhD project researches stress in gray whales along the Oregon coast. I have been evaluating gray whale overall health by using different tools like photogrammetry, endocrinology and acoustics to monitor these individual whales. The more I read about stress and all the physiological response that occurs within the bodies of all vertebrates, the more I imagine it happening to me and all of the possible consequences. However, I do not consider myself a specialist on the theme yet, so I leave my mental health to a specialist. I have been seeing a psychiatrist and a psychologist and I have been learning that work-life balance is crucial, and it helps us maintain sanity. I have also been learning some “exercises” to help me with anxiety and impostor syndrome. This topic may not be an easy to talk about, but it is extremely important. If you are reading this and identify yourself, contact a professional who can help you. It has helped me.

Institutions should also increase their efforts to systematically map and monitor stressors and its outcomes in PhD students (Levecque et al. 2017). Identifying the problems and working towards solutions will benefit the institutions as students will do a better job.

Right now, I am just trying my best to achieve a work-life balance while I am still getting things done on time. All of my data has been analyzed and now I just need to write my chapters and prepare my defense presentation! It is hard to believe that in only 57 days I will be done.  

Source: Reddit (2019).

I feel like I have succeeded in painting a grim picture of life as a PhD student. If you were thinking of going to grad school and now you have doubts about it, stop right there! Grad school is challenging, but it is not impossible. There are many things that will bring you joy in grad school like a successful fieldwork season, a successful experiment, a good grade on an exam you studied really hard for, a compliment from your advisor, a R code that is finally running correctly, or an accepted manuscript in a relevant journal.

By the way… I just had a manuscript of my first thesis chapter accepted for publication and I could not be happier:

Getting a PhD is hard, but it is also rewarding. Also, any path you take in your career will have pros and cons. What determines your success is your resilience and how you deal with the challenges that come. You may be asking if I would still do a PhD if I could go back in time, right? The answer is yes! Even though I have been facing many (personal) challenges I am really proud of my PhD project findings and am glad to be contributing to the knowledge and conservation of these amazing animals.

But please, if you see me around don’t forget:

Source: Costanza (2015).

References:

Costanza T. 2015. 10 memes relate to PhD students. Available at: https://www.siliconrepublic. com/careers/10-memes-relate-to-phd-students. Date of assess: 01/20/2020

Reddit. 2019. Made a meme for my boyfriend who’s doing his PhD. Available at: https://www.reddit.com/r/memes/comments/9fq2pq/made_a_meme_for_my_boyfriend_whos_doing_his_phd/. Date of assess: 01/20/2020

Levecque, K., F. Anseel, A. Beuckelaer, J. V. Heyden, and L. Gisle. 2017. Work organization and mental health problems in PhD students. Research Policy 46:868–879.

The teamwork of conservation science

Dr. Leigh Torres
PI, Geospatial Ecology of Marine Megafauna Lab, Marine Mammal Institute
Assistant Professor, Oregon Sea Grant, Department of Fisheries and Wildlife, Oregon State University

I have played on sports teams all my life – since I was four until present day. Mostly soccer teams, but a fair bit of Ultimate too. Teams are an interesting beast. They can be frustrating when communication breaks down, irritating when everyone is not on the same timeline, and disastrous if individuals do not complete their designated job. Yet, without the whole team we would never win. So, on top of the fun of competition, skill development, and exercise, playing on teams has always been part of the challenging and fulfilling process for me: everyone working toward the same goal – to win – by making the team fluid, complimentary, integrated, and ultimately successful.

I have come to learn that it is the same with conservation science.

A few of my teams through the ages, as player and coach. Some of my favorite people are on these teams, from 1981 to 2018.

Conservation efforts are often so complex, that it is practically impossible to achieve success alone. Forces driving the need for conservation typically include monetary needs/desires, social values, ecological processes, animal physiology, multi-jurisdictional policies, and human behavior. Each one of these forces alone is challenging to understand and takes expertise to comprehend the situation. Hence, building a well-functioning team is essential. Here’s a recent example from the GEMM Lab:

Since 2014 entanglements of blue, humpback and gray whales in fishing gear along the west coast of the USA have dramatically increased, particularly in Dungeness crab fishing gear. Many forces likely led to this increase, including increased whale population abundance, potential shifts in whale distributions, and changes in fishing fleet dynamics. While we cannot point a finger at one cause, many people and groups recognize that we cannot continue to let whales become entangled and killed at such high rates: whale populations would decline, fisheries would look bad in the public eye and potentially lose profits, whales have an intrinsic right to live in the ocean without being bycaught, and whales are an important part of the ecosystem that would deteriorate without them. In 2017, the Oregon Whale Entanglement Working Group was formed to bring stakeholders together that were concerned about this problem to discuss possible solutions and paths forward. I was lucky to be a part of this group, which also included members of the Dungeness crab fishery and commission, the Oregon Department of Fish and Wildlife (ODFW), other marine mammal scientists, and representatives of the American Cetacean Society, The Nature Conservancy, and a local marine gear supplier.

We met regularly over 2.5 years, and despite some hesitation at first about walking into a room of potentially disgruntled fishermen (I would be lying if I did not admit to this), after the first meeting I looked forward to every gathering. I learned an immense amount about the Dungeness crab fishery and how it operates, how ODFW manages the fishery and why, and what people do, don’t and need to know about whales in Oregon. Everyone agreed that reducing whale entanglements is needed, and a frequent approach discussed was to reduce risk by not setting gear where and when we expect whales to be. Yet, this idea flagged a very critical knowledge gap: We do not have a good understanding of whale distribution patterns in Oregon. Thus leading to the development of a highly collaborative research effort to describe whale distribution patterns in Oregon and identify areas of co-occurrence between whales and fishing effort to reduce the risk of entanglements. Sounds great, but a tough task to accomplish in a few short years. So, let me introduce the great team I am working with to make it all happen.

While I may know a few things about whales and spatial ecology, I don’t know too much about fisheries in Oregon. My collaboration with folks at ODFW, particularly Kelly Corbett and Troy Buell, has enabled this project to develop and go forward, and ultimately will lead to success. These partners provide feedback about how and where the fishery operates so I know where and when to collect data, and importantly they will provide the information on fishing effort in Oregon waters to relate to our generated maps of whale distribution. This spatial comparison will produce what is needed by managers and fishermen to make informed and effective decisions about where to fish, and not to fish, so that we reduce whale entanglement risk while still harvesting successfully to ensure the health and sustainability of our coastal economies.

So, how can we collect standardized data on whale distribution in Oregon waters without breaking the bank? I tossed this question around for a long time, and then I looked up to the sky and wondered what that US Coast Guard (USCG) helicopter was flying around for all the time. I reached out to the USCG to enquire, and proposed that we have an observer fly in the helicopter with them along a set trackline during their training flights. Turns out the USCG Sector North Bend and Columbia River were eager to work with us and support our research. They have turned out to be truly excellent partners in this work. We had some kinks to work out at the beginning – lots of acronyms, protocols, and logistics for both sides to figure out – but everyone has been supportive and pleasant to work with. The pilots and crew are interested in our work and it is a joy to hear their questions and see them learn about the marine ecosystem. And our knowledge of helicopter navigation and USCG duties has grown astronomically.

On the left is a plot of the four tracklines we survey for whales each month for two years aboard a US Coast Guard helicopter. On the right are some photos of us in action with our Coast Guard partners.

Despite significant cost savings to the project through our partnership with the USCG, we still need funds to support time, gear and more. And full credit to the Oregon Dungeness Crab Commission for recognizing the value and need for this project to support their industry, and stepping up to fund the first year of this project. Without their trust and support the project may not have got off the ground. With this support in our back pocket and proof of our capability, ODFW and I teamed up to approach the National Oceanographic and Atmospheric and Administration (NOAA) for funds to support the remaining years of the project. We found success through the NOAA Fisheries Endangered Species Act Section 6 Program, and we are now working toward providing the information needed to protect endangered and threatened whales in Oregon waters.

Despite our cost-effective and solid approach to data collection on whale occurrence, we cannot be everywhere all the time looking for whales. So we have also teamed up with Amanda Gladics at Oregon Sea Grant to help us with an important outreach and citizen science component of the project. With Amanda we have developed brochures and videos to inform mariners of all kinds about the project, objectives, and need for them to play a part. We are encouraging everyone to use the Whale Alert app to record their opportunistic sightings of whales in Oregon waters. These data will help us build and test our predictive models of whale distribution. Through this partnership we continue important conversations with fishermen from many fisheries about their concerns, where they are seeing whales, and what needs to be done to solve this complex conservation challenge.  

Of course I cannot collect, process, analyze, and interpret all this data on my own. I do not have the skills or capacity for that. My partner in the sky is Craig Hayslip, a Faculty Research Assistant in the Marine Mammal Institute. Craig has immense field experience collecting data on whales and is the primary observer on the survey flights. Together we have navigated the USCG world and developed methods to collect our data effectively and efficiently (all within a tiny space flying over the ocean). In a few months we will be ¾ of the way through our data collection phase, which means data analysis will take over. For this phase I am bringing back a GEMM Lab star, Solene Derville, who recently completed her PhD. As the post-doc on the project, Solene will take the lead on the species distribution modeling and fisheries overlap analysis. I am looking forward to partnering with Solene again to compile multiple data sources on whales and oceanography in Oregon to produce reliable and accurate predictions of whale occurrence and entanglement risk. Finally I want to acknowledge our great partners at the Cascadia Research Collective (Olympia, WA) and the Cetacean Conservation and Genomics Lab (OSU, Marine Mammal Institute) who help facilitate our data collection, and conduct the whale photo-identification or genetic analyses to determine population assignment.  

As you can see, even this one, smallish, conservation research project takes a diverse team of partners to proceed and ensure success. On this team, my position is sometimes a player, coach, or manager, but I am always grateful for these amazing collaborations and opportunities to learn. I am confident in our success and will report back on our accomplishments as we wrap up this important and exciting conservation science project.   

A fin whale observed off the Oregon coast during one of our surveys aboard a US Coast Guard helicopter.

What are the ecological impacts of gray whale benthic feeding?

Clara Bird, Masters Student, OSU Department of Fisheries and Wildlife, Geospatial Ecology of Marine Megafauna Lab

Happy new year from the GEMM lab! Starting graduate school comes with a lot of learning. From skills, to learning about how much there is to learn, to learning about the system I will be studying in depth for the next few years. This last category has been the most exciting to me because digging into the literature on a system or a species always leads to the unearthing of some fascinating and surprising facts. So, for this blog I will write about one of the aspects of gray whale foraging that intrigues me most: benthic feeding and its impacts.

How do gray whales feed?

Gray whales are a unique species. Unlike other baleen whales, such as humpback and blue whales, gray whales regularly feed off the bottom of the ocean (Nerini, 1984). They roll to one side and swim along the bottom, they then suction up (by depressing their tongue) the sediment and prey, then the sediment and water is filtered out of the baleen. In fact, we use sediment streams, shown in Figure 1, as an indicator of benthic feeding behavior when analyzing drone footage (Torres et al. 2018).

Figure 1. Screenshot of drone video showing sediment streaming from mouth of a whale after benthic feeding. Video taken under NOAA/NMFS permit #21678

Locations of benthic feeding can be identified without directly observing a gray whale actively feeding because of the excavated pits that result from benthic feeding (Nerini 1984). These pits can be detected using side-scan sonar that is commonly used to map the seafloor. Oliver and Slattery (1985) found that the pits typically are from 2-20 m2. In some of the imagery, consecutive neighboring pits are visible, likely created by one whale in series during a feeding event. Figure 2 shows different arrangements of pits.

Figure 2. Different arrangements of pits created by feeding whales (Nerini 1984).

Aside from how fascinating the behavior is, benthic feeding is also interesting because it has a large impact on the environment. Coming from a background of studying baleen whales that primarily feed on krill, I had not really considered the potential impacts of whale foraging other than removing prey from the environment. However, when gray whales feed, they excavate large areas of the benthic substrate that disturb and impact the habitat.

The impacts of benthic feeding

Weitkamp et al. (1992) conducted a study on gray whale benthic foraging on ghost shrimp in Puget Sound, WA, USA. This study, conducted over two years, focused on measuring the impact of benthic foraging by its effect on prey abundance. They found that the standing stock of ghost shrimp within a recently excavated pit was two to five times less than that outside the pit, and that 3100 to 5700 grams of shrimp can be removed per pit. From aerial surveys they estimated that within one season feeding gray whales created between 2700 and 3200 pits. Using these values, they calculated that 55 to 79% of the standing stock of ghost shrimp was removed each season by foraging gray whales. Interestingly, they found that the shrimp biomass within an excavated pit recovered within about two months.

Oliver and Slattery (1985) also found a recovery period of about 2 months per pit in their study on the effect of gray whale benthic feeding on the prey community in the Bering Sea. They sampled prey within and outside feeding excavations, both actual whale pits and man-made, to test the response of the benthic community to the disturbance of a feeding event. They found that after the initial feeding disturbance, the excavated area was rapidly colonized by scavenging lysianassid amphipods, which are small (10 mm) crustaceans that typically eat dead organic material. These amphipods rushed in and attacked the organisms that were injured or dislodged by the whale feeding event, typically small crustaceans and polychaete worms. Within hours of the whale feeding event, these amphipods had dispersed and a different genre of scavenging lysianassid amphipods slowly invaded the excavated pit further and stayed much longer. After a few days or weeks these pits collected and trapped organic debris that attracted more colonists. Indeed, they found that the number of colonists remained elevated within the excavated areas for over two months.

Notably, these results on how the disturbance of gray whale benthic feeding changes sediment composition support the idea that this foraging behavior maintains the sand substrate and therefore helps to maintain balanced levels of benthic dwelling amphipods, their primary source of prey in this study area (Johnson and Nelson, 1984). Gray whales scour the sea floor when they feed and this process leads to the resuspension of lots of sediments and nutrients that would otherwise remain on the seafloor. Therefore, while this feeding may seem like a violent disturbance, it may in fact play a large role in benthic productivity (Johnson and Nelson, 1984; Oliver and Slattery, 1985).

These ecosystem impacts of gray whale benthic feeding I have described above demonstrate the various stages of invaders after a feeding disturbance, and the process of succession. Succession is the ecological process of how a community structure builds and grows. Primary succession is when the structure grows from truly nothing and secondary succession occurs after a disturbance, such as a fire. In secondary succession, there are typically pioneer species that first appear and then give way to other species and a more complex community eventually emerges. Succession is well documented in many terrestrial studies after disturbance events, and the processes of secondary succession is very important to community ecology and resilience.

Since gray whale benthic foraging does not impact an entire habitat all at once, the process is not perfectly comparable to secondary succession in terrestrial systems. Yet, when thinking about the smaller scale, another example of succession in the marine environment takes place at a whale fall. When a whale dies and sinks to the ocean floor, a small ecosystem emerges. Different organisms arrive at different stages to scavenge different parts of the carcass and a food web is created around it.

To me the impacts of gray whale benthic feeding are akin to both terrestrial disturbance events and whale falls. The excavation serves as a disturbance, and through secondary succession the habitat is refreshed via stages of different species colonization until the system eventually returns to the pre-disturbance levels. However, like a whale fall the feeding event leaves behind injured or displaced organisms that scavengers consume; in fact seabirds are known to take advantage of benthic invertebrates that are brought to the surface by a gray whale feeding event (Harrison, 1979). 

So much of our research is focused on questions about how the changing environment impacts our study species and not the other way around. This venture into the literature has provided me with an important reminder to think about flipping the question. I have enjoyed starting 2020 with a reminder of how cool gray whales are, and that while a disturbance can initially be thought of as negative, it may actually bring about important, and positive, change.

References

Nerini, Mary. 1984. “A Review of Gray Whale Feeding Ecology.” In The Gray Whale: Eschrichtius Robustus, 423–50. Elsevier Inc. https://doi.org/10.1016/B978-0-08-092372-7.50024-8.

Oliver, J. S., and P. N. Slattery. 1985. “Destruction and Opportunity on the Sea Floor: Effects of Gray Whale Feeding.” Ecology 66 (6): 1965–75. https://doi.org/10.2307/2937392.

Torres, Leigh G., Sharon L. Nieukirk, Leila Lemos, and Todd E. Chandler. 2018. “Drone up! Quantifying Whale Behavior from a New Perspective Improves Observational Capacity.” Frontiers in Marine Science 5 (SEP). https://doi.org/10.3389/fmars.2018.00319.

Weitkamp, Laurie A, Robert C Wissmar, Charles A Simenstad, Kurt L Fresh, and Jay G Odell. 1992. “Gray Whale Foraging on Ghost Shrimp (Callianassa Californiensis) in Littoral Sand Flats of Puget Sound, USA.” Canadian Journal of Zoology 70 (11): 2275–80. https://doi.org/10.1139/z92-304.

Johnson, Kirk R., and C. Hans Nelson. 1984. “Side-Scan Sonar Assessment of Gray Whale Feeding in the Bering Sea.” Science 225 (4667): 1150–52.

Harrison, Craig S. 1979. “The Association of Marine Birds and Feeding Gray Whales.” The Condor 81 (1): 93. https://doi.org/10.2307/1367866.