Peel Joanne R, Mandujano María del Carmen
Rev Biol Trop. 2014 Dec;62(4):1343-52. doi: 10.15517/rbt.v62i4.13389.
The queen conch Strombus gigas represents one of the most important fishery resources of the Caribbean but heavy fishing pressure has led to the depletion of stocks throughout the region, causing the inclusion of this species into CITES Appendix II and IUCN's Red-List. In Mexico, the queen conch is managed through a minimum fishing size of 200 mm shell length and a fishing quota which usually represents 50% of the adult biomass. The objectives of this study were to determine the intrinsic population growth rate of the queen conch population of Xel-Ha, Quintana Roo, Mexico, and to assess the effects of a regulated fishing impact, simulating the extraction of 50% adult biomass on the population density. We used three different minimum size criteria to demonstrate the effects of minimum catch size on the population density and discuss biological implications. Demographic data was obtained through capture-mark-recapture sampling, collecting all animals encountered during three hours, by three divers, at four different sampling sites of the Xel-Ha inlet. The conch population was sampled each month between 2005 and 2006, and bimonthly between 2006 and 2011, tagging a total of 8,292 animals. Shell length and lip thickness were determined for each individual. The average shell length for conch with formed lip in Xel-Ha was 209.39 ± 14.18 mm and the median 210 mm. Half of the sampled conch with lip ranged between 200 mm and 219 mm shell length. Assuming that the presence of the lip is an indicator for sexual maturity, it can be concluded that many animals may form their lip at greater shell lengths than 200 mm and ought to be considered immature. Estimation of relative adult abundance and densities varied greatly depending on the criteria employed for adult classification. When using a minimum fishing size of 200 mm shell length, between 26.2% and up to 54.8% of the population qualified as adults, which represented a simulated fishing impact of almost one third of the population. When conch extraction was simulated using a classification criteria based on lip thickness, it had a much smaller impact on the population density. We concluded that the best management strategy for S. gigas is a minimum fishing size based on a lip thickness, since it has lower impact on the population density, and given that selective fishing pressure based on size may lead to the appearance of small adult individuals with reduced fecundity. Furthermore, based on the reproductive biology and the results of the simulated fishing, we suggest a minimum lip thickness of ≥ 15 mm, which ensures the protection of reproductive stages, reduces the risk of overfishing, leading to non-viable density reduction.
女王凤凰螺（Strombus gigas）是加勒比地区最重要的渔业资源之一，但过度捕捞压力导致该地区的种群数量减少，致使该物种被列入《濒危野生动植物种国际贸易公约》附录二以及世界自然保护联盟的红色名录。在墨西哥，女王凤凰螺的管理方式为规定最小捕捞尺寸为壳长200毫米，并设定捕捞配额，该配额通常占成年生物量的50%。本研究的目的是确定墨西哥金塔纳罗奥州谢哈地区女王凤凰螺种群的内在种群增长率，并评估模拟抽取50%成年生物量的规范捕捞影响对种群密度的作用。我们使用了三种不同的最小尺寸标准来证明最小捕捞尺寸对种群密度的影响，并讨论其生物学意义。通过标记重捕抽样获取人口统计学数据，由三名潜水员在谢哈河口的四个不同采样点，在三小时内收集所有遇到的动物。2005年至2006年期间每月对凤凰螺种群进行采样，2006年至2011年期间每两个月采样一次，总共标记了8292只动物。测定了每只个体的壳长和唇厚度。谢哈地区有唇的凤凰螺平均壳长为209.39±14.18毫米，中位数为210毫米。一半有唇的采样凤凰螺壳长在200毫米至219毫米之间。假设唇的出现是性成熟的指标，可以得出结论，许多动物可能在壳长大于200毫米时形成唇，应被视为未成熟。根据用于成年分类的标准不同，相对成年丰度和密度的估计差异很大。当使用壳长200毫米的最小捕捞尺寸时，26.2%至54.8%的种群符合成年标准，这意味着模拟捕捞影响了近三分之一的种群。当使用基于唇厚度的分类标准模拟凤凰螺捕捞时，对种群密度的影响要小得多。我们得出结论，对于女王凤凰螺来说，最佳管理策略是基于唇厚度的最小捕捞尺寸，因为它对种群密度的影响较小，而且基于尺寸的选择性捕捞压力可能会导致出现繁殖力降低的小型成年个体。此外，根据生殖生物学和模拟捕捞结果，我们建议最小唇厚度≥15毫米，这既能确保对繁殖阶段的保护，降低过度捕捞的风险，又能避免导致不可持续的密度降低。
