Chart Datum and Bathymetry Correction To Support Managing Coral Grouper In Lepar And Pongok Island Waters, South Bangka Regency

Abstract

Corrected bathimetry data is highly required to improve the quality of sea floor map, for a range of purposes including coastal environmental monitoring and management. This research was aimed to know chart datum values used for correctting bathymetry data at Bar-cheeked coral trout grouper (Plectropomus maculates) fishing ground in Lepar and Pongok Island waters 02o57’00”S and 106o50’00”E and 02o53’00”S and 107o03’00”E, respectively, South Bangka Regency, Indonesia. The study was carried out from November 2016 to October 2017, tidal data used for 15 days from September 16–30, 2017 using simple random sampling technique with the total of 845 points of measurements. To calculate tyde harmonic constituents values this study employed admiralty method resulting 10 major components. Results of this research indicated that harmonic coefficient values of M2, M2, S2, N2, K1, O1, M4, MS4, K2, and P1, were 0.0345 m, 0.0608 m, 0.0276 m, 0.4262 m, 0.2060 m, 0.0119 m, 0.0082 m, 0.0164 m, and 0.1406 m, respectively. Values of mean sea level, chart datum, and F, were 0.9620 m, 0.0500 m, and 0.0664 m, respectively, with diurnal type (F= 6.64). Correcting bathymetry values of surveyed location results a deviation about 1.2 m in depth. The calculated chart datum as well as corrected bathymetry provides information that can be used as vertical refrerence datum for generating sea floor map for determining the fishing ground area of bar-cheeked coral trout grouper. Fishing depth usually ranges between 4.2 and 40.8 m. Average water depth in the fishing ground ranged from 14.7 to 22.5 m.

Fishery potencies as environmental services of Pongok Islands, Bangka Belitung Province

“…The average catch of each commodity and fishing ground for grouper, squid, and mackerel kingfish is presented in Table 1 as follows. Research regarding fishing trap use on Pongok Island was conducted in 2013 [44] and 2018 [53]. This fishing gear is still used by the local people due to reasons like being easy to operate and monitor, not needing any baits, and catching specific fish with high prices in life conditions.…”

“…However, in the long-term, catching this fish also should take into account for the fish sustainability in both biological and environmental aspects like catch per unit efforts (CPUE) and spawning as well as feeding ground in coral reefs. Another consideration also has been described by Adibrata et al [54] to ensure the longterm management of the bar-cheeked coral trout grouper fishery by giving critical information to both fishery managers and fishermen. Unfortunately, this fish had been a premium fish product for years, but due to a forbidden transshipment policy issued by The Ministry of Marine and Fishery Affairs of Indonesia, the price down sharply of its life commodity.…”

“…However, practices of those fishery activities need more attention from different perspectives to be sustainable in the future. Sudirman et al [53] have recommended that fishery activities in Pongok Island and its surrounding waters be through sustainable management techniques, including a cautious approach, safeguarding spawning sites, employing marine protected areas, and regulating fishing attempts. These measures aim to minimize the burden on affected species and encourage sustainable fishing techniques.…”

Minimum legal size of commercially important groupers in the Coral Triangle Sulawesi Sea, Indonesia

“…Habitat is also an important factor for these grouper species [11], so that habitat degradation can also affect abundance and recruitment [12] and lead to grouper overfishing [13]. Overfishing can result in a reduction of the reproductive capacity, the mean size of individuals in the population, and intra-specific genetic variation [14,15]. Current fisheries management policies have failed to prevent overfishing, especially capture during the spawning season, with the result that grouper stock abundance has declined.…”