Abundance and demography of common bottlenose dolphins (Tursiops truncatus truncatus) in the Indian River Lagoon, Florida: A robust design capture-recapture analysis

Abstract

Common bottlenose dolphins (Tursiops truncatus truncatus) inhabiting the Indian River Lagoon (IRL) estuarine system along the east coast of Florida are impacted by anthropogenic activities and have had multiple unexplained mortality events. Given this, managers need precise estimates of demographic and abundance parameters. Mark-recapture photo-identification boat-based surveys following a Robust Design were used to estimate abundance, adult survival, and temporary emigration for the IRL estuarine system stock of bottlenose dolphins. Models allowed for temporary emigration and included a parameter (time since first capture) to assess evidence for transient individuals. Surveys (n = 135) were conducted along predetermined contour and transect lines throughout the entire IRL (2016–2017). The best fitting model allowed survival to differ for residents and transients and to vary by primary period, detection to vary by secondary session, and did not include temporary emigration. Dolphin abundance was estimated from 981 (95% CI: 882–1,090) in winter to 1,078 (95% CI: 968–1,201) in summer with a mean of 1,032 (95% CI: 969–1,098). Model averaged seasonal survival rate for marked residents was 0.85–1.00. Capture probability was 0.20 to 0.42 during secondary sessions and the transient rate was estimated as 0.06 to 0.07. This study is the first Robust Design mark-recapture survey to estimate abundance for IRL dolphins and provides population estimates to improve future survey design, as well as an example of data simulation to validate and optimize sampling design. Transients likely included individuals with home ranges extending north of the IRL requiring further assessment of stock delineation. Results were similar to prior abundance estimates from line-transect aerial surveys suggesting population stability over the last decade. These results will enable managers to evaluate the impact of fisheries-related takes and provide baseline demographic parameters for the IRL dolphin population which contends with anthropogenic impacts and repeated mortality events.

Morbidity and Mortality Patterns of Indian River Lagoon Common Bottlenose Dolphins (Tursiops Truncatus Truncatus) 2002–2020

“…Morbillivirus mortality in the IRL was relatively low when compared to coastal events (NOAA 2015). This was likely because of decreased exposure in estuarine dolphins (Balmer et al 2018), preexisting morbillivirus titers in IRL dolphins (9.8%; Bossart et al 2010), and the low exchange rate between Mosquito Lagoon and the remainder of the IRL (Durden et al 2021). These retrospective comparisons of mortality, during UME and non-UME years, illustrate the importance of long-term data sets to compare regional mortality trends.…”

“…Although case studies of individual pathological findings provide valuable information, few studies have systematically examined the cause of morbidity and mortality of marine mammal populations over an extended time period (Cowan et al 1986; Gerber et al 1993; Greig et al 2005; Zagzebski et al 2006; McFee and Lipscomb 2009; Bogomolni et al 2010; Ashley et al 2020). Along the east coast of central Florida, US, a population of common bottlenose dolphins ( Tursiops truncatus truncatus ) inhabiting the Indian River Lagoon (IRL) estuary system (NOAA 2009) has been the focus of several ecological and health-related studies (Odell and Asper 1990; Bossart et al 2003; Goldstein et al 2006; Reif et al 2006; Durden et al 2007, 2009, 2019, 2021; Stolen et al 2007, 2013a; Fire et al 2020). Dolphins exhibit year-round IRL residency and strong site fidelity (Odell and Asper 1990; Mazzoil et al 2005) with relatively small linear ranging patterns (mean±standard deviation [SD] 28.1±9.49 km; Durden et al 2019).…”

“…Dolphins exhibit year-round IRL residency and strong site fidelity (Odell and Asper 1990; Mazzoil et al 2005) with relatively small linear ranging patterns (mean±standard deviation [SD] 28.1±9.49 km; Durden et al 2019). Six distinct communities of dolphins inhabit the IRL (Titcomb et al 2015) which has a mean population size of approximately 1,032 dolphins (Durden et al 2021). As a long-lived top-level predator, IRL dolphins are exposed to and accumulate persistent pollutants (Stavros et al 2011) that may increase susceptibility to disease (Fair and Becker 2000).…”

Abundance and effect of health status on apparent survival of Guiana dolphins,Sotalia guianensis, in an open embayment in north‐eastern Brazil

“…Information on demographic parameters of dolphin populations is essential for species and habitat conservation because it can guide best‐practice management (e.g. Bradford, Burdin & Wade, 1996; Taylor et al, 2000; Bedjer et al, 2006; Bearzi et al, 2008; Currey et al, 2008; Hunt et al, 2017; Durden et al, 2021) and be applied to extinction risk assessments (Frankham, 2005; O'Grady et al, 2006; Santostasi et al, 2021).…”