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Abstract Spinner dolphin (Stenella longirostris) is considered one of the most worldwide distributed dolphins where they geographically distributed in tropical and subtropical areas. Although, Egyptian coasts of the Red Sea represent one of the most common resting areas for spinner dolphin’s population, knowledge about their population structure, occurrence, and biometrics is not clear especially. Accordingly, the aim of this study is to investigate the population structure of spinner dolphins at Satayah reef in relation to some environmental variables. In addition, the study introduces a preliminary perception on the impacts of dolphin watching activities in the study area. Moreover, applying a laser photogrammetry technique to describe the morphological characteristics, allometric growth, growth rates, and sexual dimorphism of the studied population. Finally, the study introduces, for the first time, a molecular characterization of Stenella longirostris population at Satayah reef. Population structure; including abundance, group age, and occurrence of spinner dolphin, environmental variables; including sea surface temperature, wind speed, wind direction, sea level height, and cloud cover, and tourism activities; including number of boats and zodiacs were monitored at Satayah Reef during October 2014 to April 2016. For biometric study, morphometric data (Total length (TL); tip of upper jaw to apex of the melon (M1); tip of upper jaw to gape of mouth (M2); tip of upper jaw to center of eye (E); tip of upper jaw to anterior insertion of flipper (P); tip of upper jaw to tip of dorsal fin (DF); max girth (MG); axilla girth (AG); dorsal fin base length (DFB) and dorsal fin height (DFH); pectoral fin width (PB) and pectoral fin length (PL)) were collected using paired-laser photogrammetry English Summary 170 technique from a sample of 64 spinner dolphins composed of 19 adult females, 34 adult males and 11 calves collected from April 2015 until April 2016. Furthermore, the genetic identity of the spinner dolphin samples collected during 28 February until 28 April 2016 by using biopsy pole system for the bow-riding dolphins at the study area were resolved using COI molecular phylotyping technique. Results showed that, out of 84 survey days of the whole study period in Satayah Reef, spinner dolphins were sighted 78 days (93 % of the total survey days). However, the population abundance fluctuated non-significantly with months and seasons (one-way ANOVA, P > 0.05). In general, the overall mean of the group size in the study area was 57.4 ± 25.09 individuals. Calves were observed through all the study period. The birth season of spinner dolphin population in Satayah reef was estimated. Mean number of pregnant females showed a seasonal pattern, they start to appear at November, a sharp peak (3.50 ± 2.64 individuals) in June 2015, concurrently with the occurrence of neonates (giving birth season which start at May until July) and then they disappear suddenly together at the end of the giving birth season on August. Occurrence of the neonates have a seasonal variability with obvious trend. Changes in the mean daily presence of the dolphins was not related to the changes in the environmental variables (one-way ANOVA, P > 0.05). Statistically, number of zodiac and number of boats have no effect on the dolphin’s abundance. However, the presence of tourists showed an obvious effect on the behavior of the dolphins inside the study area. The current study showed a fluctuation in their behavior between avoiding and attracting to or from the snorkelers. English Summary 171 In terms of morphometric data, out of 112 measurements for the population of spinner dolphin, TL ranged from 61.65 to 174.85 cm. Sexual size dimorphism was remarkable in most of the external measurements (TL, DFH, DFB, PB, and PL) between the adult males and females (one-way ANOVA, P<0.05). Male spinner dolphin was larger in the most external measurements, excluding tip of upper jaw to apex of the melon (M1); tip of upper jaw to gape of mouth (M2) which were larger in adult females (one-way ANOVA, P<0.05). All the linear body measurements of the measured body parts exhibited a negative allometric growth (where b < 1). These characteristics were compared with each other to estimate the biometric relationships between the different body parts. As an important morphometric characteristic, relationships between the total length and the other body characteristics was compared. Nevertheless, total length and other morphometric characteristics exhibited high correlations in the regression equations where the coefficients of correlation displayed high values of more than 0.9. The growth rate was determined by tracking the increasing in the total length (TL) of 6 calves, 6 adult males and 3 adult females during the study period from April 2015 to April 2016. A comparative analysis was conducted to estimate the differences in the growth rate of the dolphins when there are mature and calves. The mean total lengths of adult males and females increased by 1.48 ± 0.36 and 1.26 ± 0.28 cm/year, respectively, while the total length (TL) of calves increased by 47.82 ± 6.21 cm/year. Similarly, DF characteristic has a high mean rate of 35.81 ± 8.83 cm/year in calves. Similar trend was found for other morphometric characters such as PB and M1. English Summary 172 The molecular analysis of Cox 1 indicated that S. longirostris at Satayeh reef is genetically different from their relatives. The phylogenetic analysis of COI sequences resolved by the current study and that available at NCBI GenBank indicated that S. longirostris at Satayeh reef form a unique and distinct population. These morphometric results conclude that the total length considered as a main morphometric character which can be used to show the difference in lengths between the two sexes and through the maturity stages. Although, the positive initial response of the dolphin toward the human but recently it can have a negative impact on dolphin fitness. On the other hand, spinner dolphins are clearly easier to visit their common resting areas e.g. Satayah reef than the other nearby reefs along the southern Egyptian coast of the Red Sea. Despite of the continuous presence of tourist. This showed that dolphins are used to being vicinity of people than else where. |