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Assessing Guiana dolphin abundance and density in the Southwestern Atlantic: insights from conservation areas

Published online by Cambridge University Press:  25 July 2023

Inaê Guion de Almeida Open the ORCID record for Inaê Guion de Almeida [Opens in a new window] ,
Alexandre Reis Percequillo Open the ORCID record for Alexandre Reis Percequillo [Opens in a new window]  and
Mario Manoel Rollo Open the ORCID record for Mario Manoel Rollo [Opens in a new window]
Inaê Guion de Almeida
Affiliation:
Departamento de Ciências Biológicas, Universidade de São Paulo, Avenida Pádua Dias, 11, Caixa Postal 9, Piracicaba, SP 12418-900, Brasil
Alexandre Reis Percequillo
Affiliation:
Departamento de Ciências Biológicas, Universidade de São Paulo, Avenida Pádua Dias, 11, Caixa Postal 9, Piracicaba, SP 12418-900, Brasil
Mario Manoel Rollo*
Affiliation:
Universidade Estadual Paulista ‘Júlio de Mesquita Filho’, Instituto de Biociências, Campus do Litoral Paulista, Pça Infante D. Henrique s/n, Parque Bitaru, São Vicente, SP 11330-900, Brasil Department of Ecology and Environmental Science, Umeå University, Linnaeus väg 6, 901 87 Umeå, Sweden
*
Corresponding author: Mario Manoel Rollo; Email: mario.rollo@umu.se
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Abstract

Accurate demographic data play a critical role in implementing conservation strategies and identifying key areas for species preservation. The population abundance and density of Sotalia guianensis were estimated in the estuarine-lagoon complex of Cananéia, Brazil, using distance sampling. The survey covered 1339.91 km with 83 h 05 min in effort. A half-normal model with cosine adjustments was evaluated as the best fit to estimate an abundance of 193 individuals (95% CI 158–237) and a density of 2.55 ind km−2. The majority of sightings occurred in the Baía de Trapandé (48.72%), followed by the Mar de Cananéia (32.72%) and Mar de Cubatão (18.56%), the three areas surrounding the Ilha de Cananéia. The study confirmed the heterogeneous distribution of the estuary and found that the Mar de Cananéia and the Baía de Trapandé were more densely populated, with 2.76 ind km−2 (95% CI 1.93–3.96) and 2.76 ind km−2 (95% CI 2.07–3.66), respectively, while the Mar de Cubatão was less densely populated, with 1.59 ind km−2 (95% CI 1.04–2.44). The findings support previous research indicating a stable population over the last few decades. The Cananéia estuary is an ecologically diverse region located between protected areas under different categories of environmental protection and harbours a significant population of S. guianensis, providing essential resources for feeding and breeding. Protected areas have proven to be effective tools for preserving both marine and terrestrial environments. Despite the close proximity to humans and constant threats, the study underscores the importance of the area for the conservation of the species.

Keywords

abundancedensitydistance softwarelinear transectprotected areasSotalia guianensis

Information

Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 103 , 2023 , e57
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
Copyright © The Author(s), 2023. Published by Cambridge University Press on behalf of Marine Biological Association of the United Kingdom

Introduction

Protected areas have been recognized as a primary and effective tool for preserving both marine and terrestrial environments. To achieve worldwide conservation objectives, the countries that are signatories to the Convention on Biological Diversity (CBD) have agreed to substantially increase the extent of protected areas across the globe in the coming years (O'Leary et al., Reference O'Leary, Winther-Janson, Bainbridge, Aitken, Hawkins and Roberts2016; Claudet et al., Reference Claudet, Loiseau, Sostres and Zupan2020). Targeting top predator species has been identified as an important conservation strategy. It ensures their own protection and benefits other species involved in the food chain, maintaining a healthier environment (Zacharias and Roff, Reference Zacharias and Roff2001; Sergio et al., Reference Sergio, Caro, Brown, Clucas, Hunter, Ketchum, McHugh and Hirald2008). However, common species tend to be overlooked when priority measures and conservation strategies are set. Neglecting once-common species can lead to their decline and even local disappearance when faced with threats (Vermeulen and Bräger, Reference Vermeulen and Bräger2015).

To establish effective conservation action plans, information on demographic parameters and population dynamics in both common and less abundant species is essential. Likewise, identifying central areas where biologically and socially relevant behaviours are associated (e.g. feeding, reproduction, rest) is critical (Smith et al., Reference Smith, Frère, Kobryn and Bejder2016; Tardin et al., Reference Tardin, Maciel, Espécie, Melo-Santos, Simão and Alves2020). Combining data on density, abundance, distribution and habitat use is key to identifying priority conservation areas. Therefore, efforts to obtain robust estimates of demographic and ecological parameters are necessary to evaluate and monitor populations (Azevedo et al., Reference Azevedo, Lailson-Brito, Cunha and Van Sluys2004; Cantor et al., Reference Cantor, Wedekin, Daura-Jorge, Rossi-Santos and Simões-Lopes2012). However, obtaining such information is challenging, particularly for marine mammals like cetaceans. These animals spend long periods underwater, occupy large areas, can distance themselves from the coast and present complex social organization and patterns of spatial use (Whitehead et al., Reference Whitehead, Reeves, Tyack, Mann, Connor, Tyack and Whitehead2000; Rollo, Reference Rollo2002; Sandercock, Reference Sandercock2006; Azevedo et al., Reference Azevedo, Oliveira, Viana and Van Sluys2007; Dawson et al., Reference Dawson, Wade, Slooten and Barlow2008).

Sotalia guianensis (van Bénéden, 1864) is one of the most observed resident species along the Atlantic coast of South and Central America. It is a small cetacean found primarily in bays and estuaries, with its occurrence generally associated with mangroves, shallow waters, beaches with slopes and rocky coasts (Borobia et al., Reference Borobia, Siciliano, Lodi and Hoek1991; Da Silva et al., Reference Da Silva, Fettuccia, Rodrigues, Edwards, Moreno, Moura, Wedekin, Bazzalo, Emin-Lima, Carmo, Siciliano and Utreras2010; Cantor et al., Reference Cantor, Wedekin, Daura-Jorge, Rossi-Santos and Simões-Lopes2012). Due to its coastal habits, near-shore distribution and high site fidelity, the species is highly susceptible to cumulative and constant anthropogenic pressure and urbanization (Borobia et al., Reference Borobia, Siciliano, Lodi and Hoek1991; Cantor et al., Reference Cantor, Wedekin, Daura-Jorge, Rossi-Santos and Simões-Lopes2012).

Over the last decades, studies addressing ecological and reproductive parameters, abundance and population density of S. guianensis throughout its distribution have intensified (Borobia et al., Reference Borobia, Siciliano, Lodi and Hoek1991; Lodi and Hetzel, Reference Lodi and Hetzel1998; Geise et al., Reference Geise, Gomes and Cerqueira1999; Ramos et al., Reference Ramos, Di Beneditto and Lima2000; Rollo, Reference Rollo2002; Rosas and Monteiro-Filho, Reference Rosas and Monteiro-Filho2002; Rosas et al., Reference Rosas, Barreto and Monteiro-Filho2003; Di Beneditto and Ramos, Reference Di Beneditto and Ramos2004; Araújo et al., Reference Araújo, Araújo, Souto, Parente and Geise2007; Crespo et al., Reference Crespo, Alarcon, Alonso, Bazzalo, Borobia, Cremer, Filla, Lodi, Magalhães, Marigo, Queiróz, Reynolds JE, Schaeffer, Dorneles, Lailson-Brito and Wetzel2010; Da Silva et al., Reference Da Silva, Fettuccia, Rodrigues, Edwards, Moreno, Moura, Wedekin, Bazzalo, Emin-Lima, Carmo, Siciliano and Utreras2010; Hardt et al., Reference Hardt, Cremer, Tonello and Simões-Lopes2010; Santos et al., Reference Santos, Cremer, Secchi, Flach, Filla, Hubner and Dussán-Duque2010a; Havukainen et al., Reference Havukainen, Monteiro-Filho and Filla2011; Lima et al., Reference Lima, Carvalho, Azevedo, Barbosa and Silveira2017; Monteiro-Filho et al., Reference Monteiro-Filho, Deconto, Louzada, Wanderley, Godoy, Medeiros, Rossi-Santos and Finkl2018; Santos et al., Reference Santos, Laílson-Brito, Flach, Oshima, Figueiredo, Carvalho, Ventura, Molina and Azevedo2019; Tardin et al., Reference Tardin, Maciel, Espécie, Melo-Santos, Simão and Alves2020). The distance sampling method has been widely used and recommended for estimating the density and abundance of cetacean species and all sorts of biological populations (Thomas et al., Reference Thomas, Buckland, Burnham, Anderson, Laake, Borchers, Strindberg, El-Shaarawi and Piegorsch2002).

Different populations of the species have been accessed for these data in Brazil, at the Baía do Emboraí (Pará state), Baía de Guanabara and Baía de Sepetiba (Rio de Janeiro state), Cananéia estuary (São Paulo state), Paranaguá and Guaratuba estuaries (Paraná state) and Baía de Babitonga (Santa Catarina state) (Santos et al., Reference Santos, Cremer, Secchi, Flach, Filla, Hubner and Dussán-Duque2010a; Azevedo et al., Reference Azevedo, Carvalho, Kajin, Van Sluys, Bisi, Cunha and Lailson-Brito2017; Monteiro-Filho et al., Reference Monteiro-Filho, Deconto, Louzada, Wanderley, Godoy, Medeiros, Rossi-Santos and Finkl2018). Population estimates are also available for Venezuela (Gulf of Venezuela), Colombia (Gulf of Morrosquillo) and Nicaragua (Miskito Cayos Reserve) (Santos et al., Reference Santos, Cremer, Secchi, Flach, Filla, Hubner and Dussán-Duque2010a; Espinoza-Rodríguez et al., Reference Espinoza-Rodríguez, De Turris-Morales, Takahiro and Barrios-Garrido2019).

Despite increasing efforts, there is still a significant gap in knowledge regarding the abundance, density, survival rates and population trends of S. guianensis, which is classified as near threatened in the IUCN Red List of Threatened Species and as vulnerable in the Red Book of Brazilian Endangered Fauna (ICMBio, 2018; Secchi et al., Reference Secchi, Santos and Reeves2018; IUCN, 2019). The Cananéia estuarine-lagoon complex, an estuarine region located in southern São Paulo state, has previously been studied in terms of population estimates of S. guianensis, as observed in Geise et al. (Reference Geise, Gomes and Cerqueira1999), Bisi (Reference Bisi2001), Rollo (Reference Rollo2002) and Havukainen et al. (Reference Havukainen, Monteiro-Filho and Filla2011). However, considering the conservation status of this species in Brazil and the threats faced by this region in recent years (including fishing, tourism, harbour activities and changes in environmental protection laws), it is necessary to regularly update these estimates. Therefore, the present study aims to provide additional data regarding abundance and density estimates and to consolidate distribution information for the S. guianensis population in the Cananéia estuary, located at the natural confluence of several protected areas, such as Ilha do Cardoso State Park, Lagamar de Cananéia State Park and Mandira Extractive Reserve.

Materials and methods

The Cananéia estuarine-lagoon complex (Lat. 25°1′28″S; Lon. 47°55′56″W) has a land area of approximately 3400 km2 and a marine area of 2450 km2 (Tessler and Mahiques, Reference Tessler and Mahiques1998) (Figure 1) and is part of a vital continuum of rainforest preservation in the São Paulo state of Brazil, known for its elevated levels of ecological diversity (Secretaria do Meio Ambiente, São Paulo, 1990). This UNESCO World Heritage site is also included in the Federal Environmental Protection Area of Cananéia-Iguape-Peruíbe and in the Wilderness Conservation Zone, forming part of the Lagamar Mosaic of Protected Areas (Federal Decree No. 90.347 dated 23 October 1984, and complemented by Decree No. 91.892 of 06/11/1985). The complex is home to rare and common species of cetaceans, such as Pontoporia blainvillei and S. guianensis, respectively (Secchi et al., Reference Secchi, Ott, Crespo, Kinas, Pedraza and Bordino2001; Desvaux, Reference Desvaux2013).

Figure 1.

Study area showing the survey design with line transects and group sightings of Sotalia guianensis at the Cananéia estuarine-lagoon complex, São Paulo, Brazil.

The entire complex is highly productive, dominated by mangroves, with the predominant species being Rhizophora mangle, Laguncularia racemosa and Avicennia schaueriana, which are characteristics of the Atlantic Forest biome. The system is characterized by its year-round concentration of nutrients and fish (Domit, Reference Domit2006; Oliveira and Monteiro-Filho, Reference Oliveira and Monteiro-Filho2008). The rainfall in the area is highest between December and April, and the dry season is between May and November (Kumpera, Reference Kumpera2007). The mean annual temperature is 21.5 °C, while the sea temperature is 23.9 °C (Oliveira and Monteiro-Filho, Reference Oliveira and Monteiro-Filho2008).

The estuary surrounding Ilha de Cananéia is characterized by varying physical features in the Baía de Trapandé, Mar de Cananéia and Mar de Cubatão, which separate it from the continent and the neighbouring Ilha Comprida and Ilha do Cardoso. The Mar de Cananéia and Mar de Cubatão are narrow channels, ranging from 1 to 3 km in width and reaching depths of up to 20 m in some areas, with an average depth of around 6 m (Tessler and Souza, Reference Tessler and Souza1998). The Mar de Cananéia is larger than the Mar de Cubatão, covering areas of 24.25 and 13.53 km2, respectively, and is closer to the open sea. The Baía de Trapandé, which connects the two channels and opens to the Atlantic Ocean, has an area of 37.92 km2 and presents the highest values of width, depth and salinity in the estuary.

The tidal waves and temporal variation of freshwater discharge have a major influence on the channels and bay, affecting the salinity levels that vary according to the tides and freshwater inputs, with the highest levels recorded in winter and the lowest in summer (Domit, Reference Domit2006; Kumpera, Reference Kumpera2007). Although there are few beaches in the area, the estuary is a unique ecosystem shaped by the interplay between its physical features and environmental factors.

Estimates of abundance and density of S. guianensis in the Cananéia estuary were obtained using distance sampling methods, which involve scanning a series of transect lines for sightings of individual animals or groups (Buckland et al., Reference Buckland, Anderson, Burnham, Laake, Borchers and Thomas2001, Reference Buckland, Rexstad, Thomas, Borchers, Aston, Mulholland and Tant2016; Thomas et al., Reference Thomas, Buckland, Burnham, Anderson, Laake, Borchers, Strindberg, El-Shaarawi and Piegorsch2002). The distances from the sightings are measured to estimate the total number of individuals present in the area (Thomas et al., Reference Thomas, Buckland, Burnham, Anderson, Laake, Borchers, Strindberg, El-Shaarawi and Piegorsch2002; Cullen and Rudran, Reference Cullen, Rudran, Cullen, Rudran and Valladares-Padua2003; Buckland et al., Reference Buckland, Rexstad, Thomas, Borchers, Aston, Mulholland and Tant2016). For the method to be effective, it is important to adhere to several premises: (1) all objects located on the transect line will be sighted; (2) objects are detected in its initial place; (3) distances and angles are accurately measured; (4) the same animal, or group, cannot be counted more than once in the same sampling effort. Another recommendation is to achieve an appropriate number n of records, such as a minimum of 60–80 observations per line transect survey (Buckland et al., Reference Buckland, Anderson, Burnham, Laake, Borchers and Thomas2001; Thomas et al., Reference Thomas, Buckland, Burnham, Anderson, Laake, Borchers, Strindberg, El-Shaarawi and Piegorsch2002; Cullen and Rudran, Reference Cullen, Rudran, Cullen, Rudran and Valladares-Padua2003).

Each detected object is recorded with its radial distance and angle of detection from the transect line, and the perpendicular distance from the object to the line is then calculated. A decrease in detectability is expected with increasing perpendicular distance. Thus, observed distances are incorporated into a detection function to estimate the proportion of objects lost in the sampling. The function g (x) represents the probability of an object being detected at a distance x, where g (0) = 1 is assumed, that is, all objects in the path line are detected, respecting the premise of the method. Therefore, the density is estimated based on the number of individuals sighted, the length of the transects travelled and the area sampled, the distances recorded and the probabilities of detection of individuals using available software (Distance; Miller et al., Reference Miller, Rextad, Thomas, Marshall and Laake2019).

The study area was previously surveyed in a pilot effort to establish the sampling sectors and design the transects. The experimental design developed by Rollo (Reference Rollo2002) was used as a reference, in which transects were drawn within the contour of the study area previously digitized in AutoCAD (Autodesk Inc.). The angles between the lines were adjusted to maintain a constant ratio of length(l)/area(a). Zigzag transects were used to increase the distance between consecutive transects, reducing the likelihood of multiple sightings of the same individual and ensuring more uniform coverage in the area (Rollo, Reference Rollo2002; Chen et al., Reference Chen, Zheng, Zhai, Xu, Sun, Wang and Yang2008; Dawson et al., Reference Dawson, Wade, Slooten and Barlow2008). A total of 218 zigzag transects were distributed in the three sampled areas (Baía de Trapandé, Mar de Cananéia and Mar de Cubatão) and a stratified analysis was chosen due to the previous knowledge of the heterogeneous distribution of the species in the habitat and the different physical characteristics of the estuary (Rollo, Reference Rollo2002).

The data were collected during four seasonal campaigns, each comprising of four survey days, between July 2011 and July 2012. Each transect around Ilha de Cananéia was completed over 2 days, resulting in two full paths per campaign. The starting and direction point of the route, i.e. north or south, were randomly chosen on the first day of the campaign. Eight replicates were performed for each of the 218 transects established. The surveys were conducted between 8 am and 4 pm, with good sea and wind conditions (Beaufort 0–3), using an aluminium boat of 4–5 m in length, elevated 1.10 m from sea level, with an average speed of 16.08 km h−1 and a crew of three to four people (pilot and observers) respecting a visual field of 90° left and 90° right of the line of sight.

For each individual or group observed, the date and time, sampling area, geographical position, group size, radial distance and observation angles were recorded. Group was defined as a set of individuals with close spatial cohesion developing similar behavioural activities (Chen et al., Reference Chen, Qiu, Jia, Hung and Liu2011). The perpendicular distance was estimated from the angle and radial distances with the aid of binoculars with reticles and a laser rangefinder. Perpendicular distances over 500 m were truncated to avoid difficulties in fitting the functions to the data due to the discontinuous occurrence of records at greater distances (Buckland et al., Reference Buckland, Anderson, Burnham, Laake, Borchers and Thomas2001; Rollo, Reference Rollo2002). The lengths of the transects were measured using Google Earth, Garmin BaseCamp and GPS TrackMaker tools, and the areas of the sample sectors were calculated using the GE-PATH 1.4.6 software.

The analysis ran using the Distance software and tested the models half-normal with cosine adjustment, half-normal with simple polynomial adjustment, half-normal with hermite polynomial adjustment and uniform with cosine adjustment. The model and adjustment with the lowest Akaike information criterion (AIC) value was selected. The AIC is a quantitative method of estimator selection that identifies which model best fits the data with the smallest number of parameters used and less violation of assumptions (Akaike, Reference Akaike1981).

Results

During the field surveys, a total of 1339.91 km of transects were covered in 75.70 km2 with 83 h 05 min of effort. Throughout the year and along the estuary, 241 groups of S. guianensis were observed, composed by 1–20 individuals, and totalling 975 individuals sighted.

The model that best fits the data with support from the AIC in the Distance software was the half-normal with cosine adjustments. With the model and adjustment selected, the estimated total population abundance was 193 individuals (10.46% CV, 95% CI 158–237) and the average density was 2.55 ind km−2 (10.46% CV, 95% CI 2.08–3.13). The expected mean group size was 4.15 individuals (4.93% CV, 95% CI 3.76–4.57). The coefficient of variation (CV) is the ration of standard deviation to the mean, and the confidence interval (CI) is a range of values that lies between an upper and lower interval that is likely to include a population value with a certain degree of confidence.

The distribution of the species was heterogeneous in the study area, with 48.72% (n = 120, Δ = 475) of the sightings in Baía de Trapandé, followed by the Mar de Cananéia 32.72% (n = 78, Δ = 319), and Mar de Cubatão 18.56% (n = 43, Δ = 181) (Figure 1).

A stratified analysis confirmed the heterogeneous distribution of the species in the sampled sectors, with the Mar de Cananéia and Baía de Trapandé being more densely populated with 2.76 ind km−2 (18.35% CV, 95% CI 1.93–3.96) and 2.76 ind km−2 (14.64% CV, 95% CI 2.07–3.66), respectively, and the less dense Mar de Cubatão, with 1.59 ind km−2 (21.93% CV, 95% CI 1.04–2.44). Tables 1 and 2 present the results found by the Distance analyses.

Table 1.

Parameters from half-normal model and cosine adjust with the lowest AIC value, for density and abundance estimates of Sotalia guianensis at the Cananéia estuarine-lagoon complex, São Paulo, Brazil

D, density; DS, group density; N, abundance.

Table 2.

Parameters from half-normal model and cosine adjust with the lowest AIC value, for density and abundance estimates of Sotalia guianensis in each surveyed area at the Cananéia estuarine-lagoon complex, São Paulo, Brazil

D, density; DS, group density; N, abundance; n, number of records; L, transect length.

Discussion

The basis for the design and development of this survey in the Cananéia estuary was the experimental model applied by Rollo (Reference Rollo2002), which estimated 118 individuals. The effort and total area sampled in this survey were very similar to that model. In this study, the estimated abundance value was 193 individuals, which is comparable to Havukainen et al.'s (Reference Havukainen, Monteiro-Filho and Filla2011) estimate of 195 individuals in the estuary. However, Havukainen et al. (Reference Havukainen, Monteiro-Filho and Filla2011) surveyed only the Baía de Trapandé region, which is a smaller area than that sampled in this study. When comparing the abundance obtained only for the Baía de Trapandé region, Havukainen et al. (Reference Havukainen, Monteiro-Filho and Filla2011) estimate of 105 individuals (95% CI 79–139) is slightly higher than the value presented here, considering the CI. Geise et al. (Reference Geise, Gomes and Cerqueira1999) obtained the highest abundance estimate for the estuary, with 704.8 individuals (±367.7). However, their use of the negative exponential model, which tends to inflate values, may have contributed to this high estimate, as well as the experimental design applied and the low survey effort of about 82 km, which is below the recommended minimum for reliable results (Buckland et al., Reference Buckland, Anderson, Burnham, Laake, Borchers and Thomas2001).

The density of dolphins estimated in this study, 2.55 ind km−2, is relatively high compared to some physiographically similar regions, such as Baía de Guaratuba (0.15 ind km−2; Filla, Reference Filla2004) and Miskito Cayos Reserve in Nicaragua, with 0.486–0.647 ind km−2 (Edwards and Schnell, Reference Edwards and Schnell2001). Rollo (Reference Rollo2002) and Havukainen et al. (Reference Havukainen, Monteiro-Filho and Filla2011) found some of the highest densities recorded for the area, with 24.36 and 12.41 ind km−2, respectively. Rollo (Reference Rollo2002) suggests that remarkably high values of local density in some sampled sectors, in contrast with the small number found in other sectors, could have influenced the overall value. Havukainen et al. (Reference Havukainen, Monteiro-Filho and Filla2011) concentrated their surveys in Baía de Trapandé, which is known for its intense use by dolphins, and this could also explain the high value estimated by their analysis.

The average group size of S. guianensis, at 4.15 individuals, was higher than previously recorded in the Cananéia estuary by Geise et al. (Reference Geise, Gomes and Cerqueira1999), Rollo (Reference Rollo2002), Filla and Monteiro-Filho (Reference Filla and Monteiro-Filho2009) and Havukainen et al. (Reference Havukainen, Monteiro-Filho and Filla2011). Typically, S. guianensis forms small groups of 2–16 individuals (Lodi and Hetzel, Reference Lodi and Hetzel1998; Geise et al., Reference Geise, Gomes and Cerqueira1999; Da Silva et al., Reference Da Silva, Fettuccia, Rodrigues, Edwards, Moreno, Moura, Wedekin, Bazzalo, Emin-Lima, Carmo, Siciliano and Utreras2010), although larger groups have been observed in the bays of Rio de Janeiro state (Lodi, Reference Lodi2003; Azevedo et al., Reference Azevedo, Viana, Oliveira and Van Sluys2005; Flach et al., Reference Flach, Flach and Chiarello2008), Baía de Paranaguá (PR) and Baía do Norte (SC) (Daura-Jorge et al., Reference Daura-Jorge, Wedekin, Piacentini and Simões-Lopes2005; Santos et al., Reference Santos, Cremer, Secchi, Flach, Filla, Hubner and Dussán-Duque2010a), and in the Gulf of Venezuela (Espinoza-Rodríguez et al., Reference Espinoza-Rodríguez, De Turris-Morales, Takahiro and Barrios-Garrido2019). The formation of larger groups is driven by social purposes such as reproduction, protection against injury and predation and foraging when prey abundance is higher, and it varies based on the activity performed (Edwards and Schnell, Reference Edwards and Schnell2001; Araújo et al., Reference Araújo, Araújo, Souto, Parente and Geise2007; Santos et al., Reference Santos, Oshima, Pacífico and Silva2010b). The distribution of trophic resources can influence the composition and size of groups, as well as social organization and vagility (Chen et al., Reference Chen, Qiu, Jia, Hung and Liu2011). In areas with few predators, such as the study area, the presence of the species may be related to the physical characteristics of the habitat that affect the availability of resources, which may vary seasonally (Lodi, Reference Lodi2003; Godoy et al., Reference Godoy, Andriolo and Filla2015).

A stratified analysis confirmed that dolphins in the Cananéia estuary use different areas heterogeneously. The most densely populated areas, Mar de Cananéia and Baía de Trapandé, are closer to the ocean and have less variation in salinity and reduced freshwater intake. This pattern has been found for S. guianensis in many studies (Geise et al., Reference Geise, Gomes and Cerqueira1999; Rollo, Reference Rollo2002; Oliveira and Monteiro-Filho, Reference Oliveira and Monteiro-Filho2008; Godoy et al., Reference Godoy, Andriolo and Filla2015; Oshima and Santos, Reference Oshima and Santos2016; Mello et al., Reference Mello, Molina, Kajin and Santos2019). Areas close to the open sea, such as Baía de Trapandé, may offer greater diversity and availability of resources, with deeper depth gradients providing more feeding strata. Conversely, shallower areas such as Mar de Cananéia provide protection for mothers and calves against predators (Garaffo et al., Reference Garaffo, Dans, Pedraza, Crespo and Degrati2007). The preference for shallow or deep water varies among populations and their habitats, and the fact that the species is found at different depths demonstrates its behavioural flexibility under different environmental conditions (Araújo et al., Reference Araújo, Araújo, Souto, Parente and Geise2007; Azevedo et al., Reference Azevedo, Oliveira, Viana and Van Sluys2007; Da Silva et al., Reference Da Silva, Fettuccia, Rodrigues, Edwards, Moreno, Moura, Wedekin, Bazzalo, Emin-Lima, Carmo, Siciliano and Utreras2010). The distribution pattern of the species in each area demonstrates areas with greater intensity of use and behaviours strongly associated with specific sites (Wedekin et al., Reference Wedekin, Daura-Jorge, Piacentini and Simões-Lopes2007; Cremer et al., Reference Cremer, Hardt, Tonello and Simões-Lopes2011; Godoy et al., Reference Godoy, Andriolo and Filla2015; Monteiro-Filho et al., Reference Monteiro-Filho, Deconto, Louzada, Wanderley, Godoy, Medeiros, Rossi-Santos and Finkl2018).

The distribution and abundance of cetacean prey and other marine predators can be influenced by various environmental factors, both short and long term. Topography and associated currents are among these factors, which can lead to vertical mixing of water layers and nutrient distribution. Additionally, the presence of tides in channels can concentrate fish and impact the local distribution and foraging behaviour of cetaceans, as demonstrated in certain areas (Anderwald et al., Reference Anderwald, Evans, Dyer, Dale, Wright and Hoelzel2012). Food availability has been identified as the main factor influencing the spatial, behavioural and foraging strategies of delphinids (Bräger and Bräger, Reference Bräger and Bräger2019). Marine environments are complex, three-dimensional habitats with specific physical and chemical regimes (Bräger et al., Reference Bräger, Harraway and Manly2003). The distribution of cetaceans reflects their preference for specific habitats, which are associated with a wide range of biotic and abiotic factors that may directly affect species according to their physiological limits or by influencing prey availability (Bräger et al., Reference Bräger, Harraway and Manly2003; Garaffo et al., Reference Garaffo, Dans, Pedraza, Crespo and Degrati2007).

The persistence of the species throughout the year indicates that the environment offers sufficient resources for the population (Hardt et al., Reference Hardt, Cremer, Tonello and Simões-Lopes2010; Monteiro-Filho et al., Reference Monteiro-Filho, Deconto, Louzada, Wanderley, Godoy, Medeiros, Rossi-Santos and Finkl2018). Residency is common for this species throughout its distribution, as observed in Caravelas (Rossi-Santos et al., Reference Rossi-Santos, Wedekin and Monteiro-Filho2007), Baía de Sepetiba (Campos et al., Reference Campos, Fernandes, Marques and Simão2004), Baía de Babitonga (Hardt et al., Reference Hardt, Cremer, Tonello and Simões-Lopes2010; Cremer et al., Reference Cremer, Hardt, Tonello and Simões-Lopes2011), Costa Rica (Gamboa-Poveda and May-Collado, Reference Gamboa-Poveda and May-Collado2006) and the Gulf of Venezuela (Espinoza-Rodríguez et al., Reference Espinoza-Rodríguez, De Turris-Morales, Takahiro and Barrios-Garrido2019). Activities such as feeding, reproduction and parental care usually indicate a residential life area (Gamboa-Poveda and May-Collado, Reference Gamboa-Poveda and May-Collado2006). Therefore, residency patterns may reflect differences in individual responses to essential activities such as feeding and reproduction in a heterogeneous environment (Rossi-Santos et al., Reference Rossi-Santos, Wedekin and Monteiro-Filho2007).

The distribution of natural resources in small patches creates differences in densities among populations and within a habitat, which is a common tendency for most populations (Begon et al., Reference Begon, Harper and Townsend1996). The variations observed in the estimates for the Cananéia estuary probably reflect fluctuations in the population due to natural interannual changes in the balance between additions (births and immigration) and deletions (death and emigration). The movement of individuals in and out of the Cananéia estuary occurs daily, and some individuals may move between the two estuarine complexes that form the Lagamar estuarine complex, Cananéia and Paranaguá estuaries, which are connected by a long artificial channel constructed in the 1950s (Geise et al., Reference Geise, Gomes and Cerqueira1999; Oshima and Santos, Reference Oshima and Santos2016; Mello et al., Reference Mello, Molina, Kajin and Santos2019; Santos et al., Reference Santos, Laílson-Brito, Flach, Oshima, Figueiredo, Carvalho, Ventura, Molina and Azevedo2019).

Anthropogenic impacts can also lead to differences in densities in the same habitat (Chen et al., Reference Chen, Zheng, Zhai, Xu, Sun, Wang and Yang2008; Cremer et al., Reference Cremer, Hardt, Tonello and Simões-Lopes2011; Azevedo et al., Reference Azevedo, Carvalho, Kajin, Van Sluys, Bisi, Cunha and Lailson-Brito2017). Coastal species are particularly vulnerable to the cumulative impact of anthropogenic activities due to their proximity to areas of intense human presence and high site fidelity, which may exacerbate these impacts (Ramos et al., Reference Ramos, Di Beneditto and Lima2000; Chen et al., Reference Chen, Zheng, Zhai, Xu, Sun, Wang and Yang2008; Dawson et al., Reference Dawson, Wade, Slooten and Barlow2008; Smith et al., Reference Smith, Frère, Kobryn and Bejder2016; Azevedo et al., Reference Azevedo, Carvalho, Kajin, Van Sluys, Bisi, Cunha and Lailson-Brito2017). Habitat degradation, fisheries, urbanization and industrial development, chemical and noise pollution and dolphin and whale watching have all been identified as negatively affecting population decline (Chen et al., Reference Chen, Qiu, Jia, Hung and Liu2011; Smith et al., Reference Smith, Frère, Kobryn and Bejder2016; Karczmarski et al., Reference Karczmarski, Huang and Chan2017). Repeated exposure to these threats can lead to long-term effects, disrupting critical behaviours, changing acoustic communication patterns and causing displacement and area abandonment (Rollo et al., Reference Rollo, Jodas and Natal2016; Smith et al., Reference Smith, Frère, Kobryn and Bejder2016).

Sotalia dolphins face several direct threats such as bycatch in fishing nets, harvesting of natural resources, vessel traffic and tourism (Crespo et al., Reference Crespo, Alarcon, Alonso, Bazzalo, Borobia, Cremer, Filla, Lodi, Magalhães, Marigo, Queiróz, Reynolds JE, Schaeffer, Dorneles, Lailson-Brito and Wetzel2010; Flores et al., Reference Flores, Da Silva, Fettuccia, Würsig, Thewissen and Kovacs2018; Secchi et al., Reference Secchi, Santos and Reeves2018). The Scientific Committee of the International Whaling Commission (IWC) has identified incidental mortality of Sotalia as a significant threat (Crespo et al., Reference Crespo, Alarcon, Alonso, Bazzalo, Borobia, Cremer, Filla, Lodi, Magalhães, Marigo, Queiróz, Reynolds JE, Schaeffer, Dorneles, Lailson-Brito and Wetzel2010). Bycatch is considered one of the most significant threats to marine life globally, affecting not only individual species but also entire communities (Breen et al., Reference Breen, Brown, Reid and Rogan2017).

The world's oceans have suffered from centuries of human exploitation and overfishing, resulting in local extinctions, high pollution levels, habitat loss and degradation and altered ecosystems with compromised trophic relations (Costello and Ballantine, Reference Costello and Ballantine2015; Woodcock et al., Reference Woodcock, O'Leary, Kaiser and Pullin2017). Constant and increasing threats to marine diversity have raised concerns about ocean preservation and local population maintenance. As a result, several protected areas have been designated and established worldwide (Bossley et al., Reference Bossley, Steiner, Rankin and Bejder2017; Venter et al., Reference Venter, Magrach, Outram, Klein, Possingham, Di Marco and Watson2017). The implementation of protected areas and habitat management improvements has shown positive effects towards species presence and population increase, especially for coastal species (Bossley et al., Reference Bossley, Steiner, Rankin and Bejder2017). For example, Bossley et al. (Reference Bossley, Steiner, Rankin and Bejder2017) observed population growth in an industrial estuary where previously there had been a decline due to environmental degradation, particularly from tourism and port dredging.

However, over 90% of protected areas still allow some form of fishing, and more than half of coastal countries have not designated any protected areas (Costello and Ballantine, Reference Costello and Ballantine2015; Woodcock et al., Reference Woodcock, O'Leary, Kaiser and Pullin2017). In Brazilian waters, studies show that most protected areas do not include the entire home range of many marine mammals and still allow human activities that interfere with the species' distribution and habitat use, including S. guianensis, leading to negative effects on local biodiversity (Santos et al., Reference Santos, Figueiredo and Bressem2017; Tardin et al., Reference Tardin, Maciel, Espécie, Melo-Santos, Simão and Alves2020).

Identifying the habitats used by wildlife for essential natural behaviours, such as feeding, resting, parental care and breeding, is critical for determining priority areas for conservation and designing strategies to mitigate human impacts on animal populations (Smith et al., Reference Smith, Frère, Kobryn and Bejder2016; Venter et al., Reference Venter, Magrach, Outram, Klein, Possingham, Di Marco and Watson2017; Tardin et al., Reference Tardin, Maciel, Espécie, Melo-Santos, Simão and Alves2020). This is the first step in developing effective conservation strategies that can achieve long-term goals, using scientific evidence to evaluate the effectiveness of the actions implemented and identify the factors that influence it (Karczmarski et al., Reference Karczmarski, Huang and Chan2017; Woodcock et al., Reference Woodcock, O'Leary, Kaiser and Pullin2017). Long-term assessments and continuous monitoring of population demographic patterns are therefore necessary, as they allow for the identification of key habitats and the evaluation of potential anthropogenic threats and animal responses (Bailey and Thompson, Reference Bailey and Thompson2009; Campbell et al., Reference Campbell, Thomas, Whitaker, Douglas, Calambokidis and Hildebrand2015).

The Cananéia estuary has been identified as a vital area of residence for S. guianensis, providing resources for this and other marine populations. This species is highly valued by the local population of Cananéia, as well as by traditional fishermen, and is also a popular attraction for tourism, contributing significantly to the community's income. Reinforcement of existing protective measures for the habitat and greater involvement by the local community and stakeholders are crucial to achieving priority goals. The combination of different protected areas may bring balance between biodiversity, habitat protection and natural resource use and exploitation, leading to sustainable development and the continued presence of this species.

Data

The authors confirm that the data supporting the findings of the current study are available within the article. Interested readers to other materials and datasets could request them from the corresponding authors.

Acknowledgements

We would like to express our gratitude to several individuals and organizations for their support during our field research. The Instituto Oceanográfico, Universidade de São Paulo (IOUSP) provided valuable logistical assistance. Dr Felipe Fornazari, Júlia Dombroski (MSc.), Rodrigo Araújo de Souza (MSc.) and Ingrid Zwar (MSc.) generously assisted us during our field surveys. Dr Ricardo S. Bovendorp provided us with helpful information during our population estimates. We are also thankful to the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the Scholarship and Cetacean Society International (CSI) for the small grants.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Inaê Guion de Almeida and Mario Manoel Rollo Jr. The first draft of the manuscript was written by Inaê Guion de Almeida and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Financial support

The author Inaê Guion de Almeida received a doctoral scholarship from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and three small grants from the Cetacean Society International (CSI) to carry out field surveys and participate in national and international scientific events.

Competing interest

None.

Ethical standards

Not applicable.

References

Akaike, H (1981) Likelihood of a model and information criteria. Journal of Econometrics 16, 3–14. http://doi.org/10.1016/0304-4076(81)90071-3CrossRefGoogle Scholar
Anderwald, P, Evans, PGH, Dyer, R, Dale, A, Wright, PJ and Hoelzel, AR (2012) Spatial scale and environmental determinants in minke whale habitat use and foraging. Marine Ecology Progress Series 450, 259–274. https://doi.org/10.3354/meps09573CrossRefGoogle Scholar
Araújo, JP, Araújo, ME, Souto, A, Parente, CL and Geise, L (2007) The influence of seasonality, tide and time of activities on the behaviour of Sotalia guianensis (Van Bénéden) (Cetacea, Delphinidae) in Pernambuco, Brazil. Revista Brasileira de Zoologia 24(4), 1122–1130. https://doi.org/10.1590/S0101-81752007000400032CrossRefGoogle Scholar
Azevedo, AF, Lailson-Brito, J Jr, Cunha, HA and Van Sluys, M (2004) A note on site fidelity of marine tucuxis (Sotalia fluviatilis) in Guanabara Bay, southeastern Brazil. Journal of Cetacean Research and Management 6(3), 265–268.CrossRefGoogle Scholar
Azevedo, AF, Viana, SC, Oliveira, AM and Van Sluys, M (2005) Group characteristics of marine tucuxis (Sotalia fluviatilis) (Cetacea: Delphinidae) in Guanabara Bay, south-eastern Brazil. Journal of the Marine Biological Association of the United Kingdom 85, 209–212. https://doi.org/10.1017/S0025315405011082hCrossRefGoogle Scholar
Azevedo, AF, Oliveira, AM, Viana, SC and Van Sluys, M (2007) Habitat use by marine tucuxis (Sotalia guianensis) (Cetacea: Delphinidae) in Guanabara Bay, south-eastern Brazil. Journal of the Marine Biological Association of the United Kingdom 87, 201–205. https://doi.org/10.1017/S0025315407054422CrossRefGoogle Scholar
Azevedo, A, Carvalho, R, Kajin, M, Van Sluys, M, Bisi, T, Cunha, H and Lailson-Brito, J (2017) The first confirmed decline of a delphinid population from Brazilian waters: 2000–2015 abundance of Sotalia guianensis in Guanabara Bay, South-eastern Brazil. Ecological Indicators 79, 1–10. https://doi.org/10.1016/j.ecolind.2017.03.045CrossRefGoogle Scholar
Bailey, H and Thompson, PM (2009) Using marine mammal habitat modelling to identify priority conservation zones within a marine protected area. Marine Ecology Progress Series 378, 279–287. https://doi.org/10.3354/meps07887CrossRefGoogle Scholar
Begon, M, Harper, JL and Townsend, CR (1996) Ecology: Individuals, Populations and Communities, 3rd Edn. Oxford: Blackwell Science Ltd.CrossRefGoogle Scholar
Bisi, TL (2001) Estimativa da densidade populacional do boto-cinza Sotalia guianensis (Cetacea: Delphinidae) na região estuarina lagunar de Cananéia, SP. Monography. São Paulo, Brazil: Universidade Estadual Paulista.Google Scholar
Borobia, M, Siciliano, S, Lodi, L and Hoek, W (1991) Distribution of the South American dolphin Sotalia fluviatilis. Canadian Journal of Zoology 69, 1025–1039. https://doi.org/10.1139/z91-148CrossRefGoogle Scholar
Bossley, MI, Steiner, A, Rankin, RW and Bejder, L (2017) A long-term study of bottlenose dolphins (Tursiops aduncus) in an Australian industrial estuary: Increased sightings associated with environmental improvements. Marine Mammal Science 33, 277–290. https://doi.org/10.1111/mms.12368CrossRefGoogle Scholar
Bräger, S and Bräger, Z (2019) Movement patterns of odontocetes through space and time. Ethology and Behavioral Ecology of Odontocetes, 117–144.CrossRefGoogle Scholar
Bräger, S, Harraway, JA and Manly, BFJ (2003) Habitat selection in a coastal dolphin species (Cephalorhynchus hectori). Marine Biology 143, 233–244. https://doi.org/10.1007/s00227-003-1068-xCrossRefGoogle Scholar
Breen, P, Brown, S, Reid, D and Rogan, E (2017) Where is the risk? Integrating a spatial distribution model and a risk assessment to identify areas of cetacean interaction with fisheries in the Northeast Atlantic. Ocean and Coastal Management 136, 148–155. https://doi.org/10.1016/j.ocecoaman.2016.12.001CrossRefGoogle Scholar
Buckland, ST, Anderson, DR, Burnham, KP, Laake, JL, Borchers, DL and Thomas, L (2001) Introduction to Distance Sampling: Estimating Abundance of Biological Populations. Oxford: Oxford University Press.CrossRefGoogle Scholar
Buckland, ST, Rexstad, E, Thomas, L and Borchers, DL (2016) Distance sampling surveys of population size: Enabling better decision-making by wildlife managers. In Aston, P, Mulholland, A and Tant, K (eds), UK Success Stories in Industrial Mathematics. Cham: Springer International Publishing, 45–51.CrossRefGoogle Scholar
Campbell, GS, Thomas, L, Whitaker, K, Douglas, AB, Calambokidis, J and Hildebrand, JA (2015) Inter-annual and seasonal trends in cetacean distribution, density and abundance off Southern California. Deep Sea Research Part II: Topical Studies in Oceanography 112, 143–157. https://doi.org/10.1016/j.dsr2.2014.10.008CrossRefGoogle Scholar
Campos, PG, Fernandes, MF, Marques, VCL and Simão, SM (2004) Estimativa populacional de Sotalia fluviatilis (GERVAIS,1853) da Baía de Sepetiba (RJ). Revista Universidade Rural: Série Ciências da Vida 24(2), 175–180.Google Scholar
Cantor, MC, Wedekin, LL, Daura-Jorge, FG, Rossi-Santos, MR and Simões-Lopes, PC (2012) Assessing population parameters and trends of Guiana dolphins (Sotalia guianensis): An eight-year mark-recapture study. Marine Mammal Science 28(1), 63–83. https://doi.org/10.1111/j.1748-7692.2010.00456.xCrossRefGoogle Scholar
Chen, B, Zheng, D, Zhai, F, Xu, X, Sun, P, Wang, Q and Yang, G (2008) Abundance, distribution and conservation of Chinese white dolphins (Sousa chinensis) in Xiamen, China. Mammalian Biology 73, 156–164. https://doi.org/10.1016/j.mambio.2006.12.002CrossRefGoogle Scholar
Chen, T, Qiu, Y, Jia, X, Hung, SK and Liu, W (2011) Distribution and group dynamics of Indo-Pacific humpback dolphins (Sousa chinensis) in the western Pearl River Estuary, China. Mammalian Biology 76, 93–96. https://doi.org/10.1016/j.mambio.2010.01.001CrossRefGoogle Scholar
Claudet, J, Loiseau, C, Sostres, M and Zupan, M (2020) Underprotected marine protected areas in a global biodiversity hotspot. One Earth 2, 380–384. https://doi.org/10.1016/j.oneear.2020.03.008CrossRefGoogle Scholar
Costello, MJ and Ballantine, B (2015) Biodiversity conservation should focus on no-take marine reserves: 94% of marine protected areas allow fishing. Trends in Ecology & Evolution 30, 507–509. https://doi.org/10.1016/j.tree.2015.06.011CrossRefGoogle ScholarPubMed
Cremer, MJ, Hardt, FAS, Tonello, AJ Jr and Simões-Lopes, PC (2011) Distribution and status of the Guiana dolphin Sotalia guianensis (Cetacea, Delphinidae) population in Babitonga Bay, Southern Brazil. Zoological Studies 50(3), 327–337.Google Scholar
Crespo, EA, Alarcon, D, Alonso, M, Bazzalo, M, Borobia, M, Cremer, M, Filla, G, Lodi, L, Magalhães, FA, Marigo, J, Queiróz, HL, Reynolds JE, III, Schaeffer, Y, Dorneles, PR, Lailson-Brito, J and Wetzel, DL (2010) Report of the working group on major threats and conservation. Latin American Journal of Aquatic Mammals 8(1/2), 47–56. https://doi.org/10.5597/lajam00153CrossRefGoogle Scholar
Cullen, R Jr and Rudran, R (2003) Transectos lineares na estimativa de densidade de mamíferos e aves de médio e grande porte. In Cullen, R Jr, Rudran, R and Valladares-Padua, C (eds), Métodos de estudos em biologia da conservação e manejo da vida silvestre. Curitiba: Editora da Universidade Federal do Paraná, 169–179.Google Scholar
Da Silva, VMF, Fettuccia, D, Rodrigues, ES, Edwards, H, Moreno, IB, Moura, JF, Wedekin, LL, Bazzalo, M, Emin-Lima, NR, Carmo, NAS, Siciliano, S and Utreras, VB (2010) Report of the working group on distribution, habitat characteristics and preferences, and group size. Latin American Journal of Aquatic Mammals 8(1/2), 31–38. https://doi.org/10.5597/lajam00151CrossRefGoogle Scholar
Daura-Jorge, FG, Wedekin, LL, Piacentini, VQ and Simões-Lopes, PS (2005) Seasonal and daily patterns of group size, cohesion and activity of the estuarine dolphin, Sotalia guianensis (P.J. van Bénéden) (Cetacea, Delphinidae), in southern Brazil. Revista Brasileira de Zoologia 22(4), 1014–1021. https://doi.org/10.1590/S0101-81752005000400029CrossRefGoogle Scholar
Dawson, S, Wade, P, Slooten, E and Barlow, J (2008) Design and field methods for sighting surveys of cetaceans in coastal and riverine habitats. Mammal Review 38(1), 19–49. http://doi.org/10.1111/j.1365-2907.2008.00119.xCrossRefGoogle Scholar
Desvaux, JAS (2013) Captura acidental da Toninha, Pontoporia blainvillei (Cetacea: Pontoporiidae) e do Boto-cinza, Sotalia guianensis (Cetacea: Delphinidae) em redes de pesca no Complexo Estuarino Lagunar de Cananéia, Litoral Sul do estado de São Paulo (Master dissertation). Universidade Federal do Paraná, Paraná, Brazil.Google Scholar
Di Beneditto, APM and Ramos, RMA (2004) Biology of the marine tucuxi dolphin (Sotalia fluviatilis) in south-eastern Brazil. Journal of the Marine Biological Association of the United Kingdom 84, 1245–1250. http://doi.org/10.1017/S0025315404010744hCrossRefGoogle Scholar
Domit, C (2006) Comportamento de pesca do boto-cinza, Sotalia guianensis (van Bénéden, 1864) (PhD thesis). Universidade Federal do Paraná, Paraná, Brazil.Google Scholar
Edwards, HH and Schnell, GD (2001) Status and ecology of Sotalia fluviatilis in the Cayos Miskito Reserve, Nicaragua. Marine Mammal Science 17(3), 445–472. https://doi.org/10.1111/j.1748-7692.2001.tb00998.xCrossRefGoogle Scholar
Espinoza-Rodríguez, N, De Turris-Morales, K, Takahiro, S and Barrios-Garrido, H (2019) Guiana dolphin (Sotalia guianensis) in the southern Gulf of Venezuela: Seasonal distribution, group size, and habitat use. Regional Studies in Marine Science 32, 1–8. https://doi.org/10.1016/j.rsma.2019.100874CrossRefGoogle Scholar
Filla, GF (2004) Estimativa da densidade populacional e estrutura de agrupamento do boto-cinza Sotalia guianensis (Cetacea, Delphinidae) na Baía de Guaratuba e na porção norte do Complexo Estuarino da Baía de Paranaguá, PR. PhD thesis. Universidade Federal do Paraná, Paraná, Brazil.Google Scholar
Filla, GF and Monteiro-Filho, ELA (2009) Monitoring tourism schooners observing estuarine dolphins (Sotalia guianensis) in the estuarine complex of Cananéia, southeast Brazil. Aquatic Conservation: Marine and Freshwater Ecosystems 19, 772–778. https://doi.org/10.1002/aqc.1034CrossRefGoogle Scholar
Flach, L, Flach, PA and Chiarello, AG (2008) Density, abundance and distribution of the Guiana dolphin, (Sotalia guianensis van Benéden, 1864) in Sepetiba Bay, Southeast Brazil. Journal of Cetacean Research and Management 10(1), 31–36.CrossRefGoogle Scholar
Flores, PAC, Da Silva, VMF and Fettuccia, DC (2018) Tucuxi and Guiana dolphins: Sotalia fluviatilis and S. guianensis. In Würsig, B, Thewissen, JGM and Kovacs, KM (eds), Encyclopedia of Marine Mammals. San Diego: Academic Press, 1024–1027.CrossRefGoogle Scholar
Gamboa-Poveda, M and May-Collado, LJ (2006) Insights on the occurrence, residency, and behaviour of two coastal dolphins from Gandoca-Manzanillo, Costa Rica: Sotalia guianensis and Tursiops truncatus (Family Delphinidae). International Whaling Commission, Cambridge, SC/58/SM4, 1–9.Google Scholar
Garaffo, GV, Dans, SL, Pedraza, SN, Crespo, EA and Degrati, M (2007) Habitat use by dusky dolphin in Patagonia: How predictable is their location? Marine Biology 152, 165–177. https://doi.org/10.1007/s00227-007-0686-0CrossRefGoogle Scholar
Geise, L, Gomes, N and Cerqueira, R (1999) Behaviour, habitat use and population size of Sotalia fluviatilis (Gervais, 1853) (Cetacea, Delphinidae) in the Cananéia estuary region, São Paulo, Brazil. Revista Brasileira de Biologia 59(2), 183–194. https://doi.org/10.1590/S0034-71081999000200002CrossRefGoogle Scholar
Godoy, DF, Andriolo, A and Filla, GF (2015) The influence of environmental variables on estuarine dolphins (Sotalia guianensis) spatial distribution and habitat used in the estuarine lagoon complex of Cananéia, Southeastern Brazil. Ocean and Coastal Management 106, 68–76. https://doi.org/10.1016/j.ocecoaman.2015.01.013CrossRefGoogle Scholar
Hardt, FAS, Cremer, MJ, Tonello, AJ Jr and Simões-Lopes, PCA (2010) Residence patterns of the Guiana dolphin Sotalia guianensis in Babitonga bay, south coast of Brazil. Latin American Journal of Aquatic Mammals 8(1/2), 117–121. https://doi.org/10.5597/lajam00160CrossRefGoogle Scholar
Havukainen, L, Monteiro-Filho, ELA and Filla, GF (2011) Population density of Sotalia guianensis (Cetacea: Delphinidae) in the Cananéia region, Southeastern Brazil. Revista de Biología Tropical 59(3), 1275–1284. http://doi.org/10.15517/rbt.v0i0.3398Google ScholarPubMed
Instituto Chico Mendes de Conservação da Biodiversidade (2018) Livro Vermelho da Fauna Brasileira Ameaçada de Extinção: Volume I. Brasília: ICMBio/MMA.Google Scholar
International Union for Conservation of Nature (2019) IUCN red list of threatened species: Version 2019.3. Available at http://www.iucnredlist.org (accessed 2 July 2020).Google Scholar
Karczmarski, L, Huang, S and Chan, SCY (2017) Threshold of long-term survival of a coastal Delphinid in anthropogenically degraded environment: Indo-Pacific humpback dolphins in Pearl River Delta. Scientific Reports 7, 42900. https://doi.org/10.1038/srep42900CrossRefGoogle ScholarPubMed
Kumpera, B (2007) Contribuição ao processo sedimentar atual no Canal do Ararapira, sistema-estuarino-lagunar de Cananéia-Iguape (PhD thesis). Universidade de São Paulo, São Paulo, Brazil.Google Scholar
Lima, JY, Carvalho, APM, Azevedo, CT, Barbosa, LA and Silveira, LS (2017) Variation of age and total length in Sotalia guianensis (Van Bénéden, 1864) (Cetacea, Delphinidae), on the coast of Espírito Santo state, Brazil. Brazilian Journal of Biology 77(3), 437–443. https://doi.org/10.1590/1519-6984.13215CrossRefGoogle Scholar
Lodi, LF (2003) Tamanho e composição de grupo dos Botos-Cinza, Sotalia guianensis (van Bénéden, 1864) (Cetacea, Delphinidae), na Baía de Paraty, Rio de Janeiro, Brasil. Revista Atlântica 25(2), 135–146.Google Scholar
Lodi, LF and Hetzel, B (1998) Grandes agregações do boto-cinza (Sotalia fluviatilis) na Baía da Ilha Grande, Rio de Janeiro. Bioikos 12(2), 26–30.Google Scholar
Mello, A, Molina, J, Kajin, M and Santos, M (2019) Abundance estimates of Guiana dolphins (Sotalia guianensis; Van Bénéden, 1864) inhabiting an estuarine system in Southeastern Brazil. Aquatic Mammals 45, 56–65. https://doi.org/10.1578/AM.45.1.2019.56CrossRefGoogle Scholar
Miller, DL, Rextad, E, Thomas, L, Marshall, L and Laake, JL (2019) Distance sampling in R. Journal of Statistical Software 89(1), 1–28. https://doi:10.18637/jss.v089.i01CrossRefGoogle Scholar
Monteiro-Filho, ELA, Deconto, LS, Louzada, CN, Wanderley, RP, Godoy, DF and Medeiros, E (2018) Long-term monitoring of dolphins in a large estuarine system of Southeastern Brazil. In Rossi-Santos, M and Finkl, C (eds), Advances in Marine Vertebrate Research in Latin America: Technological Innovation in Ecology and Conservation. Cham: Springer, 15–40.CrossRefGoogle Scholar
O'Leary, BC, Winther-Janson, M, Bainbridge, JM, Aitken, J, Hawkins, JP and Roberts, CM (2016) Effective coverage targets for ocean protection. Conservation Letters 9, 398–404. https://doi.org/10.1111/conl.12247CrossRefGoogle Scholar
Oliveira, LV and Monteiro-Filho, ELA (2008) Individual identification and habitat use of the estuarine dolphin Sotalia guianensis (Cetacea: Delphinidae) in Cananéia, south-eastern Brazil, using video images. Journal of the Marine Biological Association of the United Kingdom 88(6), 1199–1205. https://doi.org/10.1017/S0025315408000398CrossRefGoogle Scholar
Oshima, JEF and Santos, MCO (2016) Guiana dolphin home range analysis based on 11 years of photo-identification research in a tropical estuary. Journal of Mammalogy 97(2), 599–610. https://doi.org/10.1093/jmammal/gyv207CrossRefGoogle Scholar
Ramos, RMA, Di Beneditto, APM and Lima, NRW (2000) Growth parameters of Pontoporia blainvillei and Sotalia fluviatilis (Cetacea) in northern Rio de Janeiro, Brazil. Aquatic Mammals 26(1), 65–75.Google Scholar
Ramos, RMA, Di Beneditto, APM and Souza, SM (2001) Bone lesions in Sotalia fluviatilis (Cetacea) as a consequence of entanglement: Case report. Brazilian Journal of Veterinary Research and Animal Science 38(4), 192–195. http://doi.org/10.1590/S1413-95962001000400009CrossRefGoogle Scholar
Rollo, MM Jr (2002) Modelagem da distribuição do boto Sotalia guianensis van Bénéden 1863 (Cetacea, Delphinidae) na região de Cananéia, sul do Estado de São Paulo (PhD thesis) Universidade de São Paulo, São Paulo, Brazil.Google Scholar
Rollo, MM Jr, Jodas, A and Natal, RG (2016) A computational model of Guiana dolphin (Sotalia guianensis) responses to the sound fields produced by noise sources. Proceedings of Meetings on Acoustics 27, 010039. https://doi.org/10.1121/2.0000371CrossRefGoogle Scholar
Rosas, FCW, Barreto, AS and Monteiro-Filho, ELA (2003) Age and growth of the estuarine dolphin (Sotalia guianensis) (Cetacea, Delphinidae) on the Paraná coast, southern Brazil. Fishery Bulletin 101(2), 377–383.Google Scholar
Rosas, FCW and Monteiro-Filho, ELA (2002) Reproduction of the estuarine dolphin (Sotalia guianensis) on the coast of Paraná, southern Brazil. Journal of Mammalogy 83(2), 507–515. http://doi.org/10.1644/1545-1542(2002)083<0507:ROTEDS>2.0.CO;22.0.CO;2>CrossRefGoogle Scholar
Rossi-Santos, MR, Wedekin, LL and Monteiro-Filho, ELA (2007) Residence and site fidelity of Sotalia guianensis in the Caravelas River Estuary, eastern Brazil. Journal of the Marine Biological Association of the United Kingdom 87, 207–212. https://doi.org/10.1017/S0025315407055683CrossRefGoogle Scholar
Sandercock, BK (2006) Estimation of demographic parameters from live-encounter data: A summary review. Journal of Wildlife Management 70(6), 1504–1520. http://doi.org/10.2193/0022-541X(2006)70[1504:EODPFL]2.0.CO;2CrossRefGoogle Scholar
Santos, MCO, Cremer, MJ, Secchi, ER, Flach, L, Filla, G, Hubner, A and Dussán-Duque, S (2010 a) Report on the working group on population abundance and density estimation. Latin American Journal of Aquatic Mammals 8(1/2), 39–45. https://doi.org/10.5597/lajam00152CrossRefGoogle Scholar
Santos, MCO, Oshima, JEF, Pacífico, ES and Silva, E (2010 b) Group size and composition of Guiana dolphins (Sotalia guianensis) (Van Bénèden, 1864) in the Paranaguá Estuarine Complex, Brazil. Brazilian Journal of Biology 70, 111–120. https://doi.org/10.1590/S1519-69842010000100015CrossRefGoogle Scholar
Santos, MCO, Figueiredo, GC and Bressem, MFV (2017) Cetaceans using the marine protected area of ‘Parque Estadual Marinho da Laje de Santos’, Southeastern Brazil. Brazilian Journal of Oceanography 65(4), 605–613. https://doi.org/10.1590/s1679-87592017130606504CrossRefGoogle Scholar
Santos, MCO, Laílson-Brito, J, Flach, L, Oshima, JEF, Figueiredo, GC, Carvalho, RR, Ventura, ES, Molina, JMB and Azevedo, AF (2019) Cetacean movements in coastal waters of the southwestern Atlantic Ocean. Biota Neotropica 19(2), e20180670. https://doi.org/10.1590/1676-0611-bn-2018-0670CrossRefGoogle Scholar
Secchi, ER, Ott, PH, Crespo, EA, Kinas, PG, Pedraza, SN and Bordino, P (2001) A first estimate of franciscana (Pontoporia blainvillei) abundance off southern Brazil. Journal of Cetacean Research and Management 3(1), 95–100.CrossRefGoogle Scholar
Secchi, E, Santos, MCO and Reeves, R (2018) Sotalia guianensis (errata version published in 2019). In The IUCN Red List of Threatened Species 2018, e.T181359A144232542. https://doi.org/10.2305/IUCN.UK.2018-2.RLTS.T181359A144232542.en Acessed online 02 July 2020.CrossRefGoogle Scholar
Secretaria do Meio Ambiente (1990) Macrozoneamento do complexo estuarino-lagunar de Cananéia e Iguape: Plano de Gerenciamento Costeiro. São Paulo: SMA, 41.Google Scholar
Sergio, F, Caro, T, Brown, D, Clucas, B, Hunter, J, Ketchum, J, McHugh, K and Hirald, F (2008) Top predators as conservation tools: Ecological rationale, assumptions, and efficacy. Annual Review of Ecology, Evolution, and Systematics 39, 1–19. https://doi.org/10.1146/annurev.ecolsys.39.110707.173545CrossRefGoogle Scholar
Smith, H, Frère, C, Kobryn, H and Bejder, L (2016) Dolphin sociality, distribution and calving as important behavioural patterns informing management. Animal Conservation 19(5), 462–471. https://doi.org/10.1111/acv.12263CrossRefGoogle Scholar
Tardin, RH, Maciel, IS, Espécie, MA, Melo-Santos, G, Simão, SM and Alves, MAS (2020) Modeling habitat use by the Guiana dolphin Sotalia guianensis, in south-eastern Brazil: Effects of environmental and anthropogenic variables, and the adequacy of current measures. Aquatic Conservation: Marine and Freshwater Ecosystems 30(4), 775–786. https://doi.org//10.1002/aqc.3290CrossRefGoogle Scholar
Tessler, MG and Mahiques, MMD (1998) Erosional and depositional processes on the Southern Coast of the State of Sao Paulo: A case study of Cananeia-Iguape System. Anais da Academia Brasileira de Ciências 70(2), 267–275.Google Scholar
Tessler, MG and Souza, LAP (1998) Dinâmica sedimentar e feições sedimentares identificadas na superfície de fundo do sistema Cananéia-Iguape, SP. Revista Brasileira de Oceanografia 46(1), 69–83. http://doi.org/10.1590/S1679-87591998000100006CrossRefGoogle Scholar
Thomas, L, Buckland, ST, Burnham, KP, Anderson, DR, Laake, JL, Borchers, DL and Strindberg, S (2002) Distance sampling. In El-Shaarawi, AH and Piegorsch, WW (eds), Encyclopedia of Environmetrics. Chichester: John Wiley, 544–552.Google Scholar
Venter, O, Magrach, A, Outram, N, Klein, CJ, Possingham, HP, Di Marco, M and Watson, JEM (2017) Bias in protected-area location and its effects on long-term aspirations of biodiversity conventions. Conservation Biology 32(1), 127–134. https://doi.org/10.1111/cobi.12970CrossRefGoogle ScholarPubMed
Vermeulen, E and Bräger, S (2015) Demographics of the disappearing bottlenose dolphin in Argentina: A common species on its way out? PLoS ONE 10(3), 1–19. https://doi.org/10.1371/journal.pone.0119182CrossRefGoogle ScholarPubMed
Wedekin, LL, Daura-Jorge, FG, Piacentini, VQ and Simões-Lopes, PC (2007) Seasonal variations in spatial usage by the estuarine dolphin, Sotalia guianensis (van Bénéden, 1864) (Cetacea; Delphinidae) at its southern limit of distribution. Brazilian Journal of Biology 67(1), 1–8. http://doi.org/10.1590/S1519-69842007000100002CrossRefGoogle Scholar
Whitehead, H, Reeves, RR and Tyack, PL (2000) Science and the conservation, protection, and management of wild cetaceans. In Mann, J, Connor, RC, Tyack, PL and Whitehead, H (eds), Field Studies of Dolphins and Whales. Chicago: University of Chicago Press, 308–332.Google Scholar
Woodcock, P, O'Leary, BC, Kaiser, MJ and Pullin, AS (2017) Your evidence or mine? Systematic evaluation of reviews of marine protected area effectiveness. Fish and Fisheries 18, 668–681. https://doi.org/10.1111/faf.12196CrossRefGoogle Scholar
Zacharias, MA and Roff, JC (2001) Use of focal species in marine conservation and management: A review and critique. Aquatic Conservation: Marine and Freshwater Ecosystems 11, 59–76.CrossRefGoogle Scholar
Figure 0

Figure 1. Study area showing the survey design with line transects and group sightings of Sotalia guianensis at the Cananéia estuarine-lagoon complex, São Paulo, Brazil.

Figure 1

Table 1. Parameters from half-normal model and cosine adjust with the lowest AIC value, for density and abundance estimates of Sotalia guianensis at the Cananéia estuarine-lagoon complex, São Paulo, Brazil

Figure 2

Table 2. Parameters from half-normal model and cosine adjust with the lowest AIC value, for density and abundance estimates of Sotalia guianensis in each surveyed area at the Cananéia estuarine-lagoon complex, São Paulo, Brazil