Abundance of bottlenose dolphins, Tursiops truncatus (Cetacea: Delphinidae), inhabiting the Patos Lagoon estuary, southern Brazil: implications for conservation

Section: Southern Brazil and Uruguaymentioning

confidence: 99%

Report of the Working Group on the Distribution of Tursiops truncatus in the Southwest Atlantic Ocean

Lodi¹,

Domit

Laporta

et al. 2017

“…This suggests that the estimates from both methods used in this pilot study are within the range expected for this local unit. Although coastal bottlenose dolphins populations are often small, with estimates ranging from 56 to 290 individuals (Wells and Scott, 1990;Wilson et al, 1999;Haase and Schneider, 2001;Currey et al, 2007;Bearzi et al, 2008;Fury and Harrison, 2008;Fruet et al, 2011), estimates θ presented here (50 individuals by mark-recapture and 61 by line-transect) suggest that the bottlenose dolphin population from Laguna is one of the smallest among those measured by the aforementioned studies. This number demonstrates the vulnerability of this population to local anthropogenic impacts and justifies the need for developing an effective long-term monitoring program (Sutherland, 2000).…”

Section: Discussionmentioning

confidence: 61%

Mark-recapture vs. line-transect abundance estimates of a coastal dolphin population: a case study of Tursiops truncatus from Laguna, southern Brazil

Daura‐Jorge

Simões-Lopes

2017

Abstract. Cetacean populations in coastal habitats are increasingly threatened by multiple anthropogenic impacts. Monitoring these populations to obtain robust estimates of abundance and detect trends over time is critical to achieve conservation goals. Here, we conducted a pilot study to evaluate the effectiveness of two commonly used abundance estimation methods: mark-recapture and distance sampling line-transect. Surveys were conducted to estimate the abundance of bottlenose dolphins in Laguna, southern Brazil. We implemented power-analysis models and compared both techniques in terms of cost, time and effectiveness to detect trends over a five-year period. Mark-recapture models were analyzed in MARK and resulted in an abundance of 50 individuals (CI = 39-64) with a coefficient of variation (CV) of 0.13. The line-transect models were implemented using the program DISTANCE and resulted in an estimate of 62 individuals (CI = 38-103), with a CV of 0.24. Comparing both approaches, mark-recapture resulted 1.30 time more expensive than line-transect for a single season of effort, but was twice as effective in terms of precision. As a consequence, the probability of detecting a 5% trend during a five-year period is 2.08 times higher with mark recapture. Conversely, the final cost to detect a trend with distance sampling is 1.19 time higher but considering six more years of effort. These results highlight the importance of selecting a-priori sampling design techniques that include developing pilot studies that evaluate the bias, precision and accuracy of estimates while considering costs involved. Considering the small population size estimated herein, the sensitivity of both approaches for detecting trends is not sufficient because the original population would be markedly reduced by the time a declining trend was detected. Thus, a precautionary approach is still imperative, even when robust estimates are obtained.Resumo. Populações costeiras de cetáceos estão expostas a múltiplos impactos antropogênicos, sendo o monitoramento destas populações essencial para questões conservacionistas. Para isto, estimativas robustas de abundância são necessárias, principalmente quando o objetivo é detectar tendências populacionais. Por um estudo piloto, foi avaliada a efetividade de dois métodos comumente utilizados, captura-recaptura e transecção linear, para estimar a abundância do boto-datainha Tursiops truncatus, em Laguna, sul do Brasil. Ambas as técnicas foram comparadas em termos de custos, tempo e poder em detectar tendências, considerando um programa hipotético de cinco anos de monitoramento. Os modelos de captura-recaptura, analisados no programa MARK, geraram uma abundância de 50 indivíduos (IC = 39-64) com um coeficiente de variação (CV) de 0,13. O método de transecção linear, utilizando o programa DISTANCE, estimou uma abundância de 62 indivíduos (IC = 38-103), com um CV de 0,24. Comparando as duas abordagens, quando considerado apenas um ano de esforço, o método de captura-recaptura foi 1,30 vez mais dispendioso que ...

“…Group sizes seemed stable in populations studied over long-term periods (i.e. more than one decade in Laguna: Simões-Lopes, 1991;Daura-Jorge et al, 2013;and Tramandaí River: Simões-Lopes, 1991;Hoffmann et al, 2008;Giacomo and Ott, 2016 this volume; and more than two decades in the PLE: Möller, 1993;Dalla Rosa, 1999;Mattos et al, 2007;Fruet et al, 2011;2015).…”

Section: Behaviormentioning

confidence: 98%

Report of the Working Group on the Behavioral Ecology of bottlenose dolphins in the Southwest Atlantic Ocean

Domit

Laporta²,

Zappes

et al. 2017

In this report, we present a compilation of the behavioral patterns of bottlenose dolphins and social structure throughout the Southwest Atlantic Ocean. We have compiled and summarized available data concerning: (i) behavioral activities (states and events), (ii) social structures (group size and composition), (iii) acoustic behavior and (iv) intra and interspecific interactions of bottlenose dolphin populations throughout the SWAO, from northern Brazil to southern Argentina. Lack of systematic and standardized methodologies for data collection precludes robust data analyses in respect of bottlenose dolphin behavior. Available information suggests that the studied populations presented weak intra-population associations and that coastal individuals tend to form smaller groups than their oceanic counterparts. Bottlenose dolphins from SWAO produce stylized whistles in which the acoustic parameters are similar to published ranges around the world and some results indicate significant local inter-population variation in the acoustic parameters of the whistles. Data of intra and interspecific interactions of bottlenose dolphins in the SWAO are scarce and therefore do not fully allow a comprehensive analysis of the situational contexts.