Long Beach Research and Extension Unit

A brief review of the research efforts to control burrowing shrimp
By Kim Patten, WSU Long Beach Research and Extension Unit
Two species of burrowing shrimp, ghost shrimp and mud shrimp, are major pests to shellfish
growers in Willapa Bay and Grays Harbor, Washington. These indigenous crustaceans reside
inside burrows 20 to 60 cm beneath the mudflat surface where they constantly bioturbate and
resuspend sediment. High densities of burrowing shrimp cause surface-dwelling organisms, like
oysters, to literally sink in the mud and die. Populations of burrowing shrimp in these two
estuaries increased dramatically in the 1950’s, at which time the industry started experimenting
with control methods.
Carbaryl was first screened by state agencies for use in burrowing shrimp control in the late
1950s. It was registered for commercial use in 1963, and its use continued until 2013. Efforts to
find alternatives to carbaryl have been ongoing since the 1960s. The results of the endeavors
were summarized in a review conducted by Battelle Marine Science Lab in 1997. They
reviewed the various mechanical efforts that had been assessed by the industry and scientists to
date, including shell pavementing, dredge harvesting of shrimp, sediment compaction, diking,
disking, and sediment barriers. None of these control methods was found suitable, but they did
suggest that additional work should focus on water jets and electro-shocking. The Battelle group
also assessed the practical and economic feasibility of switching from the on-bottom culture,
which was practiced by ~ 95% of the industry, to off-bottom production systems that were less
susceptible to the habitat abrogation caused by burrowing shrimp. They concluded that longlines, stake and floating bag culture could be viable options, but only in areas within these
estuaries that had minimal pressure from burrowing shrimp and that were protected from
excessive wind and wave action. The vast majority of commercial shellfish grounds in Willapa
Bay and Grays Harbor, however, are subject to intense winter storms, where off-bottom culture
has not been viable.
For biological control, they reviewed methods for predator (native fish and Dungeness crab)
enhancement. None of these proved practical. Battelle also reviewed all available insecticides
that could be suitable for this use pattern. They concluded that two insecticides, abamectin and
imidacloprid, had potential. Based on screening tests in Willapa Bay, only imidacloprid showed
efficacy. However, it was cost prohibitive and the registrant company, Bayer, was not interested
in its registration for this purpose. Five critical research needs were identified in the Battelle
document: development of more accurate shrimp population census methods, characterizing the
density damage function, alternative methods of insecticide delivery, understanding the factors
affecting population dynamics, and refinement of the decision-making criteria for control tactics.
The industry, state and federal agencies and environmental groups signed an agreement to pursue
integrated pest management (IPM) in 2000. Major new research efforts were initiated following
the carbaryl phase-out agreement between the shellfish industry and environmental groups in
2002. Over a million dollars in funding was secured to help a team of scientists from WSU,
UW, OSU, Univ. of Idaho, Pacific Shellfish Institute (PSI), federal agencies, and several

 commercial labs find a viable alternative control. That research effort was segregated into
biological, mechanical, and chemical controls.
Biological control research efforts assessed both micro and megafauna predators of burrowing
shrimp, several non-native parasites, and competitive benthic macroinvertebrates. Populations of
micro and macropredators, small and large fish, were sampled in Willapa Bay and their diet
composition assessed to determine what predators were consuming burrowing shrimp. No fish
species had a diet specializing in burrowing shrimp, but consumption of adult burrowing shrimp
by green sturgeon was significant. Although the density of shrimp was reduced in feeding pits
made by green sturgeon, they had very limited potential to be used for a management tool for
shrimp control, especially confined to shellfish beds. On-bed caging studies with adult
Dungeness crab found no reduction of shrimp populations under these conditions. Two invasive
isopod parasites were identified that affected burrowing shrimp. One species, specific to mud
shrimp, appears to have been responsible for reducing population densities along the west coast.
However, the other species, specific to ghost shrimp, was found at very low prevalence and had
no effect on populations of these shrimp. Overall, none of the research efforts in biological
control provided a practical means to control burrowing shrimp or indicated a direction for
additional research focus.
While not considered traditional biological control, there was also research conducted on the
basic biology of the shrimp that was expected to contribute to better control strategies. This
included characterizing the shrimp density – crop loss function and refinement of the decisionmaking criteria for control tactics, tracking pelagic larvae movement in the ocean, artificially
rearing juveniles, monitoring the subterranean movement of shrimp as a function of diurnal and
tidal cycles, assessing the use of feeding attractants, monitoring annual recruitment patterns,
monitoring and quantifying the age distribution and population dynamics of burrowing shrimp,
monitoring movement of adults to new locations, and developing new monitoring techniques for
juvenile shrimp. These studies found that ghost shrimp were long lived (>10 years), recruited
seasonally during flood tides at night, did not vary much in their horizontal position in burrows,
had limited movements towards feeding attractants, and didn’t migrate off-site as adults. While
none of these studies provided immediate avenues for active control, they suggested that shrimp
populations are controlled by annual recruitment and, provided a control mechanism is found,
are expected to contribute to developing a better control strategy and IPM. Detailed knowledge
of these annual recruit patterns will be pivotal to burrowing shrimp IPM in the future.
A wide array of mechanical control research efforts was assessed by this team. This included
high pressure low-flow water jets, high pressure-high flow water jet sled, electroshocking, thin
layers of fast setting cement, mechanical compactions using amphibious tracked and wheeled
vehicles, 3-dimension sediment compaction, explosion via injecting and igniting a calibrated
mixture of propane and oxygen into burrows, and exposure to high and low frequency sound and
vibrations. None of these methods proved useful for a large-scale control tactic. High-pressure
jets didn’t penetrate deeply enough. The water jet-sled destroyed the benthos and had mobility
control issues. Electroshocking drove shrimp deep into the burrows rather than out of the
burrows and seemed impractical to implement when applied with enough power to kill the
shrimp. Shrimp created permanent burrows before the cement could harden. Mechanical
compaction only provided temporary control at best. The propane-oxygen mix didn’t flow into
burrows and was not ignitable. Three-dimensional engineering tests using intertidal sediment and

 adult shrimp indicated that neither surface compaction nor any other method to solidify
sediment, such as explosions, would be lethal. Ghost shrimp were not sensitive to any of the
sound frequencies tested.
A team of WSU scientists focused on finding an alternative chemical control. For the first two
years they focused on screening softer "green" chemistries. This included a) essential plant oils
(clove oil, cinnamon oil, citronella oil, cedar oil, linseed oil, garlic oil, geranium oil, peppermint
oil, rosemary oil, thyme oil, neem oil), b) plant extracts or “natural” insecticides (crushed
chrysanthemums, naturally extracted pyrethrums, Pyganic, Pryrenone, mustard seed meal,
habanero pepper extract, yucca extract, sabadilla, caffeine, 2-phenethyl propionate, white pepper,
geranial, citric acid, malic acid, hydrogen peroxide, potassium salts of fatty acids, and
menadione (Vitamin K3), c) fertilizer and mineral products (sulfur, lime, copper, urea,
ammonium nitrate, aqua ammonium, ammonium thiosulfate, sodium aluminofluoride,
ammonium sulfate, magnesium chloride, calcium chloride, and sodium chloride), and oxidizing
agents (bleach & potassium permanganate).
None of the “safer” compounds provided any reasonable control. Elemental sulfur and
magnesium chloride provided a little efficacy at extremely high rates (tons/ac), but not enough to
warrant additional development. After the search for more benign but efficacious chemicals
failed, several traditional insecticides and biocides were assessed. They included lower rates of
carbaryl (0.5 to 6 lbs ai/ac), Spectrus CT1300, clothianidin, pyriproxyfen, methoprene,
deltamethrin, bifenthrin, zeta-cypermethrin, and imidacloprid. During this time, several of the
chemicals were also assessed using subsurface injection methods, including shanking and
spikewheel injection. These tests were conducted when the tide was out using large amphibious
tractors or from the water using a barge with a dropdown spike wheel injector. A few traditional
insecticides had good efficacy, but were not supported by the registrant for this use, including
imidacloprid.
After imidacloprid went off-patent, a registrant (NuFarm) was found that would support this
minor use. From 2008 to 2010, research was conducted that assessed formulations of
imidacloprid (liquid and four different granular formulations), rates (0.25 to 2 lbs ai/ac) and
application methods (boom spraying, shanking, and spikewheel for liquid formulation; aerial,
ground and boat broadcast of the granular formulation, and a combination of imidacloprid with
post-treatment disking, harrowing and compaction. Higher rates of imidacloprid were more
efficacious, but not supportable for registration. Subsurface application methods that targeted
where the shrimp lived were not found to work any better than surface applications, and were
much more problematic. Post-treatment mechanical control did not improve efficacy. Prior to
imidacloprid being submitted to EPA for registration, scientists from UW, WSU, PSI and federal
agencies conducted four years of approved field and lab research to assess its potential non-target
impacts and its fate and persistence. For several years prior to its registration in 2014, EPA
issued federal experimental use permits (EUPs) to allow the scientists to conduct large-scale
commercial trials to gather baseline data for these assessments. These studies were conducted
under conditions set forth by WA Department of Agriculture and WA Dept. of Ecology (DOE).
Findings of these studies were used by DOE to set the conditions for the NPDES permit.
Details can be found at http://www.ecy.wa.gov/programs/wq/pesticides/imidacloprid/.

 Scientists involved in burrowing shrimp research from 2000 to 2015.
Universities
WSU: Jim Durfey, Kim Patten, Steve Bollens, Steve Sylvester, Alan Felsot, Vince Hebert,
Doug Walsh, Mike Kahn
UW: Chris Grue, Alan Trimble, Miranda Wecker, Brett Vadopalas, Kristine Feldman, Dave
Armstrong, John Frew
University of Idaho: Jim Liou, Thomas Weaver
OSU: John Chapman, Anthony D’Andrea, Katelyn Bosley
University of Oregon: Alan Shanks
San Jose State University: Leslee Parr, Josh Mackie
Evergreen State Univ.: David Milne
Federal Agencies
USDA: Brett Dumbauld
EPA: Ted Dewitt
IR4: Keith Dorschner, Rebecca Sisco
Others
Pacific Shellfish Institute: Steve Booth, Dan Cheney, Andrew Suhrbier
Ag. Development Group: Alan Schreiber
Taylor Resources: Chris Barker, Kurt Johnson
Smith Root: Lisa Harlan