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At least 37 records · Page 2Linked to original sources
USGS2022

Modeling of historical and current distributions of lone star tick, Amblyomma americanum (Acari: Ixodidae), is consistent with ancestral range recovery

The lone star tick, Amblyomma americanum L., is a three-host hard tick notorious for aggressive feeding behavior. In the early to mid-20th century, this species’ range was mostly limited to the southern USA. Since the 1950s, A. americanum has been detected in many new localities in the western, northcentral, and northeastern regions of the country. To examine the influence of climate on this apparent expansion, we used historical (1748–1950) lone star locations from the literature and museum records to model areas suitable for this species based on past environmental conditions in the late 1800s – early 1900s. We then projected this model forward using present (2011–2020) climatic conditions and compared the two for evidence of climate-associated distributional shifts. A maximum entropy distribution or Maxent model was generated by using a priori selected climatic variables including temperature, precipitation, and vapor pressure deficit. Temperature and vapor pressure deficit were selected as the most important factors in creating a sensitive and specific model (success rate = 82.6 ± 6.1%) that had a good fit to the existing data and was significantly better than a random model [partial ROC (receiver operating characteristic) to AUC (area under the ROC curve) ratio = 1.97 ± 0.07, P < 0.001]. The present projected model was tested with an independent dataset of curated museum records (1952–2020) and found to be 95.6% accurate. Comparison of past and present models revealed > 98% A. americanum niche overlap. The model suggests that some areas along the western fringe are becoming less suitable for A. americanum , whereas areas in some Great Lakes and coastal northeastern regions are becoming more suitable, results that are compatible with possible effects of climate change. However, these changes are minor, and overall climate in North America does not appear to have changed in ways significant to A. americanum ’s distribution. These findings are consistent with an alternative hypothesis that recent changes in A. americanum ’s distribution are a result of this species re-occupying its historical range, driven predominantly by factors other than climate, such as shifts in land use and population densities of major hosts.

Experimental and Applied Acarology↗
USGS2004

Red imported fire ant impacts on wildlife: A decade of research

The negative impacts of biological invasion are economically and ecologically significant and, while incompletely quantified, they are clearly substantial. Ants (family Formicidae) are an important, although often overlooked, component of many terrestrial ecosystems. Six species of ants are especially striking in their global ability to invade, and their impacts. This paper focuses on the impacts of the most destructive of those species, the red imported fire ant ( Solenopsis invicta ), and focuses on impacts on native vertebrates. Red imported fire ants often become the dominant ant species in infested areas outside of their native range due to their aggressive foraging behavior, high reproductive capability and lack of predators and/or other strong competitors. The evidence suggests that mammals, birds and herpetofauna are vulnerable to negative impacts from fire ants, and some species are more likely to experience negative population-level impacts than other species. Assessing the ecological impacts of fire ants on wild animal populations is logistically difficult, and very few studies have combined replicated experimental manipulation with adequate spatial (>10 ha) and temporal (>1 y) scale. Thus, most studies have been observational, opportunistic, small-scale or 'natural' experiments. However, significant research, including an increase in experimental and mechanistic investigations, has occurred during the past decade, and this has led to information that can lead to better management of potentially affected species.

American Midland Naturalist↗
USGS2017

Sexually dimorphic aggression indicates male gray wolves specialize in pack defense against conspecific groups

Aggression directed at conspecific groups is common among gregarious, territorial species, and for some species such as gray wolves ( Canis lupus ) intraspecific strife is the leading cause of natural mortality. Each individual in a group likely has different measures of the costs and benefits associated with a group task, such as an aggressive attack on another group, which can alter motivation and behavior. We observed 292 inter-pack aggressive interactions in Yellowstone National Park between 1 April 1995 and 1 April 2011 (>5300 days of observation) in order to determine the role of both sexes, and the influence of pack, age, and other traits on aggression. We recorded the behaviors and characteristics of all individuals present during the interactions (n = 534 individuals) and which individuals participated in each step (i.e. chase, attack, kill, flight) of the interaction. Overall, all wolves were more likely to chase rivals if they outnumbered their opponent, suggesting packs accurately assess their opponent’s size during encounters and individuals adjust their behavior based on relative pack size. Males were more likely than females to chase rival packs and gray-colored wolves were more aggressive than black-colored wolves. Male wolves and gray-colored wolves also recorded higher cortisol levels than females and black-colored wolves, indicating hormonal support for more intense aggressive behavior. Further, we found a positive correlation between male age and probability of chasing, while age-specific participation for females remained constant. Chasing behavior was influenced by the sex of lone intruders, with males more likely to chase male intruders. This difference in behavior suggests male and female wolves may have different strategies and motivations during inter-pack aggressive interactions related to gray wolf mating systems. A division of labor between pack members concerning resource and territory defense suggests selection for specific traits related to aggression is an adaptive response to intense competition between groups of conspecifics.

Behavioural Processes↗
USGS2022

Social effects of rabies infection in male vampire bats (Desmodus rotundus)

Rabies virus (RABV) transmitted by the common vampire bat ( Desmodus rotundus ) poses a threat to agricultural development and public health throughout the Neotropics. The ecology and evolution of rabies host-pathogen dynamics are influenced by two infection-induced behavioral changes. RABV-infected hosts often exhibit increased aggression which facilitates transmission, and rabies also leads to reduced activity and paralysis prior to death. Although several studies document rabies-induced behavioral changes in rodents and other dead-end hosts, surprisingly few studies have measured these changes in vampire bats, the key natural reservoir throughout Latin America. Here, we take advantage of an experiment designed to test the safety and efficacy of an oral rabies vaccine in captive male vampire bats to quantify for the first time how rabies affects allogrooming and aggressive behaviors in the vampire bat. Compared to non-rabid vampire bats, rabid individuals reduced their allogrooming prior to death, but we did not detect increases in aggression among bats. To put our results in context, we review what is known and what remains unclear about behavioral changes of rabid vampire bats.

Biology Letters↗
USGS2015

Agonistic behavior among three stocked trout species in a novel reservoir fish community

The popularity of reservoirs to support sport fisheries has led to the stocking of species that did not co-evolve, creating novel reservoir fish communities. In Utah, the Bear Lake strain of Bonneville Cutthroat Trout Oncorhynchus clarkii utah and tiger trout (female Brown Trout Salmo trutta &times; male Brook Trout Salvelinus fontinalis ) are being more frequently added to a traditional stocking regimen consisting primarily of Rainbow Trout O. mykiss . Interactions between these three predatory species are not well understood, and studies evaluating community interactions have raised concern for an overall decrease of trout condition. To evaluate the potential for negative interactions among these species, we tested aggression in laboratory aquaria using three-species and pairwise combinations at three densities. Treatments were replicated before and after feeding. During the three-species trials Rainbow Trout initiated 24.8 times more aggressive interactions than Cutthroat Trout and 10.2 times more aggressive interactions than tiger trout, and tiger trout exhibited slightly (1.9 times) more aggressive initiations than Cutthroat Trout. There was no significant difference in behavior before versus after feeding for any species, and no indication of increased aggression at higher densities. Although Rainbow Trout in aquaria may benefit from their bold, aggressive behavior, given observations of decreased relative survival in the field, these benefits may be outweighed in reservoirs, possibly through unnecessary energy expenditure and exposure to predators.

North American Journal of Fisheries Management↗
USGS2003

Rare male aggression directed toward females in a female-dominated society: Baiting behavior in the spotted hyena

Spotted hyenas ( Crocuta crocuta ) are gregarious carnivores. The females are socially dominant to males, and adult males rarely direct aggression toward adult females. This study analyzed all cases in which adult immigrant males behaved aggressively toward adult females in a large population of free-living hyenas in Kenya, observed for 11 years. Our goals were to describe the conditions under which male attacks on females occur, and address possible adaptive functions. Most aggression directed by adult immigrant males against females occurred when coalitions of two or more males attacked a single adult female, who typically responded by defending herself and fighting back. Male aggression against females frequently occurred at sites of ungulate kills, but males never behaved aggressively toward females over food, and all male attacks on females were unprovoked. Although no mounting or other copulatory behaviors ever occurred during or immediately after an attack, the number of male attacks on females peaked around the time of conception. Daily rates at which males attacked females did not vary with female social rank. However, daily attack rates did vary significantly with female reproductive state, and the highest rates of male attack on females were observed during the two stages of the reproductive cycle during which females were most likely to conceive litters. The adaptive significance of male aggression against females in this species remains unknown, but a tight association between male attacks on females and a female's time of conception provides strong evidence of some role for male aggression in hyena sexual behavior. In particular, our data are consistent with hypotheses suggesting that male aggression toward females in this species either serves to inform females about male fitness or represents sexual harassment.

Aggressive Behavior↗
USGS2022

Mississippi Kite nest defense: Is there an influence of nest phenology or human activity?

Birds that have adapted to urban landscapes often display changes in their behavioral responses to human disturbance. This habituation may result in a decreased wariness and secrecy near their nest and an increased inclination to engage in aggressive nest defenses. Aggressive defense of nests has been noted among Mississippi Kites ( Ictinia mississippiensis ), a raptor that has become a common and abundant urban nesting species across the Southern Great Plains. Defensive behaviors include swoops at, and occasional physical contact with, humans who venture close to nests. Previous research found aggressive responses by kites in 16–20% of experimental passes under nests. However, the type of human pedestrian activity around nests may influence the occurrence of aggressive responses. We assessed adult Mississippi Kite responses to experimental nest area intrusions during each week of the first four weeks of nestling development to explore increases or attenuation of aggressive behaviors. We also assessed responses in context of three types of pedestrian passes to nests. We conducted 84 trials consisting of 252 passes and found 90% elicited no response from the attending kite, 8% elicited a flight response, and 2% elicited an attack. There was no difference in response to pass type, but we found evidence that responsiveness may be associated with nestling age. Our results suggest aggression by Mississippi Kites is uncommon, but infrequent events that gain local attention may increase the perceived risk from the species due to the availability heuristic. Additionally, individual nesting pairs may tend toward aggression and become persistent nuisance birds that gain attention but are not representative of the majority of nesting pairs.

Journal of Raptor Research↗
USGS1998

Attraction of brown bears to red pepper spray deterrent: Caveats for use

Humans in brown bear ( Ursus arctos ) country may unexpectedly encounter hears with sometimes harmful consequences. Firearms may be an effective defense, but they destroy bears, their use is illegal in most national parks, and many people prefer not to carry them, Consequently, nonlethal bear deterrents have long been sought as a means of self-defense against bear attacks. In the 1970s a liquid spray containing oleoresin capsicum (the chief irritant in red peppers) was developed. This mixture could be defensively discharged at aggressive bears (Herrero and Higgins 1995), and today, several commercially manufactured products, generically called "red pepper spray," are sold for the purpose of deterring aggressive bear attacks. Many hikers, campers, and outdoor enthusiasts carry this spray for self-defense in bear country Additionally, some states (eg, Wyoming) and many national parks (e.g., Glacier National Park) highly recommend that back-country users carry red pepper spray for use in an aggressive beat encounter. Herrero and Higgins (1998) found that red pepper spray was effective in halting aggressive brown bear behavior in 88% (1 of 16) of incidents studied. However, red pepper spray is not claimed to be a bear repellent when applied to objects. Nonetheless, instances have been reported of people applying red pepper spray to objects and around campsites in order to repel curious bears. The impetus for this study came from an observation I made of a bear rolling vigorously on beach gravels that had been accidentally sprayed with red pepper spray. To further investigate brown bear reaction to red pepper spray residues, I conducted systematic observations of bear responses to spray discharged at selected sites. I discuss those findings and their implications in this report.

Alaska↗
USGS2008

Differences in aggression, activity and boldness between native and introduced populations of an invasive crayfish

Aggressiveness, along with foraging voracity and boldness, are key behavioral mechanisms underlying the competitive displacement and invasion success of exotic species. However, do aggressiveness, voracity and boldness of the invader depend on the presence of an ecologically similar native competitor in the invaded community? We conducted four behavioral assays to compare aggression, foraging voracity, threat response and boldness to forage under predation risk of multiple populations of exotic signal crayfish Pacifastacus leniusculus across its native and invaded range with and without a native congener, the Shasta crayfish P. fortis. We predicted that signal crayfish from the invaded range and sympatric with a native congener (IRS) should be more aggressive to outcompete a close competitor than populations from the native range (NR) or invaded range and allopatric to a native congener (IRA). Furthermore, we predicted that IRS populations of signal crayfish should be more voracious, but less bold to forage under predation risk since native predators and prey likely possess appropriate behavioral responses to the invader. Contrary to our predictions, results indicated that IRA signal crayfish were more aggressive towards conspecifics and more voracious and active foragers, yet also bolder to forage under predation risk in comparison to NR and IRS populations, which did not differ in behavior. Higher aggression/voracity/ boldness was positively correlated with prey consumption rates, and hence potential impacts on prey. We suggest that the positive correlations between aggression/voracity/boldness are the result of an overall aggression syndrome. Results of stream surveys indicated that IRA streams have significantly lower prey biomass than in IRS streams, which may drive invading signal crayfish to be more aggressive/voracious/bold to acquire resources to establish a population. ?? 2008 The Authors.

Oikos↗
USGS2010

Aggressive interactions between the invasive Rio Grande cichlid (Herichthys cyanoguttatus) and native bluegill (Lepomis macrochirus), with notes on redspotted sunfish (Lepomis miniatus)

The Rio Grande cichlid (Herichthys cyanoguttatus) has been established in the Greater New Orleans Metropolitan area for at least 20 years, and its effect on native fishes is unknown. Behavioral trials were performed to determine if aggressive interactions occur between invasive H. cyanoguttatus and native bluegill (Lepomis macrochirus). When defending a territory as the resident, L. macrochirus were markedly aggressive, averaging 11.6 aggressive actions per lO-min behavioral trial. In contrast, L. macrochirus were extremely passive as invaders, with 0.5 aggressive actions per trial. Herichthys cyanoguttatus were equally aggressive as residents and as invaders, averaging 4.9 and 6.0 aggressive actions per trial, respectively. Herichthys cyanoguttatus interacted aggressively with native species whether they held territory or not, indicating that this invasive species may have fundamentally different strategies of aggression compared with native L. macrochirus. These differences may explain the continued success of H. cyanoguttatus as an invasive fish in southeastern Louisiana.

Journal of Ethology↗
USGS2008

Environmental enrichment in steelhead (Oncorhynchus mykiss) hatcheries: Field evaluation of aggression, foraging, and territoriality in natural and hatchery fry

Reforms for salmonid hatcheries include production of hatchery fish with behavioral characteristics similar to wild conspecifics. Enrichment of the hatchery environment has been proposed to achieve this goal. Field experiments of steelhead (i.e., sea-run rainbow trout, Oncorhynchus mykiss) fry from a common stock reared under natural (i.e., stream), enriched hatchery, and conventional hatchery conditions indicated no significant differences in the rates of foraging or aggression between rearing treatments. However, the rates of foraging and aggression of natural fry were significantly affected by the type of hatchery fry stocked with them. Natural steelhead fry fed at lower rates and exhibited higher rates of aggression when stocked with steelhead fry raised in enriched hatchery environments. Territory sizes of steelhead fry ranged from 0.015 to 0.801 m2; were significantly, positively related to body length; and were not significantly different between rearing treatments. We conclude that hatchery steelhead fry released into streams establish territories that are proportional to their body length and similar in size to territories of natural steelhead fry. Our results indicate that both conventional and enriched hatchery environments produce natural social behaviors in steelhead released as fry and that fry from enriched hatchery environments may alter the foraging and aggressive behavior of natural, resident steelhead fry. ?? 2008 NRC.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2020

Black bear movement and food conditioning in an exurban landscape

Conflicts between humans and wildlife have become increasingly important challenges for resource managers along the urban‐wildland interface. Food conditioning (i.e., reliance by an animal on anthropogenic foods) of American black bears (Ursus americanus ) is related to conflict behavior (i.e., being bold or aggressive toward humans, consuming human food or garbage, causing property damage) and often occurs in communities adjacent to Great Smoky Mountains National Park (GRSM or Park), USA. The goal of our study was to evaluate black bear space use in GRSM and in exurban areas on surrounding private lands and to identify factors associated with food conditioning and conflict behavior. We radio‐collared 53 bears (29 males, 24 females) from 2015 to 2017 to compare space use characteristics and used carbon isotopic signatures (δ13C) from bear hair to assess food conditioning. We then performed an integrated step selection function (iSSF) analysis to characterize and compare movement and resource use as related to food conditioning. Based on the stable isotope analyses, 24 bears were classified as food conditioned (FC; 16 males and 8 females) and 37 were not food conditioned (NFC; 14 males and 23 females). Annual 95% kernel density estimate (KDE) home ranges and 50% KDE core area estimates of female and male bears did not differ by level of food conditioning (i.e., mean δ13C), but 95% and 50% home ranges of FC females were smaller than NFC females when data from 2015, a year of food scarcity and abnormally large home ranges, were excluded. The mean proportion of exurban development (e.g., roads, buildings, openings) within 95% KDE and 50% KDE home ranges of females increased with mean δ13C (i.e., greater food conditioning). The iSSF models indicated that FC bears were more likely to use forest openings associated with higher levels of development than NFC bears. We used those models to demonstrate how landscape modifications can reduce bear use of exurban areas, particularly for NFC bears. Our stable isotope, movement, and resource use data indicate that conflict behaviors displayed by many bears within GRSM were learned in areas outside Park boundaries. © 2020 The Wildlife Society.

Tennessee, North Carolina↗
USGS1999

Use of behavioral endpoints to determine protective concentrations of the insecticide fonofos for bluegill (Lepomis macrochirus)

This research compared the results of laboratory and mesocosm studies to determine the effectiveness of using behavioral measures of sublethal exposure to define environmental concentration ranges that are protective of free-ranging populations of bluegill (Lepomis macrochirus) exposed to the organophophate insecticide fonofos. Thirty-day laboratory chronic studies were conducted to determine the relative sensitivity of standard (e.g. survival and growth) and non-standard behavioral (e.g. swimming capacity, feeding efficiency, and aggression) endpoints in predicting concentrations of fonofos protective of bluegill growth and survival. The lowest observable effect concentration (LOECs) for the standard measures of survival and growth was 5.6 ??g/L. Two behavioral endpoints were of similar sensitivity to the standard measures: swimming capacity, LOEC of 5.6 ??g/L; and prey strike frequency, LOEC of 5.6 ??g/L. However, aggressive interactions were ten-fold more sensitive than swimming or feeding behavior with a LOEC occurring at 0.6 ??g/L. Lab results were compared to an aquatic mesocosm study which exposed adult and juvenile bluegill to a 9.41 ??g/L concentration of fonofos. The dissipation half-life of fonofos was 5 days in 0.1 hectare aquatic mesocosms. Significant mortality among caged bluegill occurred within 4 days of exposure at 9.41 ??g/L. However, the 9.41 ??g/L concentration of fonofos had no statistically significant effects on survival, growth, reproduction, or total biomass of free-ranging populations of bluegill. We conclude from these studies that laboratory data can accurately estimate concentrations that are lethal in the field and that the use of behavioral endpoints can provide ecologically relevant, yet conservative estimates of concentrations that are protective of field populations.

Conference Paper↗
USGS2018

Canid vs. canid: Insights into coyote–dog encounters from social media

While the relationship between coyotes ( Canis latrans ) and house cats ( Felis catus ) may be characterized as one between predators and their prey, coyote interactions with domestic dogs ( C. lupus familiaris ) appear to be more varied and may include behaviors associated with canid sociality. While encounters between coyotes and dogs are difficult to observe, we capitalized on publicly available video recordings of coyote-dog encounters to observe canid behaviors and examined 35 video clips downloaded from YouTube during fall 2014. We identified coyote-dog interactions that were playful, agonistic, or predatory; those that we could not clearly categorize were labeled as other/undetermined. We found that both species were recorded directing play to the other species, which led to mutual play bouts. We observed a similar number of agonistic encounters, which included dogs biting coyotes and coyotes biting dogs. The main difference in agonistic behavior was that coyotes usually showed defensive aggression while dogs did not show defensive aggression. We also observed coyotes ambushing and bite-shaking small dogs in 3 video clips, from which the dogs escaped, but we did not see predatory behavior of dogs towards coyotes. Dog size may be related to types of interactions. No small dogs were involved in agonistic interactions, and only 1 small dog was observed playing with a coyote. From these videos, we conclude that the relationship between coyotes and dogs cannot be simply described as predator-prey; indeed, much of it appears to be social behavior divided between playful and agonistic. Future work that aims to explain the proximate correlates of play and aggression would provide more information for managers who wish to educate humans to reduce wildlife-human-dog conflicts.

Human-Wildlife Interactions↗
USGS2014

Aggression and coexistence in female caribou

Female caribou ( Rangifer tarandus ) are highly gregarious, yet there has been little study of the behavioral mechanisms that foster coexistence. Quantifying patterns of aggression between male and female, particularly in the only cervid taxa where both sexes grow antlers, should provide insight into these mechanisms. We asked if patterns of aggression by male and female caribou followed the pattern typically noted in other polygynous cervids, in which males display higher frequencies and intensity of aggression. From June to August in 2011 and 2012, we measured the frequency and intensity of aggression across a range of group sizes through focal animal sampling of 170 caribou (64 males and 106 females) on Adak Island in the Aleutian Archipelago, Alaska. Males in same-sex and mixed-sex groups and females in mixed-sex groups had higher frequencies of aggression than females in same-sex groups. Group size did not influence frequency of aggression. Males displayed more intense aggression than females. Frequent aggression in mixed-sex groups probably reflects lower tolerance of males for animals in close proximity. Female caribou were less aggressive and more gregarious than males, as in other polygynous cervid species.

Alaska↗
USGS2002

Effects of Photoperiod on Behavior and Courtship of the Neosho madtom (Noturus placidus)

To test effects of long and short day-length on behavior of the Neosho madtom ( Noturus placidus ), we held six pairs of fish in separate tanks under 16 hr (L): 8 hr (D) (long-day) and six pairs under 12 hr (L): 12 hr (D) (short-day) photoperiods. An ethogram was created and behavior was electronically and continuously recorded. Two-minute intervals for each hour over four 4-day periods were examined, and proportion of time active and performing specific behaviors in each tank was analyzed to compare differences between treatments. Individuals held under 16 L, 8 D were more active during the light cycle than those in 12 L, 12 D. Specific behaviors examined included resting, swimming, feeding, aggression, cavity enhancement, and courtship. A higher proportion of time was spent performing cavity enhancement, cavities were deeper, and gravel size in cavities was smaller for those fish in the long-day treatment. Throughout the experiment various courtship behaviors were observed in male-female pairs held in 16 L, 8 D, but no such behaviors were observed in 12L, 12D. The relationships between a long photoperiod and activity, cavity enhancement, and courtship behaviors illustrate the influence of photoperiod on the Neosho madtom reproductive cycle.

Journal of Freshwater Ecology↗
USGS1998

Outcome of aggressive interactions between American black ducks and mallards during the breeding season

American black duck (Anas rubripes) numbers have declined during the past several decades, while mallards (A. platyrhynchos) have expanded their range eastward. Competitive exclusion of black ducks from wetlands by mallards has been proposed as a principal cause of the decline. We studied a sympatric population of black ducks and mallards in Maine during the early breeding season to document behavior and interactions. We observed 832 aggressive interactions; most (72%) were interspecific. When a choice was available, both species interacted more often with conspecifics than with the other species (P < 0.028). On wetlands occupied simultaneously by both species, numbers of intraspecific interactions initiated by each species were similar (P = 0.470). The proportions of won (initiator displaces recipient of attack), lost (initiator displaced), and "no change" outcomes of these interactions were different (P < 0.001). When black ducks initiated interactions with mallards, black ducks did not lose any interactions and displaced mallards 87.2% of the time; no change occurred during 12.8% of the interactions. When mallards initiated interactions with black ducks, mallards displaced black ducks 63.3% of the time but were displaced by black ducks 15.0% of the time; no change occurred during 21.7% of the interactions. Displacement from wetlands was rare (38 of 229 interspecific interactions) and was equal between species.

Journal of Wildlife Management↗
USGS1990

Underwater research methods for study of nuclear bomb craters, Enewetak, Marshall Islands

Three craters, created by the explosion of nuclear fusion devices, were mapped, sampled, core drilled and excavated with airlifts at Enewetak Atoll in the Marshall Islands by using scuba and a research submersible. The craters studied were Mike, Oak, and Koa. Tests took place near sea level at the transition between lithified reef flat and unlithified lagoonal sediments, where water depth ranged from 1 to 4 m. Craters produced by the blasts ranged from 30 to 60 m in depth. The purpose of our study was to determine crater diameter and depth immediately after detonation. Observations of submerged roadways and testing structures and upturned crater rims similar to those characteristic of meteor impacts indicate that the initial, or transient, craters were smaller than their present size. At some later time, while the area was too radioactive for direct examination, the sides of the craters slumped owing to dewatering of under lying pulverized rock. Core drilling of crater margins with a diver-operated hydraulic coring device provided additional data. On the seaward margin of the atoll, opposite Mike, a large portion of the atoll rim approximately the size of a city block had slumped into the deep ocean, leaving a clean vertical rock section more than 400m high. An abundance of aggressive grey reef sharks displaying classic territorial behavior prevented use of scuba at the Mike slump site. The two-person submersible R.V. Delta provided protection and allowed observations down to 300 m. During the 6-week period of study, we made more than 300 scuba and 275 submersible dives. Mapping was with side scan sonar and continuous video sweeps supplemented by tape-recorded verbal descriptions made from within the submersible. A mini-ranger navigation system linked to the submersible allowed plotting of bottom features, depth and sediment type with spatial accuracy to within 2 m.

Conference Paper↗