Monitoring densities of the giant clam Tridacna maxima in the Lakshadweep Archipelago

Abstract

Giant clams are endangered in many parts of their Indo-Pacific range owing to adult specific overharvesting that threatens recruitment, a demographic parameter exhibiting high sensitivity to environmental disturbances and adult densities among tridacnids. Lakshadweep reefs are not subjected to commercial giant clam fishery, and population assessment has not been carried out in these waters so far. We monitored the small giant clam Tridacna maxima populations in confined waters of 12 reefs in Lakshadweep Archipelago during 2005 -2007 using a systematic line transect based distance sampling framework. Overall T. maxima density in the Archipelago was estimated at 141.2/ha (95% CL 118.2 -168.7) in 2005 and 122.7/ha (103.60 -145.37) in 2006. Populations showed wide variation in densities and relative proportions of different age-classes between reefs. While Agatti, Bitra and Chetlat lagoons harboured high clam densities, Amini harboured the most impoverished population. Data simulation showed that total clam count along transects of 100 m length × 2-5 m strip width, in a minimum of 140 replicates, stratified by area among lagoons, would provide a viable monitoring index for rapid assessments of T. maxima in Lakshadweep. Compared to unbiased absolute abundance estimates, this monitoring index could be achieved more easily, without much compromise on accuracy and precision, necessary for meaningful spatio-temporal comparisons.

Distribution and abundance of the giant clams (Cardiidae: Bivalvia) on Kei Islands, Maluku, Indonesia

“…Giant clam population density in Kei Islands was lower than in some other regions, for example 0.53 individuals/m 2 was reported in North Sulawesi Arbi 2010 (Rees et al 2003), and 0.001-0.03 individuals/m 2in the Indian Ocean and Southeast Asia (Besker 1991;Apte et al 2010;Ramah et al 2018). The difference in population density might result from variations in substrate conditions, exploitation pressures and whether the area is protected or not.…”

Effect of a fishing closure on Chamelea gallina stocks along the Turkish coast

“…As widely recognized, recruitment itself is a very complex and little-known process. Recruitment is related to climate and weather conditions, constant changes immediately after the breeding period in the hydrodynamics of the region, reproductive potential, suitability of substrate, natural predations on adult and juvenile individuals, and competition with other species in the food chain (Osman & Whitlatch, 1995; Eckman, 1996; Apte et al ., 2010). To be able to assess this process successfully, it is necessary to understand and analyse all the elements in this complex system.…”

Best Management Strategies for Sustainable Giant Clam Fishery in French Polynesia Islands: Answers from a Spatial Modeling Approach

“…Recruitment is dependent on a wide array of processes including climate and weather forcing, local hydrodynamics immediately after spawning periods, reproduction potential (according to sizes and aggregations, which can be modified by fishing), substrate suitability [57], larval dispersal [23], [58], natural predation on larvae and adults [23], [58]; and competition with other species [23], [58]. Perfect analytical understanding of all these parameters and processes is unlikely to be achieved for most sites without extensive (and prohibitive) fieldwork.…”