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Indirect evidence is presented that human disturbances are having a profound effect on reproductive efforts of Larus occidentalis livens at several colonies in the Gulf of California. Breeding adults that lose their eggs or chicks apparently practise conspecific predation whether or not humans are present, thus increasing effects of human intrusions. These combined effects could lead to a severe decline in numbers or even pose a threat to the survival of this endemic population, if human disturbance is widespread. Attempts to assess breeding success throughout the Gulf seem warranted and, if necessary, some action to regulate human contact may be essential.

During 1978-1981 I studied age- and sex-related dispersal and foraging patterns of Western Gulls (Larus occidentalis) that breed on Southeast Farallon Island, California. Most adults were sedentary and foraged primarily on oceanic food during all seasons except autumn, when human refuse was of major importance. Autumn was the only period when adults did not maintain breeding territories, and also the time of primary molt when flight capabilities were reduced. During the breeding season many subadults moved north to areas where oceanic productivity is high. During autumn/winter most moved south to the Gulf of the Farallons/San Francisco Bay Area, where birds ate both oceanic food and refuse. Dispersal patterns of first-year gulls varied markedly between years, apparently as a result of annual differences in oceanic productivity. The consistency of movement patterns of other age classes resulted from an age-related increase in fidelity to foraging locations. This was most pronounced in adults. Most adults dispersed each year to the same site, and minimized competition by reducing concentrations at each location. Males were more sedentary than females, probably because they are responsible for securing and holding breeding territories.

Stable-carbon isotope analyses of bone collagen of gulls (Larus spp.) were used to estimate the relative proportion of marine and terrestrial protein in the diets of gulls that are known to use both types of food sources. Mean δ13C values for Glaucous-winged Gulls (n = 23) collected at a Vancouver dump and for Western Gulls (n = 18) from Southeast Farallon Island were −15.0 ± 1.3 and −15.1 ± 0.5‰, respectively. No significant difference in δ13C values was found between adult male and female Western Gulls. Archaeological gull bones (n = 3) show a mean δ13C value of −13.6 ± 1.0‰ and support the assumed marine end point of −13.0‰. The range of terrestrial protein in the diets of coastal gulls was 0–61%. The narrow distribution of δ13C values for Western Gulls from the Southeast Farallon Island colony suggests that gull colonies may be calibrated so that changes in dependence on terrestrial protein can be monitored.

and Summary Four species of gulls (Larus occidentalis, L. livens, L. atricilla, L. novaehollandiae) were studied in captive and free-living situations to determine which sex of paired gulls is dominant, if either, with respect to pair-bonded behaviour. Aggression against a mate was rare (all four species). Conflicts during nest reliefs (L. o. occidentalis) or feeding (all four species) were not resolved by dominance but by egalitarian mechanisms: access to the nest was decided on a case-by-case basis and food was shared (large items) or acquired on a first-come-first-served basis (small items). Analysis of the use of vocal signals (Head Toss, Mew, and Choking) during nest duty interactions suggests that reduction of signaling occurred when a pair's priorities were most in agreement. Egalitarian conflict resolution is defined and selective factors favoring egalitarian behaviour patterns are proposed. Zusammenfassung Um zu bestimmen, welches Geschlecht in Mowenpaaren dominant ist, wurden vier Arten (Larus occidentalis, L. livens, L. atricilla, L. novaehollandiae) auf ihre Paarbindungsverhaltnisse untersucht. Aggression gegen den eigenen Geschlechtspartner war bei beiden Geschlechtern selten (alle vier Arten). Mowenpaare losen Sozialkonflikte bei der Nestablosung (L. occidentalis) oder Futterung (alle vier Arten) nicht mit Hilfe von Dominanzverhaltensweisen; keiner der Partner last dem anderen standig den Vortritt. Der Zugang zum Nest wird von Fall zu Fall entschieden, und die Nahrung wird entweder geteilt (wenn die Objekte gros sind) oder nach dem Motto “wer zuerst kommt mahlt zuerst” verzehrt (bei kleinen Bissen). Zur Diskussion gestellt werden die moglichen Selektionsfaktoren, die bei verpaarten Mowen den Gebrauch egalitarer Verhaltensmuster zur Losung von Sozialkonflikten begunstigen.

This study examined the occurrence and cause of supernormal clutches (SNC; 4-6 eggs) in Ring-billed (Larus delawarensis) and California (L. californicus) gulls, species that normally lay twoto three-egg clutches. In Washington and Oregon, clutches of five to six eggs constituted 0.8% of the clutches in Ring-billed Gulls (n = 20,353) and 0.1% in California Gulls (n = 6,117) during the mid-incubation period. The frequency of supernormal clutches in Ring-billed Gulls varied significantly both among colonies and years on a region-wide basis but this was not true in California Gulls. The frequency of four-egg clutches was correlated with that of fiveto six-egg clutches within each species, but no correlation existed between the two species. Multi-female associations were responsible for 30% of the examined four-egg clutches (n = 20) in Ring-billed Gulls and 27% of them (n = 11) in California Gulls. All examined clutches of five or six eggs in Ring-billed Gulls (n = 11) and California Gulls (n = 1) were incubated by multi-female associations. In Ring-billed Gulls, 79% of the detected multi-female associations were female-female pairs, 16% were polygynous groups, and one was a group of three females but no males. In California Gulls, for these clutches, only female-female pairs were detected. Gulls normally lay clutches of one to three eggs but clutches of four to seven eggs are occasionally found. These unusually large or supernormal (Bonner 1964) clutches have attracted the attention of ornithologists for many years (Call 1891, Jones 1906, Willett 1919). Not until 1977, however, was it discovered that supernormal clutches (SNCs) are produced by female-female pairs in Western Gulls (Larus occidentalis; Hunt and Hunt 1977). Such pairs have since been found also attending SNCs in California Gulls (L. californicus; Conover et al. 1979a), Ring-billed Gulls (L. delawarensis; Conover et al. 1979a, Ryder and Somppi 1979) and Herring Gulls (L. argentatus; Fitch 1980, Shugart 1980). Some SNCs also result from polygyny (Conover et al. 1979a, Lagrenade and Mousseau 1983). Hereafter, I will refer collectively to these associations where two or more females lay eggs in the same nest and share parental responsibilities (polygyny, female-female pairings, or multi-female groups) as "multi-female associations" (MFAs). It is unclear why female-female pairs or polygynous associations occur in gulls that are normally monogamous, but one hypothesis is that they result from a shortage of breeding males. Support for this hypothesis comes from the finding that females outnumbered males at a Western Gull colony where there was a high frequency of female-female pairs (Hunt et al. 1980). Conover and Hunt (1984) also showed that SNC frequencies increased in Ring-billed and California gull colonies after the breeding adult sex-ratios were skewed by removing breeding males. These findings, how ver, do not explain why a shortage of b eeding males should exist in some gull populations. One hypothesis is that DDT can feminize male gull embryos so that these individuals do not breed as adults (Fry and Toone 1981). Thi hypothesis may explain the increase in SNC frequencies since the 1940s in Wester Gulls breeding off the California coast (Hunt and Hunt 1977), in Herring Gulls breeding in the Great Lakes (Conover 1984), and in the United States population of Caspian Te ns (Sterna caspia; Conover 1983). In most larids, however, SNC frequencies have not increased significantly in recent years (Conover 1984). Too little is yet known about proximate factors affecting SNC frequencies, or the variability of SNC frequencies, to understand the significance of these large increases in SNC frequencies. In this study, I examined variability in SNC frequencies by testing the hypotheses that within the same population: 1) SNC frequencies change during the incubation period and 2) their frequency varies both among years and colonies. A major difficulty with studying female-female pairs or polygynous associations in gulls is identifying them. Sexual dimorphism is so slight in these birds that many individuals can be sexed only by head or bill measurements or by laparotomy. For this reason, nests containing SNCs are often used to identify female

Although the breeding biology, ecology, and behavior of many gull species are well documented, Western Gulls (Larus occidentalis) have received little attention from ornithologists. This lack of data on such a conspicuous bird, the only gull breeding along the California coast, is perhaps not too surprising since Western Gulls nest primarily on islands to which ready access is difficult. Summaries in Bent (1921) and various state bird books, and short articles by Dickey and van Rossem (1925), Ferris (1940), Pearse (1946), Woodbury and Knight (1951), Bartholomew and Dawson (1952), and Bennet and Erickson (1962) are the only references I found to Western Gulls. As a member of the Smithsonian Institution's Pacific Ocean Biological Survey Program (POBSP), I studied the breeding biology of Western Gulls on San Nicolas Island, Channel Islands, California, on the following days in 1968: 10-23, 27-31 May; 5-10, 14-17 June; 2-5, 16-18 July, and 22 August. San Nicolas Island, the Channel Island farthest from the mainland, is situated at 33o14' N, 119o32' W, 62 statute miles from Point Mugu, California. It is oval in shape, with the long axis (9.8 statute miles) oriented approximately WNW-ESE; the maximum width is 3.6 miles. The island is 21,000 acres in area, with the highest point a broad plateau 906 ft above sea level. The south portion rises abruptly, eroded by deep gullies. The north side is less rugged and the northwest point is a sand dune of 200 ft elevation. Western Gulls nest on the western side of this dune in an area approximately 1 mile by 200 yards on a hillside rising from the beach cliff. This gradual slope is traversed by many gullies eroded to a depth of 20 ft. Waterand winderoded boulders up to 5 ft high are scattered across the area. Vegetation in the colony consists of low-growing ice plant (Mesembryanthemum crystallinum), ground heliotrope (Heliotropium currassavricum, var. oculatum), sand verbena (Abronia maritima), beach burr (Franseria chamissonis bipinnatisecta), alkali heath (Frankenia grandifolia), sea blite (Suaeda california pubescens), and lupine ( Lupinus hirsutus). An initial survey showed it impossible to census accurately the entire colony, so four study plots were established, comprising approximately one-third of the area and one-half of th nests of the entire colony. In these plots I marked each nest with spray-painted numbers that remained legible throughout the study. I surveyed the entire colony three times and checked marked nests every two or three day during May and early June, and on each visit in July and August.

1. Two-year plumage-cycle (like Larus philadelphia):-Xema sabini, Rhodostethia rosea, Larus minutus, Larus franklini, Larus atricilla, Rissa brevirostris and Rissa tridactyla. 2. Three-year plumage-cycle:-Larus heermanni, Larus canus, Larus brachyrhynchus, Larus delawarensis and Pagophila alba. 3. Four-year plumage-cycle (like Larus argentatus):-Larus californicus, Larus vegae, Larus affinis, Larus occidentalis, Larus schistisagus, Larus marinus, Larus nelsoni, Larus kumlieni, Larus glaucescens, Larus leucopterus and Larus hyperboreus. 43 W. 70th Street, New York, N. Y.

The breeding biology of some gull species has been fairly well studied. A notable exception is the Western Gull ( Larus occidentalis), a resident of the west coast of the United States, Baja California and Sonora, Mexico, and British Columbia. The difficulty of reaching island nesting colonies has deterred investigators until recently. Reports by Schreiber (1970) and Coulter (1969) have added much to our understanding of the nesting biology of the species, especially the egg-laying and hatching phases. During 1965 and 1966 I studied a small colony of Western Gulls (L. o. wymani) on Bird Rock, Santa Catalina Island, California. Emphasis was given to population ecology of the colony from egg laying through fledging, nest site preference, nest distribution pattern, and territoriality. Also examined were the nesting success of this small colony and the effect of colony size on survivorship for this and other gull species.

CONOVER, M. R., AND G. L. HUNT, JR. 1984. Experimental evidence that female-female pairs in gulls result from a shortage of breeding males. Condor 86:472-476. CONOVER, M. R., D. E. MILLER, AND G. L. HUNT, JR. 1979. Female-female pairing and other unusual reproductive associations in Ring-billed and California gulls. Auk 96:6-9. COULSON, J. C., AND C. S. THOMAS. 1985. Changes in the biology of the Kittiwake Rissa tridactyla: a 31 year study of a breeding colony. J. Anim. Ecol. 54:2-26. FISHER, R. A. 1958. The genetical theory of natural selection. Dover, New York. FITCH, M. A., AND G. W. SHUGART. 1983. Comparative biology and behavior of monogamous pairs and one male-two female trios of Herring Gulls. Behav. Ecol. Sociobiol. 14:1-7. FITCH, M. A., AND G. W. SHUGART. 1984. Requirements for a mixed reproductive strategy in avian species. Am. Nat. 124:116-126. Fox, G. A., AND D. BOERSMA. 1983. Characteristics of supernormal Ring-billed Gull clutches and their attendants. Wilson Bull. 95:552-559. Fox, G. A., C. R. COOPER, AND J. P. RYDER. 1981. Predicting the sex of Herring Gulls by using external measurements. J. Field Ornithol. 51:1-9. HUNT, G. L., JR., AND M. W. HUNT. 1977. Femalefemale pairing in Western Gulls (Larus occidentalis) in Southern California. Science 196:14661467.

Pairs of females that remain together from one year to the next are associated with the presence of supernormal clutches in western gull nests. Intervals between laying of eggs in supernormal clutches are less than those found in normal clutches, a result indicating both females in a pair contribute to the clutch. Most eggs in supernormal clutches are infertile. The pairs of females occupy territories that are not shared with a resident male. In three homosexual pairs one of the females exhibited behaviors normally ascribed only to males.

Western Gull (Larus occidentalis) chicks on Santa Barbara Island, California, had a sex ratio at hatching of 1.12 M/F (n = 609); the sex ratio of chicks ->35 days of age was 0.89 (n = 189). The sex ratio at hatching and fledging did not vary significantly from 1.0 or from each other, but the data suggest that male mortality before fledging exceeded that of females. Depressed growth rates of male chicks hatched third may be responsible for these higher male mortality rates. We found no evidence for seasonal or hatching-order effects on sex ratios at hatching. We suggest that postfledging differences in mortality be- tween the sexes are in part responsible for the skewed sex ratio (0.67 males/female) observed in the adult breeding population. Received 4 October 1985, accepted 11 June 1986. biased sex ratios in species in which young are sexually dimorphic in size at the termination of parental care. Numerous recent studies have investigated the hatching and fledging sex ratios of sexually dimorphic birds. Newton and Marquiss (1979), working with the Eurasian Sparrowhawk (Ac- cipiter nisus), Fiala (1981) with Red-winged Blackbirds (Agelaius phoeniceus), Lombardo (1982) with Eastern Bluebirds (Sialia sialis), and Harmsen and Cooke (1983) with Lesser Snow Geese (Chen caerulescens) found no deviation from a 1:1 sex ratio at hatching or fledging. Others found variation in sex ratios at hatching as a function of hatching order (Ankney 1982, Lesser Snow Goose; Davies and Payne 1982, domestic fowl, Gallus domesticus; Ryder 1983, Ring-billed Gull, Larus delawarensis; Weather- head 1985, Red-winged Blackbird) or season (Howe 1977, Common Grackle, Quiscalus quis- cula). Differential chick mortality resulting in biased sex ratios at fledging were found for Common Grackles (Howe 1976), Common Cap- ercaillie (Tetrao urogallus; Wegge 1980), North- ern Harriers (Circus cyaneus; Picozzi 1980), and Red-winged Blackbirds (Blank and Nolan 1983). 33 In Western Gulls (L. occidentalis), males are larger than females. The breeding population of Western Gulls on Santa Barbara Island (SBI), California, has an estimated adult sex ratio of 0.67 (males/female) (Hunt et al. 1980). The fe- male-biased sex ratio in the adult population could result from differential mortality after fledging. Alternatively, differential mortality of chicks could initiate sex-ratio bias at hatching, particularly if males required greater parental investment and an adjustment of the sex ratio before the termination of parental care result- ed. We tested the hypothesis that a female bias in the sex ratio of chicks before fledging was responsible for the observed bias in the adult breeding population on SBI. Additionally, we sought evidence for mechanisms that might re- suit in a biased prefledging sex ratio.

We studied the predation of the Western Gull (Larus occidentalis) on the Eared Grebe (Podiceps nigricollis) from December 2002 to June 2003 at a solar saltworks. Mechanisms of predatory behavior, such as use of perching site, attack maneuvers and killing and catching grebes, as well as behavior of the grebes as a response to the presence and attacks by gulls, were recorded. In all 35 cases where a gull attempt to feed was seen, it was successful in every case. This is the first report about predation by the Western Gull on the Eared Grebe.

The breeding period of Western Gulls (Larus occidentalis) extends from April to mid-August (Sowls et al. 1980), overlapping with that of California sea lions (Zalophus californianus) that breed from late May to the end of July (Peterson and Bartholomew 1967). Both species may occupy the same beaches, thus favoring the occurrence of a commensalist relationship in which gulls consume sea lion placentas (Hunt and Butler 1980). Sea lions on the other hand, may be alerted by gull squawks when the seabirds detect some possible danger (pers. observ.). Interactions among gulls and sea lions, however, may take another context as referred to below. During the beginning of the California sea lion breeding season of 1982, we visited the rookery located on Santa Margarita Island (24018' to 24032'N; 111042' to 11201 'W) and counted the first 20 pups born that year. Of these, three animals were dead and exhibited rounded holes on the belly and no eyes. At that time, about 200 Western Gulls were present on the beach, many of them walking around the sea lions. During our observations we made some noise that caused many mothers of the pups to go to the sea. Immediately after the mothers were gone, many gulls surrounded the pups and began to peck them. Based on these observations we supposed that the gulls could have caused the wounds on the dead pups. To test this hypothesis, we planned an experiment for the first week of June 1983. For that purpose we selected a place for observing a small section of the sea lion colony from which the disturbances were minimized. The numbers of females, pups, and gulls were recorded, as well as the interspecific attacks. Pecking on a pup body was considered to be a gull attack and a sea lion attack was any attempt to bite or pursue the gulls. The observations were registered under two conditions, undisturbed and disturbed colony. In the first case, the gulls walked around the sea lions sometimes attempting to peck the pups and doing so on a few ' Received 5 December 1986. Final acceptance 1 June 1987. SHORT COMMUNICATIONS 923

The frequency and cause of supernormal clutches were investigated in two Caspian Tern (Sterna caspia) colonies in the Pacific Northwest. Over 4% of the nests contained four eggs and 0.8% contained five to six eggs. Trapping and sexing all attendants at two three-egg nests, two four-egg nests, and one fiveegg nest revealed that the three-egg nests were incubated by heterosexual pairs and the supernormal clutches (four to six eggs) by female-female pairs. Although supernormal clutches in Caspian Terns were rare throughout North America before 1940, they have increased in frequency since 1950 in the U.S. but not in Canada. Female pairings occur when one female associates with another instead of with a male during the breeding season. Both females lay eggs in the same nest, often producing a "supernormal" clutch of four to six eggs, twice the normal number. The two females share parental responsibilities including incubation duties, territorial defense, and care of any chicks resulting from promiscuous matings with males (Hunt and Hunt 1977). This phenomenon has been discovered in four gull species: Western Gull (Larus occidentalis; Hunt and Hunt 1977), Ring-billed Gull (L. delawarensis; Ryder and Somppi 1979, Conover et al. 1979a), California Gull (L. californicus; Conover et al. 1979a) and Herring Gull (L. argentatus; Shugart 1980). Heretofore, female pairs have been reported only in gulls. In this study, I surveyed Caspian Tern (Sterna caspia) colonies in eastern Washington and Oregon in order to determine the relative frequency of supernormal clutches and if they resulted from female pairings. I also examined whether the frequency of supernormal clutches had increased since 1950, an expected occurrence if DDT contributed to the frequency of female pairings in this species by feminizing male embryos, as Fry and Toone (198 1) have hypothesized, or by causing higher male mortality.

Post-fledging parental care of Western Gulls (Larus occidentalis) was examined by following in-colony and post-dispersing movements of marked adults and young. At a large offshore colony, parental care ceased when young dispersed at a mean age of 70 days, but at some mainland and nearshore Western Gull colonies parental care may last longer. At the latter sites competition for food appeared low, foraging territories and food items could be defended by adults, and food sources were near nest sites. A low incidence of prolonged parental care in this species may result from activities of a few well-adapted individuals who specialize in foraging techniques facilitating extended breeding efforts.

Westmove (Larus occidentalis). Bonner Zool. Beitrage 3/4:202-227. MAY, A. W. 1964. An assymetrical pair of cod otoliths. J. Fish. Res. Bd. Canada 21:413-414. MESSERSMITH, J. D. 1965. Southern range extensions for chum and silver salmon. Calif. Fish Game 51:220. MESSIEH, S. N. 1972. Use of otoliths in identifying herring stocks in the southern Gulf of St. Lawrence and adjacent waters. J. Fish. Res. Bd. Canada 29:1113-1118. MOSHER, K. H. 1969. Identification of Pacific salmon and steelhead trout by scale characteristics. U. S. Fish Wildl. Serv., Circular 317. NIJSSEN, H. 1964. Otoliths of the wolf-fishes (genus Anarrhichas, Linnaeus 1758) from the northern Atlantic (Pisces, Perciformes). Beaufortia 11(146):179-183. NORDEN, C. R. 1961. Comparative osteology of representative salmonid fishes, with particular reference to the grayling (Thymallus arcticus) and its phylogeny. J. Fish. Res. Bd. Canada 18:679-791. OSBORNE, D., A. BRYAN AND R. H. CRABTREE. 1961. River basin surveys papers, No. 24. The Sheep Island site and the mid-Columbia valley. Bull. Bur. Amer. Ethnol. 179:267-306. PIETSCH, T. W. 1972. A review of the monotypic deep-sea anglerfish family Centrophrynidae: taxonomy, distribution and osteology. Copeia 1972:17-47. SKALKIN, V. A. 1961. Otolity treskovykh ryb (sem. Gadidae) dal'nevostochnykh morei. Voprosy Ikhtiologii, 1(2)(19):286-289. SCHMIDT, W. 1968. Vergleichend-morphologische Studie fiber die Otolithen mariner Knockenfische. Archiv Fischereiwiss. 19:1-96. SCHULZ, P. D., AND D. D. SIMONS. 1973. Fish species diversity in a prehistoric central California Indian midden. Calif. Fish Game 59: 107-113. SIEGEL, S. 1956. Nonparametric statistics. McGraw-Hill, New York. SOUTAR, A., AND J. D. ISAACS. 1969. History of fish populations inferred from fish scales in anaerobic sediments off California. Calif. Mar. Res. Comm., CalCOFI Rept. 13:63-70. TICHIJ, M. 1929. Fische aus dem Palaolithikum der Krim. Akademia Nauk S.S.S.R. Komissiia po izucheniiu chetvertichnogo perioda. Biulleten 1:43-48. VLADYKOV, V. D. 1962. Osteological studies on Pacific salmon of the genus Oncorhynchus. Bull. Fish. Res. Bd. Canada 136.

Philophthalmus hegeneri sp. n. is described from adults reared from megalurous cercariae developing in the marine snail, Batillaria minima (Gmelin, found infected at numerous shore localities along the Gulf of Mexico from Dunedin to Key West, Florida. Metacercariae in flask-shaped cysts were infective orally and ocularly to various experimental birds including domestic chickens and pigeons, Mute Swan (Cygnus olor), Western Gull (Larus occidentalis), and the Southern Chachalaca (Ortalis ruficauda). Natural avian hosts include the Royal Tern (Thalasseus maximus), Yellow-crowned Night Heron (Nyctanassa violacea), Laughing Gull (Larus atricilla), and the Willet (Catoptrophorus semipalmatus). The genus Ophthalmotrema is considered a synonym of Philophthalmus. This is the first time a marine gastropod has been implicated in the biology of any member of this genus. A marine-acquired species of Philophthalmus which reached maturity under the nictitating membrane of a variety of experimental avian hosts has been mentioned by Penner and Fried (1961), Fried and Penner (1961), and Fried (1962a, b, c). The adult flukes were noted as related to the lucipetus group of 4 of the 23 species previously described in having follicular rather than tubular vitellaria. These were P. lucipetus, P. lachrymosus, P. offlexorius, and P. skriabini. Because our material from both experimental and natural infections differs from all previously described species of Philophthalmus, it is necessary to report the species as new. All measurements are in millimeters. Philophthalmus hegeneri sp. n.

Background OMEGA is an integrated aquatic system to produce biofuels, treat and recycle wastewater, capture CO2, and expand aquaculture production. This system includes floating photobioreactors (PBRs) that will cover hundreds of hectares in marine bays. To assess the interactions of marine mammals and birds with PBRs, 9 × 1.3 m flat panel and 9.5 × 0.2 m tubular PBRs were deployed in a harbor and monitored day and night from October 10, 2011 to Janurary 22, 2012 using infrared video. To observe interactions with pinnipeds, two trained sea lions (Zalophus californianus) and one trained harbor seal (Phoca vitulina richardii) were observed and directed to interact with PBRs in tanks. To determine the forces required to puncture PBR plastic and the effects of weathering, Instron measurements were made with a sea otter (Enhydra lutris) tooth and bird beaks. Results A total of 1,445 interactions of marine mammals and birds with PBRs were observed in the 2,424 hours of video recorded. The 95 marine mammal interactions, 94 by sea otters and one by a sea lion had average durations of three minutes (max 44 min) and represented about 1% of total recording time. The 1,350 bird interactions, primarily coots (Fulica americana) and gulls (Larus occidentalis and L. californicus) had average durations of six minutes (max. 170) and represented 5% of recording time. Interactive behaviors were characterized as passive (feeding, walking, resting, grooming, and social activity) or proactive (biting, pecking, investigating, and unspecified manipulating). Mammal interactions were predominantly proactive, whereas birds were passive. All interactions occurred primarily during the day. Ninety-six percent of otter interactions occurred in winter, whereas 73% of bird interactions in fall, correlating to their abundance in the harbor. Trained pinnipeds followed most commands to bite, drag, and haul-out onto PBRs, made no overt undirected interactions with the PBRs, but showed avoidance behavior to PBR tethers. Instron measurements indicated that sea-otter teeth and gull beaks can penetrate weathered plastic more easily than new plastic. Conclusions Otter and bird interactions with experimental PBRs were benign. Large-scale OMEGA systems are predicted to have both positive and negative environmental consequences.