Density, abundance, survival, and ranging patterns of common bottlenose dolphins (Tursiops truncatus) in Mississippi Sound following the Deepwater Horizon oil spill

Abstract

After the Deepwater Horizon (DWH) oil spill began in April 2010, studies were initiated on northern Gulf of Mexico common bottlenose dolphins (Tursiops truncatus) in Mississippi Sound (MSS) to determine density, abundance, and survival, during and after the oil spill, and to compare these results to previous research in this region. Seasonal boat-based photo-identification surveys (2010–2012) were conducted in a section of MSS to estimate dolphin density and survival, and satellite-linked telemetry (2013) was used to determine ranging patterns. Telemetry suggested two different ranging patterns in MSS: (1) inshore waters with seasonal movements into mid-MSS, and (2) around the barrier islands exclusively. Based upon these data, dolphin density was estimated in two strata (Inshore and Island) using a spatially-explicit robust-design capture-recapture model. Inshore and Island density varied between 0.77–1.61 dolphins km−2 ( = 1.42, 95% CI: 1.28–1.53) and 3.32–5.74 dolphins km−2 ( = 4.43, 95% CI: 2.70–5.63), respectively. The estimated annual survival rate for dolphins with distinctive fins was very low in the year following the spill, 0.73 (95% CI: 0.67–0.78), and consistent with the occurrence of a large scale cetacean unusual mortality event that was in part attributed to the DWH oil spill. Fluctuations in density were not as large or seasonally consistent as previously reported. Total abundance for MSS extrapolated from density results ranged from 4,610 in July 2011 to 3,046 in January 2012 ( = 3,469, 95% CI: 3,113–3,725).

How long do dolphins live? Survival rates and life expectancies for bottlenose dolphins in zoological facilities vs. wild populations

“…Both of these factors should be taken into account in order to interpret and contextualize the data from that population. No such pervasive health challenges have been suggested for the other wild population (Mattson et al 2006) during the time period discussed here (although several years after these data the Deepwater Horizon oil spill undoubtedly impacted the survival of wild dolphins in that area; Mullin et al 2017).…”

“…) during the time period discussed here (although several years after these data the Deepwater Horizon oil spill undoubtedly impacted the survival of wild dolphins in that area; Mullin et al . ).…”

“…Such techniques have served as invaluable tools for tracking mortality trends in specific populations, providing insight into the effects of environmental challenges such as the Deepwater Horizon oil spill ( e.g ., Mullin et al . ) and freshwater input from a hydroelectric power station tunnel ( e.g ., Currey et al . ).…”

“…Because of the nature of these data, studies of wild dolphins in recent years have begun to calculate something called an "apparent survival rate," using complicated statistical models constructed on the basis of how often individual animals are resighted over independent sequential samples (e.g., Corkrey et al 2008, Speakman et al 2010, Fruet et al 2015. Such techniques have served as invaluable tools for tracking mortality trends in specific populations, providing insight into the effects of environmental challenges such as the Deepwater Horizon oil spill (e.g., Mullin et al 2017) and freshwater input from a hydroelectric power station tunnel (e.g., Currey et al 2009). However, there is wide variability in the specifics of how these techniques have been applied to studies of different populations with respect to factors such as definitions to determine which animals are calves to exclude, the mathematical models utilized, and ways of determining and weighting which model(s) with which set of assumptions to use, which has resulted in apparent survival rates in wild populations ranging from 0.86 per week (Brusa et al 2016) (which, if equated to ASR, would convert to a life expectancy of less than a year) to 1.0 (Reisinger andKarczmarski 2010, Methion andLópez 2018) (which would equate to immortality).…”

Robust design capture-recapture analysis of abundance and demographic parameters of Indian River Lagoon common bottlenose dolphins (Tursiops truncatus truncatus)

“…Recently, much attention has been given to assessing the status of bottlenose dolphin populations in bays, sounds, and estuaries [1–3, 13, 73, 86]. Measuring abundance and demography of these populations is often difficult due to uncertainty about population boundaries [2, 13, 73, 86]. This study is the first to implement a Robust Design capture-recapture design to estimate bottlenose dolphin abundance in the Indian River Lagoon estuary.…”