ผลกระทบของโครงสร้างแนวไม้ไผ่ป้องกันชายฝั่งต่อประชากรหอยแครง Anadara granosa (Linnaeus, 1758) ตำบลแหลมใหญ่ จังหวัดสมุทรสงคราม

• 主要作者: สุเมธ แก้วน้อย
• 其他作者: ณิฏฐารัตน์ ปภาวสิทธิ์
• 格式: Theses and Dissertations
• 語言: Thai
• 出版: จุฬาลงกรณ์มหาวิทยาลัย 2015
• 主題: หอยแครง; การป้องกันชายฝั่ง; Cockle fisheries; Coast defense
• 在線閱讀: https://digiverse.chula.ac.th/Info/item/dc:34323
• 機構: Chulalongkorn University

Impact of bamboo fencing as coastal defense structure on blood cockle Anadara granosa (Linnaeus,1758) population at Tambon Laemyai, Samut Songkharm Province was conducted during December 2013 to November 2014. Comparative study on the abundance, distribution and growth as well as the reproductive cycle and larval abundance of the cockle population was carried out in the three respective areas; the area behind the bamboo fencing, the area in front of the bamboo fencing and the cockle fishing ground in front of the bamboo fencing. Changes in sediment characteristics in relation to the changes in population structures were also carried out. The result showed the annual density of cockles in Tambon Laemyai, Samut Songkharm Province was in the range of 4-32 individuals per square meter. Temporal and spatial differences in the cockle density were significant. Highest cockle density recorded from the cockle fishing ground in front of the bamboo fencing of 18.68 individuals per square meter. The area in front of the bamboo fencing area behind the bamboo fencing showed lower density inrespective order. High density was recorded during the dry season as compared to the wet season. The cockle size found in this area ranged from the smallest shell length of 1.00-1.25 cm. to the largest of 4.51-4.75 cm. Dominant cockle size group both males and females that widely distributed in the three areas and throughout the year were in the range of 2.26-2.50 to 3.26-3.50 cm. Large size cockles of 3.51-3.75 to 4.51-4.75 cm. were found in abundance in the cockle fishing ground in front of the bamboo fencing. The reproductive cycle and size at maturation of each gonadal stage as revealed from the histological study revealed the first sexual maturation size of cockles both in males and females was 2.35 cm. This indicated that the dominant cockle size group found in the area was sexually matured and can spawn throughout the year. Similar gonad development patterns were observed in the three areas. The male and female ratio was 1.13:1 Cockle at Tambon Laemyai spawned all year round with two highest peaks in December to March and from Jury to October. High condition indices of 15.03-25.19 occurred throughout the year with the highest peaks in January to February and September to October. Settled larval density can be found during April, June, August and October. Highest settled larval density found throughout the area in front of the bamboo fencing. The growth patterns in the three areas were similar with the lower growth rate in the small cockle appeared in the area behind the bamboo fencing. In the large size cockles, the growth patterns from the three areas were similar. The study revealed the impact of bamboo fencing as coastal defense structure on the blood cockle population at Tambon Laemyai was due to the changes in sediment characteristics seasonally and period of the construction of bamboofencing. The silt and sand fractions showed the increasing trend with the reduction of clay fractions in the sediment. Reduced organic content also apparent. Three important environmental parameters affecting the cockle population were the clay fractions, the organic content and the salinity in the sediment. Changes in sediment characteristics showed profound effect in the long term on the declining cockle population in the area both the matured and juvenile cockles. Measures on the cockle management in the area were proposed in order to sustain the productive cockle bed at Tambon Laemyai Samut Songkharm Province. Fishing regulations were proposed on controlled fishing catch, fishing size for cockle and fishing season. Conserved area for parental stocks and grow out as well as the mangrove reforestation in the area were also recommended to ensure the sustainability of the Tambon Laemyai cockle fishing ground.