Month: February 2024

Is Too Much Algae Bad for Fish?

Figure 1: Rainbow Trout (photo courtesy of the U.S Fish and Wildlife Service)

Rainbow Trout are one of the many fish species that are affected by harmful algal blooms (HABs). Harmful algal blooms occur all over the world, in freshwater and seawater, which makes them a very troubling issue. Not only do they cause damage to fish and aquatic ecosystems, but they can also negatively impact many other factors such as tourism, public health, and recreation (Gobler, 2020). Humans play a significant role in causing HABs, whether its adding extra nutrients (for example, phosphorous or nitrogen) into the water or contributing to climate change (Sellner et al., 2003). Two examples of humans adding extra nutrients into the water are agricultural runoff and industrial activity. The extra nutrients that these activities provide promotes higher rates of algae growth than usual (Sellner et al., 2003). Further, humans have contributed significantly to climate change, which raises water temperature, providing an excellent habitat for algae to live in and take over (Ho and Michalak, 2019). HABs also occur in Lake Erie, mostly in the Ohio Maumee watershed because of the agricultural practices that are dominant within that watershed.

In aquatic ecosystems, HABs cause hypoxia, which is condition where there are extremely low levels of oxygen in the water (Golber, 2020). Fish, such as the rainbow trout, do not breath air, but they still need oxygen in order to survive. The fish’s gills are huge compared to the fish’s body, which provides a lot of help when absorbing oxygen (Ness Foundation, 2019). In addition, when a fish breathes, the water flowing over the gills runs the opposite direction of the blood running through the gills, which allows the amount of oxygen in the blood to be less than the oxygen of the water (Ness Foundation, 2019). This allows oxygen to move to places where there are low amounts of oxygen, which refers to a process called diffusion. Once in the fish’s body, the oxygen attaches to a protein called hemoglobin, and it is transferred all throughout the body (Ness Foundation, 2019). Algae effect the fish’s ability to breathe by irritating the gills, which decreased the amount of oxygen that the fish receives (Svendsen et al., 2o18). If there is more algae in the water, then fish have a higher chance of suffering from this condition.

 

Figure 2: Oxygen transferred to blood via the veins as water flows through

(Photo courtesy of Charles Molar and Jane Gair, CC BY 4.0 DEED https://creativecommons.org/licenses/by/4.0/)

In order to prevent further damage caused by HABs, there has to be a reduction in agricultural runoff entering the water body. There is action being taken to minimize impacts caused by agricultural runoff, such as a reducing pesticide use, managing irrigation systems, and conservation tilling (Marsh, 2022). Industrial activity needs to be reduced or better managed to prevent nutrient-rich runoff that comes from industrial plants. The whole problem of climate change is an extremely complex problem, and there are many measures that humans can take to reduce their impact. For example, carpooling or taking the bus instead of driving most times can limit emissions from cars, which contributes to climate change. Fish are a huge part of the aquatic ecosystem, and humans need to do their part to reduce excess nutrient input into water bodies in order to protect fish.

Sources:

Gobler, C. J. (2020). Climate change and harmful algal blooms: Insights and perspective. Harmful Algae, 91, 101731. https://doi.org/10.1016/j.hal.2019.101731

Ho, J. C., & Michalak, A. M. (2019). Exploring temperature and precipitation impacts on harmful algal blooms across continental U.S. lakes. Limnology and Oceanography, 65(5), 992–1009. https://doi.org/10.1002/lno.11365

How do fish breathe? The Science Behind Gills. New England Science & Sailing (NESS). (2019, August 8). https://nessf.org/how-do-fish-breathe-the-science-behind-gills/

Marsh, J. (2022). Protecting water quality from agricultural runoff. Agrilinks. https://agrilinks.org/post/protecting-water-quality-agricultural-runoff

Sellner, K. G., Doucette, G. J., & Kirkpatrick, G. J. (2003). Harmful algal blooms: Causes, impacts and detection. Journal of Industrial Microbiology and Biotechnology, 30(7), 383–406. https://doi.org/10.1007/s10295-003-0074-9

Svendsen, M., Andersen, N., Hansen, P., & Steffensen, J. (2018). Effects of harmful algal blooms on fish: Insights from Prymnesium Parvum. Fishes, 3(1), 11. https://doi.org/10.3390/fishes3010011

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

Eastern Hellbender Response to Changing Temperatures

The Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) is a fully-aquatic salamander species. They live in cool, fast, and highly-oxygenated streams in the Appalachian Mountains. Sadly, this species has been on the decline since the 1970’s, and climate change continues to pose threats against them (Virginia Department of Wildlife Resources).

A study by Terrell et al. (2021) analyzed the potential physiological affects of climate change on hellbenders. In a laboratory setting, growth rates and immune system functions were studied at a variety of temperatures to test Eastern Hellbenders ability to cope with climate change. It was found that both growth rate and immune function suffered at higher temperatures. Hellbender immune systems were found to be most susceptible at high and low temperatures. While global average temperatures are rising, it is also predicted that we will have lower minimum temperatures. Exposure to both higher and lower temperatures could cause problems for hellbender immune health. The salamanders experienced slower growth rates during warmer summer temperatures following the breeding season. This lack of growth after an energy-demanding reproduction phase, may lead to population struggles with warming temperatures.

Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis). Photo courtesy of the Virginia Department of Wildlife Resources.

Eastern Hellbenders are already threatened or endangered in many of the states they inhabit (Virginia Department of Wildlife Resources). With a changing climate, these animals will continue to struggle. Much effort and continued research is necessary if we wish to save the beloved hellbender.

 

References:

Eastern Hellender. Virginia Department of Wildlife Resources. https://dwr.virginia.gov/wildlife/information/eastern-hellbender/

Terrell KA, Quintero RP, Galicia VA, Bronikowski E, Evans M, Kleopfer JD, Murray S, Murphy JB, Nissen BD, Gratwicke B (2021) Physiological impacts of temperature variability and climate warming in hellbenders (Cryptobranchus alleganiensis). Conservation Physiology 9 (1). doi:10.1093/conphys/coab079

 

Water ‘air conditioning’ For Fish Facing Climate Change

Rising air and water temperatures caused by human-induced climate change can prove deadly for some species of fish. When temperatures get too high, past where many species can tolerate, the fish that cannot adjust to the warmer temperatures will die. High water temperatures means less available oxygen for fish to be able to breathe. Many fish species can temporarily adjust their lifestyles by reducing activity which allows them to consume less oxygen. However, this is only a short-term solution. Many species like the Atlantic Salmon have very active lifestyles and need to use a lot of energy to find food, mate and lay eggs. Higher temperatures can also reduce the chance of survival for fish eggs laid during spawning season. One of the questions I asked myself is “What can be done to help fish species that are sensitive to warmer temperatures?” Fish water-conditioning may be an answer!

Kathryn Smith and her colleagues from Dalhousie University in Halifax, Canada, pumped naturally cooled groundwater into the Wrights River in Nova Scotia in an attempt to provide reprieve from the warming waters to the native Atlantic Salmon. She said that they saw salmon in varying life stages congregating in the cold plumes this cooled water created. 

Smith and her colleagues also tried a pump-less method by rerouting some of the water from the river to cool in a ground trench before returning to the river. This method they said only cooled the water a few degrees Celsius, however, fish were still seen throughout the summer sheltering in the colder water. Creating safe havens for these fish species to stay cool and literally breathe a sigh of relief is only a first step to helping fish survive in a climate warming world. Large areas, especially sensitive breeding areas, will need to be cooled to make the environments these fish are living in comfortable enough so that they can resume normal activity.

Image US Fish and Wildlife Service: Atlantic Salmon (Salmo salar)

Source: Ogasa N (2023) Pumping cold water into rivers could as as ‘air conditioning’ for fish. Science News. https://www.sciencenews.org/article/cold-water-river-salmon-fish-climate

The Impacts of Global Warming on the Common Toad

Common Toad. Photo Taken by Karamel. https://upload.wikimedia.org/wikipedia/commons/9/93/Common_Toad_%28Bufo_bufo%29.jpg

Over the last couple of decades, amphibians globally have experienced huge population declines that have resulted in the extinction of some species (AmphibiaWeb, 2017). Amphibians are ectothermic, meaning they cannot regulate their own body temperature. They instead rely on external sources like the sun to thermoregulate. This means that amphibians are particularly sensitive to changes in their environment. With global temperatures rising due to global warming, the summers are becoming longer and the winters are becoming shorter and milder (Reading, 2006). The hibernation periods of toads are disrupted in the process, leading to detrimental and even fatal health complications for toads. 

In a study on Common Toads, a widespread species in Europe, Jorgenson (1986) found that female toads who were given unlimited access to food during the winter and prevented from hibernating, grew slower and died at higher rates than female toads that hibernated. He also found that female toads reached reproductive age younger and at a smaller size than female toads that hibernated. A study conducted by Reading (2006) on the same species yielded the same results and found that mild winters caused female toads to reach breeding age at smaller sizes. This can be detrimental to toad populations because the amount of eggs a mother toad lays is dependent on how big she is. 

Amphibians have structures called fat bodies that allow them to store energy that can be used while they hibernate (Reading, 2006). When the winters are cold, metabolism slows down and energy usage is minimal. However, when the winters are only mild, the toad’s metabolism doesn’t slow down enough to minimize energy usage. The toads emerge hibernation with less energy availability and their body condition is decreased. In some cases, the toads’ energy reserves are depleted before they emerge from hibernation and they die in the process (Reading, 2006). 

Unfortunately, global mean temperatures are expected to rise by 1-7 in the coming years (IPCC, 2001). The Common Toad and other amphibian species populations will likely face more challenges as temperatures continue to rise. In order to help these species see the future, we can continue to study them and their physiological limitations further. Although amphibians may not seem important enough to preserve, we must remember that they help control mosquito populations that can reduce our risk of disease exposure (Morris, 2020).

References

AmphibiaWeb: Worldwide Amphibian Declines (2024). https://amphibiaweb.org/declines/ (last accessed 12 February 2024).

External and internal control of patterns of feeding, growth and gonadal function in a temperate zone anuran, the toad Bufo bufo – Jørgensen – 1986 – Journal of Zoology – Wiley Online Library (2024). https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.1986.tb03631.x?casa_token=mZ2kbsVtPwQAAAAA:WkOXqMUoUJ2XXl-546g0FEczyBwOPNJxCTVoN7fRJk5ghTBgPCo6SseiegGljrfTahwqCbLqSivC4bM (last accessed 12 February 2024).

Kerlin KE (2020) Amphibian Declines Affect Human Health. UC Davis. https://www.ucdavis.edu/climate/what-can-i-do/amphibian-declines-affect-human-health (last accessed 12 February 2024).

Reading CJ (2007) Linking global warming to amphibian declines through its effects on female body condition and survivorship. Oecologia 151: 125–131.

Watson RT, Albritton DL, Intergovernmental Panel on Climate Change, Intergovernmental Panel on Climate Change, Intergovernmental Panel on Climate Change, eds. (2001) Climate Change 2001: Synthesis Report. Cambridge University Press, Cambridge ; New York.

Physiological Response of Fish in Polluted Environments

Figure 1: Fish in Contaminated Water https://stock.adobe.com/search?k=dead+fish+water&asset_id=431095511

Human activities contribute to various forms of pollution that may directly or indirectly travel into water bodies and contaminate aquatic ecosystems. Common aquatic pollutants include hydrocarbons, polychlorinated biphenyls, plastics, heavy metals such as mercury, lead, and chromium, and various forms of pesticides. Continued exposure to these pollutants, especially at high levels, may cause extensive oxidative stress to fish, which can be defined as an imbalance of antioxidant systems (Padmini, 2010).

 

 

 

Continued environmental stress caused by pollution triggers cellular Mitochondria to produce reactive oxygen species (ROS). These ROS are free radicals that can cause permanent damage to proteins. Fish have been found to respond physiologically to protein damage caused by ROS with “cytoprotective” heat shock proteins (HSP), also known as stress proteins. These heat shock proteins function to mend the proteins damaged by ROS by facilitating appropriate protein folding and conformations. Heat shock proteins are generated in high volumes upon the stimulus of oxidative stress caused by pollution within the aquatic environment (Padmini, 2010).

Figure 2: Heat Shock Protein Stimulus in Fish (Mohanty, 2018)

Without the response of heat shock proteins, fish may continually accumulate damaged macromolecules. This accumulation can then hinder reproduction or cause infection or death. Therefore, heat shock proteins allow fish to combat (to a degree) the environmental stress they may be subject to. Researchers track levels of these cellular components to measure aquatic contamination and disturbance. With this, heat shock proteins can be used as a method to assess environmental quality overall (Padmini, 2010).

 

References

Mohanty BP, Mahanty A, Mitra T, Parija SC, Mohanty S (2018) Heat shock proteins in teleosts. Regulation of Heat Shock Protein Responses 13:71-94. doi:10.1007/978-3-319-74715-6_4.

Nattawit. (n.d.). Dead fish floating on water surface, Ecosystem and environmental problem from contaminated water. Adobe Stock. Retrieved from https://stock.adobe.com/search?k=dead+fish+water&asset_id=431095511.

Padmini E (2010) Physiological adaptations of stressed fish to polluted environments: role of heat shock proteins. Reviews of Environmental Contamination and Toxicology 206:1-27.doi:10.1007/978-1-4419-6260-7_1.

Problems of Gene Flow for Grey Wolf Populations on Isle Royale National Park

In Isle Royale National Park (Michigan), there is an established population of both gray wolves and moose.  It is believed that the wolves arrived on Isle Royale sometime during the 1940s when an ice bridge formed, allowing for wolves to cross over the water to the island.  Ever since the wolves arrived, they have been an important predator on the island, helping to control the local moose population.  The wolves do this by preying on ill or injured moose.  Recently, the wolves have faced the threat of extinction in Isle Royale National Park due to inbreeding (National Park Service, 2022).

There have been fluctuations in the wolf and moose populations in Isle Royale for many years. Some factors include the available amount of food resources and weather changes.  However, a common pattern that has been seen is that when the wolf populations spike, the moose populations decrease and vice versa.  This can be seen in the following graph below.  From 2011 to 2014, the wolves had reached a population size that was unsustainable.  Around 2011, the wolf population decreased, and the moose population increased. (National Park Service, 2021).

(National Park Service, 2021)

If there is low genetic variation within a population, then a species risks extinction, therefore lowering its fitness.  The wolves on Isle Royale are facing this problem, likely due to climate change not allowing for the ice bridges to form anymore.  With no ice bridges forming, the amount of gene flow that occurs in the populations has decreased.  For example, in 1997, a wolf known as M93 crossed the ice bridge to Isle Royale, creating gene flow within the population.  By 2008, 59.4 % of the wolf population descended from wolf M93.  Once this ice bridge was no longer forming, the gene flow in the population decreased, causing increases in inbreeding.  By 2012, there were only 9 wolves left, and 5 of them, through genetic testing, were found to be full siblings (Hedrick, 2014).

To save the wolf populations, a technique that can be used is called genetic rescue.  Genetic rescue allows members from outside the struggling population to be introduced either naturally or by humans to add more genetic variation into the population (Hedrick, 2014).  In June 2018, the National Park Service decided to do this to help control the moose populations.  If the wolves are not present on Isle Royale, the moose population will negatively impact the island’s vegetation.  The plan is for the National Park Service to introduce a total of 20 to 30 wolves onto the island (National Park Service, 2018).

Citations

Hedrick PW, Peterson RO, Vucetich LM, Adams JR, Vucetich JA et al. (2014) Genetic rescue in Isle Royale wolves: genetic analysis and the collapse of the population. Conservation Genetics 15: 1111–1121. https://link.springer.com/article/10.1007/s10592-014-0604-1

National Park Service. 2018 Press Release National Park Service Releases Record of Decision to Introduce Wolves at Isle Royale National Park. Version 2018.6. https://www.nps.gov/isro/learn/news/press-release-national-park-service-releases-record-of-decision-to-introduce-wolves-at-isle-royale-national-park.htm. (date last accessed 12 February 2024).

National Park Service. 2021 Wolf & Moose Populations. Version 2021.5. https://www.nps.gov/isro/learn/nature/wolf-moose-populations.htm.  (date last accessed 12 February 2024).

National Park Service. 2022 Wolves. Version 2022.1. https://www.nps.gov/isro/learn/nature/wolves.htm.  (date last accessed 12 February 2024).

Rising Climate Leading to the Rise of Female Sea Turtles


Figure 1: Photo of sea turtle. (Courtesy of Cindy Spence of University of Florida)

As global temperatures continue to increase du to climate change, populations of sea turtles are on the decline. Sea turtles are considered an ambassador flagship species that helps draw the society’s attention to help conserve them since they are on the brink of extinction. The concern for the future of sea turtles is more important than ever as the global climate continues to rise.

Sea turtles are ectotherms with temperature-dependent sex determination. This means that the outcome of the eggs produced by sea turtles is dependent on the temperature of the sand in which the female turtles lay their eggs in. Studies have found that the temperatures of the sand that green sea turtles lay their eggs on affects the sex of the offspring and if not at an optimal temperature could mess up the sex ratio of offspring (Tomillo and Spotila 2020). Warmer sand temperatures have been found to produce females and cooler sand temperatures produce males. If the temperature of the sand is continuing to rise then we will continually see clutches with only female offspring which is an issue because with no males in the population the sea turtles will not be able to continue to reproduce. There have been studies done using incubation to study the effects of the temperature on the sex of the eggs and the mortality rates of the eggs in incubation to study possible management processes to help stop the declining population of sea turtles and to hopefully learn more about the future thermal tolerance of sea turtles (Booth 2017; Laloë et al. 2017).


Figure 2: Baby sea turtles. (Courtesy of Cindy Spence of University of Florida)

Sea turtles also face the challenge of decreasing food availability. This decrease in food availability traces back to the increasing climate because the increase is affecting the coral that sea turtles depend on for food. With coral populations declining and dying, the sea turtles food supply gets lower and lower. The decreasing food supply for sea turtles has led to more time in between nesting periods since the turtles do not have the energy needed to reproduce and provide for the embryos. A study done by Stubbs et al. used a model to predict a continued increase in time between nesting periods for female sea turtles in situations with decreasing food availability (2020). With more time in between nesting there is less reproduction of sea turtles happening which makes the whole population begin to decline.

There is still more research needed to fully understand the future of sea turtle populations but the increasing climate is not predicted to decrease any time in the near future so the sea turtles are under a lot of pressure. With increased frequency of marine heatwaves reducing reproductive output and decreasing food availability, the reproductive output of eggs produced is on the decline along with the sex ratio of the eggs becoming mostly if not all female. Future research could look into the thermal tolerance of sea turtles and the thermal tolerance of the offspring to see if sea turtles could become more tolerant to these increasing temperatures. Along with this, more research needs to be done to understand the future of the food availability of sea turtles to be able to have the energy and resources needed to reproduce successfully.

References:
Booth DT (2017). Influence of incubation temperature on sea turtle hatchling quality. Integrative Zoology. https://onlinelibrary.wiley.com/doi/abs/10.1111/1749-4877.12255

Laloë JO, Cozens J, Renom B, Taxonera A, and Hays GC (2017). Climate change and temperature-linked hatchling mortality at a globally important sea turtle nesting site. Global Change Biology. https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13765

Spence C (2019). Sea Turtles Without Borders. Explore

Turtles Without Borders

Stubes JL, Marn N, Vanderklift MA, Fossette S, and Mitchell NJ (2020). Simulated growth and reproduction of green turtles (Chelonia mydas) under climate change and marine heatwave scenarios. Science Direct. 431. https://doi.org/10.1016/j.ecolmodel.2020.109185

Tomillo PS and Spotila JR (2020). Temperature-Dependent Sex Determination in Sea Turtles in the Context of Climate Change: Uncovering the Adaptive Significance. BioEssays. https://onlinelibrary.wiley.com/doi/abs/10.1002/bies.202000146

Texas State Aquarium Saves Over 300 Cold Stunned Sea Turtles During Polar Vortex

Climate change has lead to increasing extreme weather events in the past few years. While warming global temperatures may be the most well-known effect of climate change, it can also cause episodic periods of severe cold weather, which are known as polar vortexes. In mid-January 2024, a polar vortex swept across the United States, sending temperatures plummeting and shocking wildlife in Southern states that are unaccustomed to the frigid weather.

In Corpus Christi, Texas, 323 green sea turtles were found cold stunned in Laguna Madre. Sea turtles are ectothermic, which is more commonly known as being “cold-blooded”. This means that they do not have any internal physiological mechanisms to maintain a constant body temperature like mammals and birds. Instead, they must rely on external environmental or behavioral sources to retain heat. When temperatures are below an ectotherm’s ideal range, their metabolism slows and they become lethargic (Schulte, 2015).

When these cold snaps happen, the outside temperature changes so abruptly that the sea turtles do not have time to acclimate. They become cold shocked and are essentially immobile in the water, which leaves them vulnerable to pneumonia, collisions, and drowning. Luckily, wildlife biologists at the Texas State Aquarium and Padre Island National Seashore had been anticipating the polar vortex and had emergency hospital pools prepared for the turtles. Between January 16-19 2024, all 323 sea turtles were rescued, placed in rehab tanks, and treated based on condition.

The operation proved to be an overwhelming success. Most turtles were simply cold shocked, and by January 23rd, 275 of them were well enough after treatment that they were ready to be released back into the Gulf of Mexico. The remaining 48 are at the Sea Turtle Hospital on Padre Island to receive additional treatment and monitoring. The rescue would not have been possible without collaboration between the Texas State Aquarium, Padre Island National Seashore, NOAA, USFWS, Texas A&M University, and the Texas Sealife Center.

This story is personal to me because I grew up in Corpus Christi and participated in cold stunned turtle rescues when I was in middle school. As unfortunate as these events are, it makes me proud to see so many people collaborating to save these wonderful creatures.

This blog post is based on an article from The Association of Zoos and Aquariums (Gilsoul, 2024).

Photo credit: Texas State Aquarium

Gilsoul, S. (2024). Texas state aquarium treats and releases cold-stunned sea turtles. Association of Zoos and Aquariums. https://www.aza.org/connect-stories/stories/texas-state-aquarium-treats-and-releases-cold-stunned-sea-turtles
Schulte, P. M. (2015). The effects of temperature on aerobic metabolism: Towards a mechanistic understanding of the responses of ectotherms to a changing environment. Journal of Experimental Biology, 218(12), 1856–1866. https://doi.org/10.1242/jeb.118851