Long-Term Decline of the Spotted Salamander (Ambystoma maculatum) in an Undeveloped Landscape

Worldwide, amphibians are experiencing high rates of decline. Large-scale, long-term studies of amphibians are crucial for uncovering potential causes of the declines; however, such long-term studies remain rare, particularly for salamanders. In this study, we monitored populations of Spotted Salamanders (Ambystoma maculatum) in 90 Connecticut, USA, ponds. Populations were divided between an inland, undeveloped landscape monitored for up to 23 yr and a coastal, developed landscape monitored for up to 9 yr. We measured the density of egg masses (number of egg masses per unit of search effort) each year at each pond for a total of 1392 pond-years of sampling effort and asked how egg mass densities and breeding probability relate to local environmental and climatic conditions. In the undeveloped landscape, average egg mass densities have declined by ∼30% over the course of 2 decades. The presence of salamander breeding activity was positively associated with spring pond depth, and pond depth itself has declined by ∼20% during the survey period. We also found that egg mass density was related to road proximity and developed land cover: egg mass densities tended to be higher in ponds near roads and in ponds with less development within a 200-m buffer. In the developed landscape, egg mass densities showed a nonsignificant declining trend from 2014 to 2022 and salamander breeding activity was positively associated with higher canopy cover and larger pond surface area. Our findings suggest that even in a protected landscape with increasing forest cover, spotted salamander egg mass densities are declining at a rate of 1.6%/yr. Decreasing pond depths are likely linked to decreased water yield as forests grow, which could affect pond hydroperiods (aquatic larval habitat) as well as forest soil moisture levels (adult habitat). Overall, increasing development may continue to negatively affect habitat of Spotted Salamanders and it is possible that forest maturation also has a negative influence on salamanders—an effect not documented previously.