Offshore Rocks Research Articles

Status of Ashy Storm-Petrel Breeding Colonies at Santa Cruz Island, California, 1912–1998

We summarized historical knowledge from 1912 to 1998 of 13 known breeding colonies of Ashy Storm-Petrels (Oceanodroma homochroa) at Santa Cruz Island, California. Breeding was first reported by naturalists at Painted Cave (1912), Scorpion Rocks (1928), and Orizaba Rock (1937). During early seabird colony surveys of the Channel Islands, breeding was also noted at Cavern Point Cove Caves (1970), Diablo Rocks (1976), and Gull Island (1977). During 1991–1998, more extensive surveys of nearly all sea caves and offshore rocks documented additional breeding at Bat Cave, Cave of the Birds' Eggs, Del Mar Cove Cave, Del Mar Rock, Dry Sandy Beach Cave, Shipwreck Cave, and Willows Anchorage Rocks. Historical impacts apparently occurred from specimen collecting and interference by other nesting seabirds; however, guano harvesting may have had major impacts on nesting habitats at Scorpion Rocks (main rock) and Orizaba Rock. Impacts from organochlorine pollutants were likely extensive, and population sizes at all colonies may have been lower in the 1960s and 1970s when organochlorine pollution was at its highest level. Standardized monthly nest monitoring during 1995–1998 was used to measure reproductive success and population size at 5 colonies, creating a baseline for long-term trend monitoring that has continued annually to 2016. Mist net captures were used to estimate population sizes at 2 colonies in 1991. Estimated population size for Santa Cruz Island in 1991–1998 was 338 pairs, greater than previously reported for 1976–1977 (45–55 pairs), but the more recent estimate includes more colonies (especially 3 large colonies in sea caves), different methods of estimation, and likely some recovery from impacts associated with organochlorine pollution.

Fracture Analysis of basement rock: A case example of the Eastern Part of the Peninsular Malaysia

In general, reservoir rocks can be defined into carbonates, tight elastics and basement rocks. Basement rocks came to be highlighted as their characteristics are quite complicated and remained as a significant challenge in exploration and production area. Motivation of this research is to solve the problem in some area in the Malay Basin which consist fractured basement reservoirs. Thus, in order to increase understanding about their characteristic, a study was conducted in the Eastern part of the Peninsular Malaysia. The study includes the main rock types that resemble the offshore rocks and analysis on the factors that give some effect on fracture characteristic that influence fracture systems and fracture networks. This study will allow better fracture prediction which will be beneficial for future hydrocarbon prediction in this region.

Status, Distribution, and Conservation of Scripps's Murrelet at Santa Catalina Island, California

The small population of Scripps's Murrelets (Synthliboramphus scrippsi) at Santa Catalina Island, California, has been restricted for at least several millennia to isolated pairs nesting in cliff and shoreline habitats that are mostly inaccessible to island fox (Urocyon littoralis catalinae). Prior to 1994, the only evidence of murrelets breeding at Catalina was a single nest reportedly found on Bird Rock in 1967. In 1994–1995, a larger and more widespread population estimated at 25–75 pairs was indicated through vocal detection surveys of murrelets attending nocturnal at-sea congregations in nearshore waters near breeding areas. Murrelets were heard at 11 of 25 survey stations, with highest vocal activity between Land's End and Ribbon Rock (6–62 detections per survey). In 2004 and 2012, round-island spotlight surveys better assessed the distribution and abundance of murrelets in congregations, with 101 and 291 individuals, respectively, observed along the 82-km transect. Highest numbers in 2012 suggest a current breeding population of roughly 100–200 pairs at Catalina, the fourth largest colony in southern California. Congregations were strongly associated with coastal cliffs between (1) Isthmus Cove and Twin Rocks and (2) Iron Bound Bay and Catalina Harbor. In 2000–2013, night-lighting captures of 79 birds in congregations recorded 10 (13%) murrelets with brood patches, usually indicative of egg-laying. During captures in 2008 and spotlight surveys in 2012, three family groups (adults with small downy chicks) departing island nests were observed in nearshore waters. No nests were found during searches on offshore rocks (including Bird Rock) in 1991–1996, but 7 nests were discovered in 2012–2013 during searches of boataccessible shoreline cliffs between Isthmus Cove and Twin Rocks. Overall, 6 of 8 clutches (75%) with known fates were successful, but evidence of mammalian predators preying on murrelet eggs was also present. A long-term monitoring, research, and restoration program is needed at Catalina. Initial restoration efforts should focus on reducing predation by introduced mammals and reducing impacts from oil pollution and bright lights.

Application of four sets of tectonomagmatic discriminant function based diagrams to basic rocks from northwest Mexico

Abstract Discrimination diagrams are being widely used for the past four decades to infer the tectonomagmatic affiliation of old rocks. There are several major- and trace-element composition based bivariate, ternary and multi-element discriminant function diagrams in the literature. Recent evaluation of the performance of these diagrams indicates that four sets of recent discriminant function based diagrams, in which the tectonic boundaries are determined from probability estimates for four tectonic settings of island arc, continental rift, ocean-island and mid-ocean ridge, have shown very high success rates. In this work, we have created an extensive geochemical database for on-land and off-shore basic rocks of northwest Mexico and applied these four sets of recent and highly successful tectonomagmatic discriminant function based diagrams to infer their tectonomagmatic origin. Each of these four sets of diagrams (two for major- and two for trace-elements) contained five diagrams. All the four sets of diagrams confirmed a continental rift setting for on-land basic rocks of 13 Ma age, major-element based diagrams also indicated a rift setting. However, one set of trace-element based discrimination diagrams indicated an arc to rift transition and the other set of trace- element based discrimination diagrams for the only sample from the Comondu arc, which has the required complete dataset, indicated an arc setting. All the four sets of discrimination diagrams indicated MORB setting (success rates 90%-98% and 100% for major-element and trace-element based diagrams, respectively) for off-shore rocks (most of the samples were obtained from DSDP drilled sites in the Gulf of California and some dredged rock samples from the Gulf of California) with very high success rates. All the inferred tectonic settings from these four sets of new discrimination diagrams, in general, are in conformity with those reported in the literature based on other methods. The results show that these discrimination diagrams may successfully discriminate the original tectonic setting of comparatively younger and older on-shore rocks as well as sea-water altered deep-sea rocks and dredged material.

Storms and heat limit the nest success of Bank Cormorants: implications of future climate change for a surface-nesting seabird in southern Africa

The Bank Cormorant Phalacrocorax neglectus is endemic to the Benguela Upwelling System of southern Africa. Most breeding colonies occur on offshore rocks, islands or man-made structures close to the high-water mark. Despite adaptations for breeding close to the water, nests can be lost to storms. Using data from two colonies where food is not considered limiting, we present a comparative study on nest survival in Bank Cormorants. Using a combination of the Mayfield method and parametric survival analysis, nest success was compared in nests on man-made structures at Robben Island, South Africa, where birds breed during the austral winter, with nests on man-made and natural structures at Mercury Island, Namibia, where Bank Cormorants breed during the austral summer. Overall, the probability of a nest surviving the breeding attempt was lower at Robben Island than at Mercury Island in all three seasons. Nest failures at Robben Island were related to wave heights and air temperature, with trends to suggest reduced chick survival in years where major storm events occurred during peak breeding. A heat wave appeared to cause major chick mortality at Mercury Island in 2005. Nest survival was relatively invariable between years at the main site monitored on Mercury Island, where nests were partially sheltered from the sun, but breeding productivity was poor in comparison to other cormorant species. Winter breeding in South Africa may increase the risk from storms but reduce the risk of heat exposure. An understanding of the impact of stochastic events on Bank Cormorants may be important in safe-guarding the continued survival of the species, particularly in light of the risks posed by future climate change.

Jurassic–Cretaceous boundary ammonite Blanfordiceras (Mollusca: Cephalopoda) from Fortissimo-1 Wildcat Well, Browse Basin, Northwest Shelf, Australia

Jurassic–Cretaceous ammonites are particularly robust fossil tools in global stratigraphy and correlation. The successive evolution and extinction of these cephalopod mollusks was so rapid that many ammonite zones are no more than one million years in duration. A well-preserved ammonite specimen from the Fortissimo-1 core, Browse Basin, NW Australia is assignable to the widespread latest Jurassic dimorphic berriaselline genus, Blanfordiceras Cossmann, recorded previously from the Spiti area, Nepal, Tibet, Madagascar, Papua-New Guinea, Antarctica, and southern South America. This is the first report of ammonites of this age in the Australian region. The evolute shell of an estimated 90-100 mm diameter (when extrapolated) and pronounced ornamentation of variably bifurcating, curvilinear and flexuous ribs, intercalated with simple, non-bifurcating ribs, is consistent with Blanfordiceras wallichi (Gray, 1832), which has traditionally been restricted to the uppermost Tithonian Stage, ca. 146.5-145.5 Ma, but may well have survived into the earliest part of the Berriasian. The first recorded occurrence of this ammonite in Australia fills an anomalous absence in the paleobiogeographic distribution of Jurassic–Cretaceous boundary ammonites in the Indo-SW Pacific Subrealm with important implications for the calibration of offshore rocks and wells in Australia.

The Diablo Canyon Fauna: A Coarse-Grained Record of Trans-Holocene Foraging from the Central California Mainland Coast

Decades ago the Diablo Canyon site (CA-SLO-2) on the central California mainland revealed one of the oldest and longest sequences (ca. 9400 radiocarbon years ago to contact) of coastal occupation on the shore of the northeastern Pacific. The artifacts from these important deposits were reported in detail by Greenwood (1972), but only a fraction of the site's faunal collections was analyzed in the original site report. Acquisition of 30 additional radiocarbon dates and analysis of the complete vertebrate fauna have produced a coarse-grained record of human foraging on the California mainland from 8300 cal B.C. to cal A.D. 1769. The temporally controlled faunal matrix, constituting one of the largest trans-Holocene records from western North America, speaks in a meaningful way to two significant issues in hunter-gatherer prehistory: early Holocene foraging strategies and economic intensification/resource depression over time. The site’s earliest component suggests a population invested in watercraft and intensely adapted to the interface of land and sea along the northeastern Pacific coastline. While boats were used to access offshore rocks, terrestrial mammals (e.g., black-tailed deer) were also of primary importance. Dominance of deer throughout the Diablo occupations is inconsistent with recent generalizations about big-game hunting as costly signaling in western North American prehistory. Diachronic variation, correlated with superimposed burials that show growth in human populations through the Holocene, includes: (1) modest incremental changes in most taxa, suggesting resource stability and increasing diet breadth; (2) gradual but significant variation in a few taxa, including the flightless duck which was hunted into extinction and eventually replaced by sea otters; (3) punctuated, multidirectional change during the late Holocene related to historic contingencies of the Medieval Climatic Anomaly and protohistoric disruptions.

COMMON MURRES PROSPECTING WITHIN CORMORANT COLONIES IN DEL NORTE AND HUMBOLDT COUNTIES, CALIFORNIA, 1996 to 2004

Between the 1940s and 1960s, common murres (Uria aalge) colonized or recolonized several islands in Del Norte and Humboldt Counties, northern California, during an extended period of population growth following heavy prior impacts from early settlers and native peoples (Carter and others 2001). The exact timing of these colony formations and various factors influencing them were not well documented. Since the 1st complete northern California seabird colony survey in 1979–80 (Sowls and others 1980), almost annual June aerial photographic surveys have been conducted of breeding colonies of murres and cormorants (Brandt’s and double-crested, Phalacrocorax penicillatus and P. auritus) in northern California (Briggs and others 1983; Takekawa and others 1990; Carter and others 1992, 1995, 1996, 2001; Capitolo and others 2004a; US Fish and Wildlife Service [USFWS], unpubl. data). While several murre colony formations have been documented in Mendocino County primarily with aerial photographs since 1979–80, no colony formations have been documented in Del Norte and Humboldt Counties. In 1996–2004, we documented (1) the 1st known attendance by murres on 4 offshore rocks in Del Norte County (High Bluff South, White Rock, Prince Island, Unnamed Small Rocks); (2) continued sporadic attendance by murres without recent confirmed breeding on 2 other offshore rocks in Del Norte County (Rock R and Sister Rocks); and (3) the 1st recent attendance by murres on 1 offshore rock in Humboldt County (Sea Lion Rock). In this note, we describe these observations of prospecting murres, show relationships with nesting cormorants, and discuss their potential importance to understanding possible future colony formations. We use the term ‘‘prospecting’’ to describe murres attending potential breeding habitats on land where murre breeding has not been recently documented, though we usually did not know what activities occurred on land nor how long murres were present on land. Because murres do not attend such habitats without a breedingrelated purpose, we consider that prospecting for a breeding site or mate are the chief reasons for such attendance (see later discussion). However, without marked birds or access to colonies, source colonies for these prospecting murres cannot be specifically determined.

Abundance, seasonal haul-out patterns and conservation of spotted seals Phoca largha along the coast of Bak-ryoung Island, South Korea

The spotted seal Phoca largha, which is found in the Okhotsk, Bering, Chukchi, Beaufort and Yellow seas, is Critically Endangered in the Yellow Sea of China and Korea because of habitat destruction and human harassment in the region. Shipboard surveys were conducted in the inshore waters of Bak-ryoung Island off western South Korea from March 2000 to October 2002 to investigate the distribution, abundance and seasonal haul-out patterns of spotted seals and thereby to lay a foundation for developing conservation measures. Seals were seen on every survey during the study period, hauled out on offshore rocks rather than on beaches. The highest concentration of spotted seals occurred on Mul-Beum Rock, probably because of the relatively lower exposure of this site to waves and spray. There was a seasonal pattern in the total number of seals hauled out, with the highest numbers seen from late spring to late summer. Spotted seals arrived as early as 15 March and left the area by late December. We suggest that spotted seals spend the spring, summer and autumn feeding along the coast of Bak-ryoung Island and return to their breeding grounds in Liaodong Bay, China, in October. Because the spotted seal populations of China and South Korea are small and seasonally dispersed, the establishment of an international protected areas network and research cooperation between China and South Korea is urgently required.

Reasserting a Prehistoric Tragedy of the Commons: Reply to Lyman

R. Lee Lyman has challenged our assertion that prehistoric hunting of marine mammals along the west coast of North America approximated a prehistoric tragedy of the commons in which highly ranked migratory sea lions and fur seals were reduced by overexploitation, necessitating pursuit of smaller, more elusive harbor seals and sea otters late in time. In response, we review alternative theoretical perspectives, rebut Lyman's characterization of marine mammal reproductive behaviors, reanalyze seal and sea lion NISP data from the California and Oregon coasts, and reinterpret three regional prehistories. Because migratory pinnipeds need to breed on land, are vulnerable to terrestrial predation when congregated in breeding colonies, and employ migration corridors thousands of kilometers in length, they were susceptible to overexploitation. In areas where rookeries persisted on remote islands and offshore rocks, sophisticated weaponry and watercraft were developed to facilitate pursuit of dwindling populations and more elusive taxa as part of intensive, socially complex maritime economies.

Abundance and Distribution of Harbor Seals (Phoca vitulina) in Oregon, 1975-1983

Harbor seals were observed on 32 haulout sites in Oregon during aerial counts conducted from 1975 to 1983; 90% were seen on 14 sites. The greatest number of seals seen on a haulout was 985 recorded at Cape Arago in July 1982. Counts of harbor seals in 1982 and 1983 were 38.6% greater than counts from 1975 to 1980. These data indicate an increase in numbers of harbor seals in Oregon, an increase corroborated by other information, namely, lower counts made before 1975 and increased use of new haulout sites since 1975. Between 1975 and 1983, numbers within bays increased, whereas numbers on most offshore rocks remained somewhat constant. Decreased harassment and mortality since implementation of the Marine Mammal Protection Act of 1972 doubtless allowed harbor seals to increase in numbers and to reoccupy protected haulout sites in bays. The harbor seal (Phoca vitulina richardsi) is one of five pinniped species common in Oregon. It is the most abundant and ubiquitous pinniped in the state, found in most bays and estuaries, and on many offshore rocks. Harbor seal abundance has been determined at specific haulout sites along the Oregon coast (Graybill 1981; Brown and Mate 1983; Roffe and Mate 1984; Bayer 1985), although there is only one published account of their state-wide distribution and abundance (Pearson and Verts 1970). From 1967 to 1968, Pearson and Verts (1970) conducted four counts from land and one aerial count along the Oregon coast and concluded that there were fewer than 500 harbor seals in the state. More than 3800 harbor seals were killed in Oregon between 1925 and 1972 by statehired and bounty hunters (Pearson 1969). Harbor seals were harassed at inshore areas where they rested and pupped, and their number in Oregon was probably reduced. Harassment and killing of harbor seals were greatly reduced after 1972 when the Marine Mammal Protection Act became effective. Protection probably has resulted in an increase in abundance and redistribution of animals into bays and estuaries. The objectives of this study were to determine the location and use of haulout sites and to document any changes in abundance and distribution of harbor seals in Oregon from 1975 to 1983. METHODS Aerial photographic surveys of seals on land along the entire Oregon coast were performed annually from a high-winged, single-engine aircraft (Cessna 172 or 182) during 1 month in the summer (June, July, or August) from 1975 to 1983 (Fig. 1). Surveys were begun approximately 2 hr before low tide and ended approximately 2 hr after low tide to maximize the number of seals visible on haulout sites (Schneider and Payne 1983; Terhune and Almon 1983). The entire Oregon coastline was scanned during annual surveys to determine locations of harbor seals ashore and to locate new haulout sites. When more than five seals were ashore, the group was photographed from an altitude of 215-305 m using a hand-held 35 mm camera and 300 mm or 70 to 210 mm zoom lens. Photographs were taken within 15° of vertical. Photographic images of seals on land were projected onto a white surface, and each seal was counted. Photographic surveys required 2 days; flights were made from Newport to the north or south on consecutive days. Surveys of some haulout sites were not possible because of inclement weather.

OBSERVATIONS ON THE COMMUNAL ROOSTING OF AFRICAN BLACK OYSTERCATCHERS

Summary Hockey P. A. R. 1985. Observations on the communal roosting of African Black Oystercatchers. Ostrich 56: 52–57. There are currently three main hypotheses for the adaptive significance of avian communal roosts: physiological advantages, predator avoidance and information centres. The African Black Oystercatcher Haematopus moquini is territorial throughout the year and forms communal roosts during the nonbreeding season, but does not breed communally. Roosts generally are small, and site fidelity is high. Roosts are normally sited on a rocky promontory with adjacent offshore rocks (west coast), or in flat areas with extensive all-round visibility. The main predators of African Black Oystercatchers are nocturnal terrestrial mammals and nocturnal communal roosts are larger and more tightly packed than daytime roosts. Breeding birds do not roost communally during the breeding season and at this time of year mortality due to mammal predators at a study site in Saldanha Bay was greatest (X2 = 9.46; p<0.0...

A Comparsion of Nesting‐Ledges Used by Seabirds on St. George Island

Measurements of 288 nesting—ledges of six species of seabirds on St. George Island, Alaska, revealed significant interspecific differences in the size, shape, and overhang of ledges used. Typically, Red—legged Kittiwakes used ledges 1 dm deep; Northern Fulmars, Black—legged Kittiwakes, and Thick—billed Murres used ledges of an intermediate 2—4 dm depth; Red—faced Cormorants used ledges 3—6 dm deep; and Common Murres occurred singly on shallow ledges or in groups on deeper ledges. Fulmars and murres, which did not build nests, used nearly horizontal ledges exclusively; the nest—building species occurred on a wider range of slopes. Only the Red—legged Kittiwake regularly used ledges with over 50% cover by overhanging cliff within 5 dm of the ledge. Classification of the measured ledges of the cormorant, the two kittiwakes, and the Thick—billed Murre by a discriminant function analysis revealed significantly greater overlap than expected between the species pairs of cormorant with Thick—billed Murre, Black—legged with Red—legged Kittiwake, and Black—legged Kittiwake with Thick—billed Murre. Observations of 43 interspecific exchanges of nest sites during and between three breeding seasons agreed with the predictions by the discriminant analysis of overlap or lack thereof in three of four significant cases. Exchanges occurred significantly more frequently than expected between the species pairs of cormorant with Black—legged Kittiwake, cormorant with Thick—billed Murre, and Black—legged with Red—legged Kittiwake.

DISTRIBUTION, POPULATION SIZE, BREEDING AND CONSERVATION OF THE KELP GULL IN SOUTHERN AFRICA

Summary Crawford, R. J. M., Cooper, J. & Shelton, P. A. 1982. Distribution, population size, breeding and conservation of the Kelp Gull in southern Africa. Ostrich 53:164:177. The Kelp Gull Lams dominicanus in Africa occurs coastally between Luanda, Angola and Delagoa Bay, Mocmbique. It breeds between Cape Cross Lagoon, South West Africa/Namibia and Riet River, eastern Cape, South Africa. Censuses of nests and breeding birds at all known southern African breeding localities in the period 1976–1981 indicated that 11 199 pairs bred at 52 localities; 79.5% of this population occurred in South Africa, 57,1% in the Saldanha Bay to Dassen Island region, southwestern Cape. Of the breeding pairs 83% occurred on offshore islands and rocks. Colony size at islands is related to their surface area andMayalso be influenced by food availability and the level of human disturbance. The species breeds in a wide variety of habitats ranging from cliffs and rock stacks to wooden platforms, lowlying vegetation among sand dune...

Tertiary Basalts Dredged From Baffin Bay

Three dredge hauls were recovered from scarps on the West Greenland continental shelf in Baffin Bay. Two of the dredge hauls consisted essentially of basalts but the third, at the mouth of Disko Bay, contained some 50% Precambrian erratics. Both the mineralogy and chemistry of these offshore rocks are very similar to the most evolved basaltic compositions found elsewhere in the West Greenland Tertiary volcanic province. The dredged samples show none of the features expected for submarine tholeiites and were therefore probably erupted subaerially and later subsided below present day sea-level. A petrogenetic model, involving equilibration of a basaltic magma at a pressure in the range 5–8 kb, is proposed to account for the chemistry of this suite of rocks.

Depositional Model--upper Cretaceous Gallup Beach Shoreline, Ship Rock Area, Northwestern New Mexico

To provide an example of ancient deposits across a sand-beach shoreline for comparison with both Recent and other ancient deposits, a cross-sectional model was constructed from surface exposures across the Upper Cretaceous Gallup shoreline in the Ship Rock area of northwestern New Mexico. Tile model shows lower Gallup regressive-beach sandstone overlain unconformably by upper Gallup transgressive offshore-bar sandstones. Landward, the beach sandstone interfingers with coal-swamp deposits or is truncated and overlain by dune standstone. Seaward, the beach sandstone grades through shoreface sandstone into a transition that gives way to offshore siltstone and mudstone. Offshore siltstone and mudstone overlie and in part grade laterally into offshore-bar sandstone, which has no contiguous landward equivalents and transgresses all beach and related facies. Within their particular stratigraphic frameworks, sedimentary structures, supported by lithologic and paleontologic data, identify both the beach and the offshore-bar sandstones as well as their related facies. Both the beaches and the offshore bars consist of imbricate patterns of parallel beds. Beds in the backshore beach consist of cross laminae that dip either in diverse directions or landward and that compose laminasets, which are swale fillings; cross laminae in the foreshore beach dip uniformly seaward at low angles. Beds of shoreface sandstone are either churned by burrowing organisms or composed of large-scale truncated wave-ripple laminae. in the transition between shoreface and offshore siltstone and mudstone, beds of mudstone interfinger with bells of sandstone and siltstone, which show small-scale truncated wave-ripple laminae and churned structure. Siltstone and mudstone beds alternate in offshore rocks, and the siltstones contain both current-ripple and truncated wave-ripple laminae, except where burrowing organisms have destroyed the laminae. Most beds of offshore-bar sandstone are churned, but some show high-angle cross laminae that dip parallel with the length of the bar and approximately parallel with the distant shoreline. Burrowing organisms have completely churned the muddy sandstone beds of the offshore-bar transition.