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Using Applied Statistics for Accurate Size Classification of the Endangered Tachypleus tridentatus Horseshoe Crab
Rozihan Mohamad 1  
,   Nur Alisa Paul 1  
,   Nor Syuhaida Isa 1  
,   Joni Haryadi Damanhuri 2  
,   Salwa Shahimi 3  
,   Siddhartha Pati 4, 5  
,   Akbar John 6  
,   Bryan Raveen Nelson 7  
 
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1
Department of Aquaculture, Faculty of Agriculture University Putra Malaysia, 43400, Serdang Selangor, Malaysia
2
Research and Development Centre for Aquaculture, Marine and Fisheries Research and Development, Jakarta Selatan 12540, Jakarta, Indonesia
3
Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu
4
Association for Biodiversity Conservation and Research, Devine Colony, Balasore, 756001 Odisha, India
5
Centre of Excellence, Khallikote University, Berhampur, 761008 Ganjam, Odisha, India
6
Institute of Oceanography and Maritime Studies, Kulliyyah of Science, International Islamic University Malaysia, 25200 Kuantan, Pahang, Malaysia
7
Institute of Tropical Biodiversity and Sustainable Development, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu
CORRESPONDING AUTHOR
Bryan Raveen Nelson   

Institute of Tropical Biodiversity and Sustainable Development, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu
Publication date: 2021-04-01
 
J. Ecol. Eng. 2021; 22(4):273–282
 
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ABSTRACT
Horseshoe crabs (Tachypleus tridentatus) are arthropods that restrict their distributions to natal vicinities. Briefly, shore perturbation from boating (Kudat), electric, cyanide and bombing (Kunak) and tourism (Semporna) in Sabah can impair the T. tridentatus growth and produce sexually mature adults with unusual size. The 8-point morphometry of Tachypleus tridentatus from Kudat (Sulu Sea), Kunak and Semporna (Celebes Sea), produces the final output constituting accurate size classification for the species. Meanwhile, T. tridentatus are sexually dimorphic (p = 0.968-0.989), where male T. tridentatus (from Kudat) has prosoma width (27.75 ± 2.68 cm) and weight (1050 ± 610 g) in smaller ranges when compared to the female (33.27 ± 4.68 cm; 3020 ± 1480 g) using the same comparison. In addition, the T. tridentatus populations from Kunak (prosoma width: male = 28.91 ± 1.48 cm, female = 29.44 ± 5.47 cm; weight: male = 800 ± 275 g; female = 2550 ± 155 g) and Semporna (prosoma width: male = 21.73 ± 1.34 cm, female = 24.42 ± 1.36 cm; weight: male = 485 ± 306 g, female = 1320 ± 640 g) differed site-wise. The descriptive statistics (average and standard deviation) relate 7.1-23.0% of T. tridentatus with negative size class. However, the applied statistics using stepwise analysis and regression curve (r2 = 0.566-0.833), relates 30.4% of T. tridentatus with negative size class. Considering weight to produce 100 % T. tridentatus with positive size class, it is biased because some crabs are gravid with eggs and if attained unpaired (male and female), they may have recently fed. Therefore, the prosoma (male), interorbit (female) and telson lengths are identified as most appropriate for the size classification of T. tridentatus. Thus, the findings provide a novel baseline for conservation studies that monitor symmetrical and unusual growth in the T. Tridentatus wild stocks.