On 24th May, Wanwiwa Tumnoi will be giving a talk entitled: The Ecology and Fishery of Tapes philippinarum (Adams and Reeve, 1850) in Southampton Water, UK.
Abstract:
The non-indigenous species Tapes philippinarum (Manila clam) was introduced in the Solent system and Southampton Water in 2005. They have been intensely harvested by the local fishers due to their high marketable value. Apart from Minimum Landing Size (MLS) legislation based on EU fishery regulations, other clam fishing management techniques have not been established because of knowledge insufficiency. The population status, reproductive cycle, size at maturity, and potential to sustain a population are the fundamental scientific information required for fishery management.
T. philippinarum in the area of Bird Pile, Southampton Water was studied between December 2008 and January 2010. The population structure revealed that the clams with 30-35 and 35-40 mm in shell length dominated the population, with 25.60% and 28.32% respectively. The proportion of clam smaller than 25 mm increased from August to December 2009 most likely because of spat settlement during this period. The signal of fishing impact was reflected by the low share (8.6%) of clam larger than 40 mm. The preliminary study of reproduction from December 2008 to June 2009 showed that sex ratio of male to female was 1:1.68. Gametogenesis of both males and females was synchronised. The spawning period began in May and continued through the summer, no reproductive activity was found in December. However, further investigation is required to confirm our present results. The smallest clam containing oocytes is 17.5 mm in shell length. The oocytes were found to be measurable from March to June. The size significantly increased with time and reached the largest in June (39.56 + 13.13 µm). Moreover, the mature female examined in June revealed that egg diameters rose according to the degree of size classes with an average of 24.6 + 13.18 µm (20-25 mm in shell length) to 47.98 + 13.38 µm (40-45 mm in shell length). Changes in haemocyte number and phagocytic activity corresponded to not only season but also spawning period. No particular pattern was found in phagocytic capacity. The monthly growth rates of T. philippinarum (shell dimensions and total wet weight) gradually rose between March and June, rapidly increased from June to September, and then slowed down after October. The final cumulative growth rates of length, height, width, and total weight were 8.23%, 10.08%, 15.04%, and 39.02% consecutively. The updated data of T. philippinarum observed in Southampton Water revealed that the conditions in the area are favourable for reproduction and growth of this commercially important species.
