Abstract

There is a paucity of basic life history data for harbor seals (Phoca vitulina) of the California current. Active tagging with radiofrequency transmitters, in conjunction with stringent tracking, allows simple but valuable data collection of animal position and some information about lifespan. These data over time support inferences of survivability, site fidelity and other measures important to understanding of the status and behaviors of these animals.¹

Active tags are frequently applied to the haircoat of a seal with adhesives; however, the tags are lost during the annual molt. Implantation of tags ensures tag retention beyond annual molt cycles and increases the duration of data collection substantially. However, implantation requires a surgical procedure and thus attention to aseptic technique, analgesia, and animal welfare. Prior investigations have utilized inhalant general anesthesia and aseptic technique including multiple layer closures requiring significant logistic and time investment.²

Over the period February 2010 through July 2011 we implanted 41 harbor seals with Telonics^TM IMP/300/L RF tags in field conditions using an anxiolytic and local anesthesia. The initial 2 animals were implanted on a beach and fitted with an externally attached satellite transmitter (Spot5, Wildlife Computers, Redmond, WA, USA) in addition to the RF tag. One of these animals was noted to move approximately 17 kilometers and remain for 8 days at one site; however, the satellite signal was lost on day 8 following surgery. To follow up and monitor for complications, an additional 5 animals were implanted at TMMC facilities in a dedicated enclosure (not the surgical facility) meeting USDA size standards to hold animals for research purposes. These animals were held for approximately 14 days prior to release. No complications were observed.

Over the next 7 months, 34 additional animals were implanted in the field. Animals were caught with standard net sets, immediately transported to the work site ashore, weighed with a tripod suspended scale, blood collected, and diazepam (0.2–0.25 mg/kg via the extradural intervertebral sinus) administered to reduce anxiety. While additional biological samples and data were collected, the implantation site along the dorsal cervical area was aseptically prepped and infused with 1% lidocaine. Care was taken to keep total infused doses below 0.8 mg/kg of body mass.

The tags were placed in the subcutaneous tissues between the muscular fascia of the dorsal cervical muscles and the dermis (blubber) of the overlying skin. Closure was a single layer technique. Two sutures of 2-0 PDS II suture material were placed in the skin encompassing the epidermis and modified dermis into a near-far-far-near pattern alternating deep and superficial bites with the suture. Triple antibiotic ointment was applied to the closure and the animals were immediately released to the water.

Following completion of tag placements, surveillance efforts (aerial tracking and use of a passive listening station) have located numerous tagged animals including the initial animal that had moved but was lost to satellite monitoring after 8 days. The two initially tagged animals were relocated via their RF tags; one six months and one ten months after implantation. Multiple additional animals have been relocated and re-sighted and have shown no evidence of complications at the implantation site.

Acknowledgements

We thank the numerous MLML and TMMC volunteers who participated in the captures, data collection and implantation procedures. This work was conducted under NOAA NMFS Permit # 555-1870-03, SJSU IACUC # 931 and TMMC IACUC protocol 2009-01.

References

1.  McConnell B, Fedak M, Hooker S, Patterson T. Telemetry. In: Boyd IL, Bowen WD, Iverson SJ, eds. Marine Mammal Ecology and Conservation: A Handbook of Techniques. New York, NY: Oxford University Press; 2010.

2.  Lander ME, Haulena M, Gulland FMD, Harvey JT. Implantation of subcutaneous radio transmitters in the harbor seal (Phoca vitulina). Marine Mamm Sci. 2005;21(1):154–161.