MARINE MAMMAL SCIENCE, 13( 1): 141-147 (January 1997) 0 1997 by the Society for Marine Mammalogy

KILLER WHALES (ORCINUS ORCA) IN THE NORTHERN GULF OF MEXICO

Killer whales (Orcinus orca) are found in nearly all marine environments throughout the world and, besides man, are the most widely ranging mam- mals on earth (Heyning and Dahlheim 1988, Ford et al. 1994). However, killer whale records are rare from the Gulf of Mexico (Gulf). The first re- ported Gulf record was a stranding from Cuba in 1886 that may have been a killer whale but was apparently later identified as Pseudorca crassidens (Cuni 1918). Katona et al. (1988) reviewed ten published and previously unpub- lished Gulf records from 1921 through 1987 (Table 1). Four stranding re- cords consisted of a single tooth in 1921, a skull in 1948, and one animal in 1956, all from Florida; and an unconfirmed single animal from Texas in 1969. Six sighting records were included from off Florida in 1921 and 1979; and Texas in 1951, 1985 (two sightings) and 1987. The significance of these records was not clear because of their paucity and wide spatial and temporal distributions; that is, are killer whales only occasional inhabitants of the Gulf, or do they inhabit it regularly?

Prior to 1989 knowledge of cetaceans in the oceanic Gulf (waters > 200 m deep) was restricted to information from opportunistic sightings (Schmidly 1981) and very limited aerial surveys by Fritts et al. (1983). In 1989 the Southeast Fisheries Science Center (SEFSC) began conducting assessment sur- veys of cetaceans in the oceanic northern Gulf (i.e., U.S. exclusive economic zone-an area approximately north of a line from the tip of southern Florida to the Texas-Mexico border; Fig. 1) during which nine killer whale sightings were made. Additional records consist of three opportunistic sightings made by SEFSC personnel, and three that include photographic records made by laypersons. Our purpose here is to present details of the sightings which in- clude group size, water depth, sea-surface temperature, and distribution (Table 1, Fig. 1). Additionally, photographs or videotape recordings from 15 sight- ings (archived at the SEFSC Laboratory in Pascagoula, Mississippi) were ana- lyzed to study individual occurrence and location patterns, based on charac- teristics that can be used to uniquely identify individuals (i.e., dorsal fin, saddle patch; Bigg 1982).

Ship and aircraft line-transect techniques were used to conduct cetacean surveys (Buckland et al. 1993). Ship surveys employing 25 X 150 binoculars from the NOAA Ship Oregon II encompassed the entire oceanic northern Gulf during the boreal spring (April-June) from 1990 to 1994, the northwestern oceanic Gulf during the winter (January-February) of 1993, and the north- eastern continental shelf and slope during the summer (August-September) of 1994. Transect lengths totaled 24,328 km for spring, 4,017 km for winter, and 2,884 km for summer. Two aerial survey studies with more limited geo- graphic coverage were used to study the seasonal abundance and distribution

141

142 MARINE MAMMAL SCIENCE, VOL. 13, NO. 1, 1997

Table I. Records of killer whales in the Gulf of Mexico (G-estimated group size for SEFSC ship and aircraft sightings, ID-number photoidentified from all ship sight- ings, NA-no photographs or video available, SST-sea surface temperature).

Date SST Depth

G ID (“0 (4 Position Source

Historical records Strandings

1986 26 Dee 1921

Mar 1948 27 May 1956 21 Jan 1969

Sightings 1921

Nov 1951 20 May 1979 27 Aug 1985

1 Sep 1985 9 Aug 1987

14 May 1990 18 Sep 1992

New records Sightings

05 May 1978 18 May 1978

Sep 1989 6 Jun 1991 5 Jun 1992

13 Jun .1992 4 May 1993 8 Jun 1993 9 Jun 1993

13 Jun 1993 7 May 1994 8 Jun .1994

31 May 1995

- NA - - NA - - NA - - 4 - - NA - - 4 -

8 - - 10 - -

10 NA 22.7 1,253 27”20’N 9O”OO’W 10 NA 27.2 732 20”OO’N 92”lO’W - NA - 1,653 29”OO’N 87’3O’W - 2 - 685 28”OO’N 89”08’W 10 10 26.7 2,571 26”52’N 90”07’W - 1 12 14 22.7

784 28”22’N 89”08’W 479 27”47’N 91”21’W

12 10 28.0 779 27”48’N 9O”OO’W 11 3 28.1 1,739 27”36’N 89”OO’W 12 8 28.6 2,227 26”47’N 85”02’W

1 ii

26.2 2,652 26”34’N 9O”OO’W 12 280

28:2 1,792 28”14’N 88”28’W

12 1 1,376 29”07’N 88”02’W

- - - - -

72 <lo 256

49 369 896 874

23”lO’N 82”18’W 1” 25”41’N 81”26’W 2 24”30’N 81”3O’W 2 30”20’N 86”3O’W 3 26”OO’N 97”2O’W G4

24”30’N 81”3O’W 28”OO’N 96”OO’W 27”32’N 82”46’W 26”38’N 96”18’W 27”39’N 96”34’W 26”16’N 96”14’W 28”15’N 89”lS’W 28”47’N 88”39’W

i ‘7 j**

5 5”” 8 9

10 10 11 12 1.3 1:2 1.3 13 1.3 1.3 1.3 1.3 10

Source: l--Cum (1918), 2-Moore (1953), 3-Caldwell et al. (1956), 4-Schmidly and Melcher (1974), 5-Katona et al. (1988), 6-Gunter (1954), 7-Schmidly (1981), 8-SEFSC (aircraft, Mullin et al. 1994), 9-SEFSC (aircraft, Hansen et al. 1996), lo- SEFSC (ship, opportunistic), 11-R. Shipp (personal communication), 12-M. Frenette (personal communication), 13-SEFSC (ship).

* This was apparently later identified as Pseudorca crassidens. ** More accurate coordinates were obtained subsequent to Katona et al. (1988) from

personal communications with L. Roden and T. Reisinger, the original sources.

of cetaceans. Both focused on the upper continental slope (depth generally lOO-1,000 m) with one in the north-central Gulf (87.5”-91.O’W) (Mullin et al. 1994), and the other in the northwestern Gulf (west of 87.5”) (Hansen et al. 1996). These surveys covered 20,593 and 48,633 transect km, respectively, with effort generally spread equally throughout the year.

NOTES 143

9848 8O"OO' 31°00' 31°00'

. . . . . . . .

GULF OF MEXI

.,!‘ .:, :+(;- ,, . ,. .,_~,

18"OO' 18'00' 98’48’ 80'00

Figure 1. Locations of killer whale groups sighted in the Gulf of Mexico (triangles: SEFSC ship surveys; circles: SEFSC aerial surveys; squares: opportunistic sightings with photos; crosses: opportunistic sightings with no photos; diamonds: strandings; small dots: daily 0800, 1200, and 1600 positions of NOAA Ship Oregon II during cetacean surveys).

Two killer whale groups were sighted during the SEFSC aerial surveys, and seven groups were sighted during the five spring ship surveys; none was sight- ed from the ship during the winter and summer. Killer whale sightings con- stituted 0.3% (Z/639) and 0.5% (7/1,354) of all cetacean groups observed from the aerial and ship surveys, respectively. In the eastern tropical Pacific killer whales constituted 1.5% of cetacean sightings (Wade and Gerrodette 1993). During surveys of the mid- and north-Atlantic U.S. continental shelf and slope waters, killer whales constituted 0.1% of cetacean sightings (CeTAP 1982).

Three of the six previously unreported opportunistic sightings were from the Oregon II during non-cetacean surveys, two in May 1978 (one in the south- ern Gulf) and one in May 1995. Robert Shipp (personal communication) ob- tained a 1989 videotape of a group of killer whales off northwestern Florida. In June 1991 and June 1992, not more than 11 km apart, a charter boat captain photographed groups of killer whales off southern Louisiana, with one identifiable male present at both sightings (Mike Frenette, personal commu- nication).

All killer whale sightings in the Gulf, except one, occurred between May and September. Although the chances for opportunistic sightings may improve with increased human recreational activity in the warmer months, this ob-

144 MARINE MAMMAL SCIENCE, VOL. 13, NO. 1, 1997

served seasonality may also reflect true killer whale occurrence patterns in the northern Gulf. Only 54% of all SEFSC cetacean survey effort occurred during this five-month period (46% aerial, 80% vessel).

Killer whale sightings in the Gulf were generally oceanic and clumped in distribution. Thirteen sightings occurred in a broad region south of the Mis- sissippi River delta in the central Gulf, and most (17/20) were in oceanic waters that averaged 1,242 m and ranged in depth from 256 to 2,652 m. Killer whales may have a more oceanic distribution in warmer waters (Dahlheim et ul. 1982). Wade and Gerrodette (1993) reported 57 killer whale sightings distributed throughout the oceanic eastern tropical Pacific. In contrast, in cooler waters of the Northeast Pacific region, concentrations of killer -whales occur in continental shelf waters (< 200 m) (Braham and Dahlheim 1982, Bigg et al. 1987).

The continental shelf (water < 200 m deep) in most parts of the northern Gulf is very wide (up to 260 km). No killer whale sightings on the shelf, other than those included in Katona et al. (1988), have been recorded despite extensive directed line-transect surveys of cetaceans and other vertebrate ma- rine life in coastal and outer continental shelf waters (Fritts et al. 1983, Scott et al’. 1989, Scott 1990, Lohoefener et al. 1990, Mullin et al. 1990, Blaylock and Hoggard 1994). Also, many years of activity on the continental shelf by fisheries research vessels, fishing vessels, and vessels associated with the offshore oil and gas industry have yielded no killer whale sightings (Lowery 1974; Schmidly 1981; Kevin Rademacher, personal communication).

Group size and composition could not be reliably ascertained in the non- SEFSC sightings. Killer whale group sizes from the 12 SEFSC sightings ranged from 1 to 12 animals but averaged 10.0 animals. Ten groups included at least one adult male, and nine groups at least one calf. Mean group sizes of killer whales from other studies typically range from about 5 to 12 animals (Wade and Gerrodette 1993, Kasuya 1971, CeTAP 1982, Bigg et al. 1990).

During five sightings, killer whales rode the bow and quarter waves of the Oregon II, in one case for about 60 min. On one occasion there were as many as 10 animals, including a cow and calf, riding the bow wave in a chorus-line formation. Dahlheim (1980) reported bow-riding behavior by killer whales near Alaska.

On 8 June 1993, 12 k’ll 1 er whales, including a large bull with a distinctive lopped-off dorsal fin, were sighted from the Oregon II traveling in an easterly direction. Twenty-seven hours later a group of 11 with this same bull was sighted 111 km to the southeast. The bull’s travel speed was at least 4.1 km/ h, comparable to the 5.2 km/h reported by Kruse (1991) for undisturbed killer whales and 6.5 km/h reported by Bigg et al. (1987).

Thirty-two individual killer whales, including nine bulls, have been pho- toidentified so far in the Gulf. While not every individual was photographed from each group, cataloged photographs showed that at least one individual from each sighting could be identified in at least one other sighting. One SEFSC sighting was of a single adult male that one year before had been sighted on two occasions with a group of killer whales.

NOTES 145

At least some individual killer whales have a wide temporal and spatial distribution in the Gulf. Six individuals have been sighted over a five-year period, with one animal being resighted over 10 yr. Some individuals range throughout the northern Gulf; three animals have been sighted in the central Gulf and the extreme western and eastern Gulf, a linear distance of over 1,100 km apart. Bigg et A. (1987) found maximum ranges of 800-1,450 km for killer whales in the coastal Northeast Pacific.

These sightings indicate that killer whales, while still rare relative to some other cetacean species in the Gulf, may not be as uncommon as once believed. It is probable that the paucity of historical killer whale sightings and strand- ings is due to killer whales’ apparent preference for oceanic waters in the Gulf. They may rarely inhabit the extensive continental shelf, which reduces the chances of human observation. Killer whales, including specific individuals, appear to be, at least seasonally, regular inhabitants of the northern Gulf of Mexico.

ACKNOWLEDGMENTS

We would like to thank Sonja Kromann and Steve Katona for being most gracious with their time and resources. We are grateful to Denice Drass, Larry Hansen, Eric Hawk, Leslie Higgins, Wayne Hoggard, Jon Peterson, Carol Roden, and Carolyn Rog- ers for their support. We thank all of the persons involved with the opportunistic sightings for their contributions and for answering numerous inquiries. Marilyn Dah- lheim, Thomas Jefferson, Robert Pitman, and two anonymous reviewers gave valuable input that contributed substantially to the final draft. The U.S. Minerals Management Service (Department of Interior) funded part of this research, under Interagency Agree- ment Numbers 16917 and 14-12-0001-30398 with the Southeast Fisheries Science Center.

LITERATURE CITED

BIGG, M. 1982. An assessment of killer whale (Orcinus orca) stocks off Vancouver Island, British Columbia. Report of the International Whaling Commission 32: 655-666.

BIGG, M. A., G. M. ELLIS, J. K. B. FORD AND K. BALCOMB. 1987. Killer whales: A study of their identification, genealogy and natural history in Brirish Columbia and Washington state. Phantom Press, Nanaimo, B.C.

BIGG, M. A., P. I? OLESIUK, G. M. ELLIS, J. K. B. FORD AND K. C. BALCOMB III. 1990. Social organization and genealogy of resident killer whales (Orcinus orca) in the coastal waters of British Columbia and Washington State. Phantom Press, Na- naimo, B.C.

BLAYLOCK, R. A., AND W. HOGGARD. 1994. Preliminary estimates of bottlenose dol- phin abundance in southern U.S. Atlantic and Gulf of Mexico continental shelf waters. NOAA Technical Memorandum NMFS-SEFSC-356. 10 pp.

BRAHAM, H. W., AND M. E. DAHLHEIM. 1982. Killer whales in Alaska documented in the Platforms of Opportunity Program. Report of the International Whaling Commission 32:643-646.

BUCKLAND, S. T., D. R. ANDERSON, K. P. BURNHAM AND J. L. LAAKE. 1993. Distance sampling: Estimating abundance of biological populations. Chapman and Hall, London, U.K.

146 MARINE MAMMAL SCIENCE, VOL. 13, NO. 1, 1997

CALDWELL, D. K., J. N. LAYNE AND J. B. SIEBENALER. 1956. Notes on a killer whale, Orcinus orca, from the northeastern Gulf of Mexico. Quarterly Journal of the Flor- ida Academy of Science 19: 189-196.

CETAP. 1982. A characterization of marine mammals and turtles in the mi.d- and north-Atlantic areas of the U.S. outer continental shelf. Final Report of the Ce- tacean and Turtle Assessment, Program Bureau of Land Management, Contract No. AA551-CT8-48, U.S. Department of Interior, Washington, DC. 450 pp.

CUN~, L. A. 1918. Contribution al estudio de mamiferos acuaticos observados en las costas de Cuba. Memorias de la Sociedad Cubana de Historia Natural “Felipe Poey” 3:83-123.

DAHLHEIM, M. E. 1980. Killer whales observed bowriding. Murrelet 61:78. DAHLHEIM, M. E., S. LEATHERWOOD AND W. F. PERRIN. 1982. Distribution of killer

whales in the warm temperate and tropical eastern Pacific. Report of the Inter- national Whaling Commission 32:647-653.

FORD, J. K. B., G. M. ELLIS AND K. C. BALCOMB. 1994. Killer whales: the natural history and genealogy of Orcinzls orca in British Columbia and Washington state. University of British Columbia Press, Vancouver, B.C.

FRITTS, T. H., A. B. IRVINE, R. D. JENNINGS, L. A. COLLUM, W. HOFFMAN AND M. A. MCGIZHEE. 1983. Turtles, birds, and mammals in the northern Gulf of Mexico and nearby Atlantic waters. U.S. Fish and Wildlife Service, Division of Biological Services, Washington, DC., FWSIOBS-82165. 455 pp.

GUNTER, G. 1954. Mammals of the Gulf of Mexico. Fishery Bulletin, U.S. 5 5:543- 551.

HANSEN, L. J., K. D. MULLIN, T. A. JEFFERSON AND G. P. SCOTT. 1996. Visual surveys aboard ships and aircraft. Pages 55-132 in R. W. Davis and G. S. Fargion, eds. Distribution and abundance of marine mammals in the north-central and western Gulf of Mexico: Final Report. Volume II: Technical Report. OCS Study MMS 96-0027. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of .Mexico OCS Region, New Orleans, LA.

HEYNING, J. E., AND M. E. DAHLHEIM. 1988. Orcinus orca. Mammalian Species 304: l-9.

KASUYA, T. 1971. Consideration of distribution and migration of toothed whales off the Pacific coast of Japan based upon aerial sighting record. Scientific Reports of the Whales Research Institute, Tokyo 23:37-60.

KATONA, S. K., J. A. BEARD, P. E. GIRTON AND F. WENZEL. 1988. Killer whales (Orcinzls orca) from the Bay of Fundy to the equator, including the Gulf of Mexico. Rit Fiskideildar 11:205-224.

KRUSE, S. 1991. The interactions between killer whales and boats in Johnstone Strait, B.C. Pages 149-159 in K. Pryor and K. S. Norris, eds. Dolphin societies: Dis- coveries and puzzles. University of California Press, Berkeley, CA.

LOHOEFENER, R., W. HOGGARD, K. MULLIN, C. RODEN AND C. ROGERS. 1990. Asso- ciation of sea turtles with petroleum platforms in the north-central Gulf of Mex- ico. OCS Study/MMS 90-0025. U.S. Department of the Interior, Minerals Man- agement Service, Gulf of Mexico OCS Regional Office, New Orleans, LA. 90 pp.

LOWERY, G. H., JR. 1974. The mammals of Louisiana and its adjacent waters. Loui- siana State University Press. Baton Rouge, LA.

MOORE, J. C. 1953. Distribution of marine mammals to Florida waters. American Midland Naturalist 49: 117-158.

MULLIN, K. D., R. R. LOHOEFENER, W. HOGGARD, C. RODEN AND C. M. ROGERS. 1990. Abundance of bottlenose dolphins, Tursiops truncatus, in the coastal Gulf of Mex- ico. Northeast Gulf Science 11:113-122.

MULLIN, K., W.’ HOGGARD, C. RODEN, R. LOHOEFENER, C. ROGERS AND B. TAI;GART. 1994. Cetaceans on the upper continental slope in the north-central Gulf of Mexico. Fishery Bulletin, U.S. 92:773-786.

SCHMIDLY, D. J. 1981. Marine mammals of the southeastern US. coast and Gulf of

NOTES 147

Mexico. U.S. Fish and Wildlife Service, Office of Biological Services, Washington, DC. FWYOBS-80/41. 163 pp.

SCHMIDLY, D. J., AND B. A. MELCHER. 1974. Annotated checklist and key to the cetaceans of Texas waters. The Southwestern Naturalist l&453-464.

SCOTT, G. I?, D. M. BURN, L. J. HANSEN AND R. E. OWEN. 1989. Estimates of bottlenose dolphin abundance in the Gulf of Mexico from regional aerial surveys. Contribution Number CRD-88/89-07. Miami Laboratory, National Marine Fish- eries Service, 75 Virginia Beach Drive, Miami, FL. 70 pp.

Scorr, G. P. 1990. Management-oriented research on bottlenose dolphins by the Southeast Fisheries Center. Pages 623-639 in S. Leatherwood and R. R. Reeves, eds. The bottlenose dolphin. Academic Press, San Diego, CA.

WADE, l? R., AND T. GERRODETTE. 1993. Estimates of cetacean abundance in the eastern tropical Pacific. Report of the International Whaling Commission 43:477- 493.

SEAN O AND KEITH D. MULLING, Southeast Fisheries Science Center, National Marine Fisheries Service, NOAA, P. 0. Drawer 1207, Pascagoula, Mississippi 39568, U.S.A. Received 25 July 1995. Accepted 31 March 1996.

’ Present address: 606 Lake Avenue, Pascagoula, MS 39567, U.S.A. 2 Corresponding author.