Assessing the population of this species is difficult. The world's largest known breeding colony is on Baccalieu Island, off Newfoundland’s east coast. Although some data on this and other colonies are available from Seabird Colony Counts, the results vary widely among colonies and are difficult to interpret at the national level. Breeding colony estimates vary widely (see Huntington et al. 1996), and many breeding colonies may be as yet undiscovered. However, updated information on breeding pair estimates is available for several breeding colonies in the Atlantic Region (Wilhelm et al. 2015a, and summarized in Hedd et al. 2018). Results suggest that several of these large colonies have undergone significant declines (by about 50%) relative to the late 1970s or 1990s. This contrasts with previous assessments, which suggested that large Leach's Storm-Petrel colonies were stable in the northwestern Atlantic from the 1970s to early 2000s, and only small colonies showed declines (Robertson et al. 2006). However, the now second-largest colony in the northwest Atlantic, Grand Colombier, located in the French waters off St. Pierre et Miquelon, which is off Newfoundland’s southeast coast, appears to be stable (Lormée et al. 2012). While current information from some of these large breeding colonies suggests significant decreases in abundance, there are still many smaller colonies in the Atlantic Region for which current information is not available, and little information exists for storm-petrels breeding in Quebec and British Columbia. Thus, current data are considered insufficient to determine the population status of Leach's Storm-Petrel in Canada. As such, a national population goal for this species has not yet been determined.
