Status of White Sturgeon in the Lower Fraser River, British Columbia

ABSTRACT

Sturgeon (Acipenseridae) stocks worldwide are generally in decline, with many populations close to extirpation. One prominent species, the White Sturgeon (Acipenser transmontanus) with spawning populations distributed throughout three large, western North American watersheds (the Sacramento, Columbia, and Fraser rivers), has experienced population declines in the past decade. In 2003, the Committee on the Status of Endangered Wildlife in Canada designated all six populations of White Sturgeon in Canada “endangered.” To assist sturgeon recovery initiatives in the lower Fraser River (British Columbia), a stewardship-based monitoring and assessment program was developed by the Fraser River Sturgeon Conservation Society. A descriptive population model was developed to provide reliable annual population estimates by size/age group and location, based on tag release and recapture data collected by trained volunteers. As of January 2011, the population estimate (from 40- to 279-cm fork length) was 44,713 (95% confidence level 42, 634–46, 792). Group size analyses suggest that abundance decreases have been greatest for juvenile sturgeon under 100-cm fork length. Recruitment decline may be the result of several factors, including destruction of important spawning and early life history rearing habitats; fewer successful adult spawners due to in-river fisheries; and/or impacts of reduced food supply and ecological imbalances on both early life and adult stages.

RESUMEN

en términos generates, los stocks de esturiones (Acipenseridae) alrededor del mundo están reduciéndose, e incluso varias poblaciones se encuentran cerca de ser extirpadas. Una especie importante, el esturión blanco (Acipenser transmontanus), cuenta con poblaciones reproductoras que se distribuyen a lo largo de tres cuencas hidrológicas del noroeste americano (ríos Sacramento, Columbia y Fraser), sin embargo ha experimentado reducciones poblacionales en la última década. En 2003, el Comité sobre el Estatus de la Vida Salvaje en Peligro, en Canada, designó a las seis poblaciones de esturión blanco el estado de “amenazadas”. La Sociedad para la Conservación del Esturión en el Río Fraser desarrolló un programa de evaluación y monitoreo con el fin de apoyar las iniciativas de recuperación del esturión en el bajo Río Fraser (Columbia Británica). Se desarrolló un modelo poblacional descriptive para estimar anualmente, y de manera confiable, el tamaño de la población por grupo de talla y edad y por locación, sobre la base de datos de captura-recaptura colectados por voluntaries debidamente entrenados. La población estimada para el año 2011 (40–279 cm de longitud furcal) fue de 44,713 (95% de confianza 42,634–46,792). El análisis del tamaño por grupo indica que la reducción de la abundancia ha sido más importante en los juveniles de esturión de menos de 100 cm de longitud furcal. El decremento del reclutamiento puede ser el resultado de varies factores que incluyen la destrucción del hábitat de desove y desarrollo de los primeros estadios de vida de la especie; poca abundancia de adultos desovadores debido a la pesca en los ríos; y/o los impactos que tienen la reducción de alimento y otros desbalances ecológicos en los adultos y en los juveniles.

ACKNOWLEDGMENTS

We acknowledge the extensive effort provided by FRSCS volunteers and thank them for their individual contributions to the program. Key organizations that provided volunteers include the Albion Test Fishery, the Fraser Valley Angling Guides Association, the BC Institute of Technology, the BC Ministry of Environment, Fisheries and Oceans Canada, Lower Fraser River First Nations, the Pacific Salmon Commission, Simon Fraser University, and the University of British Columbia. Special acknowledgments go to Jim Rissling for field program coordination and volunteer training (1999-present), Tony Mochizuki for database management, and Robin Tamasi for the study area graphics.

Program funding was provided by the Habitat Conservation Trust Foundation, BC Environment, the Willow Grove Foundation, and numerous sponsors coordinated by the FRSCS. Support for this article was provided by the FRSCS, the North Growth Foundation, and LGL Limited Environmental Research Associates.

This article is dedicated to Rick Hansen. Rick's vision, leadership, and commitment to conservation of Fraser River Sturgeon were critical for initiating and maintaining support for the work reported in this article.

Notes

^a Zone S is the Main (South) Arm including Canoe Pass.

^b Zone 5 includes the lower 4 km of the Pitt River, from the Fraser mainstem to the Hwy 7 Bridge.

^c Zone 7 is the lower 2 km of the Stave River, downstream of the dam.

^a 2000–2004 population estimates are for sturgeon 40–239 cm fork length; 2005–2011 population estimates are for sturgeon 40–279 cm fork length.

^b HPD – Highest probability density.

^c CV = Coefficient of variation.