Integrating Multiple Techniques to Estimate Population Size of an Impacted Dusky Dolphin’s Population in Patagonia, Argentina

Mariana Degrati,Enrique A Crespo,Rocio Loizaga,Nicolás Sueyro,Mariano A Coscarella,Silvana L Dans

doi:10.3389/fmars.2020.00289

Abstract

Successful conservation strategies require an accurate estimation of population size and this parameter is one of the most important factors that determine the rate of various evolutionary processes. In this study we integrated information from genetic, photo-identification and aerial surveys of dusky dolphins to determine the effective population size and the number of dolphins that inhabit the gulfs of Peninsula Valdes (GN and GSJ) and are exposed to tourism vessel traffic. Photo-identification sessions and biopsies samples were collected from a research vessel between 2004 and 2013 to estimate the number of dolphins in the area by capture-recapture methods and the effective population size using mtDNA data. In addition, 4 aerial surveys were carried out using line transects to estimate density via distance sampling. The long-term effective size estimated was 992.87-1103.19 individuals. During the photo-identification period and applying a mark rate of 0.416 the total estimated individuals in GN was 374 (95% CI:237-511). For GSJ the estimated individuals in the area was 55 (95% CI: 2-108, mark rate 0.692). From aerial surveys, the overall density estimate was D =0.13 dolphins/km2 (95% CI: 0.052 - 0.35; CV:49.60). The estimation for GN was 325 (95% CI:130-875), while for GSJ, was 104 (95% CI:42-280) individuals. These are the first estimations of the number and the effective population size for dusky dolphins in a small-scale area along north Patagonia. Dusky dolphins groups are impacted by anthropogenic activities, therefore the information reported here contributes population information to help to the species management and conservation.

Highlights

Information on population status of a species is essential to implement correct management actions (Sveegaard et al, 2015)
Population Size of Dusky Dolphin’s Population strategies require an accurate estimation of population size, and this parameter is one of the most important factors that determine the rate of various evolutionary processes, for example, the loss of genetic diversity and ability to evolve in response to environmental change and the deleterious effects of inbreeding on reproduction and survival (Frankham, 2003; Ansmann et al, 2013)
We integrated information from genetic, photo-identification, and aerial surveys of dusky dolphins to determine the effective population size and the number of dolphins that inhabit the gulfs of Península Valdés and are exposed to the tourism vessels in Golfo Nuevo (GN)

Summary

INTRODUCTION

Information on population status of a species is essential to implement correct management actions (Sveegaard et al, 2015). The estimation of the longterm effective population size based on mtDNA provides the number of reproductive adults that are found all along the northern Patagonian gulfs (Golfo San Matías, GSJ, and GN), through the capture–recapture and aerial line transect methodology, the number of dolphins that inhabit the gulfs of Península Valdés (GSJ and GN) was estimated. These results will increase knowledge of the dusky dolphins in Argentinean waters and will provide information essential to monitoring this population, which is subject to different anthropogenic pressures throughout their distribution

MATERIALS AND METHODS

Sampling Procedures

RESULTS

DISCUSSION

ETHICS STATEMENT