Resource use in Whiteleg shrimp Litopenaeus Vannamei farming in Ecuador

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By: por Claude E. Boyd, Robert P. Davis, Arturo González Wilson, Fabrizio Marcillo, Susanna Brian and Aaron A. McNevin

Ecuador, India, Indonesia, Thailand, and Vietnam are the main sources of farmed shrimp in the international market. Concern that excesses resource use and environmental degradation caused by food production is jeopardizing the sustainability of the world food system extends to aquaculture production and to shrimp farming. The present study was conducted to obtain data from a sample of farms and to use this information to estimate amounts of land, water, energy, wild fish, and other resources used at Ecuadorian shrimp farms.

Materials adn methods

The office of the World Wildlife Fund in Ecuador, Guayaquil, Ecuador, obtained a list of Ecuadorian shrimp farms from the Under Secretariat of Aquaculture of the Ministry of Agriculture, Livestock, Aquaculture, and Fisheries of Ecuador. An attempt was made to randomly select several farms in each province proportional to their frequencies in the list.

The farm survey instrument used in Ecuador was a slight modification of the one used in Asia. The modifications were made primarily to gather information about the large pumps used at Ecuadorian shrimp farms. Production and resource use variables were calculated on an individual farm basis to reveal variation among farms in management and resource use within and among provinces. These variables also were calculated separately as weighted averages for all farms in a province combined and all farms combined. Resource (land, water, and energy) use statistics were compared with an ANOVA and subsequently analyzed for pairwise differences with a post hoc Tukey test when warranted based on the results.

RESULTS Physical features

Farms contained 19,241 ha of property of which 17,731 ha were devoted to farms with a total of 14,249 ha of production ponds. The dedicated shrimp farm area consists of production pond area plus embankments, reservoirs, canals, settling basins, parking and staging areas, etc.

The ratio of the dedicated farm area to the production pond area was called the land to production water surface area ratio or LWR. The LWR had an average of 1.24 for all farms and a range of 1.18–1.53 by province. The property to production pond ratio was greater (1.35 with a range of 1.26–1.87). The farms were constructed on soils that were predominately clayey, silty clay, sandy clay, loamy, silty, and sandy.

The soils generally had a sufficient mixture of particle sizes to allow good compaction of embankments to minimize seepage. It should be noted that the average LWR is much larger when based on the average of individual farms than for the overall province LWR estimates. This resulted from larger farms typically having a lower LWR than did smaller farms. Ponds typically had a water inlet gate at one end and a water outlet gate at the other end. Flow was controlled by dam boards fit with slots in the sidewalls.

Of the 101 farms, 87 had reservoirs and 42 had canals. In farms without canals, the main inlet channel served as both an elongated reservoir and canal from which ponds were supplied. Fourteen farms pumped water directly into production ponds.

“Farms discharged water into separate canals or drainage ways.“

Water supplies for filling and exchanging water in ponds were estuaries or estuarine reaches of streams, and some farms were several kilometers inland. Ninety-eight percent of the pumps were operated with diesel engines and the rest with electric motors. Farms had variable numbers of vehicles and other farm machinery depending upon farm size. Most farms had at least one flatbed truck, one dump truck, one pickup truck, and three or four motor bikes. They also usually had at least one tractor, one backhoe, two or more outboard motors, several small boats, and a larger barge.

Pond management

Production was feed-based, and an undetermined number of farms stocked postlarvae (pls) at high density into ponds, which served as nurseries before transferring the larger juvenile shrimp to other ponds at lower density for grow-out to harvest size. All farms applied pelleted shrimp feed containing 28.0–38.5% crude protein. The crude protein content typically was reduced as shrimp grew. Feed was applied daily in amounts adjusted for shrimp size and standing crop of biomass in ponds. Feed was broadcast over pond surfaces from a small boat or by automatic feeders.

The farms used a wide range of pond amendments for water quality improvement, wild fish destruction, and shrimp health. The most applied amendments were liming materials, fertilizers, and molasses. Forty-seven (46.5%) farms applied mechanical aeration in some or all ponds. Electric aerators were used at 12 farms, diesel aerators at 29 farms, and six farms used both. Shrimp ponds were completely drained at harvest so that pond bottoms could dry for sanitary purposes. In 87 farms, sediment was not removed from pond bottoms following draining for harvest. Liming materials usually were applied to moist pond bottoms soon after draining. Two farms reported removing sediment after each crop, five removed sediments annually, five removed sediment at 2- to 3-year intervals, and two conducted the task at 5- to 6-year intervals.

Production

Annual yield intensity did not differ (p > .05) among provinces because of the great variation among farms. Weighted average annual pond yield intensities based on total annual production and total production pond area of survey farms by province were slightly different from averages based on individual farm performance.

The farm-level FCR averaged 1.32 for all provinces with a range of 1.19 (Manabi) to 1.44 (Guayas). However, the FCR calculated on total production and feed use by province had an average of 1.48 and range of 1.20–1.54. Adjusting this average FCR for 0.5 t/ ha/year of shrimp biomass from natural productivity results in an FCR of 1.60.

Resource use

The energy required for construction and maintenance of farm earthen infrastructure was based on a unit the area of which was that the average production pond (6.59 ha) plus the average ratio of canal and reservoir area to production pond area (0.92 ha). The survey farms were repaired at 1–10-year intervals—the average interval was about 3 years. Based on con- versations with a shrimp farm design consultant, the maintenance and repair work over a 30-year period would consume an amount of fuel at least equal to that used for initial farm construction.

At an FCR of 1.48 and a national production of 510,000 t shrimp, an estimated 754,800 t of shrimp feed were produced. This suggests a fish meal inclusion rate in Ecuadorian shrimp feed of around 6.62%. Shrimp feeds in general probably contain an average of 5% fish meal from the reduction fishery, because many large feed producers use fish meal made from trimmings from fish processing.

When the fish meal inclusion rate is 4.44 times or more than the fish oil inclusion rate in a feed, all the fish oil can be accounted as a byproduct of making the meal. Assuming Ecuadorian shrimp feed has an average of 5.6% fish meal and 2.5% fish oil from the reduction fishery, more wild fish use would be accrued than for the fish meal alone. Aquaculture certification programs usually require that the wild fish embodied in harvested shrimp be 1.0 t/t shrimp or less. Based on the estimated fish meal and fish oil inclusion rates in Ecuadorian shrimp feed, farms must have an FCR of 1.54 or less to comply with the standard of 1.0 t wild fish or less per ton of shrimp. Twenty-two (21.8%) of the farms had FCR values above 1.54.

Energy and wild fish use did not differ among provinces. There was, however, a wide range among individual farms with respect to the use of these resources. Land embodied in feed exceeded direct land use for production pond water surface area. The sup- port area on farms made up about one-fourth of direct land use. Saline water was used for filling ponds and exchanging water accounted for 88.5% of total water use. Embodied freshwater was mainly in feed and fuels. Embodied energy in pond amendments when spread over the farm sample production was only 3.04 GJ/t shrimp. More than one-half of the energy use was incurred as embodied energy, and 49.4% of the embodied energy resulted from feed.

DISCUSSION

Based on production pond area calculated from data provided and national production data from 2020, the average pond yield in Ecuador has increased as follows: 1984, 0.49 t/ha/ year; 1991, 0.88 t/ ha/year; 2006, 1.45 t/ha/year; 2018, 3.18 t/ha/year. The farms in the present survey outperformed the national average for 2018, and there is much potential for greater intensification in the country.

Moreover, greater intensification will not increase land, water, and energy use per ton of shrimp and will tend to decrease resource use per ton of shrimp. The national farmed-shrimp production of Ecuador could be increased to about 1,000,000 t annually by simply increasing the average national pond yield to that of the farms in the survey without the need of constructing new farms or expanding existing ones. Despite the farms surveyed having higher than average production, some farms produced more shrimp and used resources more efficiently in doing so than did other farms.

Variation in efficiency and resource is introduced at the farm level through specific farming practices, such as the use of fertilizers or liming materials, water exchange rate, and feed management. There is much opportunity to improve yield and resource use efficiency even among the surveyed farms.

“The main technique for increasing production obviously would be greater use of mechanical aeration.“

The increase in yield possible with mechanical aeration is dependent on the amount of aeration applied because aerators have the capacity to allow 300–500 by more shrimp per horsepower. Aeration generally does not increase the energy input per ton of shrimp but allows greater shrimp yield in proportion to the amount of aeration applied. Aeration also lessens the necessity for water exchange and could reduce energy use for pumping.

This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “Resource use in whiteleg shrimp Litopenaeus vannamei farming in Ecuador” developed by: Claude E. Boyd, Robert P. Davis, Arturo González Wilson, Fabrizio Marcillo, Susanna Brian and Aaron A. McNevin. The original article was published on May 2021 through the Journal of the World Aquaculture Society, by Wiley Periodicals LLC.