science for a changing world Beyond the Golden Gate — Oceanography, Geology, Biology, and Environmental Issues in the Gulf of the Farallones Circular 1198 U.S. Department of the Interior U.S. Geological Survey From the collection of International Bird Rescue Research Center Cordelia, California in association with 7 n ^ m o Prelinger • a library San Francisco, California 2006 U.S. Department of the Interior U.S. Geological Survey Beyond the Golden Gate — Oceanography, Geology, Biology, and Environmental Issues in the Gulf of the Farallones Edited by Herman A. Karl, John L. Chin, Edward Ueber, Peter H. Stauffer, and James W. Hendley II Circular 1198 U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat, Director Any use of trade, product, or firm names in this publica- tion is for descriptive purposes only and does not imply endorsement by the U.S. Government. U.S. Geological Survey, Reston, Virginia: 2001 For additional copies please contact: USGS Information Services Box 25286 Denver, CO 80225 This report and any updates to it are available at http://geopubs.wr.usgs.gov/circular/c1198/ Additional USGS publications can be found at ht1p://geology.usgs.gov/products.html For more information about the USGS and its products: Telephone: 1-800-ASK-USGS (1-888-275-8747) World Wide Web: http://www.usgs.gov ISBN 0-607-95030-7 Published in the Western Region, Menlo Park, California Manuscript approved for publication June 18, 2000 Production and design by Sara Boore and Susan Mayfield Text and illustrations edited by Peter H. Stauffer, James W. Hendley II, and George A. Havach CD-ROM prepared by Michael F. Diggles Cooperating Organizations Bodega Marine Laboratory (University of California at Davis) British Geological Survey California Department of Health Services Environmental Protection Agency Kernfysisch Versneller Instituut, Groningen, The Netherlands National Oceanic and Atmospheric Administration Gulf Of The Farallones National Marine Sanctuary Cordell Bank National Marine Sanctuary National Marine Fisheries Service National Park Service Point Reyes Bird Observatory U.S. Army Corps of Engineers U.S. Geological Survey U.S. Navy Contributors Bodega Marine Laboratory (University of California at Davis) Stephen R. Wing British Geological Survey David G. Jones Philip D. Roberts California Department of Health Services Gregg W. Langlois Patricia Smith Environmental Protection Agency Allan Ota Kernfysisch Versneller Instituut, Groningen, The Netherlands Johannes Limburg National Oceanic and Atmospheric Administration Gulf of the Farallones National Marine Sanctuary Jan Roletto Edward Ueber Cordell Bank National Marine Sanctuary Dan Howard National Marine Fisheries Service Peter Adams Tom Laidig National Park Service Scot Anderson Point Reyes Bird Observatory Scot Anderson Peter Pyle U.S. Geological Survey John L Chin Walter E. Dean James V. Gardner Russell W. Graymer James W. Hendley II Herman A. Karl Kaye Kinoshita Marlene A. Noble Stephanie L. Ross Holly F. Ryan William C.Schwab Peter H. Stauffer Florence L Wong Contents 7 Foreword Charles G. Groat 2 Beyond the Golden Gate — Introduction Herman A. Karl and Edward Ueber 4 Techniques and Technology of Exploration in the Gulf of the Farallones Kaye Kinoshita and John L. Chin 6 Oceanography and Geology of the Gulf of the Farallones 8 Regional Setting John L. Chin and Russell W. Graymer 12 Earthquakes, Faults, and Tectonics Holly F. Ryan, Stephanie L. Ross, and Russell W. Graymer 16 Landscape of the Sea Floor Herman A. Karl and William C. Schwab 20 Current Patterns Over the Continental Shelf and Slope Marlene A. Noble 24 Sediment of the Sea Floor Herman A. Karl 26 Chemical Composition of Surface Sediments on the Sea Floor Walter E. Dean and James V. Gardner 28 Heavy-Mineral Provinces on the Continental Shelf Florence L. Wong 30 Biology and Ecological Niches in the Gulf of the Farallones 32 Pliytoplankton Gregg W. Langlois and Patricia Smith 36 Krill Dan Howard 40 Free-Floating Larvae of Crabs, Sea Urchins, and Rockfishes Stephen R. Wing 42 Salmon Peter Adams 44 Seabirds Peter Pyle 48 Marine Mammals Jan Roletto 52 White Sharks Scot Anderson 56 Continental Slope Communities Tom Laidig 60 Issues of Environmental Management in the Gulf of the Farallones 62 Disposal of Dredged Material and Other Waste on the Continental Shelf and Slope John L Chin and Allan Ota 66 Search for Containers of Radioactive Waste on the Sea Floor Herman A. Karl 68 Measuring Radioactivity from Waste Drums on the Sea Floor David G. Jones, Philip D. Roberts, and Johannes Limburg 72 Further Reading 72 Oceanography and Geology 73 Biology 75 Environmental Issues 77 Glossary Back pocket CD-ROM containing full-length technical version of Circular 1198 Foreword Both scientists and decisionmakers have become increasingly aware of the need to understand the complexity of natural systems when considering actions that affect individual aspects of resources and the environment. The interconnectedness of the physical and biological elements of a natural system is often appreciated in the abstract, but sometimes not as much as it should be in scientific studies. Too frequently, how the interaction of all elements of a system influence the organism, habitat, or process being focused on is given only lip service or general observations. Although not intended to be an integrated study, this report on oceanographic, geological, biological, and environmental aspects of the Gulf of the Farallones is an excellent example of a study describing the many facets of a complex marine system. In marine systems, the geologic foundation and sediment dynamics of the sea floor define the basic environment for communities of bottom-dwelling organisms, which are influenced by circulation patterns that also affect organisms living in the water column. Decreased light penetration caused by turbidity affects the plankton, the base of the marine food web, and thus affects fish and other marine populations. We sometimes consider the most dynamic and influential elements of marine systems to be the currents, waves, and mobile species that are monitored regularly because they change frequently on a human time scale. However, this report demonstrates how geologic processes, including crustal processes manifested as earthquakes, can also be influential on the same time scale. The inclusion of a chapter on tectonics brings this point home. This report also demonstrates the impact that a past tendency towards an "out of sight, out of mind" approach to the use of the ocean floor for waste disposal has had on future use of marine resources and how new technology can improve the situation. Concerns over possible leakage from drums of radioactive waste dumped until about 1970 on the ocean floor in the Gulf of the Farallones affected the marketability offish caught in the area. Technology has only recently enabled scientists to locate the drums and begin assessing the actual risk. Similarly, new technology has allowed proposed sites for disposal of dredged material to be evaluated with a more thorough understanding of bottom conditions and processes. Studies that help provide an integrated knowledge of complex natural systems, like these on the Gulf of the Farallones, give decisionmakers and the public an enhanced ability to avoid the mistakes of the past and promote sustainable use of environments and resources essential to human society. Charles G. Groat Director, U.S. Geological Survey Beyond the Golden Gate — Introduction Herman A. Karl and Edward Ueber The beauty and power of the ocean fascinate many people. The sea has been a source of sustenance, recreation, contemplation, and inspiration, as well as a challenge for explo- ration and discovery, for mankind since pre- history. Although much has been discovered and reported about them, the sea, the life in the sea, and the landscape beneath the sea continue to be largely shrouded in mystery. Despite the fact that the oceans occupy 7 1 percent of the Earth's surface and are crucial to our survival, we invest more in learning about other planets than we invest in learn- ing about the world beneath the sea. Perhaps more than any other open space remaining on our planet, the oceans are a common-use area for both work and play for much of the world's population. This observation is particularly true in those areas of the coastal ocean off major urban com- plexes. In these multiuse "urban oceans," environmental and ecological concerns must be balanced against the human, economic, and industrial demands of adjacent large population centers. With ever-increasing stress being placed on the ecosystems of the oceans by human activities, many areas of the oceans around the United States have been designated as protected sanctuaries and reserves. Three contiguous National Marine Sanctuaries — Cordell Bank, Gulf of the Far- allones, and Monterey Bay — stretch more than 185 miles from Bodega Bay north of San Francisco to Cambria south of Mon- terey. They protect an area larger than the States of Connecticut and Rhode Island combined, about 7,000 square miles of the California coastal ocean. The U.S. Geological Survey (USGS) began a major geologic and oceanographic study of the Gulf of the Farallones in 1989. This investigation, the first of several now being conducted adjacent to major popula- tion centers by the USGS, was undertaken to establish a scientific data base for an area of 1,000 square nautical miles on the Continen- tal Shelf adjacent to the San Francisco Bay region. The results of this study can be used to evaluate and monitor human impact on the marine environment. In 1990, the project expanded in scope when the USGS sponsored a multidis- ciplinary investigation with four other Fed- eral agencies — Environmental Protection Agency, Army Corps of Engineers, U.S. Navy, and Gulf of the Farallones National Marine Sanctuary (part of the National Oce- anic and Atmospheric Administration) — to survey and sample the Continental Slope west of the Farallon Islands. This study was primarily designed to provide infor- mation on the location and distribution of approximately 47,800 containers of low- level radioactive waste and obtain data on areas being considered as potential sites for the disposal of sediments dredged from San Francisco Bay. Many other organizations eventually par- ticipated in this work, including Point Reyes Bird Observatory, California Department of Health Services, and the British Geological Survey. The information from these studies is being used by the Gulf of the Farallones National Marine Sanctuary to better manage and protect the unique ecological resources of the gulf. This information was also used in 1994 by the Environmental Protection Agency in designating the first deep-ocean disposal site for dredged material on the Pacific coast of the United States, west of San Francisco on the Continental Slope out- side the boundaries of the sanctuary. This USGS Circular endeavors to pull back the shroud of mystery that covers the ocean waters seaward of the Golden Gate, revealing to the reader some of the diverse habitats and ecosystems in the Gulf of the Farallones and discussing issues of contam- ination and waste disposal. The sections of this book cover the topics of Oceanogra- phy and Geology, Biology and Ecological Niches, and Issues of Environmental Man- agement in the Gulf of the Farallones. The chapters in the paper version of the book are short, less technical summaries. The full chapters are contained on the CD-ROM in the pocket at the back of the book. Links to the complete Circular and related topics can be found at http:// walrus.wr.usgs.gov. Acknowledgments. — The view of the Gulf of the Farallones presented here resulted from the efforts of scores of people over a 1 2-year period, from the first sampling and surveying cruise in 1989 to final publication of this book in 200 1 . It is not possible to single out each person who contributed in one way or another to this endeavor. The work of each is greatly appreciated, but some deserve special mention. William Schwab. David Twichell, David Drake, and David Rubin served as co-chief scientists with John Chin and Herman Karl on the 1989 and 1990 cruises and contributed significantly to their design and implementation. William Dan- forth and Thomas O'Brien led the teams that pro- cessed sidescan-sonar data in near-real time while at sea. Arthur Wright of Williamson and Associates provided helpful insights during the search for bar- rels of radioactive waste using the SeaMARCl A sidescan sonar. Pat S. Chavez, Jr., and his group did preliminary computer enhancements of sidescan images that helped identify nongeologic features on the sea floor, such as radioactive waste barrels. John Penvenne of Triton Technologies developed the principal methodology to detect barrels and clas- sify objects in the SeaMARC 1 A imagery. Kaye Kinoshita and Norman Maher supported the early stages of assembling this book. William van Peelers coordinated the use of the U.S. Navy's DSV Sea Cliff and Advanced Tethered Vehicle. The USGS Marine Facility in Redwood City, California, pro- vided operational support on shore and at sea. The officers and crews of the USGS ship R/V Farnella. NOAA ship R/V McArthur, the Navy's ship Pacific Escort, and the support vessel Laney Chouest greatly aided the work in the gulf. 2 Beyond the Golden Gate— Introduction MAP OF THE SAN FRANCISCO BAY REGION AND THE GULF OF THE FARALLONES Bodega Head (•OROIil.I. BANK vMIONAl, MARINL.- Point Reyes Farallon Islands BoJojii Bay Tomules Bin I- PACIFIC OCEAN — i — 123°00'W North Farallon Middle Farallon Maintop Southeast Island LFarallon Seal" Rock Sun Pablo Ha\ Vallejo Boliruu Lagoon A 4 Richmond D "0"1 ^z- OAKLAND SAN ° Alameda FRANCISCO ^ Half Moon Bay Afio Nuevo KI-:Y ii N.VIIONAI. MARINL s \\CTI :ARY 20 MILES 20 KILOMETERS 38 DON I iverniore 37 30 - S \\ !()SI Cm/ 37rOO - 122"30'W 122 00' Moiuerev Beyond the Golden Gate — Introduction 3 Techniques and Technology of Exploration in the Gulf of the Farallones Kaye Kinoshita and John L. Chin Although the oceans occupy 7 1 percent of the Earth's surface, they continue to be largely shrouded in mystery. From the surface it is impossible to see into the ocean depths, and actually going into those depths is both costly and hazardous. Because the oceans are crucial to our survival, we must try to understand the interactions of their complex physical and biological systems. In pursuit of this understanding, scientists seek many kinds of information — the depth, composition, temperatures, and movements of the water; the shape and composition of the sea bottom; and the types and abundances of the animals and plants living in the water and at the bottom. Some of these kinds of information can be obtained at the sur- face from ships, others require the low- ering of cameras and sampling devices, and still others are best acquired through exploration in submersible vehicles, both manned and unmanned. Exploration in the Gulf of the Farallones has made use of a wide variety of such techniques. When collecting multiple sets of geo- physical and geological data over a wide area of the sea floor, precisely determining the location of an object or feature is criti- cal. Navigation was therefore the common denominator that linked all data types together in a spatial frame of reference. Four types of navigation sensors were used to determine the locations of objects and features on the sea floor — Global Position- ing System (GPS) satellites, Loran-C, and two ranging navigation systems (Del Norte and Benthos). The output from the GPS, Loran-C, and Del Norte systems was fed directly into a navigation program running on a microcomputer. This program pro- vided important real-time location infor- mation, which was relayed to computers in onboard science laboratories and the ship's bridge. The Benthos system was a stand- alone system, which had its own program and display and ran separately from the integrated navigation system.- Two types of equipment using sound waves — sidescan sonar and seismic-reflec- tion systems — were used to map the sea floor in the gulf. Images from three differ- ent sidescan systems were cut and pasted together to create "mosaics," which pro- vide excellent map views of the area of sea floor studied in the gulf. Both 3.5-kilo- hertz (kHz) and 4.5-kHz high-resolution seismic-reflection systems were used to profile and look at the shallow subbottom (uppermost 160 feet) of the sea floor. A 10-kHz system was also used to provide accurate bathymetric information. A towed seabed gamma-ray spectrom- eter belonging to and operated by the British Geological Survey, called the EEL because of its eel-like appearance, was used to measure the radioactivity of the sea floor. The gamma detector can measure both natural and artificial radioactivity in surficial sea-floor material to an effective maximum subbottom depth of about a foot. As the probe is towed, data are sent up the towing cable to a shipboard computer and recorded continuously. Physical samples of the sea bottom were taken with two devices. A gravity corer, driven into the bottom by a heavy weight, was used to obtain round cores about 4 inches in diameter and as much as 10 feet long. This type of coring device was used where the sediment was expected to be soft and muddy. The other sampling device used was a Van Veen grab sampler, which works very much like a clam shell. When the two sides of the shell touch the sea floor they close and scoop up a sample. This device was used where the sea floor was expected to be sandy, because sand would not easily be penetrated by or retained in a gravity corer. Instrument packages were attached to lines moored to the sea floor to measure the velocity and direction of ocean currents in the Gulf of the Farallones. These instru- ment packages also measured water clarity, conductivity, salinity, and temperature. A camera sled designed and built by the U.S. Geological Survey was towed from a research vessel along a preplanned trackline to take pictures of the sea floor in the gulf. Video was recorded continuously and still photographs were taken every 10 to 15 seconds. The images of the sea floor obtained with the camera sled were used to visually verify information col- lected from both sidescan-sonar mapping and physical sampling. Visual observations were also made with Sea Cliff, a manned deep-submer- gence vehicle (DSV) operated by the U.S. Navy. Sea Cliff also had the capability to take physical samples with the use of mechanical arms. The Navy's unmanned Advanced Tethered Vehicle (ATV) was also used to obtain additional video and photographs of the sea floor. The ATV can be remotely "driven" to a specific site, and it proved to be the most precise way used so far in the Gulf of the Farallones to view objects on the sea floor. 4 Techniques and Technology of Exploration in the Gulf of the Farallones Sea Cliff [above), a manned deep-submergence vehicle operated by the U.S. Navy, was used to directly ol the sea bottom and to take physical samples with its mechanical arms. The Navy's unmanned Advanced Tethered Vehicle (above right) was also used to take video footage and still photographs of the sea floor. Two types of equipment using sound waves — sidescan sonar and seismic-reflection systems — were used to map the sea floor in the Gulf Of the Farallones. Each system is housed in a hydrodynamic "towfish" that is towed just below the ocean surface from a ship. The SeaMARd A sidescan-sonar system is shown here outside of its protective shell. The inset shows the towfish that was used for high-resolution seismic-reflection systems. This U.S. Geological Survey camera sled, towed from a research vessel along pre- planned tracklines, was used to take pictures of the sea floor in the Gulf of the Farallones. Samples of the sea bottom were taken with two devices. A gravity corer (above) was used where the sediment was expected to be soft and muddy. A clam-like Van Veen grab sampler (left, in closed position), used where the sea floor was expected to be sandy, collected samples such as the sand and brittle stars shown (top). Techniques and Technology of Exploration in the Gulf of the Farallones 5 of the Gulf of the harallones The San Francisco Bay region of California is famous for its stunning landscapes and complex geology. Adjacent to this region, in the watery world of the Pacific Ocean beyond the Golden Gate, lies the Gulf of the Farallones, a physical environment equally complex and fascinating, but less obvious, less visible, and therefore more mysterious. Scientific studies are revealing that the sea floor of the gulf, like the region onshore, was crafted by geologic forces that include movements of the San Andreas Fault system, major changes in sea level, and the action of rivers. The ceaseless work of oceanic currents has further sculpted the sea bottom in the gulf into landscapes that today range from flat plains and giant sand ripples to deep canyons and rugged mountains, some of whose highest summits poke above the water to form the Farallon Islands. ' " • <*<£ ^ Oceanography and Geology of the Gulf of the Farallones Regional Setting John L. Chin and Russell W. Graymer The Gulf of the Farallones lies in the off- shore part of the San Francisco Bay region just beyond the Golden Gate. The bay region is home to more than 6 million people and has long been regarded as one of the most beautiful regions in the United States. It annually draws hundreds of thousands of tourists from all over the world to enjoy its hilly, often fog- shrouded terrain and its mild, Mediterra- nean climate, as well as to experience its cultural richness and diversity. The histori- cal settlement of the bay region is inti- mately related to its geography, natural harbors, and mild climate. The San Francisco Bay region extends from the Point Reyes Peninsula southward to Monterey Bay and from the coast east- ward to the Sacramento-San Joaquin Delta and also includes the offshore area out to a water depth of about 1 1 ,500 feet, which is the outer edge of the Continental Slope. This offshore area, where many residents of the region and tourists go to watch the annual migration of whales, as well as to boat and fish, includes the Gulf of the Far- allones and the Farallon Islands. Although the sea floor in this area cannot be visually observed, scientists have learned much about it by using acoustic instruments (instruments that utilize sound sources and listening devices) and underwater cameras and video equipment. The landscape features of the San Francisco Bay region are the cumulative result of millions of years of Earth his- tory, involving the building and subse- quent wearing down of mountains, volca- nic eruptions and resulting outpourings of lava, large and small earthquakes, and the never-ending processes of wind and water erosion and deposition. Many of these processes are occurring today, although some of them occur at rates so slow that little change may be perceived over the course of a human lifetime. The sedi- mentary deposits and rocks of the region range in age from hundreds qf millions of years to those still forming today. The entire spectrum of rocks present in the region records only a fraction of the Earth's history. The rock types range from the salt-and-pepper granitic rocks at Point Reyes and on the Farallon Islands, through various types of volcanic rocks (such as the pillow basalts in the Marin Headlands), to sedimentary rocks, such as the red to brown bricklike chert that forms the cliffs of the Marin Headlands and many of the hills of San Francisco, and the young sand-dune deposits that occur along the Pacific Coast. The San Francisco Bay region strad- dles the boundary zone between two of the Earth's major tectonic plates. The Pacific Plate is slowly moving northward relative to the North American Plate, and this motion takes place along the San Andreas Fault and a network of associated sub- parallel faults, collectively called the San Andreas Fault Zone (see chapter on Earth- quakes, Faults, and Tectonics). Rocks east of the San Andreas Fault Zone were mainly formed in approximately their present positions. However, many of the rocks found within the zone, like the Fran- ciscan chert at the Marin Headlands, are ocean-floor rocks that have been scraped off onto the edge of North America over the past 150 million years. The oldest of the rocks found west of the San Andreas Fault were formed hun- dreds of miles to the south, some near the present site of Los Angeles, and subsequently transported northward by movement along the San Andreas and its associated faults. Rocks west of the fault are, in fact, still being transported north- ward at about 2 inches per year and after millions of years may reach the area where Alaska is today. Mountain ranges in the San Francisco Bay region trend mostly northwest and are separated by broad basins and narrow val- leys. Many of the ridgecrests in the Coast Range, the major mountain range in the region, rise above 1 ,000 feet, and a few above 4,000 feet. The highest peaks include Mount Hamilton at 4,373 feet, Mount Diablo at 3,849 feet, and Mount Tamalpais at 2,606 feet. As recently as about 10,000 years ago, at the end of the last ice age, great sheets of ice (glaciers) covered much of Earth's northern hemisphere. Because so much water was stored in these glaciers, sea level was about 300 feet lower than at present, and the coastline of the San Fran- cisco Bay region was situated as much as 35 miles seaward of its present position, near coastal hills whose tops are now the Farallon Islands. The melting of the ice sheets caused worldwide sea level to rise, forming the Gulf of the Farallones and San Francisco Bay. If the vast volume of ocean water that now covers the floor of the gulf could be removed, people would see a varied land- scape. That landscape is as rich in diver- sity and rugged splendor as that on the nearby shore (see chapter on Landscape of the Sea Floor). 8 Oceanography and Geology of the Gulf of the Farallones 123°00'W 38°00'N 37 30' 37 Bodega Bodcgu Ba\ Head 122°30' I 122°00' I 20 MILES Tomales Bay San Pablo Bay 20 KILOMETERS un Bav Point Reyes Bolinas Lagoon Mount \ Tamalpais Richmond Mount Diablo Farallon Islands PACIFIC OCEAN G° SAN T FRANCISCO OAKLAND Alameda Half Moon Ba\ • along fault segments Individual fault probabilities are uncertain by 5 to 10% Expanding urban areas In 1999, the U.S. Geological Survey and cooperators released this earthquake probability map for the San Francisco Bay region. The threat of earthquakes extends across the entire region, and a major quake is likely before 2030. As continuing research reveals new information about earthquakes in the bay region, these probabilities are revised. Earthquakes, Faults, and Tectonics 15 Oceanography and Geology of the Gulf of the Farallones Landscape of the Sea Floor Herman A. Karl and William C. Schwab Various forces sculpt the surface of the Earth into shapes large and small that range from mountains tens of thousands of feet high to ripples less than an inch high in the sand. We can easily see these morphologic features on dry land, and most are accessible to be explored and appreciated by us as we walk and drive across or fly over them. In contrast, people can travel at sea without ever being aware of the existence of large mountains and deep valleys hidden by tens of feet to tens of thousands of feet of water. At one time, it was impossible to see the landscape beneath the sea except by direct observation, and so the bottom of the deep oceans remained as mysterious as the other side of the Moon. Methods of using sound to map the fea- tures of the sea floor were developed in the decades after World War I, and we now know that mountains larger than any on land and canyons deeper and wider than the Grand Canyon exist beneath our oceans. Images of large areas of the land sur- face are taken by cameras in aircraft and acquired by sensors in satellites. Optical instruments (cameras) record reflected light to produce images (photographs) of mountains, plains, rivers, and valleys. However, light does not penetrate far in water, and so photographs cannot be pro- duced that show entire mountains and valleys beneath the sea. Just as under- water cameras can take photographs of only very small areas and objects not far distant, divers and submersibles can observe only very small areas of the ocean bottom. Such methods of observa- tion are analogous to walking around at night with a flashlight and trying to see a mountain or a forest. It is possible in this way to see rocks, pebbles, leaves, and trees along your path, but not the entire mountain and forest. To observe and make images of the mountains and valleys under the sea, scientists have developed instruments that use sound (acoustic energy) as a way to "insonify" (flood with sound waves) rather than illuminate (flood with light) those fea- tures. Computers are used to process the acoustic data so that the resulting sound images (sonographs) resemble aerial photographs (light images). Data collected from the Continental Shelf in the Gulf of the Farallones by the U.S. Geological Survey (USGS) reveal various features on the seabed, including outcropping rock and several types of ripples, dunes, lineations, and depres- sions (these features are collectively called bedforms). A regional map com- piled from these data established that at least four major discrete fields of bed- forms occur on the Continental Shelf between Point Reyes and Half Moon Bay. These fields are separated by monotonous stretches of flat, featureless sea floor. Of particular interest is a series of depressions floored by ripples with wavelengths of about 3 feet. These depressions, which are common east of the Farallon Islands between Point Reyes and the Golden Gate, form the largest of the four fields of bedforms. The shelf in the study area is morphologically com- plex. This complexity reflects an intri- cate geologic history and a wide variety of geologic and oceanographic processes that operate on the shelf to transport, erode, and deposit sediment. Data collected from the Continental Slope by the USGS show that the rugged northern part of the Gulf of the Faral- lones is scarred by numerous small can- yons. Sediment cover is thin or absent. This northern part contrasts markedly with the southern part of the gulf, which is much less rugged and draped by a thin blanket of sediment. Sediment in the southern part appears stable because no large underwater landslides were dis- cerned on the sonographs. Conspicuous geomorphic features in the southern part include Pioneer Canyon and Pioneer Seamount. Sediment is accumulating in Pioneer Canyon and on Pioneer Sea- mount, suggesting that this area is depo- sitional, in contrast to the active trans- port environment found on the shelf. USGS sonographs made of the Gulf of the Farallones have several practical applications. For example, the evidence of strong currents, as indicated by large ripples in coarse sand, suggests that dredge material and pollutants disposed of at sites on the Continental Shelf could be redistributed over large areas. Also, commercial fisherman can use these images to locate the substrates preferred by bottom fishes and crabs. 16 Oceanography and Geology of the Gulf of the Farallones MAPPING THE SEA FLOOR USING SIDESCAN SONAR Towfish 0 Sidescan s wa th In the diagram above, a sidescan- sonar "towfish" is pulled behind a ship, imaging a broad swath of the sea floor. When combined, such swaths form sidescan-sonar "mosaics" or maps of large areas of the sea bottom. The mosaic at left shows depressions (dark areas) floored by sand ripples east of the Farallon Islands between Point Reyes and the Golden Gate, and the mosaic at right shows unusual and complex bedforms, possibly ribbons of sand moving over the sea floor. Landscape of the Sea Floor 17 MAPPING THE SEA FLOOR USING NARROW-BEAM SONAR In the diagram above, ahull- mounted, narrow-beam sonar system is producing a continuous profile of the sea floor as the ship moves. The sample profile at right, taken across a submarine canyon, shows the rugged sea- bottom topography typical of the northern Gulf of the Farallones. Sonar beam NARROW-BEAM-SONAR PROFILE Ship's track 18 Oceanography and Geology of the Gulf of the Farallones 0 10 KILOMETERS BATHYMETRIC IDEPTHI CONTOUR INTERVAL 200 METERS (t METER= 3.281 FEETI 37°30 37°00 Three-dimensional bathymetric map of the Continental Slope in the Gulf of the Farallones. This image was created using sonar. Landscape of the Sea Floor 19 Oceanography and Geology of the Gulf of the Farallones Current Patterns Over the Continental Shelf and Slope Marlene A. Noble The waters of the Gulf of the Farallones extend along the central California coast from Point Reyes southeastward to Ano Nuevo. This unique region of coastal ocean contains valuable biological, rec- reational, commercial, and educational resources. Sandy beaches provide living space for a wide variety of organisms. Seabirds nest along the beaches, in the rocky cliffs above them, and on the Far- allon Islands. Animals ranging from the small anemones found in tide pools to the elephant seals off Ano Nuevo live in these waters. This coastal region is also a play- ground for people, Californians and visi- tors alike. In addition, fishing and com- mercial shipping activities are an integral part of the economy in the region. Tides are the most familiar ocean phe- nomenon. They are easily seen at the sea shore; beaches are covered and exposed twice a day. Tidal currents, the largest cur- rents in San Francisco Bay, move water in and out of the estuary. At the Golden Gate, ebb-current velocities during spring tide can reach 7 miles per hour. Small sail- boats bucking a strong tide can have trou- ble just getting back in through the Golden Gate. Timing of the return is critical. Out- side the Golden Gate, in the coastal ocean, tidal currents are strong near the coastline. They diminish offshore, becoming over- whelmed by steadier currents as water depth increases. Tidal currents and waves are important in the coastal ocean. They mix the water column, allowing nutrients near the seabed to reach plants growing in the lighted sur- face regions. Tides move nutrients and other suspended materials vertically and back and forth, but they generally do not transport these materials large distances. On the Continental Shelf and Slope in the Gulf of the Farallones oceanic cur- rents flow through the area transporting sus- pended sediment, nutrients that allow plants to grow, and possible pollutants. Until recently, however, not much was known about how strong the currents are, in what direction they flow, or how rapidly flow pat- terns change with time or location. Even less was known about how current patterns affect the many creatures that live in the coastal ocean, how currents modify the nat- ural sediment on the sea floor, or about the eventual fate of natural sediment or mate- rials dumped in the gulf. Knowledge is needed about these important factors so that people can make reasonable decisions about how to manage the coastal waters, ensuring that recreational and commercial activities do not harm the environment. During the 1 990's, several programs were undertaken by the U.S. Geological Survey and other organizations to gather information about how currents, nutrients, and suspended material move through the Gulf of the Farallones. The area studied by the USGS covers about 1 ,000 square nauti- cal miles of the gulf and ranges in water depth from 660 to 10,500 feet. These stud- ies showed that the general features of the complex current patterns in the area are similar to those observed elsewhere along the central and northern California conti- nental margin. Currents over the Continental Shelf tend to flow southeastward and slightly offshore in summer, causing nutrient-rich cool waters to upwell onto the shelf. Shelf currents flow mostly northwestward in winter. Tidal currents are strong over the shelf and tend to be the dominant features in flow patterns near the shoreline or within estuaries. The strong waves that occur during winter storms commonly cause sediment on the sea floor to be resuspended and carried both along and off the shelf. The currents on the Continental Slope flow dominately northward in all seasons. Tidal currents over the slope are weak except for regions near the seabed or within the conspicuous submarine canyons that cut into the continental margin. However, many of the current patterns in the Gulf of the Farallones are altered by the region's unique sea-floor topography; therefore, the local characteristics of flow, such as the amplitude of currents, their detailed response to winds, and the strength of the summer upwelling, are spe- cific to an area. In summer, the promon- tory of Point Reyes causes shelf currents to turn offshore and flow over the slope. The abrupt steepening of the slope in the northern part of the area studied also causes northwestward-flowing slope cur- rents to turn toward the deep ocean. Both of these features enhance the exchange of water, nutrients, and other suspended materials among the shelf, slope, and deep ocean relative to what happens along the simple, straight shelf more common north of the gulf. The complex current patterns in the Gulf of the Farallones help to make the coastal waters of the area a truly unique resource. Knowledge of these patterns is essential if competing demands on this resource are to be balanced. 20 Oceanography and Geology of the Gulf of the Farallones 180° 123°W 20 The California Current is part of a permanent, ocean- wide gyre in the surface waters of the North Pacific. It 38°N forms the east part of this gyre, which is defined in the west by the Kuroshio Current (Pacific Gulf Stream), in the north by the North Pacific Current, and in the south by the North Equatorial Current. In the Gulf of the Farallones, currents over the Continental Slope are quite distinct from the southeastward-flowing water of the California Current farther offshore. These slope currents are confined to a relatively narrow band sea- ward of the Continental Shelf and flow northwest- ward, parallel to the topography, as the California Undercurrent. In the gulf, the undercurrent is generally found over the slope in water depths less than 2,600 feet. Bathymetry in meters (1 m = 3.281 ft). WATER MOVEMENTS AND WINDS OFF THE NORTHERN CALIFORNIA COAST In spring and summer, strong winds blowing toward the equator, together with the Corio- lis effect (the tendency of winds and currents to veer to the right in the Northern Hemi- sphere and to the left in the Southern Hemi- sphere), push surface water away from the California coast. To fill its place, nutrient- rich colder water rises to the surface in \ Typical spring and summer conditions, intensified during Las Ninas the yearly upwelling that makes the ocean off northern California so cold in spring and summer and the Gulf of the Farallones so biologically productive. When El Nino atmo- spheric phenomena occur, they disrupt this pattern and cause downwelling, which pre- vents the replenishment of nutrients to sur- face waters and can have a major impact on sea life. For example, in 1997-98, thousands of seals and sea lions starved to death when downwelling warm water drove away many of the fish and squid on which they normally fed. Young animals, such as the sea lion pup shown here, were particularly vulnerable. Areas of cold, upwelled water (blue) along the central California coast are shown in the satellite image below (NOAA AVHRR satellite data, pro- cessed at Naval Postgraduate School). Strongly reversed conditions, common during El Nifios 124°W - 37°N Current Patterns Over the Continental Shelf and Slope 21 STRINGS OF INSTRUMENT PACKAGES ARE USED TO MEASURE OCEAN CURRENTS SURFACE MOORING SUBSURFACE MOORING One method the U.S. Geological Survey has used to measure ocean currents in the Gulf of the Farallones is strings of instrument packages attached to mooring lines anchored on the sea bottom. Surface moorings are mainly used in shallower water. Photograph below shows a cur- rent meter with an attached transmissometer (instrument to measure water clarity) being lowered into the waters of the gulf. Inset shows surface mooring (float) used for a bottom-anchored string of intrument packages. 22 Oceanography and Geology of the Gulf of the Farallones These photographs were taken from a U.S. Geological Survey instrument station lowered to the sea floor in the Gulf of the Farallones. Strong bottom currents can create sand ripples (left), and weaker currents can leave a smooth sea bottom (right, with a curious seal). Current Patterns Over the Continental Shelf and Slope 23 Oceanography and Geology of the Gulf of the Farallones Sediment of the Sea Floor Herman A. Karl Many people perceive the sea floor to be a smooth blanket of sand similar to a sandy beach. For some areas of the sea floor this is true, but just as the sandy beach is flanked by rocky headland and muddy wetland, so are the smooth sandy plains of the sea floor flanked by various different substrates. This is the case for much of the sea floor in the Gulf of the Farallones. The earliest general model of sedi- ment distribution across the sea floor was that the size of sediment particles gradually decreased with increasing water depth. According to this model, the nearshore consisted of a blanket of sand — an extension of the sandy shore — that was gradually replaced by silt and then by clay in deeper water. This model was based on the concept that the energy of ocean currents and waves decreased from shallow water to deeper water and that, therefore, smaller particles could only settle to the bottom in less ener- getic, deeper water. This early model was based on very limited data. These limited data led sci- entists to believe that the deep ocean floor, from which very few samples had been collected and of which no direct observations were possible, consisted of a uniform and monotonous layer of fine- grained sediment. As sampling tech- niques improved and more information was collected, scientists learned that the ocean bottom is as texturally varied and morphologically complex as the land surface. The physical characteristics (for example, size, shape, composition) and the distribution of sediment are the result of a complex interaction among geologic, oceanographic, and biologic processes. Moreover, scientists know that the distribution of sediment on the Continental Shelf is made more complex by deposits of relict sediment. Relict sediment is that material, gener- ally coarse sand and gravel, left on the shelf when it was exposed during times of lower sea level. Evidently, then, the distribution of different types and grain sizes of sed- iment and rocks provides clues about the geologic history of an area and the types of ocean currents that deposited or reworked the sediment. Moreover, the different substrates provide habitats for the various organisms that live on, in, and near the sea floor. Information about substrates in Gulf of the Farallones National Marine Sanctuary is used by scientists investigating biodiversity and ecologic systems to help understand and manage the variety of animals and plants that live in the sanctuary. Such informa- tion is also used by commercial fisher- men as an aid for locating fishes and crabs that prefer a particular substrate. The sea floor in the Gulf of the Farallones consists of many different types of substrate, including rock out- crops, gravel, sand, clay, and deposits of broken shells. Some of these different types of substrate are found very close to each other and have abrupt boundar- ies between them. On the Continental Shelf a wide corridor of sand extends westerly from the Golden Gate to the Farallon Islands. Silty sand and sandy silt bound the corridor to the northwest and southeast, and a band of silt extends around Point Reyes. In general, the sediment on the sur- face of the Continental Slope is finer and more uniform than that on the Con- tinental Shelf in the Gulf of the Faral- lones. Nonetheless, most of the surficial sediment on the Continental Slope in the area of the Gulf of the Farallones stud- ied is very sandy, a condition that is unusual (continental slopes are gener- ally characterized by silt and clay). The reason for this abundance of sand is not fully understood. In general, excep- tionally strong currents are required to transport large amounts of sand from the shelf to the slope, but such situations are extremely uncommon. It is not yet known whether the textural patterns and bedforms on the Continental Shelf in the Gulf of the Farallones reflect entirely present-day processes or whether some of these fea- tures are remnants of processes that operated during lower stands of sea level in the past. During the glacial cycles of the past several million years, sea levels were lowered to as much as 445 feet below present-day sea level. Therefore, ancient relict features created during lower stands of sea level are common on Continental Shelves worldwide. Such lowstands of sea level would have exposed virtually all of the shelf in the Gulf of the Farallones. 24 Oceanography and Geology of the Gulf of the Farallones • '.• ' >. .'- ••• . \ : * , • ; ••• * .- • -• • • » " v- * • v .0 . 2 CM 2 MILES 2 KILOMETERS BATHYMETRIC (DEPTH) CONTOUR INTERVAL 10 METERS (1 METER = 3.281 FEET) 37°53'N GRAIN SIZE i |H Very coarse sand .§ [ 1 Coarse sand to ' ' I I I Medium sand ] Fine sand j» | | Very find sand 6 Photographs of sediment samples and correspond- ing collection sites Samples and photographs of the sea floor in the Gulf of the Faral- lones collected by the U.S. Geo- logical Survey reveal a variety of substrates, including rock out- crops, gravel, sand, clay, and deposits of broken shells. Some of these different types of sub- strate are found very close to each other, and the boundaries between them are abrupt. In general, surficial sediment on the Continental Slope in the gulf is finer and less varied in compo- sition and texture than that on the Continental Shelf. This map shows sediment size distribution on an area of the shelf to the northeast of the Farallon Islands. 123 10'W 37 43' 122 55 Sediment of the Sea Floor 25 Oceanography and Geology of the Gulf of the Farallones Chemical Composition of Surface Sediments on the Sea Floor Walter E. Dean and James V. Gardner Sediments cover most of the sea floor in the Gulf of the Farallones, with a few areas of exposed bedrock. To help deter- mine the origin and distribution of these sediments, 112 core samples were taken by the U.S. Geological Survey at sites on the sea floor from the shallow shelf down to a water depth of about 10,000 feet. These samples were analyzed for 28 major and trace elements, organic carbon, and calcium carbonate. Many factors have affected the history, transport, and distribution of sediments in the Gulf of the Farallones, including the shape of the sea floor, sea-level fluctua- tions, and current patterns. The Continen- tal Shelf in much of the gulf has a low gradient of about 0. 1 degree, and water depth ranges from less than 1 60 feet to about 400 feet. The Continental Slope in much of the gulf has a steeper gradient of about 3 degrees, and water depth reaches about 1 1 ,500 feet at its base. Although the shelf is uncut by channels and canyons, the upper slope is incised with numerous gullies and submarine canyons, including Pioneer Canyon. Before 500,000 years ago, the main sources of sediment to the Gulf of the Farallones were the nearby onshore areas with their variety of sedimentary, metamorphic, and igneous rocks. About 500,000 years ago, drainage from interior California broke through to the Pacific Ocean at the Golden Gate, providing addi- tional sources of sediment from as far away as the Sierra Nevada. The Conti- nental Shelf between the Golden Gate and the Farallon Islands is covered with sandy sediment, which has been repeat- edly reworked by fluctuations in sea level and great (100-year) storms. Major low- erings of sea level during global glacia- tions have exposed the shelf in the gulf as dry land several times, most recently from about 20,000 to 15,000 years ago. In these glacial periods, sea level was lowered by hundreds of feet, because of the large amount of water tied up in ice sheets on land. During these lowstands, a river prob- ably coursed across all of what is now the Continental Shelf in the gulf, although no channel has yet been identified. About 15,000 years ago, rising sea level caused by the melting of the ice sheets once again drowned the Continental Shelf. Water movement in the Gulf of the Far- allones affects the distribution of sediment on the sea floor and the movement of sedi- ment across the Continental Shelf to the deep sea (see chapter on Current Patterns over the Continental Shelf and Slope). The main oceanographic influences on cir- culation in the gulf include the south- ward-flowing California Current during the winter and the northward-flowing Cali- fornia Undercurrent during the summer. Strong offshore currents can also be caused by summer northwesterly winds, leading to coastal upwelling of cold water. Currents generated by tides also help account for the seaward transport of sedi- ment in the gulf. The results of chemical analysis of the core samples collected from the sea floor in the Gulf of the Farallones can be used as "fingerprints" to identify sources and transport patterns of sediment (see chapter on Heavy-Mineral Provinces on the Con- tinental Shelf). The sandy sediments on the Continental Shelf between the Golden Gate and the Farallon Islands contain abundant heavy minerals that are rich in iron, magnesium, titanium, phosphorus, and many trace elements. The sediments immediately adjacent to the Farallon Islands contain low concentrations of heavy minerals and the chemical elements associated with them; instead, these sedi- ments are rich in silica (SiO2). Sediments deposited on the Continental Slope have higher contents of organic matter and clay and, consequently, have higher con- centrations of elements associated with clay minerals, such as aluminum, lithium, potassium, and sodium. Calcium carbon- ate (CaCO3), mainly from the shells of pelecypods (oysters, clams, and mussels), is a very minor constituent of surface sedi- ments in the gulf. 26 Oceanography and Geology of the Gulf of the Farallones CONTENT OF SILICA AND ORGANIC CARBON IN SEA-FLOOR SEDIMENTS 123J20'W 123"00' 122'40' 123'20'W 123-00' 122 40 38 OO'N 37:'40' 37 20' ~~6& — Contours of silica content (weight percent) • Sample site ^•—Contours of organic-carbon content (weight percent) Sea-floor sediments on the Continental Shelf in the Gulf of the Farallones have high contents of silica (Si02), especially adjacent to the Farallon Islands, where granitic sand has been shed from the islands. The silica content of sediments is lower on the Continental Slope, because the clay minerals making up much of the sea-bottom mud there are lower in silica. The higher silica content in sediments on the slope at the south end of the map probably reflects sand moving down Pioneer Canyon. The content of organic carbon (carbon from the remains of organisms) in sea-floor sediments from the Gulf of the Farallones is relatively high for an area of ocean adjacent to a continent, reflecting the high biologic productivity supported by the nutrient-rich seasonal upwelling of the California Current system. The finer-grained sediments on the Continental Slope in the gulf have higher contents of organic carbon than the mostly sandy sediments on the Continental Shelf. Chemical Composition of Surface Sediments on the Sea Floor 27 Oceanography and Geology of the Gulf of the Farallones Heavy-Mineral Provinces on the Continental Shelf Florence L. Wong Minerals are integral to every aspect of our lives — from esthetically pleasing gem stones to more mundane but essential components of concrete. In geology, min- erals are useful in unraveling certain questions, such as where do large bodies of sediment come from (source), how do they move around (transport processes), and where do they settle (distribution). This chapter looks at these geologic issues in the Gulf of the Farallones by examining small (sand-size) mineral grains of high specific gravity ("heavy minerals" — in this study, minerals at least 2.96 times as dense as water). Small grains are apt to be transported great dis- tances by natural processes. In contrast, large mineral grains are not transported far before coming to rest in a depositional basin and thus are not as diagnostic as smaller grains. Therefore, small particles of heavy minerals are good clues to sedi- ment source, transport, and distribution. The Gulf of the Farallones extends from Point Reyes on the north to Ano Nuevo on the south and from the Golden Gate westward across the Continental Shelf to the Continental Slope beyond the Farallon Islands-Cordell Bank ridge. Water depths on the shelf are generally less than 330 feet. Most of the gulf lies west of the major tectonic feature known as the San Andreas Fault Zone, which separates two different types of basement rock: granitic rocks of the Salinian block on the west, and various sedimentary, vol- canic, and metamorphic rocks of the Fran- ciscan terranes to the east (see chapter on Earthquakes, Faults, and Tectonics). The surficial sediment in the Gulf of the Farallones was initially eroded from rocks onshore and then transported and deposited in the present offshore basin. The agents of this process included fault- ing and folding of the Earth's crust and changes in global climate, including gla- ciation. The sediment of the sea floor in the gulf (see chapter on Sediment of the Sea Floor) is composed of sand, mud, some gravel, and biologic debris, such as shells and bone fragments. Sediment on the Continental Shelf in the Gulf of the Farallones west of San Francisco Bay was systematically sam- pled by the U.S. Geological Survey in 1989 to study its characteristics, distribu- tion, and origin. Various properties of the samples were analyzed, including grain size and mineralogic and chemical com- position (see chapter on Chemical Com- position of Surface Sediments on the Sea Floor). The minerals present in the sam- ples reflect two major sources in the central California region: (1) the large variety of rock types of the Franciscan terranes and (2) granitic materials shed from the Sierra Nevada and similar rocks in the central California region. The two mineralogical assemblages are distrib- uted in different areas of the shelf; how this distribution developed is less clear. The mineral and chemical composi- tion of sediments from the Gulf of the Farallones define four depositional prov- inces— two that are composed of granitic debris and two that reflect sources in the Franciscan terranes of northern Califor- nia. The granitic sediment comes from two sources. The dominant source is the Sierra Nevada. The sediment from this source was transported down the Sacra- mento-San Joaquin drainage and through San Francisco Bay and the Golden Gate. The lesser source is the granitic base- ment rocks of the Salinian block west of the San Andreas Fault system. Sediment from a Sierran source is spread over the Gulf of the Farallones to a limited extent north of the Golden Gate and to at least the shelf edge south of the Gate. A small contribution of sediment from Salinian rocks of the Farallon Islands- Cordell Bank ridge, along the west edge of the shelf, is also found on the shelf near the ridge. Minerals derived from the Franciscan terranes characterize surface sediment on the Continental Shelf in the northern Gulf of the Farallones. These minerals represent reworked shelf deposits, ero- sion of dune deposits accumulated during the last low stand of sea level, and coastal erosion of Franciscan bed- rock exposures. 28 Oceanography and Geology of the Gulf of the Farallones 123"00 122°30' Width of image is 4 millimeters. Width of image is 2.25 millimeters. Length of bar is 0.5 millimeters. 38;00'N Photographs taken through microscopes of samples of bottom sediments collected from the Gulf of the Faral- lones (1 millimeter equals 0.04 inch). A, Sample consisting mostly of medium-grained shell material. B, Sample con- sisting of "light" (less than 2.96 times as heavy as water) mineral grains; most light-colored grains are of the miner- als quartz or feldspar; dark grains are glauconite, a clay mineral. C, Grains of two "heavy" minerals — nypersthene (left) and hornblende (right) — mounted on a glass slide for examination under a microscope in polarized light. D, The same grains photographed in cross-polarized light. The characteristics of the grains under each type of illumina- tion were used to identify the minerals. 8ATHYMET HIC IDEPTHI CONTOUR INTERVAL 10 METERS OOWf, TO 100-METER DEPTH li METER = 3.281 FEET; Map of the Gulf of the Farallones. showing sites where the U.S. Geological Survey collected bottom-sediment samples for mineralogical analysis. Grains of fine and very fine sand (about 0.002 to 0.01 0 inch in diameter) were separated and then divided into "light" minerals (less than 2.96 times as heavy as water) and "heavy" minerals (more than 2.96 times as heavy as water). Numbers on the map show the abundance of heavy minerals as a percent of sample weight, and the sizes of the shaded boxes are proportional to this abundance. The thick blue line marks the approximate boundary between areas covered by different heavy-mineral assemblages. The mineralogy and geochemistry of sediments from the Gulf of the Farallones define two main depositional provinces — one composed of granitic debris and one that indicates a source in the Franciscan terranes of northern California The granitic sediment comes from two sources. The dominant source of granitic sediment is the Sierra Nevada. The sediment from this source was transported down the Sacramento-San Joaquin drainage and through San Francisco Bay and the Golden Gate. The lesser source of granitic sediment is the basement rocks of the Salinian terranes west of the San Andreas Fault system, including the Farallon Islands. Minerals derived from the Franciscan terranes characterize surface sediment on the Continental Shelf in the northern Gulf of the Farallones. These minerals represent reworked Continental Shelf deposits, erosion of dune deposits accumulated during the last lowstand of sea level, and coastal erosion of Franciscan bedrock. Heavy-Mineral Provinces on the Continental Shelf 29 and f~ co logical Niches in the Gulf of the Farallones Year round, thousands of people are attracted to the cold waters of the Gulf of the Farallones for its whale and bird watching, beautiful coastal tide pools, and com- mercial and sport fishing. Few realize that the organisms that they see and catch are only a small pan of a rich and complex marine ecosystem. Scientists have found that the distribution and abundance of marine flora and fauna in the gulf are directly related to the physical and chemical conditions of its waters. Upwelling of deep nutrient-rich waters along the coast during the spring and summer months of most years feeds microscopic plankton that support a complex but fragile web of organisms, from Dungeness crabs, chinook salmon, and brown pelicans to elephant seals, great white sharks, and giant blue whales. The Cordell Bank, Gulf of the Farallones, and Monterey Bay National Marine Sanctuaries help to protect and preserve this marine abundance. Biology and Ecological Niches in the Gulf of the Farallones Phytoplankton Gregg W. Langlois and Patricia Smith Phytoplankton play a key role in the marine ecology of the Gulf of the Farallones. These microscopic, single-celled plants are found in greatest abundance in nearshore coastal areas, typically within the upper 160 feet of the water column. The name "phytoplankton" consists of two Greek words meaning "plant" (phyto) and "wan- derer" (plankton). There are two major groups of phytoplankton — (1) fast-growing diatoms, which have no means to propel themselves through the water, and (2) flagellates and dinoflagellates, which can migrate vertically in the water column in response to light. Each group exhibits a tremendous variety of cell shapes, many with intricate designs and ornamentations. All species of phytoplankton are at the mercy of oceanic currents for transport to areas that are suitable for their survival and growth. Thus, physical processes can play a significant role in determining the distribu- tion of phytoplankton species. Rapid cell division and population growth in phyto- plankton can produce millions of cells per liter of seawater, resulting in visible blooms or "red tides." With the potential for such high produc- tivity, it is not surprising that phytoplankton are the first link in nearly all marine food chains. Without phytoplankton, the diver- sity and abundance of marine life in the Gulf of the Farallones would be impos- sible. Phytoplankton provide food for a tre- mendous variety of organisms, including zooplankton (microscopic animals), bivalve molluscan shellfish (mussels, oysters, scal- lops, and clams), and small fish (such as anchovies and sardines). These animals, in turn, provide food for other animals, including crabs, starfish, fish, marine birds, marine mammals, and humans. The coastal area of the Gulf of the Far- allones undergoes periods of strong upwell- ing during the spring and summer months (see chapter on Current Patterns over the Continental Shelf and Slope). In addition to delivering colder, nutrient-rich waters from depth, coastal upwelling concentrates phy- toplankton near the surface. This concen- tration of cells in sunlit surface waters, together with increased nutrients, may pro- vide a competitive edge for the faster grow- ing diatoms during upwelling events. Con- versely, a stratified water mass consisting of a layer of warmer surface water and a deeper layer of colder, nutrient-rich water can form following upwelling. These con- ditions favor the development of dinofla- gellate blooms, such as toxic "red tides," because these types of phytoplankton can actively swim to the surface to photo- synthesize during the day and migrate to deeper areas at night to absorb nutrients. Such conditions can also be associated with downwelling, in which warmer off- shore waters move shoreward, pushing coastal surface waters down and along the sea floor to deeper areas. Research in other parts of the world has shown that dino- flagellates are commonly associated with such nearshore downwelling. Of the more than 5,000 known species of marine phytoplankton, approximately 40 species worldwide have been linked with production of toxins. These marine biotox- ins can have subtle to lethal effects on various forms of marine life. Human con- sumers of certain seafood items (especially clams, oysters, and mussels) are also at risk. It remains difficult to avoid the harm- ful effects associated with blooms of these toxic species because phytoplankton ecol- ogy is not fully understood. Within the Gulf of the Farallones, red tides are a common natural phenomenon, usually occurring from August through October, when a relaxation of coastal upwelling results in a warmer, more stable water mass nearshore that appears to favor dinoflagellate populations. The commonly used term "red tide" is misleading, because phytoplankton blooms frequently are other colors, such as brown, green, and yellow, and are in any case not a tidal phenomenon. Nearly all phytoplankton blooms along the California coast and within the Gulf of the Farallones involve nontoxigenic spe- cies. Conversely, most incidents of paralytic shellfish poisoning (PSP) in humans caused by eating shellfish caught in California waters have occurred in the absence of vis- ible blooms of toxin-producing phytoplank- ton. Because the coastal area encompassed by the marine sanctuary has been the focal point for PSP toxicity in California, and because of the continued increase in com- mercial bivalve shellfish aquaculture within this area, the California Department of Health Services has intensified its biotoxin- monitoring efforts in the area. The key to understanding the combina- tion of physical, chemical, and biological factors that result in blooms of the phyto- plankton species that produce PSP toxins may lie within the Gulf of the Farallones. Such understanding would greatly assist in the protection of public health. 32 Biology and Ecological Niches in the Gulf of the Farallones SIMPLIFIED DIAGRAM OF THE FOOD WEB IN THE GULF OF THE FARALLONES Phytoplankton Scallops Zooplankton Oysters Without phytoplankton, the diversity and abundance of marine life in the Gulf of the Farallones would be impos- sible. Phytoplankton provide food for a tremendous variety of organisms, including zooplankton (microscopic animals), bivalve molluscan shellfish (mussels, oysters, scallops, and clams), and small fish (such as anchovies and sardines). These animals, in turn, provide food for other animals, including crabs, starfish, fish, marine birds, marine mammals, and humans. Phytoplankton 33 Photographs of diatoms taken through a microscope. Coscmodisais(\eft} and the chain of Chaetocems (right) are centric diatoms. Pseudonittschia (bottoml produces domoic acid, which can contaminate shell- fish and cause "amnesic shellfish poisoning" in humans who eat the shellfish. Symptoms include abdominal cramps, vomiting, disorientation, memory loss, and even death. Scale bars are in micrometers (urn); 1 micrometer is one-millionth of a meter or about 1/25,000 of an inch. 34 Biology and Ecological Niches in the Gulf of the Farallones Photographs taken through a microscope of the armored dinoflagellates Ceraf/um(left|. Dinophysis (right) and Alexandrium catene/fe (bottom). Some spe- cies of Dinophysis produce toxins that can cause severe diarrhea (diarrhetic shellfish poisoning) in humans who eat contaminated shellfish. Alexandrium catene/la produces toxins that can cause "paralytic shellfish poisoning" in humans who eat contaminated shellfish. Symptoms include nausea, vomiting, diar- rhea, abdominal pain, and tingling or burning lips, gums, tongue, face, neck, arms, legs, and toes and later shortness of breath, dry mouth, a choking feel- ing, confused or slurred speech, lack of coordination, and even death. Scale bars are in micrometers (\un); 1 micrometer is one-millionth of a meter or about 1/25,000 of an inch. Phytoplankton 35 Biology and Ecological Niches in the Gulf of the Farallones Krill Dan Howard Just as there are growing seasons on land, so there are growing seasons in the ocean as well. In the Gulf of the Farallones, the grow- ing season begins in early spring, when the first phytoplankton blooms (large increase of microscopic plants) of the year fuel growth at higher levels of the marine food web. In California, as in many parts of the world, euphausiid shrimp, commonly called "krill," are one of the beneficiaries of this early-sea- son production and are a critical link in the marine food web. Feeding on phytoplankton (microscopic plants) and small zooplankton (animals), krill populations expand and by being eaten by other marine animals, trans- fer energy from the lowest (primary pro- ducer) level into the upper levels of the marine food web. They are often referred to as "keystone" species because they play such an important role in the functioning of many marine ecosystems. Krill hatch from free-floating eggs and pass through larval and juvenile stages before maturing into adults. This development pro- cess involves a series of molts (casting off the rigid outside skeleton that restricts growth), during which segments and appendages are gradually added. While the new outside skel- eton is still soft, the individual can increase its size. Adult euphausiids have the unique ability to actually shrink in size after a molt if food resources are scarce. Because krill can increase and decrease their size, it can be difficult to determine their age or the age distribution of a population of animals from their sizes. Krill have legs called "swimmerets" that have evolved to look like small feathers and function like fins, giving them great mobility and agility for life in the water column. They feed while swimming, using their modified front legs to form a food basket that strains food from the water while they swim. Krill are typically very gregarious, which means they are often found in large, concen- trated groups, including dense swarms with as many as 100,000 krill per cubic yard of ocean water. This swarming behavior makes krill especially vulnerable to preda- tors. Swarming activity starts sometime in spring and continues through the fall. These aggregations can commonly be located in the Gulf of the Farallones by finding flocks of diving seabirds or clusters of birds picking at the surface. Fishermen use these feeding flocks to help them locate salmon feeding on the undersides of the krill swarms. Lunging humpback whales that break the surface of the water are also a good indication that krill are swarming at or near the surface. Surface swarms provide ideal feeding condi- tions for these large filter feeders. With its huge mouth, a gaping humpback (and other baleen whales) is capable of engulfing a large volume of krill in a single gulp. These dense aggregations of prey provide the several tons of food per day required by these whales during the summer feeding season. In the Gulf of the Farallones, the two most abundant species of krill are Thysanoessa spi- nifera and Euphausia pacifica. They are typi- cally about 3/4 inch long and live for about 2 years. Thysanoessa spinifera is found mostly in shallower water over the continental shelf, whereas Euphausia pacifica is usually found in deeper water towards the margin of the shelf and beyond. Between them they are a major food source for salmon (krill pigments give salmon flesh its characteristic pink to orange color), rockfish, seabirds, and whales. Krill are the main reason hungry humpback and blue whales visit the gulf in the sum- mer— to fatten up for the rigors of the coming year. Both of these krill species dem- onstrate special adaptations that enable them to succeed despite constant predation pres- sure. From spring through fall, Thysanoessa spinifera swarm at the surface during the day. Though it is unclear what is driving this behavior, the benefits must outweigh the cost, which is increased predation. Euphausia pacifica, controlled by light intensity, migrate out of ocean depths and into surface waters each night. As dawn approaches, they return to deep water for the day. This migration pattern is shared with many other organisms in the ocean, and during the day krill form part of the so-called "deep scattering layer" that fishermen see on their depth sounders. The timing of this daily event in response to changing light intensities provides Euphausia pacifica with several advantages. By moving upward at night, Euphausia pacifica minimizes expo- sure to daytime predators, while grazing in surface waters where food is abundant. They also realize an energy gain by returning during the day to the colder deep water, where metabolism slows. Releasing eggs in wanner surface waters speeds development times, thus reducing the time exposed to predators; it also ensures that hatching larvae are in productive waters when they start feed- ing, increasing their chances of survival. Krill are a critical link in the Gulf of the Farallones marine food web and in marine food webs around the world. They directly or indirectly support the survival and well-being of many animals living in different oceans. Knowing the key position filled by krill in many marine ecosystems, we need to ensure that their populations remain healthy — for the well-being of all. 36 Biology and Ecological Niches in the Gulf of the Farallones 37 The two species of krill common in the Gulf of the Farallones are Euphausia pacifica (right, photograph courtesy of Steven Haddock) and Thysanoessa spi- nifera (below, photograph from Gulf of the Farallones National Marine Sanctuary.) 38 Biology and Ecological Niches in the Gulf of the Farallones Seabirds feeding on swarming krill in the Gulf of the Farallones. (Photograph from Gulf of the Farallones National Marine Sanctuary.) ungmg humpback whales feeding on surface swarms of krill are a common sight in the Gulf of the Farallones in the summer. (Photograph courtesy of Thomas R. Kieckhefer, Pacific Cetacean Group.) Krill 39 Biology and Ecological Niches in the Gulf of the Farallones Free-Floating Larvae of Crabs, Sea Urchins, and Rockfishes Stephen R. Wing Free-floating larvae of bottom-dwelling marine organisms play an important role in the ecology of the Gulf of the Farallones and are a major food source for many species, including salmon and seabirds. Free-floating larvae are also the primary means by which several important species are dis- persed along the northern California coast. Most commercially harvested invertebrates (for example, sea urchins and crabs) and some fish populations are made up of a net- work of adult subpopulations spread along the coastline, connected almost solely by larval dispersal. In the Gulf of the Farallones many com- mercially important coastal species, such as Dungeness crab (Cancer magister), red sea urchin (Strongylocentrotus francisca- nus), and rockfish (Sebastes spp.), have swimming larval forms that drift as plank- ton during the spring. These larvae are subject to the strong offshore and south- ward flow present in the California Current system during the spring upwelling season (see chapter on Current Patterns Over the Continental Shelf and Slope). Understand- ing how larvae of these species maintain themselves at latitude and are transported inshore into suitable juvenile habitat is important in ensuring the long-term viabil- ity of these fisheries. In 1992, a study was begun to understand how coastal oceanographic processes influ- ence the distribution of crab and sea-urchin larvae around Bodega Head, a coastal head- land at the northern margin of the gulf. This required the cooperative efforts of many organizations, including Gulf of the Faral- lones and Cordell Bank National Marine Sanctuaries, U.S. National Marine Fisheries Service, Scripps Institution of Oceanogra- phy, Point Reyes Bird Observatory, Oregon State University, California Department of Fish and Game, and Pacific Fisheries Envi- ronmental Group. Sampling extended over several years and was done both from aboard ships and at shore stations. Results indicate that during periods of upwelling, larvae accumulate in the warm water that collects between the Farallon Islands and Point Reyes in the northern gulf. Larval accumulation was also observed in the upwelling shadows, or eddies, that form behind other capes and headlands when the wind is blowing from the north and surface water is moving in a southerly offshore direction. When the northerly winds that cause upwelling relax, this larvae-rich water moves north in buoy- ancy-driven currents that remain coastally trapped. During this time many larvae that have been retained in the gulf are trans- ported to the north, and some settle out of the water column and onto the sea floor for their next life stage. In both 1994 and 1995, an upwelling jet seaward of Point Reyes and an upwelling shadow downwind (south) of the point were evident from the currents, temperature, and salinity of the surface waters. Information was collected at the boundaries between four distinct water masses: (1) newly upwelled water, (2) oceanic water from offshore, (3) San Francisco Bay outflow, and (4) a mix- ture of these water types that was called "gulf water." The different water masses con- tained different types of larvae. In general, all stages of larval development for crabs of several species could be found within, but not outside, the gulf water. This water mass is found in the wind shadow south of Point Reyes. In contrast, rockfish larvae were found in high concentrations offshore in oce- anic water and at the boundary between newly upwelled water and gulf water. The Gulf of the Farallones provides a pathway along which distinct masses of water con- taining both crab and rockfish larvae are likely to be transported to suitable juvenile habitats within the gulf and to the north. Larval settlement becomes more epi- sodic and less frequent with increasing northward movement away from the area of larval retention/accumulation south of Point Reyes. Nearly twice as many crab larvae settle at Point Reyes and to the south, where warmer gulf water is constantly present, than to the north, where settlement occurs only when the northerly winds that cause upwell- ing subside and relaxation currents move northward. Sea urchin larvae also settle during specific oceanic conditions, but less predictably than crabs. Consistent larval dispersal from any sub- population of adult animals may be limited to the length of an embayment. For example, two such embayments on the northern Cali- fornia coast are from Point Reyes to Point Arena and from Point Arena to Cape Men- docino. Because strong seaward currents form at each end of these embayments during upwelling, larvae caught in these cur- rents would be swept out to sea and have no chance of developing and becoming a part of the adult population. The data collected in this study on the distribution of free-floating larvae in the Gulf of the Farallones provide critical infor- mation on the lifecycles of commercially important bottom-dwelling species. Because these larvae are a food source for many marine species, this information is crucial to the effective management and conservation of coastal marine ecosystems in the gulf. 40 Biology and Ecological Niches in the Gulf of the Farallones Larval crab from the Gulf of the Farallones, greatly magnified. -• Sample of plankton collected in the Gulf of the Farallones, showing a larval rockfish, euphausiid shrimp (krilll, and other zooplankton. (Photograph from Gulf of the Farallones National Marine Sanctuary.) i Red sea urchins, harvested for sushi, are one of many commercially important coastal species in the Gulf of the Farallones with swimming larval forms that drift as plankton during the spring. (Photograph from Gulf of the Farallones National Marine Sanctuary.) Free-Floating Larvae of Crabs, Sea Urchins, and Rockfishes 41 I Biology and Ecological Niches in the Gulf of the Farallones Salmon Peter Adams Two species of salmon — chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) — are commonly found in the Gulf of the Farallones. Chinook salmon fishing is the activity that brings the most people out on the waters of the gulf. In 1995, the chinook fishery in the gulf was valued at more than $24 million. Chinook (or king) salmon are key pred- ators in the gulf, and their distribution and occurrence are related to their seasonal diet cycle. Most chinook salmon found in the gulf are 3-year-old fish returning from the open ocean that are preparing to enter the Sacramento River system, where they will spawn and then die. After the eggs hatch the following spring, the juvenile salmon will grow for 7 months in freshwa- ter. They then migrate to the ocean, where they will live for 2 years before returning to the gulf. Coho (or silver) salmon along the California coast are listed as a threat- ened species under the Endangered Spe- cies Act, and their capture has been pro- hibited since 1993. Native-run (versus hatchery) chinook salmon are also a candi- date for a threatened-species listing. Chinook salmon returning from the open ocean move into the Gulf of the Far- allones in February and March, when they are found off the Golden Gate from Boli- nas Point in the north to Point San Pedro in the south. While in this area they feed almost equally on Pacific herring and anchovies. The herring have just migrated back to their feeding grounds outside of the Golden Gate from San Francisco Bay, where they spawned from November through February, and anchovies are gath- ering in nearshore waters before moving into the bay beginning in April. In April, chinook salmon are found from north of the Golden Gate to Point Reyes and offshore to the Farallon Islands. There they feed on invertebrates, largely the euphausiid shrimp (krill) Thysanoessa spinifera. Krill are taken as prey from surface and subsurface swarms that occur over a wide area of the gulf during April and May. The pink to orange color of salmon flesh during this period is due to a carotenoid pigment in the exoskeleton of the krill (for more information, see chapter on Krill). This flesh color has become so popular that now there are fisheries for krill, which are freeze-dried and fed to pen-reared salmon as a finishing product to produce this color. For a brief 2- or 3-week period in April, the Chinook's diet is dominated by the megalopa larvae of the Dungeness crab (Cancer magister) (see chapter on Free- Floating Larvae of Crabs, Sea Urchins, and Rockfishes). These larvae are the last pelagic (free-floating or swimming) stage before the crabs sink to the bottom and take on their adult shape. More than 7,000 Dungeness megalopa have been found in a single chinook-salmon stomach. In May and June, chinook start feeding on krill and juvenile rockfish offshore near the Farallon Islands. These rockfish are late pelagic-stage fish that as adults will migrate to bottom habitats. In years when juvenile rockfish are abundant, they are the preferred prey and dominate the chi- nook diet during these months, whereas in low-abundance years, chinook salmon feed mainly on krill. Sometime between mid-June and mid- July, the chinook salmon abruptly move from near the Farallon Islands to directly in front of the Golden Gate, the so-called "middle grounds." Here, chinook salmon feed exclusively on anchovies, which had moved into San Francisco Bay in May and June to begin spawning in the warmer water. After June, when the water in the gulf warms up because of the absence of cold upwelled water, anchovies move out of the bay and into the gulf where they continue spawning into October. Chinook Salmon remain in front of the Golden Gate until October, but in lower and lower concentrations as they move up the Sacra- mento River system to spawn. The follow- ing February, the next year's 3-year-old chinook salmon begin to enter into the gulf, and the cycle begins again. During strong El Nino years, the normal sequences of chinook salmon prey do not develop because the large increase in ocean temperature disrupts the prey's normal behavior. As a result, the aggrega- tions of salmon that feed on these prey do not form, and chinook salmon of a given length weigh much less than normal. California's commercial salmon catch also drops severely, and the recreational catch is far below average. 42 Biology and Ecological Niches in the Gulf of the Farallones 123°00'W 122°30' 38°00'N - SAN 1-RANCISCO * 37°30' A Chinook salmon (Oncorhynchus tshawytcha). Most chinook salmon found in the Gulf of the Farallones are 3-year-old fish that are returning from the open ocean and preparing to enter the Sacramento River system, where they will spawn and then die. (Photograph from U.S. Food and Drug Administration.) As shown in this simplified diagram, 3-year-old chinook salmon return- ing from the open ocean move into the Gulf of the Farallones in February and March and feed on Pacific herring and anchovies off the Golden Gate from Bolinas Point in the north to Point San Pedro in the south. In April, they feed on invertebrates, largely the euphausiid shrimp (krill) Thysanoessa spinifera. For a brief 2- or 3-week period in April, the chinook salmon's diet is dominated by larvae of the Dungeness crab (Cancer magistei). In May and June, chinook salmon start feeding on krill and juvenile rockfish near the Farallon Islands. Sometime between mid-June and mid-July, chinook salmon abruptly move from near the Farallon Islands to directly in front of the Golden Gate, the so-called "middle grounds." Here, chinook salmon feed exclusively on anchovies. Chinook salmon remain in front of the Golden Gate until October, but in lower and lower concentrations as they move up the Sacramento River system to spawn. The following February, the next year's 3-year-old chinook salmon begin to enter into the gulf, and the cycle begins again. Chinook salmon fishing is the activity that brings the most people out on the waters of the Gulf of the Farallones. This large salmon was caught in the gulf. (Photograph from National Marine Fisheries Service.) Salmon 43 Biology and Ecological Niches in the Gulf of the Farallones Seabirds Peter Pyle Among the animals of the Gulf of the Faral- lones, seabirds are the easiest to study. Resid- ing above the water surface (for the most part), seabirds are readily observed by land- or boat-bound humans. They generally nest in huge colonies on islands, facilitating research on their breeding-population sizes and nest- ing requirements. For these reasons, seabirds are commonly used as barometers of the health of marine ecosystems. This observa- tion is true in the gulf, where a widely varying marine environment supplies an interesting extra dimension for study. "Seabirds" is not a technical term but refers to individuals among a hodgepodge of different bird families that share in common their ability to make a living on the ocean. In the Gulf of the Farallones there are 1 1 or 12 species of breeding seabirds, including common murres, Cassin's and rhinoceros auklets, western gulls, Brant's and pelagic cormorants, storm petrels, pigeon guillemots, and tufted puffins. Another 35 species of migrant seabirds are regular visitors to the gulf but do not breed there; examples of these species include Pacific and red-throated loons, red-necked and western grebes, black- footed albatross, pink-footed, Buller's, and black-vented shearwaters, herring and glau- cous-winged gulls, and black and surf sco- ters. About 25 additional species of non- breeding seabirds have been recorded rarely or as vagrants in the gulf, including the manx shearwater, an Atlantic species that has recently been seen sporadically and could even begin to breed in the gulf. All of the breeding species in the Gulf of the Farallones nest on the Farallon Islands, which are in the center of the gulf. Since 1968, biologists from the Point Reyes Bird Observatory have monitored the size and productivity of these populations. Only through such long-term research can a full understanding of the population dynamics of these species and of their relation to the marine environment be achieved. Some of these species also nest on cliffs and small islets along the Marin County coast, north of the Golden Gate. The common murre typifies breeding sea- birds in the Gulf of the Farallones. Before the 1850's, an estimated 400,000 to 600,000 murres bred on Southeast Farallon Island, but this population was decimated by egg collect- ing in the wake of the California Gold Rush, before chickens had arrived in sufficient num- bers to provide eggs for the burgeoning San Francisco populace. Other threats, such as oilspills, human disturbance on the islands, and the depletion of Pacific sardine stocks, reduced populations further until they reached a low of about 6,000 birds during the 1950's. Southeast Farallon Island became a National Wildlife Refuge in 1969, and through pro- tection and increased environmental aware- ness, populations in the Gulf of the Farallones gradually climbed to about 100,000 individu- als by the year 2000. Common murres, along with the other seabirds breeding at the Farallones, have "good years" in which 90 percent or more of the pairs successfully fledge a chick, and "bad years" in which failure rates reach 50 percent or more. These good and bad years generally reflect the strength of the California Current, the intensity of coastal upwelling, the pres- ence and absence of "El Nino" events (see chapter on Current Patterns Over the Conti- nental Shelf and Slope), and the effects that these processes have on juvenile rockfish, anchovies, sardines, and other food resources. Because of the high levels of marine pro- ductivity found in the Gulf of the Farallones, many species that nest far away also come to the region during their non-breeding seasons. The most common of these species is the sooty shearwater, which visit the Gulf of the Farallones in late summer by the hundreds of thousands, if not a million or more at a time. Every autumn there is also a great northward dispersal of organisms into the Gulf of the Farallones from the south, follow- ing the northward migration of the northern anchovy. Among the birds that follow this migration are brown pelicans, Heermann's gulls, and elegant terns. Many species of loons, grebes, ducks, gulls, and alcids (a family of diving seabirds having a stocky body, short tail and wings, and webbed feet — they include the horned puffin, the ancient murrelet, Xantu's murrelet, and the threat- ened marbled murrelet) take up winter resi- dence in the Gulf of the Farallones, escaping the harsher winters of their Alaskan breeding grounds. Finally, a few species of seabirds breed to the north and winter primarily or entirely to the south of the gulf. These long- distance migrants, including phalaropes, jae- gers, and Sabine's gull, can be seen passing through the Gulf of the Farallones from July to October and in April and May. Current threats to seabird populations in the Gulf of the Farallones region include effects of contaminants from San Francisco Bay, overrishing, low-level or "chronic" oil pollution, and mortality associated with gill- netting in Monterey Bay. Declines in some seabird populations in the gulf are occurring because of these and other effects. Data on the reproductive success and survival of these seabirds, integrated with knowledge of food resources and the marine environment, can be used to assess the status and health of the Gulf of the Farallones marine ecosystem. 44 Biology and Ecological Niches in the Gulf of the Farallones The common murre typifies breeding seabirds in the Gulf of the Farallones. Before the 1850's. an esti- mated 400,000 to 600.000 murres bred on Southeast Farallon Island, but this population was decimated by egg collecting in the wake of the California Gold Rush (see inset, courtesy of the California State Library), before chickens had been brought in suffi- cient numbers to provide fresh eggs for the burgeon- ing San Francisco populace. Seabirds 45 i A South Polar skua, the avian "king of the sea" with a 4-foot wingspan, in search of victims in the Gulf of the Farallones. Breeding deep in the Southern Hemisphere, skuas disperse over the oceans during the nonbreeding seasons (summer and fall in the Northern Hemisphere), as far north as the Gulf of Alaska. Skuas are piratic and forcibly extract food from their victims — shearwaters, petrels, gulls, and even albatrosses. They are solitary marauders, nowhere common, but in the gulf they are always a menace to visiting seabirds. A tufted puffin eating a small fish. Only 50 or 60 of these birds breed on the Farallon Islands each year, in deep rocky crevices within the cliffs. Where these striking birds go in the winter is unknown, evidently somewhere far out at sea. Populations of tufted puffins numbered in the thousands during the 1800's; recent declines are attributed to a degradation in the marine environ- ment and, possibly, to the disappear- ance of Pacific sardines in the 1940s. (Photograph from Gulf of the Faral- lones National Marine Sanctuary.) »- 46 Biology and Ecological Niches in the Gulf of the Farallones Western gulls (chick shown below) nesting on South- east Farallon Island. Populations of western gulls in the Gulf of the Farallones since 1950 have benefited from feeding at land-based dumpsites and fish-pro- cessing plants, expanding from about 6.000 breeding birds historically to more than 25.000 birds during the early 1990s. (Photographs from Gulf of the Farallones National Marine Sanctuary.) Seabirds 47 Biology and Ecological Niches in the Gulf of the Farallones Marine Mammals Jan Roletto Many people are attracted to the Gulf of the Farallones by the variety and abundance of marine mammals that can be seen there. In the gulf, they reign as both apex predators and high-profile or "heroic" species. Some marine mammals migrate through the gulf, whereas others come there to "haul out" on land, rest, and (or) rear their young. They are attracted to the gulf because of the high biological productivity of its waters and the variety of prey species that are distributed and retained there by oceanic circulatory patterns and intense upwelling of nutrient- rich water. The gulf attracts at least 33 species of marine mammals. Of the 1 1 species that dominate the coastal and pelagic (open ocean) zones, the humpback whale and blue whale are Federally listed as endangered species and the Steller sea lion is listed as a threatened species. The other dominant spe- cies are the gray whale, Pacific white-sided dolphin, harbor porpoise, Dall's porpoise, California sea lion, northern fur seal, north- ern elephant seal, and harbor seal. From the shore, the gray whale is the most commonly seen of the cetaceans (whales, dolphins, and porpoises) in the gulf. Gray whales annually migrate from their feeding grounds in the Arctic Ocean and Bering Sea to the warm lagoons of Baja California (Mexico), where they give birth to their young. They can be seen migrating southward through the gulf beginning in November, and peak sightings are during January and March. A few juveniles may be seen year round. Gray whales are "baleen" whales — instead of teeth, they have numer- ous long overlapping strips of elastic fin- gernail-like material (baleen) hanging from their upper jaws that they use to filter out food. Gray whales feed primarily on the shallow bottom (less than about 400 feet deep), where they swim on their sides while shoveling up mouthfuls of mud and water to strain out small crustaceans, such as amphi- pods, and other animals living in the sedi- ment. They also feed in the water column on euphausiid shrimp (krill) and a few fish species, such as herring. Humpback whales are the most acro- batic of the baleen whales seen in the gulf. They use the gulf and Cordell Bank to the north as feeding grounds during the summer and fall months. Their prey consist primar- ily of the krill species Thysanoessa spi- nifera and Euphausia pacifica, and they also feed on schooling fish, such as herring, juvenile rockfish, and anchovy. Blue whales migrate to the Gulf of the Farallones during the late summer and are found there throughout the fall. As adults, these giant whales generally weigh more than 100 tons and may be the largest ani- mals that ever lived on Earth, possibly exceeded only by the dinosaur Ultrasaurus. These baleen whales feed primarily on krill and, infrequently, red pelagic crabs. Red pelagic crabs are found in the gulf only during warmer-water conditions, such as occur when El Nino events affect the gulf (see chapter on Current Patterns Over the Continental Shelf and Slope). The most familiar of the pinnipeds (seals and sea lions) in the gulf is the California sea lion. During its nonbreeding season from August through May, males, juveniles, and some females of this species are abun- dant in the gulf. During that period, 10 to 40 percent of the total local population are females. The sea lions are seen locally on docks, on nearshore rocks, and in large numbers on the Farallon and Ano Nuevo Islands, along the Point Reyes headlands, and at Bodega Rock. They feed on anchovy, herring, hake, mackerel, crabs, and squid. In times of low productivity, they have been known to feed on red pelagic crabs, sharks, eels, birds, and algae. Also common in the Gulf of the Faral- lones is the northern elephant seal, one of the deepest-diving marine mammals. Adult female elephant seals can dive to depths of 4,000 feet and males to 5,700 feet. While at sea, these seals are submerged 80 to 90 percent of the time. Hunting, feeding, and sleeping all take place underwater. They come on land only to breed and molt. Their breeding season begins during December and ends in mid-March. Deep-water fish and invertebrates — squid, octopus, hagfish, ratfish, hake, and rockfish — are their pri- mary foods. Other marine mammals observed in the gulf include four species Federally listed as endangered — fin whale, sei whale, right whale, and sperm whale. Two other species are listed as threatened — Guadalupe fur seal and southern sea otter. Many addi- tional species of marine mammals have been observed in the gulf. Apart from the minke whale, which is a baleen whale, these species are all members of the group known as "toothed whales." They include the northern right-whale dolphin, short- beaked common dolphin, long-beaked common dolphin, bottlenose dolphin, striped dolphin, spotted dolphin, Risso's dolphin, killer whale, short-finned pilot whale, pygmy sperm whale, dwarf sperm whale, Cuvier's beaked whale, Baird's beaked whale, Hubb's beaked whale, and Blainville's beaked whale. 48 Biology and Ecological Niches in the Gulf of the Farallones Gray whale straining water from its mouth (photo- graph courtesy of Jim Cubbage). Gray whales are "baleen" whales— instead of teeth, they have numer- ous long overlapping strips of elastic fingernail-like material, called baleen (inset), hanging from their upper jaws that they use to filter out food (photograph from Gulf of the Farallones National Marine Sanctu- ary). "Whale watching" is a popular activity in the Gulf of the Farallones and helps to highlight the important ecological roles played by marine mammals. Marine Mammals 49 Humpback whale swimming underwater. (Photograph from Gulf of the Farallones National Marine Sanctuary.) *- Pacific white-sided dolphin (above) and northern right-whale dolphin (below) swimming under- water. (Photograph courtesy of Ken Balcomb.) T Adult females and immature northern ele- phant seals at Southeast Farallon Island. Inset shows the characteristic nose of an adult male. (Photographs from Gulf of the Farallones National Marine Sanctuary.)*- 50 Biology and Ecological Niches in the Gulf of the Farallones -• Immature California sea lions at play in the surf. (Photograph by Jan Roletto, Gulf of the Farallones National Marine Sanctuary.) y Adult male and female Steller sea lions at a breed- ing colony. This species is Federally listed as threat- ened under the Endangered Species Act. (Photograph courtesy of Robert Wilson.) (arbor seals resting on shore. (Photograph from Gulf of the Farallones National Marine Sanctuary.) Marine Mammals 51 Biology and Ecological Niches in the Gulf of the Farallones White Sharks Scot Anderson Each fall, white sharks (Carcharodon car- charias) are observed around the Farallon Islands, preying on seals and sea lions (pin- nipeds) (see chapter on Marine Mammals). The shark's dark back and light underbelly blend with the surrounding environment, hiding the shark from unsuspecting pinni- peds. White sharks spend a great deal of time searching for food; it may be weeks or a month between feeding opportunities. The peak in predation, in the fall months, is related to the number of young (1- and 2-year-old) northern elephant seals arriving at the islands at this time. These immature seals are the preferred prey of the white shark at the Farallon Islands. Observations there indicate that the white sharks eat young elephant seals seven times more fre- quently than they eat other pinnipeds, such as California sea lions and harbor seals. Immature elephant seals arrive at the Far- allon Islands to come ashore beginning in September and continuing through Novem- ber. The small pocket beaches and surge channels around the islands offer undis- turbed "haul out" sites and resting areas. Unlike California sea lions, which are the most numerous pinnipeds on the islands, elephant seals cannot climb high up on the islands' rocky shores. Therefore, they are restricted to the pocket beaches and surge channels. The fall haul out of elephant seals is commonly their first visit to the islands. Many of these seals are from other colonies, such as those at the Channel Islands or Point Ano Nuevo to the south, and they may be unaware of white sharks patrolling the waters around the Farallon Islands. Studies of white sharks in the Gulf of the Farallones begun in 1987 have revealed the remarkable way in which these predators are able to locate and catch pinnipeds. Using photographs of dorsal and tail fins, and underwater videotapes of entire sharks, it has been possible to identify individual white sharks and follow their movements in the gulf over many years. Several of the larger sharks have been seen in the same areas for more than 5 years. When individual sharks are identified, they are always seen in the same area. However, some of the sharks are regular visitors, whereas others are only intermittently seen in the gulf. By 1995, monitoring of individual white sharks around the Farallon Islands, using small transmitters swallowed by the animals, had documented their movement patterns and internal temperatures. The movement patterns indicate that each shark has an area that it covers by zigzagging back and forth. These sharks are not swimming aimlessly; they increase their odds of finding pinnipeds by looking in familiar areas where they have previously been successful. The largest sharks covered the smallest home ranges and the smallest shark tracked covered the larg- est home range. The larger, older sharks seem to be more experienced and therefore know where to search. Monitoring found that white sharks in the Gulf of the Farallones maintain a con- stant body temperature of nearly 80°F in the cold (54 to 57°F) water of the gulf. This allows them to move quickly and to capture warm-blooded marine mammals, such as pinnipeds. Most of the world's predatory sharks cannot increase their body tempera- ture above the ambient water temperature, and so their range is limited to warmer trop- ical waters. High tides and large swells affect the rate of white shark predation on pinnipeds in the waters around the Farallon Islands. Such conditions force many of the seals to move from their haul-out space. This displacement may explain why significantly more attacks on elephant seals — sometimes two or three in one day — are observed when large swells are combined with high tides. Despite the white shark's fearsome rep- utation and Hollywood image, attacks on humans are relatively rare. In northern and central California, there is on average one or two white shark attacks on humans per year and about one fatality per decade (chances of drowning in the State's coastal waters are at least 100 times greater). In most of these instances, the shark has bitten only once and then released the person immediately. Those bitten usually survive if they can make it to shore, so swimming alone is not advised. Some evidence suggests that white sharks do not like the "taste" of people but sometimes mistake them for there favorite prey, pin- nipeds. Therefore, it is not advisable to swim or surf near colonies of pinnipeds, where white sharks may be actively feeding. Areas where there has been a history of shark attacks should also be avoided. For these reasons, sport divers avoid the waters around the Farallon Islands. The population of white sharks off Cal- ifornia's coast is probably small, having perhaps a few hundred to a few thousand adults. White sharks are important predators in the State's marine ecosystems. In 1994, with the support of scientists, fishermen, surfers, divers, and others, the State of Cali- fornia placed the white shark on the list of species protected in its waters. 52 Biology and Ecological Niches in the Gulf of the Farallones The white shark is a fearsome preda- tor, well adapted to live in cold water, where food is more abundant. It is far from a "primitive" cold-blooded fish but is actually a highly evolved warm- blooded animal. MOVEMENTS OF A WHITE SHARK OVER 9 DAYS Mimunga Bay White sharks do not swim aimlessly; they increase their odds of finding seals by looking in familiar areas where they have previously been successful. The map shows the movements of a white shark tracked during October 21-29, 1993, around Southeast Farallon Island, using a transmitter swallowed by the animal. 100 200 METERS White Sharks 53 The white shark searches for food visually, staying near the sea bottom in water less than 90 feet deep (top) and paralleling the ocean's surface in deeper water (bottom). In both situations, the shark's dark back and light under- belly blend with the surrounding environment, hiding the shark from seals and sea lions, its usual prey. WHITE SHARKS SEARCH FOR FOOD VISUALLY 10:36 0 10:51 1 -- 1 SHALLOWER WATER Time — i — 11:06 T T 11:21 a.m. 10 - 20 J L J I I L J I I 30 40 Time 11:57 12:12 •> r 12:27 T — — T 12:42 p.m. 10 30 - 60 - 90 120 150 — i — — i — r DEEPER WATER 10 J I I L 54 Biology and Ecological Niches in the Gulf of the Farallones -« Gulls hover over a predatory attack by a white shark on a northern elephant seal. Southeast Farallon Island is in the background. y Attack by white sharks is violent and quick; the sharks can strike quickly because they are warm blooded. White Sharks 55 Biology and Ecological Niches in the Gulf of the Farallones Continental Slope Communities Tom Laidig In the shallow coastal areas of the Gulf of the Farallones, as in other regions of the world, fishing pressure has increased and numbers of fish have decreased over the past few decades. As many fish stocks have declined, some fishermen have been forced to look elsewhere to fill their nets. Traditional fishing grounds in the gulf have been located on the Continental Shelf, a rather flat, relatively shallow area of the sea floor adjacent to the coast. At a depth of about 600 feet, the bottom starts to drop off more rapidly on what is called the Con- tinental Slope. It is on upper and middle parts of this steeper slope that the new fish- ing grounds have been established. Because the fish inhabiting these deeper waters are less understood than those in shallower water, there is a danger of overharvesting, which could threaten the long-term viabil- ity of these newer fisheries. The deep waters of the Continental Slope are characterized by nearly freezing temperatures, extremely low light condi- tions, and very high pressures. Because of the cold, organisms that live at these depths have slower metabolisms — they eat less frequently, are slower in digesting their food, and move and grow more slowly. They also attain greater ages than their counterparts that live in shallower waters — some deep-sea rockfish live more than 70 years. Many of the animals living in the perpet- ual darkness of the Continental Slope have developed light-producing organs. These serve various functions, such as communi- cating with members of their own kind (as in courtship), attracting food (like attracting moths to a flame), and avoiding being eaten (flashing a light in a predator's eyes can give an animal a chance to get away). Another adaptation to the darkness is an absence of color diversity. With no light, colors have little function. Therefore, animals living on the Continental Slope are generally a dark color, like black, brown, or red. Among the fishes, rockfish and thornyheads are dominantly red. Red objects appear black at depth, allowing red organisms to blend in with their dark sur- roundings. The water pressure on the sea floor at the top of the Continental Slope is more than 10 times higher than at the surface, and at the bottom of the slope the pressure can be more than 100 times higher than at the surface. To compensate for this high pres- sure, organisms have a large percentage of water in their tissues, bones, and shells that replaces other substances, such as gases and calcium. Owing to the high water content of their tissues, many larger, older fish caught from deeper waters are limp and soft when brought to the surface. Fishes living at different depths on the Continental Slope have different life his- tories. Species living near the top of the slope produce pelagic (open-ocean) young that spend the first few months to years of life swimming in the upper water column and then settle out in relatively shallow water and migrate downslope as they grow and mature. Dover sole, sablefish, and rock- fish have this type of life history; however, most species living deeper, such as rattails, deep-sea soles, and slickheads, have young that live in the same depths as the adults. Relatively few species occur at all or most depths on the Continental Slope. Spe- cies occupying one depth commonly are replaced by similar species at other depths. An exception is the eel-like hagfish, which is found at all depths on the slope. Productive commercial fisheries operat- ing today on the Continental Slope off California's coast catch Dover sole, sable- fish, deep-living rockfishes, and thorny- heads. Many of these fishes occupy similar habitats and generally are caught together. One increasingly active fishery is for rat- tails, a deep-living fish with a large head and a long tail that tapers to a point. One major fishery of note is for hagfish, the skin of which is used to make what are sold as "eel skin" wallets. Hagfish are not true eels but are a primitive group of fish that have no bones or jaws. Instead of bones, they have cartilage, and instead of jaws, they have a large sucker-like mouth similar to that of a lamprey or a leech. Once attached, hagfish use a tongue with many tiny teeth to dig into their prey. Once inside, the prey is eaten from the inside out. Besides its unique method of eating, the hagfish has another interesting trait — it produces copious amounts of slime, probably used to discourage predators, which gives the fish its nickname, the "slime eel." Except for fishing activities, the Con- tinental Slope and its communities of fish and invertebrates are still virtually untouched by humans, offering scientists the opportunity to study a generally undis- turbed natural system. New methods, such as viewing animals and their habitat by underwater video cameras in submarines and in remotely operated vehicles, have been particularly productive in providing a new understanding of fish and invertebrates living on the slope. In the Gulf of the Faral- lones, scientists are using these methods to collect data at increasingly greater depths, providing critical information needed to better protect these areas from overuse. 56 Biology and Ecological Niches in the Gulf of the Farallones Because of the absence of light on the Continental Slope, animals living there are generally either a dark color, such as the sablefish (left), or red, such as the shortspine thornyhead (right). Continental Slope Communities 57 Juvenile rockfish swimming over Cordell Bank in the northern Gulf of the Farallones. Species of fish living near the top of the Continental Slope in the gulf pro- duce pelagic (open-ocean) young that spend the first few months to years of life swimming in the upper water column and then settle out in relatively shallow water and migrate downslope as they grow and mature. (Photograph courtesy of Robert Schmieder, Cordell Expeditions.) A red-banded rockfish on the Continental Slope in the Gulf of the Farallones. Relatively few species of fish occur at all or most depths on the slope. Those occu- pying one depth commonly are replaced by similar species at other depths. For example, greenstriped and stripetail rockfishes live on muddy bottoms on the upper part of the slope, whereas at greater depth they are replaced by species of thornyheads. 58 Biology and Ecological Niches in the Gulf of the Farallones Ihornyheads, giant brittle stars, and other animals on the deeper Continental Slope in the Gulf of the Farallones. (Photograph from Gulf of the Farallones National Marine Sanctuary.) Continental Slope Communities 59 Issues o tal in the Gulf of the Farallones Since the mid- 1800' s, when the California Gold Rush first brought frantic development to the San Francisco Bay region, the waters of the bay and of the Gulf of the Farallones, beyond the Golden Gate, have been used to dispose ofmanmade waste. Perhaps of greatest concern are thousands of barrels of low-level radioactive waste dumped in the gulf during several decades following the Second World War. To evaluate the hazard from radioactivity to the marine environment, including increasingly important fisheries, scientists have begun the search for containers of radioactive waste on the sea floor of the gulf. Another issue is the need to find suitable places in the gulf to dump material dredged from shipping channels in San Francisco Bay. Studies of the sea floor in the gulf have already enabled the Environmental Protection Agency to designate the Nation's first deep-ocean disposal site for dredge spoils. Issues of Environmental Management in the Gulf of the Farallones Disposal of Dredged Material and Other Waste on the Continental Shelf and Slope John L. Chin and Allan Ota The history of waste disposal in the Gulf of the Farallones is directly linked with the history of human settlement in the San Fran- cisco Bay region. The California Gold Rush of 1849 triggered a massive influx of people and rapid, chaotic development in the bay region. Vast quantities of contaminated sedi- ment and water from mining in the Sierra Nevada were carried by rivers into San Francisco Bay, and some was carried by currents through the Golden Gate and into the gulf. The burgeoning region's inhabitants also contributed to the waste that flowed or was dumped into the bay. Eventually, waste began to be dumped directly into the gulf. Hundreds of millions of tons of waste has been dumped into the Gulf of the Farallones. Since the 1940's, this has included sediment (sand and mud) dredged from shipping chan- nels, waste from oil refineries and fruit can- neries, acids from steel production, surplus munitions and ships from World War n, other unwanted vessels, and barrels of low-level radioactive waste. Because of navigational errors and inad- equate record keeping, the location of most waste dumped in the gulf is poorly known. Between 1946 and 1970 approximately 47,800 containers of low-level radioactive waste were dumped into the gulf south and west of the Farallon Islands. From 1958 to 1969, the U.S. military disposed of chemical and conventional munitions at several sites in the gulf, mostly by scuttling World War II era cargo vessels. The hulks of ships, possibly dating as far back as the 17th century, litter the sea floor in the gulf. From 1951 to 1987, many vessels were deliberately sunk there. Most of these probably pose little environmental hazard because they were carefully prepared before sinking. One exception may be the highly radioactive World War n aircraft carrier USS Independence, exposed in atomic tests at Bikini Atoll in 1946 and sunk by the U.S. Navy in 1951 at an unspecified location off the California coast, possibly in the gulf. Since at least 1959, some sediment dredged from San Francisco Bay and from the sandbar outside the entrance to the bay (the Golden Gate Bar) has been dumped onto the Continental Shelf in the gulf. Much of this material is from dredging to maintain shipping channels into and within the bay, but some is from other engineering projects. Until 1970, ocean disposal of both radio- active and nonradioactive waste was accept- able under government policy. That year, the United States terminated all ocean disposal of radioactive waste materials. In 1972, Con- gress passed the Ocean Dumping Act, which regulates the dumping of wastes into ocean waters. A global ban on the dumping of radio- active waste in the oceans took effect in 1983. The Environmental Protection Agency (EPA) is currently responsible for desig- nating ocean disposal sites for the United States. The U.S. Army Corps of Engineers (USAGE), with EPA's concurrence, issues permits for ocean disposal of dredged mate- rial at designated sites. Only sediments eval- uated as "clean" (non-toxic) by EPA stan- dards may be disposed of in the marine environment. San Francisco Bay's 85 miles of navi- gable waterways require annual maintenance dredging. The bay's average depth is about 19 feet, but oil tankers and container vessels need from 40 to 60 feet of water for safe transit. Environmental concerns and limited disposal capacity for dredged material in the bay have made it necessary to find suit- able dumping sites in the ocean beyond the Golden Gate. A new approach for the management of dredging and disposal of dredged material for San Francisco Bay was coordinated under a regional effort begun in 1990 as a Federal-State partnership of four agencies and later joined by about 30 other public and private organizations. This effort was formally called the Long Term Management Strategy (LTMS) for the San Francisco Bay region. The primary task of the LTMS was to develop a long-range plan for meeting the bay region's need to dispose of an estimated 300 million cubic yards of dredged material over the next 50 years. The EPA, a leading Federal agency in this effort, had the respon- sibility for selecting a location for an ocean disposal site for dredged material. In 1990, the U.S. Geological Survey (USGS) was asked by EPA, USAGE, and the Navy to investigate four study areas for locating potential disposal sites for dredged material in the Gulf of the Farallones. This survey also tested the feasibility of using sid- escan sonar to locate the radioactive-waste containers in the gulf (see chapter on Search for Containers of Radioactive Waste on the Sea Floor). Each of the four study areas was evalu- ated by the USGS for the presence of deposi- tion and erosion, sediment transport path- ways, and the likely effect deposited dredged material might have on the stability of the sea floor (see earlier chapters). Using the results of the USGS studies, EPA in 1994 designated the San Francisco Deep-Ocean Disposal Site. This site is 55 miles beyond the Golden Gate and 5 miles outside of the Gulf of the Farallones National Marine Sanctuary in 8,200 to 9,800 feet of water. 62 Issues of Environmental Management in the Gulf of the Farallones 5+ +2 Study Area Farallon . Islands SKAMOi S Independence? AlternativeS Study Area 3 BATHYMETRIC (DEPTH) CONTOURS IN METERSX (1 METER = 3781 FEET) I SITES OF HISTORICAL WASTE DISPOSAL 1-5+ Dredged material 8-10+ Low-level radioactive waste 6 + Acid waste 7 + Cannery waste Farallon Islands Radioactive Waste Dump (FIRWD) 11 - 13 Explosives and munitions Map of the Gulf of the Farallones, showing sites of historical waste disposal, as well as locations of U.S. Environmental Protection Agency (EPA] Study Areas (shaded) and Alternative Sites (dotted out- lines). Study Areas 2 through 5 and Alternative Sites 3 through 5 were investigated by the U.S. Geological Survey (USGS) for possible designation by the EPA as disposal sites for dredged material. After the USGS reconnaissance survey. Study Areas 3, 4, and 5 on the Continental Slope were retained, and Study Areas 1 and 2 on the Continental Shelf were eliminated from further consideration. In 1994, the EPA designated Alternative Site 5 as the San Francisco Deep-Ocean Disposal Site. Disposal of Dredged Material and other Waste on the Continental Shelf and Slope 63 DREDGED MATERIAL DUMPED NEAR ALCATRAZ ISLAND IN SAN FRANCISCO BAY Historically, much of the sediment dredged from the San Francisco Bay to maintain shipping channels has been disposed of in the bay itself, particularly in its deeper parts, such as near Alcatraz Island. These computer-generated oblique images of the bay floor south of Alcatraz Island show the effects of dumping millions of cubic yards of dredged material between 1 894 and the mid-1 980"s in the area outlined by the red circles. The images were created by the U.S. Geo- logical Survey using historical bathymetric data and recent multibeam (acoustic) mapping. (Grid squares are 100 yards on a side, and submarine vertical exag- geration isxIO.) Alcatraz Island 1894 1997 Alcatraz Island \ 64 Issues of Environmental Management in the Gulf of the Farallones Detail of a U.S. Geological Survey sidescan-sonar mosaic from an area of the upper Continental Slope about 20 miles southwest of the Farallon Islands. On this image was discovered what is interpreted to be the USS Independence (CVL 22), a dangerously radioac- tive aircraft carrier scuttled in 1951 . Also visible is the stern section of the SS Puerto Rican. an oil tanker that sank in 1 984. The USS Independence during active service as a U.S. Navy aircraft carrier (left). The ship is shown below as it appeared after being exposed to atomic tests at Bikini Atoll in 1946. (U.S. Navy photographs.) Disposal of Dredged Material and other Waste on the Continental Shelf and Slope 65 Issues of Environmental Management in the Gulf of the Farallones Search for Containers of Radioactive Waste on the Sea Floor Herman A. Karl Between 1946 and 1970, approximately 47,800 large containers of low-level radio- active waste were dumped in the Pacific Ocean west of San Francisco. These con- tainers, mostly 55-gallon drums, were to be dumped at three designated sites in the Gulf of the Farallones, but many were not dropped on target, probably because of inclement weather and navigational uncertainties. The drums actually litter a 540-square-mile area of sea floor, much of it in what is now the Gulf of the Far- allones National Marine Sanctuary, which was established by Congress in 1981. The area of the sea floor where the drums lie is commonly referred to as the "Farallon Islands Radioactive Waste Dump." Because the actual distribution of the drums on the sea floor was unknown, assessing any potential environ- mental hazard from radiation or contami- nation has been nearly impossible. Such assessment requires retrieving individual drums for study, sampling sediment and living things around the drums, and directly measuring radiation levels. In 1974, an unmanned submersible was used to explore a small area in the Farallon Islands Radioactive Waste Dump, but only three small clusters of drums were located. Two years later, a single drum was retrieved from this site by a manned sub- mersible. However, use of submersibles in this type of operation is highly inefficient and very expensive without a reliable map to direct them. In 1990, the U.S. Geological Survey (USGS) and the Gulf of the Farallones National Marine Sanctuary began a coop- erative survey of part of the waste dump using sidescan sonar — a technique that uses sound waves to create images of large areas of the ocean floor. Because of limited time and funding, the survey only covered about 80 square miles, or 1 5 percent of the waste dump area. Expert skills are required to distinguish waste drums and other manmade objects from natural geologic features or acoustic noise on ordinary sidescan-sonar images produced onboard ship. USGS scientists developed new techniques for enhancing the sidescan-sonar data from the Farallon Islands Radioactive Waste Dump to detect waste drums more easily and to distinguish them from other targets with a high level of confidence. Using these techniques, it was also possible to differentiate real tar- gets (drums) from acoustic noise. The enhanced images from the survey showed the locations of many objects that the scientists interpreted to be radioactive waste containers. In 1994, the USGS, the Marine Sanctuary, and the U.S. Navy used the Navy's DSV (Deep Submergence Vehi- cle) Sea Cliff and unmanned Advanced Tethered Vehicle (ATV) to verify these interpretations by direct observation of the sea bottom. The previous attempts in the mid-1970's to locate waste drums in the Gulf of the Farallones using submersibles had been like trying to find a needle in a haystack and had little success. Using the enhanced sidescan-sonar images as guides, Sea Cliff and ATV were able to "drive" directly from one suspected drum site to the next. In every instance, waste containers and other physical features were found where the enhanced images showed them to be, and no containers were found where they were not indicated. This was the first successful test of locating barrels by regional mapping and, in that regard, represents a breakthrough. By using the new USGS maps to detect suspected barrel sites and U.S. Navy tech- nology to directly view the sea floor, many barrels and other containers were found during just a single 24-hour ATV deploy- ment, and each DSV Sea Cliff and ATV dive verified the predicted absence or presence of barrels. Visual observations revealed that the condition of the barrels ranged from completely intact to com- pletely deteriorated. This work proved that enhanced sides- can-sonar images are a cost-effective and time-efficient method for locating relatively small objects on the sea floor and could be used to locate containers of hazardous waste in other ocean areas, such as Boston Harbor in Massachusetts and the Kara Sea in the Arctic Ocean north of Russia. Besides being the site of a marine sanc- tuary, the Gulf of the Farallones supports a major commercial fishery. In the past, fear of radiation contamination from leak- ing drums in the "Farallon Island Radioac- tive Waste Dump" has adversely affected the market for fish caught in the gulf. In 1998, the actual impact of the drums on the marine ecosystem began to be evaluated. Preliminary results suggest that it is much less than feared (see chapter on Measuring Radioactivity from Waste Drums on the Sea Floor). 66 Issues of Environmental Management in the Gulf of the Farallones RADIOACTIVE-WASTE DRUMS IN THE GUL LLONES 123°45'W 123°30' 38°25'N MF5T [— 123D00' 122°30' 20 MILES I 20 KILOMETERS 38°00' Gulf of Farallones Nutioitiit Miiriiw Sam lii