Spinner dolphins<i>Stenella longirostris</i>off south-west Mauritius: abundance and residency

Webster, Imogen; Cockcroft, Victor G.; Cadinouche, Adèle

doi:10.2989/1814232x.2015.1017004

Cited by 11 publications

(6 citation statements)

References 48 publications

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“…The mixed composition and size estimates of Satayah schools fell in ranges reported for spinner dolphins elsewhere (Karczmarski et al, ; Lammers, ; Norris et al, ; Notarbartolo di Sciara et al, ; Oremus et al, ; Webster, Cockcroft, & Cadinouche, ). Schools were slightly larger than those encountered at Samadai Reef over the same time period (Fumagalli, ), but the two populations were similar in including calves and pregnant females in the summer months (Cesario, ; Notarbartolo di Sciara et al, ) and long‐term resident individuals with high survival rate (Samadai population: φ = 0.99 ± 0.02 SE ; Cesario, ).…”

Section: Discussionsupporting

confidence: 59%

Population ecology and the management of whale watching operations on a data‐deficient dolphin population

Fumagalli

Cesario

Costa

et al. 2019

Ecology and Evolution

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Whale watching is a popular commercial activity, producing socio‐ecological benefits but also potential long‐term effects on the targeted cetacean population. This industry is currently developing in data‐deficient contexts in a largely unregulated fashion. Management schemes should adopt precaution and be informed by the relevant literature, but would be more effective if the assessment of the target population vulnerability, biological impacts, and management implications was drawn from site‐specific data. This paper focuses on a reef‐associated, data‐deficient population of spinner dolphins in the Egyptian Red Sea. In Satayah Reef, new information on population size and dynamic parameters were documented using visual observation and photo‐identification‐based capture–recapture methods (Cormack–Jolly–Seber time‐since‐marking model). Dolphins occurred on 98% of the survey days. Average school size was 66 individuals (±42.1 SE), with most groups including calves. The population was equally divided into recurrent and transient individuals. An “emigration + mortality” model best described residence at the site. Five recurrent males (5% of the Satayah population) provided connectivity between this and the geographically close population of Samadai Reef. Average annual survival probability was 0.83 (±0.06 SE) in the year following first capture and 0.99 (±0.06 SE) for recurrent individuals. Mean yearly population sizes ranged 143–207 individuals. The study had the power to detect a 30% decline in the population, but not the rate of change in abundance estimated from the data (r = 0.018 ± 0.04), which would have required a 3‐ to 5‐times longer study. Synthesis and application: These findings advance the assessment of the Satayah population's intrinsic vulnerability and have three major management applications: (a) the delineation of management units; (b) the identification of key indicators for future impact monitoring and assessment; and (c) realistic estimates of the statistical power for trend detection. Based on our results, we recommend supporting future research, devising site‐specific time–area closure plans, and integrating them in a regional scheme. Approaches employed in this case study can inform the management of whale watching industries targeting other data‐deficient populations.

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Section: Discussionsupporting

confidence: 59%

Population ecology and the management of whale watching operations on a data‐deficient dolphin population

Fumagalli

Cesario

Costa

et al. 2019

Ecology and Evolution

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“…This state is easily recognized by the predictable, coordinated, synchronous slow swimming of tight groups, lack of aerial displays, coordinated breathing patterns with short surface intervals and very little acoustic communication [21]. The accessibility and the predictable occurrence of dolphin schools have favoured the establishment of dolphin watching and swim-with operations in spinner dolphin resting areas at several locations, including Hawai'i [21,[23][24][25], French Polynesia [26], Indonesia [27], Fiji [28], Mauritius [29] and Egypt [30]. At some of these tourist locations, spinner dolphins have been observed to interrupt and reduce rest in the presence of tourists [23,31,32].…”

Section: Introductionmentioning

confidence: 99%

Behavioural responses of spinner dolphins to human interactions

et al. 2018

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There is increasing evidence that whale and dolphin watching activities have detrimental effects on targeted cetacean populations. In Egypt, spinner dolphins regularly occur in the resting areas of Samadai, Satayah and Qubbat'Isa reefs. In-water human interactions with dolphins are regulated with a time-area closure system at Samadai, unregulated at Satayah and non-existent at Qubbat'Isa. This provided an ideal experimental setting to advance our understanding of the effects of tourism on a species highly sensitive to disturbances. Our study confirmed that the intensity and duration of interactions, and therefore, dolphin exposure to tourism, differed among the study sites. Compared with the Qubbat'Isa control site, behavioural reactions to boats and swimmers at the two tourism sites suggested that dolphin rest was disrupted, especially around the middle of the day and especially at Satayah, where dolphin tourism is unregulated. Our results indicate also that the dolphin protection measures at Samadai reduce the level of disturbance. We recommend that similar measures be implemented at other dolphin tourism locations, and that no new operations be initiated until the long-term impacts on dolphin populations are better understood. Our experience emphasizes the need to adopt precautionary approaches in research and management of whale and dolphin watching.

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“…A low mark ratio occurs when there is a high proportion of unmarked individuals, that makes estimation of abundance more challenging because the standard error of the total abundance estimate will increase [ 57 – 58 ]. Of the many studies that have used photo-id to examine small delphinids [ 1 – 7 , 10 – 20 , 22 – 23 , 38 , 57 , 59 – 88 ], mark ratios have been shown to vary greatly for different species and for different populations within the same species [ 5 , 38 , 59 , 67 , 72 , 74 , 87 ].…”

Section: Introductionmentioning

confidence: 99%

Challenges of implementing Mark-recapture studies on poorly marked gregarious delphinids

et al. 2018

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Population parameters of poorly marked gregarious species are difficult to estimate. This is the case for common dolphins (Delphinus sp.), a genus known for its lack of distinctive marks resulting in a low mark ratio. Furthermore, the widespread nature of common dolphins results in low recaptures. We developed reliable photo-identification protocols to ensure accurate identification of individuals in the Hauraki Gulf, New Zealand. These protocols combined the use of nicks and notches and pigmentation patterns for identification and included the development of a distinctiveness threshold. The data were further stratified by the level of distinctiveness of each individual (as distinctive or highly-distinctive). Photo-identification surveys were conducted from January 2010 to December 2013. Mark-recapture techniques were implemented through a POPAN super-population approach to estimate seasonal apparent survival, capture probability and abundance of dolphins. A total of 2,083 unique adult common dolphins were identified, 51.3% were classified as D1 (highly distinctive; n = 1,069) and 48.7% as D2 (distinctive; n = 1,014). Of all individuals identified, 34.3% (n = 704) were re-sighted over subsequent years. The proportion of marked dolphins (when compared to unmarked dolphins) was 26.3% for D1 and 46.4% for D1 & D2, respectively. Apparent survival was estimated at 0.767 (CI = 0.694–0.827) for D1 animals, and 0.796 (CI = 0.729–0.850) for D1 & D2 combined. For D1 only, seasonal abundance varied from 732 (CI = 460–1,177) in autumn 2010 to 5,304 (CI = 4,745–5,930) in spring 2013. While the inclusion of D2 individuals may offer a more precise estimate of total abundance, the inability to determine additional sources of bias (for example, arising from under or overestimated mark ratios) meant that estimates for D1 individuals were deemed the least biased for this population. The photo-identification protocol, stratification of the data and steps taken to eliminate potential model violations provided a useful and novel approach to estimate population parameters for common dolphins. These approaches could be implemented for other large gregarious populations (≥500 individuals) of animals with poor natural markings.

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Spinner dolphinsStenella longirostrisoff south-west Mauritius: abundance and residency

Cited by 11 publications

References 48 publications

Population ecology and the management of whale watching operations on a data‐deficient dolphin population

Population ecology and the management of whale watching operations on a data‐deficient dolphin population

Behavioural responses of spinner dolphins to human interactions

Challenges of implementing Mark-recapture studies on poorly marked gregarious delphinids

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