The Control of the Apple Snail, Pomacea Canaliculata in Hawaii: Challenge Or Opportunity?

The Control of the Apple Snail, Pomacea canaliculata in Hawaii: Challenge or Opportunity?

Clyde S. Tamaru,1 Harry Ako,2 and Christine C.-T. Tamaru3

Abstract

The apple snail, Pomacea canaliculata, is an aquatic freshwater snail native to South America. Originally imported to Hawaii as pets for the aquarium trade, they were soon introduced into wetland plots known as lo‘i, where taro, Colocasia esculenta, an economically and culturally significant crop, is grown. Some individuals reasoned that the snails, being edible, could be harvested as food, and that raising the snails along with the taro in the lo‘i would provide income supplemental to the taro harvest with minimal additional input. This introduction of snails into the taro lo‘i, however, proved to be a disaster. Farmers failed to take into account the voracity, reproductive potential, and rapid growth of the snails. Because of the ideal conditions in the taro lo‘i, the snails multiplied rapidly and fed heavily on the taro shoots and corms, in many cases destroying a complete crop before harvest time. Hindsight has shown that the snails are dissipated via the irrigation system throughout the lo‘i and then spread to the surrounding wetland areas. Large breeding populations are now established in wetland areas on the islands of Hawaii, O‘ahu, Kaua‘i, and Maui. Some of these wetlands are wildlife preserves with state and federal mandates that restrict the potential methods of eradication. Background information is provided on both P. canaliculata and taro in order to fully explain the challenges and opportunities that this situation presents.

Key words: taro, escargot, feeding, apple snail

1University of Hawaii at Mãnoa, School of Ocean and Earth Science and Technology, Sea Grant College Program, 2525 Correa Road, HIG 205, Honolulu, HI 96822, US; E-mail: [email protected] 2University of Hawaii at Mãnoa, College of Tropical Agriculture and Human Resources, Department of Molecular Biosciences and Biosystems Engineering, St. John 511, Honolulu, HI 96822, US; E-mail: [email protected] 3Hawaii C’s Aquaculture Consultant Services, 1157 Lunaapono Place, Kailua, HI 96734-4556, US

THE CONTROL OF THE APPLE SNAIL, POMACEA CANALICULATA IN HAWAII: CHALLENGE OR OPPORTUNITY? 41 Introduction

Taro, Colocasia esculenta, traditionally a food staple in Hawaii, is still being grown in what can be characterized as wetland plots or fields called lo‘i (references cited in Kikuchi 1976). With regard to the evolution of the culture of the early people in Hawai‘i, a recurring theme is the development of an agricultural system consisting of a complex array of irrigation ditches (‘auwai) engineered and constructed for the production of taro. The present day sentiment of many full or part Hawaiians with regard to taro is best summarized by the words of Dawn Wasson, “Taro is our life. When the taro is gone, the Hawaiian people will be gone” (Omandam 1995). Wetland production of taro (Fig. 1) continues today, with taro ranked among the top 20 agricultural commodities produced in Hawai‘i. However, the yield of processed taro in 2003 was at a record low of 2.2 million kg, down 17% from 2002 (HASS 2004). The bulk of processed taro is made into poi (cooked taro corms pounded and thinned with water), and yields across the state continue to decline due not only to adverse weather and disease, but mainly to the continued infestation of apple snails (Viotti 2004). The apple snail, Pomacea canaliculata, is thought to have originally been imported to Hawai‘i for the aquarium trade and soon thereafter was introduced into taro fields, where some individuals reasoned that the snails, being edible, could be harvested as food (Cowie, 1993). The apple snails were once touted as the “golden Maui escargot” (Tanji 1990). It was

Fig. 1. Several varieties of taro at the W.T. Haraguchi Farm, Inc. in Hanalei on the island of Kaua‘i.

42 GLOBAL ADVANCES IN ECOLOGY AND MANAGEMENT OF GOLDEN APPLE SNAILS reasoned that raising the snails in the fields would provide income supplemental to the taro harvest with minimal additional input, and thus the snails were initially allowed to be distributed throughout the state. This introduction of snails into the taro fields, however, proved to be a disaster, as farmers failed to take into account the voracity, reproductive potential, and rapid growth of the snail (Tanji 1990, Ashizawa 1992). Because of the ideal habitat in the taro fields, the snails multiplied rapidly and fed heavily on the taro, in many cases destroying a complete crop before harvest time (Fig. 2). Hindsight has shown that the snails were dispersed throughout the fields via the irrigation systems and then spread to the surrounding wetland areas. The Hanalei Valley on the island of Kaua‘i supplies the majority of the taro in the state of Hawai‘i. It is thought that the apple snails were first introduced on Kaua‘i in 1987 and then spread across the island to the Hanalei Valley. They were first noticed on the W.T. Haraguchi Farm, Inc., the largest taro farm in the state (contributing 70% to the state yield) and located inside the Hanalei National Wildlife Refuge, in February 1998. Currently, the presence of the snails is beginning to have a significant impact on taro production on the Haraguchi Farm as well as on adjacent farms in the valley. It is estimated that 20–25 person-hours per week are now spent on the Haraguchi Farm alone trying to combat the apple snail. However, picking up the snails manually and destroying the eggs has produced only marginal long-term results. In addition to the decrease in overall taro production, the sharp snail shells in the taro fields also pose health risks, such as leptospirosis, to local farm workers, who often work in the lo‘i barefoot to decrease damage to the planting area. Large breeding populations are now well established in wetland areas on the islands of Hawai‘i, O‘ahu, Kaua‘i, and Maui. Presently, because of the havoc experienced by taro producers and the danger posed to producers of other aquatic vegetables in Hawai‘i, the State of Hawai‘i Department of Agriculture has restricted movement of live apple snails between all of the main islands. Over the years, several chemical, biological, and environmental methods for the control of apple snails have been investigated outside of the state, but nothing to date

Fig. 2. Taro lo‘i showing classical signs of apple snail damage. (Arrows point to a large area of damaged taro plants.

THE CONTROL OF THE APPLE SNAIL, POMACEA CANALICULATA IN HAWAII: CHALLENGE OR OPPORTUNITY? 43 has been identified as being effective in controlling the distribution and abundance of the apple snail in Hawai‘i (Yamakawa 1999). The reality of the situation is that, “the apple snail is now well established in many of our wetlands and innovative approaches are needed to contain the snail” (Wong 1999).

Management Strategies

One biological control method that has been attempted on the islands of Maui and Hawai‘i is the use of Cayuga ducks, Anas platyrhynchos, (Fig. 3). The Cayuga duck is of American origin, and their import into the islands is allowed under current Hawai‘i State Revised Statutes. The ducks are easily trained to follow workers to the lo‘i and reportedly have been found to be somewhat effective in keeping the apple snails under control. The ducks feed on the smaller snails, ultimately decreasing the number of adult snails, which do the most damage. This has been shown to be especially true for the taro growers located in the Waipio valley on the island of Hawai‘i. However, particularly on Maui, the ducks often fall prey to free-roaming dogs. With support from various state and federal agencies, a project was developed to focus on controlling the snail infestation by utilizing wild-caught snails to produce a marketable and economically sustainable processed product. It was then estimated that the price for wild snails was US$1.10/kg. That meant that the value of the wild snails in the two major taro- producing areas on Maui, Ke‘anae and Wailua, was approximately US$500,000. Although the value of the snails appears to be significant, there are many questions and obstacles (e.g., quality of wild snails, shipping costs, efficient harvesting techniques, processing costs, establishment of alternative markets) that must be answered or accounted for to fully realize

Fig. 3: Cayuga ducks used to control apple snail infestations on the island of Hawai‘i.

44 GLOBAL ADVANCES IN ECOLOGY AND MANAGEMENT OF GOLDEN APPLE SNAILS their economic potential. However, if successful, both a new means of economic development as well as control of the snail can be realized by collecting wild snails for use as raw material. The initial goals of the project were focused on assessing the feasibility of using wild apple snails as a resource in the development and marketing of a value-added product. The goals of the project included the following objectives: z Determine the distribution and abundance of the apple snail infestation in two taro- producing areas (Ke‘anae on Maui and Hanalei on Kaua‘i). z Determine the cost-effectiveness of raising wild-caught snails on commercially available diets. z Assess the quality of the snail product. z Develop a cost-effective method of processing snails as a value-added product. z Ascertain production costs. All the objectives were met, and the results are summarized in the following sections. Evidence is also presented to show that the concept of marketing the apple snails from the wild as a means to alleviate the apple snail infestation does have merit.

Results

Distribution and Abundance The results of a survey, conducted in November 1995 of infested taro lo‘i in Ke‘anae and Wailua reveal the extent of the snail infestation in this area during the initial work phase (Table 1). Replicate transects were conducted in two taro lo‘i and the number of snails that were greater than 0.5 g in body weight (BW) were extrapolated to 71 ha of land currently planted with taro. The mean number of snails/m2] using the combined data was found to be 1.20 ± 0.38. The total area under taro cultivation at both Ke‘anae and Wailua is estimated at 71 ha and using the mean density of snails from the combined data it is estimated that 98.6 x 106 snails (>0.5 g BW) were present at the time of the initial survey.

Table 1. Results of traznsects at two taro lo‘i in Ke‘anae, Maui.

Snail Density (snails/m2) Category Lo‘i 1 Lo‘i 2

Transect 1 1.03 0.82 Transect 2 1.84 1.12 Average 1.43 0.97 Standard Deviation 0.40 0.15

A similar assessment was made at the Haraguchi Farm in Hanalei, Kaua‘i in August 2002. The estimated total number of snails that were greater than 0.5 g BW is summarized in Table 2. The range in the estimated number of snails on the farm was between 1.7 million and 6.8 million. It was felt that the lower number of snails observed at the Haraguchi Farm compared with those on the lo‘i on Maui was a reflection of the investment of a dedicated employee spending 20 hours/week manually destroying the snails.

THE CONTROL OF THE APPLE SNAIL, POMACEA CANALICULATA IN HAWAII: CHALLENGE OR OPPORTUNITY? 45 Table 2. Estimated number of snails on W.T. Haraguchi Farm in Hanalei, Kaua‘i, August 2002.

Average Density Estimated Number of Taro Lo‘i (snails/m2) Snails on the Farm (12 ha planted with taro)

1 0.48 6,790,000 4 0.16 2,221,000 20 0.31 4,312,000 31 0.12 1,699,000 14 0.28 3,920,000

Average 0.27 3,789,000 Standard deviation 0.13 1,798,000

Using a digital camera to take close-up photographs of taro corms in a 1 ft2 [0.093 m2] quadrat from Field 1 at the Haraguchi farm also resulted in an estimate of the number of snails <0.5 g BW not being collected manually. The number of taro plants was 26,889 per ha. Using this value, the number of small snails on the taro plants themselves was estimated at 41.2 x 106 and the number of small snails on the ground was estimated at 86.6 x 106. This would mean that approximately 127.8 x 106 small snails (<0.5 g BW) were also present on the farm at the time the estimate was made.

Size Frequency Distribution Samples of snails (approximately 100 each) were randomly obtained from taro lo‘i in Ke‘anae and Wailua in December 1995. The sex, body length, and body weight were obtained for each snail (Table 3). Although it appears that on average the snails found in Ke‘anae were smaller than those found in Wailua, the values are not statistically different. There were no detectable differences in sex ratio, which was 1:1. The sex ratio and average size of both groups of snails not being different allowed for the pooling of data and calculating a size frequency distribution (Fig. 4). As seen in the graph, the sexes were evenly distributed among the various size classes. From information to be presented later, marketable snails are 10 g BW or greater. Therefore, for marketing purposes, the preponderance of undersized snails is an obvious challenge. A similar result was obtained in August 2002 at the Haraguchi Farm in Hanalei, Kaua‘i. Use of the snails as a raw material from taro-producing areas must also incorporate a means to grow the snails to the appropriate market size.

Table 3. Shell length, total body weight, and sex ratio of snails from Ke‘anae and Wailua.

Location Shell Length Total Body Sex Ratio (mm) Weight (g)

Ke‘anae 23.1 ± 8.0 2.9 ± 2.6 1.1 Wailua 31.3 ± 5.3 6.6 ± 3.2 1.0

46 GLOBAL ADVANCES IN ECOLOGY AND MANAGEMENT OF GOLDEN APPLE SNAILS 60 Female

Male

Minimum 40 Market Size

20 Number of individuals

0 1357911131517 Body Weight (g)

Fig. 4. Size frequency distribution of apple snails infesting taro lo‘i in Ke‘anae and Wailua on Maui, November 1995.

Cost-effectiveness of Raising Wild-caught Snails on Commercially Available Diets A feed experiment utilizing snails that were approximately 30 mm in shell length was implemented in 37.8 l aquaria. Five feed regimens (lettuce + chicken feed, chicken feed, catfish feed, trout feed, and mahimahi feed) were used in the experiments (Table 4). The duration of the feed trial was a grow-out period of 1 month. In addition to the types of feed used, the amounts were adjusted to optimize growth. The regimen resulting in the best growth was catfish feed, registering a 4–5 g increase per month and a food conversion ratio (FCR) of just under 1.0 (0.97). All the aquarium trials, each using a different feed regimen, resulted in relatively high mortality due to deterioration in the water quality. For comparison purposes the price per kilogram of the various feeds used in the feeding trial is also presented. An interesting observation is that the higher priced feeds also resulted in a higher mean weight gain. The relationship of shell length to body weight was calculated for snails caught in the taro lo‘i and for the snails being intensively fed in the experiment using the catfish feed treatment. The data in Fig. 5 show a difference significant (P<0.05) in the body weight to shell length ratio of the two snail populations. The snails fed catfish feed had a much higher body weight in relationship to their shell length. This can be compared with feed-lot operation in the cattle industry, where animals are “fattened” by intensive feeding.

THE CONTROL OF THE APPLE SNAIL, POMACEA CANALICULATA IN HAWAII: CHALLENGE OR OPPORTUNITY? 47 Table 4. Summary of feeds used for the apple snail grow-out. Values with different suffixes are significantly different (P<0.05) (from Nishimura et al. 1996).

Average Mean Mean Feed Price per Feed Mortality Weight Gain Conversion Kilogram (%) (g) Ratio (US$)

Chicken feed + Lettuce 23.0 ± 4.0 2.6 ± 0.0a 1.1 ± 0.1 — Chicken feed 21.0 ± 5.0 3.1 ± 0.4a 1.7 ± 0.3 0.44 Catfish feed 15.5 ± 4.5 4.7 ± 0.1b 1.0 ± 0.0 0.86 Trout feed 25.0 ± 4.0 4.0 ± 0.8b 1.3 ± 0.2 1.01 Mahimahi feed 33.0 ± 1.0 4.2 ± 0.1b 0.9 ± 0.0 2.20

[1 lb = 2.2 kg]

Taro Lo‘i Snails 26 Wt = (LT*0.314) –4.39 R2 = 0.93 22 N = 102 P

18 Cultured Snails Wt = (LT*0.891) –21.804 14 R2 = 0.811 N = 240 P 10 Body Weight (g) Body Weight

6 Cultured 2 Wild 0 10 20 30 40 50 Body Length (cm)

Fig. 5. Comparison of shell length vs body weight relationships between snails intensively fed and those directly from the taro lo‘i (from Nishimura et al. 1996).

Based on those laboratory results, a field test of the experimental results was conducted at Ke‘anae/Wailua on Maui for 1 month, with similar results observed (Table 5). The control tanks consisted of snails fed taro tops, and two feeding regimens using commercial diets were a1 tested. One treatment group received catfish feed at 3 the feeding rate as that used in the laboratory experiment. The second treatment group consisted of a floating trout feed mixed 1 with chicken feed, again at a3 the feeding rate used in the laboratory. The lower feeding rate was used to insure that problems with water quality did not arise during the field trial. The snails fed the taro leaves did not grow very much during the course of the experiment. In contrast, snails fed catfish or trout + chicken feed grew an average of 2 g over the course of the 1 experiment. Although only a3 of the feeding rate used in the laboratory experiment was used

48 GLOBAL ADVANCES IN ECOLOGY AND MANAGEMENT OF GOLDEN APPLE SNAILS Table 5. Summary of feed trial conducted at Ke‘anae/Wailua. Values in a column not sharing a superscript are significantly different (P<0.01) (from Nishimura et al. 1996).

Feed Initial Weight Final Weight Weight Gained (g) (g) (g)

Taro tops (control) 8.0 ± 2.9a 8.6 ± 2.7a 0.6a Catfish feed 8.1 ± 3.8a 10.0 ± 3.8b 2.2b Trout feed + chicken feed 8.5 ± 4.0a 11.0 ± 4.4b 2.5b

1 in the field test, approximately 22 of the growth rate of that observed in the laboratory was observed. Commercial feeds provided at intensive feeding rates thus result in faster growth. The data presented indicate a particular feeding regimen and feeding rate that result in optimal growth. A similar field test was also conducted in Hanalei on Kaua‘i. In that trial, nine 567-liter plastic tanks were stocked with approximately 1000 snails each, which represents a density of approximately 37.8 snails/liter of water. By instructing the employees that only a certain size snail was to be collected, a method for size-grading the snails coming into the tanks could easily be implemented. This method represented substantial savings in labor compared with sorting the snails after the fact. Three feeding regimens were used during the course of the experiment, with three tanks used for each treatment group. The feeds used in the trials were (a) catfish chow (Nutrena Feeds™, with 32% protein, 4% fat, 3% fiber, and 9% ash), (b) chicken feed (Nutrena All Purpose™, with 16% protein, 3% fat, 7% fiber, and 10% ash, and (c) a 1 1 combination of 2 chicken + 2 catfish feed. The feeding trial was run for one month. In addition to the nine experimental tanks, a “no-feed” tank in which snails were stocked at the same density but with no feed provided over the course of the experiment was used as a control. 1 1 One treatment tank of ½2 chicken + ½2 catfish feed was lost because of an accident and was eliminated from the summary of the data (Table 6). Overall survival among the tanks that received food ranged between 43.8% and 53.1%. No statistical differences (P>0.05, c2 test) in survival could be detected between tanks that received feed. Overall, survival in the tanks that received feed was significantly lower (P<0.01, c2 test) than in the tank that did not receive any feed. The “no-feed” control group exhibited a relatively high survival of 89.7%. At the end of the experiment, the extra tank was stocked with wild snails that were collected and then purged for 72 hours. These snails were used for the taste testing trials described in a later section. The snails held in the tanks for 72 hours also exhibited very high (99.3%) survival.

Table 6. Summary of feeding trials in Hanalei, Kaua‘i in 2002. Values in a column not sharing a superscript are significantly different (P<0.01).

Survival Weight Length x Weight Retail Price Feeding Regimen (%) Gain (g) Regression per Kilogram Slope of Feed (US$)

Catfish feed 48.4 ± 10.4b 2.3 ± 1.6 0.869a 0.90 Chicken feed 53.1 ± 9.4b 0.5 ± 0.4 0.747b 0.42 Catfish feed + chicken feed 43.8 ± 9.7b 1.3 ± 1.3 0.697b 0.64 No feed 89.7 ± 0.0a 0.4 ± 0.0 0.712b — Wild-caught snails 99.3 ± 0.0a — 0.752b —

THE CONTROL OF THE APPLE SNAIL, POMACEA CANALICULATA IN HAWAII: CHALLENGE OR OPPORTUNITY? 49 Estimates of weight gain by the snails exposed to the various feed treatments are also summarized in Table 6. The average weight gain appears to exhibit a trend, with the snails that were fed catfish feed showing the highest weight gain. However, the values are not statistically significant (P>0.05, one-way ANOVA), apparently because of the large degree of variability observed within the treatments. Shell length and total weight determinations were made for snails (n=50) in all tanks. The data were then statistically analyzed for treatment effects using analysis of covariance (Snedecor and Cochran 1967), with shell length being the covariate. Interestingly, there were no statistical differences (P>0.05) between the snails held for 72 hours and those that had not been fed for the duration of the trial (the “no-feed” control). There were also no statistical differences detected between the snails in the “no-feed” control group and those in the various treatments, with the exception of snails that were fed catfish feed. The snails that were fed catfish feed were found to be significantly (P<0.01) heavier in relation to their shell length than the snails from all other treatments. The results of the feeding trials conducted both in the laboratory and in the field on two separate islands in Hawai‘i indicate that the feed of choice for snails collected from taro fields is catfish feed. Current retail prices of the feeds used in the various feed treatments are presented in Table 6. The retail price of catfish feed is US$0.90 per kg, which reflects the feed costs to produce 1 kg of snails. This price reflects only the cost of feed, not the total production cost.

Cost-Effective Method of Processing Snails as a Value-Added Product Snails from each feeding treatment were either pressure steamed for approximately 20 minutes (Treatment 1) or parboiled for no more than 5 minutes (Treatment 2). As the first step in processing the snails, either method is sufficient to sterilize them of possible pathogens. Each method also satisfies the standard methods of operation required for certified kitchens (Alicata 1967, 1990). All snails were then shucked by hand, and the foot (edible portion) was separated from the entrails. The average time to complete this step in the process was four snails per minute. The processed snails were then stored in two ways: (a) placed in Ziploc™ plastic bags and frozen or (b) vacuum-packed and frozen. These snails were then used in the taste tests by chefs. Because there were detectable differences in the shell length to total weight ratio of snails from the feeding trials, estimates of the useable amount of snail meat after the initial processing had to be established. Individual total body weights (shell removed) from a sample (n=10) of snails from each feed treatment group were obtained, and the resulting foot mass (edible portion) was weighed (Table 7). The snails that were purged for 72 hours and the snails that were starved for 1 month (the control) clearly resulted in a significantly (P<0.05, one-way ANOVA) lower BW (shell removed), foot weight, and percent edible portion. Snails fed catfish feed also resulted in significantly (P<0.05) heavier snails and foot weights. An important aspect of this analysis is that an estimated 75% of the snail mass, including the shells, is not used in the finished processed product. Finding a use for these waste materials needs further investigation. The data presented also allow for an estimation of the number of snails needed to produce a finished product. Using a value of 3 g as the average amount of edible portion obtained from an individual snail means that 151 snails would be needed to result in 454 g (1 pound) of marketable product.

50 GLOBAL ADVANCES IN ECOLOGY AND MANAGEMENT OF GOLDEN APPLE SNAILS Table 7. Summary of weights of snail parts in relation to various feeding regimens. Values in a column not sharing a superscript are significantly different (P<0.05) from one another.

Feed Treatment Mean ± SD Mean ± SD Mean ± SD Body Weight (g) Foot Weight (g) % Edible

Control snails (starved) 10.9 ± 2.2b 1.8 ± 0.5bc 17.3 ± 5.8b Wild snails (purged 72 h) 9.1 ± 2.7b 1.5 ± 0.4c 17.2 ± 3.6b Chicken feed only 9.6 ± 3.2b 2.2 ± 0.7b 24.0 ± 7.2a Chicken feed + catfish feed 13.4 ± 3.9a 2.1 ± 0.6b 15.8 ± 2.7b Catfish feed only 15.4 ± 2.4a 3.6 ± 0.4a 24.0 ± 2.7a

Assessing Quality of the Snail Product One of the most crucial portions of the project was the evaluation of the apple snail product by a competent authority with regard to taste and texture. The project work group solicited the assistance of executive chef Todd Oldham and his staff (Jeremy Lloyd, Ikaika Manuku, and Mike Valentino) of the Princeville Resort, Hanalei, Kaua‘i. The Princeville Resort is a four-star establishment, and the cuisine provided by the hotel is considered high end. The chef was asked to prepare dishes at his discretion using snails from the various feed treatment groups and the two processing methods (pressure steamed and parboiled). Eight packages of frozen snails were presented to him and labelled “A” through “H” without his knowledge of how the snails were processed or what they had been fed. In addition, he was asked to prepare the same dishes using snails that were vacuum-packed or fresh-frozen. The culinary department staff decided that two dishes would be prepared: one to satisfy the tastes of visitors from the US mainland and a second that would have a more local flair. In total, 20 individual servings were prepared and tasted. The two dishes created were (a) apple snail ragout with exotic mushrooms and heart of palm (“A” in Fig. 6); and (b) fricassee of Hawaiian escargot with edamame and ogo (“B” in Fig. 6). Both dishes were prepared as an appetizer to serve four persons. The chef and staff proceeded to evaluate the snails for both taste and texture on a scale of 1 to 5 (with 5 being the highest). Samples A, B, C, and D represented snails fed catfish 1 1 feed, chicken feed, ½2 chicken and ½2 catfish feed, and wild-caught snails, respectively. These samples also represented the group that were pressure-steamed for 20 min. The remainder of 1 the samples, E, F, G and H, represented snails fed catfish feed, chicken feed, ½2 chicken and 1 ½2 catfish feed and wild-caught snails, respectively. These samples were prepared by parboiling for five minutes. The results obtained by the Culinary Department of the Princeville Resort clearly indicated that snails fed catfish feed were superior to all other snails in both taste and texture, earning a score of 5 in both categories. Second place with a rating of 4 for both taste and texture were snails that were fed chicken feed and parboiled. There was no reported difference between the snails that were presented as a fresh-frozen product or vacuum-packed and frozen. The chef and his staff stated a preferred size of the edible portion of the snail to be 0.75 of an inch (1.9 cm, which equates to a snail that is approximately 10 g in total BW when collected in the wild). The preferred bulk size of the package was 1 lb (454 g). It is recommended that the product be marketed as presented in the taste tests (cooked, with shells and entrails removed, leaving only the foot portion). Another suggestion made by the staff was for the project work group to consider marketing the product as a flavored item (e.g., poached in bouillon, peppercorns, and white wine).

THE CONTROL OF THE APPLE SNAIL, POMACEA CANALICULATA IN HAWAII: CHALLENGE OR OPPORTUNITY? 51 The results of the taste test clearly demonstrate that a high-end product can result from the processing of wild-caught snails. The results are consistent with a previous investigation (Tamaru et al., 1999) in which executive chef Alan Wong and his staff from Wong’s Restaurant, located in Honolulu, Hawaii, preferred snails that had undergone the same feeding regimen (catfish feed). They were scored as being superior in both taste and texture out of the five feed treatments.

Ascertaining Production Costs The main constraint to producing a marketable product is the processing, which entails parboiling the snails; shucking them from the shells; removing the foot (edible portion) from the viscera, which are later discarded; packaging the snails; followed by freezing the end product. It appears that on average, approximately four snails/minute can be processed by one person. Undoubtedly, the efficiency could be improved, but for the purposes of this report, this number was used to obtain an initial estimate of the associated costs of production of a marketable apple snail product. Using this value, the number of snails that one person can process in a month was estimated to be 38,400. Using 10 g as the average total weight of the target individual snail to be used by an executive chef, the estimated total weight of snails would be 460 kg. Using that value, the estimated collection fee, feed costs, amount of labor needed, and fringe benefits were determined. The summary of the breakdown of production costs presented in Table 8 represents a single module that accounts for approximately 460 kg (1,015 pounds) of processed snails/month. Acquisition of the raw material for producing a marketable product is to be accomplished by placing a bounty on the snails from the wild at the rate of US$0.50/lb (US$1.10/kg). The associated costs to obtain 1,015 lbs (460 kg) of snails would be US$425. During the current project, it was found that the payment of a bounty for the collection of snails also provided a means by which the snails could be sorted. By clearly indicating to the collectors the size range of useable snails, only those of a certain size were initially collected from the fields. This greatly reduced the labor requirements and improved the efficiency during the latter stages of feeding and processing. Over the course of the feeding trial it was found that approximately one hour/day is required to feed and care for the snails. Labor costs were calculated for a full-time worker at an hourly wage of US$9.00/hour. The same pay rate

Fig. 6. Two dishes (see text for description) prepared for use in the assessment of taste.

52 GLOBAL ADVANCES IN ECOLOGY AND MANAGEMENT OF GOLDEN APPLE SNAILS Table 8. Summary of production costs to process approximately 1,000 lb (454 kg) of snails per month.

Category Estimated Costs (US$)

Snails 425.00 Processing labor 1,440.00 Field labor 270.00 Fringe benefits 430.00 Supplies 225.00 Feed costs 70.00 Utilities 90.00 Total 2,950.00 Gross @ US$12.00/lb 3,045.00

Balance 95.00 % Profit 3.1%

was used to calculate the labor costs for both the feed activities and the processing steps conducted in the kitchen. Fringe benefits were calculated by multiplying the total labor costs by 25%. The required feed costs estimated to finish the 460 kg (1,015 pounds) of snails were obtained by utilizing the weight gain of 2 g per snail. The feed conversion ratio of catfish feed to snail flesh was reported to be 1:1 (Tamaru et al. 1999). This estimate was made by multiplying the amount of weight gained by US$0.41, as this is the landed cost for catfish feed on Kaua‘i. An estimate of utility costs is 3% of the gross value of the processed product. The gross value of the marketable product was obtained by first estimating what the amount of edible weight of snails would be (25% of the total weight). This value was then multiplied by US$12.00/lb (US$26.46/kg), which is the current price chefs are paying for canned escargot. From the information provided there is a small profit of 3.1%, indicating that the process is economically sustainable.

Conclusion

The ultimate question that remains to be answered is whether the use of wild apple snails as a raw product in the production of a value-added product can affect an infestation. The only evidence that suggest that this approach has merit is by observing the temporal changes in taro production that have occurred on Maui. To obtain the required quantity of snails (1000 lb [454 kg]) for the initial feed trial, a bounty of US$1.00/lb (US$2.20/kg) of live snails was offered to the community. The process that was being employed was overseen by a nonprofit community group, Na Moku Aupuni O Ko‘olau. Between 1996 and 1999, the following scenario was used: (a) snails collected from the taro fields were bought at US$1.00/lb (US$2.20/kg) and placed into a community grow-out facility; (b) snails were fed at the prescribed rate determined from the feeding experiments and were sold live at US$4.00/lb (US$8.80/kg) to local markets or to high-end restaurants as escargot. The US$4.00/lb (US$8.80/kg) accounts for the cost to purchase more snails, grow-out costs, and a profit that was placed in a community general fund. The most exciting part of the project was that there was approximately a 10-fold reduction in the density of snails in the taro fields with the placement of the bounty (Table 9). This large reduction ultimately resulted in a return of taro production that initially exceeded levels of

THE CONTROL OF THE APPLE SNAIL, POMACEA CANALICULATA IN HAWAII: CHALLENGE OR OPPORTUNITY? 53 production prior to the infestation (Fig. 7). Interestingly, there was a dramatic decline in taro output in 2000. The causes of this decline were many, but a major contribution was a resurgence of apple snails that occurred after the record 1999 year. Currently the apple snails are still present but are being kept in check by the use of a biological control (Cayuga ducks), which are allowed to forage in the taro lo‘i. While an option for Maui, there is no possibility of using ducks on Kaua‘i, as the infested area lies within the US Department of Interior Fish and Wildlife Service Hanalei National Wildlife Refuge. The refuge is home to five endemic Hawaiian birds, the Koloa duck, the Hawaiian stilt, the Hawaiian coot, the mud hen, and the nene goose that are currently classified as endangered. An additional 27 other native species of birds are known to use the refuge. Because of the endangered status of the Koloa duck, introduction of other ducks is prohibited. Although the results are clearly encouraging, the one-time bounty placed on the wild apple snails that resulted in a dramatic decrease in the wild population was possible only because of the availability of grant funds. Whether this activity can be sustained still needs to be determined. The most logical approach would be to bring forth a product that, at a minimum, generates enough revenue to cover all of the collection and processing costs of the activity. In other words, for the process to be successful, the creation of a new enterprise would be required.

Table 9. Average snail density in Ke‘anae, Maui before and after implementation of the apple snail project.

Category Snail Density Snail Density, November 1995 July 1997

Plot 1 1.43/m2 0.009/m2 Plot 2 0.97/m2 0.046/m2

30 Start of Project

20 Fresh Taro (t) Fresh Taro

0 1991 1993 1995 1997 1999 2001 2003 Year

Fig. 7. Temporal changes in the production of fresh taro from Maui/Honolulu between 1991 and 2003 (from HASS 2004).

54 GLOBAL ADVANCES IN ECOLOGY AND MANAGEMENT OF GOLDEN APPLE SNAILS Acknowledgements

The authors would like to recognize the various resources that contributed to the information presented in this report. Partial funding for support of this work was obtained from the Department of Hawaiian Homelands through a grant titled “Control of the Apple Snail (Pomacea canaliculata) Planning Project,” Contract Number 40785, Reporting Period: 2/8/96 - 6/30/97; United States Department of Agriculture Small Business Innovative Research Program through a grant entitled “The Apple Snail (Pomacea canaliculata): Pest to Profit” Project Number 2001- 00351; the State of Hawai‘i Department of Agriculture Aquaculture Development Program as part of the Aquaculture Extension Project Contracts 9325 and 9638 and through the Hawaii Department of Land and Natural Resources and Aquasearch Undergraduate Summer Research Programs. This paper is also funded in part by a grant/cooperative agreement from the National Oceanic and Atmospheric Administration, Project A/AS-1, which is sponsored by the University of Hawaii Sea Grant College Program, SOEST, under Institutional Grants Numbers NA86RG0041 and NA16RG2254 from NOAA Office of Sea Grant, Department of Commerce. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or any of its sub-agencies. UNIHI-SEAGRANT- BC-98-01

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56 GLOBAL ADVANCES IN ECOLOGY AND MANAGEMENT OF GOLDEN APPLE SNAILS