Using rapid and repeatable side scan sonar methods for a second assessment of the Shortnose Sturgeon (Acipenser brevirostrum) population in the Saint John River, New Brunswick, Canada

Abstract

Population estimates are a key component of fisheries management, particularly when assessing species of concern. However, the time and effort required to conduct those estimates logistically limits their frequency. To facilitate assessment of Shortnose Sturgeon (Acipenser brevirostrum; SNS) which are a species of concern in the Saint John River, New Brunswick, Canada, a combined side-scan sonar and acoustic telemetry-based method was employed to enumerate SNS within high density winter aggregations. During this study 12,005 SNS were enumerated in one main winter aggregation and 2,186 SNS were counted within a second in the Kennebecasis Bay. Winter residency patterns determined from acoustic tracking of 18 tagged SNS over 8 years (2015/16-2022/23) indicated that these two aggregations represented on average 74.3% of the overall population suggesting that the total Saint John River population was ~19,100 SNS > 40 cm FL in winter 2022/23. Although the development of more in depth, robust, and repeated assessments are needed to verify this estimate of abundance and size classes, we conclude that the abundance of SNS in the Saint John River has probably remained stable since the earliest population estimate completed in 1977.