Development and Implementation of Integrated Pest Management of Burrowing Shrimp on Washington State Commercial Oyster Beds
THE DAMAGE/DENSITY RELATIONSHIP – B. Dumbauld, S. Booth
Small Arena Experiments
Initial experiments were begun in 2002. The “Mansfield” Bed had not been treated with carbaryl for 4 years and was highly infested with burrowing shrimp over most of the bed. However, burrowing shrimp were present at more moderate densities within a smaller area of ground near the area targeted for commercial application. On May 30, 2002, we placed 60 seeded oyster shells (cultch) on each of 12 small (2 x 2 m) plots, with 4 plots placed in an area of very high shrimp density (> 90 burrows per m2), 4 plots in the area of moderate density (20/m2 – 35/m2), and 4 separate plots in an area of high shrimp density (35-55 /m2) but inside the area to be treated. To prevent shell loss due to effects of severe weather or tide, each plot was surrounded with short (20 cm) plastic fencing. On that and several subsequent dates, the number of shrimp burrows in each of 4 ¼ m2 plots that diagonally crossed the plots were recorded, along with the number of oyster shell, eel grass turions, and percentage algae cover in each of the 4 quadrants within the plot.
Within 28 days after oyster shell placement, over 95% of shells in plots of very high burrow density had sunk beneath the substrate surface (Fig 1A). Oyster shell survival was higher over longer intervals in plots of moderate burrow density, but that trend was not uniform (Fig 1B). An average of 54% of shells in plots of 40 – 50 burrows / m2 sank within 40 days.
Conditions changed dramatically in some plots during the summer as oysters sank in plots of high shrimp infestation, allowing us to take advantage of a second set of experimental variables. Plots of very high burrow density were abandoned after June 27 and 4 new plots were established on grounds of more moderate burrow density on August 9. Shell density declined from an average of 7.5/m2 on that date to 7.3/m2 on September 6 while average burrow density shifted slightly from 18.2 to 22.0/m2.
Four plots were treated with carbaryl during commercial application on August 9, when burrow density averaged 33.5 per m2 and shell density averaged 4.4 per m2 among them. On September 6, burrow density had declined to 6.2 per m2 while shell density remained at 4.4 per m2.
Similar observations were conducted in summer 2003 on 4 different oyster beds within Willapa Bay of generally lower shrimp infestation. A uniform density of oyster seed shell (15 / m2 ) was again enclosed within each of several small (2×2 m) arenas of differing shrimp burrow density (<10 to > 40 burrows / m2). The arenas were surrounded with short (40 cm tall) plastic fencing to prevent shell loss due to effects of severe weather or tide. Unfenced arenas of similar surface area were also established as checks for net effects of the fences. Total oysters and shrimp burrows in 4 ¼ m2 (50×50 cm) plots were counted in each arena at neap tide during one or more subsequent tidal series.
Results were similar to those of the 2003 experiments, with percentage oysters remaining showing great variability over both various burrow densities and time (Figure 2). High densities of polychaetes were also present in many arenas, further confounding burrow counts.
Multiple regression analysis reflected the seeming random affects of burrow density on oyster survival (Table 1). Although a general linear model was significant (df = 62; F = 54.894) and the R2 was reasonable, the resulting equation indicates that oyster survival does not decline with increasing burrow density, a phenomenon that does not generally occur. The small arenas likely introduced, rather than reduced, experimental error.
Large Plot Experiment
Accordingly, an experiment was initiated to measure the effects of burrowing shrimp over time at a larger scale. A 1.4 ac (135 × 45 m ) plot was laid out on a commercial oyster bed (Bay Center Mariculture) that was heavily infested with burrowing shrimp (Figure 3). Half of the plot was aerially treated with Sevin 80S in June as part of the 2003 burrowing shrimp control program while the other half remained untreated. In August, after the treated substrate had become suitably firm, the upper halves of both treated and untreated plots were planted with seed shell (cultch) while medium sized developing (or “fattening”) oysters were moved onto the lower halves. Shrimp burrows and oysters were counted within each of 20 or more 1 m2 plots aligned along 2 intersecting diagonal transects in each plot before and periodically after shell placement. Oyster density was measured as both percent cover and absolute numbers.
Oyster density depended somewhat on the unit of measurement (Figure 4). Surviving oysters, both fattening and seed, increased in size during the observation period, but the rate of growth was higher among the seed oysters. Upon planting, both number and percent cover of seed oyster were smaller than the measures for fattening oysters. Seed increased in size and number as multiple individuals developed and broke from the initial shell fragment, but did not attain the same size as the fattening oysters.
Although they were not weighed in this study, fattening oysters are substantially heavier than seed shell and so were expected to sink in shrimp infested ground faster. However, density of seed shells in the unsprayed plots declined to near zero within 8 months after planting. A good portion of seeded shell sank in the sediment, as corners and fragments were visible emerging from the sediments, but some loss was also due to waves and storms that washed the plot. In fact, the few seed shells observed in late September 2003 and in May 2004 were likely erratic fragments washed into the plot.
While the number of individual oysters is an important measure, especially as related to economic assessments, percent cover provided a more standardized unit of measurement and was used for further assessment.
Furthermore, changes in oyster density relative to shrimp burrow density were more apparent when the former was normalized to their maximum density within each of the 4 treatments (Figure 5). As expected, oysters survived longer in sprayed plots compared to unsprayed plots. Burrow density was very low in the sprayed plots upon planting but increased somewhat over the 20 month observation period, mostly likely due to immigration by adult shrimp, as juvenile recruitment has been very limited at several standard observation sites throughout the bay. Burrow densities were higher in the unsprayed plots, especially during the warm summer months when shrimp were most active, but the average at the end of the observation period was very similar to what it had been at the beginning.
The distribution of oysters across burrow density varied among treatment and sample date. Densities of both fattening and shell oysters dropped sharply during the first winter after planting, even at low burrow densities. The large proportion of oysters remained concentrated at low burrow densities, especially in the sprayed plots where higher burrow densities did not exist. Oysters were more randomly distributed across burrow densities in the unsprayed plots until Spring 2004, when oyster density was practically nil. The relationship among oyster yield, burrow density, and time was not clearly discerned.
These experiments were not able to clearly show the relationship between oyster survival and shrimp burrow density, largely due to the inability to standardize experimental variables. Oyster density varied across time due to growth and tidal and storm movements. Efforts to stabilize these movements within small arenas were not successful. Measurements at larger scales were not well replicated and were still obscured by shrimp moment and the lack of suitable replication.
Further experiments will involve better standardization within controlled laboratory conditions.
ALTERNATIVES TO CARBARYL TO SUPPRESS BURROWING SHRIMP
Habitat Crushing and Disruption
Preliminary Crushing Trials – K. Patten
In August 2002, trials featured both a large-wheeled semi-amphibious vehicle (Rolligon™) and a smaller tracked-wheel vehicle (Argo™). A comprehensive report of these tests was presented in the “2002 Willapa-Grays Harbor Oyster Growers Association Burrowing Shrimp Control Annual Report,” but is summarized again here. The Rolligon was tested at three different tidal elevations at a single site, so that soil was dry, moist, or covered with standing water at the time of the test. Soil compaction was recorded in untreated parts of each soil type as the amount of pressure (psi) needed to push a 1″ diameter probe 3″ into the substrate and number of burrows were recorded inside 32 ¼ x ¼ m 2 grids.
Burrow density was significantly reduced at two days after treatment (DAT) compared to pre-treatment counts, and in areas treated with the Rolligon vs immediately adjacent untreated areas (Table 2). Soil was significantly compacted in treated vs untreated areas of moist and shallow water substrates, but not at the dry area (Table 3). Unfortunately, treated areas in these experiments were not large enough to prevent immigration from shrimp over a seasonal time frame, and subsequent assessments showed little difference between treated and untreated areas.
Furthermore, the Rolligon became stuck in the substrate frequently enough to halt the tests. Trials of the Argo were of similar design, but the vehicle was able to travel through the mud more easily than the Rolligon. At short post application intervals densities of shrimp burrows were reduced to similar levels as those in the Rolligon experiments.
Large-scale crushing trials – K. Patten
In 2004, a large-scale (3 ac) crushing experiment was conducted using WSDA’s Marsh Master II. Three sequential crushing events were conducted in June, July, and September. Plots were placed in areas of low, medium, or high initial shrimp density and were crushed either once or twice during each event. Number of shrimp burrows were counted in 25 x 25 cm grids after each event. Burrow density was reduced after the first crushing events across all shrimp densities (Figure 6). There were only minor changes in shrimp densities after the next two crushing events. At the high density zones there was little difference between crushing them once or twice per event. In the areas of high or medium initial density, burrow density never declined below the currently accepted threshold for oyster production of 10 burrows/m2.
Crushing preferentially targeted male shrimp, as more males were observed on the substrate surface immediately after crushing by a ratio of 5.6/1.0. Uninjured but exposed female shrimp also burrowed back into the substrate faster than males. Fifty percent of the female population reburrowed at an average of 6.0 min while 50% of the males took 7.6 min.
Sub-surface delivery and post-application harrowing or rolling – J. Durfey, S. Booth
Trials in 2003 featured comparisons of the reduced risk material acetamiprid (Assail 70 WP) applied at either 14.4 or 7.2 oz a.i./ac, two low rates of carbaryl (Sevin 80W @ 3 or 1 lb a.i./ac) using 2 different methods of application (on the surface using CO2 backpack at ~30 psi vs sub-surface shank injection using an apparatus designed by Mr. Durfey) (Figure 7). Two post-application tactics to enhance the penetration of material through the bed surface were also compared: rolling of a large 500 lb water-filled cylinder and harrowing. The resulting 13 treatment combinations were made inside 2×6 m plots arranged and replicated within strips. The strips were also replicated among 3 blocks (Figure 8). A 3 m buffer was placed between each strip (not shown in Figure 8). Treatments were applied on July 30 at low tide and were assessed by counting shrimp burrows within a m2 grid placed in each plot at 1 and 28 days after treatment (DAT). Results were analyzed using analysis of variance featuring orthogonal contrasts and t-tests.
Only 2 of 6 relevant contrasts were significant at 30 DAT (Table 4). Significantly fewer shrimp burrows were observed in plots treated with the high rate of Assail than in plots treated with the high rate of carbaryl (16.03 ± 0.84 vs 20.73 ± 1.15; mean ± SE).
Sub-surface pesticide delivery and habitat crushing: material and vehicle – J. Durfey, S. Booth, K. Patten, D. Cheney
The objectives of these studies were twofold: 1) to test the potential of a heavy overland vehicle to deliver water at high pressures in combination with subsurface shanking to disrupt shrimp habitat, and 2) to compare the efficacy of pesticides and other material delivered subsurface for efficacy against burrowing shrimp. The experiments featured a semi-amphibious heavy vehicle that applied materials subsurface at high volumes and pressures in combination with vibrating shanks. The vehicle, initially manufactured as the Rolligon™, was donated by Taylor Shellfish, Inc., and modified by WSU to carry a higher capacity hydraulic pump, applicator tanks, and a toolbar holding shanks and injectors that could be hydraulically raised and lowered, as well as vibrate due to an attached rotating off-center cylinder (Figure 9).
The trials were conducted on property owned by Richard Wilson (Bay Center Mariculture) at Rosetta Beach on the west side the Bay Center Peninsula (Figure 10). Three sets of trials featuring different treatments and different sets of experimental blocks were conducted (Figure 11). Two distinct types of substrates were present at the area: 1) a sandy /silty substrate close to the beach, and 2) a very silty substrate beyond a shallow drainage channel located about 600 m from shore. Treatments were replicated over both space (usually 4 replicated plots per treatment) and time (usually 3 treatments on 3 consecutive days). Treatment plots were 24 x 48 ft and separated by 6 ft buffers.
Treatments were applied using the Rolligon in first gear at 3.57 ft/sec for a theoretical field capacity of 1.8 ac/hr or an estimated (80%) actual field capacity of 1.4 ac/hr. Number of shrimp burrows and clam holes in ¼ x ¼ m grids and percent coverages of eel grass (Zostera marina) and water in 1 x 1 m grids, as well as water depth, was noted both before and after treatment. If deep water and high percent cover of eel grass frequently obscured the shrimp burrows and clam holes, those counts were eliminated. Numbers and coverages were recorded in 6 grids per treatment.
Mean number shrimp burrows and clam holes were compared among treatments and blocks using analysis of variance. Because mean burrow and hole densities were not randomly distributed before treatment, average differences between mean densities in each plot before and after treatment were also compared.
Blocks A and B, treated during mid August, showed quite conclusively that subsurface injection of low rates of carbaryl (Sevin 80SP™) (1.5 and 3.0 v s the standard rate of 8.0 a.i./ac) significantly suppressed density of shrimp burrows (Table 5). Other Rolligon treatments also significantly suppressed burrowing shrimp compared to the untreated check. Treatment effects on clam holes were less apparent at 2 weeks after treatment and not significant when compared to pre-treatment levels.
Shrimp burrows and clam holes at Block C were counted during the second low tidal interval after treatment, rather than along with Blocks A and B during the first. so results were analyzed separately. A recent storm had also obscured the difference between shrimp burrows and clam holes. Consequently, treatment effects were sometimes not significant or difficult to interpret, so are not presented here.
A second set of trials in late August again featured the extreme low rate of Sevin (1.5 lb a.i./ac) along with a low rate of clothianidin (Poncho™)) (1.5 lb a.i./ac), and a moderate rate of flowable sulfur (THAT™) (3.0 lb a.i./ac). Because block effects (Blocks D, E, and F) significantly interacted with treatment effects on shrimp burrow density, results from each block were analyzed separately. Neither shrimp burrow nor clam hole density was significantly affected compared to the untreated check at Blocks D and E, regardless of how they were measured (Tables 6, 7).
Mean numbers of shrimp burrows were significantly lower in all plots treated with pesticides than in the untreated check at Block F (Table 8). According to the difference between counts before and after treatment, THAT flowable sulfur was especially effective. Mean number of clam holes were not significantly different among treatments.
Due to the coming of nocturnal extreme low tides and increasingly inclement weather, another set of trials featuring the organic sulfur (Kumulus™) were not replicated over consecutive days as were the previous trials. Instead, 8 plots per treatment were replicated within a single large block (Block G). Results showed that both a moderate rate of Kumulus as well as half that rate significantly suppressed both shrimp burrows and clam holes (Table 9).
In general, these trials demonstrated that both the shanking of shrimp-infested oyster ground and subsurface injection of pesticides can effectively suppress burrowing shrimp under certain circumstances. Some results also indicated that subsurface injection of appropriate materials (e.g., Poncho or THAT sulfur) may be less detrimental to clam populations. Variation in efficacy among the various blocks likely resulted from differences in substrate type, water depth, and both the distribution and density of shrimp. Trials were initiated in the firmer sandy areas for safety and logistic reasons, but, as noted above, Blocks A – E were located in sandy areas where shrimp were very patchily distributed and tidal channels frequently intersected the blocks. Blocks F and G were located further from the shore in silty areas of higher, more uniform shrimp densities. These results reiterated that large plots and high replication are needed for good experimental protocol in the extremely patchy inter-tidal areas of Willapa Bay. Future enhancements of these experiments will feature enhanced vibration technique and operation from an oyster barge.
Trial of “The Kansas Machine” to suppress burrowing shrimp – S. Booth, D. Penny
Observations in 2002 during trials of an airboat modified to cut the invasive cordgrass, Spartina alternaflora, suggested that shallow rototilling may have some potential to suppress burrowing shrimp. Airboat modifications were by Master’s Dredging, Inc. (Lawrence, Kansas) and consisted of an exceptionally large engine and a front-mounted shaft equipped with tines that could be hydraulically raised and lowered to a maximum rototilling depth of 4″. Some shrimp were killed outright, but more were consumed as they emerged from the disturbed substrate by seagulls.
Arrangements were made in 2003 to assess the potential of the modified airboat (e.g., “the Kansas machine”) to suppress burrowing shrimp. As in 2002, these trials were contingent on ancillary jobs against aquatic weeds in California and additional tests against cordgrass in Willapa Bay. Consequently, a trial was not conducted until October 5, when conditions were no longer optimal. Burrowing shrimp become less active and burrow deeper as temperatures cool in the fall. The maximum low daylight tide on that date in North Willapa Bay occurred at 4:00 PM and was +2 ft in height. Consequently, the study was sited on slightly higher ground than that of most commercial oyster beds (Figures 12A and 12B) and was of moderate to low burrow density (mean = 13.8 vs > 20 burrows per m2 on heavily infested ground). The exotic eelgrass Zostra japonica was patchily distributed over the study area, while the native species, Z. marina, was rare. Four somewhat parallel transects, each ~200 m long, were placed perpendicular to the waterline at 2:30 (Figure 12C).
Beginning at 3:30 PM, the Kansas Machine rototilled twice along the 4 transects. Each rototill pass lasted 4 – 5 minutes and, with discussion between passes, all 8 were completed by 4:30. A fifth, single pass path was rototilled into shallow water (~20 cm at the deep end) as the Kansas Machine left the study site. No shrimp were observed leaving burrows during the course of the trial. Shrimp burrow density inside 3 of the rototilled paths were compared with densities on adjacent untreated ground on October 14 during a +2 ft low tide. Burrows were counted within 20 m2 grids spaced 10 m apart within and beside each transect. Percent cover of Z. japonica was also estimated in each grid to compare affects of rototilling on that species. Z. marina was absent from all grids.
Burrow density was significantly lower on untreated ground than on immediately adjacent rototilled ground (Figure 13A). Rototilling most likely temporarily exposed burrows that were less apparent in undisturbed substrate. Although percent cover of Z. japonica was significantly lower in the rototilled plots (Figure 13B), only the grass stems had been cut and much of the root remained.
Although preliminary results suggest the Kansas Machine has low potential to suppress burrowing shrimp, they are strongly qualified by the sub-optimal conditions under which they were acquired. Suppression would most likely be better during summer months and at lower tidal elevations when and where shrimp are more active and shallow. While a similar trial against cordgrass concluded that the “Kansas Machine” currently lacks sufficient power and speed to efficiently suppress the large acreage of that weed, these concerns were less of a concern here, given the smoother substrate and smaller acreage of commercial oyster ground. Nevertheless, more power and deeper rototilling could improve the machine’s potential to suppress burrowing shrimp.
The Potential of Habitat Crushing and Disruption: A Summary
Both gulls and crows were observed feeding on exposed shrimp in all trials of crushing and habitat disruption tactics. The number of gulls, in particular, was often quite large, and increased daily when trials were conducted at the same site over several days. The gulls obviously learned to associate the sound of the vehicles with the presence of shrimp. The impact of bird predation on shrimp abundance, however, was difficult to measure. Many gulls appeared to reach satiation fairly quickly and then either stopped feeding or regurgitated live shrimp and continued to feed. In general, the impact did not appear substantial.
CONTROLLED MICROCOSM STUDIES – J. Colt
Field experiments with burrowing shrimp are difficult because it is very time consuming and expensive to determine the number of shrimp at the beginning and ends of experiments. It is much easier to determine the number of shrimp under laboratory conditions but holding protocols for burrowing shrimp are not currently available. The primary objective of this research was to develop collection, holding, and feeding protocols for the ghost shrimp, Neotrypaea californiensis. The first year’s work will be restricted to the holding of unfed ghost shrimp without sediment cover. Following work will repeat the experiments with sediment cover.
Materials and Methods
Ghost shrimp were collected from the lower intertidal zone approximately ½ mile west of the Mukilteo Ferry Dock in Snohomish County, WA during November and December 2004. Shrimp were collected using a 4″ diameter PVC slurper tube. Shrimp were stored in 5 gal buckets filled with sea water for the 1.5 – 2.0 hours during collection and transportation to the laboratory (about 0.5 miles).
Shrimp were placed into a large glass aquarium (35″ x 47″x 10″) with flowing filtered seawater (1 – 2 gpm). Light levels were maintained at low levels by lowering the window shades and keeping the overhead light off. The overhead lights were turned on during the mortality checks. The shrimp were counted the next morning to determine the number of shrimp killed or damaged by the collection process and distributed to the experimental units. No sand was added to the aquariums. The shrimp were not fed during the experiments. Mortalities were observed every 1 – 3 days and removed after each observation. The number of shrimp that did not appear to be acting normally, such as lying on their backs or sides, was also recorded. Shrimp were observed for 30 – 40 days. Cumulative mortality over time was plotted and time to 50% mortality (LT50) were estimated by a linear fit of the data.
Three experiments were conducted: 1) Two aquaria at 28 shrimp/m2, 2) One aquarium at 60 shrimp/m2, and 3) One aquarium at 46 shrimp/m2 with substrate.
These experiments were largely exploratory, so some of the experiments were not replicated and statistical analyses were fairly simple.
Results and Discussion
In Experiment 1, 20% of the total shrimp collected were killed or damaged directly as a result of the collection process, usually due to the slurper tube slicing through the shrimp. Mortality was low during the first 10 days, followed by 25 days of higher mortality, and a final period of 10 days with no mortality (Figure 14). The time to 50% mortality (LT50) was in the range of 31 – 35 days. The number of shrimp not acting normal was relatively constant over the entire experiment. At the end of the experiment, 6 shrimp were missing from the Tank A and 5 shrimp from the Tank B. Missing shrimp likely escaped through the drain standpipe. The drain will be screened in the future to prevent such escapes.
In Experiment 2, collection of the shrimp resulted in the death or damage to 25% of the total number collected. Mortality was rapid with an LT50 of 9 – 10 days (Figure 15).
In Experiment 3, 2 types of substrate were used: 1) various 4″ ABS plastic tees and elbows, and 2) 6″ sections of 3/4″ and 1″ PVC pipe. Without exception, no shrimp were found inside either of the 2 types of substrate.
An interesting ancillary observation was the presence of high densities of small red ( ~ 1 mm diameter) copepods present on most shrimp after day 20. The copepods were quite visible on the claws of the males and on the carapace and moved quite rapidly. Upon more detailed examination, they were also present inside of carapace covering the gills. In some animals, there were enough copepods present inside the gill covering so that the gill cover look reddish or dark brown. Brett Dumbauld (USDA/ARS) assumed that the copepods are likely Clausidium vancouverense. He has observed large numbers of that species on ghost shrimp collected from the Palix River. They are commensal and not particlularly harmful to the shrimp.
Another observation was that the gill cover of dead shrimp was filled with fluid (2 – 3 mm in thickness) and looked like an oblong sac.
In general, the observed mortality was much higher than desired. The next experiment will test two holding protocols during the collection process. The control holding protocol will be the water filled bucket used in Experiments 1-3 and the other treatment will use a dry bucket. Mortality will be monitored for a 30 day period. Based on the work conducted in 2004, it appears that shrimp should not be held without sand for more than 3 – 4 days.
APPRAISE THE ECONOMIC COSTS OF BURROWING SHRIMP AND MANAGEMENT TACTICS – S. Booth
Preliminary information on farm economics, especially as related to the burrowing shrimp control program, was gathered from interviews conducted with growers with tidelands that had been closely observed by WDFW scientists for the last few years. Questions were standardized and mailed to the growers before the interview took place and responses recorded in person at the interview (Table 10).
The six growers we interviewed owned together approximately 12,300 acres and actively farmed about 76,000 acres of tidelands in Willapa Bay and Grays Harbor. The farms ranged in size from 190 acres to 7,110 acres. Most grounds under discussion were currently used for ground culture. They were either “seed beds” where seed was planted and after 2 –3 years moved to a “fattening bed” until harvest, or seed-harvest beds where seed was planted and allowed to mature to harvest all on the same bed. Most growers reported good growth and attributed this to either specific conditions like tidal elevation or proximity to channels or to recent ocean conditions. Eight of the twelve beds were harvested by dredge; the rest were picked by hand. Most of the beds were also harrowed with a pasture harrow at some point during the growth cycle to bring oysters up to the surface and/or break up clusters. All of the beds had been previously treated with carbaryl. Most beds were treated regularly on a 3-4 year cycle although at least one bed had not been treated for a decade. The growers reported that shrimp were a consistent problem with only one bed being reported as receiving moderate re-infestation. Eelgrass was reported present on all of the beds, but clearly more common on some. Most of the growers answered that they could not afford not to plant oysters on these beds, except one grower who felt he might be able to do so if market conditions changed. Interestingly, most growers reported that they did not pay close attention to the shrimp burrow count information provided as part of the pesticide application program. They were most concerned that the legally defined treatment threshold of 10 burrows per m2 was not exceeded.
WRITE, IMPLEMENT, AND DELIVER THE IPM PLAN – S. Booth
A framework for the development of “A comprehensive plan toward the development of an integrated program for burrowing shrimp management on commercial oyster beds” was submitted to Washington Deptartment of Ecology in March 2003 (Appendix A). The plan was also presented at the Annual PCSGA / NSA conference and the spring workshop, described below. The plan was comprehensive as it included descriptions of relevant concepts, definitions and goals, references, lists of principal authorities and policies, and 5 interconnected key IPM elements: 1) funding, 2) research & development, 3) implementation, 4) evaluation / regulatory compliance, and 5) dissemination. The final 3 of the 5 IPM elements were included in our WSARE objectives as grower surveys, workshops, and newsletters. This plan will be updated to include current progress and repriotization in the very near future.
A grower survey was mailed to the 33 members of the WGHOGA on November 26, 2003. Twenty-one survey questions queried growers on their expectations and current status of the IPM plans. Eleven growers responded. In general, the results indicated that although the growers were united in their willingness to collaborate in the research process and their reluctance to pay more to manage burrowing shrimp, they differed substantially in their concept of IPM program direction.
A grower workshop, held February 20, 2004, was attended by approximately 30 growers, 10 researchers, 10 agency representatives, and a few public citizens. The workshop focused on improved monitoring tactics and updated growers on the status of alternative tactics development (Figure x). The workshop resulted in the scheduling of a field day to teach growers and field men methods to more accurately identify burrowing shrimp mounds.
In April 2003, a newsletter was mailed to ~120 persons interested in or impacted by the burrowing shrimp management program. Articles covered the recent workshop, the planned field day, the IPM Plan, and research updates (Figure 16). Another newsletter will be mailed in April 2005.
- Determine the relationship between burrowing shrimp density and oyster yield (e.g., the damage/density relationship) to improve monitoring techniques and develop economically based action thresholds.
Evaluate the efficacy of alternatives to carbaryl-based tactics to suppress burrowing shrimp, such as sub-surface applications of registration-exempt compounds, or the mechanical crushing or shallow rototilling of shrimp burrows, within a tier of experimental designs that progress from small tightly controlled arenas, through larger microcosm studies, to field plot trials.
Using grower interviews and surveys, appraise the financial costs of burrowing shrimp damage and potential alternative management tactics to derive economically based action thresholds.
Write an IPM plan for burrowing shrimp; implement and deliver it to oyster producers using workshops, newsletters and demonstration trials; to the scientific community using conferences and articles and to the public using a pre-existing website, and adopt the plan into an Environmental Code of Practice for the West Coast shellfish industry.
- The relationship between burrowing shrimp density and oyster yield was approached at several experimental scales with mixed results. A more accurate description will require more experiments.
The potential to suppress burrowing shrimp using heavy vehicles, a modified airboat, and sub-surface injection of alternative compounds was addressed experimentally. The potential of the first two was limited, but the latter tactic showed greater promise.
Initial experiments featuring controlled microcosms showed high shrimp mortality over long time periods.
Preliminary interviews and written surveys of oyster growers showed them to be a diverse group economically, operationally, and strategically.
A framework of the development of “A comprehensive plan toward the development of an integrated program for burrowing shrimp management on commercial oyster beds” was written and presented at the Annual PCSGA/NSA Conference and at a spring workshop. (The plan was also submitted as an index in the hard copy of this report and is available by request from Steve Booth.)
A grower workshop was attended by approximately ~50 persons. The workshop focused on improved monitoring tactics and updated growers on the status of alternative tactics development and resulted in the scheduling of an instructional field day.
A newsletter was mailed to ~120 persons interested in or impacted by the burrowing shrimp management program. Articles covered the recent workshop, the planned field day, the IPM Plan, and research updates.
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