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MARINE MAMMAL SCIENCE, 14(3):599-604 (July 1998) 0 1998 by the Society for Marine Mammalogy

MONITORING A REHABILITATED HARBOR PORPOISE USING SATELLITE TELEMETRY

Each year between February and May, immature harbor porpoises (Pbocoena phocoenu) strand along the mid-Atlantic coast of the United States (Haley and Read 1993). Occasionally, harbor porpoises strand alive, providing an oppor- tunity to rehabilitate and release these animals back into the wild. To date, the survival of rehabilitated individuals after release has not been examined. This note describes the behavior of a rehabilitated harbor porpoise after release in the coastal waters of the mid-Atlantic United States, as monitored by sat- ellite telemetry.

On 1 April 1995 a 121-cm, 23-kg female harbor porpoise stranded near the town of Dennisville, NJ, in a tributary of Delaware Bay. The animal was recovered by the Marine Mammal Stranding Center in Brigantine, NJ, and was transported by the Marine Mammal Rescue Program of the National Aquarium in Baltimore (NAIB) to their hospital pool located at NAIB. The entire recovery and transport procedure took less than six hours. The animal was severely emaciated and suffered from parasitic and bacterial skin infections. The porpoise responded well to treatment of both infections, but behavioral and blood parameter abnormalities postponed the animal's release for 13 mo.

During its rehabilitation, the porpoise was housed in a 4-m-deep, 370,000- liter pool at NAIB. After an initial period of assisted feeding, the porpoise was maintained on a diet of dead Atlantic herring (Cltlpeu barengtls), capelin (Mal lo tm villosis), and squid (Lolzgo sp.) at a rate of ca. 11% body masslday (144 kcallkg). Prior to release the porpoise was also fed live herring. At the time of release the porpoise had a standard length of 146 cm, a body mass of 47 kg, and based on its size was approximately 2 yr of age (Read and Tolley 1997).

The porpoise was released at 0852 EST on 29 April 1996, 55 km east of Ocean City Inlet, MD (38.28"N, 74.43"W). During transport the porpoise

600 MARINE MAMMAL SCIENCE, VOL. 14, NO. 3, 1998

was supported in a stretcher suspended in a water-filled carrier. Transport took place aboard a United States Coast Guard cutter. The release site was selected because it was offshore of an area where extensive gillnet fishing typically takes place. At the time of release clinical examination showed the porpoise was healthy and in excellent body condition.

For physical identification the animal was given a three-digit mark (508) on the right and left flanks using 5-cm brands supercooled in liquid nitrogen. Just prior to release, a satellite-linked transmitter, or platform transmitter terminal (PTT), was attached to the dorsal fin of the porpoise. Prior to the attachment of the transmitter, the dorsal fin was cleaned with a topical anti- septic (Povidone-iodine lo%), and an analgesic (lidocaine 2%) was injected at the site of each attachment pin (ca. 2 cc), utilizing the infiltration method. The PTT consisted of a flat-board ST-10 (Telonics, Mesa, AZ) mounted in a low profile rectangular lexan box. The transmitter was attached directly to the side of the dorsal fin using three 6.5-mm diameter delrin pins. The pins passed through the backing plate and dorsal fin and were secured on the opposite side of the fin with steel lock nuts backed with small (30 X 1.5 mm) delrin washers. Both the backing plate and washers were lined with 4-mm open cell foam. The PTT had a 17-cm whip antenna, measured 11 X 5 X 2 cm and weighed approximately 150 g in air. Incorporated into the PTT was a surface- time counter, which provided a cumulative record of the time the tag was above the water’s surface. The value of the surface-time counter was transmit- ted twice during each signal, allowing us to detect transmission errors. The tag also incorporated a saltwater switch, which prevented underwater trans- missions. To further conserve battery life, we used a duty cycle of eight hours operation each day.

In addition to the location and surface-time data, we obtained information on the quality of each estimated location from Service Argos (Argos 1996). Location quality was dependent on the number of uplinks received during a satellite overpass, the time elapsed between these receptions, movement of the PTT, and the stability of the transmitter oscillator. Each location was classified into one of four categories: Class 3 (at least six uplinks received in a single satellite pass, position accuracy better than 150 m), Class 2 (five uplinks re- ceived in a single satellite pass, position accuracy within 350 m), Class 1 (four uplinks received in a single satellite pass, position accuracy within 1 km), Class 0 (less than four uplinks received in a single satellite pass, position accuracy greater than 1 km). In addition, location estimates in Classes A (three uplinks received) and B (two uplinks received) were provided. The location estimates of these latter two classes were of unknown quality. All estimated locations were filtered using a speed plausibility check; consecutive positions resulting in an average travel speed of greater than 7.5 km/h were excluded. This filter value was selected based on published travel speeds (Gaskin et al. 1975, Westgate e t al. 1995) and field observations of wild harbor porpoises.

Analysis of movement data was performed using ArcView Geographic In- formation System (GIS) (ESRI 1994). We included only the most accurate position obtained each day to prevent bias associated with multiple daily po-

NOTES 60 1

sitions. Mean akily distance traveled was calculated by summing the distance (km) between the best position received per day for all days of the deployment and then dividing this value by the number of days of the deployment. Mean rate of travel was calculated by dividing the distance (km) between sequential best daily positions by the time (h) that had elapsed between those positions. Mean distance from shore (km) was calculated by averaging the distance from the best daily position to the nearest mainland shoreline. Depth was estimated using bathymetry data on digitized National Ocean Service (USA) marine charts. The proportion of time spent at the surface was estimated using telemetered data from the surface-time counter.

A total of 142 positions was received from the harbor porpoise during a tracking period that lasted for 50 d. On average we received 2.9 2 1.8 po- sitions per day. The movements of this porpoise can be divided into three distinct phases: an initial 16-d period characterized by rapid movements off- shore, a 26-d period during which the porpoise milled near shore, and a final 8-d period when the porpoise resumed travel in a northeasterly direction (Fig. 1). Immediately after release, the porpoise made a series of zigzag movements across the continental shelf moving offshore into water over 1,800 m in depth. During this phase the porpoise’s mean distance from shore was 79.8 -+ 49.9 km, and its mean rate of travel was 2.2 2 1.1 km/hr. The final movements of the initial phase were towards New Jersey (see inset, Fig. 1). The porpoise remained in the nearshore region for nearly four weeks, milling along the coast of New Jersey and outside the approaches to New York City. During this phase the porpoise’s mean distance from shore was 5.0 ? 5.5 km, and its mean rate of travel was 0.7 Ifr: 0.5 km/h. On June 11 the porpoise started to travel northeast along the coast of Long Island, generally staying close to shore and traveling towards Cape Cod. During this final phase the animal main- tained a mean distance from shore of 8.5 * 9.9 km and traveled at a mean rate of 1.9 ? 0.7 km/h. We received the last position on 18 June from outside Buzzard’s Bay, MA (Fig. 1).

Other PTT deployments (Read and Westgate 1997) have shown that por- poises generally travel quickly between productive habitat regions where they may remain for extended periods. The movements of the rehabilitated porpoise adhered to this pattern. Little is known about the winter ranges and habitat utilization patterns of this species, but our observations suggest that the New Jersey shore and approaches to New York harbor may represent an important winter habitat. Analysis of the stomach contents of stranded juvenile harbor porpoises from the mid-Atlantic revealed a dominance of nearshore prey items (A. J. Read, unpublished data), indicating the importance of coastal habitats. Harbor porpoises do not carry long-term energy stores (Koopman 1994), so it is unlikely that the porpoise would have remained in this vicinity for four weeks if it had been unable to forage successfully. It is difficult to interpret the significance of the initial rapid movements that were made by this por- poise. Harbor porpoises are not tied to shallow nearshore waters during winter (Read et al. 1996), but given that this behavior was observed only during the

602 MARINE MAMMAL SCIENCE, VOL. 14, NO. 3, 1998

Figrare 1. Track of rehabilitated harbor porpoise obtained from satellite telemetry. Only best daily positions are shown (closed squares). Stations from which SST were obtained are indicated by open polygons. The site of stranding (closed star) and release are also indicated.

first days of the deployment, i t may represent a period when the animal was establishing orientation.

We monitored sea-surface temperature (SST) throughout this deployment from moored weather buoys and the Coastal-Marine Automated Network (C- MAN) (Fig. 1). SST varied between 9.3" and 10.0"C while the porpoise was

NOTES 603

Table 1. Comparison between the behavior of the harbor porpoise from the present study and wild harbor porpoises from the Bay of Fundy/Gulf of Maine as monitored by satellite telemetry.

Other PTT Rehabilitated deployments

Parameter porpoise on P. pbocoenaa

Mean distance from shore 30.5 2 45.5 km 6.6-81.4 km Mean daily distance traveled 32.8 km 1 3.9-5 8.5 km Mean rate of travel 1.4 2 1.0 km/h 0.6-2.3 km/h Proportion of time at the surface 0.03 0.03-0.07

a Read and Westgate 1997.

in the first phase of deployment. SST ranged from 13.8" to 17.2"C while the porpoise was close to the New Jersey shore and, as the animal began its northeasterly trek, it passed buoy 44025 on June 13 when the SST was 18.4"C. At the time of final contact, buoy 44028 in Buzzard's Bay recorded an SST of 16.4"C. These movements are consistent with observations that harbor por- poises are rarely found in water warmer than 17°C (Gaskin et a/. 1993).

We compared values for mean distance from shore, mean rate of travel, mean daily distance traveled, and proportion of time at the surface with those obtained from seven PTT deployments on this species in the Bay of Fundyl Gulf of Maine (Read and Westgate 1997) (Table 1). All observations from the rehabilitated porpoise were within reported ranges from wild animals. This suggests that this animal was behaving in a similar fashion to wild porpoises, and from this we conclude that the reintroduction was successful. We do not know why we lost satellite contact after 50 d (similar PTTs have lasted be- tween 33 and 212 d in the Bay of FundylGulf of Maine), but we suspect that it was due to loss or failure of the PTT. It seems unlikely that the animal died given that it was traveling rapidly just prior to tag loss, its monitored parameters did not dramatically change prior to loss of contact and were sim- ilar to those obtained from other tagged porpoises (Read and Westgate 1997), and 50 d had elapsed since its release.

Satellite telemetry offers a powerful and inexpensive tool to obtain long- term data after release of rehabilitated animals. While several rehabilitated harbor porpoises have been tracked after release using VHF telemetry (A. J. Westgate, unpublished data), this represents the longest and most compre- hensive track obtained from a porpoise that was reintroduced into the wild. From our observations of this animal, we conclude that rehabilitation and reintroduction can be successful for stranded harbor porpoises, even if they are maintained in husbandry facilities for moderate periods (1 3 mo). We also stress the utility of monitoring the behavior of rehabilitated marine mammals for extended periods after release, as a means of determining whether or not such efforts are successful.

604 MARINE MAMMAL SCIENCE, VOL. 14, NO. 3 , 1998

ACKNOWLEDGMENTS

We thank everyone at the National Aquarium in Baltimore including: the veterinary technician staff, the Department of Lab Services, Dr. Joseph Geraci, Dr. Michael Wise, Dr. Andrew Stamper, and especially all the volunteers of the Marine Mammal Rescue Program for their dedicated assistance throughout the rehabilitation of this animal. We also gratefully acknowledge the logistic support we received from the United States Coast Guard Group, Ocean City, MD, and the Baltimore Washington Fire Department. This manuscript was improved by comments from Heather Koopman, Randall Wells, and Randall Davis.

LITERATURE CITED

ARGOS. 1996. User manual 1.0. Service Argos, Landover, MD. 176 pp. ESRI. 1994. Environmental Systems Research Institute. Redlands, CA. GASKIN, D. E., G. J. D. SMITH AND A. P. WATSON. 1975. Preliminary study of the

movements of harbour porpoises Phocoena phocoena in the Bay of Fundy using radiotelemetry. Canadian Journal of Zoology 53: 1466-1 47 1.

GASKIN, D. E., S. YAMAMOTO AND A. KAWAMIJRA. 1993. Harbor porpoise, Phocoena phocoena (L.), in the coastal waters of northern Japan. Fishery Bulletin, U.S. 91: 440-452.

HALEY, N. J., AND A. J. READ. 1993. Summary of the workshop on harbor porpoise mortalities and human interactions. U.S. Department of Commerce, NOAA Tech- nical Memorandum NMFS-F/NER-5. 32 pp.

KOOPMAN, H. N. 1994. Topographical distribution and fatty acid composition of blubber in the harbour porpoise (Phocoena phocoena). M.Sc. thesis, University of Guelph, Guelph, Ontario. 148 pp.

READ A. J., AND K. A. TOLLEY. 1997. Postnatal growth and allometry of harbour porpoises from the Bay of Fundy. Canadian Journal of Zoology 75:122-130.

READ A. J., AND A. J. WESTGATE. 1997. Monitoring the movements of harbour por- poises (Phocoena phocoena) with satellite telemetry. Marine Biology 130:3 15-322.

READ A. J., J. R. NICOLAS AND J. E. CRADDOCK. 1996. Winter capture of a harbor porpoise in a pelagic drift net off North Carolina. Fishery Bulletin, U.S. 94381- 383.

WESTGATE, A. J., A. J. READ, P. BERGGREN, H . N. KOOPMAN AND D.E. GASKIN. 1995. Diving behaviour of harbour porpoises, Phocoena phocoena. Canadian Journal of Fisheries and Aquatic Sciences 52: 1064-1073.

ANDREW J. WESTGATE, ANDREW J. READ, TARA M. Cox, Duke University Marine Lab, 135 Duke Marine Lab Road, Beaufort, Nor th Carolina 28516, U.S.A.; e-mail: westgate@acpub.duke.edu; T. DAVID SCHOFIELD, BRENT R. WHITAKER, National Aquarium in Baltimore, 501 E. Pratt Street, Baltimore, Maryland 21202, U.S.A.; KURT E. ANDERSON, Duke University Marine Lab, 135 Duke Marine Lab Road, Beaufort, Nor th Carolina 28516, U.S.A. Received 24 March 1997. Accepted 15 July 1997.