Patuxent Wildlife Research Center

In the Spring of 1994 I began marking larval Pacific Giant Salamanders (Dicamptodon tenebrosus) in their natal streams in the Chilliwack River Drainage Basin which is approximately 100 km east of Vancover, British Columbia. This basin (20km x 50 km) is the only known range of  D. tenenbrosus in Canada. For this reason, and due to the amount of forest harvest in the valley, this species is considered at risk in B.C.

Larvae were marked as part of multi-year mark-recapture project aimed at understanding the demographics of this salamander and the potential impacts forest harvest may pose to its continued survival. The majority of the small (<1.5m wide) headwater streams we study are at high enough  elevation to be covered by snow, are cold enough to reduce larval activity, or are inaccessible for six months of every year. It was therefore important that we devised methods to mark larvae so that marks would persist from season to season. For larger larvae (>5cm snout-vent-length) passive integrated transponders (PIT tags) were implanted successfully, but smaller larvae proved a problem to mark easily. By default we opted to toe-clip smaller larvae until a better technique could be developed. I worried, however, that conspecifis may be biting off toes or limbs, that toes may be regenerating quickly, and that stream dwelling larvae might heavily rely upon specialized toes to navigate the stream bottom in fastflowing waters.

In the winter of 1996 I monitored the regeneration of clipped toes of Nortwestern Salamander larvae (A. gracile), and D. tenenbrosus in the laboratory. I documented the regrowth of toes photographically and used a digitizer to measure the extent of regrowth over time. The data for D. tenenbrosus remains to be analyzed but the trend is very similar to the regeneration rate of A. gracile. Basically, toe clipping as a marking method for larval salamanders of this size was not a viable method for studies lasting longer than approximately 3 months. After that time it becomes difficult to discern, with certainty, marked animals from unmarked.

Also in winter of 1996 I experimented with a bio-compatible fluorescent elastomer marking system developed by Northwest Marine Technology Inc. (www.nmt-inc.com/).
Thirty larval A. gracile were anesthetized using diluted MS-222 (0.33 g/l) until flaccid. Mixed fluorescent elastomer was then injected into the dorsal tail-fin as close to the base of the tail as possible. Injections were made using 0.3 cc syringes resulting in clearly visible lines of color ranging from 2 - 6 mm in length. Eight of the larvae, upon recovery from the anesthetic were put into an exercise regime where they were made to swim the length of a plexiglas channel (1m) for 5 minutes. This process was repeated 10 times over 17 days. No marks were lost during the exercises. Retention and visibility of the elastomer marks were monitored for several months as was the visibility of larvae that had been toe-clipped.

The positive results of my small laboratory experiment prompted me to begin using the elastomer marking technique in the 1996 field study. Our hope was to gain over winter growth and movement data on the smaller size classes of  larvae in our study streams. Prior, only larger, recaptured PIT tagged individuals could provide such information. 421 D. tenebrosus larvae were marked in 11 streams between June and October 1996. 55 of these larvae were recaptured at least once during the season and 63 were recaptured at least once the following season (summer 1997). Continuing with elastomer marking in 1997 I marked 471 larvae in that season and recaptured 127 at least once. I anticipate more over-season recaptures for the 1998 season. Marking in the field was done by carring 0.3 cc syringes, each containing  a small amount of the mixed elastomer, in an insulated thermos bottle half filled with ice. Larvae were captured with dip-nets and anesthetized before one or two lines of elastomer were injected into the dorsal tail-fin while the larvae was help in the palm of my hand with the tail flat. It is also possible to inject elastomer marks on the ventral tail-fin and on the belly, directly in front of the hind limbs. Identification of marked larvae in the field is fairly easy as marks are quite  visible in the tail-fin region. At times , a hand-held UV light was employed to facilitate mark recognition.