Harvesting the Beach Clam Tivela mactroides: Short‐ and Long‐Term Dynamics

Abstract

Small‐scale fisheries are frequently overlooked for research and management, and their social and environmental impacts are often overlooked as well, preventing the implementation of appropriate actions for their sustainability. Additionally, the dynamics of beach clam fisheries and their importance for local communities are not well understood. A study on the population biology of the clam Tivela mactroides in Caraguatatuba Bay, southeastern Brazil, revealed intense harvesting of this resource by both residents and tourists. To assess the extent and dynamics of clamming, the number of harvesters was recorded during the course of the day in vacation and nonvacation periods throughout 2003–2005 and 2007–2008; the number of other beach users, weather conditions, and tide height were also recorded. The overall amount of clams harvested was estimated based on censuses of clammers and interviews to calculate the amount of clams harvested per collecting event. The intensity and dynamics of the harvesting activity varied on all the temporal scales evaluated. The estimated amount of clams harvested per year decreased from the first (24.6 kg/year) to the second (8.8 kg/year) group of sampling years, presumably due to clam mass‐mortality events and smaller shell sizes in 2007–2008, although clam abundance increased enormously. Vacation periods (presence of tourists) influenced the number of harvesters and the daily dynamics of clamming activity, although this relationship was only evident during 2003–2004. The number of harvesters increased with the number of tourists, except in periods of very high tourist activity, when harvesting decreased. Clamming was more widespread during the day under high tourist activity but during nonvacation times was concentrated in morning low‐tide periods. Weather had a partial influence on clamming, with harvesters absent only during intense rain occasions. The understanding of the dynamics of this Tivela mactroides fishery highlights key points for planning and implementing management measures, which will involve continuous monitoring of stocks, harvesting, and food safety. Received February 4, 2014; accepted December 21, 2014

Frequency, Magnitude, and Possible Causes of Stranding and Mass-Mortality Events of the Beach Clam Tivela mactroides (Bivalvia: Veneridae)

“…It is important to understand these high-mortality events, since large numbers of stranded clams may cause socioeconomic and environmental problems for the local residents. Harvesting of this species decreased by one-third during high-mortality periods [ 34 ]. The strong unpleasant odor of the dead clams accumulated on the sand affects tourism and raises public-health concerns, because the clams are decomposing along the most intensively used part of the beach.…”

“…In addition, in view of the high importance of sandy-beach clams in recreational and artisanal fisheries of developing countries in South America, mass-mortality events of these organisms can be socioeconomically significant [ 18 , 22 , 24 – 26 ]. The trigonal clam Tivela mactroides is an important sandy-beach species, both economically and ecologically [ 20 , 27 – 34 ]. It has a wide distribution from Venezuela to Brazil (Pará to Santa Catarina states) and in the West Indies [ 35 ].…”

“…Also for this population, an assessment of harvesting intensity showed that under ordinary conditions, the amount of clams harvested yearly is about 25 tons. The same study showed that the mass-mortality events are also socioeconomically important, since a decrease in harvesting was attributed partly to these events [ 34 ]. The authors suggested that the foul odor and unpleasant sight caused by the stranded and dead clams were responsible for a decrease in recreational use of the beaches in Caraguatatuba Bay.…”

Variação morfométrica de Tivela mactroides (Bivalvia, Veneridae) no litoral Norte-Nordeste do Brasil

“…Vários estudos têm sido realizados sobre Tivela mactroides no Brasil envolvendo a morfologia (Denadai et al, 2006), distribuição (Denadai et al, 2005;Medeiros et al, 2014;Rocha & Matthews-Cascon, 2015), dinâmica populacional (Denadai et al, 2015c), crescimento relativo (Turra et al, 2018), aspectos ecológicos (Turra et al, 2014), incluindo análise de predação multiespecífica (Turra et al, 2015; Batalla 2017), mortalidade (Turra et al, 2016a) e reprodução de indivíduos (Denadai et al, 2015b), bem como pesquisas voltadas para a pesca (Denadai et al, 2015a) e aspectos socioeconômicos (Turra et al, 2016b).…”