Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Dec 19;9(1):533-544.
doi: 10.1002/ece3.4772. eCollection 2019 Jan.

Variations in age- and sex-specific survival rates help explain population trend in a discrete marine mammal population

Mònica Arso Civil  1 , Barbara Cheney  2 , Nicola J Quick  1   3 , Valentina Islas-Villanueva  1   4 , Jeff A Graves  5 , Vincent M Janik  1 , Paul M Thompson  2 , Philip S Hammond  1
Affiliations

Variations in age- and sex-specific survival rates help explain population trend in a discrete marine mammal population

Mònica Arso Civil et al. Ecol Evol. .

Abstract

Understanding the drivers underlying fluctuations in the size of animal populations is central to ecology, conservation biology, and wildlife management. Reliable estimates of survival probabilities are key to population viability assessments, and patterns of variation in survival can help inferring the causal factors behind detected changes in population size. We investigated whether variation in age- and sex-specific survival probabilities could help explain the increasing trend in population size detected in a small, discrete population of bottlenose dolphins Tursiops truncatus off the east coast of Scotland. To estimate annual survival probabilities, we applied capture-recapture models to photoidentification data collected from 1989 to 2015. We used robust design models accounting for temporary emigration to estimate juvenile and adult survival, multistate models to estimate sex-specific survival, and age models to estimate calf survival. We found strong support for an increase in juvenile/adult annual survival from 93.1% to 96.0% over the study period, most likely caused by a change in juvenile survival. Examination of sex-specific variation showed weaker support for this trend being a result of increasing female survival, which was overall higher than for males and animals of unknown sex. Calf survival was lower in the first than second year; a bias in estimating third-year survival will likely exist in similar studies. There was some support first-born calf survival being lower than for calves born subsequently. Coastal marine mammal populations are subject to the impacts of environmental change, increasing anthropogenic disturbance and the effects of management measures. Survival estimates are essential to improve our understanding of population dynamics and help predict how future pressures may impact populations, but obtaining robust information on the life history of long-lived species is challenging. Our study illustrates how knowledge of survival can be increased by applying a robust analytical framework to photoidentification data.

Keywords: Tursiops; calf survival; capture–recapture; mortality rate; population dynamics; sex‐specific survival.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Bottlenose dolphins from the east coast of Scotland (photograph by Mònica Arso Civil, taken during this study)
Figure 2
Figure 2
Map showing the two main study areas (circles) located in the Moray Firth Special Area of Conservation (SAC; dashed area) and in St Andrews Bay and the Tay estuary
Figure 3
Figure 3
Time trend in juvenile/adult estimated survival probability (with associated 95% confidence intervals) from the most supported RD model
Figure 4
Figure 4
Time trend in sex‐specific estimated survival probabilities with associated 95% confidence intervals for juvenile/adult bottlenose dolphins. The estimated parameters are derived from multistate model number 5 in Supporting Information Table S2
See this image and copyright information in PMC

References

    1. Altwegg, R. , Crawford, R. J. , Underhill, L. G. , & Williams, A. T. J. (2008). Long‐term survival of de‐oiled Cape gannets Morus capensis after the Castillo de Bellver oil spill of 1983. Biological Conservation, 141, 1924–1929. 10.1016/j.biocon.2008.04.030 - DOI
    1. Arso Civil, M. (2014). Population ecology of bottlenose dolphins (Tursiops truncatus) off the east coast of Scotland. University of St Andrews, UK. Unpublished PhD thesis.
    1. Arso Civil, M. , Cheney, B. , Quick, N. J. , Thompson, P. M. , & Hammond, P. S. (2017). A new approach to estimate fecundity rate from inter‐birth intervals. Ecosphere, 8, e01796.
    1. Bradford, A. L. , Wade, P. R. , Weller, D. W. , Burdin, A. M. , Ivashchenko, Y. V. , Tsidulko, G. A. , … Brownell, R. L. (2006). Survival estimates of western gray whales Eschrichtius robustus incorporating individual heterogeneity and temporary emigration. Marine Ecology‐Progress Series, 315, 293–307. 10.3354/meps315293 - DOI
    1. Branch, T. A. , Matsuoka, K. , & Miyashita, T. (2004). Evidence for increases in Antarctic blue whales based on bayesian modelling. Marine Mammal Science, 20, 726–754. 10.1111/j.1748-7692.2004.tb01190.x - DOI

LinkOut - more resources