Efficacy, non-target impacts, and costs of mechanical control options against a bioturbator in bivalve aquaculture

Authors: RUESINK, JENNIFER - University Of Washington; MAWSON, C HALEH - University Of Washington; ALLEN, BRIAN - Puget Sound Restoration Fund; BARRETT, JEFFREY - Paradox Nr; BEUGLI, DAVID - Willapa/grays Harbor Oyster Growers Association; BOOTH, STEVEN - Pacific Shellfish Institute; BUTLER, LAURA - Washington Department Of Agriculture; DEWEY, BILL - Taylor Shellfish, Inc; DONOGHUE, CINDE - Washington State Department Of Ecology; Dumbauld, Brett; FELDMAN, KRISTINE - University Of Washington; FORSTER, ZACHARY - Washington Department Of Fish & Wildlife; GARCIA, S MARIA - University Of Washington; GROSS, JACKSON - University Of California, Davis; HUDSON, BOBBI - Pacific Shellfish Institute; HULL, WESLEY - University Of Washington; IYER, VIKRAM - University Of Washington; KATLA, ASPEN - University Of Washington; KRAFT, LAURA - Washington State University; PAUL, BLAIR - Skokomish Department Of Natural Resources; PRUITT, CASEY - Washington State Department Of Natural Resources; VASHISTH, ANIRUDDH - University Of Washington; PATTEN, KIM - Washington State University Extension Service

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2024
Publication Date: 2/15/2025
Citation: Ruesink, J.L., Mawson, C., Allen, B., Barrett, J., Beugli, D., Booth, S., Butler, L., Dewey, B., Donoghue, C.R., Dumbauld, B.R., Feldman, K., Forster, Z., Garcia, S., Gross, J.A., Hudson, B., Hull, W., Iyer, V., Katla, A., Kraft, L., Paul, B., Pruitt, C., Vashisth, A., Patten, K. 2025. Efficacy, non-target impacts, and costs of mechanical control options against a bioturbator in bivalve aquaculture. Aquaculture. 596(1). Article 741788. https://doi.org/10.1016/j.aquaculture.2024.741788.
DOI: https://doi.org/10.1016/j.aquaculture.2024.741788

Interpretive Summary: Bivalve aquaculture benefits from non-chemical, operational-scale pest management tools to sustain or increase production. Mechanical methods to control ghost shrimp (Neotrypaea californiensis), which build extensive burrows in the mud/sand and cause oysters to be smothered have been examined in Washington State (USA) and provide a useful roadmap for application elsewhere. This review compiles data from twenty-two mechanical control trials that had quantitative data for both treated and untreated plots enabling effect size calculations to be made. Field trials were grouped into three categories: 1) surface barriers including shell additions, 2) direct shrimp removal, and 3) sediment disruption. A fourth control category included tools like electricity, microwaves, and pressure mostly trialed in the laboratory and indicated an extensive amount of energy would be required to control shrimp at scale on oyster beds. Efficacy for the other control methods improved with the amount of effort (person-hours) devoted. Treated sediment showed reduced penetrability and increased muddiness and both positive and negative non-target effects were observed for infauna. Community effects were more pronounced one month after treatment, consistent with a response to shrimp removal and bioturbation, rather than from treatment itself. While surface barriers to exclude shrimp have been deployed, expense and permitting constraints limit wide scale use. The position of burrowing shrimp up to 1m below the surface of water-saturated sediment, along with their unique tolerance to pressure and anoxia, has generally put them out of reach for most attempted mechanical control. The resulting challenge is to engineer tools with practical delivery that can be carried out without permits and economically reduce shrimp to densities compatible with culture at farm scale.

Technical Abstract: Bivalve aquaculture benefits from non-chemical, operational-scale pest management tools to sustain or increase production. Mechanical methods to control a bioturbating pest (burrowing shrimp Neotrypaea californiensis) have been tested in Washington State (USA), providing a roadmap for other regions affected by native or widespread pests. These shrimp smother and bury ground-cultured oysters on tidal flats even when the shrimp are at low densities. Therefore, control methods with high efficacy are required, also considering non-target effects and costs to implement. Of 55 total trials from 2002 to 2023, 22 had quantitative data for treatment and reference plots suitable for effect size calculations. Two more shell-addition trials were included from earlier research. Methods included: 1) surface barriers, 2) shrimp removal, 3) sediment disruption, and 4) physical conditions intended to cause direct mortality (e.g. electricity, heat). Most large-scale surface barriers were not effective because they were penetrated by shrimp or insufficiently anchored; an exception was application of five inches (12.7 cm) of gravel. Shrimp removal was effective with a water-jet technique developed to collect shrimp for bait at low tide, but efforts to deploy multiple jets with a boat-towed mechanized device were unsuccessful. Sediment disruption through surface compaction was the most common farm-scale approach but did not reliably reduce shrimp densities, whereas consolidating sediment with vibration to 1 m depth had high efficacy but has been applied only in small plots. Effect sizes were not available for any field trials of direct mortality methods, but energy required to kill shrimp was calculated from laboratory studies (1-50 kW-hr m-3 in water, and higher energy required in saturated sediment). Across all field methods, efficacy improved with effort (person-hours per area). Sediment showed reduced penetrability and increased muddiness following treatment. Non-target effects on infauna became more pronounced after one month, including both positive and negative effect sizes, consistent with a community change following a reduction in shrimp density, rather than directly from treatment. In the six studies measuring epibenthic species, no overall positive response to control of shrimp occurred, even though the reason for control is to protect surface-dwelling species from bioturbation by shrimp. This outcome illustrates the importance of pairing efficacy in terms of reduction of shrimp and improvement of farming. The vertical position of N. californiensis below nearly a meter of water-saturated sediment, along with an innate tolerance to pressure and anoxia, has placed them out of reach of most attempted mechanical methods. Although progress has been made in recent years, mechanical control options remain limited that can be carried out without permits and that economically reduce shrimp to densities compatible with benthic shellfish aquaculture at a farm scale.