[MARMAM] New Publication on Survival Rates and Capture Heterogeneity of Bottlenose Dolphins in the Shannon Estuary in Ireland

Kim Ludwig kim.e.ludwig at gmail.com
Tue Mar 30 09:39:35 PDT 2021

Dear MARMAM community,

It is our great pleasure to share a new publication on the resident
bottlenose dolphin population in the Shannon Estuary, Ireland, with you:

Ludwig KE, Daly M, Levesque S and Berrow SD (2021) Survival Rates and
Capture Heterogeneity of Bottlenose Dolphins (*Tursiops truncatus*) in the
Shannon Estuary, Ireland. *Front. Mar. Sci.* 8:611219. doi:

Adult survival is arguably the most important demographic parameter for
long-lived species as it has a large impact on population growth, and it
can be estimated for cetacean populations using natural markings and
mark-recapture (MR) modelling. Here we describe a 26-year study of a
genetically discrete, resident population of bottlenose dolphins in the
Shannon Estuary, Ireland, conducted by an NGO using multiple platforms. We
estimated survival rates (SRs) using Cormack-Jolly-Seber models and
explored the effects of variable survey effort, multiple researchers, and
changes in camera equipment as well as capture heterogeneity induced by
changes in marks and site fidelity variation, all common issues affecting
longitudinal dolphin studies. The mean adult SR was 0.94 (±0.001 SD) and
thus comparable to the estimates reported for other bottlenose dolphin
populations. Capture heterogeneity through variation in mark severity was
confirmed, with higher capture probabilities for well-marked individuals
than for poorly marked individuals and a “transience” effect being detected
for less well-marked individuals with 43% only recorded once. Likewise,
both SR and capture probabilities were comparatively low for individuals
with low site fidelity to the Shannon Estuary, and SR of these individuals
additionally decreased even further toward the end of the study, reflecting
a terminal bias. This bias was attributed to non-random temporal migration,
and, together with high encounter rates in Brandon Bay, supported the
hypothesis of range expansion. Our results highlight the importance of
consistent and geographically homogenous survey effort and support the
differentiation of individuals according to their distinctiveness to avoid
biased survival estimates.

The article is freely accessible via

All the best,

Kim Ludwig

*former affiliation:*
Marine and Freshwater Research Institute,
Galway-Mayo Institute of Technology,
Galway, Ireland

*present position: *
PhD Candidate
Working Group: Marine Ecosystems*,*
Thünen Institute for Sea Fisheries,
Bremerhaven, Germany
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