Homing by released captive California sea lions ...

Homing by released captive California sea lions, Zalophus californianus, following release on distant islands S. H. RIDGWAYAND C. C. ROBISON Biosciences Division, Naval Ocean Systems Center, Snn Diego, CA, U .S.A. 92152

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Received December 20. 1984 RIDGWAY,S. H., and C. C. ROBISON.1985. Homing by released captive California sea lions, Zalophus californianus, following release on distant islands. Can. J. Zool. 63: 2162-2164. Captive male California sea lions were twice flown to offshore breeding islands and released. Three animals returned to their pen in San Diego Bay after discharge on San Clemente Island, about 1 15 km away. Two of four returned to the same facility from San Nicolas Island, about 240 km away. The fastest sea lion returned in 2 days from San Clemente and in 4 days from San Nicolas. This is the first evidence for such specific east-west navigation by sea lions and suggests that these animals are good navigators. RIDGWAY, S. H., et C. C. ROBISON.1985. Homing by released captive California sea lions, Zalophus californianus, following release on distant islands. Can. J . Zool. 63: 2162-2164. Des lions de mer de Californie gardds en captivitd ont CtC transportds par air deux fois et IibCrCs sur des iles qui servent de temtoires de reproduction. Trois animaux sont retournks a leur aire de captivitk dans la baie de San Diego apres avoir CtC IibCrCs sur I'ile San Clemente, a environ 115 km de distance. Deux des quatre lions de mer relPchCs a I'ile San Nicolas, a 240 km de distance, sont retournds a la meme aire de captivitk. Le lion de mer le plus rapide a mis 2 jours a retourner a son point de dCpart a partir de San Clemente, et, de San Nicolas, le plus rapide a mis 4 jours. C'est la premiere fois que de tels ddplacements sp6cifiquement est-ouest sont observds chez des lions de mer et ce comportement semble indiquer que ces animaux sont de bons navigateurs. [Traduit par le journal]

Introduction California sea lions, Zalophus californianus californianus, breed on islands (Peterson and Bartholomew 1967) throughout the southern portion of their range from Nayarit, Mexico (20" N), to the Farallon Islands off San Francisco, California (37" N). They do not breed on mainland beaches of California. During winter, male sea lions migrate as far north as Vancouver Island (5 1" N), 1900 km from the northernmost primary breeding island of San Miguel (34" N) (Mate 1975; Ode11 1981). No equivalent migrations by females have been documented. Young sea lions of both sexes are commonly seen on beaches and in harbors of Southern California. Some of these are sick or dying (Ridgway et al. 1975), and many are rehabilitated at oceanaria and other facilities on the California coast (Otten 1979; Ridgway and Prescott 1979; Sweeney and Geraci 1979). We have obtained information on the sex of 1856 beached sea lions from Southern California and 620 from north-central California. Of those collected from Southern California beaches by Marineland near Los Angeles and Sea World in San Diego, 948 (51%) were males and 908 (49%) were females, while further north, beached animals collected at the California Marine Mammal Center near San Francisco consisted of just over 82% males (5 10 males, 1 17 females). In 1983, 786 sea lions were taken in and over 200 released near the mainland. We have discovered no documented attempts to release such animals on the distant offshore islands where their rookeries are common. This report documents releases of male sea lions on San Clemente and San Nicolas islands in the spring of 1984 and their rapid return to captive quarters in San Diego Bay. Materials and methods Sea lion A apparently crawled aboard the deck of a U.S. Navy vessel in San Diego Bay and was found there in a lethargic condition on 11 May 1978. The animal was about 8 to 10 months old and

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FIG. 1. Map showing areas where sea lions were released on San Clemente Island in February and on San Nicolas Island in April. weighed about 15 kg. We treated the sick sea lion with antibiotics and vitamins for 2 weeks and fed him daily with 3-4 kg of a mix of three different fish (Columbia River smelt, Thaleichthys vetulus; Pacific mackerel, Scomber diego; and hemng, Clupea harengus). In May 1979, the animal weighed 33 kg, in May 1980 54 kg, and in May 1983 100 kg. During succeeding years this sea lion was trained for Project "Quick Find" (Conboy 1975). Because the animal never achieved high reliability compared with other sea lions, a decision was made to release the animal back to the wild; before release, he was freeze branded on the right hip (Farrell et al. 1966; Cornell et al. 1979). Sea lion B, a male of about 100 kg in weight, was taken in on 10 February 1983 when he came to our facility in San Diego Bay and began attempts to steal fish by pursuing our dolphin trainers. Because the animal was not sick and was very tame, we suspected that he may have been released from Sea World or Marineland. However, examination revealed no marks or brands, nor did any of our contacts at the oceanaria claim the animal. Because the animal would not leave, we placed him in our sea lion holding enclosure. In December 1983, this


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FIG.2. The four sea lions run for water after release on San Nicolas Island. From left: A, C, B, D. Photograph courtesy of Mr. Matthew Klope. sea lion was 191 cm in length from tip of nose to base of tail and weighed 115 kg. He also received some "Quick Find" training, but ultimately was rejected for the program. Sea lion C, a small male, had beached in a sick condition on 20 May 1983. Fully rehabilitated by July 1983, he had grown to 100 cm and weighed 25 kg. In April 1984 he was 105 cm long and weighed 35 kg. Sea lion D, another small male of about 30 kg, appeared quite healthy when he came to our facility in April 1984, bearing a shave brand (a small area of hair clipped to show a symbol with numerical designation; Cornell et al. 1979). This sea lion had been rehabilitated by Sea World and released in the local area. The animal was delivered to Sea World by truck. A day later this sea lion appeared again at our facility. To reach our facility on San Diego Bay from Sea World on Mission Bay, the animal had to swim about 20 km. On 15 February 1984, animals A, B, and C were transported by helicopter to San Clemente Island, about 115 km northwest of our facility. Each sea lion was in a cage inside the helicopter and could not see outside during the trip to the island. They were released into the Pacific at Eel Point about midway along the western side of the island (see Fig. I ) just north of a large sea lion rookery area. On 17 April 1984, we transported animals A, B, C, and D, the first three of which had returned after their initial release, by truck to Point Mugu, California, and then flew them, again fully enclosed, to San Nicolas Island, about 240 km northwest of our facility, where we released all four animals near the southeastern end of the island (Fig. 2).

Results All three sea lions (A, B, and C) released at San Clemente Island in February returned to our facility in San Diego Bay. Animal A returned in 2 days, animal B in 5 days, and animal C in 7 days. The animals were not weighed on return but there was no apparent weight loss. We would have noticed weight

loss if it was over about 10% of body weight. Of the sea lions (A, B, C, and D) that were released on 17 April 1984 at San Nicolas Island, only the larger animals (A and B) returned. Sea lion A was next seen on the morning of 21 April 1984, when the attendant who feeds facility animals arrived on Saturday morning to commence the day's feeding and animal care. Sea lion A was found sleeping adjacent to the sea lion pen gate. Sea lion B was next seen on the afternoon of 25 April when he swam up to our facility. The sea lion immediately followed an attendant into the pen containing sea lion A when the gate was opened. During May, June, and again in July the two sea lions were released in San Diego Bay but each time they refused to leave the facility area. When at liberty, the two animals persisted in attempts to steal food from other animals and their trainers working nearby. Consequently, the two sea lions became a considerable nuisance, and it was decided to keep them inside the facility.

Discussion All three sea lions released on San Clemente Island returned to their site of captivity in San Diego Bay. Of the four sea lions released at San Nicolas Island, only the two larger animals returned. The two smaller sea lions had each returned from shorter distances, animal C from San Clemente and animal D from Sea World on Mission Bay; however, we can only speculate as to why they did not return to our facility from San Nicolas Island. It is possible that they had not developed the longer distance navigation capability or stamina of the older animals. Because sea lion B is nearing sexual maturity, his refusal to


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remain at the nearby rookeries on the islands during the spring or to leave for the rookeries during the summer breeding season appears remarkable. As to the factors motivating the sea lion's return, we can only guess that the reliable source of desirable food fish at the bay facility was most important. It would seem that the animals have good memory as to the location of their home in captivity. Because they were flown to both islands, there is no possibility that they followed a trail or scent to return. The ability of the animals to navigate and their stamina in swimming long distances are particularly notable aspects of these events. If sea lion A's ability to navigate is so exceptional that he was able to take the most direct route from the release point to our facility, we must conclude that he averaged at least 60 km per day. The effect of currents and waves would likely make the course longer than a straight-line route, although it is entirely possible that the animals use sea conditions to their benefit. Sea lions are adept wave riders. The sea lion's navigational ability is unstudied. The north-south migration of male California sea lions is well established (Mate 1975) but their east -west movements have not been previously documented. Groups of sea lions, especially males (R. J. Schusterman, personal communication), are often seen on rocks and pilings along the California coast. These animals make short east-west trips in going to sea to feed and many of them probably make longer east- west journeys in returning to the islands for the breeding season. However, there are no reports of long-distance homing by captive sea lions after release offshore nor are there any documented east-west movements by specific wild individuals.

Acknowledgements We thank Lt. Donna Kline and personnel of Project "Quick Find" for releasing the sea lions on San Clemente Island. Biologist Matthew Klope of Naval Air Station - Pacific Missile Test Center, Point Mugu, assisted in the release at San Nicolas Island. Mr. Brad Andrews of Marineland of the Pacific, Mr. Jim Antrim of Sea World, and Ms. Lynn Amaya and Dr.

Laurie Gage of California Marine Mammal Center, Fort Cronkhite, provided information on the sex of beached animals collected or treated by their facilities. Dr. C. A. Jacobs, Ms. Michelle Jeffries, and Ms. Tricia Kamolnick provided valuable help with the animals. Mr. F. G. Wood and Dr. R. J. Schusterman reviewed the manuscript and made helpful suggestions. CONBOY,M. E. 1975. Project "Quick Find": A marine mammal system for object recovery. Rapp. P. V. Reun. Cons. Int. Explor. Mer. 169: 487-500. CORNELL, L. H., E. D. ASPER,K. OSBORN, and M. J. WHITE.1979. Investigations on cryogenic marking procedures for marine mammals. U.S. NTlS PB Rep. No. 291570, Washington, DC. FARRELL, R. K . , L. M. KOGER,and T. D. WINWARD. 1966. Freeze branding of cattle, dogs and cats for identification. J . Am. Vet. Med. Assoc. 149: 745-752. MATE,B. R. 1975. Annual migrations of the sea lions Eumetopias jubatus and Zalophus californianus along the Oregon coast. Rapp. P. V. Reun. Cons. Int. Explor. Mer. 169: 445-461. ODELL,D. K. 198 1. California sea lion. In Handbook of marine mammals. Vol. I. Edited by S. H. Ridgway and R. J . Harrison. Academic Press, Inc., London. pp. 67-97. O'ITEN,T. 1979. Nursing care of strandlings. In Biology of marine mammals: Insights through stranding. Edited by J. R. Geraci and D. J. St. Aubin. U.S. NTlS PB Rep. No. 293890, Washington, DC. pp. 264-267. PETERSON, R. S., and G. A. BARTHOLOMEW. 1967. The natural history and behavior of the California sea lion. Am. Soc. Mammal. Spec. Publ. No. I. RIDGWAY, S. H., J . R. GERACI, and W. MEDWAY. 1975. Diseases of pinnipeds. Rapp. P. V. Reun. Cons. Int. Explor. Mer. 169: 327 - 337. 1979. The quandary of whether RIDGWAY, S. H., and J . H. PRESCOTT. to retain or release rehabilitated strandlings. In Biology of marine mammals: Insights through stranding. Edited by J . R. Geraci and D. J . St. Aubin. U.S. NTlS PB Rep. No. 293890, Washington, DC. pp. 298-299. J . C., and J . R. GERACI.1979. Medical care of strandlings. SWEENEY, In Biology of marine mammals: Insights through stranding. Edited by J . R. Geraci and D. J . St. Aubin. U.S. NTlS PB Rep. No. 293890, Washington, DC. pp. 279-289.