|Harlan, Lisa - SMITH-ROOT INC.|
Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 31, 2008
Publication Date: April 30, 2009
Citation: Dumbauld, B.R., Harlan, L. 2009. The Potential Use of Electricity to Control Burrowing Shrimp in Oyster Aquaculture Beds. North American Journal of Aquaculture. 71: 178-188. Interpretive Summary: Two species of shrimp (the ghost shrimp Neotrypaea californiensis and mud shrimp Upogebia pugettensis) burrow into and soften intertidal sediments causing extensive problems for the shellfish aquaculture industry on the West Coast of North America. The oyster aquaculture industry has treated this problem by applying a pesticide (carbaryl) directly to the tideflats at low tide for the past 45 years. This practice causes environmental concerns however and the industry is currently searching for alternative means to manage and control shrimp. Laboratory experiments were conducted to determine whether electrofishing might be one such alternative control measure. Electricity has been used, primarily in freshwater systems as a means to capture fish and invertebrates, but has rarely been applied in marine systems because it requires high power due to the conductivity of the water. Experiments conducted in aquaria showed that ghost shrimp responded with forced swimming reactions to a pulsed direct current (1V cm-1, 2 Hz, and a pulse width of 0.001 s and 0.005 s) when in saltwater alone. Unfortunately, they moved towards the bottom of their burrows when placed in sediment, which means this technique could not be used to capture them at the sediment surface as hoped. Separate experiments designed to kill the shrimp were also successful using higher voltage levels (5 V cm-1) but mortality only resulted when exposure times to electrical current exceeded 100 s. These sustained levels of electricity would also be impractical to achieve for control on oysterbeds.
Technical Abstract: Thalassinid shrimp cause significant problems for oyster aquaculture in the Pacific Northwest (USA) where oysters succumb to the physical disruption of the sediment by the burrowing activity of these animals. While electrofishing is a commonly used technique to capture fish and some invertebrates in freshwater, applications in marine systems are limited due to the high conductivity of the water medium. Experiments conducted in aquaria showed that burrowing ghost shrimp (Neotrypaea californiensis) responded best (forced swimming with directed movement) to a pulsed direct current waveform with optimal parameter settings of 1 V• cm-1, a frequency of 2 Hz and a pulse width of 0.001 – 0.005 s. Unfortunately, when shrimp were allowed to burrow in the substrate, they displayed a similar reaction, but moved towards the bottom of their burrows, thus ruling out the envisioned use of this technique to attract them to the surface for capture. In experiments designed to induce mortality, paralysis or tetany could be achieved using higher power with direct current, pulsed direct current, and alternating current, but the animals recovered unless voltage exceeded 5 V• cm-1 and exposure time exceeded 100 s. These sustained levels would be difficult to achieve in the field due to the substrate, depth of the shrimp burrows and high power necessary to obtain adequate field strength.