The lower Fraser river provides significant habitat to White Sturgeon (Acipenser transmontanus), and per a collaborative assessment between the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and the BC Ministry of Environment, is designated one of six distinct stocks based on geographic and genetic differentiation. The Fraser River Sturgeon Conservation Society (FRSCS) is a non-profit volunteer contributed organisation set up to assess the population abundance of this species classified as endangered by COSEWIC (2003). The main objective is to increase the understanding of the population dynamics in this area, something that previous research has failed to fully provide.
Background
The White sturgeon has traditionally been a valuable food source and is present in many traditional tales and songs. However, overfishing at the turn of the 20th century, increasing water borne pollution in addition to habitat degradation and fragmentation have severely diminished the population levels within BC. A lack of baseline levels led to a province wide research program in 1995, however in 1999 it was clear that there was still a serious lack of information regarding the population level with the Lower Fraser river systems. The FRSCS was set up as a volunteer based not for profit committee that could gather abundant scientifically rigorous data through PIT tagging mark recapture techniques. This latest report represents a midterm round up of the 24-month collection of data in comparison to the previous 15 years of data to assess trends in population decline, migration and seasonal variability in the core study areas downstream of the Mission Bridge (regions A and B) and from Lady Franklin Rock near Yale upstream from Mission Bridge (sampling regions C and D),
Methods
Volunteers were trained in the field in safe capture/release methods and in specifics of PIT tagging in partnership with fishery managers. The fish were tagged using Biomark Inc (Boise, Idaho) pit tags were hypodermically inserted near the first dorsal scute posterior to the bony head plate, a position shown to have extremely high tag retention. Tags emit a specific alphanumeric code at 125khz readable on a handheld device to ensure identification. Four sampling regions were defined within the lower Fraser river area in accordance with geographic aspects serving to pinpoint the location in addition to the date of capture. Biometric data was also collected to assess the level of growth and the habitat exploitation of different life stages. Fork length was recorded to the nearest 0.5cm measuring along the lateral line from snout to tail fork. Girth measured the circumference around the pectoral fins. The collection of data was coordinated by the field program manager. Abundance was measured as sturgeon caught that were of a fork length of 40-279cm within the Lower Fraser river system caught over the two-year period.
Results
- Between October 1999 and December 2015 over 130,000 sampling events were performed, nearly 65,000 of which were tag and release and over 63,000 recapture or repeat recapture events.
- Consistently between 2000 and 2015 an average of 8,000 events were reported each year, however this is diminishing as the level of tagged Sturgeon increases.
- Seasonal variation in catch rate is suggested to be governed by fishing effort and Sturgeon catchability as 98% of data derived from angling.
- Recapture showed that migrations occur throughout the lower Fraser River system with sometimes kilometres between locations.
- Marine migration was extremely low with a return to the river system within months or weeks.
- Significant declines in abundance are apparent with 2015 being 20.4% lower in abundance than 2003.
- Sturgeon growth rate has slowed per annum since 2005.
Discussion
This report represents the first comprehensive assessment of white sturgeon in the lower Fraser river system, and while it shows strong intra river system migration, there is a significant decline in abundance of sturgeon. A significant decline in the number of smaller sturgeon in the populations could be regarded because of modernisation of fishing techniques and practices which favour the recapture of larger specimens, however further assessment should evaluate this more extensively, establishing if it is indeed these changes that skew the capture results or if an additional variable has impacted on population levels of fish in earlier life stages, causing this discrepancy with previous years.
This midterm assessment, with further data due in 2017, represents the active and systematic involvement of communities and interested parties within the Fraser river area that are concerned with white sturgeon populations. Establishing these new baselines in tandem with providing involvement for volunteers should lead to a positive action being taken to stabilise stocks of white sturgeon within this region.
- Source Nelson, T. C., D. Robichaud, T. Mochizuki, J. Rissling, K. K. English, and W. J. Gazey. 2016. Status of White Sturgeon in the Lower Fraser River: Report on the Findings of the Lower Fraser River White Sturgeon Monitoring and Assessment Program 2015. Manuscript report prepared by LGL Limited, Sidney, BC. PDF Available at : http://frasersturgeon.com/wp-content/uploads/2019/01/Status-of-Lower-Fraser-River-White-Sturgeon-2015_Manuscript-Report.pdf [Accessed 03/2021].