Biodiversity and ecology of elasmobranchs in the waters off northeastern Sabah
This study examined the biodiversity and ecology (in the fields of species distribution, length-weight relationship, fecundity and diet) of elasmobranchs (sharks and batoids) in the waters off northeastern Sabah (included the waters off east Kudat Division and Sandakan Division). Samplings were car...
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| Format: | Thesis |
| Language: | English |
| Published: |
2011
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| Subjects: | |
| Online Access: | https://eprints.ums.edu.my/id/eprint/7531/1/mt0000000250.pdf |
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| Summary: | This study examined the biodiversity and ecology (in the fields of species distribution, length-weight relationship, fecundity and diet) of elasmobranchs (sharks and batoids) in the waters off northeastern Sabah (included the waters off
east Kudat Division and Sandakan Division). Samplings were carried out from April 2009 to March 2010 on-board a commercial trawler operating in the study area. Overall, 340 specimens of elasmobranchs were collected and identified as
belonging to 22 species (10 shark species and 12 batoid species). The distribution of species was known based on the locations of specimens caught. These locations were divided to seven zones, in which the position of these seven zones was distinguished to north (zone 1 and 2), centre (zone 3, 4 and 5) and south (zone 6 and 7) of study area. The species was supposed as either abundant or rare species in the study area. The different elasmobranch species were caught with different catch per unit effort (CPU E) at different locations, such as Himantura gerrardi was caught with high CPUE at the north and centre, Neotrygon kuhlii and Dasyatis zugei were caught with high CPUE at the south, Narcine prodorsalis and Narcine timlei restrictedly at the north of study area were caught with high CPUE at there, and so
on. The five most abundant species (H gerrardi, 28.2%; N. kuhlii, 12.9%; Rhizoprionodon acutus, 11.8%; D zugei, 9.4% and Sphyrna lewini, 6.2%) owned more than 20 individual species to meet the criteria of analysing length-weight
relationship. All these five species exhibited positive allometric growth. Only two species (N. kuhlii and D zugel) were caught with pregnant female to investigate fecundity. The fecundity of N. kuhlii is one pup and that of D. zugei is one to two pups. The stomach contents of 14 species were analysed by using the quantitative diet analysis method to find out their main diet. It was found out that the species from the same family preyed on the same important food items. The marine resources partitioned by different elasmobranch species in the study area were overviewed as shrimp resource which was mostly taken by four dasyatid stingrays (H gerrardi, Himantura uamacoides, N. kuhlii and D. zugel) and two hemiscylliid sharks (Chiloscyllium plagiosum and Chiloscyllium punctatum). Fish resource was
mostly taken by three carcharhinid sharks (Carcharhinus dussumieri, carcharhinus sorrah and R. acutus), a scyliorhinid shark (Atelomycterus marmoratus) and a
sphyrnid shark (S. lewim). Octopus resource was mostly taken by a hemigaleid shark (Hemigaleus microstoma), and polychaeta resource was mostly taken by two narcinid electric rays (N. prodorsalis and N. timlei). |
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