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MARINE SCIENCE, 11(2):23 l-240 (April 1995) 0 1995 by the Society for Marine Mammalogy

OBSERVATIONS OF RISSO , ’ GRAMPUS GRiseuS WITH GRAY , ROBUSTUS

There are no published accounts of Risso dolphins (Grampus griseus) in- teracting with gray whales (Eschrichtius robustus). However, there have been numerous observations of Risso dolphins associating with Pacific white-sided dolphins ( obliquidens), northern right dolphins (Lisso- delphis borealis), pilot whales (Globicephala spp.), Dall (Phocoenoides dalli), and on occasion sperm whales (Physeter macrocephalus) and whales ( physalus) (Hubbs 1960, Fiscus and Niggol 1965, Leatherwood et al. 1982, Dohl et al. 1983). This report describes eleven sightings of Risso dolphins in the company of gray whales in the waters off Monterey, , within the last 13 yr (1981-1994) (Table 1, Fig. 1). s The majority of sightings were provided by charter vessels operating in the waters off Monterey during the southbound and northbound gray whale mi- gration. Census records collected by the National Laboratory (NMML) from shore-based stations operating during the southbound migration (1960, 1967-1981, 1984-1986, 1988, 1993-1994), and from aerial surveys flown during the census (1988, 1993-1994), were also searched for sightings. Searches of field logs maintained by other researchers conducting surveys along ’ the California coastline did not yield any additional sightings. Because Risso dolphins were often not the focal of these surveys, it is possible that sightings may have only been gathered on an opportunistic basis or not reported at all. The increase in the number of interactions between these two species over the past few years may be explained in part by the return of the gray whale population to prewhaling size (Buckland et al. 1993) and an increase in the number of Risso dolphins observed in the Monterey area over the last 20 yr (Leatherwood et al. 1980, Shane 1994). Help Volumes Main Menu

Table 1. Eleven encounters observed between Risso’s dolphins (Grampus griseus) and gray whales (Eschrichtius robustus) in the waters off Monterey and Carmel, California.

Map Encounter key date present Behavior(s) observed A 17 Jan 8 1 130+ Risso’s dolphins Dolphins encircled 2 gray whales, some riding their bow waves. Whales stayed close lOO+ northern dolphins together (touching), sometimes rolling ventrum up, other times facing ventrum to 60 + Pacific white-sided dolphins ventrum. Risso’s were highly “excited”, dividing time between the vessel and 2 gray whales whales (loo-yard distance), Interactions ended when the whales swam under the vessel and made a sounding dive (D. Cheeseman and G. Cheeseman, personal communication). B 3 1 Jan 81 33 Risso’s dolphins Three pods of Risso’s (numbering 6, 12, and 15) chased, encircled, and stopped 2 2 gray whales migrating gray whales. The whales rolled ventrum up. The Risso’s divided time between the whales and the research vessel (A. Baldridge and D. L. Shearwater). C 30 Jan 82 130+ Risso’s dolphins A pod of Risso’s chased and encircled 3 gray whales (penis visible, possible copula- 3 gray whales tion). The whales kept close together, rolled ventrum up, and occasionally splashed flukes. One whale departed the group, SWimrning rapidly east, creating a wake of white water. The remaining 2 began SWnnming’ away but were again encircled by the dolphins. The whales stopped and rolled ventrum up. Platform: vessel (A. Baldridge and D. L. Shearwater). D 17 Jan 86 30+ Risso’s dolphins Eleven southbound gray whales encountered a northbound pod of Risso’s. The Risso’s 13 gray whales encircled the whales. The whales splashed pectorals and flukes, rolled ventrum up, changed direction, and swam northeast. Six Risso’s encircled a second pod of gray whales, also turning them northeast. One whale swam rapidly toward a kelp bed with 4 Risso’s giving chase. The whale followed the kelp line north into breaking surf, flanked on each side by 2 Risso’s. The pod of 11 whales was seen near shore continuing their southbound migration 15 min later. Platform: shore (M. E. Dahl- heim, personal communication; NMFS, unpublished data). E 13 Jan 87 15 Risso’s dolphins Two trios of gray whales (penis visible, possible copulation) were flanked by dolphins. SO+ northern right whale dolphins Risso’s were participating at a “more intense level” than the other dolphins. Plat- 6 gray whales form: vessel (D. L. Shearwater, personal communication). Help Volumes Main Menu

Table 1. Continued.

Map Encounter key date Animals’ present Behavior(s) observed F 18 Jan 87 400+ Risso’s dolphins Three gray whales were encircled by a large mixed school of dolphins. One whale was 400+ northern right whale dolphins ventrum up. Platform: vessel (J. Vandevere, personal communication). lOO+ Pacific white-sided dolphins 3 gray whales G 16 Jan 93 200+ Risso’s dolphins Risso’s (4-5) were riding bow waves of 3 gray whales (2 were seen ventrum to ven- 3+ gray whales trum) a short distance from a larger group of Risso’s (200+). On two occasions a cut sharply in front of a whale, bumping up against the rostrum with its flukes. Whales reacted by rolling ventrum up, splashing flukes, and lifting pectoral Iins into the air. Platform: aircraft (K. E. W. Shelden and D. E. Withrow). H 14 Jan 94 15 + Risso’s dolphins Gray whales were rolling at the surface, often making body contact. A pod of Risso’s 2 gray whales (containing animals of varying length) approached and formed a tight circle around the whales. Whales reacted with lateral sweeps of their flukes and moved farther inshore. The interaction lasted for 30 min. Platform: vessel (J. Loomis, personal communication). I 16 Jan 94 lOO+ Risso’s dolphins Gray whales were migrating south in a tight group when they made a sudden 90” 3 gray whales turn to the west and rapidly swam offshore (following the approach of 6 Risso’s). A larger group of Risso’s (lOO+) remained at a distance of several hundred me- ters. The 6 Risso’s circled the whales closely. The whales did not show any addi- tional visible reaction to the dolphins presence. Fifteen minutes later the dolphins rejoined their main group. Platform: vessel (J. Vandevere, personal communica- tion) . J 17 Jan 94 lOO+ Risso’s dolphins A pod of gray whales (10) was seen headed south very rapidly, their heads almost 12 gray whales clearing the water and creating a wake of white water as they surfaced. About 200 m from the pod, a pair of gray whales were encircled by 6-8 Risso’s. The remain- der of the Risso’s group (loo+) was observed 300 m away. One of the gray whales was ventrum up, raising its head at a 45” angle out of the water and slap- Help Volumes Main Menu

Table 1. Continued.

Map Encounter key date Animals present Behavior(s) observed ping it .audibly on the surface at least 4 times in addition to making lateral sweeps across the surface with its flukes as the Risso’s circled. After 20 min of circling the whales, the Risso’s rejoined their main group. Platform: shore (A. Baldridge). K 17 Jan 94 20+ Risso’s dolphins Risso’s were rapidly circling 2 pods of gray whales. One dolphin breached 10 times in 6+ gray whales sequence. Whales were observed lifting their heads at a 45” angle out of the water, rolling ventrum up with pectoral held out of the water for 3-5 min, and spyhopping. One whale lifted its tail well out of the water and twisted its body sideways before crashing back down into the water. Another repeatedly slapped its flukes on the surface for 3 min. Another twisted its body on the surface, spiralling through the water. Observations ended when it suddenly became calm. Dolphins dispersed and there was no sign of the whales (animals were not seen swimming away or sounding). The interaction lasted 26 min. Platform: shore (K. E. W. Shel- den and .J. C. Cesarone). Help Volumes Main Menu

NOTES 235

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:.. .:I:.. SERAiES PI-‘. ZANITE CANYON ..

Figure 1, Locations of gray whale (Eschrichtius robustus) and Risso’s dolphin (Gram- pus griseus) interactions observed in the National Marine Sanctuary, Cal- ifornia, January 1981-1994. Help Volumes Main Menu

236 MARINE MAMMAL SCIENCE, VOL. 11, NO. 2, 1995

Each of the encounters with Risso’s dolphins reported here occurred in January in an area where gray whales migrate across deep submarine canyons near Monterey and Carmel. These deep canyons are a preferred habitat of Risso’s dolphins (Leatherwood et al. 1980). These dolphins typically occur seaward of the 180-m depth contour and appear in coastal waters only where the continental shelf is relatively close to shore (Leatherwood et al. 1982, Kruse 1989). The Monterey and Carmel Canyons are among the few areas where the Risso’s dolphins’ affinity for very deep water overlaps with the gray whales’ neritic migration. For this reason these interactions may occur more frequently in this region than in other areas along the migration route; however, a lack of survey effort in other regions makes this impossible to prove at this time. Based on the sightings, Risso’s dolphins appear to be initiating many of these interactions (Table 1). In those cases where interactions were not already un- derway at the time of the observation, Risso’s dolphins were seen swimming up to and/or following after gray whales rather than the reverse. It is unclear which dolphins within the group were initiating contact, or the reasons why each species behaved as it did during the encounter. The following are possible explanations for the behaviors observed. There may be several explanations for the approach of Risso’s dolphins to gray whales. Risso’s dolphins frequently occur in herds. Segregation by age and sex typically occurs in larger schools (greater than 60 animals) where distinctive groups of calfless adult animals, juveniles, and females with calves are obvious (Kruse 1989). Larger animals, possibly males, have been found to approach and place themselves between a potential intruder (in this case a charter vessel) and the rest of the herd, circling the vessel while the rest of the group moves away (A. Baldridge, personal observation). In 1993 only a small portion of the dolphin group that we observed from the air was actively interacting with gray whales. The remainder of the group, approximately 200 animals, continued traveling south. Only 6 or so of a group of more than 100 dolphins were observed with gray whales during two encounters in 1994 (Table 1, Map Key I and J). During both of the 1981 observations dolphins divided their time between gray whales and charter vessels, though there is no mention as to the location of the rest of the herd. Kruse (1989) found that Risso’s dolphin cow/ calf groups never approached her research vessel and tended to keep the main body of the herd between them and her vessel. The presence of newborn calves during the time when these encounters are occurring is likely as parturition in these dolphins is believed to occur with greater frequency in December, January, and February (Dohl et al. 1983). It may be that the larger, adult dolphins are attempting to protect the herd, particularly cows with calves, by chasing and encircling the gray whales until the rest of the herd has moved off to a safe distance. A second explanation may be that younger Risso’s dolphins are initiating these interactions and engaging in play behavior. Kruse (1989) found that on occasion juvenile Risso’s dolphins approached her vessel in order to bow ride. Bow-riding Pacific white-sided and northern right whale dolphins often attracted younger Risso’s dolphins to the research vessel. In the 17 January 1981 sighting Help Volumes Main Menu

NOTES 237

(Table l), observers believed that all three dolphin species they saw were bow- riding on pressure waves created by the gray whales. Some of the Risso’s dolphins that we saw in 1993 also appeared to be bow-riding on the whales. Gray whales have been seen in association with other small cetaceans such as Pacific bottlenose dolphins (Tursiops sp.), northern right whale dolphins, Pacific common dolphins (Delphinus sp.), Pacific white-sided dolphins, and Dall’s (Leatherwood 1974; Leatherwood et al. 1987; National Marine Mammal Laboratory, NMFS, NOAA, Fisheries Science Center, 7600 Sand Point Way NE, BIN C 15 700, Seattle, WA 98 115-0070 unpublished data). During these encounters these dolphins were observed riding the whales’ bow waves. In each instance Leatherwood (1974) suggested that the gray whales were “passive participants,” and that they were not being harassed. During five of the eleven encounters (Table l), gray whales were observed ventrum to ventrum, possibly copulating (in two cases a penis was visible but penetration was not observed). In the 3 1 January 198 1, 1982, and 14 January 1994 sightings (Table l), Risso’s dolphins increased their speed to catch up to and encircle ‘copulating’ whales, Copulating gray whales have been observed on three other occasions with Pacific white-dolphins, northern right whale dol- phins, and another group of unidentified dolphins (National Marine Mammal Laboratory, NMFS, NOAA, Alaska Fisheries Science Center, 7600 Sand Point Way NE, BIN C15700, Seattle, WA 98115-0070 unpublished data). The surface activity of copulation may be attracting the dolphins. In the case of Risso’s dolphins, however, the energy level of the ensuing interaction seems to be much higher than that demonstrated by other small cetaceans present at the same time (as noted in the 17 January 1981 and 13 January 1987 sightings (Table 1)). Kruse (1989) described social behaviors among Risso’s dolphins as “rough and obviously physical. ” This behavior included slapping, splashing, and oc- casionally striking one another. The skin of Risso’s dolphins is highly scarred which might be attributed to this intraspecific behavior (Leatherwood et al. 1982, Kruse 1989). These dolphins are highly gregarious with other small cetaceans as well, splashing, slapping, and chasing one another (Dohl et al. 1983, Kruse 1989). In 1993 we observed two instances in which a Risso’s dolphin appeared to strike the rostrum of a gray whale with its flukes as it cut across the whale’s path. In one case a lone dolphin moved up alongside a whale that was swimming rapidly toward shore, struck the rostrum then raced ahead of the whale, surfaced then turned around sharply. It then headed straight back at the whale, turning at the last moment to strike the rostrum before swimming off. In the second case a lone dolphin (maybe the same one) crossed back and forth in front of a whale, again appearing to strike the rostrum as it passed. This behavior appears to be normal based on the intraspecific behaviors docu- mented for these dolphins. After each episode the gray whale surfaced abruptly (causing a splash pattern around the back) and rolled ventrum up. A possible explanation for this behavior, which was observed in similar forms during every encounter with Risso’s dolphins, may be that it is a response based on agitation or fear. Help Volumes Main Menu

238 MARINE MAMMAL SCIENCE, VOL. 11, NO. 2, 1995

For example, this behavior may be a result of the number of similarities between these encounters with Risso’s dolphins and encounters between gray whales and killer whales (Orcinus orca). Peaks in attacks on gray whales by killer whales have occurred in January and April/May in the Monterey Bay National Marine Sanctuary and have usually been associated with the presence of gray whale calves. Ternullo et al. (1993) described 10 attacks on gray whales by killer whales along the coastline between Monterey Bay and Lopez Point. These sightings were not randomly distributed, and the encounters took place in areas of high bottom relief and were centered near canyon walls and shelf breaks. This places the attacks in the same area and around the same time of year that Risso’s dolphins are also encountering gray whales. Gray whales, in the presence of killer whales, have reacted by fleeing, heading into shallow water, into kelp beds, or into breaking surf (Burrage 1964, Morejohn 1968, Baldridge 1972, Goley and Straley 1994), a reaction also elicited by the Risso’s dolphins observed in 1982, 1986, and during three of the observations in 1994 (Table 1, Map Key H, I, and J). Gray whales have also reacted to the presence of killer whales by remaining motionless at the surface with their ventrum up (Andrews 19 14, Kellogg 1940, Tomilin 19 5 7) or grouping tightly together (Ljungblad and Moore 1983, Goley and Straley 1994). This reaction was also observed during nine of the eleven encounters with Risso’s dolphins. The chasing and encircling of gray whales by Risso’s dolphins during eight of the sightings (1981, 1982, 1986, 1987, 14 and 16 January 1994 (Table 1)) appeared to be similar to the herding and flanking technique used by killer whales when attacking large cetaceans (Tarpy 1979, Ljungblad and Moore 1983), though at no time was blood observed during the interactions. In all cases gray whales deviated from their migratory course after encountering the Risso’s dolphins. It appears that, at times, the behavior of the Risso’s dolphins may cause or at least correlate with a gray whale’s behavior. It might be suggested from these observations that the behavior displayed by Risso’s dolphins caused agitation and defensive posturing by gray whales. Gray whales probably do not confuse Risso’s dolphins with killer whales; however, the similarities between some of the behaviors of Risso’s dolphins and killer whales, as well as the similarities in location and time of year of encounters, may explain why gray whales also react similarly to these two different species. In terms of the behavior of the Risso’s dolphins, it is likely that these animals are engaging in normal intraspecific social behavior. However, it is not known what this behavior might reflect-an ag- gressive defense of their herd, curiosity, or a playfulness on the part of younger dolphins, or possibly none of these. Further study of the interactions between these two species is necessary before any conclusions can be made regarding the behaviors described in this paper.

ACKNOWLEDGMENTS

We thank Douglas and Gail Cheeseman, Judson Vandevere, and Jerry Loomis for their observations, and Debi L. Shearwater for providing a platform of opportunity for one of us (AB). We also thank our pilot, Barry Hansen (Aspen Helicopters), for his expert flying during the 1993 and 1994 surveys. Jack Cesarone, Marilyn Dahlheim, Doug Help Volumes Main Menu

NOTES 239

DeMaster, Dale Rice, David Rugh, and two anonymous reviewers provided thoughtful and thorough reviews.

LITERATURECITED

ANDREWS, R. C. 1914. Monographs of the Pacific . I. The California gray whale (Rhachianectes glaucus Cope). Its history, habits, external anatomy, osteology and relationships. Memoirs of the American Museum of Natural History (New Series) 1:227-287. BALDRIDGE,A. 1972. Killer whales attack and eat a gray whale. Journal of Mammalogy 53:898-900. BUCKLAND, S. T., J. M. BREIWICK,K. L. CATTANACH AND J. L. LAAKE. 1993. Estimated population size of the California gray whale. Marine Mammal Science 9:235-249. BURRAGE,B. R. 1964. An observation regarding gray whales and killer whales. Trans- actions of the Kansas Academy of Science 67: 5 50-5 5 1. DOHL, T. P., R. C. GUESS, M. L. DUMAN AND R. C. HELM. 1983. Cetaceans of central and northern California, 1980-1983: Status, abundance, and distribution. Final report submitted to Pacific OCS Region, Minerals Management Service, U.S. De- partment of the Interior, Los Angeles, California. OCS Study MMS 84-0045. 284 pp. FISCUS,C. H., AND K. NIGGOL. 1965. Observations of cetaceans off California, , and . U.S. Fish and Wildlife Service Special Scientific Report-Fisheries 498. 27 pp. GOLEY, P. D., AND J. M. STRALEY. 1994. Attack on gray whales (Eschrichtius robustus) in Monterey Bay, California, by killer whales (Orcinus orca) previously identified in Glacier Bay, Alaska. Canadian Journal of Zoology 72: 1528-1530. HUBBS, C. L. 1960. The marine vertebrates of the outer coast. Pages 134-147 in Symposium: The biogeography of and adjacent seas. Part II, Marine biotas. Systematic Zoology 9(3 & 4). KELLOGG, R. 1940. Whales, giants of the sea. 77(1):35-90. KrUSE, S. L. 1989. Aspects of the biology, ecology and behavior of Risso’s dolphin (Grampus griseus) of the California coast. Masters of Science. University of California Santa Cruz. 129 pp. LEATHERWOOD,J. S. 1974. A note on gray whale behavioral interactions with other marine . Marine Fisheries Review 36(4):50-5 1. LEATHERWOOD,S., W. F. PERRIN, V. L. KIRBY, C. L. HUBBS AND M. DAHLHEIM. 1980. Distribution and movements of Risso’s dolphin, Grampus griseus, in the eastern North Pacific. Fishery Bulletin, U.S. 77:95 l-963. LEATHERWOOD,S., R. R. REEVES,W. F. PERRIN AND W. E. EVANS. 1982. Whales, dolphins, and porpoises of the eastern North Pacific and adjacent Arctic waters: A guide to their identification. NOAA Technical Report NMFS Circular 444. 245~~. LEATHERWOOD,S., B. S. STEWARTAND P. A. FOLKENS. 1987. Cetaceans of the Channel Islands National Marine Sanctuary. Report to NOAA, Channel Islands National Marine Sanctuary, NMFS. 66 pp. LJUNGBLAD,D. K., AND S. E. MOORE. 1983. Killer whales (Orcinus orca) chasing gray whales (Eschrichtius robustus) in the northern . Arctic 36:361-364. MOREJOHN,G. V. 1968. A -gray whale encounter. Journal of Mammalogy 49:327-328. SHANE, S. H. 1994. Occurrence and habitat use of marine mammals at Santa Catalina Island, California from 1983-91. Bulletin of Southern California Academy Science 93(l): 13-29. TARPY, C. 1979. Killer whale attack. National Geographic 155(4):542-545. TERNULLO,R. L., N. A. BLACK,A. BALDRIDGEAND D. L. SHEARWATER. 1993. Occurrence, distribution, and predation behavior of killer whales (Orcinus orca) in Monterey Bay. stvo

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240 MARINE MAMMAL SCIENCE,VOL. ll, NO.2,1995

Abstracts of the Tenth Biennial Conference on the Biology of Marine Mammals, November 1 l- 15, Galveston, Texas. TcTomilin, A. G. 1957. Zveri SSSR i prilezhashchikh stran, Vol. IX Kitoobraznye [Mammals of the USSR and adjacent countries, Volume IX Cetacea. [In Russian) Izdatel Akademi Nauk SSSR, . (Translated by Program for ”N, Scientific Translation, Jerusalem, 1967). 7 17 pp. ’

KIM E. W. SHELDEN, National Marine Mammal Laboratory, NMFS, NOAA, Alaska Fisheries Science Center, 7600 Sand Point Way NE, BIN C15700, Seattle, Washington 98 115-0070, U.S.A.; ALAN BALDRIDGE, Hopkins Marine Station, Stanford University, Department of Biological Sciences, Pacific Grove, California 93950, U.S.A.; DAVID E. WITHROW, National Marine Mammal Laboratory, NMFS, NOAA, Alaska Fisheries Science Center, 7600 Sand Point ” ” Way NE, BIN C15700, Seattle, Washington 98115-0070, U.S.A. Received 21 December 1993. Accepted 21 November 1994.

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