Trochus (Trochus niloticus) size and abundance in Tongareva Lagoon, Cook Islands

Trochus (Trochus niloticus) were first introduced to the Cook Islands in 1957 from Fiji. Once the original population of 280 shells were well established in Aitutaki, trochus was introduced to the rest of the Cook Islands in the 1980s. The main purpose of the introduction was to develop commercially harvestable stocks to assist local economies. Four hundred and forty trochus were introduced to Tongareva (also known as Penrhyn) over 20 years ago in 1985 from the Aitutaki population (Sims 1988). Introduced populations usually reach commercially exploitable levels within 20 to 25 years, therefore, the trochus population on Tongareva should nearly be ready for harvest (Bertram 1998).
A 1996 survey conducted in Tongareva by the Cook Islands Ministry of Marine Resources (MMR) found that trochus were present in the western section of Tongareva Lagoon with the highest densities found at two sites: Patukiri and Seniseni (Ponia et al. 1997). The survey detailed in this report was designed to re-assess the density of trochus in Tongareva Lagoon, 10 years after the last survey and 20 years after the original introduction.
The specific aims of the survey were to:
• assess the size distribution of trochus,
• assess trochus abundance and density in the western section of the lagoon, and
• estimate the number of trochus that could be sustainably harvested from the surveyed area of the lagoon.

尼罗马蹄螺（Trochus niloticus）于1957年首次从斐济引入库克群岛。当初始的280只个体在艾图塔基成功定殖后，尼罗马蹄螺于20世纪80年代被引入库克群岛其余区域。此次引种的核心目标为培育可商业捕捞的种群资源，以助力当地经济发展。1985年，科研人员从艾图塔基种群中选取440只尼罗马蹄螺引入通加雷瓦（又称彭林岛，Tongareva/Penrhyn），该引种操作距今已逾20年（Sims, 1988）。通常引种种群可在20至25年内达到可商业开发的种群规模，因此通加雷瓦的尼罗马蹄螺种群已近乎达到可捕捞标准（Bertram, 1998）。

1996年，库克群岛海洋资源部（Cook Islands Ministry of Marine Resources, MMR）在通加雷瓦开展了一项调查，结果显示尼罗马蹄螺分布于通加雷瓦潟湖的西部区域，其中帕图基里（Patukiri）与塞尼塞尼（Seniseni）两个站点的种群密度最高（Ponia et al., 1997）。本报告所详述的本次调查，旨在对上一次调查结束10年、初始引种20年后的通加雷瓦潟湖尼罗马蹄螺种群密度进行重新评估。

本次调查的具体目标如下：
• 评估尼罗马蹄螺的个体大小分布情况；
• 评估潟湖西部区域的尼罗马蹄螺种群丰度与密度；
• 估算潟湖调查区域内可可持续捕捞的尼罗马蹄螺种群数量。