Research Document 2021/064

Recovery Potential Assessment for Lower Fraser River White Sturgeon (Acipenser transmontanus)

By English, K.K., Challenger, W., Robichaud, D. and Korman, J.

Abstract

The Lower Fraser White Sturgeon (Acipenser transmontanus) population is genetically and spatially isolated from fish upstream of Hells Gate, and is without genetic structure within its range. The population inhabits a wide range of habitats within its range.

The population is undergoing declines in abundance, both overall and specifically in the juvenile and subadult size/age classes. The adult size/age class has been gradually increasing over the past 20 years, but is expected to start to decline within 5 years. Candidate recovery thresholds are set to 60,000 sturgeon in the 60-279 cm fork length (FL) size range (Age 7-55) and 20,000 adult sturgeon (160-279 cm FL, Age 23-55). We have also evaluated the potential for the abundance of adult sturgeon to remain above the previously defined threshold level of 10,000 adults.

The biggest threats to recovery include: the food available for all life stages of sturgeon; further reduction in the habitat available for sturgeon, bycatch mortalities associated with in-river gillnet fisheries; and sub-lethal factors that affect the spawning frequency and spawning success for adult sturgeon.

Potential and realized mitigation actions, in the order in which they are presented in the report, include: maintaining the current moratorium on gravel extraction from the lower Fraser River; managing dredging to minimize the impacts on sturgeon; reducing the effects of fisheries on sturgeon; improving access to juvenile rearing habitat (e.g. replacing old tidal/flood gates with “fish friendly” gates); and reducing fisheries (or fishery related impacts) on important species that directly or indirectly support the food supply for sturgeon (e.g. Fraser Chum Salmon, Oncorhynchus keta, and Eulachon, Thaleichthys pacificus).

Population projections suggest that both large natural improvements to survivorship and recruitment and substantive management actions will be required in order to reverse the declining trends for the population and to meet the candidate recovery threshold of 60,000 Age 7-55 sturgeon within a 50-year horizon.

Physical habitat availability had declined over the past century, but should be sufficient to support the candidate recovery threshold of 60,000 Age 7-55 sturgeon, an abundance level that was observed as recently as the early 2000’s. Food resources available to Lower Fraser White Sturgeon, such as Eulachon and Chum Salmon, have declined in a way that matches the observed declines in juvenile White Sturgeon, and the prey base may need to be recovered in order to support White Sturgeon at the abundance levels targeted for recovery.

Research Document 2021/064 (PDF, 3,513 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.