Quantifying associations of large vertebrates with salmon in riparian areas of British Columbia streams by means of camera-traps, bait stations, and hair samples

Abstract

The importance of transfers of marine derived nutrients (MDN) in salmon between stream ecosystems and terrestrial riparian systems is a subject of much recent research which has established that MDN subsidies support populations of many animal species, affect riparian zone productivity and may control the biodiversity of riparian plant communities. Numerous biophysical processes are involved in the transfer of MDN between aquatic and riparian zones of streams but, the largest proportion of MDN transport across the aquatic-terrestrial interface appears to depend on the actions of a predator–scavenger complex (PSC) that in British Columbia includes at least 23 species of mammals and birds. Consequently, the role of salmon in maintaining riparian ecosystem integrity depends not only on spatial and temporal variations in salmon abundance but also on variations in the composition and strength of linkages between salmon and other PSC species. Measuring these linkages with traditional methods using direct observation would be prohibitively expensive and time consuming. In the current paper laser activated camera systems, salmon carcass manipulation and deoxyribonucleic acid (DNA) analysis of hair samples were employed to (1) identify large vertebrate members of the PSC of riparian zone ecosystems and (2) quantify the strength of linkages of these PSC vertebrates to spatial and temporal changes in salmon abundance. Techniques developed and applied here to gain insights into the salmon PSC have several advantages over traditional survey methods. These include semi-automated capture of large volumes of data, identification of diurnally and nocturnally active PSC members, ready inclusion of experiments in field survey design, reduced impacts of unintentional human interference on survey results, and greatly reduced cost relative to direct observational studies. Results reported here confirm black bears (Ursus americanus), pine marten (Martes americana), cougar (Felis concolor), wolverine (Gulo luscus), eagles (Haliaeetus leucocephalus), ravens (Corvus corox), and vultures (Cathartes aura) as large vertebrate members of the regional salmon PSC. However, the composition and strength of linkages between salmon and these PSC members vary so much in space and time that most appear unsuitable as generally useful indicators of the potential magnitude of salmon-dependent, MDN-transport from aquatic to riparian-zone ecosystems. Black bears however, given their high relative abundance, broad geographic distribution, and strong linkages to salmon represent a superior candidate for further development in combination with salmon, as indicators of the maintenance of MDN transport potential in future assessments of riparian ecosystem integrity of salmon bearing streams.