Annotated bibliography compiled by Elysha Iversen for Fall 2022 GEOG 560
Oregon State University
Author’s Introduction
The capstone project for my Master of Wildlife Administration focuses on the conservation of the southern sea otter, Enhydra lutris nereis, which is listed as “threatened” under the Endangered Species Act (42 FR 2965 January 14, 1977.) The current population of southern sea otters in California has characteristics of having reached carrying capacity. Managers are looking at translocation to other sites in California and Oregon as a possible next step to bolster the flatlined population. Ecological threats such as sharks, domoic acid poisoning and disease have the potential to hamper translocation efforts. For this assignment, I investigated the diverse uses of Geographic Information Systems (GIS) in the conservation of the southern sea otter to find context and information germane to my capstone. Specifically, I : 1) summarized the articles, 2) described the uses of GIS in conservation of southern sea otters and 3) noted the relevance to my capstone.
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Carrasco, S. E., B. B. Chomel, V. A. Gill, A. M. Doroff, M. A. Miller, K. A. Burek-Huntington, R. W. Kasten, B. A. Byrne, T. Goldstein, and J. A. K. Mazet. 2014. Bartonella spp. exposure in northern and southern sea otters in Alaska and California. Vector-Borne and Zoonotic Diseases 14:831–837.
In 2006, a large number of northern sea otters were found dead in Alaska. This was termed an “unusual mortality event” and the scientific community found that Bartonella spp. (a gram-negative infectious bacteria) had contributed and that both northern and southern sea otter populations are infected with multiple species of Bartonella spp. GIS was used to map all the sampling sites of northern (live captured and necropsied) and southern (necropsied) sea otters. Disease is a factor in the reintroduction of southern sea otters and this study is one for me to keep in mind.
Grimes, T. M., M. T. Tinker, B. B. Hughes, K. E. Boyer, L. Needles, K. Beheshti, and R. L. Lewison. 2020. Characterizing the impact of recovering sea otters on commercially important crabs in California estuaries. Marine Ecology Progress Series 655:123–137.
Dungeness crab is a commercially important species. Sea otters predate Dungeness crab and have been increasing in numbers in Elkhorn Slough. According to this study, sea otters have localized effects on juvenile crab abundance and size within the four estuaries studied. However, there was no evidence that Dungeness crab landings in California as a whole have been negatively affected by southern sea otters. Additionally, sea otters promote growth and expansion of nursery habitat which may actually recruit more crabs. Locations of surveyed otters were georeferenced using a GIS. The authors also created a “kernel density surface” and did “zonal statistics” using GIS. While not directly related to my capstone, it is important to keep in mind potential human conflict, such as resistance from the fishing industry against reintroduction of an apex predator.
Hessing-Lewis, M., E. U. Rechsteiner, B. B. Hughes, M. Tim Tinker, Z. L. Monteith, A. M. Olson, M. M. Henderson, and J. C. Watson. 2018. Ecosystem features determine seagrass community response to sea otter foraging. Marine Pollution Bulletin 134:134–144.
This study compared the effects of sea otter foraging between two sea grass communities, one in California (CA) and the other in British Columbia (BC). The authors then compared the ecosystem services provided by otter predation to the local cultures. They found that there is greater species richness in BC, however crabs (which provide an important role in CA) are less common in BC. The authors state that in CA the trophic effects of sea otter predation has likely enhanced sea grass habitat for fish and crabs. What’s more, seagrass sequesters carbon, which is in line with CA state-level policies to strongly support climate change initiatives. In BC sea otters and their ecosystem services, are highly valued culturally. The authors used GIS to map the sea otter range in BC and CA. This article is outside the scope of my capstone, but it is interesting to think about how local cultures affect the views of ecosystem services brought about by species.
Hughes, B. B., K. Wasson, M. T. Tinker, S. L. Williams, L. P. Carswell, K. E. Boyer, M. W. Beck, R. Eby, R. Scoles, M. Staedler, S. Espinosa, M. Hessing-Lewis, E. U. Foster, K. M. Beheshti, T. M. Grimes, B. H. Becker, L. Needles, J. A. Tomoleoni, J. Rudebusch, E. Hines, and B. R. Silliman. 2019. Species recovery and recolonization of past habitats: lessons for science and conservation from sea otters in estuaries. PeerJ 7:e8100.
Most studies and conservation efforts for the recovery of the southern sea otter have focused on exposed, rocky coastal habitats. By contrast, the authors of this study focused on estuaries as places where otters could be reintroduced. By their estimates, San Francisco Bay (SFB) alone could support about 6,600 sea otters, which is more than twice the current population. Historically, sea otters occupied estuaries and there is sufficient prey species in estuaries to support a population of sea otters. Additionally, the reintroduction of sea otters has been shown to improve ecosystem function in estuaries. GIS was used in this study to identify and characterize the four different habitats in SFB appropriate for sea otters. They also used GIS to estimate the size of the population of otters that SFB could support based on an estuary that currently supports otters, Elkhorn Slough. This study is very relevant to my capstone as SFB is one of the locations being considered by the scientific community for reintroduction.
Johnson, C. K., M. T. Tinker, J. A. Estes, P. A. Conrad, M. Staedler, M. A. Miller, D. A. Jessup, J. A. K. Mazet, and M. E. Power. 2009. Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system. Proceedings of the National Academy of Sciences of the United States of America 106:2242–2247.
Johnson et. al. identified that disease and resource limitation are constraining the central California coast population of southern sea otters. The authors believe that as certain food resources become limited, the southern sea otter looks to other resources. In this case, some look to a small marine snail and that preference was associated with higher infection rates with the protozoal parasite Toxoplasma gondii. The authors used GIS coverage data combined with foraging locations to calculate many factors in this study, including average foraging dive depth, distance to shore, and the proportion of foraging dives in kelp. This study brings up the question of food resources in future possible translocation sites.
Kieckhefer, T., D. Maldini, S. L. Reif, B. Voss, J. Cassidy, and J. Hoffman. 2007. Rise and fall (and rise again) of southern sea otters (Enhydra lutris nereis ) in Elkhorn Slough, California, 1994-2006.
This conference poster discusses the population changes of southern sea otters from 1994 to 2006 in Elkhorn Slough (attached to Monterey Bay). Included are GIS maps of otter distribution and prey type on the poster. The only mention of the use of GIS is that the base layers were provided by staff from the local university, California State University, Monterey Bay. Of direct interest to me is the high number of otter deaths in 2003, attributed to high levels of domoic acid (a fatal neurotoxin produced by marine diatoms) in the water that year.
Kone, D. V., M. T. Tinker, and L. G. Torres. 2021. Informing sea otter reintroduction through habitat and human interaction assessment. Endangered Species Research 44:159–176.
Sea otters were extirpated from the Oregon coast over a hundred years ago during the international fur trade. An effort to reintroduce them to Oregon coast failed, where reintroductions in British Columbia and Washington succeeded. It is unknown why. However, this paper addresses one of the concerns, that there was insufficient habitat. According to this study, there is enough habitat to support more then 4,500 southern sea otters. Additionally, the authors indicated where along the Oregon coast and in what estuaries habitat seems most suitable. They also compared those areas to areas of human activity (e.g., fishing, recreation, shipping lanes) to discern the locations where disturbance was most likely to occur. The authors used GIS to accomplish all spatial analyses and interpolations. This paper supports the potential for reintroduction of sea otters into Oregon, which is relevant to my capstone.
Laidre, K. L., R. J. Jameson, and D. P. Demaster. 2001. An estimation of carrying capacity for sea otters along the California coast. Marine Mammal Science 17:294–309.
The current population of southern sea otters hinges at around 3,000 individuals and has not changed much in the past two decades. In this article, which relied on data from the mid-1990s, the authors used GIS, “an innovative method” to estimate possible sea otter habitat along the California coast. Specific to the GIS techniques, they focused on detailed bathymetric contours to determine appropriate habitat. This is because varying substrate, and thus prey refugia, impact otter densities. One of three habitat types (rocky, sandy, mixed) were assigned to the area from the coastline to the 40 meter bathymetric contour (the nearshore environment that otters inhabit) along the totality of the California coast. According to their estimates, there is a large enough habitat to support nearly 16,000 individuals. This is near the estimated southern sea otter population prior to the fur trade in the 1880s, which nearly extirpated the species. Interestingly, this seems to be the first study to estimate possible carrying capacity for southern sea otters using GIS. In terms of my research, while I appreciate the groundwork of the study, many other issues may impact otter populations than just available habitat. This study left me with the question: what if GIS was used today to model not only habitat, but other factors like those of my capstone?
Miller, M. A., M. E. Moriarty, L. Henkel, M. T. Tinker, T. L. Burgess, F. I. Batac, E. Dodd, C. Young, M. D. Harris, D. A. Jessup, J. Ames, P. A. Conrad, A. E. Packham, and C. K. Johnson. 2020. Predators, disease, and environmental change in the nearshore ecosystem: mortality in southern sea otters (Enhydra lutris nereis) from 1998–2012. Frontiers in Marine Science 7:582.
This study identified population level threats to the southern sea otter. The authors looked at 15 years of data (1998-2012) from necropsies to determine leading causes of death (COD). White shark bite was the leading cause of death during the study period and increased during that time. Other CODs were infectious disease (especially acanthocephalans and protozoal infections), bacterial infections, domoic acid poisoning and cardiomyopathy. It was common to have many contributing factors leading to death. In terms of GIS, the authors used this tool to find demographic patterns of causes of death, called “heatmaps and clusters” associating cause of death with location. This study is of direct relation to my interests and includes percentages of causes of death.
Norman, S. A. 2008. Spatial epidemiology and GIS in marine mammal conservation medicine and disease research. EcoHealth 5:257–67.
This literature review is an overview of how spatial epidemiology and GIS work together to bring to light locations where disease for marine mammals may be a concern. Spatial epidemiology is the study of where disease risk or incidence occurs. In this article the authors outlined how GIS can accomplish spatial analysis as a powerful tool for spatial epidemiology. The authors described how multiple layers can be overlayed, from animal densities to habitat differences, and from human disturbance to human encroachment, all in individual layers and then analyzed to bring forth disease patterns. The author sees promise of GIS as a method for studying emerging diseases and changing climate as well as predicting how infectious disease may affect extinction risk. In relation to my research, there are several articles given as examples which I could utilize in my capstone.
Raimondi, P., L. J. Jurgens, and M. T. Tinker. 2015. Evaluating potential conservation conflicts between two listed species: sea otters and black abalone. Ecology 96:3102–3108.
Both the southern sea otter and the black abalone are federally listed under the Endangered Species Act and occur off the central California coast. The southern sea otter predates the black abalone. In the study, the authors compared 12 sites with abalone, some of which had southern sea otter. Counterintuitively, they found that the sites with higher sea otter abundance also had increased abalone population numbers. The authors used annual range-wide censuses, by the U.S. Geological Survey and California Department of Fish and Wildlife, to interpolate via GIS to find average sea otter density at each site. While raw data consisted of geo-referenced sea otter sightings made by ground-based and aerial observations, the output data was “sea otter density” or the mean number of sea otters per 500 meters of coastline. This article does not have direct relevance to my capstone, but it is interesting to wonder why the number of abalone are positively correlated with the density of sea otters.
Rudebusch, J., B. B. Hughes, K. E. Boyer, and E. Hines. 2020. Assessing anthropogenic risk to sea otters (Enhydra lutris nereis) for reintroduction into San Francisco Bay. PeerJ. <https://www.proquest.com/docview/2461129041/abstract/1D3E436CC174D61PQ/1>. Accessed 22 Nov 2022.
Sea otters historically occupied San Francisco Bay (SFB). However, there are many anthropogenic threats associated with the area. Some of these stressors include vessel collisions, commercial hunting, incidental take in fisheries, pathogens, pollutants, habitat destruction, resource extraction, and climate change. This study used GIS to create spatial indicators of each threat’s occurrence in the study area. By overlaying the layers, the authors could determine which areas of SFB had the highest number of risks and the proximity of the risky areas to those with lower risk. Central SFB had the highest cumulative risk. North and central bay had the highest vessel risk whereas south bay has the highest risk to environmental contamination. While my capstone is focusing on the ecological threats to the reintroduction of sea otters, anthropogenic factors may exacerbate those factors.
Tinker, M. T., B. B. Hatfield, M. D. Harris, and J. A. Ames. 2016. Dramatic increase in sea otter mortality from white sharks in California. Marine Mammal Science 32:309–326.
White sharks do not predate southern sea otters; however, they do bite them with “investigatory” bites, to discern whether they are prey. In this study, the authors looked at 1,870 stranded southern sea otter carcasses, collected since 1985. They discovered that the proportion of otters having white shark bites increased steeply since 2003. Now greater than 50% of the recovered carcasses have bites. The causes are not known but could potentially be attributed to changes in white shark abundance or behavior. GIS was used to do spatial cluster analysis and a finding was that spatiotemporal patterns of shark-bitten sea otters match increases of pinniped population, a prey for white sharks. This may mean that white sharks, in searching for pinniped prey, may be coming into the nearshore environments inhabited by sea otters. This article is of direct relevance to my capstone as white shark bites are now a leading cause of death of southern sea otters.
Tinker, M. T., J. L. Yee, K. L. Laidre, B. B. Hatfield, M. D. Harris, J. A. Tomoleoni, T. W. Bell, E. Saarman, L. P. Carswell, and A. K. Miles. 2021. Habitat features predict carrying capacity of a recovering marine carnivore. The Journal of Wildlife Management 85:303–323.
The authors of this article predict that if sea otters were present in all viable habitat along the California coast that the carrying capacity of that region would support over 17,000 individuals. This is in sharp contrast to the current population size near 3,000 individuals. GIS was used to geolocate all sightings of sea otters during surveys. They also used GIS to determine habitat variables such as substrate, depth, and kelp canopy layer. This article makes me wonder about other locations along the California coast where managers are considering reintroducing otters besides San Francisco Bay.
VanWormer, E., M. A. Miller, P. A. Conrad, M. E. Grigg, D. Rejmanek, T. E. Carpenter, and J. A. K. Mazet. 2014. Using molecular epidemiology to track Toxoplasma gondii from terrestrial carnivores to marine hosts: implications for public health and conservation. PLoS Neglected Tropical Diseases 8:e2852.
Felids are the only organism that shed the zoonotic protozoan parasite, Toxoplasma gondii. In an infected warm-blooded animal this can manifest as the disease toxoplasmosis. This disease can cause late term abortions and be fatal to southern sea otters. Authors of this study investigated the land-to-sea transmission of this parasite. They found that domestic cats infected with the Type X T. gondii may play an important role in marine infection. This is the type identified in over 70% of infected sea otters. The locations of tested felids were mapped on California land use layers using GIS. And the authors used categories in the land use layers to identify undeveloped and developed areas of the study area. This study implies that outdoor domestic cats combined with rainfall that washes their feces into the sea, play a role in infecting southern sea otters. Disease is a component of my capstone and the findings in this paper will be worth integrating.
Thank you for reading.
For recommendations or comments, I can be reached at iversene@oregonstate.edu
