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Title: Do Sturgeon limit burrowing shrimp populations in Pacific Northwest estuaries?

Author
item Dumbauld, Brett
item HOLDEN, DAVID
item LANGNESS, OLAF

Submitted to: Environmental Biology of Fishes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2008
Publication Date: 3/4/2008
Citation: Dumbauld, B.R., Holden, D., Langness, O. 2008. Do Sturgeon limit burrowing shrimp populations in Pacific Northwest estuaries?. Environmental Biology of Fishes.10.1007/s10641-008-9333-y

Interpretive Summary: Both the green sturgeon (Acipenser medirostris) and the white sturgeon (Acipenser transmontanus) are common seasonal inhabitants of coastal estuaries from California, USA to British Columbia, Canada. Anecdotal information from fishers and others suggested that they feed during these estuarine migrations, but this study provides the first documentation that this occurs. A large proportion (40-95%) of the fish we sampled had empty stomachs, but those fish with items in their guts fed primarily on benthic food items and fish and a primary component of their diet consisted of burrowing shrimp (Neotrypaea californiensis). We also found feeding pits in intertidal sediments of Willapa Bay, Washington which appear to have been made by these fish. Exclosure experiments and shrimp counts revealed that the predator making these pits influenced the density of shrimp present and suggests the potential for “top down” control of shrimp populations by predation. Declines in predator populations may thus be at least partially responsible for historical increases in shrimp populations in these coastal estuaries causing problems for oyster aquaculture, but sturgeon enhancement seems an unlikely solution to the current problem given the biology of these fish and constraints on their abundance and the large influence of larval ecology on shrimp abundance.

Technical Abstract: Green sturgeon (Acipenser medirostris) and white sturgeon (Acipenser transmontanus) are common seasonal inhabitants of coastal estuaries from California USA to British Columbia, Canada. Both species are anadromous spending significant portions of their lives at sea and in their natal streams, but they also move into other coastal estuaries as large immature individuals. An analysis of stomach contents from 88 green sturgeon and 5 white sturgeon taken in gill net fisheries revealed that 40 – 95% had empty stomachs, but those fish with items in their guts fed predominantly on benthic prey items and fish. Burrowing thalassinid shrimp (mostly Neotrypaea californiensis) were important food items, especially for green sturgeon in Willapa Bay, Washington where they represented 75% of the biomass ingested by fish taken during the summer of 2003. Small pits observed in intertidal areas dominated by these shrimp are likely made by these sturgeon and we present evidence from exclusion studies and field observation that the predator making the pits can have a significant cumulative affect on burrowing shrimp density. Though these burrowing shrimp present a threat and are controlled by the aquaculture industry in Washington State, it seems unlikely that shrimp as food are currently a limiting factor for threatened green sturgeon stocks, given their extensive distribution and abundance outside the aquaculture areas and in other estuaries. Clearly however these large predators may have performed an important top down control function on shrimp populations in the past when they were more abundant.