This study investigates the stock status of in the northern coastal waters of Sri Lanka. A total of 3967 shrimp were collected from the Jaffna lagoon and adjacent coastal waters during fortnightly field visits to major landing sites from April 2022 to March 2023. The monthly carapace length (CL) frequency data were grouped and analyzed using the TropFishR, LBI, and LB-SPR packages. The results revealed that intensive fishing is occurring in the Jaffna lagoon using non-selective fishing methods such as fyke nets, lagoon seine, kandi, and by trawlers in adjacent coastal waters. Although, a large number of fyke nets (n∼33,000) are operated in Jaffna lagoon compared to lagoon seine nets (n=600) and trawlers (n=275), the trawl catch rate (52.56 ± 14.64 kg boatday) is higher than that of lagoon seines (7.45 ± 3.90 kg boatday) and fyke nets (4.20 ± 3.73 kg boatday; P<0.05). The length at first maturity (L = 27.0 mm) was higher than the length at first capture (S = 18.87 mm), and immature individuals are more prevalent in lagoon catches (97%) than in trawl catches (45%). The von Bertalanffy’s growth parameters, L∞, K, and Ø, were estimated as 52.9 mm, 1.80 yr, and 3.703, respectively. The juveniles in the lagoon suffered higher fishing mortality than the adults in the coastal waters, resulting in very high fishing mortality (7.14 yr) and exploitation rate (E=0.66) in the stock compared to sustainable levels (F=5.00 yr; E=0.46). The LB-SPR model indicated that the relative fishing mortality (F/M= 1.94) is higher than 1, and the spawning potential ratio (SPR= 0.1) is lower than the limit reference point (SPR =0.2). The length-based indicators, P P P and P were projected as 0.20, 0.12, 0.02, and 0.35, respectively. This study confirms the overfishing of in northern Sri Lanka, primarily due to the high fishing pressure on juveniles using non-selective fishing methods. Immediate measures are needed to manage this resource sustainably, ensuring the livelihood of small-scale fishers.

中文翻译：

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幼体死亡率对半沟对虾种群动态的影响：以斯里兰卡为例

本研究调查了斯里兰卡北部沿海水域的种群状况。 2022 年 4 月至 2023 年 3 月，每两周对主要登陆地点进行实地考察，从贾夫纳泻湖和邻近沿海水域收集了总共 3967 只虾。使用 TropFishR、LBI 和LB-SPR 封装。结果显示，贾夫纳泻湖正在使用非选择性捕捞方法（如菲克网、泻湖围网、康迪）以及邻近沿海水域的拖网渔船进行密集捕捞。尽管与泻湖围网（n = 600）和拖网渔船（n = 275）相比，贾夫纳泻湖使用了大量的fyke网（n〜33,000），但拖网捕获率（52.56 ± 14.64公斤船日）高于泻湖围网（7.45 ± 3.90 kg 船日）和 fyke 网（4.20 ± 3.73 kg 船日；P<0.05）。首次成熟时的长度（L = 27.0 毫米）高于首次捕获时的长度（S = 18.87 毫米），且未成熟个体在泻湖渔获量（97%）中比拖网渔获量（45%）更常见。 von Bertalanffy 的生长参数 L∞、K 和 Ø 估计分别为 52.9 mm、1.80 年和 3.703。泻湖中的幼鱼的捕捞死亡率高于沿海水域的成鱼，导致与可持续水平相比（F=5.00 年；E= 0.46）。 LB-SPR模型表明，相对捕捞死亡率（F/M=1.94）高于1，产卵潜力比（SPR=0.1）低于极限参考点（SPR=0.2）。基于长度的指标 PPP 和 P 预计分别为 0.20、0.12、0.02 和 0.35。这项研究证实了斯里兰卡北部的过度捕捞，主要是由于使用非选择性捕捞方法对幼鱼造成的巨大捕捞压力造成的。需要立即采取措施可持续地管理这一资源，确保小规模渔民的生计。