A northern pocket gopher (Thomomys talpoides) border control strategy: Promising approach

From 1994 to 1996, the use of perimeter traplines to intercept immigrating northern pocket gophers (Thomomys talpoides) and maintain forage fields with low pocket gopher populations was evaluated in alfalfa (Medicago spp.) fields in central Alberta. In April-May 1994, all northern pocket gophers inhabiting six 8-ha study plots were trapped out. In two of these plots, no more trapping occurred after the spring removal. In the other four study plots, 20-60 m wide perimeter traplines were established within the plots' boundaries. In two plots with low pocket gopher population densities (< 10 animals/ha) and in two plots with high pocket gopher population densities (> 10 animals/ha), the perimeter trapline intercepted greater than or equal to 75% of immigrating pocket gophers. At the end of the summer, there were greater than or equal to 213 mounds/ha in study plots without perimeter traplines. In the protected sections of plots with a perimeter trapline, there were less than or equal to 19 mounds/ha. The evaluation of the border control strategy was continued for two more years in one of the study plots where there were 22.4 pocket gophers/ha in spring 1994. In spring 1995, there were only 1.4 pocket gophers/ha and the perimeter trapline intercepted 81% of immigrating animals during summer. In spring 1996, only one animal inhabited the study plot (density of 0.1/ha). The border control strategy is a promising approach that should be further investigated to control northern pocket gopher populations. (C) 1997 Elsevier Science Ltd.