The Omani abalone, Haliotis mariae, is the only species of abalone found in Omani waters. Given the rarity of this species and the high price it can fetch on the market (US$ 150 kg-1 dry weight), the wild abalone fishery in the Dhofar region has been regarded as a valuable income source for the past decade. The present study was undertaken set to investigate the mortality of abalone held at the Mirbat Research Center, through bacteriological and histopathological based investigations and challenge tests. Only the adult wild abalone that had been kept for a year in the hatchery, visually, appeared to be clear of disease symptoms. Infected individuals typically were swollen around the mouth, had fluid tinged with blood, bubbles in the intestines, and, very weak adhesive strength. The foot area (muscle) of diseased animals was noticeably very soft and individuals that were seen lying upside down on the bottom of the tank subsequently died. On dissection, the intestinal organs released bubbles and a foul smelling odour. Identification of the isolated bacteria using various identification methods indicated that individuals were infected with Staphylococcus sciuri. Histopathology of infected individuals revealed spongiosis of the tissues with evident bacterial infection. Neither of these histopathological conditions were seen in healthy abalone. The study concludes that the bacterium Staphylococcus sciuri may be the likely cause of abalone mortalities.
Surveys were conducted along the eastern Dhofar coast of Oman to investigate densities and habitat preferences of juvenile Haliotis mariae (< 3 cm SL). Average density was 0.62 m-2 (SD 0.56); average urchin density was 3.4 urchins m-2 (SD 3.9). Relationships between juvenile abalone densities and small boulders (<30 cm in diameter (Ø)) tested significant (p = 0.049), as did those between juvenile abalone and urchin densities (p = 0.031). Selectivity (w) and standardized (B) ratios quantifying the relative probability of selection by juvenile abalone for different categories of resource available were calculated. For the studied area B values tested significantly different for (p = 0.004) the different habitats, urchins, boulders <30 cm, 30> <50 cm, and >50 cm Ø, respectively. B values were highest for urchins (6 times that for small boulders), and for boulders <30 cm Ø (double that for boulders 30> <50 cm Ø). B values for boulder habitats decreased as boulder size increased. Urchin utilisation by juvenile abalone as shelter ranged between geographic areas from a minimum of 15.5% to a maximum of 47.6%. The proportion of total habitat that is preferred by more than 97% of juvenile abalone found, including urchins and boulders < 50 cm Ø, comprises 29% of surveyed substratum. While the role urchins play on wild juvenile H. mariae has not proved vital, it is definitely significant. Although juvenile densities are low and are not currently limited by the availability of suitable habitat, it is crucial to identify and conserve those microhabitats that support recruitment of H. mariae. The abundance of these areas should be among the criteria used in selecting protected conservation areas.
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