Farallones Research Articles

Intra- and interannual variation in the foraging behavior of common Murres (Uria aalge) in the Central California current

Seabirds modify their behavior during the breeding season as they transition from incubation (self-feeding) to chick-rearing (self-feeding + chick provisioning) periods, which affects parental foraging patterns and distribution. However, it is less clear how much flexibility parents have to modulate their behavior when environmental conditions are unusually poor. Using GPS loggers and time depth recorders, we examined the foraging flexibility of common murres (Uria aalge) at Southeast Farallon Island as adjustments were made between breeding phases and across consecutive years (2019 and 2020) with contrasting oceanographic conditions (i.e. prominent marine heatwave in 2019). Foraging trips were longer during the incubation period (2019: 31.7 ± 20.1 h; 2020: 23.5 ± 7.2 h) compared to the chick provisioning period (2019: 12.2 ± 9.9 h; 2020: 7.5 ± 8.3 h). Moreover, parents generally ventured farther from the colony during incubation (2019: 34.7 ± 17.6 km; 2020: 30.1 ± 11.5 km) than when foraging to provision chicks (2019: 22.6 ± 17.1 km; 2020: 14.1 ± 15.0 km) in each year. Nevertheless, overall foraging ranges had a high degree of overlap (> 60%) within breeding phases and across years, suggesting that murres at this colony are constrained by the habitats primarily based on foraging range. Murres dove deeper during incubation compared to chick-rearing in 2020 (36.0 ± 24.4 vs 19.5 ± 15.2 m), but there were no other differences within or across years in diving behavior, suggesting that diving effort was less affected by breeding stage. Interannual differences in foraging behavior only occurred during chick-feeding trips and were likely driven by the prey species present. For example, rockfish were more common in chick diets in 2020, when ocean temperatures were cooler compared to 2019. Despite similarities in trip parameters between years, breeding productivity was much lower in 2019 compared to both long-term averages and the 2020 season, suggesting a potential constraint on murre behavioral flexibility when oceanographic variation occurs. These results emphasize the importance of examining behavior on multiple time scales to gain a better understanding of how predators respond to changes in their environment.

Effectiveness of novel artificial seabird nest modules for reducing ambient temperature transfer in a warming climate

AbstractArtificial habitat for cavity nesting birds can provide excellent opportunities for research and conservation efforts but may expose species to the negative impacts of warming ambient temperatures with climate change. Artificial nest boxes have been successfully used to monitor the breeding activity of the Cassin's auklet (Ptychoramphus aleuticus), a small burrow‐nesting seabird, on Southeast Farallon Island (SEFI) since 1971. Mean monthly ambient air temperatures on SEFI during the summer months have increased at an annual rate of roughly 0.03°C from 1971 to 2022, along with an increase in the number of extreme heat days and average maximum temperature, confirming a warming trend at this seabird colony. Given a projected increase in global temperature, we assessed the effectiveness of traditional wooden nest boxes vs. newer ceramic modules at buffering external ambient air temperatures in normal and extreme heat days across a gradient of microclimates on SEFI. Results from fitting linear mixed effects models indicated that, on average, internal temperatures of wooden and ceramic nests (of comparable size and shape) exhibited similar rates of deviation from ambient air temperature of approximately 0.15°C, even during extreme heat events. Ceramic modules did keep nest chambers cooler by approximately 1.2°C than wooden boxes during extreme events at the warmer, drier southern location of the island. Our results can help guide future efforts to design artificial nests that can effectively provide habitat for seabirds as ambient temperatures increase.

First Record of the Small-billed Elaenia (Elaenia parvirostris) for Western North America

The Small-billed Elaenia (Elaenia parvirostris) is a small flycatcher common on the Atlantic slope of South America. The species breeds below 1000 m elevation in open woodlands, gardens, and forest edges from southern Brazil to northeastern Argentina and migrates north to spend the nonbreeding season in the northern Amazon Basin. Since 2012, it has been documented as a vagrant to North America, with four records from the United States and Canada to date. On the basis of one photographed on Southeast Farallon Island on 4 September 2022, we record a fifth Small-billed Elaenia in North America, a first for California and the Pacific coast. Its novelty notwithstanding, it represents an outlier of an established pattern of vagrancy of tyrant flycatchers from South America reaching North America via overshooting or reverse migration.

Physiological and behavioral responses of northern elephant seals (Mirounga angustirostris) to global change among three northern California rookeries

The California coast provides a unique study system for investigating the effects of warming and habitat quality on the thermoregulatory capacity of the northern elephant seal (NES). In California, island rookeries such as the offshore site at the Farallon Islands National Wildlife Refuge are experiencing habitat loss and reduced suitable haul-out surfaces due to erosion from storm events. Extreme weather events are increasing in frequency and severity with global change. Semi-aquatic animals face a unique thermal challenge. They possess adaptations to conserve heat when immersed in cold water during deep dives but must compensate for such heat-conserving properties of their physiology when transitioning to heat exposure on land. Therefore, these animals must precisely thermoregulate with physiological and behavioral adjustments across a broad thermal range. We investigated how environmental variables affect seal thermoregulation at three northern California rookeries, the southeast Farallon Island (SEFI), Point Reyes National Seashore (PORE) and Año Nuevo State Park (ANSP). Infrared thermography was used to determine seal skin surface temperature and weather data was collected at each site. We found that average surface temperature increases with solar radiation, maximum surface temperature decreases with increasing wind speed, and thermal window area percentage decreases with relative humidity and increases with ambient temperature. Climatic variation may present physiological and behavioral challenges for marine mammals that experience significant life-history stages on land. Such ongoing findings will be fundamental in predicting climate change vulnerabilities and will be critical in mitigating the impacts of anthropogenic warming and promoting resilience in these populations. Carol Baird Graduate Student Award for Field Research; The Neubacher Fund for Marine Science at Point Reyes National Seashore. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Population dynamics and resource availability drive seasonal shifts in the consumptive and competitive impacts of introduced house mice (Mus musculus) on an island ecosystem.

BackgroundHouse mice (Mus musculus) are widespread and invasive on many islands where they can have both direct and indirect impacts on native ecological communities. Given their opportunistic, omnivorous nature the consumptive and competitive impacts of house mice on islands have the potential to vary over time in concert with resource availability and mouse population dynamics.MethodsWe examined the ecological niche of invasive house mice on Southeast Farallon Island, California, USA using a combination of mouse trapping, food resource surveys, and stable isotope analysis to better understand their trophic interactions with native flora and fauna. Specifically, we coupled the analysis of seasonal variation in resource availability over a 17-year period (2001–2017), carbon (δ13C) and nitrogen (δ15N) stable isotope values of mouse tissue and prey resources in a single year (2013), and isotopic niche and mixing models to quantify seasonal variation in mouse diets and the potential for resource overlap with native species.ResultsWe found that plants were the most important resource for house mice during the spring months when vegetation is abundant and mouse populations are low following heavy precipitation and declines in mouse abundance during the winter. While still consumed, plants declined in dietary importance throughout the summer and fall as mouse populations increased, and seabird and arthropod resources became relatively more available and consumed by house mice. Mouse abundance peaks and other resource availability are low on the island in the fall months when the isotopic niches of house mice and salamanders overlap significantly indicating the potential for competition, most likely for arthropod prey.DiscussionOur results indicate how seasonal shifts in both mouse abundance and resource availability are key factors that mediate the consumptive and competitive impacts of introduced house mice on this island ecosystem. As mice consume and/or compete with a wide range of native taxa, eradication has the potential to provide wide-reaching restoration benefits on Southeast Farallon Island. Post-eradication monitoring focused on plant, terrestrial invertebrate, salamander, and seabird populations will be crucial to confirm these predictions.

ISOLATION, CHARACTERIZATION, AND ANTIMICROBIAL SUSCEPTIBILITY OF BACTERIA ISOLATED FROM SEA LION (ZALOPHUS CALIFORNIANUS) PUPS IN NORTHWESTERN MEXICO.

Bacterial infections have been documented in marine mammals for decades, and some are considered emerging pathogens with zoonotic potential. The aerobic oral (n=16) and rectal (n=17) bacterial microbiota and their antimicrobial resistance were characterized for 17 apparently healthy California sea lion pups (Zalophus californianus) captured with a hoop net in Farallon Island, Sinaloa, Mexico, in 2016. Bacteriologic cultures, Analytical Profile Index, and PCR were used to identify bacterial species. The Escherichia coli phylogenetic groups were identified by PCR, Salmonella serotypes were identified, and resistance to antibiotics was evaluated. Overall, 39 bacterial species were isolated, including E. coli and Salmonella spp. (35.9% each) and Pseudomonas aeruginosa (28.2%). For E. coli, UNKNOWN phylogroup was the most prevalent (57.7%), followed by the A phylogroup (37.1%). Most Salmonella serotypes were identified as Newport (92.8%); serotype Saintpaul was also identified (7.2%). Sea lions with bacterial co-colonization included 24.2%, from which two bacterial species were isolated, and 3% with three species. Overall, 59% of bacteria were resistant to at least one antibiotic tested, and 25.6% were extensively drug resistant. Bacteria were highly resistant to ampicillin and cefotaxime. This study demonstrates the importance of characterizing the microbiome of sea lions, and the potential effect of pathogens with antimicrobial resistance on wildlife conservation and public health.

Bayesian network-based risk assessment of synthetic biology: Simulating CRISPR-Cas9 gene drive dynamics in invasive rodent management.

Gene drive technology has been proposed to control invasive rodent populations as an alternative to rodenticides. However, this approach has not undergone risk assessment that meets criteria established by Gene Drives on the Horizon, a 2016 report by the National Academies of Sciences, Engineering, and Medicine. To conduct a risk assessment of gene drives, we employed the Bayesian network-relative risk model to calculate the risk of mouse eradication on Southeast Farallon Island using a CRISPR-Cas9 homing gene drive construct. We modified and implemented the R-based model "MGDrivE" to simulate and compare 60 management strategies for gene drive rodent management. These scenarios spanned four gene drive mouse release schemes, three gene drive homing rates, three levels of supplemental rodenticide dose, and two timings of rodenticide application relative to gene drive release. Simulation results showed that applying a supplemental rodenticide simultaneously with gene drive mouse deployment resulted in faster eradication of the island mouse population. Gene drive homing rate had the highest influence on the overall probability of successful eradication, as increased gene drive accuracy reduces the likelihood of mice developing resistance to the CRISPR-Cas9 homing mechanism.

Western Gull Foraging Behavior as an Ecosystem State Indicator in Coastal California

With accelerating climate variability and change, novel approaches are needed to warn managers of changing ecosystem state and to identify appropriate management actions. One strategy is using indicator species—like seabirds as ecosystem sentinels—to monitor changes in marine environments. Here, we explore the utility of western gulls (Larus occidentalis) breeding on Southeast Farallon Island as a proxy of ecosystem state in coastal California by investigating the interannual variability in gull foraging behavior from 2013 to 2019 in relation to upwelling conditions, prey abundances, and overlap with humpback whales (Megaptera novaeangliae) as gulls frequently feed in association with whales. Western gulls have a flexible diet and forage on land and at-sea. We combined gull GPS tracking data during the incubation phase, ecosystem survey data on multiple predator and prey species, and derived oceanographic upwelling products. When foraging at sea, gulls overlapped with cool upwelled waters. During 2015–2017, 25% more gull foraging trips visited land than in other years, where land trips were on average ∼8 h longer and 40% further than sea trips, which coincided with high compression of coastally upwelled waters (habitat compression) in 2015–2016. Gull foraging behavior was related to local prey abundances, where more foraging occurred near shore or on land when prey abundances were low. However, visual surveys indicated that ∼70% of humpback whale observations co-occurred with gulls, and the year with the most foraging on land (2017) corresponded to regionally low relative whale abundances, suggesting gull movement patterns could be an indicator of whale presence. Further, both whales and gulls forage near-shore under high upwelling habitat compression and low krill abundance. Hence, the deployment of year-round tags on gulls with the capability of near real-time data accessibility could provide important fine-scale metrics for conservation and management of the threatened yet recovering eastern Pacific humpback whale population between infrequent and coarse surveys. Entanglement in fishing gear and ship strikes are major inhibitors to whale recovery and have increased concomitantly with human use of ocean resources. Moreover, as climate variability and change increase, novel indicators should be explored and implemented to inform marine spatial planning and protect species across multiple scales from new risks.

Effects of winter storms and oceanographic conditions on survival to weaning: a 37 year study of northern elephant seals on the Farallon Islands

Northern elephant seals Mirounga angustirostris were extirpated from California in the 19th century, and only in recent decades have they recolonized. A key demographic parameter underlying population viability is the survival of pups, from birth to weaning. We evaluated local factors acting directly on pup survival prior to weaning and basin-wide factors reflecting oceanic conditions which may impact maternal condition and behavior, using a 37 yr time series from 2 adjacent islands off central California: Southeast Farallon Island (SEFI) and West End Island (WEI). Mixed-effects logistic regression indicated that annual pup survival decreased with increasing frequency of extreme waves during January and February, which may inundate haulout locations when pups are present, and increased with the North Pacific Gyre Oscillation (NPGO) index, reflecting increased primary productivity. Moreover, the impact of extreme waves was manifest only for WEI, which may reflect a greater risk of inundation compared to SEFI. Annual pup survival was most highly correlated with NPGO values during the 6 mo period preceding and including arrival and the pupping period (fall and winter). Our findings suggest that favorable foraging conditions for females during the 4 mo prior to hauling out led to better maternal condition, which improved pup survival. Impacts of storm surges on pup survival is of concern since the frequency and severity of storms is expected to increase in the future. To support population recovery, we recommend studies consider demographic parameters such as recruitment of females to the Farallon breeding population and to adjacent coastal California colonies.

Northward migration, molting locations, and winter residency of California breeding pigeon guillemots Cepphus columba

Pigeon guillemots Cepphus columba are ubiquitous along the coasts of the eastern North Pacific, yet little is known about their winter migration patterns, habitat needs, and potential threats faced during the non-breeding period. We used 3 seasons of year-long light level data from tagged individuals to estimate the migration timing and winter residency of pigeon guillemots breeding on Southeast Farallon Island in California (USA). Light level data were combined with a movement model to estimate positions of tagged animals, revealing that individuals from this population undertook a coordinated coastal migration north in the fall, stopping at sites near Haida Gwaii in British Columbia (Canada), presumably during a flightless prebasic molt, before continuing north to stationary overwintering sites in coastal British Columbia and Southeast Alaska. Birds then made an uninterrupted migration south in the spring, returning to waters around Southeast Farallon in late March and early April. Wet/dry data indicated nocturnal resting on land during the breeding season and likely on the water throughout the non-breeding months. This is the first study to confirm the migratory patterns of pigeon guillemots from California, and highlights the importance of the waters of British Columbia and Southeast Alaska for the studied population and possibly other major populations of this species.

Ocean-influenced estuarine habitat buffers high interannual variation in seabird reproductive success

Seabirds in more variable habitats generally live longer and more readily forgo or reduce breeding investments in poor resource seasons to maximize their overall lifetime fitness. Their breeding success is dependent on factors including diet, prey availability, and proximity to foraging habitat. Furthermore, seabird colonies in upwelling ecosystems are subject to interannual variation in oceanic conditions that drive bottom-up processes. Adjacent estuarine ecosystems, while less affected by upwelling, are also influenced by freshwater input and may experience less interannual variation in seabird prey resources. Here, we compare the breeding ecology and diet of pigeon guillemots Cepphus columba from an estuarine colony (Alcatraz Island, California) and an isolated offshore colony (Southeast Farallon Island, California) from 2015 to 2017 to understand how habitat location and surrounding environment differentially influence diet and reproduction. Breeding phenology in pigeon guillemots was similar between colonies, but reproductive success was higher and more stable at the estuarine site than at the offshore colony, where productivity was explained primarily by ocean conditions. Interannual and estuarine/offshore variability in chick diet composition was partially explained by upwelling and the influence of freshwater inputs. Variation in offshore pigeon guillemot productivity was related to the prey species composition. With increasingly variable conditions offshore in the California Current, the availability of alternative estuarine and nearshore breeding sites inshore may become increasingly important for the regional pigeon guillemot population and other seabirds capable of exploiting nearshore prey resources.

Modeling changes in baleen whale seasonal abundance, timing of migration, and environmental variables to explain the sudden rise in entanglements in California.

We document changes in the number of sightings and timing of humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), and gray (Eschrichtius robustus) whale migratory phases in the vicinity of the Farallon Islands, California. We hypothesized that changes in the timing of migration off central California were driven by local oceanography, regional upwelling, and basin-scale climate conditions. Using 24 years of daily whale counts collected from Southeast Farallon Island, we developed negative binomial regression models to evaluate trends in local whale sightings over time. We then used linear models to assess trends in the timing of migration, and to identify potential environmental drivers. These drivers included local, regional and basin-scale patterns; the latter included the El Niño Southern Oscillation, the Pacific Decadal Oscillation, and the North Pacific Gyre Oscillation, which influence, wind-driven upwelling, and overall productivity in the California Current System. We then created a forecast model to predict the timing of migration. Humpback whale sightings significantly increased over the study period, but blue and gray whale counts did not, though there was variability across the time series. Date of breeding migration (departure) for all species showed little to no change, whereas date of migration towards feeding areas (arrival) occurred earlier for humpback and blue whales. Timing was significantly influenced by a mix of local oceanography, regional, and basin-scale climate variables. Earlier arrival time without concomitant earlier departure time results in longer periods when blue and humpback whales are at risk of entanglement in the Gulf of the Farallones. We maintain that these changes have increased whale exposure to pot and trap fishery gear off the central California coast during the spring, elevating the risk of entanglements. Humpback entanglement rates were significantly associated with increased counts and early arrival in central California. Actions to decrease the temporal overlap between whales and pot/trap fishing gear, particularly when whales arrive earlier in warm water years, would likely decrease the risk of entanglements.

Projecting long‐term impacts of a mortality event on vertebrates: incorporating stochasticity in population assessment

AbstractWildlife managers must be able to assess the long‐term, population‐wide impacts of mortality events on long lived vertebrates, taking into account the stochastic nature of population fluctuations. Here, we present a case study of the potential impacts on Western gulls (Larus occidentalis) of a single, non‐target mortality event, potentially resulting from exposure to rodenticide directed at eradicating house mice (Mus musculus) on the Farallon Islands National Wildlife Refuge. Firstly, we conducted a population viability analysis based on over 25 yr of Farallon Western gull demographic data to model future population trends under varying environmental conditions. Future population trends for Farallon Western gulls, independent of any potential mouse eradication‐related mortality, depend on the frequency of years with near‐failure in reproductive success, as was observed in 2009, 2010, and 2011. We modeled population trends under three environmental scenarios defined by the probability of near‐failure in future breeding: optimistic (probability of near‐failure = 0.0), realistic (probability = 0.115), or pessimistic (probability = 0.25). Secondly, we determined the maximum level of additional mortality,C, that would result in a population outcome distribution that cannot be effectively distinguished from a no additional mortality scenario after 20 yr (defined as 95% overlap in the two frequency distributions). We determined the threshold of detection to be an additional mortality of 3.3% beyond normally observed levels under the realistic scenario, 2.8% under the optimistic scenario, and 4.2% under the pessimistic scenario. Results demonstrate that the greater the background stochasticity, the greaterCmust be to be able to discriminate a long‐term effect of the mortality event against the backdrop of environmental variability. We demonstrate that incorporation of stochasticity is critical for evaluating one‐time mortality events given the high degree of variability characterizing many ecosystems; deterministic projections alone may provide poor guidance. While the need to account for stochasticity in Population Viability Analysis models is well established, this study is innovative in addressing how to evaluate a future or retrospective one‐time mortality event in the context of stochasticity. Our approach can help resource managers' plan for both best‐case and worst‐case scenarios when evaluating impacts of mortality events.

Using habitat risk assessment to assess disturbance from maritime activities to inform seabird conservation in a coastal marine ecosystem

Habitat prioritization is a powerful tool for identifying critical wildlife areas for conservation. This study evaluates the risk of disturbance from maritime activities to seabirds in order to prioritize critical seabird foraging habitat for conservation thereby providing a much-needed methodological contribution demonstrating how to transparently incorporate metrics of “cost” based on risk to support ocean zoning. We standardized and combined predicted seabird distributions for six nonresident species foraging in the non-coastal “offshore” waters in the Greater Farallones National Marine Sanctuary and Cordell Bank National Marine Sanctuary, which we predicted using ten years of Applied California Current Ecosystem Studies (ACCESS) at-sea data for the month of July. We obtained maritime activity data from the California Ocean Use Atlas, whale-watching data, expert consultation, and primary literature. Activities included benthic fishing with fixed and mobile gear, military operations, oil spill, shipping, and whale-watching. Risk calculations were based on management effectiveness, spatial and temporal overlap of activities with seabird distributions, changes in area, and severity of negative impacts. Of those activities evaluated with the InVEST Habitat Risk Assessment (HRA) model, higher risk activities were oil spill, benthic fishing with fixed or mobile gear, and military activities. Looking at all risks spatially, highest cumulative risk areas concentrated to the north and northeast of Cordell Bank, along segments of the shelf break, and along areas of the shipping lanes. We demonstrated the use of the HRA tool to quantify costs for use in Marxan habitat prioritization software. The HRA model provided a transparent and replicable cost metric that partitioned risk into exposure and consequence. This approach provided two options for meeting high priority seabird foraging protection goals in the Sanctuaries: 1) protecting the low cost Marxan-prioritized areas or 2) managing high risk maritime activities highlighted by the HRA model. Waters around the Farallon Islands, nearby and northeast of Cordell Bank, and to the southwest of the continental shelf break in the southern region of Greater Farallones National Marine Sanctuary were identified as areas where seabirds would benefit from a combination of adding protections to some low cost Marxan-prioritized areas and enhancing management of the primary disturbance resulting from higher risk activities of oil spill, benthic fishing with mobile or fixed gear, and military activities, each of which have spatial footprints contributing to high cost Marxan prioritized areas. Either approach could be scaled up to include a larger habitat area, multiple habitat types, and different maritime activities. Our methods can be applied globally to improve ocean zoning where critical wildlife areas are threatened by human activities.

Cassin's Auklet (Ptychoramphus aleuticus) Population Size, Reproduction, and Habitat Management on a Recently Colonized Island in California, USA

Responses to climate change by seabirds in the North Pacific may include range restrictions and require colonizing new habitats. To inform conservation actions supporting climate adaptations, we examined the colonization of Ano Nuevo Island, a nearshore island in central California, by Cassin's Auklets (Ptychoramphus aleuticus). We quantified population growth, reproduction, band returns, mortality, and habitat metrics from 1995-2017 and described habitat management that facilitated colony persistence. Cassin's Auklet breeding population grew to 136 birds by 2014, despite population declines during 2005-2007 and 2016-2017 concurrent with reproductive failures and die-offs that affected Cassin's Auklets regionally. Annual productivity of this small colony was similar to larger populations in the region at 0.72 ± 0.23 SD chicks fledged per pair from 1999-2017 (n = 15 years). Band returns indicated population connectivity with the Farallon Islands, California. Annual rates of burrow damage were 14 ± 8%, with up to 30% damaged a year. Habitat management to prevent erosion damage to nesting burrows included sea lion exclusion, erosion control, and ceramic artificial burrows. Describing conditions that facilitated the colonization and growth of this Cassin's Auklet breeding site can inform actions that support other locations and multiple burrowing seabird species.

Oceanographic drivers of winter habitat use in Cassin's Auklets.

Reduced prey abundance and severe weather can lead to a greater risk of mortality for seabirds during the non-breeding winter months. Resource patterns in some regions are shifting and becoming more variable in relation to past conditions, potentially further impacting survival and carryover to the breeding season. As animal tracking technologies and methods to analyze movement data have advanced, it has become increasingly feasible to draw fine-scale inference about how environmental variation affects foraging behavior and habitat use of seabirds during this critical period. Here, we used archival light-sensing tags to evaluate how interannual variation in oceanography affected the winter distribution of Cassin's Auklets from Southeast Farallon Island, California. Thirty-five out of 93 geolocators deployed from 2015 to 2017 were recovered and successfully recorded light-level data, from which geographic positions were estimated. Step-selection functions were applied to identify environmental covariates that best explained winter movement decisions and habitat use, revealing Cassin's Auklets dispersed farther from the colony during a winter with warm SST anomalies, but remained more centralized near the breeding colony during two average winters. Movement patterns were driven by avoidance of areas with higher sea surface temperatures and possible limits of dispersal from the breeding colony, and selection for areas with well-defined mesoscale fronts and cooler surface waters. Through multiple years of tagging and the application of step-selection functions, a robust and widely applied approach for analyzing animal movement in terrestrial species, we show how interannual differences in the movement patterns of a small seabird are driven by oceanographic variability across years. Understanding the winter habitat use of seabirds can help inform changes in population structure and measures of reproductive success, aiding managers in determining potential causes of breeding failures.

Impact of satellite linked radio transmitting (SLRT) tags on the dorsal fin of subadult and adult white sharks (Carcharodon carcharias)

Satellite linked radio transmitting (SLRT) tags provide long-term, high accuracy, near real-time tracking data for marine wildlife. Adult white sharks (Carcharodon carcharias Linnaeus, 1758) in the northeastern Pacific at both Guadalupe Island, Mexico and Southeast Farallon Island, USA were tagged with SLRT oval and inline finmout tags. These tags provided up to 7.4 yrs of tracking data. A previous study showed structural dorsal fin damage for SLRT tagged juvenile and subadult white sharks off South Africa. Sharks tagged in the northeastern Pacific were resighted between 1 and 11 yrs post tagging and included 10 adults and 2 subadults. Sharks that were resighted did not exhibit significant fin deformation, although in one case the oval finmount tag did cause bending of the dorsal fin due to tag shape, weight, and placement of the tag on the dorsal fin. Four inline tags came off after deployments of at least 2.2 to 3.7 yrs (based on date of last message received), and two of these caused a tear to the trailing edge of the dorsal fin upon release. Overall, SLRT tags provided long-term tracking data and there was no apparent impact on the behavior or migration cycles of the sharks. Serious dorsal fin deformation seems to occur in the case of juvenile and subadult white sharks where the fin is rapidly growing and thus for tracking juvenile white sharks, alternate methods should be considered.

Evaluating population impacts of predation by owls on storm petrels in relation to proposed island mouse eradication

AbstractWe quantify the expected demographic benefit to a seabird of conservation concern, the ashy storm‐petrel Oceanodroma homochroa, from the proposed eradication of introduced house mice Mus musculus on the South Farallon Islands, California. A key objective of the eradication is to reduce storm petrel predation by burrowing owls Athene cunicularia, which stopover on the island during their fall migration. Mouse trapping and field surveys of both owls and depredated storm petrel carcasses conducted during 2000–2012 reveal a strongly seasonal, inter‐related pattern among the three species: When owls arrive during the fall, mice are super‐abundant and the overwhelming choice of prey for those owls that remain. In the winter, the mouse population crashes just as storm petrels begin to arrive in large numbers; owls that remain on the island switch to preying upon storm petrels until May, when they depart to breed. Capture–recapture analyses of storm petrels showed (1) annual adult survival was inversely related to owl abundance, especially during January–April, and (2) storm petrels demonstrated a declining trend in abundance 2006–2012. The latter was associated with low rates of adult survival, high abundance of overwintering burrowing owls, and high incidence of depredated storm petrels. To evaluate projected impacts to storm petrels of a change in owl predation, we developed a Leslie matrix model, incorporating environmental stochasticity. We modeled future storm petrel population trajectories, allowing for different levels of owl‐mediated predation. Our results suggest that a reduction in owl abundance, a projected consequence of the elimination of mice, has the potential to substantially reduce overall storm petrel mortality, thereby reducing storm petrel declines and increasing the likelihood of stable trends in the future. While long‐term benefits to storm petrels of mouse eradication are apparent, the risk of increased predation due to prey‐switching by owls also needs to be addressed. This study highlights uncertainty of outcomes, which must be considered in evaluating management impacts. This study demonstrates the value of concurrent, continuous, long‐term datasets in providing a quantitative basis for management to aid the conservation of species of concern.

Seventy Years of Archaeological Research on California’s Farallon Islands

ABSTRACTThe Farallon Islands are a cluster of small islands ∼32 km off the coast of San Francisco Bay. These islands total < 1 km2 in area and lack surface freshwater, but are home to scores of breeding seabirds and seals and sea lions. At least three archaeological projects have been conducted on Southeast Farallon, focusing on the islands’ two known archaeological sites (CA-SFR-1 and CA-SFR-24), both primarily related to an early nineteenth century Russian fur trade hunting camp with no evidence of prehistoric human occupation. Little has been published on these expeditions despite their implications for understanding colonialism and culture contact, historical ecology, and the history of San Francisco. We synthesize the history of archaeological research on the Farallon Islands. We discuss the artifacts and faunal remains recovered from these projects, the state of the collections, and how these data articulate with broader California archaeology and the archaeology of small islands.

Killer whales redistribute white shark foraging pressure on seals

Predatory behavior and top-down effects in marine ecosystems are well-described, however, intraguild interactions among co-occurring marine top predators remain less understood, but can have far reaching ecological implications. Killer whales and white sharks are prominent upper trophic level predators with highly-overlapping niches, yet their ecological interactions and subsequent effects have remained obscure. Using long-term electronic tagging and survey data we reveal rare and cryptic interactions between these predators at a shared foraging site, Southeast Farallon Island (SEFI). In multiple instances, brief visits from killer whales displaced white sharks from SEFI, disrupting shark feeding behavior for extended periods at this aggregation site. As a result, annual predations of pinnipeds by white sharks at SEFI were negatively correlated with close encounters with killer whales. Tagged white sharks relocated to other aggregation sites, creating detectable increases in white shark density at Ano Nuevo Island. This work highlights the importance of risk effects and intraguild relationships among top ocean predators and the value of long-term data sets revealing these consequential, albeit infrequent, ecological interactions.