Abundance of introduced Pacific whiteleg shrimp Penaeus vannamei (Boone, 1931) along the east coast of Thailand.
Pacific whiteleg shrimp Penaeus vannamei (Boone, 1931), a highly significant global commodity, has been introduced for aquaculture to many countries outside its native range, including Thailand. In Thailand, this species was introduced to replace Penaeus monodon for aquaculture in 1998, and it has represented more than 90 percent of total cultured shrimp production since 2005. The rapid expansion ofP. vannamei aquaculture has led to escapes of P. vannamei into natural waters. We examined abundance, size and sex ratio of P. vannamei caught by commercial fishing gears, namely trammel, trawl and push nets, to determine the extent to which this species has entered the natural ecosystems in the Gulf of Thailand. Sampling was performed from August 2009 to October 2010 at five locations along the east coast of Thailand. We consistently found P. vannamei in shrimp catches in all three fishing gears across all locations. The frequency of occurrence of P. vannamei ranged from 0.13 (trawl nets) to 0.99 (push nets). The relative abundance by weight of wild-caughtP. vannamei ranged from 0 to 5.43%, with highest mean abundance in Chanthaburi (0.42 ± 0.72%) and lowest mean abundance in Chonburi (0.04 ± 0.15%). All 4,041 individuals collected were sub-adults or adults (total length = 82 to 212 mm, weight = 3.2 to 71.8 g), with a 0.92:1 female to male ratio. The samples consisted of approximately 22% adults, suggesting a notable proportion of potential breeders in the wild. Our study can serve as a baseline for monitoring programs for aquaculture escapes. Our report is among the few studies that document substantial numbers of P. vannamei specimens throughout the study period. Participation by fishers proved valuable for detecting P. vannamei in the wild. Incorporating a similar sampling approach in fisheries monitoring programs will provide a consistent means of detecting population trends of P. vannamei in the wild.