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From Descriptive to Accurate Horseshoe Crab Size Variations in Wild Populations

Chan Li Yu, John Akbar, Shahimi Salwa, Meilana Lusita, Lian Chong Ju, Hoe Loh Ing, Ho Wong Chee, Kumaran Jayaraj Vijaya, Pati Siddhartha, Nelson Bryan Raveen

Journal of Ecological Engineering

2022

Vol. 23, nr 12

273--284

Horseshoe crabs have survived until Holocene, but their persistence beyond the Anthropocene is challenged by drastic environment changes that entail impoverishments and the resultant unusual growth sizes. Previously, allometry via morphometric ratio was introduced to classify horseshoe crabs into normal-abnormal growth. However, the descriptive size and weight analysis indicated a considerable portion of Tachypleus gigas with normal allometry. This error was caused by the median sorting of values. Therefore, the same data was treated with correlation before generating a linear equation. By being sexual dimorphs, these arthropods actually have gender-specific morphology indicators which could generate a functional allometry. Since the assessed arthropods were mature, the 19 % yield of smaller female T. gigas was possibly due to degradation effects from poor diets or stress. Yet, for this population, an added risk was female-only harvest. Perhaps, close sizing to male counterparts could be perceived a survival strategy by the female T. gigas. More evidence is needed to strengthen this opinion but for now, this assessment method is novel for accurate allometry assessments in the species with sexual dimorphism. Overall, capture fisheries could have negative impacts and when made severe by sex-specific harvest, the unaccounted practices could collapse sustaining populations.

Using Applied Statistics for Accurate Size Classification of the Endangered Tachypleus tridentatus Horseshoe Crab

Mohamed Rozihan, Paul Nur Alisa, Isa Nor Syuhaida, Damanhuri Joni Haryadi, Shahimi Salwa, Pati Siddhartha, John Akbar, Nelson Bryan Raveen

Journal of Ecological Engineering

2021

Vol. 22, nr 4

273--282

The Tachypleus tridentatus (Chelicerata: Xiphosura) is an arthropod that usually displays high site fidelity by restricting its distribution 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.

Predicting Tachypleus gigas Spawning Distribution with Climate Change in Northeast Coast of India

Pati Siddhartha, Shahimi Salwa, Nandi Debabrata, Sarkar Tanmay, Acharya Satya N., Sheikh Hassan I., Acharya Dipti Kanta, Choudhury Tanupriya, Akbar John B., Nelson Bryan R., Dash Bisnu Prasad, Edinur Hisham Atan

Journal of Ecological Engineering

2021

Vol. 22, nr 3

211--219

Species distribution models are used to predict ideal grounds, species range, and spatial shifts in an ecology over a span of time. With an aim to use Maximum entropy model (MaxEnt), presence records and pseudo-absence points are used to predict the Tachypleus gigas spawning activity for 2030 and 2050 in northeast India. The bearings of sixty T. gigas spawning grounds identified in 2018 were inserted into ArcGIS v.10.1. Meanwhile, 19 environment variables were inserted into MaxEnt v. 3.3.3, before the model performance was tested using receiver operational characteristics and area under curve (AUC). With an AUC of 0.978,85% was achieved for isothermality (bio3) and 74% for temperature (x̄= average) of the wettest quarter (bio8), all of which were inserted into ArcGIS to produce spatial maps. Although we learnt that T. gigas are still spawning in Odisha in 2030 and 2050, their distribution range is predicted to shrink due to the coastal morphology change. The climate conditions in Odisha revolve with the monsoon, summer and winter seasons from which, temperature variations do not only influence the annual absence/presence of spawning adults but also, the survival of juveniles in natal beaches. The use of MaxEnt offers novelty to predict population sustainability of arthropods characterized by oviparous spawning (horseshoe crabs, turtles, terrapins and crocodiles) through which, the government of India can take advantage of the present data to initiate the coastal rehabilitation measures to preserve their spawning grounds.