Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

UNITED STATES DEPARTMENT OF DEFENSE LEGACY RESOURCE MANAGEMENT PROGRAM

FINAL REPORT FOR DEPARTMENT OF DEFENSE LEGACY PROJECT NUMBER 9401280 & 9510014

U. S. AIR FORCE 611TH AIR SUPPORT GROUP 611TH CIVIL ENGINEER SQUADRON ELMENDORF AIR FORCE BASE, ALASKA

Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

FINAL REPORT FOR DEPARTMENT OF DEFENSE LEGACY PROJECT NUMBER 9401280 & 9510014

Prepared for: United States Air Force Pacific Air Forces 611th Air Support Group 611th Civil Engineer Squadron/Environmental Flight 6900 9th Street, Suite 360 Elmendorf Air Force Base, Alaska 99506-2270

Prepared by: J. A. Estes, B. Konar and M. T. Tinker UC Santa Cruz/USGS Biological Resources Division A316 Earth and Marine Sciences Bldg. Santa Cruz, CA, 95064

April, 1999

Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Sea otter (Enhydra lutris) feeding on a sea urchin (Strongylocentrotus polyacanthus) in the Aleutian Islands, Alaska

Key words: Alaska, Alaska Maritime National Wildlife Refuge, Shemya Island, Aleutian Islands, Bering Sea, near-shore ecosystem, algal subtidal community ecology, top-down effects, keystone predator, sea otter, green sea urchin, annual algae, grazing effects

Cite as: Estes, J. A., B. Konar and M. T. Tinker. 1999. Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska. Final report for Department of Defense Legacy project number 9401280 & 9510014. Prepared for U. S. Air Force, 611th Air Support Group, Civil Engineer Squadron/Environmental Flight, Elmendorf Air Force Base, Alaska. 47 pp.

ii Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Abstract Sea otter population biology and subtidal algal community ecology were studied between 1995 and 1997 at Eareckson Air Force Station on Shemya Island, Alaska. Sea otter numbers and population structure were assessed during comprehensive skiff surveys of Shemya and the two other Islands within the Semichi Island group. A maximum of 163 otters was counted in 1995 and 128 in 1997, indicating an overall decline from 1994 when 390 otters were counted. Sea otter biology was more closely studied at Shemya Island through monthly shore-based surveys, and movements and habitat use were investigated by monitoring 8 focal animals instrumented with VHF radio transmitters. These data revealed differences in habitat use between age-sex classes, as well as temporal and individual variation in patterns of habitat use, group size and haul-out behavior. Sea otter diet was studied by direct observation of feeding otters and by composition analysis of collected scats. The diet of sea otters at Shemya consisted primarily of sea urchins (86%), and showed very little seasonal variation. Sea urchin density and the algal subtidal community were monitored for long-term (inter-annual) and short-term (seasonal) changes. Between 1987 and 1997 there were slight changes in mean sea urchin density, maximum urchin test diameter and algal cover that could be attributed to the effect of sea otter predation on sea urchins. These long-term changes were highly variable and patchy in nature: a few localized areas changed from high urchin density/low algal density to low urchin density/high algal density, but many other areas showed no significant change. There were, however, considerable short- term changes in community structure: experimental manipulations suggested that both winter storm activity and seasonal variation in algal cover influenced sea urchin density and behavior, probably enhancing kelp bed persistence. In the winter, urchin movement and grazing was inhibited by rough sea conditions. In the summer, there was a reduction in storm activity but the dense seasonal cover of annual algae appeared to inhibit sea urchin grazing behavior. As a result, sea urchin grazing activity and associated damage to kelp stands was greatest in the early fall, when seas were still relatively calm and annual algal species were senescing.

iii Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Table of Contents Abstract...... iii Table of Contents ...... iv List of Figures...... v List of Tables ...... vi List of Appendices...... vi Foreword...... vii Acknowledgments ...... ix 1. Introduction ...... 1 2. Methods...... 3 2.1. Study Area...... 3 2.2. Sea Otter Captures ...... 4 2.3. Sea Otter Movements and Habitat Use Patterns...... 5 2.4. Sea Otter Surveys ...... 5 2.5. Sea Otter Foraging Data Collection...... 5 2.6. Subtidal Sampling and Experiments...... 6 2.6.1. Long-term and Short-term changes in community structure...... 6 2.6.2. Urchin Physical Parameters...... 6 2.6.3. Algal Drift Distribution and Urchin Movement...... 6 2.6.4. Causes of Urchin Inhibition and Kelp Forest Persistence...... 7 3. Results and Discussion...... 9 3.1. Results of Captures...... 9 3.2. Morphological Data...... 9 3.3. Sea Otter Movements and Habitat Use...... 9 3.4. Surveys ...... 11 3.4.1. Shemya Surveys...... 11 3.4.2. Semichi Island Surveys ...... 13 3.5. Mortality ...... 15 3.6. Foraging...... 15 3.6.1. Composition of Diet ...... 15 3.6.2. Composition of Scats...... 15 3.7. Subtidal Community Structure ...... 16 3.7.1. Long-term changes in community structure...... 16 3.7.2. Short-term (seasonal) changes in community structure...... 19 3.7.3. Urchin Physical Parameters...... 22 3.7.4. Algal Drift Distribution and Urchin Movement...... 25 3.7.5. Causes of Urchin Inhibition and Kelp Forest Persistence...... 29 4. Conclusions...... 34 5. Literature Cited...... 35 6. Appendices ...... 37

iv Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

List of Figures Figure 1 Map of Shemya Island, showing sea otter survey sections and subtidal study sites. Subtidal sampling sites are indicated by arrows. Inset shows the approximate location of Shemya Island within Alaska’s Aleutian Island Archipelago...... 3 Figure 2 Mean monthly and seasonal (±1 S. E.) swell heights for Shemya Island, Alaska. Estimates are based on weekly measurements taken off the Alcan Harbor pier...... 4 Figure 3. The percent time spent by instrumented sea otters within 7 survey sections at Shemya Island, Alaska, between September 1995 and July 1996. See map (Figure 1) for locations of survey sections...... 11 Figure 4. The relative number of sea otters sea otters found within 7 survey sections at Shemya Island, Alaska, between July 1995 and August 1997. See map (Figure 1) for locations of survey sections...... 12 Figure 5 Mean group size (± 1 S. D.) of sea otters between July 1995 and August 1997, as determined from monthly surveys along the coast of Shemya Island, Alaska. Group size designates the number of otters in each observed group (a solitary animal was considered to have a group size of 1)...... 12 Figure 6. The percent of otter groups found rafted in offshore kelp stands or hauled out on intertidal rocks at Shemya Island, Alaska, between September 1995 and August 1997. Data for this analysis are limited to groups of 5 or more otters...... 13 Figure 7. Composition of sea otter diet at Shemya Island, Alaska, between June 1995 - June 1997. Percentages are based on the relative frequency with which prey types were brought to the surface during observed foraging dives...... 15 Figure 8 Composition of sea otter diet at Shemya Island, Alaska, between June 1995 - June 1997. Based on the mean percentage composition (by volume) of sea otter scats. Percent values are weighted by the proportion of scats in which the prey type was found...... 16 Figure 9. The ratio of sea urchins to Alaria at all shallow sampling sites at Shemya Island, Alaska, in 1987, 1994 and 1997...... 17 Figure 10 The ratio of sea urchins to Alaria at all deep sampling sites at Shemya Island, Alaska, in 1987, 1994 and 1997...... 17 Figure 11 Mean diameter of sea urchins (±1 S.E.) for 1987, 1994 and 1997 at Shemya Island, Alaska...... 18 Figure 12 Average maximum diameter of sea urchins (±1 S.E.) for 1987, 1994 and 1997 at Shemya Island, Alaska.18 Figure 13 Mean number of sea urchins and percent cover of all foliose algae at Pacific sampling sites, Shemya Island, Alaska...... 19 Figure 14 Mean number of sea urchins and percent cover of all foliose algae at Kenmore sampling sites, Shemya Island, Alaska...... 20 Figure 15. Mean number of sea urchins and percent cover of all foliose algae at Alcan sampling sites, Shemya Island, Alaska...... 21 Figure 16 Mean number of sea urchins and percent cover of all foliose algae at the pinnacles sampling sites, Shemya Island, Alaska...... 22 Figure 17. Gonad and gut indices of urchins in a kelp stand, on the edge of a kelp stand and in adjacent barrens in the Pacific at Shemya Island, Alaska...... 23 Figure 18 Gonad indices of urchins at the tops, sides and bottoms of pinnacles in the Bering and in a kelp stand in the Pacific at Shemya Island, Alaska...... 23 Figure 19. Relative number of urchins that remained within or moved out of an orientation on the pinnacles over a 48 hour period at Shemya Island, Alaska...... 24 Figure 20 Seasonal variation in the mean amount of drift algae (grams damp weight) and movement of urchins towards kelp at shallow and deep sample sites in the Alcan area, at Shemya Island, Alaska...... 25 Figure 21 Seasonal variation in the mean amount of drift algae (grams damp weight) and movement of urchins towards kelp at shallow and deep sample sites in the Kenmore area, at Shemya Island, Alaska...... 26 Figure 22 Seasonal variation in the mean amount of drift algae (grams damp weight) and movement of urchins towards kelp at sites on the Pacific Ocean side of Shemya Island, Alaska...... 27 Figure 23 Seasonal variation in the mean amount of drift algae (grams damp weight) and movement of urchins towards kelp at sites on the tops, sides and bottoms of the pinnacles, at Shemya Island, Alaska...... 28 Figure 24 Mean density of sea urchins at experimental clearing treatments on the tops of pinnacles at Shemya Island, Alaska. Densities measured in June (when clearing was conducted), July, August and September. ....29 Figure 25 Percent cover of foliose algae at experimental clearing treatments on the tops of pinnacles at Shemya Island, Alaska. Measurements taken in June (when clearing was conducted), July, August and September....29

v Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Figure 26 Mean number of sea urchins that returned (±1 S.E.) to three experimental clearing treatments at the tops of pinnacles at Shemya Island, Alaska. Treatments: 1) the addition of flagging, 2) addition of tubing, and 3) no structural additions...... 30 Figure 27 Mean density of sea urchins (±1 S.E.) for three experimental clearing treatments conducted at Pacific study sites at Shemya Island, Alaska. . Treatments: 1) the addition of flagging, 2) addition of tubing, and 3) no structural additions...... 31 Figure 28 Mean density of sea urchins (±1 S.E.) for five experimental clearing treatments conducted at the Pinnacles, Shemya Island, Alaska. Treatments: 1) the addition of 100% structural cover, 2) the addition of 75% structural cover, 3) the addition of 50% structural cover, 4) the addition of 25% structural cover, and 5) the addition of 0% structural cover...... 31 Figure 29 Mean weight loss (±1 S.E.) for clod cards placed at the pinnacles under three treatment conditions: 1) foliose algal covered tops, 2) foliose algal cleared tops, and 3) foliose algal free bottoms. Mean weight loss of control cards is shown for comparison...... 32 Figure 30 Mean weight loss (±1 S.E.) for clod cards placed under five treatment conditions at Shemya Island, Alaska: 1) under Alaria, 2) under Desmarestia, 3) under Agarum, 4) under Laminaria, and 5) in cracks in the rock surface. Mean weight loss of control cards is shown for comparison...... 33

List of Tables Table 1 Comparison of mass (kg), length (cm), and mass to length ratios for non-territorial male sea otters at Amchitka, Adak, and Shemya Islands, Alaska. Mean values (±1 S.E.) are shown (data from Amchitka are taken from Monson 1995; data from Adak are taken from Tinker and Estes 1996)...... 9 Table 2 Summary of re-sightings of radio-tagged sea otters at Shemya Island, Alaska. Information is for animals captured and marked in June 1995 and June 1996...... 10 Table 3 Percent of time and mean water depths that radio-tagged otters were found in the 7 survey sections around Shemya Island, Alaska. See map (Figure 1) for locations of survey sections...... 10 Table 4. Number of adult sea otters, large pups and small pups counted during skiff surveys of the Semichi Islands in 1994, July and October 1995, and May and July 1997. Grand totals for each survey date, and the percent of otters found in kelp, are also shown (data from 1994 from J. A. Estes, pers. comm.) ...... 14

List of Appendices A. Summary of capture information collected from captured otters on Shemya Island, Alaska B. Summary of Shemya Island, Alaska surveys between July 1995 and August 1997. C. Summary of foraging data from Shemya Island, Alaska between June 1995 and June 1997 D. Summary of foraging diet data from Shemya Island, Alaska between June 1995 and June 1997 E. Summary of scat data from Shemya Island, Alaska between November 1995 and May 1997 F. Summary of algal community data gathered from Shemya Island, Alaska in 1995 and 1996 G. Summary of the various sea urchin parameters obtained in 1995 and 1996 from Shemya Island, Alaska H. Summary of drift algal community data gathered from Shemya Island, Alaska. I. Summary of urchin movement data on Shemya Island, Alaska

vi Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Foreword Legacy Resource Management Program The Department of Defense Legacy Resource Management Program, through the U.S. Air Force, contracted through the U.S. Fish & Wildlife Service and USGS-Biological Resources Division (BRD) to conduct a sea otter monitoring program at Eareckson Air Station, Shemya Island, Alaska. Shemya is one of three Islands in the Semichi Island group at the west end of the Aleutian archipelago, and is part of the Alaska Maritime National Wildlife Refuge. Shemya Island has been designed as a “Man in the Biosphere” Reserve by the United Nations. The Legacy Resource Management Program was established by the Congress of the United States in 1991 to provide the Department of Defense (DOD) with an opportunity to enhance the stewardship of natural and cultural resources on more than 25 million acres of land under DOD jurisdiction. The Legacy Program allows DOD to better incorporate the stewardship of irreplaceable natural and cultural resources into the military mission. To achieve this goal, DOD gives high priority to inventorying, protecting and restoring its natural and cultural resources in a comprehensive, cost-effective manner, in partnership with federal, state, and local agencies and private groups. The Legacy Program emphasizes the protection and conservation of natural and cultural resources by fully incorporating these activities into DOD mission requirements. Through the combined efforts of the various DOD components, the Legacy Program seeks to achieve its legislative purposes with cooperation, creativity, and vigor and to make the DOD a federal environmental leader. The primary objective of the FY 1994 Legacy Program was to give priority to projects that demonstrated the following applications: (1) management techniques and strategies that defined appropriate uses of a site or ecosystem, develop or test a conservation strategy, or otherwise address management of sensitive resources; (2) conservation training for installation personnel; (3) integration of natural, cultural, and earth resources stewardship; or (4) demonstration of innovative technology that benefited the management of natural, cultural and earth resources. Additional objectives of particular interest included identification of significant and sensitive resources, including: (1) federal or state listed or candidate threatened or endangered species; (2) resources eligible for listing in the National Register of Historic Places; (3) species identified as category G1 to G4 or S1 to S4 in the Nature Conservancy's Natural Heritage System: or (4) unique resources such as those on the list of National Natural Landmarks and other rare or sensitive species. Regional biodiversity themes of the FY 1994 Legacy Program included: threatened and endangered species; ecosystem protection, restoration, and management; and neotropical migratory birds. Cultural Resources initiatives were associated with: Native Americans, Native Hawaiians, and Alaska Natives; settler communities on land now under Department of Defense jurisdiction; Cold War properties and history; historic family housing; and the use of Cultural Resource Inventory System (CRIS) in support of Integrated Training Area Management (ITAM), Earth Resources focused on the interactions of land, air, and water resources and their relationships with biological and cultural resources. Integrated Resources emphasized the integration of biological, earth, and cultural resource practices. The primary objective of the FY 1995 Legacy Program was to give priority to projects that (1) conducted natural and cultural resource baseline inventories in coordination with state Natural Heritage Programs or with state Historic Preservation Offices; (2) developed or updated resource management plans that integrated natural and cultural resource stewardship into other base or installation activities, such as master planning in support of the military mission; (3) preserved, restored, or conserved significant, sensitive or endangered resources, especially in a way that integrated management of cultural and natural resources; (4) demonstrated the application of beneficial technologies in the field by encouraging the scientific and technical community to support DOD's conservation efforts; (5) participated in regional stewardship efforts; (6) promoted partnership efforts to share resources and

vii Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska exchange information; or (7) contributed to Administration-supported international efforts to manage natural and cultural resource protection and information sharing. Additional objectives of particular interest included identification of significant and sensitive resources, including: (1) federal or state listed or candidate threatened or endangered species; (2) resources eligible for listing in the National Register of Historic Places; (3) species identified as category G1 to G4 or S1 to S4 in the Nature Conservancy's Natural Heritage System: or (4) unique resources such as those on the list of National Natural Landmarks and other rare or sensitive species. Natural Resources initiatives of the FY 1995 Legacy Program included ecosystem management, protection, and restoration; threatened and endangered species; neotropical migratory birds; and coastal, marine, and aquatic systems. Cultural Resources initiatives were associated with Native Americans, Native Hawaiians, Alaska Natives, and Micronesians; curation and collection management of artifacts; and properties eligible or potentially eligible for the National Register of Historic Places, especially those related to World War II and settler communities. Initiatives associated with Integration of Natural and Cultural Resources emphasize planning and data management, training and awareness.

viii Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Acknowledgments We thank the Department of Defense Legacy Resource Management Program for financial support for this project. We are also grateful for support from the US Air Force; in particular, we thank Gene Augustine, of the 611th Civil Engineer Squadron, and John Copeland, of the 611tth Air Support Squadron, for their extensive help throughout this project. We thank the many USGS–Biological Resources Division volunteers who helped on this project: John Fox, Jeff Roller, Christian McDonald, Matt Edwards, Nicolas Ladizinski, Jeanine Sidran, Cassandra Roberts, Bill Maloney, Jos Selig, Bernard Friedman, Clare Dominic, Yale Passamaneck, Chad King, Jeanne Brown and Cynthia Clock. Assistance with sea otter captures, radio implants and subsequent monitoring was provided by Caroline McCormick, Jon Watt, and personnel from USGS–Biological Resources Division in Anchorage: Jim Bodkin, Dan Monson and George Esslinger. We are grateful to the US Coast Guard, the US Fish & Wildlife Service– Alaska Maritime Refuge, and University of California–Santa Cruz for logistical support. This project was made possible through funding and support from the Department of Defense Legacy Resource Management Program.

ix Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

1. Introduction Sea otters (Enhydra lutris) have been described as a “keystone species” (sensu Power et al. 1996) because of the profound influences they exert as top-level predators on near-shore coastal ecosystems in the north Pacific (Estes and Duggins 1995). Sea otters are voracious predators, able to consume approximately 15-20% of their body weight every day (Kenyon 1969). In the Aleutian Islands, the principal prey item of sea otters is the green sea urchin (Strongylocentrotus polyacanthus). Sea urchins are important herbivores in subtidal communities, capable of destructively grazing kelp beds (Harrold and Pearse, 1987), and sea otters are the only species in the western Aleutians known to limit and dramatically reduce urchin populations through predation. Estes and Duggins (1995) showed that where sea otter density was high, sea urchin density was low and algal cover was high. Conversely, where sea otters were rare or absent, sea urchin density was high and algal cover was low. These findings are consistent with data obtained at other locations in the north Pacific, where sea otters (and other predators) have been shown to cause dramatic changes in community structure by reducing herbivore densities and grazing pressure on plant populations (e.g. Paine 1969, Harrold and Pearse, 1987). In the Aleutian Islands, these changes are characterized as a transition from an “urchin barren” (an area with no macroalgae and an unbroken covering of sea urchins) to a dense kelp stand (Tegner and Dayton 1981, Cowen 1983, Duggins 1983, Watanabe and Harrold 1991, Estes and Duggins 1995). Following local extinction in the early 1900's (apparently due primarily to over hunting in the Pacific maritime fur trade) sea otters re-colonized the Semichi Islands in 1991, and the population presently consists of about 130 animals. The sea otter population at Shemya provides an excellent opportunity for study because this is one of the few islands in the Aleutian archipelago where sea otters are recently established and have not yet drastically reduced the sea urchin population. Information on the population biology and behavior of sea otters on Shemya can be used for comparison with other locations in the Aleutian archipelago where otter populations are well established and where prey resources (i.e. sea urchins) are limiting. Such a comparison will allow hypotheses about demographic and behavioral correlates of population status to be tested. For example, differences in diet and foraging behavior have been found between other sea otter populations and appear to be related to population status and food availability (Estes et al. 1981, Estes et al. 1982). Prey diversity is generally expected to be greater in long-established populations than in recently established populations, and individual variability in prey selection may also be affected by population density. A better understanding of these relationships may eventually allow information on diet and foraging patterns to be used to assess the status of sea otter populations. Most islands within the Aleutian archipelago are currently fringed by kelp stands, a fact thought to be largely due to sea otter re-colonization and predation on sea urchins (Estes and Duggins 1995). However, factors other than sea otter predation affect kelp community structure and plant-herbivore interactions. For example, the amount of available drift algae is believed to affect sea urchin grazing behavior. When drift is abundant sea urchins are largely sessile, whereas when drift is scarce (due to storms removing drift from the system, or low recruitment of annual algae) sea urchins actively seek out food and graze on living plants (Harrold and Reed 1985, Rogers-Bennett et al. 1995). Other factors potentially affecting sea urchin grazing intensity include storm activity, sand abrasion and the presence or absence of annual algae. Shemya Island is surrounded by habitats of varying algal cover and urchin densities, and has clearly defined seasons and seasonal extremes in weather conditions, making it ideal for a study of the factors affecting kelp community structure. As well, already-existing data from subtidal sites surveyed in 1987 (before otters re-colonized) and in 1994 (shortly after re-colonization) provide a unique baseline against which otter-induced changes can be assessed and the relative importance of other factors determined. Field research for the current project was initiated in May of 1995. The principle objectives of this study were: (1) to gather data on sea otter population biology and behavior, in order to compare the

1 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Shemya population (which is relatively small and recently re-established) with other larger, longer- established populations in the Aleutian archipelago; (2) to examine long-term and short-term changes in subtidal community structure; and (3) to determine the relative importance of various biotic and environmental factors in limiting sea urchin grazing activity and thereby maintaining kelp stands. To this end we monitored sea otter population size and structure in the Semichi Islands, and studied the movement patterns, habitat use, activity, diet, and mortality of radio-tagged individuals. We examined changes in subtidal community structure by measuring kelp density and species composition over time, as well as sea urchin density, size distribution and physical parameters. Finally, experiments were conducted to investigate the effect of algal drift on sea urchin movement patterns and to determine the importance of kelp species composition, vegetation structure and sand abrasion in limiting sea urchin activity and allowing kelp stands to persist in high herbivore density areas.

2 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

2. Methods 2.1. Study Area The Semichi Island group consists of three islands: Shemya, Nizki and Alaid. Shemya Island (52°43’N, 174°07’E) is the furthest east of these three islands, located approximately 2575 kilometers (1600 miles) southwest of Anchorage (Figure 1). It encompasses 1425 ha (3521 acres) with a shoreline of 22 kilometers (14 miles). Shemya Island is part of the Alaska Maritime National Refuge and is occupied under a Special Use Permit as Eareckson Air Station operated by the United States Air Force.

70°

Alaska

60°

180° 160° 140° A B

Pi nnacles

Bering Sea Alcan Si t es Kenmore Sites

52°44'N

Alcan Harbor Pier C Shemya Island

G Pacific Ocean Pacifi c si tes 1 KM 174°06'E

F E D

Figure 1 Map of Shemya Island, showing sea otter survey sections and subtidal study sites. Subtidal sampling sites are indicated by arrows. Inset shows the approximate location of Shemya Island within Alaska’s Aleutian Island Archipelago.

3 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

The Semichi Islands are highly exposed to swell and wave action from the Bering Sea to the north and the Pacific Ocean to the south. The Semichis also experience extreme seasonal variation in storm conditions, with particularly rough winter weather. Weekly monitoring of mean swell height showed that winter swells were considerably higher than any other season, while the summer months were relatively calm (Figure 2). The island shorelines consist of extensive tidal benches and numerous offshore rocks, while the subtidal areas are a large-scale mosaic of urchin barrens, sand patches and isolated kelp stands. Within these areas, the dominant herbivore is the green sea urchin, Strongylocentrotus polyacanthus.

season winter spring summer fall 5 5 monthly swell height 4 seasonal means swell height 3 (m) 2

0 0 dec jan feb mar apr may june july aug sept oct nov

month

Figure 2 Mean monthly and seasonal (±1 S. E.) swell heights for Shemya Island, Alaska. Estimates are based on weekly measurements taken off the Alcan Harbor pier.

Data collection for the present study took place predominantly on Shemya Island. The entire island perimeter was evenly divided into seven coastal sections (“a” through “g”) for the purposes of sea otter monitoring (Figure 1). The subtidal study areas were sectioned according to habitat: the southern (Pacific Ocean) side consisted of thick kelp stands isolated by large sandy areas, while the northern (Bering Sea) side of the Island was divided into three areas, “Alcan”, “Kenmore” and the “pinnacles” (Figure 1). Alcan had a consistently high cover of foliose algae (and therefore is referred to as the kelp area) whereas Kenmore had low foliose cover (and therefore is referred to as the barren area). The "pinnacles" was an area of large rocks approximately 10 meters in height, with low foliose algal cover at the rock bottoms and sides and high foliose cover (which varied seasonally) on the tops. At each of these three areas, multiple sites were selected haphazardly for sampling; data from sites within each area were combined for analysis only if no significant differences were found between sites.

2.2. Sea Otter Captures Study animals were captured in June of 1995 and 1996. Two capture methods were utilized: boat deployed tangle nets and re-breather equipped divers with Wilson Traps. Once captured, the otters were transported directly to an on-site laboratory where they were weighed, measured and immobilized using

4 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

intra-muscular injections of Fentanyl in conjunction with Valium. Immobilized otters were flipper tagged and surgically implanted with radio transmitters (Advanced Telemetry Systems, Isanti, Minnesota, USA). All surgical procedures were conducted by an experienced veterinarian. Morphometric measurements taken from the captured otters included body length (nose to tail), body girth (at the sternum), weight, degree of tooth wear (from which an initial age estimation was made), testicular length and baculum length. Blood samples were collected for genetic, nutritional, health and toxicological studies, and a vestigial premolar was removed for later sectioning to provide more accurate age estimates by cementum analysis. After reversal of the immobilizing drug (using Naltrexone), otters were transported to a location near their capture site and released. The entire capture process, per otter, was one to two hours in duration.

2.3. Sea Otter Movements and Habitat Use Patterns Sea otter movements and habitat use patterns were investigated by regularly determining the location of tagged and instrumented study animals. An attempt was made to locate (or “resight”) all study animals at least twice weekly by surveying the entire perimeter of Shemya Island. Otters were re-sighted by a triangulation on their transmitter signal (a “radio fix”), by visual spotting of flipper tags (a “visual fix”), or by both methods. Transmitter signals were detected by standard telemetric techniques using programmable scanning receivers (Advanced Telemetry Systems, Isanti, MN) and visual fixes were obtained using 10x binoculars and/or 30-50x spotting scopes (Questar Corp., New Hope, PA). When an otter was first located, its approximate position was recorded onto a topographic map (UTM coordinates, NAD27 datum). The appropriate coastline segment letter (a though g) was also recorded. Other data recorded included the time of the resight, the number of other otters within 10 m of the focal animal, activity at the time of resight, presence or absence of kelp canopy, ambient sea state (beaufort scale), water depth and distance from shore.

2.4. Sea Otter Surveys In order to monitor sea otter population size and structure, Island-wide surveys were periodically conducted using binoculars and a Questar 30-50x spotting scope. During a survey the entire coastline was systematically searched over a four-hour period, ensuring a complete count while minimizing the possibility of double-counting animals due to otter movement. The numbers of adults, small pups and large pups were recorded. Group size (number of otters in a group) was also recorded; animals within 10 otter lengths of another otter were considered to be within a group. It was also noted if otters were in rafts (i.e. five or more otters in a group), in or out of the kelp canopy, or hauled out on inter-tidal rocks.

2.5. Sea Otter Foraging Data Collection Foraging data were collected by direct observations of feeding otters using a high powered (30- 50x) Questar spotting scope. Data collected included the duration of each dive, the subsequent surface time, whether or not the dive was successful, and the type, number and size of the prey. A single foraging bout was defined as an unbroken sequence of dives made by one otter. A particular otter was observed until it stopped feeding, moved out of observation range, or became impossible to distinguish from other otters (usually after interaction with another otter). Sea otter diet was also assessed by compositional analysis of otter scats. All scats were examined during low tides after the otters had been hauled out for at least 2 hours. The scats were dissected in the field and the percent composition (by volume) of each food item in the scat was visually estimated.

5 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

2.6. Subtidal Sampling and Experiments 2.6.1. Long-term and Short-term changes in community structure Long-term and short-term trends in algal distribution were measured in two ways: 1) algal density was monitored by visually estimating percent cover of major algal taxa in 0.25 m2 quadrats; and 2) the number of kelp plants per quadrat was counted. For estimates of percent cover, brown algae were identified to species while foliose red algae and encrusting coralline algae were grouped by genera or family. Visual estimates of algae were used because they have been shown to be accurate, repeatable and fast (Dethier et al. 1993). Both long-term and short-term sampling sites were established along the Pacific Ocean and Bering Sea sides of the Island (Figure 1): long-term sites were sampled annually, while short-term sites were sampled seasonally. At long-term sites, 20 randomly placed quadrats were sampled at each selected site at depths of 5-7 m and 15-17 m. At short-term sites, quadrats were sampled at depths of 5-7 m and 15-17 m, with the exception of the pinnacles where quadrats were sampled from the rock tops to the rock bottoms at 1.5 m intervals. All sampling locations were selected at random. Urchin density and distribution at each site was monitored by counting the number of urchins in the each of the randomly placed 0.25 m2 algal quadrats. The size frequency distribution was determined by collecting the first 200 urchins found in the density quadrats and bringing them to the surface, where they were measured to the nearest millimeter.

2.6.2. Urchin Physical Parameters Sea urchin physical parameters were monitored throughout the study, in order to detect any seasonal variation and to determine how these parameters are related to urchin grazing behavior. At each sampling occasion, fifteen haphazardly selected urchins of varying test diameters were brought back to the lab, weighed and dissected to determine gonad and gut size. To avoid bias, no animals smaller than 40 mm were used for this procedure because it has been reported (for a similar species) that urchins smaller than 40 mm have proportionally smaller gonads (Gonar 1972). The proportion of urchin body mass allotted for reproduction was then calculated using a "gonad index" – the ratio of gonad weight to damp body weight – according to Gonar (1972). Guts were dissected and weighed to obtain a ratio of damp body weight to gut size, a measurement that has been used previously as a nutrition index (Carney 1991).

2.6.3. Algal Drift Distribution and Urchin Movement Algal drift was quantified at the Alcan and Kenmore sites to determine whether the amount of drift correlated with urchin movement, and to determine if drift varied between seasons and depths in the two types of habitats. Drift algae was quantified from the Bering Sea (north) side by collecting all drift falling within 10.0 m2 circular quadrats. Approximately six such quadrats were surveyed within each sampling area, haphazardly located on flat, rocky benches. The drift was brought to the lab and weighed (damp weight), and brown algae were identified to species. Urchin movement was measured both on the Pacific Ocean side and at the pinnacles, in order to test for correlation with the amount of attached foliose algae and to determine if the relative number of attached plants influenced urchin movement. Urchin movement was examined by testing for response (a measurable change in location with respect to the substrate) to either food or structure. For these experiments, three 0.25 m2 quadrats were marked and cleared of all urchins. In the center of one of these quadrats, a piece of drift kelp (Alaria fistulosa) was attached. In another, imitation kelp (plastic flagging tape) was attached, as a control for the addition of structure. The third quadrat was left empty to determine general urchin movement as affected by urchin density. A fourth quadrat (the experiment-wide control) was also marked, but no urchins were removed, to determine natural variation in density due to movement. Quadrats were then sampled by counting the urchins in each quadrat 1.5 hours after the initial

6 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska set-up. This time interval was selected because preliminary trials indicated that a period of 1.5 hours was sufficient to allow for measurable movement even in areas of low urchin density.

2.6.4. Causes of Urchin Inhibition and Kelp Forest Persistence Manipulative Clearings To examine the possible effects of algae on sea urchin movement, manipulative clearing experiments were conducted. On the Bering Sea side, replicate pinnacles were cleared of various algal genera in the early summer, to determine if this would stimulate movement of urchins to the tops of the pinnacles. Changes in urchin density and algal cover were monitored using six randomly placed 0.25 m2 quadrats on each pinnacle. Different species were removed from pinnacles to determine if a single species or a combination of species affected urchin movement. The clearing experiments consisted of the following treatments: 1) removal of Alaria; 2) removal of Desmarestia; 3) removal of all annuals; 4) removal of all algae; and 5) controls (no algal removal). The control pinnacles were used to monitor natural changes of urchin and algal densities through the summer and early fall. Structure Manipulations To examine the role of algal physical structure in limiting sea urchin movement and the exclusion of sea urchins from the pinnacle tops during summer, artificial kelp plants (constructed from surgical tubing and surveyors flagging tape) were placed on pinnacles cleared of urchins and algae. Surgical tubing was used to imitate Alaria and Laminaria morphology, while the surveyors flagging imitated Desmarestia morphology. Treatments (n=3) were 100%, 75%, 50%, 25%, and 0% (controls) cover of flagging. Non-manipulated pinnacles were selected as experiment-wide controls. Pinnacles were re- sampled after one week using four randomly placed 0.25 m2 quadrats, to measure sea urchin density. A similar experiment was conducted on the Pacific Ocean side of the Island, using 3m2 circular clearings (removal of all foliose algae) within a kelp stand that was adjacent to an urchin barren. Six algal clearings were made, to three of which structures were added (surveyors flagging) while three were left clear. Clearings and non-manipulated control areas were cleared of all urchins and then resurveyed three days later for urchin density, using randomly placed 0.25m2 quadrats. Clod Card Experiments A series of "clod card" experiments were conducted to determine the relative amount of mechanical abuse (abrasion and scour) that sea urchins endure in different situations. Clod cards are commonly used to measure relative scour between different areas (Doty and Doty, 1973). The "clods" are a mixture of plaster of Paris and latex paint that are put into ice-cube tray molds to harden. Once hard, the clods are glued to small "cards" of PVC, that are then placed in the field at locations of interest. For this study, the clod cards were attached by cable ties to large cinder-block bricks and placed along the bottom. For a given set of treatments a single batch of clods was mixed, to minimize variation between the relative amounts of Plaster of Paris and Latex Paint used. Before the experiment was initiated, clod cards were placed in a sea water aquarium to cure for approximately 1 week, taken out to dry, and weighed multiple times on successive days; this was repeated until a constant weight was reached. At this time, all the treatment cards were transported to the field. The controls were also transported to the field, but then immediately brought back to the laboratory and placed into the seawater aquarium: this procedure was conducted to account for scour due to the handling and transporting of the cards. When the cards were placed in the field, all urchins in the immediate vicinity were removed at regular intervals until the cards were retrieved, to reduce scour on the cards due to urchin grazing. After a pre-determined period (depending on the experiment), all the clod cards were brought back to the lab, dried and weighed

7 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska on successive days until a constant weight was reached. The amount of weight loss for each card (relative to the controls) was taken as a measure of the relative amount of scour the card had endured. The first clod card experiment was set up to examine relative scour between pinnacles with foliose algae on the tops, pinnacles with foliose algae removed from the tops, and the bottoms of pinnacles where no foliose algae was found. These clod cards were set out for a period of two weeks. A second set of clod cards was set out beneath patches of different brown algal genera, to determine which algae were associated with the most abrasion and scour. Brown algae were used because previous experiments indicated that these algae were most effective in deterring urchin movement. The Pacific Ocean side was selected for this experiment because the common brown algae were most abundant here, and because a large patch of algae was required to completely cover a cinder-block brick. In addition to the saltwater aquarium-based controls, field-based control cards were placed in cracks where algae could not abrade them. Cracks were chosen as control areas because it is typical to find urchins hiding in cracks among the dense algal stands on the Pacific Ocean side.

8 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

3. Results and Discussion 3.1. Results of Captures Eight male sea otters were captured, surgically implanted with radio transmitters, flipper tagged and released as study animals. Seven animals were captured the first year and a single male was captured the second year. Summaries of capture data for each animal are provided in Appendix A. There were no mortalities, injuries or other complications during the capture, immobilization, surgery and release of the sea otters back to the wild. All animals recovered quickly from the immobilization and on release were observed to swim away with no apparent difficulty. After release, all animals were observed within the study area and showed no signs of unusual or aberrant behavior.

3.2. Morphological Data Morphological data from the 7 male sea otters captured at Shemya (mass, length, and mass/length ratio) were summarized and compared with similar data from male otters at Adak and Amchitka Islands (Table 1). Mass to length ratio has been used previously to assess overall body condition (Monson, 1995; Bodkin, 1996). Only non-territorial males were used for this comparison because territorial males from other populations are often larger than non-territorial males (Monson, 1995; Tinker and Estes, 1996), and no territorial males were captured, or even observed, at Shemya. Male otters at Shemya were similar in body condition to males from Amchitka, but appeared somewhat larger and heavier than those from Adak (although the small sample size of Adak males, n=3, limits the utility of such a comparison). Overall, it appears that the body condition of males at Shemya is within the expected range for non-territorial males in other Aleutian Island populations.

Table 1 Comparison of mass (kg), length (cm), and mass to length ratios for non-territorial male sea otters at Amchitka, Adak, and Shemya Islands, Alaska. Mean values (±1 S.E.) are shown (data from Amchitka are taken from Monson 1995; data from Adak are taken from Tinker and Estes 1996).

Location N Mass±1S.E. Length±1S.E. Mass/Length±1S.E. Amchitka 1992 9 31.0±0.97 134±1.01 0.232±0.007 Adak 1995 3 21.3±1.18 118±1.53 0.181±0.008 Shemya 1995 7 29.0±2.10 127±3.40 0.230±0.010 Shemya 1996 1 35.0±0.00 141±0.00 0.248±0.000

3.3. Sea Otter Movements and Habitat Use Data on the movement and distribution of individuals within a population provide information on temporal and spatial patterns of habitat use. Such information is useful for management purposes because it highlights important habitat areas and increases understanding of life history phenomena such as seasonal movement patterns. Data were obtained on patterns of habitat use by monitoring the movement of instrumented otters. Between 1995 and 1997, 395 resights were made of the eight study animals (Table 2).

9 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Table 2 Summary of re-sightings of radio-tagged sea otters at Shemya Island, Alaska. Information is for animals captured and marked in June 1995 and June 1996.

Total Number of % of Total Date Otter Number Times Re-sighted Re-sights Last Seen 1 62 11 7/30/96 2 102 18 6/19/96 3 86 15 7/9/96 4 39 7 6/24/97 5 2 <1 7/31/95 6 14 2 11/19/95 7 80 14 8/10/96 8 10 2 6/29/96

Two of the otters (#5 and #6) were not seen after 1995, and none of the remaining otters (with the exception of #4) were seen after September 1996. The reason for the disappearance of the study animals is not clear, but possible causes include death, emigration, or equipment failure. Our experiences elsewhere with identical telemetry equipment and implanted transmitters make equipment, battery or transmitter failure an unlikely possibility. Only in the case of one otter (#4) was a dead battery confirmed: this animal was seen on five occasions after the battery failed, and in fact was the only otter re-sighted in 1997. In general, the tagged otters were relocated around the entire perimeter of Shemya Island, although resights were made most frequently at the Island’s southeast and southwest extremities (Table 3; Figure 1). The reason for this pattern of habitat use is unknown, although it does not appear to be correlated with food abundance (sea urchin densities were not unusually high at these locations). The tagged otters were rarely located on the south side of the island, a fact that may be related to lower prey densities on the Pacific coast. Overall, resights of study animals indicated that the preponderance of habitat use by sea otters at Shemya is restricted to relatively shallow (<10m) depths.

Table 3 Percent of time and mean water depths that radio-tagged otters were found in the 7 survey sections around Shemya Island, Alaska. See map (Figure 1) for locations of survey sections. Mean Survey Section Depth Otter Number a b c d e f g (fathoms) 1 5 2 12 22 0 16 43 2.4 2 5 4 13 48 3 8 19 2.3 3 4 4 31 32 1 8 19 2.8 4 5 13 15 62 0 0 5 2.2 5 0 0 0 50 0 0 50 3.0 6 0 0 0 64 4 0 29 3.5 7 1 4 26 43 0 8 18 3.4 8 0 10 50 0 0 20 20 4.0 Overall Mean: 2.5 4.6 18.4 40.1 1.0 7.5 25.4 3.0

The Island perimeter was scanned each week throughout the year to locate study animals, resulting in an even search effort (both temporally and spatially) and thus an unbiased appraisal of variation in habitat use. Based on relative frequencies of resight locations, there appeared to be

10 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

considerable temporal variation in the percent time spent by instrumented otters in each study area (Figure 3). In the winter months, the otters spent most of their time at the extreme ends of the island (sections d, f and g). In the spring and early summer, more time was spent on the north side (c) of the island.

100 g f 80 e d c 60 b a 40

percent time 20

0 Oct 1995 Dec 1995 Jan 1996 Feb 1996 Nov 1995 Mar 1996 Sept 1995 May 1996 July 1996 June 1996 April 1996 month Figure 3. The percent time spent by instrumented sea otters within 7 survey sections at Shemya Island, Alaska, between September 1995 and July 1996. See map (Figure 1) for locations of survey sections.

3.4. Surveys 3.4.1. Shemya Surveys Overall, the number of sea otters found around Shemya Island increased over the course of the study, although the actual number counted per month fluctuated greatly between survey dates (Appendix B). A mean of 19.7 otters was counted in 1995, 24.8 in 1996 and 29.0 in 1997. A maximum of 58 otters was counted in May 1996. The temporal patterns of habitat use, as determined by numbers of sea otters counted per survey area, were similar to those indicated by resights of the 7 study animals (as described above). In the summer months, otters were concentrated at survey sections d and g, the eastern and western extremities of the island (Figure 4). In the winter months, otters were dispersed more evenly along the north side of the island. The south (Pacific) side of the island showed consistently low otter numbers. This temporal variation in habitat use is consistent with that reported for sea otters at Adak Island (Tinker and Estes 1996). Sea otter group size also varied seasonally, consistent with observations from Adak Island (Tinker and Estes, 1996). In summer months, when seas were calm, average group size was quite large (Figure 5) and otters were frequently observed offshore in large rafts (Figure 6), often in thick kelp stands. In the winter months, when storms were frequent and offshore kelp beds disappeared, group sizes were much smaller and sea otters were more likely to be close to shore or hauled out on intertidal rocks. Haul-out behavior was most often observed between March and May, both in 1995 and 1996 (Figure 6).

11 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

100 g f 80 e d 60 c b a 40 percent time percent

Percent total otters counted 0 Oct 1996 Dec 1996 Jan 1997 Feb 1997 Oct 1995 Dec 1995 Jan 1996 Feb 1996 Nov 1996 Mar 1997 Aug 1997 Nov 1995 Mar 1996 Aug 1996 May 1997 1997 July May 1996 1996 July Sept 1996 July 1995 July Sept 1995 June 1997 June 1996 April 1997 April April 1996 April month

Figure 4. The relative number of sea otters sea otters found within 7 survey sections at Shemya Island, Alaska, between July 1995 and August 1997. See map (Figure 1) for locations of survey sections.

5 mean group size

0 Oct 1995 Dec 1995 Jan 1996 Feb 1996 Oct 1996 Dec 1996 Jan 1997 Feb 1997 Nov 1995 Mar 1996 Aug 1996 Nov 1996 Mar 1997 Aug 1997 July 1995 Sept 1995 May 1996 July 1996 Sept 1996 May 1997 July 1997 June 1996 June 1997 April 1996 April 1997

month Figure 5 Mean group size (± 1 S. D.) of sea otters between July 1995 and August 1997, as determined from monthly surveys along the coast of Shemya Island, Alaska. Group size designates the number of otters in each observed group (a solitary animal was considered to have a group size of 1).

12 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

50 hauled out 40 rafted

20 % of groups 10

0 Oct 1995 Oct 1995 Dec 1996 Jan Feb 1996 Oct 1996 Oct 1996 Dec 1997 Jan Feb 1997 Nov 1995 Nov Mar 1996 Aug 1996 Nov 1996 Nov Mar 1997 Aug 1997 Sept 1995 May 1996 May 1996 July Sept 1996 May 1997 May 1997 July June 1996 June June 1997 June April 1996 April 1997 month

Figure 6. The percent of otter groups found rafted in offshore kelp stands or hauled out on intertidal rocks at Shemya Island, Alaska, between September 1995 and August 1997. Data for this analysis are limited to groups of 5 or more otters.

3.4.2. Semichi Island Surveys Skiff-surveys of the sea otter population of the entire Semichi Island group were conducted periodically (Table 4). For each of these population surveys, sea otters were spotted (using 10x binoculars) and counted by two observers aboard a 17 foot skiff moving slowly around the Island perimeters. Skiff-surveys were conducted only when sea states were very calm (i.e. no swell or whitecaps), and were completed within 4 hours to avoid double counting otters moving between adjacent areas. In general, it appears that the number of sea otters found around the Semichi Islands has declined over the period from 1994 to 1997. The Semichi Islands were surveyed as part of another related study in 1994 (using identical methods) and at that time 390 otters were counted, 109 of which were on Shemya Island. In the current study, the maximum number observed was in July of 1995, when 163 otters were counted. In July of 1997, the total number counted was 128, 39 of which were at Shemya. This apparent decline may be attributed to one or more of the following factors: 1) emigration, i.e. movement of otters to more distant islands such as Agattu or Attu, 2) mortality, 3) reduced fecundity, and 4) imprecision of survey techniques. We believe it is unlikely that a decline of this magnitude (a 60% observed decrease between 1994 and 1997) represents an artifact of imprecise counts, and so factors 1 - 3 must be considered. This negative trend is consistent with sea otter declines reported further east in the Aleutians (Estes et al. 1998) for which increased mortality due to predation appears to be the most likely cause. The relative number of sea otters observed in kelp stands was greater at Alaid and Nizki Islands than at Shemya (Table 4). This may have been due in part to the differences in population structure between Islands: there were more females, pups and possibility territorial males on Alaid and Nizki, while most otters at Shemya appeared to be non-territorial males.

13 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Table 4. Number of adult sea otters, large pups and small pups counted during skiff surveys of the Semichi Islands in 1994, July and October 1995, and May and July 1997. Grand totals for each survey date, and the percent of otters found in kelp, are also shown (data from 1994 from J. A. Estes, pers. comm.)

Date Island Adults Lg Pups Sm Pups Totals % in kelp 1994 Alaid 153 48* - 201 unknown Nizki 68 12* - 80 unknown Shemya 104 5* - 109 unknown Group Total: 390 26-Jul-95 Alaid 64 11 17 92 unknown Nizki 29 2 5 36 unknown Shemya 34 1 0 35 unknown Group Total: 163 1-Oct-95 Alaid 48 33 0 81 98 Nizki 4 1 0 5 80 Shemya 20 0 0 20 20 _ Group Total: 106 26-May-97 Alaid 28 6 3 37 100 Nizki 41 4 4 49 80 Shemya 22 0 0 22 22 _ Group Total: 108 10-Jul-97 Alaid 46 3 12 61 100 Nizki 24 2 2 28 100 Shemya 38 0 1 39 39 _ Group Total: 128

* for 1994 data, the category "Lg pups" includes both large and small pups (pups were not classified into age classes on these surveys).

14 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

3.5. Mortality In the two years of this study, only two otter carcasses were found on Shemya Island. Both of these were adults, and were found on the north side of the island. The cause of death could not determined because only the partially decomposed skulls were found.

3.6. Foraging A total of 112 foraging bouts were observed during the study, consisting of 1,518 dives. A summary of the foraging data collected each month is provided in Appendix C and D. Overall, foraging success rate (percent of dives in which one or more prey items were captured) was 89%. Mean dive depth was 4-5 meters, and mean dive duration was 42 seconds.

3.6.1. Composition of Diet Based on the frequency of occurrence in observed feeding dives, the green sea urchin (Strongylocentrotus polyacanthus) made up the bulk of the sea otters' diet at Shemya Island (Figure 7). This is consistent with previous studies of sea otter diet in the Aleutian Islands (e.g. Estes and Duggins, 1995) that indicate sea urchins are the dietary staple. Other prey items included fish (Irish lords, rock cod and Pacific smooth lumpsuckers), bivalves (primarily the rock jingle, Pododesmes macroschisma), chitons (both small chitons such as Katharina tunicata and larger chitons such as Cryptochiton stelleri), limpets, decapods (primarily crabs) crabs and sea stars. There was no indication of seasonal variation in the otters' diet, although the limited number of foraging bouts collected some months provides very little power to detect differences.

Diet Composition from Sea Otter Foraging Observations

86.28 urchins

2.47 fish

0.82 bivalves 2.17 chitons

0.17 limpet

0.25 decapod

0.17 starfish

Figure 7. Composition of sea otter diet at Shemya Island, Alaska, between June 1995 - June 1997. Percentages are based on the relative frequency with which prey types were brought to the surface during observed foraging dives.

3.6.2. Composition of Scats Sea otter scats (n = 704) were examined each month to provide additional information on sea otter diet (Appendix E). Prey items without hard body parts were not represented in the scat data, creating a bias against such items. Nonetheless, the results from a compositional analysis were consistent with those obtained from direct foraging observations. Sea urchins again comprised the majority of the scats (Figure 8), indicating that urchins are the staple dietary item.

15 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Certain hard-shelled prey items commonly observed during foraging observations, such as chitons, were rarely found in the scats. This could be due to the way such items are processed and consumed by otters (the hard shells discarded and only the soft tissue consumed), or may represent a sampling artifact resulting from the few otters that regularly haul out and from which scats are available for collection. Decapods, primarily crabs, appeared as a significant prey item in scats but were rarely seen during foraging observations. This may be the result of a positive sampling bias created by the persistence of crab exoskeleton in sea otter scats, but could also reflect the fact that crabs are consumed more frequently when foraging observations are not conducted (either at night or when the otters are further off-shore).

Diet Composition from Sea Otter Scats

86.63 urchin

3.78 other

3.36 decapod

3.09 fish

1.60 limpet

0.39 chiton

0.16 mussel

Figure 8 Composition of sea otter diet at Shemya Island, Alaska, between June 1995 - June 1997. Based on the mean percentage composition (by volume) of sea otter scats. Percent values are weighted by the proportion of scats in which the prey type was found.

3.7. Subtidal Community Structure 3.7.1. Long-term changes in community structure In general, kelp community structure at the Semichi Islands was consistent with that reported for other western Aleutian Islands (e.g. Estes and Duggins, 1995). The principal surface-canopy forming kelp species was the large annual, Alaria fistulosa. Other brown algae included the annual species Desmarestia ligulata and D. viridis. The most common brown perennial species were Laminaria dentigera, L. yezoensis, Agarum cribrosum and Thalassiophyllum clathrus. Foliose red algae were abundant and represented by a variety of species. Encrusting coralline algae covered much of the primary substrate around the island, particularly in areas where upright algae were absent. Between 1987 and 1997, there were slight but significant overall changes to the subtidal community structure of the Semichi Islands. In 1987, a number of shallow sites had 60 or more urchins per 0.25m2, whereas in 1997, after the reappearance of sea otters, no sites with 45 or more urchins were found (Figure 9). Also, the relative abundance of Alaria appeared to vary positively with the abundance of sea otters and inversely with the abundance of sea urchins. In 1987, when no otters were present, sea urchin abundance at almost all shallow sampling sites was high and Alaria abundance was very low (Figure 9). In 1994, when sea otter counts were highest, there were fewer urchins and Alaria was very abundant at a few sites. In 1997, when sea otter numbers had declined somewhat (Table 4), certain sites again showed higher densities of urchins and lower abundance of Alaria.

16 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

shallow 80 1987 1994 60 1997

40 Urchins 20

0 0 5 10 15 20 Alaria

Figure 9. The ratio of sea urchins to Alaria at all shallow sampling sites at Shemya Island, Alaska, in 1987, 1994 and 1997.

Similar trends in kelp and urchin abundance were seen at deep sampling sites, although absolute sea urchin density and Alaria counts were lower than at the shallow sites (Figure 10). In 1987, no Alaria was found at depths of 12-15 m; however, after the re-colonization of the Semichi Islands by otters, low numbers of Alaria were found at these depths in 1994 and 1997. The observed trends in sea urchin density and Alaria abundance were not surprising, based on other studies of the effects of sea otters on kelp communities (Estes and Duggins 1995). Because the otters' primary food source is sea urchins, the continued presence of sea otters at Shemya might be expected to result in reduced sea urchin abundance and hence reduced grazing pressure on Alaria. What was surprising was that these long-term changes were, on the whole, relatively minor and highly patchy in nature: while certain sites showed a definite

Deep 80 1987 1994 60 1997

40 Urchins 20

0 0 5 10 15 20 Alaria

Figure 10 The ratio of sea urchins to Alaria at all deep sampling sites at Shemya Island, Alaska, in 1987, 1994 and 1997.

17 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska trend of decreasing urchin abundance over time, many other sites showed no such trend. This suggests that the impact of sea otter predation on the sub-tidal community of the Semichi’s has been somewhat less than that described for other Aleutian Islands (e.g. see Estes and Duggins 1995).

80 shallow deep

diameter (mm) 20

0 1987 1994 1997 year

Figure 11 Average maximum diameter of sea urchins (±1 S.E.) for 1987, 1994 and 1997 at Shemya Island, Alaska.

Another unexpected finding was the lack of a consistent trend in mean sea urchin test diameter (Figure 11). There appeared to be no significant change in mean urchin diameter between 1987 and 1994, and between 1994 and 1997 there was a actually slight increase (ANOVA, p<0.05) in mean diameter, contrary to our expectations (Figure 11). Previous work has demonstrated a clear relationship between sea urchin diameter and the presence/absence of sea otters at Islands in the Aleutian Islands (Estes and Duggins, 1995), with urchin diameter decreasing in the presence of sea otters. This relationship results from the fact that sea otters preferentially feed on larger urchins, thus causing a downward-shift in the frequency distribution of urchin diameters. The observed increase in mean diameter between 1994 and 1997 is therefore perplexing.

35 shallow deep 30 25

15 10 diameter (mm) 5 0 1987 1994 1997 year

Figure 12 Mean diameter of sea urchins (±1 S.E.) for 1987, 1994 and 1997 at Shemya Island, Alaska.

18 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

In contrast to the unexpected results for mean urchin diameter, there was a consistent decrease in average maximum diameter over time (Figure 12). Average maximum diameter, calculated as the mean of the largest urchin measured per plot, was significantly greater in 1987 than in 1994 or 1997 (ANOVA, p<0.05).

3.7.2. Short-term (seasonal) changes in community structure Urchin and algal community structure were seasonally monitored at sites on both the Pacific Ocean (south) and Bering Sea (north) sides of Shemya Island. Monitoring sites were chosen to cover a wide range of community types: sites at the Pacific Ocean side and the pinnacle tops had dense kelp communities and few urchins, while sites at Kenmore and the pinnacle bottoms had low algal cover and abundant urchins. Sites at Alcan supported intermediate levels of algal and sea urchin densities. A summary of the descriptive algal and sea urchin data collected in 1995 and 1996 are provided in Appendix F and G. The rocky areas on the Pacific Ocean side had consistently low urchin densities and very high foliose algal cover. There was little seasonal variation in this pattern, with the exception of an increase in annual foliose algae in summer months (Figure 13). This increase reflected the growth of annual algae, such as Alaria, Desmarestia and some foliose red species.

25 100 Pacific urchins 20 algae 80

15 60

10 40

5 20 percent cover

# urchins/0.25m2 0 0 summer fall winter spring season Figure 13 Mean number of sea urchins and percent cover of all foliose algae at Pacific sampling sites, Shemya Island, Alaska.

In contrast to the Pacific Ocean side, rocky areas on the Bering Sea side showed considerable variation in community structure, with urchin barrens predominating. The Kenmore area was typical of this pattern: there was little or no foliose algal cover at both deep and shallow sample sites, but a consistently high cover of encrusting coralline algae (Figure 14). Sea urchin densities were high at Kenmore, particularly at shallow sites, although in the late winter and spring there was a decline in urchin densities at both deep and shallow sites. This apparent decrease in density may have been due to the increase in storm frequency and intensity at this time, causing urchins to move to cryptic refuge areas (to avoid being swept away). The community structure at most other areas of the Bering Sea side of Shemya Island was similar to the Kenmore sites. This high density of sea urchins may explain why sea otters were more abundant on the Bering side.

19 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Kenmore 25 100 shallow urchins 20 algae 80

15 60

10 40

5 20 percent cover

# urchins/0.25m2 0 0 summer fall winter spring

25 Kenmore 100 20 deep 80

15 60

10 40

5 20 percent cover

# urchins/0.25m2 0 0 summer fall winter spring season Figure 14 Mean number of sea urchins and percent cover of all foliose algae at Kenmore sampling sites, Shemya Island, Alaska.

The Alcan area was intermediate between the Pacific and Kenmore sites in both the degree of algal cover and sea urchin density. The shallow site had a higher density of urchins and less foliose algal cover than the deep site (Figure 15). As was the case for the Kenmore sites, there was a late winter decrease in sea urchin density at both the deep and shallow site. The pinnacles area showed the greatest amount of within-site variation. The sides and bottoms were similar to Kenmore sites (high urchin densities and low foliose algal cover) but the tops were more similar to Alcan sites (low urchin densities and high foliose algal cover; Figure 16). Little seasonal variation was observed at sites on the sides and bottoms of the pinnacles, except for a slight decrease in urchin density in the winter and spring associated with high seas. However, considerable seasonal variation occurred at sites located on the pinnacle tops. In the summer, when the seas were calm, foliose algal cover was high and urchin density was low. In the fall, urchin densities increased and foliose algal cover decreased. This appeared to be due to movement of urchins from the sides and bottoms to the pinnacle tops. In the winter, as storm conditions became more frequent, urchins moved down from the pinnacle tops and their densities at these sites decreased. These trends continued into the spring.

20 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

25 Alcan 100 shallow urchins 20 algae 80

15 60

10 40

5 20 percent cover

# urchins/0.25m2 0 0 summer fall winter spring

25 Alcan 100 deep 20 80

15 60

10 40

5 20 percent cover

# urchins/0.25m2 0 0 summer fall winter spring season Figure 15. Mean number of sea urchins and percent cover of all foliose algae at Alcan sampling sites, Shemya Island, Alaska.

21 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

25 100 Top urchins 20 algae 80

15 60

10 40

5 20 percent cover

# urchins/0.25m2 0 0 summer fall winter spring

25 100 Side 20 80

15 60

10 40

5 20 percent cover

# urchins/0.25m2 0 0 summer fall winter spring

25 100 Bottom 20 80

15 60

10 40

5 20 percent cover

# urchins/0.25m2 0 0 summer fall winter spring season Figure 16 Mean number of sea urchins and percent cover of all foliose algae at the pinnacles sampling sites, Shemya Island, Alaska.

3.7.3. Urchin Physical Parameters A summary of all data collected on sea urchin physical parameters is provided in Appendix G. Comparisons were made of sea urchin gut and gonad size between urchin barrens and kelp beds. On the Pacific Ocean side, it was found that gut size was similar for urchins from kelp beds and adjacent barren

22 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska areas, but the gonads were markedly different (Figure 17). Urchins in kelp beds had much larger gonads than urchins found outside the kelp beds. This suggests that urchins inhabiting kelp stands are more fit, and have the potential to produce more offspring per individual than urchins living in barren areas. The reason that gut sizes did not reflect this pattern is not clear, but may result from the fact that urchins on the edge temporarily move in to the kelp to feed, and can retain food in their guts. In any case, these results suggest that gonad size is a more sensitive index of urchin fitness than gut size.

6 30 gonads guts 25 4 20

2 10 gut index

gonad index 5

0 0 in kelp on edge in barrens

habitat Figure 17. Gonad and gut indices of urchins in a kelp stand, on the edge of a kelp stand and in adjacent barrens in the Pacific at Shemya Island, Alaska.

These trends in gonad size were less apparent for sea urchins at the pinnacles. Gonad size was marginally higher in urchins from the pinnacle tops (as compared to the bottoms or sides) during the summer and fall, but these differences were not pronounced and in all cases gonad size was less than for kelp-bed urchins at the Pacific Ocean side (Figure 18). It is possible that urchins from the tops of pinnacles do not have larger gonads simply because they are not permanent residents of the tops.

12 top 10 side 8 bottom 6 Pacific 4 gonad index 2 0 summer fall winter spring season

Figure 18 Gonad indices of urchins at the tops, sides and bottoms of pinnacles in the Bering and in a kelp stand in the Pacific at Shemya Island, Alaska.

23 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

A study of urchin movement was conducted to determine if urchins moved preferentially between orientations on the pinnacles (i.e. the tops, sides or bottom), and if they moved more frequently when found on a particular orientation. For this experiment, 100 urchins were tagged (with uniquely colored floy tags) from each of the three orientations on three replicate pinnacles, and then monitored for gross movements. After two days, urchins that had moved to another orientation and urchins that stayed on their original orientation were counted. This experiment was done once in the summer and once in the fall, to determine if there were seasonal differences in movement. In general, it was found that sea urchins move regularly between orientations in the summer and the fall (Figure 19). This implies that urchins on the pinnacle tops, where algal cover was densest, did not necessarily stay there very long. Also, urchins at the bottom found within a coralline-dominated habitat were not permanent residents, and regularly moved in and out of denser algal areas. In the fall, when algal cover was decreasing (especially on the tops), urchins were more mobile at all orientations.

SUMMER 100 % remained 80 % moved

0 Percent number of urchins top side bottom

100 FALL % remained 80 % moved

0 Percent number of urchins top side bottom

Orientation Figure 19. Relative number of urchins that remained within or moved out of an orientation on the pinnacles over a 48 hour period at Shemya Island, Alaska.

24 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

3.7.4. Algal Drift Distribution and Urchin Movement Variation in urchin movement and grazing activities has previously been attributed to the amount of available algal drift (Harrold and Reed 1985). It has been shown that, if algal drift is abundant, sea urchins will graze on it rather than destructively graze on attached plants (Rogers-Bennett et al. 1995). Data on drift distribution and sea urchin movement patterns were collected to test these hypotheses at Shemya; results are presented below. A summary of raw data on algal drift is provided in Appendix H, while a summary of all collected sea urchin movement data is provided in Appendix I. The amount of available drift was lowest in the spring at all study sites (Appendix H). This was probably because winter storms resulted in most of the available drift being transported out of the system by spring. The amount of brown and red algal drift was approximately equal in the spring, but in all other seasons brown algal drift was more abundant. The greatest amount of variation in drift abundance occurred at the Alcan sites; drift was more abundant at sites where algal cover was higher. There was little difference in drift abundance between deep and shallow Alcan sites, except in the fall when drift was greater at shallower depths (Figure 20). This was probably due to increasing fall swells transporting dying annual algae into shallower depths. It was found that sea urchin movement at the Alcan sites increased when the amount of available drift algae was highest. At the Kenmore sites, there was a less pronounced but still significant trend of increased urchin movement associated with increased abundance of drift algae (Figure 21). Unlike the Alcan study area,

Alcan 300 60 Shallow drift movement 200 40

100 20 drift (g)

0 0

summer fall winter spring urchins) (# movement

300 60 Alcan deep 200 40

100 20 drift (g)

0 0 summer fall winter spring movement (# urchins) season

Figure 20 Seasonal variation in the mean amount of drift algae (grams damp weight) and movement of urchins towards kelp at shallow and deep sample sites in the Alcan area, at Shemya Island, Alaska.

25 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska algal drift was greater at deep sites than at shallow sites at Kenmore, and drift was highest in the summer months. This pattern is difficult to explain, but could have been due to the increase in sea urchin grazing in summer months, which might have depleted the relatively small amount of drift before it was transported to shallower depths.

Kenmore shallow 300 60 drift movement 200 40

100 20 drift (g)

0 0

summer fall winter spring movement (# urchins)

Kenmore 300 60 deep

200 40

100 20 drift (g)

0 0

summer fall winter spring movement (# urchins) season

Figure 21 Seasonal variation in the mean amount of drift algae (grams damp weight) and movement of urchins towards kelp at shallow and deep sample sites in the Kenmore area, at Shemya Island, Alaska.

Sea urchin movement was typically lowest in areas of high foliose algal cover. The Pacific Ocean side of the Island, where the greatest densities of attached algae were found, showed very low levels of urchin movement during any season (Figure 22). One possible explanation for this pattern might be that there was a constant inflow of drift on the Pacific Ocean side, from all the neighboring attached algae. This would have resulted in very little competition for available drift, especially given the low density of urchins, and hence little need for urchins to move in order to locate new food sources.

26 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Pacific

60 80 algae movement 60 40

40 20 20

0 0 movement (# urchins)

percent cover foliose summer fall winter spring

season Figure 22 Seasonal variation in the mean amount of drift algae (grams damp weight) and movement of urchins towards kelp at sites on the Pacific Ocean side of Shemya Island, Alaska.

The tops of the pinnacles were similar to the Pacific sites both in terms of the amount of algal cover and sea urchin movement patterns. The sites at the bottom and sides of the pinnacles, in contrast, were more similar to the Kenmore sites in terms of algal cover and urchin movement (Figure 23). At all three orientations in the pinnacles, urchin movement in the winter was negligible. This was likely because of the increase in storm activity. At the pinnacle tops, foliose algal cover was very dense in the summer, decreased markedly in the fall, then increased again in the winter and spring. These trends in algal abundance were correlated with patterns of urchin movement: in the summer there was very little movement but in the fall movement increased. At sites on the pinnacle sides, levels of both sea urchin movement and foliose algal cover were relatively constant (except for the lack of movement in the winter). At sites on the pinnacle bottoms, urchin movement was always high (except in the winter) and foliose algal cover was low. The seasonal urchin movement patterns at the pinnacles were somewhat surprising. It was expected that, because urchins from the sides and bottoms were so active, they would move to the tops of the pinnacles in the summer when algal cover was high and seas were calm. Instead, urchin movement toward the tops did not increase until fall, when the annual algae began to die off. By late fall, storm activity had increased enough that the urchins were forced to move back down to the sides and bottoms of the pinnacles. At all study sites around Shemya Island, sea urchin movement was lowest in the winter. This was likely due to winter storms, which deter movement and cause urchins to seek refuge in crevices. An inverse relationship has previously been found between water turbulence and urchin activity. Turbulent areas are reported to reduce urchin movement, affecting grazing activity and potentially the species composition and abundance of the benthic community. Extreme conditions may in fact completely exclude urchins from certain areas (Lissner 1980).

27 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

80 Top algae 40 movement 60 30

40 20

20 10

0 0 movement (#urchins)

percent cover foliose summer fall winter spring

80 Side 40

60 30

40 20

20 10

0 0 movement (#urchins)

percent cover foliose summer fall winter spring

Bottom 80 40

60 30

40 20

20 10

0 0 movement (# urchins)

percent cover foliose summer fall winter spring

season Figure 23 Seasonal variation in the mean amount of drift algae (grams damp weight) and movement of urchins towards kelp at sites on the tops, sides and bottoms of the pinnacles, at Shemya Island, Alaska.

28 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

3.7.5. Causes of Urchin Inhibition and Kelp Forest Persistence Manipulative Clearing Experiments Preliminary results from surveys of the kelp-community at Shemya indicated that algae negatively affected sea urchin movement. For example, sea urchins in barren areas had smaller guts and gonads than urchins in kelp-dominated areas (see above), yet did not move into adjacent kelp areas where food was more abundant. To further examine the effects of algae on urchin movement, a series of manipulative clearing experiments were conducted, the results of which are presented below. Treatments applied to the experimental sites on the pinnacles included controls (with no algae removed), removal of only Alaria, and removal of all algae, all annuals, or all Desmarestia. Sites to which the latter three treatments were applied subsequently showed an early increase in urchin density and a decrease in total foliose algal cover over time (Figure 24 and 25). By August there was very little

control 20 Alaria Urchins all algae annuals 15 Desmarestia

5 # urchins/.25m2

0 June July Aug Sept

Figure 24 Mean density of sea urchins at experimental clearing treatments on the tops of pinnacles at Shemya Island, Alaska. Densities measured in June (when clearing was conducted), July, August and September.

control 80 Foliose Algae Alaria all algae annuals 60 Desmarestia

Percent cover 20

0 June July Aug Sept Month Figure 25 Percent cover of foliose algae at experimental clearing treatments on the tops of pinnacles at Shemya Island, Alaska. Measurements taken in June (when clearing was conducted), July, August and September. 29 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska foliose algal cover remaining on these pinnacles and, by September, there were no remaining foliose algae. The control sites and the sites in which Alaria was removed showed a slightly different pattern. Urchin densities increased in August and there was a decline in foliose algae due to senescence of annual species; however, unlike the other treatments, a significant algal cover remained in September (Figure 25). These results suggest that the presence of certain algae species, particularly Desmarestia, acted as a deterrent to urchin movement to the pinnacle tops. We propose the following scenario: when urchins were prevented from climbing to the pinnacle tops during the early summer, they had insufficient time to entirely remove all foliose algae before the arrival of fall and winter storms forced them down again. When urchins were able to get to the pinnacle tops early in the summer (as was the case with the other treatments), the foliose kelp on the tops of the pinnacles was entirely removed by grazing. Structure Manipulations To test whether the inhibition of urchin movement by kelp was due to the physical structure of the kelp plants, or to some other property of the kelp, a test of the effect of structure on urchin movement was conducted. Experimental treatments included controls (no urchin and kelp removal), clearings with no structural additions, clearing with flagging tape added (to imitate Desmarestia) and clearing with tygon tubing added (to imitate Alaria). The results of this experiment suggest that Desmarestia structure alone has a significant effect on urchin density. In the pinnacles, sea urchins returned rapidly to reach their original densities after one week at sites with no structure additions and at sites with tygon tubing additions (Figure 26). However, where flagging was added to imitate the low-lying, bushy Desmarestia viridis, sea urchins failed to return to their original densities. Control pinnacles showed no significant changes. The results of structure manipulations were similar at the Pacific sites. Sea urchin densities increased rapidly at sites where algae were cleared and no structures were added (Figure 27). In contrast, sea urchin densities remained low at sites where algae was cleared and structure (flagging tape) was added, and at sites where algae were not cleared and structure was not added (controls). It was also found that the percent coverage of flagging tape was correlated with the density of returning urchins (Figure 28). Boulders with 100% cover showed very low urchin densities after 5 days. Boulders with 25%, 50% and 75% cover showed intermediate densities. On boulders with urchins and kelp cleared but no structure added, urchins quickly returned to their original densities. Control boulders with no urchins removed (but that were monitored for random urchin movement) showed little variation over the duration of this study.

n=3 CONTROL (n=3) 12 initial = 11.7±0.2 n=2 1 week = 11.8±0.6 9

n=3 3

0 No additions Flagging Tubing

# urchins which moved/0.25m2 Treatment

Figure 26 Mean number of sea urchins that returned (±1 S.E.) to three experimental clearing treatments at the tops of pinnacles at Shemya Island, Alaska. Treatments: 1) the addition of flagging, 2) addition of tubing, and 3) no structural additions. 30 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

15 n=3

urchin density/0.25m2 cleared +structure cleared -structure not cleared treatment Figure 27 Mean density of sea urchins (±1 S.E.) for three experimental clearing treatments conducted at Pacific study sites at Shemya Island, Alaska. . Treatments: 1) the addition of flagging, 2) addition of tubing, and 3) no structural additions.

15 intial non-cleared controls=11.9±0.9 5 day non-cleared controls=12.1±0.6

5 urchin density

0 0% 25% 50% 75% 100%

percent cover Figure 28 Mean density of sea urchins (±1 S.E.) for five experimental clearing treatments conducted at the Pinnacles, Shemya Island, Alaska. Treatments: 1) the addition of 100% structural cover, 2) the addition of 75% structural cover, 3) the addition of 50% structural cover, 4) the addition of 25% structural cover, and 5) the addition of 0% structural cover.

These structure manipulations strongly suggest that algal structure − specifically Desmarestia − acts as a major inhibition to sea urchin movement and therefore grazing activity. This inhibition would be expected to increase the short-term survival of kelp stands. These results are significant because such clear examples of physical inhibition of herbivore activity by plants are rare. In one previous study, it was found that the sweeping action of Laminaria sp. acted to keep herbivores away and provide protection against herbivory (Velimirov and Griffiths 1979), consistent with the current findings.

31 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Clod Cards Clod cards were used to compare the relative degree of scour between pinnacles with foliose algae on the tops, pinnacles where the foliose algae was removed from the tops, and the bottoms of pinnacles where no foliose algae was found. Control clod cards had very little weight loss (Figure 29). Clod cards placed at the tops of pinnacles where algae were not cleared showed the highest amount of weight loss. Clod cards placed at the pinnacle bottoms or at the tops of pinnacles where algae were cleared showed similar amounts of weight loss, significantly less than the non-cleared pinnacle tops. The weight loss was attributed to scour caused by kelp abrasion and movement due to swell. These results indicate that algal cover can cause mechanical abrasion over and above that which is attributable to normal swell.

25 4

15 6 10 4 weight (g) 5 9 0 Control Tops Clear Tops Bottoms

site Figure 29 Mean weight loss (±1 S.E.) for clod cards placed at the pinnacles under three treatment conditions: 1) foliose algal covered tops, 2) foliose algal cleared tops, and 3) foliose algal free bottoms. Mean weight loss of control cards is shown for comparison.

In a second experiment, clod cards were used to determine the algal genera responsible for the greatest amount of abrasion. Alaria, Desmarestia and Agarum were found to cause the most weight loss in clod cards (Figure 30). Clod cards under Laminaria and clod cards placed in cracks showed the least amount of weight loss. As before, control clod cards had very little weight loss. These results are not surprising; Alaria, Desmarestia and Agarum all have low lying structures capable of creating abrasion. Laminaria has a thick stipe that serves to keep the leaf blades off the bottom, reducing its potential to cause abrasion at low levels. It therefore seems reasonable to assume that when the annual kelp species Alaria and Desmarestia die back in the fall, sea urchins are able to invade and increase grazing activity because the perennials Laminaria and Agarum do not significantly deter urchin movement. This pattern is consistent with the results of the algal clearing experiments (as described above). Thus, the persistence of kelp stands at Shemya appears to be attributable to the combined effects of seasonal storms (fall and winter swell) and mechanical inhibition of urchin movement by annual algal species.

32 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

4 4 20 4

4 10

weight (g) 4

5 0 Controls Alaria Desmarestia Agarum Laminaria In crack treatment

Figure 30 Mean weight loss (±1 S.E.) for clod cards placed under five treatment conditions at Shemya Island, Alaska: 1) under Alaria, 2) under Desmarestia, 3) under Agarum, 4) under Laminaria, and 5) in cracks in the rock surface. Mean weight loss of control cards is shown for comparison.

33 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

4. Conclusions The sea otter population of the Semichi Islands was monitored for 2 years, between June 1995 and June 1997. During this period, the population size fluctuated between 106 and 163 otters, with the highest numbers observed in 1995. In conjunction with survey results from 1994, when 390 otters were counted, this suggests an overall decline in sea otter numbers at the Semichis. Population structure varied between the Islands: most pupping occurring at Alaid Island, while Shemya Island was utilized mainly by non-territorial males. On Shemya Island, differences in habitat use and group size were found between seasons. Sea otter diet consisted primarily of sea urchins during the entire year. However, subtidal areas high in urchin abundance were not necessarily areas where most otters were found, suggesting that factors other than urchin abundance (e.g. shelter from storms, favorable resting habitat) were also important in determining sea otter use. The sea urchin and algal subtidal communities were also monitored at Shemya Island, to study long-term and short-term (seasonal) trends. Overall, there were slight but significant long-term changes in the community structure, although these changes were highly variable and localized. Certain areas high in urchin density and low in algal cover in 1987 were low in urchin density and high in algal cover in 1997. These changes were concurrent with the re-colonization of Shemya by sea otters, suggesting that sea otters have had a significant but localized effect on community structure. Nonetheless, many areas of high urchin density and low algal cover were still present in 1997, and factors other than urchin- regulation by sea otters appeared to be responsible for short-term variation in community structure. Natural and manipulative experiments were used to evaluate the effect of seasonal variation in swell height (associated with increased winter storm activity) and seasonal variation in algal cover. In the late fall, winter and spring, sea urchin movement and grazing was inhibited by rough sea conditions. In the summer, when seas were calm, the high seasonal cover of annual algae inhibited urchin movement. Consequently, sea urchins were most active (and caused the most damage to kelp stands) in the early fall, when seas were still relatively calm but annual kelp species were senescing. Seasonal variation in storms and algal cover were the main factors limiting sea urchin grazing activity and allowing kelp beds to persist in urchin dominated areas at Shemya Island.

34 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

5. Literature Cited Bodkin, J. R., and B. E. Ballachey. 1996. Monitoring the status of the wild sea otter population: field studies and techniques. Endangered Species Update, 13:14-19. Carney, D. 1991. A comparison of densities, size distribution, gonad and total-gut indices, and the relative movements of red sea urchins, Strongylocentrotus franciscanus in two depth regimes. Thesis. University of California, Santa Cruz, California, U. S. A. Cowen, R. K. 1983. The effect of sheephead (Semicossyphus pulcher) predation on the red sea urchin (Strongylocentrotus franciscanus) populations: an experimental analysis. Oecologia 58: 249-255. Dethier, M. N., Graham, E. S., Cohen, S. and L. M. Tear. 1993. Visual versus random-point percent cover estimations: 'objective' is not always better. Marine Ecology Progress Series 96: 93-100. Doty, J. E. and M. S. Doty. 1973. Abrasion in the measurement of water motion with the clod-card technique. Bulletin of the Southern California Academy of Science 72: 40-41. Duggins, D. O. 1983. Starfish predation and the creation of mosaic patterns in a kelp-dominated community. Ecology 63: 1610-1619. Estes, J. A. and D. O. Duggins. 1995. Sea otters and kelp forests in Alaska: generality and variation in a community ecological paradigm. Ecological Monographs 65: 75-100. Estes, J. A., R. J. Jameson, and E, B. Rhode. 1982. Activity and prey selection in the sea otter: influence of population status on community structure. American Naturalist. 120:242-258. Estes, J. A., R. J. Jameson, and A. M. Johnson. 1981. Food selection and some foraging tactics of sea otters. J. A. Chapman & D. Pursley, eds. Worldwide Fubearer Conference Proceedings. Vol. 1. (pp 606:641). Baltimore, Maryland: University of Maryland Press. Estes, J. A., M. T. Tinker, T. M. Williams, and D. F. Doak. 1998. Killer whale predation on sea otters linking oceanic and nearshore ecosystems. Science, 282:473-476. Harrold, C. and J. S. Pearse. 1987. The ecological role of echinoderms in kelp forests. Pages 137-233 in M. Jangoux and J. M. Lawrence, editors. Echinoderm studies. A. A. Balkema, Rotterdam. Harrold, C. and D. C. Reed. 1985. Food availability, sea urchin grazing, and kelp forest community structure. Ecology 66:1160-1169. Gonar, J. J. 1972. Gonad growth in the sea urchin, Strongylocentrotus purpuratus (Stimpson) (Echinodermata: Echinoidea) and the assumptions of gonad index methods. Journal of Experimental Marine Biology and Ecology 10: 89-103. Kenyon, K. W. 1969. The sea otter in the eastern Pacific Ocean. North American Fauna 68: 1-352. Lissner, A. L. 1980. Some effects of turbulence on the activity of the sea urchin Centrostephanus coronatus Verrill. Journal of Experimental Marine Biology and Ecology 48: 185-193. Monson, D. 1995. Reproductive strategies in sea otters at Amchitka Island, Alaska. Masters Thesis, University of California, Santa Cruz, CA. Paine, R. T. 1969. A note on trophic complexity and community stability. American Naturalist 103: 91- 93. Power, M. E., D. Tilman, J. A. Estes, B. A. Menge, W. J. Bond, L. S. Mills, G. Daily, J. C. Castilla, J. Lubchenco and R. T. Paine. 1996. Challenges in the quest for keystones. Bioscience. 46:609:620.

35 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Rogers-Bennett, L., Bennett, W. A., Fastenau, H. C. and C. M. Dewees. 1995. Spatial variation in red sea urchin reproduction and morphology: implications for harvest refugia. Ecological Applications 5: 1171-1180. Tegner, M. J. and P. K. Dayton. 1981. Population structure, recruitment and mortality of two sea urchins (Strongylocentrotus franciscanus and S. purpuratus) in a kelp forest. Marine Ecology Progress Series 5: 255-268. Tinker, T. and J. A. Estes. 1996. The population ecology of sea otters at Adak Island, Alaska. Final Report to the Navy (12/96). Velimirov, B. and C. L. Griffiths. 1979. Wave-induced kelp movement and its importance for community structure. Botanica Marina 22:169-172. Watanabe, J. M. and C. Harrold. 1991. Destructive grazing by sea urchins Strongylocentrotus spp. in a central California kelp forest: potential roles for recruitment, depth, and predation. Marine Ecology Progress Series 71: 125-141.

36 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

6. Appendices Appendix A: Summary of morphological data collected from captured otters on Shemya Island, Alaska. Otter# Date Age-est Mass Body Testicular Braculum Area captured Length captured (kg) (cm) Length (mm) Length (cm) 1 6/17/1995 3 years 21 113 51 14 Alcan Harbor 2 6/17/1995 5 years 27 126 59 18 Alcan Harbor 3 6/21/1995 5 years 29 127 49 15.5 Alcan Harbor 4 6/26/1995 8 years 39 136 66 18 Alcan harbor 5 6/29/1995 5 years 31 137 57 15 Hammerhead Island 6 6/30/1995 3 years 25 118 55 13 Fox Point 7 7/1/1995 5 years 31 131 60 17 Alcan Harbor 8 6/10/1996 3 years 35 141 n/a 18 Fox Point Note: "Age-est" was the estimated age at the time of capture, based on degree of tooth wear

37 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix B: Summary of Shemya Island surveys between July 1995 and August 1997 Year Date # surveys Total Total Total Overall min # max # % in kelp per month Adults Lg Pups Sm Pups mean total in survey in survey 1995 July 1 34 1 0 35 35 35 unknown September 2 22 0 0 11 3 19 100 October 2 47 0 0 23.5 20 27 85 November 1 13 0 0 13 13 13 92 December 2 30 1 0 16 12 20 0 mean 1.6 29.2 0.4 0 19.7 16.6 22.8 69 1996 January 4 80 0 0 20 7 33 0 February 1 22 0 0 22 22 22 0 March 2 56 1 0 28.5 28 29 4 April 2 71 1 1 36.5 32 41 11 May 3 120 1 0 40.3 29 58 71 June 1 26 0 0 26 26 26 92 July 2 54 0 0 27 14 40 100 August 2 62 0 0 31 24 38 95 September 2 42 1 0 21.5 14 29 26 October 3 22 1 0 7.7 1 14 0 November 3 49 0 0 16.3 2 25 0 December 3 61 0 0 20.3 10 27 0 mean 2.3 55.4 0.4 0.1 24.8 17.4 31.8 33.3 1997 January 2 22 0 0 11 10 12 0 February 4 134 0 0 33.5 11 47 0 March 5 183 3 0 37.2 20 55 1 April 4 108 0 0 27 19 36 46 May 4 110 0 0 27.5 22 33 82 June 5 153 0 1 30.8 14 43 97 July 3 108 0 2 36.7 35 39 100 August 2 55 1 0 28 18 38 100 mean 3.6 109.1 0.5 0.4 29.0 18.6 37.9 53.3

38 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix C: Summary of foraging data from Shemya Island, Alaska between June 1995 and August 1997. Year Month # bouts Mean Down Up Prey # Numbe Size Time Time r * per month Depth (ft) (sec) (sec) 1,2,3 1995 June 7 47.8 55.1 0.9 0.9 2.8 July 4 50.4 51.4 0.9 0.9 3.0 November 7 10.5 34.3 46.8 0.9 1.4 1.8 December 5 15.6 34.1 52.5 1.1 1.5 1.4 1996 February 2 13.8 40.6 80.1 1.4 1.4 1.4 March 1 5.0 48.0 57.2 0.8 1.8 1.8 April 5 7.5 37.7 70.5 1.0 2.4 1.6 May 7 12.9 39.8 74.0 1.0 2.0 1.8 August 1 35.0 44.6 46.8 1.0 0.4 2.5 October 1 45.0 38.4 34.4 0.5 0.5 2.0 November 13 9.3 37.5 51.4 0.8 0.8 2.0 December 10 10.6 40.5 46.6 0.9 1.6 1.8 1997 January 6 7.9 41.1 44.6 1.0 1.9 1.7 February 9 9.9 49.2 59.8 0.8 1.4 1.7 March 6 11.0 37.1 62.7 1.0 1.6 1.8 April 12 12.0 52.0 52.1 1.0 1.0 1.0 May 3 8.2 30.5 49.2 1.0 1.8 2.0 June 7 12.3 49.2 76.0 0.8 1.3 1.6

OVERALL 5.9 14.2 41.8 56.2 0.9 1.4 1.9 MEANS: *for size of prey: 1=otter paw or smaller, 2=otter paw to otter head, 3=larger than otter head

39 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix D: Summary of foraging diet data from Shemya Island, Alaska between June 1995 and August 1997. Year Month number of % dives % % % % % % % dives unsuccessfulurchins fish bivalves chitons limpet crab starfish 1995 June 22 14 15 50 30 0 0 0 0 July 25 4 0 92 0 0 0 0 0 November 118 6 87 0 0 2 0 0 0 December 84 8 59 0 2 16 0 0 0 1996 February 41 5 77 0 10 2 0 0 0 March 5 20 100 0 0 0 0 0 0 April 43 2 99 0 0 1 0 0 0 May 83 0 96 0 0 4 0 0 0 August 15 0 39 0 0 0 0 0 0 October 9 55 100 0 0 0 0 0 0 November 138 24 73 0 0 5 0 0 0 December 131 12 98 0 0 0 0 0 1 1997 January 120 4 100 0 0 0 0 0 0 February 104 17 97 0 0 0 0 0 0 March 121 5 96 1 0 1 0 1 1 April 259 10 93 0 0 0 1 1 0 May 68 1 95 1 0 1 0 0 0 June 115 9 82 1 0 3 0 0 0

40 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix E: Summary of scat data from Shemya Island between November 1995 and May 1997.

Percent Composition Year Month # scats urchin snail mussel fish crab

1995 November 11 95-100 0 0-5 0 0

1996 February 23 95-100 0 0 0 0 March 20 75-94 0 0 0-5 0 April 30 75-94 0 0-5 0 0

1997 February 36 95-100 0 0 0 0 March 299 75-94 0 0 0 0-5 April 143 75-94 0 0 0 0 May 96 75-94 0 0-5 0 0

41 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix F: Summary of algal community data gathered from Shemya Island, Alaska. Note: The information is shown as mean percent cover ± 1 S. E. It is separated by season, location and depth. n=number of quadrats sampled.

Summer Fall Winter Spring Pacific (15m) Alaria fistulosa 10.3±2.0 6.5±1.7 2.8±0.6 2.9±0.6 other browns 53.3±0.3 23.7±3.2 22.1±2.4 16.9±1.8 foliose reds 18.7±3.9 11.7±1.9 14.6±1.5 19.7±1.6 corallines 16.0±4.6 42.5±2.3 42.5±2.0 41.0±1.6 n 24 52 83 99

Alcan (6m) Alaria fistulosa 4.9±1.0 2.2±1.0 0.2±0.2 0.6±0.4 other browns 8.6±1.8 3.7±1.6 0.2±0.2 1.1±0.7 foliose reds 19.3±1.7 14.0±2.3 8.5±2.1 5.0±1.4 corallines 56.0±2.2 68.0±2.5 76.3±2.2 79.2±2.2 n 121 40 60 66

Alcan (15m) Alaria fistulosa 8.5±1.4 2.1±0.9 0.0±0.0 3.3±0.6 other browns 18.3±2.4 32.1±3.3 20.5±2.2 14.0±1.7 foliose reds 18.1±1.7 8.6±1.5 14.4±1.9 18.9±1.2 corallines 48.2±1.9 51.8±2.9 60.0±3.1 53.5±1.7 n 115 28 78 115

Kenmore (6m) Alaria fistulosa 3.3±0.8 1.2±0.6 2.0±1.0 2.3±0.9 other browns 7.0±1.4 1.2±0.7 0.0±0.0 0.2±0.2 foliose reds 9.2±1.2 3.0±1.3 2.7±1.1 4.4±1.1 corallines 71.7±2.2 81.2±2.3 82.3±4.3 85.9±2.5 n 130 40 30 61

Kenmore (15m) Alaria fistulosa 1.5±0.8 1.9±0.7 2.0±1.0 2.9±1.0 other browns 7.9±1.5 5.1±1.4 8.0±3.3 15.6±2.6 foliose reds 6.2±0.8 7.0±2.0 14.3±2.9 9.2±1.4 corallines 69.1±2.1 80.0±3.1 65.7±3.5 64.6±2.6 n 120 53 30 84

42 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix G. Summary of the various sea urchin parameters obtained in 1995 and 1996 from Shemya Island, Alaska Note: The information is shown as means ± 1 S. E. which is separated by season, location and depth. ()=number of urchins sampled unless otherwise stated.

Summer Fall Winter Spring Alcan (6m) density (#/0.25m2, ()=number of quadrats) 12.6±0.8 (121) 11.0±0.8 (40) 9.4±1.3 (60) 12.3±0.8 (66) size (mm) 33.1±0.6 (498) 33.2±0.8 (253) 36.1±1.1 (95) 34.5±0.8(197) gonad index 5.0±0.5 (31) 9.7±0.8 (15) 10.4±0.9 (33) 5.2±0.9 (15) gut index 21.9±0.8 (31) 15.7±1.0 (15) 19.1±0.6 (15) 16.6±1.2 (15)

Alcan (15m) density (#/0.25m2, ()=number of quadrats) 8.1±0.6 (115) 2.7±1.3 (33) 0.5±0.1 (78) 1.0±0.2 (115) size (mm) 33.4±0.7 (489) 39.3±2.3 (120) 44.1±0.6 (272) 39.1±0.6(371) gonad index 6.1±0.5 (30) 7.8±0.7 (59) 12.5±1.5 (36) 4.4±0.6 (46) gut index 21.4±1.4 (30) 17.5±1.2 (15) 18.6±1.1 (15) 17.8±0.9 (46)

Kenmore (6m) density (#/0.25m2, ()=number of quadrats) 19.5±0.8 (130) 20.8±0.7 (40) 13.7±1.8 (30) 15.2±1.1 (61) size (mm) 30.6±0.5 (533) 34.1±0.8 (224) 39.3±1.2 (98) 39.1±1.2 (99) gonad index 2.8±0.2 (29) 3.2±0.3 (15) 4.4±0.6 (14) 4.4±0.6 (14) gut index 17.9±1.0 (29) 9.4±0.8 (15) 18.0±1.8 (14) 18.0±1.8 (14)

Kenmore (15m) density (#/0.25m2, ()=number of quadrats) 13.5±0.5 (120) 10.0±0.8 (63) 5.8±0.9 (30) 6.9±0.6(84) size (mm) 33.9±0.8 (451) 37.8±1.1 (213) 37.9±1.3 (111) 39.1±0.7(428) gonad index 2.0±0.2 (30) 5.3±0.4 (69) 3.2±0.5 (16) 3.3±0.4 (25) gut index 14.6±1.0 (30) 19.4±1.7 (15) 7.2±0.6 (16) 9.4±1.0 (25)

43 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix H: Summary of drift algal community data gathered from Shemya Island, Alaska. Note: The information is shown as mean wet weight (g) ± 1 S. E. which is separated by season, location and depth. n=number of quadrats sampled.

Summer Fall Winter Spring Alcan (6m) reds 19.8±5.4 31.0±7.3 9.6±2.6 5.1±0.5 browns 85.7±33.3 193.2±61.3 47.9±28.5 1.5±0.7 total 101.1±34.8 242.8±65.1 58.1±30.3 6.4±0.8 n 13 6 6 6

Alcan (15m) reds 13.6±3.4 3.6±1.9 3.0±1.1 2.7±0.8 browns 92.3±14.8 38.6±12.4 47.7±17.4 3.0±1.1 total 105.9±16.2 42.2±12.6 51.4±18.0 5.7±1.6 n 12 6 11 6

Kenmore (6m) reds 8.2±2.1 5.4±1.5 2.5±0.9 3.4±1.1 browns 28.7±11.0 15.8±7.3 7.1±2.9 3.2±2.2 total 36.9±10.4 21.2±7.6 9.8±3.6 7.0±1.8 n 12 6 6 6

Kenmore (15m) reds 0.1±0.1 4.2±1.5 1.1±0.7 0.2±0.1 browns 48.0±24.3 40.0±16.3 5.2±2.2 0.4±0.2 total 48.1±24.3 45.3±15.0 6.4±1.8 0.6±0.3 n 12 6 6 6

44 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix I: Seasonal movement of sea urchins at the various sites at Shemya Island, Alaska. Note: Mean number of urchins/0.25 m² are shown ± 1 S.E., n=number of trials

Summer Fall Winter Spring mean ± 1s.e. mean ±1s.e. mean ± 1s.e. mean ± 1s.e. Alcan shallow Initial Control 11.4 ± 2.4 12.5 ± 1.4 9.8 ± 1.2 15.5 ±3.0 1.5 hr Control 11.2 ± 2.6 12.0 ± 1.3 9.7 ± 0.9 15.7 ±2.9 Treatments Urchin Removal 2.2 ± 0.9 0.5 ± 0.3 0.3 ± 0.2 0.2 ±0.2 Kelp Addition 26.5 ± 7.0 28.7 ± 1.5 7.5 ± 1.0 22.5 ±4.7 Structure Addition 2.3 ± 0.5 0.3 ± 0.2 0.5 ± 0.3 0.0 ±0.0 n 14 6 4 6 Alcan deep Initial Control 10.6 ± 1.3 2.3 ± 0.9 0.3 ± 0.2 1.6 ±1.1 1.5 hr Control 10.5 ± 1.1 2.2 ± 0.9 0.3 ± 0.2 1.6 ±1.1 Treatments Urchin Removal 1.5 ± 0.6 0.1 ± 0.1 0.0 ± 0.0 0.0 ±0.0 Kelp Addition 12.6 ± 4.5 1.3 ± 0.6 0.0 ± 0.0 0.0 ±0.0 Structure Addition 1.8 ± 0.8 0.1 ± 0.1 0.0 ± 0.0 0.0 ±0.0 n 13 11 11 11 Bering shallow Initial Control 17.6 ± 1.7 19.0 ± 2.3 8.3 ± 0.2 17.3 ±4.1 1.5 hr Control 17.3 ± 1.4 19.7 ± 2.7 8.7 ± 0.9 18.0 ±4.4 Treatments Urchin Removal 5.1 ± 1.2 1.7 ± 0.8 0.0 ± 0.0 0.2 ±0.2 Kelp Addition 59.3 ± 3.9 36.2 ± 2.8 12.3 ± 1.8 31.3 ±9.1 Structure Addition 5.2 ± 1.7 1.3 ± 0.5 0.0 ± 0.0 0.0 ±0.0 n 15 6 3 6 Bering deep Initial Control 13.1 ± 1.5 14.0 ± 1.9 7.0 ± 1.0 8.8 ±2.0 1.5 hr Control 14.2 ± 1.7 13.4 ± 1.8 8.0 ± 0.6 9.0 ±2.2 Treatments Urchin Removal 2.9 ± 0.8 1.0 ± 0.4 0.0 ± 0.0 0.4 ±0.4 Kelp Addition 48.2 ± 3.7 25.8 ± 6.5 11.0 ± 1.2 18.5 ±4.6 Structure Addition 2.1 ± 0.5 1.4 ± 0.5 0.0 ± 0.0 0.0 ±0.0 n 13 11 3 11

45 Sea Otter Population Biology and Subtidal Community Ecology at Shemya Island, Alaska

Appendix I, continued Pacific Initial Control 0.6 ± 0.2 1.5 hr Control 0.6 ± 0.2 Treatments Urchin Removal 0.0 ± 0.0 Kelp Addition 0.0 ± 0.0 Structure Addition 0.0 ± 0.0 n Pinnacles tops Initial Control 3.9 ± 1.3 7.6 ± 1.4 6.0 ± 1.0 4.3 ±0.4 1.5 hr Control 4.0 ± 1.3 8.1 ± 1.4 6.0 ± 1.0 4.7 ±0.6 Treatments Urchin Removal 1.3 ± 0.6 0.5 ± 0.2 0.0 ± 0.0 0.2 ±0.2 Kelp Addition 5.5 ± 1.7 7.3 ± 1.5 0.0 ± 0.0 4.7 ±1.0 Structure Addition n/a 0.2 ± 0.2 0.0 ± 0.0 0.0 ±0.0 n 8 13 3 6 Pinnacles sides Initial Control 11.3 ± 2.6 10.0 ± 1.1 8.0 ± 0.4 9.3 ±0.5 1.5 hr Control 11.3 ± 2.7 9.4 ± 1.0 8.0 ± 0.7 9.5 ±0.7 Treatments Urchin Removal 1.8 ± 0.5 0.6 ± 0.2 0.0 ± 0.0 0.2 ±0.2 Kelp Addition 15.3 ± 5.3 12.5 ± 2.2 0.5 ± 0.3 10.7 ±1.9 Structure Addition n/a 0.8 ± 0.2 0.0 ± 0.0 0.0 ±0.0 n 13 4 6 Pinnacles bottoms Initial Control 17.1 ± 2.7 16.7 ± 1.3 7.3 ± 1.1 11.8 ±1.9 1.5 hr Control 16.9 ± 2.6 16.8 ± 1.4 7.5 ± 1.0 12.2 ±1.9 Treatments Urchin Removal 5.0 ± 1.6 0.9 ± 0.2 0.0 ± 0.0 0.3 ±0.3 Kelp Addition 34.5 ± 5.5 22.8 ± 3.5 0.2 ± 0.2 15.8 ±1.7 Structure Addition n/a 1.2 ± 0.3 0.0 ± 0.0 0.3 ±0.2 n 8 13 4 6