The Curious Case of Disappearing Salmon

200 years ago a father and son in Washington stand along the banks of the Columbia River. They sit in silence, watching the tumbling river rush by, breathing in the fresh air and gorgeous sights. But they’re not there just to appreciate the beautiful day. In their hands, they hold twin fishing rods, though they could have walked down to the river with nothing but their hands and a bucket, and still returned flush with fish. This father and his son are fishing for Chinook salmon, a fish that migrates in schools so abundant it seems as if the river itself was made with salmon, not water. They return home, happy with a bundle of five fish each, while millions of others rush through the water. 

Just days later, another father-son pair travel to the Columbia River, but this time they’re hundreds of miles away, in Oregon. They too return home with a bountiful catch, while thousands more pass through the river unimpeded. This pattern continues all across Washington and Oregon, into California, Idaho, and watersheds across the West Coast¹.

This Chinook Population Ratings map was created using data collected and compiled by State of the Salmon – a program of the Wild Salmon Center originally launched in 2003 in partnership with Ecotrust. However, this Chinook Population Ratings map is a secondary compilation of the data and it has not been verified or authorized by Wild Salmon Center.

Over the next couple hundred years, this pattern continues, with generations of families, fisheries, and indigenous tribes depending on these fish as an integral part of their lives². The great-great-granddaughter of one of these families travels to the Columbia River with her father, just like generations before had done. But this time something is different. Though they’ve brought along their fishing rods, their bait, and anything they could need to catch salmon, the fish just aren’t biting. The river is no longer teeming with populations in the millions, the water no longer camouflaged by the countless bodies of salmon. The pair leaves defeated, with a bare catch that pales in comparison to the bounty of the years before them. 

In the last 40 years, Chinook salmon have lost 60% of their population, with some schools at 10% of their historic numbers³. There are a variety of reasons why salmon populations are struggling, from habitat loss or degradation and harvest rates to hatchery influence and dams creating new barriers³

One of the most pressing is the changing temperatures of the waters they inhabit. As the climate warms, the world’s watersheds warm along with them, with scientists projecting average temperatures to experience a 6.9°C increase by the end of the century(4). Projections estimate that the effect of increasing temperature alone could reduce populations by almost 20% in the next 40 years². The problem gets even worse in the open ocean. Salmon spend most of their life in saltwater, returning to rivers and freshwater only to breed. One study found that the dominant driver towards extinction was increasing sea surface temperature, which could lead to a 90% decline in populations, almost guaranteed extinction².

Image Courtesy of Vince Mig

Salmon are so sensitive to increasing temperatures, not just because they prefer Christmas over the 4th of July, but because their fundamental processes of life depend upon temperature. Fish are part of a group known as ectotherms, commonly referred to as cold-blooded animals. They don’t actually have cold blood, but instead rely on the external environment to dictate the temperature inside their bodies. When a human walks outside on a really hot day, something like 115℉, our body temperature stays a cool 98℉. But if a fish were exposed to those same conditions, their body temperature really would reach close to 115℉. 

In the same way humans begin to lose functioning and face potentially lethal consequences if they have a fever that becomes too high, salmon struggle to survive in high temperatures. Everyone remembers the classic fact – “the mitochondria is the powerhouse of the cell” from their middle school days. But what does that actually mean? The mitochondria are responsible for the production of a molecule known as ATP, which all the cells in your body use as their source of energy. They produce the power your cells use to function. Without ATP, death would be almost instantaneous for any living thing. The process of creating this ATP is known as metabolism. 

Metabolism is one of those biological processes that are impacted by the environmental temperature. Energy is first directed toward basic requirements for survival – things like breathing and circulating blood. Any excess energy is then able to be used to do things- move, eat, reproduce, and more. But as temperatures rise, salmon are required to put more energy into just staying alive, leaving less available for actual use(5)

 

Image Courtesy of Andrea Stöckel

¹

Pacific salmon populations across North America are dealing with the effects of heat stress – they have less energy to expend, at a time in their life when they need it the most. Without enough energy future generations can’t survive, and the results are plain to see. The great-granddaughter of our original fisher is living in a world with salmon populations that are barely an echo of the abundance they once had. Her great-granddaughter may live in a world without any salmon at all.   

Citations

  1. Salmon Life Cycle and Seasonal Fishery Planning. (2022, June 10). NOAA. https://www.fisheries.noaa.gov/west-coast/sustainable-fisheries/salmon-life-cycle-and-seasonal-fishery-planning  
  2. Crozier, L. G., Burke, B. J., Chasco, B. E., Widener, D. L., & Zabel, R. W. (2021). Climate change threatens Chinook salmon throughout their life cycle. Communications Biology, 4(1), 1–14. https://doi.org/10.1038/s42003-021-01734-w 
  3. Chinook Salmon. (2013, April 29). US EPA. https://www.epa.gov/salish-sea/chinook-salmon 
  4. Betts, R. A., Collins, M., Hemming, D. L., Jones, C. D., Lowe, J. A., & Sanderson, M. G. (2011). When could global warming reach 4°C? Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 369(1934), 67–84. https://doi.org/10.1098/rsta.2010.0292  
  5. Poletto, J. B., Cocherell, D. E., Baird, S. E., Nguyen, T. X., Cabrera-Stagno, V., Farrell, A. P., & Fangue, N. A. (2017). Unusual aerobic performance at high temperatures in juvenile Chinook salmon, Oncorhynchus tshawytscha. Conservation Physiology, 5(1), cow067. https://doi.org/10.1093/conphys/cow067 

 

Polar bears’ fasting period increases as sea ice continues to melt

polar bear. Image by Elizabeth Labunski. Retrieved from https://digitalmedia.fws.gov/digital/collection/natdiglib/id/2761/rec/31

Polar bears (Ursus maritimus) have been experiencing the effects of climate change particularly hard.  Polar bears rely on spring feeding in order to build up fat reserves for the summer-fall fasting period, and as seal pups are birthed, it provides ample opportunity for polar bears to do so.  However, as the global temperature continues to increase, the abundance of sea ice declines.  While polar bears are strong swimmers, they rely on sea ice to use as platforms while they hunt seals.  Without the sea ice, their ability to effectively and efficiently hunt is diminished.  This results in polar bears having less fat storage going into the summer-fall fasting period in which food sources become even more scarce as the bears lose access to marine animals.  Polar bears don’t den during this time, so this period is often referred to as “walking hibernation”.  As the sea ice returns in the winter months, polar bears are once again able to access marine animals for food.  

 

Polar bears have shown increasing signs of fasting over the years.  Between 1985 and 2006, the percent of polar bears in a fasting state in April grew over 300% (Cherry et al., 2009).  The spring months are a time in which polar bears should be feasting to increase fat storages for the coming fasting period.  120-day fasts are typical for male and non-pregnant female polar bears during these summer-fall months (Robbins et al., 2012).  However, this period is predicted to increase to 180 days as temperatures continue to rise.  Over a 180-day fasting period, adult males experience a 28% mortality rate, increased from 3% during a 120-day fast.  

 

This increase in fasting time is even more concerning for pregnant females.  Since pregnant female polar bears den on land during the winter, they will have to go up to 8 months without food.  During the summer-fall fasting period, daily mass loss, energy expenses, and loss of lean mass is much higher than in hibernating bears.  By increasing this fasting period due to climate change, polar bears will go into the winter with less mass than usual. Since heavier females are more likely to produce larger cubs, and thus increase the probability of cub survival, pregnant females want to go into winter with as much fat storage as possible.  It is estimated that pregnant females would need more than 34% body fat leading into the summer-fall fasting period in order to successfully reproduce during the winter (Robbins et al., 2012).

polar bear with cub. Image by Scott Schliebe. Retrieved from https://digitalmedia.fws.gov/digital/collection/natdiglib/id/10931/rec/5

 

As temperatures continue to increase and sea ice continues to melt, the future for polar bears is tenuous.  For pregnant females in particular, an abundant spring is of extreme importance for survival of the summer-fall fasting.  As this fasting period increases due to sea ice melting earlier in the season, more and more polar bears won’t make it through to the winter.  Additionally, pregnant females won’t be able to make it through the fasting with enough fat reserves left to successfully reproduce.  Populations will continue to decrease as reproduction rates fall, making it of the utmost importance to ensure enough sea ice for an abundant spring feast. 

 

 

 

References:

Cherry, S.G., Derocher, A.E., Stirling, I. et al. Fasting physiology of polar bears in relation to environmental change and breeding behavior in the Beaufort Sea. Polar Biol 32, 383–391 (2009). https://doi.org/10.1007/s00300-008-0530-0

Labunski, Elizabeth 2008, Polar bear, U.S. Fish and Wildlife Service, accessed Feb 12, 2024, <https://digitalmedia.fws.gov/digital/collection/natdiglib/id/2761/rec/31>

Robbins, C. T., Lopez-Alfaro, C., Rode, K. D., Tøien, Ø., & Nelson, O. L. (2012). Hibernation and seasonal fasting in bears: The energetic costs and consequences for polar bears. Journal of Mammalogy, 93(6), 1493–1503. https://doi.org/10.1644/11-mamm-a-406.1

Schliebe, Scott 2010, Polar bear with cub, U.S. Fish and Wildlife Service, accessed Feb 12, 2024, <https://digitalmedia.fws.gov/digital/collection/natdiglib/id/10931/rec/5>
Wiig Ø, Aars J, Born EW. Effects of Climate Change on Polar Bears. Science Progress. 2008;91(2):151-173. doi:10.3184/003685008X324506

Stressed Out Doggies

Did you know that your hair can indicate how stressed out you are? A recent study from Utrecht University found that dogs in shelters have higher levels of the stress hormone cortisol in their hair than non-shelter dogs. Regardless of how well the shelters treat their animals, they are often still stressed out, which is a great excuse to go rescue a dog in my opinion!

A Thankful Rescued Pit Bull. Photo by Luke Holben (2022).

The researchers examined the hair of many shelter dogs when they arrived, during their stay, and once they were adopted and placed into their new forever-homes. They found that the dogs were more stressed out during their stay than when they arrived, but after they were adopted the stress levels began to drop to normal levels. The dogs were so relieved to be in their new homes! Adopting dogs from shelters is extremely rewarding, but only adopt if you are sure you can care for your new best friend. I have personally adopted two dogs, one of which is the beautiful pit bull pictured above, and I would not trade them for the world.

 

References:

Utrecht University. (2022, April 21). Cortisol in shelter dog hair shows signs of stress. ScienceDaily. Retrieved April 25, 2022 from www.sciencedaily.com/releases/2022/04/220421130949.htm

“Hey! Turn that light off!” – Sea Turtles and Light Pollution

Sea turtles (Cheloniidae and Dermochelyidae families) are beloved by many, featured in animated kids movies like Finding Nemo as well in many viral videos showing newly-hatched babies scurrying into the ocean. Many people who live near them know they are endangered and care about them. What they don’t know is that their back porch light to their beach house is causing trouble. Artificial light pollution is a relatively new threat for sea turtles, disrupting many of their physiological functions.

Florida’s beaches are where many sea turtle species call home, nesting under the sand in the dunes. As beach tourism in the state continues to grow, more and more artificial light is spreading along the coastline, threatening these nesting sites. The artificial light disrupts the turtle’s circadian rhythm, confusing them if it is nighttime or daytime, making them more vulnerable to nocturnal predators who catch them unaware (Hu et al., 2018). In addition, when baby turtles are hatching, light pollution can disorient them during their dash to the ocean (Long et al., 2022). Geo-spacial collected data shows, however, that sea turtles are already avoiding areas of high light pollution (figure 1). Therefore, continued expansion of lights along Florida’s beaches could continue to reduce usable habitat for sea turtle nesting activities.

Figure 1. Geo-spacial map of artificial light on the Florida coast vs. density of Loggerhead turtle nests (Hu et al., 2018)

Luckily, the people of Florida have the sea turtles backs. Legislation exists that prohibits certain wavelengths of light to be visible from the beach, requiring shielding of exterior light bulbs (Mascovich et al., 2018). Education programs are also conducted to inform tourists who may be staying at a place close to the beach, informing them to turn off their exterior lights at night to protect nests. These programs are conducted with mixed success, however, with guests often still leaving their lights on throughout the night (Mascovich et al., 2018).

New lighting technology has also recently become an idea of preventing further and reducing current light pollution. For example studies show that Loggerhead sea turtles (Caretta caretta) are generally more sensitive to shorter wavelengths of light at less than 560 nanometers (Long et al., 2022). Thus, the state of Florida has been testing a new 624 nanometer lamp to use along coastal highways, to try and reduce light pollution that highways create. A study conducted by Long et al. showed that these new lamps DO work, with hatching turtles finding their way to the ocean just fine (2022).

Overall, while these solutions do work, they are not strictly enforced. There must be more legislative action and encouragement to use higher frequency light near the nesting locations to reduce light pollution.

References:

Hu, Z., Hu, H., & Huang, Y. (2018). Association between nighttime artificial light pollution and sea turtle nest density along Florida coast: A geospatial study using Viirs Remote Sensing Data. Environmental Pollution, 239, 30–42. https://doi.org/10.1016/j.envpol.2018.04.021

Long, T. M., Eldridge, J., Hancock, J., Hirama, S., Kiltie, R., Koperski, M., & Trindell, R. N. (2022). Balancing human and sea turtle safety: Evaluating long-wavelength streetlights as a coastal roadway management tool. Coastal Management, 50(2), 184–196. https://doi.org/10.1080/08920753.2022.2022974

Mascovich, K. A., Larson, L. R., & Andrews, K. M. (2018). Lights on, or lights off? hotel guests’ response to nonpersonal educational outreach designed to protect nesting sea turtles. Chelonian Conservation and Biology, 17(2), 206. https://doi.org/10.2744/ccb-1299.1