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ABSTRACT Oyster culture has benefited traditional coastal communities along the Amazon macrotidal mangrove coast of Pará state in Brazil since 2006. Currently, seven oyster culture units in five municipalities are expanding production, but with no environmental monitoring, which is important for the control of the impacts of oyster culture on waters as well as for oyster management and conservation. Seasonal variation in environmental characteristics of the water was evaluated at all oyster culture units in Pará, from September to November 2013 (dry season) and February to April 2014 (wet season), to generate baseline data to evaluate future impacts and aid strategic planning, such as diversifying seed production. Salinity, dissolved oxygen, pH, oxidation-reduction potential, depth, temperature, and chlorophyll-a concentration were measured during flooding and ebbing tides, and compared between seasons and among culture units using uni- and multivariate statistics. All variables were significantly higher in the dry season, except depth, which was significantly greater in the wet season. Mean salinity, which varied from 2.4 to 46, explained most of the variation among culture units in relation to season, sampling date within each season and tidal state. However, dissolved oxygen, pH and depth were also important. Oyster culture units in Pará may be suitable for sustainable harvesting of seed/spat from the wild (lower salinity and pH), or for on-growing (higher salinity, higher pH, and greater depth). Seasonal variation is sufficient to allow both activities at most units at appropriate times of the year, which would help increase oyster production in Pará.

To complement dwindling fisheries, white shrimp (Litopenaeus vannamei) was cultured at small scale by men and women of six fishing communities in low-cost floating cages made by them at sea near-shore in the Gulf of Nicoya, Pacific coast of Costa Rica. Growth and farming data were collected for 19 separate production events, six of them including polyculture with Pacific oyster (Crassostrea gigas). Shrimp post-larvae (PL) were placed in a sequence of two or three cages in densities leading to a mean at harvest of 4.05 ± 1.16 kg m−3 of 12 g shrimp after 121 days with 59.7 ± 6.4% mean survival. Growth rate between 1.0 and 18.0 g was 1.1 g wk−1, decreasing to 0.65 g wk−1 through 35.4 g. Oysters were grown within shrimp cages in suspended socks or in simple lanterns, at a harvest density aiming at 100 70-mm oysters m−2 of cage after 5.4 ± 0.7 months of growth, with 46.8 ± 18.7% mean survival. No significant differences in growth of shrimp in monoculture between localities or in polyculture with oyster were determined. Shrimp PL were fed powdered concentrate feed until 0.1 g when they were changed into a diet of only fish discards and fish byproducts aiming at 8 g fresh feed: 1 g of shrimp growth. This feeding rate showed no significant differences in weight gain compared to a diet aiming at 2 g concentrate feed: 1 g of shrimp growth as determined in two closely-monitored separate trials. A mean fresh-feed conversion rate (FCR) of 6.0 ± 0.4 was obtained though growers used an overall fresh-FCR of 6.46 ± 1.13. Estimated financial profitability increased markedly when selling shrimp for live bait, adding oyster in polyculture and using fresh instead of concentrate feed. The latter also promoted a closer integration with fisheries as well as a use of fish and byproducts that otherwise are discarded to sea. Overall, 2.5 d of training of participants plus follow-up by project personnel were adequate for them to successfully implement the innovation, although care during early growth was sometimes faulty. Fishing moratoria, dysfunctional social organization, and theft and vandalism inhibited scaling-up, evidencing the need for institutional support and proper policies for widespread adoption. • White shrimp were successfully grown by artisanal fishers in small cages at sea fed only with fishing discards and byproducts • Shrimp growth rates of 1.1 g week−1 and high densities produced yields of 12 g shrimp of 4.05 ± 1.16 kg m−3 • Calculated financial benefits increased markedly with polyculture with oyster, fish-based feed and selling shrimp for bait • Fishing moratoria, theft and vandalism inhibited scaling-up, evidencing a need for institutional support and proper policies [ABSTRACT FROM AUTHOR]