An Analysis of the Effects of Climate Change on California s Southern Sea Otters. By Alyssa Nerida ENVS 190 5/17/17

Transcription

1 An Analysis of the Effects of Climate Change on California s Southern Sea Otters By Alyssa Nerida ENVS 190 5/17/17 1

2 Table of Contents ABSTRACT 3 INTRODUCTION 3 HISTORY OF CALIFORNIA S SEA OTTERS 4 BIOLOGY OF SEA OTTERS 6 CURRENT STATUS 7 PREDICTED EFFECTS OF CHANGING CLIMATE ON MARINE ECOSYSTEMS 9 CHANGING CLIMATE CONDITIONS AND THEIR EFFECTS ON SEA OTTERS 10 CONCLUSION 12 REFERENCES 13 Southern Sea Otter (Lonhart, 2017). 2

3 Abstract This project s goal is to evaluate the effects of climate change on this species by examining the predictions for climate change in marine ecosystems and analyzing how these scenarios would affect sea otters. This is done by referencing the history and decimation of sea otters, stating their biology and current status, introducing ways in which marine ecosystems are affected by climate change, and explaining how these effects relate to sea otters. Introduction Southern Sea Otters, Enhydra lutris nereis, have played an essential role off the coast of Central California. They serve as a keystone species, foraging on and controlling the population of invertebrates that eat kelp, thereby maintaining kelp forests and protecting biodiversity (Scott Mills et al., 1993). Russian fur traders enslaved Inuit hunters to gain unrestricted access to pinnipeds and sea otters for their dense pelts. The fur trade drove the populations of these organisms of the Pacific to near extinction (Yonge, 1978). The decimation of sea otters led to a population bottleneck, leaving them at risk of extinction (Larson et al., 2012). Eventually, the ecological importance of sea otters and their decimated population was learned, just as environmental legislation first came into effect. The sea otter was listed as a threatened species on the U.S. Endangered Species Act in 1977 and was protected under the Marine Mammal Protection Act (Wolkomir, 1995). Their protection allowed them to repopulate and get close to numbers that would allow for their delisting as a threatened species (Tinker et al., 2016). Despite this, there may be a new threat to California s sea otters: changing climate conditions. This project s goal is to evaluate the effects of climate change on this species by examining the predictions for 3

4 climate change in marine ecosystems and analyzing how these scenarios would affect sea otters. History of California s Sea Otters At one point in history, sea otters thrived on the coasts of the Pacific Rim from Japan to Baja California (Monterey Bay Aquarium, 2017). The Northern Sea Otter (Enhydra lutris kenyoni) and the Southern Sea Otter (Enhydra lutris nereis) once numbered close to one million prior to eradication by the fur trade (Riedman and Estes, 1990). Beginning in 1733, Spanish missionaries and explorers traded abalone shells with the Native Americans of California in exchange for sea otter pelts (Kenyon, 1969; Ogden, 1941). In 1741, Georg Wilhelm Steller provided the world with a scientific description of sea otters and their habitat after his expedition was shipwrecked onto the Bering Island. After he and his men returned with the pelts of sea otters and pinnipeds, an unregulated flood on hunting in the west coast of the United States and Canada occurred in seek of these valuable furs (Kenyon, 1969). The California Sea Otter Trade was an extensive and unorganized hunting movement that lasted from (Ogden, 1941). 170 years of unregulated hunting decimated the population of both subspecies, particularly the Southern Sea Otter, to near extinction (Kenyon, 1969; Ogden, 1941). The high frequency hunting did not allow sea otter populations to recover, creating a population bottleneck. It is estimated that only one percent of the original numbers remained during the fur trade (Larson et al., 2012). Figure 1. Sea otter distribution in the Pacific prior to hunting (Yonge, 1978). 4

5 In 1911, the population decline for many hunted animals became problematic and the remnant populations were given international management to allow protection from poachers. The Fur Seal Treaty of 1911 stated that contracting parties (United States, Great Britain, Russia, and Japan) would not allow its citizens to kill or capture sea otters beyond the distance of three miles from the shorn line of its territories (The Fur Seal Treaty of 1911). This first step in protection allowed for the recovery of the sea otter population. It regulated the distance in which hunters can go in order to capture an otter. At this time, there were about 50 sea otters off the coast of Big Sur (Monterey Bay Aquarium, 2017). The Bureau of Biological Survey conducted sea otter population surveys in 1935, 1936, and 1937, which revealed that populations of sea otters rose due to the decline in hunting, and some populations were able to recover in islands across the Pacific (Riedman and Estes, 1990; Doroff et al., 2003). The sea otter became listed under the Marine Mammal Protection Act and the Endangered Species Act in the 1970 s (Riedman 5

6 and Estes, 1990). The populations in these island populations continued to increase until the 1990 s, where they began to decline due to the species vulnerability to anthropogenic effects and predators (Doroff et al., 2003). Tale 1. History of sea otters from 1733 to present North Pacific The Fur Trade Sea Otter Surveys Southern sea otter (Enhydra lutris) were initially hunted by Spanish explorers. Pelts were used as currency and offered bartering positions with Indians. Russian explorers enslaved Natives to obtain the pelts (Ogden, 1941; Yonge, 1978). Thousands of sea otters are decimated. This creates population fragmentation and coastal ecosystem degradation in the pacific. Hunting occurred from British- Columbia, to Central California. Less than 3000 otters were thought to survive (Ogden, 1941) Expeditions led by the refuge managers of the Aleutians and the Bureau of Fisheries documents otter populations physiologically damaged in areas across the Pacific. Note populations increase beginning in 1937 (Yonge, 1978) World War II Otter recovery Population growth was observed, likely due to the Fur Seal Treaty of 1911, Capture and transplant of otters occurs in national parks in the Aleutians. Turning point in species endangerment (The Fur Seal Treaty of 1911; Yonge, 1978) Endangered Species Act Population was listed in the Endangered Species Act at both federal level and state level in California (Animal Welfare Institute, 1983) present Species still recovering. Seven species of sea otters were listed in the 1996 IUCN Red list of Threatened Animals. Heavily damaged by anthropogenic activities (particularly oil spills). Otter hunting heavily regulated by USFWS (Animal Welfare Institute, 1983; USFWS 2017). Biology of Sea Otters Southern Sea Otters have a unique biology. They are one of the smallest mammals, yet one of the heaviest members of their family, Mustelidae. They are a sexually dimorphic species, with males being about 34% heavier and 8% longer than females. Their most acknowledgeable trait is their fur, which so many have sought after in past centuries. It is estimated that a sea otter has over one million hairs per square inch on the most dense areas of their pelt the thickest in the entirety of the animal kingdom (Larson et al., 2012). 6

7 The density of their fur causes a layer of air to be trapped near the skin, allowing them to be insulated in the waters of the Pacific. As for their behavior, sea otters partake in high- intensity maternal care. In depth energy budgets of sea otters have shown that mother otters will spend nearly all their time dedicated to taking care of their pups who are highly dependent of them for energy (Thometz et al., 2014). In fact, compared to male otters and female otters without pups, mother sea otters will spend less time foraging in order to watch after their offspring. Mothers will risk an insufficiency of calories, harming both themselves and their pups that require their milk, in order to be at the surface with their pups, nursing, grooming, and attending to them (Thometz et al., 2016). With the prioritization of taking care of their pups, by the time of post- weaning, many mothers have become so weakened that they are vulnerable to infection, disease, and death a situation known as end- lactation syndrome. By the end of maternal care, the costs of reproduction have a detrimental impact on many female sea otters (Chinn et al., 2016). Female sea otters with pups face a high trade off during motherhood, which can cost their lives, and in some cases, the lives of their pups. Current Status Today, Southern Sea Otters remain under protection through the U.S. Endangered Species Act and the IUCN Red List. Sea otters gained protection under the Marine Mammal Protection Act of This created a hands- off policy for the animals in which they could not be commercially harvested, killed, captured, or harassed (Marine Mammals Management, 2014). In addition, they were added as a threatened species under the U.S. Endangered Species Act in The primary reasons for their listing were vulnerability to oil spills, reduced range, and decreased population size (Ventura Fish & Wildlife Office, 7

8 2017). As of now, Southern Sea Otters are found along the coast just south of Half Moon Bay to Point Conception (Landis, 2012). Federal and state protection of sea otters has lead to the recovery of their population in California. As of September 2016, the population index is 3,272, a number that has increased from the 2,939 just three years prior (Tinker et al., 2016). Despite this, the sea otters cannot be delisted until the population index exceeds 3,090 for three consecutive years, (Ventura Fish & Wildlife Office, 2017). Figure 2. Current distribution and density of Southern Sea Otters (Landis, 2012). 8

9 Predicted Effects of Changing Climate on Marine Ecosystems Marine ecosystems contain the most biodiversity on the planet. Currently, climate change is already altering these ecosystems. Imminent climate change is expected to change the composition of marine ecosystems to a state that has not been known or documented in millions of years (Hoegh- Guldberg and Bruno, 2010). Earth s climate is expected to undergo rapid warming, facing an expected decrease in ocean productivity and altered food web dynamics, shifting species distributions and creating a greater incidence of marine diseases (Stenseth, 2008; Hoegh- Guldberg and Bruno, 2010). Changing climate conditions are also expected to increase the temperature of oceans, increase CO2 concentrations, alter ph levels, and intensify the amount of solar radiation that is absorbed in the oceans. It is anticipated that these changes will degrade or eliminate important marine ecosystems (Stenseth, 2008). Over the past 50 years, major changes have occurred in the climate of the southern oceans. Climatic modeling has shown the oceans have increased by 0.31 Celsius, at observable depths of up to 3000 meters (Scavia et al, 2002). Large amounts of warm, salty water is flowing southward, causing changes in community compositions (Dicks, 2011). A spike in temperature has decreased primary production, which has caused a loss of nutrient content from species at the base of marine trophic levels (Dicks, 2011). Changing temperature and external pollution is affecting the physiology of several marine organisms by directly affecting their susceptibility and response to other abiotic factors (Sokolva and Lanning, 2008). Many species of fish and kelp are shifting their species distributions and dominance, which causes a loss of important prey for large mammals and predatory fish (Wassman et al., 2010). 9

10 Changing Climate Conditions and their Effects on Sea Otters Changing climate conditions can negatively affect sea otters in many ways. It is likely that sea otters will experience direct impacts from climate change. However, they will encounter more indirect impacts from climate change through alterations in the main food web. Sea otters will be indirectly affected with climate change through the greenhouse effect. It is estimated that methane levels are increasing by an average of 10 parts per billion annually (Earth System Research Laboratory, 2017). Since sediment acts as a sink for hydrocarbons such as methane, benthic invertebrates that live in the sediment may become contaminated. When sea otters forage on these invertebrates, they can be exposed to hydrocarbons and become ill (Harris et al., 2011). Kelp beds are likely to face mortality due to ocean acidification, warmer ocean temperatures, and high- intensity storms. As kelp forests die, the organisms that rely on them are faced to find other habitats. Degradation of kelp forest habitats impacts the sea otters, which use kelp forests to forage on many invertebrates, such as sea urchin (Dayton, 1985). 10

11 Figure 2. Globally- averaged, monthly mean atmospheric methane abundance (Earth System Research Laboratory, 2017) If the source of food of sea otters becomes less abundant, foraging will become more of a challenge. This poses a major threat to sea otters, but especially to the mothers taking care of pups. As mentioned earlier, mother pups will spend less time foraging than males and females without pups in order to care for their young. If food cannot easily be found, a mother will not optimize her foraging time, regardless of resource availability (Thometz et al., 2016). This will result in unsuccessful foraging attempts for mothers, decreasing their caloric intake. Since pups also depend on the mothers foraging successes during nursing, malnourished mothers are depleted even more of energy as the pups nurse. Such a weaken state can cause mothers to receive end- lactation syndrome, a state at which they become very vulnerable to death. (Chinn et al., 2016). 11

12 In addition to these effects, sea otters are already in a vulnerable state. Since their population has not made a full recovery in the terms specified by the U.S. Fish and Wildlife Recovery Plan for the Southern Sea Otter, they are more at risk to extinction compared to marine mammals that have large populations. This is due to chance variability, reduced genetic variation from the population bottleneck, and random events that cause mortality (Raincoast Conservation Foundation, 2017; Larson et al., 2012). Conclusion Since their demise to near extinction starting in the 1700s, sea otter populations have grown to levels that near the delisting as a threatened species under the Endangered Species Act (Tinker et al., 2016). This population growth can be attributed to the protective measures that were set on both a federal and state scale, prohibiting the capture, harvest, kill, and harassment of the species (Wolkomir, 1995). Despite their recovery, sea otters still face new threats to their population through changing climate conditions. Along with their vulnerability as a relatively small population, sea otters can be impacted through contamination of their prey and decrease in their prey (Raincoast Conservation Foundation, 2017; Harris et al., 2011; Dayton, 1985). 12

13 References Chinn, S.M., Miller, M.A., Tinker, M.T., Staedler, M.M., Batac, F.I., Dodd, E.M., and Henkel, L.A., 2016, The high cost of motherhood: End- lactation syndrome in southern sea otters (Enhydra lutris nereis) on the Central California Coast, USA, Journal of Wildlife Diseases, v. 52, p Dayton, P.K., 1985, Ecology of kelp communities, Annual review of ecology and systematics, v. 16, p Dicks, L., 2011, Arctic climate issues 2011: changes in Arctic snow, water, ice and permafrost, Arctic Monitoring and Assessment Programme, p Doroff, A. M., Estes, J. A., Tinker, M. T., Burn, D. M., and Evans, T. J., 2003, Sea otter population declines in the Aleutian Archipelago, Journal of Mammalogy, v. 84, p Earth System Research Laboratory, 2017, Recent global CH4, U.S. Department of Commerce, (April 13, 2017). Endangered Species Handbook, 1983, Otters, Animal Welfare Institute, (March 3, 2017). Harris, K.A., Yunker, M.B., Dangerfield, N., Ross, P.S., 2011, Sediment- associated aliphatic and aromatic hydrocarbons in coastal British Columbia, Canada: concentrations, composition, and associated risks to protected sea otters, Environmental Pollution, v. 159, p Hoegh- Guldberg, O. and Bruno, J., 2010, The impact of climate change on the world s marine ecosystem, Science, v. 328, p

14 Kenyon, K., 1969, The sea otter in the Eastern Pacific Ocean, North American Fauna, v. 68, p Landis, B.Y., 2012, Recovery slows for California s sea otters, 2012 survey shows, U.S. Geological Survey, (May 6, 2017). Larson, S., Jameson, R., Etnier, M., Jones, T., and Hall, R., 2012, Genetic diversity and population parameters of sea otters, Enhydra lutris, before fur trade extirpation from , PLoS ONE, v. 7, p Lonhart, S., 2017, Southern Sea Otter, National Oceanic and Atmospheric Administration, rn%20sea%20otter (May 12, 2017). Marine Mammals Management, 2014, Sea otter, U.S. Fish & Wildlife Service, (April 4, 2017). Monterey Bay Aquarium, 2017, Southern Sea Otter, Monterey Bay Aquarium, guide/marine- mammals/southern- sea- otter (March 1, 2017). Ogden, A., 1941, The California Sea Otter Trade, , University of California Press, Berkeley, p Raincoast Conservation Foundation, 2017, Cumulative impacts on sea otters, Raincoast Conservation Foundation, content/uploads/cumulative- impacts- on- sea- otters.pdf (April 17, 2017). Riedman, M. and Estes, J., 1990, The sea otter (Enhydra lutris): behavior, ecology, and natural history, Biological report (USA), v. 90, p

15 Scavia, D., Field, J.C., Boesch, D.F., Buddemeier, R.W., Burkett, V., Cayan, D.R., Fogarty, M., Harwell, M.A., Howarth, R.W., Mason, C., Reed, D.J., Royer, T.C., Sallenger, A.H., and Titus, J.G., 2002, Climate change impacts on U.S. coastal and marine ecosystems. Estuaries, v. 25, p Scott Mills, L., Soule, M.E., and Doak, D.F., 1993, The keystone- species concept in ecology and conservation, BioScience, v. 43, p Sokolva, I. and Lanning, G., 2008, Interactive effects of metal pollution and temperature on metabolism in aquatic ectotherms: implications of global climate change, Climate Research, v. 37, p Stenseth, N., 2008, Effects of climate change on marine ecosystems, Climate Research, v. 37, p The Fur Seal Treaty of Thometz, N.M., Staedler, M.M., Tomoleoni, J.A., Bodkin, J.L., Bentall, G.B., Tinker, M.T., 2016, Trade- offs between energy maximization and parental care in a central place forager, the sea otter, Behavioral Ecology, v. 27, p Thometz, N.M., Tinker, M.T., Staedler, M.M., Mayer, K.A., Williams, T.M., 2014, Energetic demands of immature sea otters from birth to weaning: implications for maternal costs, reproductive behavior and population- level trends, The Journal of Experimental Biology, v. 217, p Tinker, T., Soileau, S., Spratt, A., Michaels, D., 2016, Sea otter survey encouraging, but comes up short of the perfect story, United States Fish & Wildlife Service, otter- survey- encouraging- but- comes- up- short- of- the- perfect- story - &_ID=35806 (April 1, 2017). 15

16 Ventura Fish & Wildlife Office, 2017, Southern Sea Otter, U.S. Fish & Wildlife Service, (April 1, 2017). Wassman, P., Duarte, C., Agusti, S., and Sejr, M., 2010, Footprints of climate change in the Arctic marine ecosystem, Global Change Biology, v. 17, p Wolkomir, R., 1995, The fragile recovery of California sea otters, National Geographic v. 187, p Yonge, C.M., 1978, The sea- otter and history, History Today, v. 28, p