LB 10-103 - Building a case criteria for newt mass die-off events

Newts in the genus Taricha are endemic to the West coast of North America. Recent unpublished reports identify enigmatic mass mortality events across the range. Disease is a leading contributor to amphibian declines, as evidenced by epizootics caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) globally. To document the extent of enigmatic mass mortality events in Taricha we created an online survey for herpetologists conducting research within Tarichas range. To determine whether Bd is implicated, we collected repeated disease diagnostic data (skin swabs, body condition, water quality measurements), and collected sick animals from targeted populations where mortality events were reported. Skin swabs were analyzed using a standard Bd qPCR assay. The survey identified 13 sites with the presence of emaciated or dead newts, and 3 sites with mass die-offs. Based on available permits and access, we selected two populations (Palomarin trail, Point Reyes National Seashore, Marin Co., CA; PMT; and Pine Lake, Mason Co., WA; PL) as focal study areas where mass die offs were seen in 1991 (PMT), 2014 (PMT), and 2022 (PL). We collected skin swab data from PMT in 1991, 2014, and 2023, and at PL in 2023. In 1991, PMT swabs were collected from preserved museum specimens at the Museum of Vertebrate Zoology, all other samples were collected from live animals at the focal sites. In 2014, three moribund Taricha granulosa were collected and sent for histopathological analyses at the National Wildlife Health Center in Madison, Wisconsin (Case #24780). We found no evidence of Bd from PMT swabs collected in 1991 (n=6), but 63% of samples from 2014 were Bd-infected (154 Bd positive out of 254 total), seven had infection intensity scores above a mortality threshold identified in other species. Histopathology reports found evidence of Bd infection, but the cause of death was inconclusive. Preliminary 2023 surveys at PMT revealed 26 emaciated animals and one dead (out of 61 collected), but PL remains covered in snow. In 2023, we will collect an additional 120 swabs and up to 20 sick animals for histopathological analysis from each site. In summary, our study documents die offs and emaciated individuals across a broad geographic range. Currently, our results are inconclusive whether Bd is implicated, but additional data will help direct future studies and could change the focus towards other possible causes such as Bsal or other pathogens, food availability, water quality, or climate-related changes.