Boubyan Island is essentially undeveloped and the largest island in the northwest of the Arabian Gulf. Small otter trawls were used to sample 12 stations circling Boubyan Island each month, except November, from February 2004 through February 2005. All trawl catches, with the exception of large Skates and Rays, were returned to the laboratory for identification and processing. The total number of individuals captured by all 431 five-minute trawl tows was 81659. Species caught included 31 Crustaceans, 7 Mollusks, 5 Echinoderms, 1 Tunicate, 90 fishes, and 1 Sea Snake. The monthly total occurred species ranged from 27 to 78 and was high in the summer months (June to August) and low in the winter (December to February). Species richness and Shannon’s diversity showed a similar seasonal change pattern with a range of 3.41–7.93 and 0.80–2.58, respectively. The seasonal changes of the number of species, abundance, species richness and diversity were probably caused by the migration and reproductive circle of the organisms. However, the variations for all these indices among different stations were relatively small and suggested a similar environmental conditions for the areas around Boubyan Island.
Boubyan Island is located in the Arabian Gulf's extreme northwest corner. It is essentially undeveloped, and with an area of 942 km2, Boubyan Island offers offers significant potential for development. From a fisheries perspective, Boubyan Island's waters occupy a transition zone between the Gulf's hyper-salinities and the fresh waters of Shatt Al-Arab and Khor Az Zubair (Shatt Al-Basrah) (Fig. 1).
Boubyan Island has tidal creeks, marshes, extensive mudflats and oyster reefs. The tidal creeks are deep, often exceeding 25 m in depth and reach a maximum of 33 m at low tide. These conditions easily qualify Boubyan Island as an area of special scientific interest. Published information on Boubyan Island and studies of intertidal mudflats in Kuwait Bay indicate that the shallow waters surrounding Boubyan Island are likely to be some of the most biologically productive areas in the Gulf (Bishop et al., 2002). This area serves as an important spawning and nursery ground for penaeid Shrimps (Al-Attar, 1984; Bishop and Khan, 1999). It is also an important spawning and nursery area for many fin-fish species, such as Silver Pomfret (Pampus argenteus) and Mullet (Liza klunzingeri). Furthermore, the waters around the island, including the Iraqi waters, host some indigenous species such as the paracalanid Copepod Bestiolina arabica (Ali et al., 2007), the acartiid Copepod Acartia faoensis (Khalaf, 1991; Ali et al., 2009), and the liprotintinnid Leprotintinnus bubiyanicus (Skriyabin and Al-Yamani, 2006).
The significance of estuaries, bays, and inshore waters in terms of productivity and their importance to life history stages of fish and shrimp are well-documented (Qasim, 1973; Blaber and Blaber, 1980; Al-Attar 1984; Bennett, 1989; Blaber and Milton, 1990; Potter et al., 1990; Bishop et al., 2001). These water masses almost account for 60% of the world fish catch, which is reported to be fished from these coastal ecosystems (Lie, 1983). Among the shellfish hosted by these habitats and of high demands are Penaeid Shrimp, as this family is distributed in Indo-Pacific region including Arabian Gulf as well as Mediterranean (Sealifebase, 2018). Two species from this family, the Jinga Shrimp Metapenaeus affinis and Kiddi Shrimp Parapenaeopsis stylifera are the second and third most important Shrimp species respectively in Kuwait after the Green Tiger Prawn Penaeus semisulcatus (van Zalinge et al., 1981; Bishop et al., 2001). These two species are regularly fished in Kuwait and the Arabian Gulf (Bishop, 1989; Xu et al., 1995; Mohammed et al., 1998; Bishop and Khan, 1999; Ye et al., 1999; Bishop et al., 2006; Bishop et al., 2008)
The objective of this study was to characterize the diversity and abundance of coastal marine species around Boubyan Island, using trawl survey for a 13 month period starting in February 2004.
Trawling activities were conducted at twelve sampling stations (St01 to St12) (Fig. 2). Sampling at each station consisted of three separate trawl tows in depths of 1 m, 2 m, and a companion trawl tow in deeper waters. Trawling activities were conducted from February 2004 to February 2005; no sampling took place during the month of November 2004 due to persistent high winds. During the 12 months of sampling, only one tow was not completed: i.e. 2 m depth at station St05 in May.
A speed boat of 36 feet powered by two 186.5-kW (250 hp) engines was used in trawling. Engine speeds of the boat during trawling operations varied from 600 to 1200 rpm, depending on wind and currents. Boat speed varied from 2.1 to 6.1 km h−1, but generally averaged 4.1 km h−1. Each trawl interval was 5 minutes. Swept width was estimated by observing the distance between the otter doors while trawling. A 5 m chain-line length otter trawl of 34-mm stretch mesh with a 10-mm cod end of stretch mesh swept a width of 3 m and covered from 1012 ± 230 m2 (ranging from 225 to 1675 m2) during a timed five-minute tow.
J' is constrained between 0 and 1. The less evenness in communities between the species (and the presence of a dominant species), the lower J' is, and vice versa. S is the total number of species.
To examine the differences of all calculated indexes between the seasons, investigated periods were further divided as warm and cold, based on water temperature. Months with water temperature more than 23 °C (April through October) were classified as warm seasons; those with water temperature less than 23 °C (November through March) were cold seasons. The differences between warm and cold seasons for all total species, total organisms, species richness, diversity and evenness were tested for significances using t-tests.
Results and discussion
A total of 431 five-minute trawl tows swept a total of 436236 m2 of bottom habitat (Table 1). Monthly trawl tows swept an area ranging from 32125 m2 in December 2004 to 39850 m2 in March 2004. Tidal currents and tow direction accounted for the monthly differences.
Species caught during the trawl survey included 32 Crustaceans, 9 Mollusks, 5 Echinoderms, 1 Tunicate, 90 fishes and 1 Sea Snake, with the total catch amounted for 81659 individual animal (Table 2).
Temporal marine biodiversity indices of the waters around Boubyan Island are presented in Table 3. The total species found among the sampling months show a big difference and ranged from 27 in January 2005 to 78 in June 2004, with an average of 51. In summer (June to August), the total species number is much higher than that in the winter (December to February). The total organisms were also higher in the summer months and ranged from 570 in February 2004 to 16580 in June 2004, with an average of 6805. Species richness is highest in summer months and lowest in the winter months with a range of 3.41–7.93. Shannon Diversity is higher in spring and summer months, and lower in fall and winter with a range of 0.80–2.58. However, the Shannon diversity in February 2004 is the highest, and almost lowest in February 2005, and this may indicate the year to year variation in diversity. Evenness is relatively higher in the summer months, and lower in fall and winter. However, evenness is highest in February and March 2004, indicating that different species are more evenly distributed in these two months, which explain why diversity was the highest in these two months.
Spatial marine biodiversity indices of the waters around Boubyan Island are presented in Table 4. The total species found among the sampling stations are similar and ranged from 48 in station St02 to 70 in station St11, with an average of 58. The variation in total individuals among stations is relatively larger and ranged from 3270 at station St03 to 13291 at station St09, with an average of 6805. Species richness among stations is also similar, but relatively higher at stations St01, St03, St11 and St12 (more than 7). The high values at these stations may be due to the fact that these stations are in the open water areas and could receive more species than the inner stations. However, station St02 is in the same area with those of higher species richness, but had low values, for example 48 total number of species and lowest species richness of 5.55, and that could be due to coast guard boat trafficking activity and gillnet fishing by people living in the chalets in the western side of the khor (personal observation). Shannon Diversity is also highest in the areas with highest species richness, but lowest in the inland station St07. Evenness values at most of the stations are similar and around 0.5, which means that species distribution are similar for the different areas.
The results from t-test indicated that there were significant differences between warm and cold seasons for total species, total organism and species richness. All total species, total organism and species richness were significantly higher in the warm season than that of the cold season (Table 5). There were no significant differences between warm and cold season for Shannon Diversity and evenness.
Results of trawling activities in 2004/05 have shown the waters of Boubyan Island to be some of the most productive areas in Kuwait and possibly the entire Gulf region. The area provides rich nursery habitat for a number of commercial and non-commercial species, the latter of which are of indirect commercial importance. The total reported species is 138 with 90 species of fin fishes. The total fin fish species is higher than 80 overall fish species reported by Chen et al. (2009) in Kuwait Bay (Fig. 1). Our estimated average diversity is 1.96, which is also higher than the overall diversity (1.48) from Chen et al. (2009), indicating that this area is a more diverse area than Kuwait Bay. Meanwhile, the Kuwait’s second and third most important Shrimp species Metapenaeus affinis and Parapenaeopsis stylifera dominated numerically overall, in spring and autumn season in the trawl survey. The important commercial fish species such as Zubaidy (Pampus argenteus) and Suboor (Tenualosa ilisha) frequently occurred in the gill net surveys around Boubyan Island (Bishop et al., 2006). Considering all the above mentioned, Boubyan Island and its surrounding waters can be summed up from three perspectives: 1) it is a nursery area of major importance for renewable resources of commercial species; 2) it is an area of special scientific interest; and 3) it is a biologically diverse area to maintain the marine diversity for the region. Therefore, the waters around Boubyan should be protected from all trawling and gillnetting activities. The most important “enhancement” policy that could be followed is to prevent any man-made degradation of the environment, particularly in the intertidal zone.
Of all Kuwait's marine environment, Boubyan Island remains relatively pristine, and every effort should be made to maintain these environments in as natural state as possible, to benefit the nursery fish and shrimps, the specific interested species and the diversity of the region.
The water around Bouyan Island is a diverse area with more caught species of fishes, Crustaceans and Mollusks than nearby Kuwait Bay. The biodiversity of this area showed more temporal variations than that in the spatial scale. Two of Kuwait’s important Shrimp species, Metapenaeus affinis and Parapenaeopsis stylifera, dominated numerically during spring and autumn seasons in trawl survey. Important commercial fish species, such as Pampus argenteus and Tenualosa ilisha, frequently occurred in the gill net survey around Boubyan Island. All these factors made Boubyan Island and its surrounding waters an important nursery area with special scientific interest and high biodiversity. Therefore, this area should be protected from both fishing and any man-made degradation of the environment in order to benefit the nursery fish and shrimp, the specific interested species and the diversity of the region.