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Inter-individual association levels correlate to behavioral diversity in coastal bottlenose dolphins (Tursiops truncatus) from the Southwestern Gulf of Mexico


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Introduction: Societies in mammal species are influenced by intrinsic and extrinsic factors that affect the temporality of the associations among individuals. Coastal bottlenose dolphins generally live in small fluid aggregations variable in composition, but the nature of their associations is commonly unknown. Our goal was to determine if school size was influenced by dolphins’ behavior, and if individuals associated to develop particular activities within the coastal waters of Alvarado, Mexico. Methods: In total, 80 boat-based surveys were conducted (2002 - 2003 and 2006 - 2009), where group size, behavior, and photo-identification data were collected. From 237 sightings and 2,021 dolphins the mean school size was 8.5 animals (s. d. = 8.6), but individuals and pairs were observed more frequently (33 %). Results: Temporal differences in school sizes and behavior conveyed with habitat seasonality (P < 0.05), but were inconsistent across years; thus short-term factors such as marine traffic and fisheries intensity were deemed important. Dolphins were commonly feeding (29 %) corresponding to groups of 4 - 6 animals, whereas solitary individuals typically showed evasion (P < 0.01). Discussion and Conclusions: Association coefficients computed for 89 of the 232 identifiable dolphins proved not random only in 6 % of the 3,915 combinations (P < 0.05), and these coefficients were positively correlated to the diversity of activities developed by each dyad (P < 0.01), thus the nature of their associations in most cases (93 %) became richer with time. The community is likely formed by very small units that frequently exchange members; this may be due to large food availability and low predator abundance in the area, but also to avoid detection and threats posed by local artisanal fisheries.
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THERYA, 2015, Vol. 6(2): 337-350 DOI: 10.12933/therya-15-270, ISSN 2007-3364
Las asociaciones entre individuos se correlacionan
con la diversidad de las conductas en delnes costeros
(Tursiops truncatus) del Sureste del Golfo de México
Inter-individual association levels correlate
to behavioral diversity in coastal bottlenose
dolphins (Tursiops truncatus) from the
Southwestern Gulf of Mexico
Marah García-Vital1, Eduardo Morteo1, 2*, Ibiza Marnez-Serrano3, Alberto Delgado-Estrella4 y Carmen Bazúa-Durán5
1Instituto de Ciencias Marinas y Pesquerías, Universidad Veracruzana. Calle Hidalgo Núm. 617, Col. Río Jamapa, CP 94290, Boca del
Río, Veracruz, México. E-mail: (MGV).
2Instituto de Investigaciones Biológicas, Universidad Veracruzana. Calle Dr. Luis Castelazo Ayala s/n, km 2.5 Carr. Xalapa-Veracruz,
Col. Industrial Ánimas, CP 91190, Xalapa, Veracruz, México. E-mail: (EM).
3Facultad de Biología, Universidad Veracruzana. Museo de Zoología. Facultad de Biología, Universidad Veracruzana. Circ. Gonzalo
Aguirre Beltran s/n Zona Universitaria. CP 91090. Xalapa, Veracruz, México. E-mail: (IMS).
4Facultad de Ciencias Naturales, Universidad Autónoma del Carmen. Calle 56 Núm. 4, Esq. Av. Concordia, Col. Benito Juárez, 24180,
Cd. del Carmen, Campeche, México. E-mail: (ADE).
5Facultad de Ciencias, Universidad Nacional Autónoma de México. Circuito exterior s/n, Ciudad Universitaria, 04510 México, D. F.,
México. E-mail: (CBD).
*Corresponding author
Introduction: Societies in mammal species are inuenced by intrinsic and extrinsic factors that aect the temporality
of the associations among individuals. Coastal bottlenose dolphins generally live in small uid aggregations variable in
composition, but the nature of their associations is commonly unknown. Our goal was to determine if school size was
inuenced by dolphins’ behavior, and if individuals associated to develop particular activities within the coastal waters
of Alvarado, Mexico.
Methods: In total, 80 boat-based surveys were conducted (2002 - 2003 and 2006 - 2009), where group size, behavior,
and photo-identication data were collected. From 237 sightings and 2,021 dolphins the mean school size was 8.5
animals (s. d. = 8.6), but individuals and pairs were observed more frequently (33 %).
Results: Temporal dierences in school sizes and behavior conveyed with habitat seasonality (P < 0.05), but were
inconsistent across years; thus short-term factors such as marine trac and sheries intensity were deemed important.
Dolphins were commonly feeding (29 %) corresponding to groups of 4 - 6 animals, whereas solitary individuals typically
showed evasion (P < 0.01).
Discussion and Conclusions: Association coecients computed for 89 of the 232 identiable dolphins proved not
random only in 6 % of the 3,915 combinations (P < 0.05), and these coecients were positively correlated to the diversity
of activities developed by each dyad (P < 0.01), thus the nature of their associations in most cases (93 %) became richer
with time. The community is likely formed by very small units that frequently exchange members; this may be due to
large food availability and low predator abundance in the area, but also to avoid detection and threats posed by local
artisanal sheries.
Key words: Avoidance; behavior; group size; membership; socialization; sheries.
338 THERYA Vol.6(2): 337-350
Societies in mammal species are dynamic and complex (e. g. carnivores, primates, cetaceans),
in which many of their members may interact and associate with other known or unknown
individuals, forming distinctive assemblages (Goodall 1986). The structure of such social units is
often aected by age, sex, reproductive status, hierarchy and kin selection (Beddia 2007); all these
aspects may modify the behavior of individuals (Bräger 1993) and determine how the animals
spend their time in certain areas, thus producing dierent patterns of residency, seasonality or
migration that change their associations and the social structure of the population (Scott and
Chivers 1990).
Dolphin societies or communities (sensu Wells et al. 1987) are generally composed by individuals
that inhabit the same general area and have frequent interactions with each other (Goodall 1986);
thus marine mammalogists often use this term to describe assemblages of individuals of the same
species, instead of assemblages of dierent species as referred in texts of classic ecological theory
(Roughgarden 1989). Such aggregations are loose and uent, where individual and genetic
exchange may occur over time within the limits of the community (Wells et al. 1987).
Individual interactions are inuenced by intrinsic factors such as the presence of recurrent
associations (Connor et al. 2001), which in turn may be determined by extrinsic factors such as
habitat variability (e. g. food abundance and availability, as well as natural and human-related
threats (Lusseau et al. 2006; Quintana-Rizo 2006; Morteo and Hernández 2007; Morteo et al. 2012).
Social and ecological pressures may dictate the temporality of the associations at dierent scales
(McDonald and Carr 1989; Quintana-Rizzo 2006; Morteo et al. 2014). For instance, some species
are known to maintain strong permanent and even multilevel associations such as killer whales
(Orcinus orca) and sperm whales (Physeter microcephalus; Bräger et al. 1994; Whitehead et al. 2012),
whereas other like the spinner dolphin (Stenella longirostris) are very loose (Chilvers and Corkeron
The social structure of coastal bottlenose dolphins (Tursiops truncatus) has been characterized
as ssion-fusion, involving small groups that constantly exchange individuals forming a wide range
of social bonds (Goodall 1986; Wells et al. 1987; Connor et al. 1992). Several communities of the
coastal form of this species are known to present segregation related to sex, age and reproductive
status, thus the nature of their associations is highly variable (Wells et al. 1987; Wells 1991; Connor
et al. 1992; Smolker et al. 1992; Connor et al. 2000; Quintana-Rizzo and Wells 2001; Morteo et al.
Living in social groups facilitates feeding, protecting against harassment, predation, enhances
reproductive output, and promotes communication and learning (Bräger et al. 1994). Individuals
may join or leave a group in response to the gains or losses of participating with the partners
involved within a given social unit (Wrangham et al. 1993). Thus recording the activities of animal
groups is useful to establish behavioral patterns in a specic habitat (Bräger 1993; Steiner 2011),
but also to determine the current state of individuals within a community (Beddia 2007).
Coastal bottlenose dolphins inhabiting the waters o Alvarado in the state of Veracruz have
been studied intermittently since 1993 (García 1995) and reliable data on individual identities has
been collected since 2002 (Del Castillo 2010; Morteo et al. 2014). Many of these dolphins are
known to associate and develop a range of activities, but little is known on how these animals
interact and form groups, and if they do it with dierent purposes (Morteo 2011; García-Vital
2012). The goal of this study is to establish if school size is determined by the activities of the
dolphins, and if individuals associate with specic partners to develop particular sets of activities. 339
García-Vital et al.
Materials and methods
Study area. The Alvarado region is a shallow (< 20 m depth) open coastal habitat in the
southwestern Gulf of Mexico, strongly inuenced by river dischargesFigure 1; habitat
modication is the major threat to the area (Del Castillo 2010; Morteo 2011; García-Vital 2012).
It is the third largest coastal lagoon system in Mexico, and according to the National Institute
of Fisheries (INAPESCA), it’s the most important shrimp shing ground in the state of Veracruz,
which takes place year-around depending on weather and market demands. Sea surface
temperature ranges from 20 to 32.5 °C, with an annual average of 27 °C. The regional climate is
tropical with three seasons: a Dry season (March-June) with a signicant reduction in average
precipitation; a Rainy season (July-October), in which runo from rivers into the adjacent lagoon
and mangrove forest causes high organic matter and nutrient input into coastal waters; and a
Windy season (November-February, locally known as Nortes”), featuring strong winds (up to
80 km h-1) associated with the incursion of northern cold fronts, which may last several days.
Fisheries are relevant to coastal dolphin populations due to the frequent adverse interactions
between dolphins and local sheries, causing incidental mortality of dolphins in nets (Morteo
2011; Morteo et al. 2012). Around 2000 shermen were active in the area, most of which (75 -
85 %) operate in the lagoon and the rest operate in open waters. No ocial data is available on
marine trac or shing eort and port facilities are dedicated to shing, therefore there is no
alternative commercial seagoing activity.
Surveys. Photographic line-transect surveys were conducted at least twice per month from
October 2002 to September 2003 and from May 2006 to April 2009. The extent of the surveyed
area was dependent on the duration of daily operations, and intended to maximize the chance
Figure 1. Study area and survey trajectories (bold lines). Dashed lines show depth contours every 5 m.
340 THERYA Vol.6(2): 337-350
of encountering coastal dolphins, based on their habitat preferences (Fazioli et al. 2006). Surveys
were carried out at constant speed (15 - 18 km h-1) always in low swell conditions (sea state
Beaufort 3, where wind speed < 15 km h-1) on board of a 7 m outboard berglass ski (40 / 60
hp). When dolphins were sighted, the survey was paused to allow habituation (10 min) while
their location was recorded using a GPS (Garmin eTrex Legend). Dolphins were then observed
until their behavior was determined ad libitum (Altmann 1974) and classied into one of the most
commonly used categories which were: 1) Feeding, 2) Socializing, 3) Traveling, 4) Avoiding, 5)
Resting, and 6) Undetermined, following the literature (see Shane 1990; Bräger 1993; Chilvers and
Corkeron 2002; Constantine et al. 2004; Steiner 2011). Subsequently, the group was approached
with caution to avoid disturbing them, at the time that group size was estimated; we used an
inclusive denition of group, consisting in all dolphins observed in apparent association, moving
in the same direction and often, but not always, engaged in the same activity (Bräger et al. 1994);
however, some groups included only one dolphin (Fazioli et al. 2006). Dolphins were followed
until all dorsal ns were photographed or until they were lost from sight; we used SLR cameras,
both analogical (Canon EOS Rebel 2000 with lm Kodak Tri-X-pan ISO 400) and digital (Canon
Rebel XT and Nikon D50) with 70 - 300 mm lenses. The survey was then resumed and the search
proceeded until the study area was completed.
Group size and behavior. All sighting records from 2002 - 2003 and 2006 - 2009 (2002 - 2009
henceforth) were arranged into histograms to determine the most common types of aggregations
and behaviors within the area. Average group size was computed for comparison, whereas
dierences among months, seasons and years were examined for both group size and behavior
frequencies using non-parametric tests (α = 0.05). Also, a correspondence analysis was performed
to explore the relation between group size and the behavioral categories using Statistica 7.0.
Photographic identication. Individual dolphins were identied by the marking patterns on
their dorsal ns (Würsig and Jeerson 1990; Morteo 2011). Markings such as tooth rakes, scars,
pigmentation marks, supercial wounds, and epiphytic organisms are temporary, thus these were
considered unidentiable and were excluded. Only dolphins with permanent and conspicuous
markings were included, only if they were sighted in ve or more survey days (Bräger et al. 1994;
lix 1997; Bejder et al. 1998; Rogers et al. 2004); thus, analyses were performed only for dolphins
with a certain degree of residency.
Association patterns and behavioral diversity. Photographic data were also used to compute
half-weight (i. e. controlled for sighting frequencies) coecients of association (COA) for each
dyad (pair of individuals; e. g. Smolker et al. 1992; Bräger et al. 1994; Félix 1997; Quintana-Rizzo
and Wells 2001; Rogers et al. 2004) using SOCPROG 2.4 (Whitehead 2009). COA values range from
zero for dolphins that are never seen together, to one for a pair that is always seen together. COA
values were categorized as infrequent (0.0 - 0.2), casual (0.2 - 0.4), fair, (0.4 - 0.6), moderate (0.6
- 0.8) or strong (0.8 - 1.0; Smolker et al. 1992; Quintana-Rizzo and Wells 2001). Also, to prevent
the occurrence of articial dyads (i. e. individuals photographed together by chance due to our
inclusive denition of group), a preferred/avoided partner assessment was developed through a
permutation test (Smolker et al. 1992; Bejder et al. 1998; Gero et al. 2005).
The recorded behaviors were used to calculate a measure of diversity for the activities
developed by all paired individuals; therefore, the Shannon-Wiener index was used as a proxy
for each dyad; the latter was standardized to meet the COA range values (0 - 1) and renamed as
activity diversity index (ADI). Since dolphin sightings containing more than two individuals would
use the same behavioral records for the computation of the ADI in their respective dyads, the
result would overestimate the contribution of each pair to the index (Hurlbert 1984); therefore, we
randomly removed photographic data from individual dolphins until the statistical distribution of
the ADI and the COA values stabilized. We then computed new COA and ADI in order to reduce 341
García-Vital et al.
the bias from the pooling fallacy (Machlis et al. 1985). Finally, the resulting COA and ADI matrices
were analyzed using a Mantel’s one tailed test, which measures the correlation between the values
within two symmetrical matrices containing the data from all the possible combinations between
individuals, throughout a randomization process (α = 0.05, Spearman correlation, Monte Carlo
method and 10,000 permutations).
Survey eort and group size. The Alvarado area was sampled on 80 photographic surveys
accounting for 237 groups and 2,021 sighted dolphins. Average school size was 8.5 (s. d. = 8.6) but
single animals (16.7 %) and pairs (16.3 %) accounted for almost a third of the recorded sightings
(Figure 2). Groups were signicantly larger in specic months (June and April, P < 0.01, Table 1),
seasons (dry, P < 0.01, Table 1) and years (2002-3, 2007-8, P < 0.01, Table 1) across the study period.
Table 1. Group size (numbers) and prevalent behaviors of bottlenose dolphins observed
within dierent periods in the study area (n = 237, * = P < 0.01).
Period Mean (s.d.) Group size Behavior
2002-2003 10.3 (1.1) * Apr*, Jun* Feeding*, Resting*
2006-2007 7.6 (0.6) - Feeding*
2007-2008 9.6 (0.9) * Sep* Socializing*
2008-2009 8.2 (0.7) Nov*, Feb* -
Rainy 8.4 (0.7) Sep* Feeding*
Windy 7.6 (0.8) Nov*, Feb* -
Dry 9.3 (0.7) * Apr*, Jun* -
Proportion %
Group size
Figure 2. Group size proportion for bottlenose dolphins sighted in the study area during 2002 - 2009 (n = 237).
Behavior and group size. Behavioral records existed for 220 of the 237 sightings, where feeding was
the most common activity in the area (29 %, χ2 = 15.22, P < 0.05), but this was true only for years
2002-2003 and 2006-2007 (P < 0.05, Table 1). Seasonal dierences were observed only for the
rainy months, were feeding was also signicantly more frequent (χ2 = 23.05, P < 0.05).
Group size was arranged into class intervals according to its frequency in order to homogenize
sample sizes (Figure 2). Correspondence between group size and behavior was signicant within
the studied period (χ2 = 69.47, P < 0.01) where the rst two dimensions explained 76.1 % of the
342 THERYA Vol.6(2): 337-350
variance, and only three behavioral categories were associated to group size: dolphin pairs were
mostly resting, whereas feeding aggregations were formed of four to six dolphins, and solitary
individuals commonly showed evasion (Figure 3).
Association patterns and behavioral diversity. A total of 232 dierent dolphins were individually
identied, but only 89 were sighted at least ve times, and only one was recognized on up to
47 occasions. Association values (COA) changed annually (Figure 4), as the composition of the
members within the community was very uid, and only eight individuals were consistently
identied over the years. The combination of these 89 individuals resulted in 3,915 possible dyads
and 67.2 % of these were photographed at least once; however, the permutation test showed that
only 237 pairs (6 %) were non-random (P < 0.05). From the latter, visual inspection of COA values
showed that 11 % avoided each other (0.0 - 0.2), or met infrequently (0.2 - 0.4), whereas 68 % were
moderately associated (0.4 - 0.6), and the remaining were either close (7 %; 0.6 - 0.8) or very close
(0.8 - 1.0) partners (3 %; Figure 5).
The diversity of activities (ADI) for each dyad showed a wide range of values, and its statistical
distribution stabilized upon the random elimination of half of the records from the 237 signicant
pairs (Figure 5). Only 5 % of the dyads had very high diversity (0.8 - 1.0), 9 % had high diversity
(0.6 - 0.8), 31 % were fairly diverse (0.4 - 0.6), 34 % developed a low diversity of activities (0.2 - 0.4),
and 20.3 % of the dyads were selective (0.0 - 0.2, all null values corresponded to avoided partners,
i. e. COA = 0; Figure 5).
The Mantel’s test showed signicant correlation between the COA and ADI matrices (r(AB) =
0.98, P < 0.01), thus the diversity of activities developed by each dyad increased signicantly with
their level of associations; however, a few instances deviated signicantly from this pattern. For
instance, 7.2 % of the dyads had moderate to very high associations but developed a low or very
low diversity of activities (low-right corner in Figure 6), specically feeding and socializing.
Figure 3. Correspondence analysis between activities and group class (size) for bottlenose dolphins sighted in the study area
during 2002 - 2009. F = Feeding; T = Travel; E = Evasion S = Social; R = Rest (n = 220). 343
García-Vital et al.
Group size. Aggregations in animals are widely variable in size and composition, and their study
is closely linked to the criteria used to dene their limits (Shane et al. 1986; Wells et al. 1987; Shane
1990; Wells 1991; Smolker et al. 1992; Bejder et al. 1998; Whitehead 1999; Connor et al. 2000;
Mareike 2003; Morteo 2011). The number of individuals in a group has been related to advantages
while overcoming selective pressures, including but not limited to protection against harassment
and predation, improving food acquisition and energy eciency, thus leading to enhanced
reproductive output (Wells et al. 1980; Shane et al. 1986; Mareike 2003).
Mean group size is often helpful to represent the optimal number of individuals for a community
within a specic habitat (Würsig 1979), and the average group size found here (8.5 ± 8.6 s.d.) was
similar to other coastal locations across the Gulf of Mexico, the Caribbean and the Atlantic (Shane
et al. 1986; Wells et al. 1987; Scott and Chivers 1990; Delgado 2002; García 1995; Morteo and
Hernández 2007; Hernández-Candelario 2009; Martínez-Serrano et al. 2011). However, since the
statistical distribution was skewed towards smaller aggregations (i. e. one third of the sightings
were composed of solitary individuals and pairs) despite our inclusive denition (Figure 2), this
value seems inconclusive. Morteo et al. (2014) anticipated this for bottlenose dolphins within
the same study area, and determined that many of these small aggregations were likely single
sexed. This strongly suggests that the community may be divided into small social units that join
in common activities (Campbell et al. 2002).
Behavior. The general behavioral pattern suggested for most bottlenose dolphin communities
is: Travelling > Socialization or Feeding > Resting > Evasion (Morteo 2002). Feeding has been
reported as a common activity in many dolphin communities (Shane 1990; Bräger 1993; Morteo
Figure 4. Annual sociograms for dolphins identied at least 5 times in the study area during 2002 - 2009. Line thickness shows
the values for coecients of association between dyads. Individuals with COA < 0.6 were removed (n = 27, n = 89), and also diagrams
and line thickness were scaled dierently to t the gure.
344 THERYA Vol.6(2): 337-350
2002; Beddia 2007; Steiner 2011) and was the single most frequent activity (29%) within the
studied period, especially in the rainy months (15.5 %). Maze and Würsig (1999) hypothesized
that dolphins may use environmental cues such as continental water runos to congregate over
shallow coastal areas close to rivers and lagoons, taking advantage of increased prey populations;
in fact, coastal bottlenose dolphins in this and in neighboring locations are known to experience
seasonal expansions in their distribution during this time of the year (Martínez-Serrano et al. 2011;
Medellín-Ortiz 2012). Although the latter may seem to enhance the possibilities of interacting with
other dolphins in larger aggregations, Morteo (2011) suggested that as food seems abundant and
predators are scarce in this study area, large groups might not necessarily imply an advantage for
foraging or protection. The statistical distribution for group size is consistent with this hypothesis
and it also explains the correspondence between the feeding records and the groups composed
by 4 - 6 dolphins (Figure 3), thus strengthening the notion of a small-unit based social structure.
Following the same hypothesis, solitary individuals were signicantly associated to evasive
behavior (17 % of recorded sightings, Figure 3), which may be due to the frequent and antagonistic
interactions between dolphins and artisanal sheries using gillnets in this location. Resident
Figure 5. Proportion of non-random dyads by association (COA) and behavioral diversity (ADI) class in the study area during
2002 - 2009 (n = 237).
Very Low
Low (0.2-
High (0.6-
Very high
Index value
Figure 6. Mantel’s correlation test (r = 0.98, P < 0.01) between association coecients (COA) and diversity of activities (ADI) for
non-random dyads identied in the study area during 2002 - 2009 (n = 237). Half of the individual data was randomly removed. 345
García-Vital et al.
individuals face the inherent risk of being harassed, entangled or even killed, thus individuals rather
than groups are more likely to evade detection by shermen due to the extremely low visibility
below the sea surface (Morteo et al. 2012). The latter also supports the argument that individuals
in general gain larger benets by aggregating in small groups (Figure 2) within this heavily shed
area, and in extreme cases points to a “selsh strategy” as a mean for auto-preservation.
Habitat seasonality agreed with temporal dierences found in both group size and behavior
(Table 1; Del Castillo 2010; Martínez-Serrano et al. 2011; Morteo 2011; Medellín-Ortiz 2012);
however, short-term habitat variability also seems to play an important role, since both of these
variables were inconsistent throughout the studied period (Table 1). Morteo et al. (2012) pointed
out the importance of boat trac and shing activities in the area, which seem to inuence the
presence and distribution of dolphins on a daily basis or even instantaneously (Constantine et al.
2004; Lusseau et al. 2006; Hernandez-Candelario 2009). Although many cetaceans seem to have
habituated to certain levels of marine trac, other evidence suggest that it may cause severe
alterations in their behavior and in this case may promote the separation of group members,
probably altering the social bonds within the community (Constantine et al. 2004; Morteo et al.
2012; Morteo et al. 2014).
Association patterns and behavioral diversity. A social organization is dened by the relations
and interactions among individuals within the sampled population (Chapman et al. 1995).
Societies are believed to gain from all the variety in their associations (Dunbar 1989); however,
even in ssion-fusion societies, partners could be selected to maximize eciency or benets while
joining to develop their activities (Gero et al. 2005). In this study, up to 94 % of all possible paired
associations were non-signicant, rearming the uid nature of the community; however, 78 %
of the non-random pairs exhibited moderate to high membership (Figure 4). The congregation of
prey within a limited area could help explain the random encounters for many of these dolphins
(Morteo et al. 2012); on the other hand, the close associations for a small part of the community
is likely the result of male alliances, and female bands (sensu Connor et al. 2000), by means of the
sexual segregation occurring in the area (Morteo et al. 2014).
We found that dolphin interactions seem to modulate group size (Figure 2), and these are
inherently associated to their own activities (Connor et al. 2001; Figure 3 and 5). The positive
correlation between the level of association and the diversity of activities (Figure 6) was expected,
as the context of the interactions between dyad members should become richer over time (Gero et
al. 2005); however, the fact that 17 of the 237 signicant dyads involved partnerships with specic
purposes suggests that only a handful of these individuals nd larger benets from exploiting
the specic abilities of selected partners. Lusseau et al. (2006) evidenced the importance of roles
for specic individuals within a social network, where previous knowledge of group members
and reduced number of participants helped to coordinate actions and facilitated cooperation;
however such interactions were rare and deserve further attention.
Knowledge of the social structure of dolphin communities is important for assessing their
ecological and evolutionary patterns; and behavioral data helps to understand how the animals
adapt to the habitat and its selective pressures. However, both aspects are rarely combined to
determine the nature of their associations, and how these are modied by their life conditions,
including natural and anthropogenic factors. Human developments cause that coastal bottlenose
dolphins face increasing disruptions within their core areas of distribution, therefore these aspects
should be considered while developing and applying conservation and management strategies
and policies.
346 THERYA Vol.6(2): 337-350
This research is part of the lead author’s MSc thesis at the Universidad Veracruzana, Mexico,
where she obtained fellowship from CONACyT. J. Montano, I. Hernández, V. Del Castillo and N.
Medellín were involved in surveys and data collection. Fieldwork was carried with authorization
from SEMARNAT permits SGPA/DGVS/00351/06 (E. Morteo) and SGPA/DGVS/00870/07, 02788/07,
01344/08 and 01649/08 (C. Bazúa). This work was supported by the following grants: PROMEP
Apoyo a Nuevo PTC (E. Morteo) and CAMyCRA (E. Morteo, and H. Pérez-España), CONACyT grant
45468 (E. Velarde) and the Marine Mammal Laboratory of Universidad Veracruzana and Acuario de
Veracruz, A.C.
Introducción: Las sociedades en mamíferos están inuenciadas por factores intrínsecos y extrínsecos afectando
la temporalidad de las asociaciones entre individuos. Los tursiones costeros generalmente viven en agregaciones
pequeñas y uidas de composición variable, pero comúnmente se desconoce la naturaleza de sus asociaciones.
Nuestro objetivo fue determinar si el tamaño de grupo se relaciona con el comportamiento de los delnes y si los
individuos se asocian para desarrollar actividades particulares en las costas de Alvarado, México.
Metodología: Se realizaron 80 navegaciones (2002 - 2003 y 2006 - 2009) para registrar la conducta, el tamaño
de grupo y para foto-identicar a los delnes. De 237 avistamientos, con 2,021 delnes observados, se obtuvo un
promedio de 8.5 (d. e. = 8.6) animales por grupo, donde las parejas y los individuos fueron más frecuentes (33 %).
Resultados: Las diferencias en tamaño de grupo y comportamiento concordaron con la estacionalidad del
hábitat (P < 0.05), siendo inconsistentes entre años, por lo que los factores de corto plazo (i e. tránsito marino e
intensidad de pesca) fueron importantes. La alimentación fue común (29 %) y correspondió con grupos de 4 – 6
animales, mientras los individuos solitarios típicamente mostraron evasión (P < 0.01).
Discusión y conclusiones: Los coecientes de asociación calculados para 89 de 232 delnes identicables fueron
no aleatorios en sólo 6 % de las 3,915 combinaciones (P < 0.05); dichos valores se correlacionaron positivamente con
la diversidad de actividades de cada pareja (P < 0.01) y la naturaleza de sus asociaciones se volvió más rica con el
tiempo en el 93 % de los casos. Se cree que esta comunidad se compone de pequeñas unidades que intercambian
miembros; esto puede deberse a una alta abundancia de alimento y bajo número de depredadores en el área, pero
también a una estrategia para evitar la detección y las amenazas derivadas de la pesca artesanal.
Palabras clave: Comportamiento; evasión; membresía; pesquerías; socialización; tamaño de grupo.
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Summited: February 13, 2015
Review: April 8, 2015
Accepted: April 21, 2015
Associated editor: Juan Pablo Gallo
350 THERYA Vol.6(2): 337-350
... En la estructura social de los tursiones se evidencian ensambles de individuos en los cuales varios delfines se asocian, cohabitan e interactúan entre sí de acuerdo con un beneficio (Chilvers y Corkeron, 2001), formando lazos con otros individuos (Nowacek y Wells, 2001;García-Vital et al., 2015). Las formaciones denominadas "bandas" es un ejemplo de estas agrupaciones compuestas por hembras y crías, tienen el objetivo de aumentar la seguridad de éstos frente a los depredadores y contar con el beneficio de la experiencia de otras hembras (Quintana-Rizzo, 2006;Morteo et al., 2014). ...
... Al respecto de la formación de grupos, los machos adultos por lo general tienden a desplazarse en compañía de otro similar formando alianzas (Wells, 2001;Owen et al., 2002;Morteo 2011;Morteo et al., 2014); estas formaciones se mantienen por más tiempo en relación con las demás asociaciones, proporcionándoles mejor protección y aumentan la posibilidad de encontrar pareja (Connor et al., 2001). Algunas de sus actividades son realizadas manteniendo la alianza de los individuos y actuando sincrónicamente o como apoyo en el desarrollo de un fin en particular (Chilvers y Corkeron, 2001;García-Vital et al., 2015). ...
... En este trabajo se puso especial atención en la descripción de la conducta de los delfines en presencia de actividades de pesca, dado que promueven la modificación de sus actividades en respuesta a un estímulo en su hábitat. En estos términos, por ejemplo, Jaiteh y colaboradores (2013), reportaron las diferentes formas en que los delfines se desplazan hacia las redes de arrastre, y al igual que en el presente estudio, ingresan y salen de estas, aun cuando el estilo es más cerrado comparado con redes agalleras en la pesca artesanal sugiriendo que el pescadores los harían más vulnerables ante respuestas violentas (Morteo et al., 2012;García-Vital et al., 2015). ...
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relationship of organisms with their environment influences their behavioral plasticity, modifying their behavior in response to stimuli or pressures, and consequently affecting the ecological relations of species. The expansion of human activities leads to conflicts between humans and wildlife, and these are mainly associated with interactions during competition for space and / or food availability. These conflicting interactions have been reported on the shores of the Gulf of Mexico, where the artisanal fishermen denounce the looting and damage of their equipment by tursiones (Tursiops truncatus), which are sometimes injured or killed. The objective of this work was to study the behavior of bottlenose dolphins in their interaction with artisanal fishery in the coastal waters of Alvarado, establishing: 1) the first etogram for the case, 2) the behavioral differences associated with fishing, and 3) the variations in relation to the age and group size of the dolphins interacting with this activity. Between 2015 and 2016, 64 groups have been observed by sampling scanning from boats and fixed points. We obtained 4,898 records that used body patterns and other characteristics associated with the behavioral deployment form. The events were organized in the states: food, locomotion, social, socio-sexual, play and rubbing with objects. There were significant differences in the frequency (X2 = 55.93, gl = 5, p <0.001) and the local rate of behavior in the presence and absence of fishing activity (X2 = 25.16, gl = 5; However, their intensity was lower than in the absence of fishing (5.3 min-1 vs 7.0 min-1) and in relation to the other behaviors, that in general had low frequencies. During the fishing activity, the dolphins that interacted most were adults, however, no significant group differences were found in the proportion of individuals by age in relation to the fishery ( X2 = 1429, gl = 2, p <0.4894). The average group size comprised two individuals in both conditions (without = 42% and con = 54% interaction), so no differences were observed (X2 = 1.56, gl = 15, p <0.001); however, the direct operational interaction to the net was performed by 51% individually, and mostly (84%) in the first 30 m. The behavioral differences partially support the hypotheses and evidence the influence of human activities on the behavioral display of the T. truncatus dolphins in Alvarado. The lack of evidence on differences in age and group size suggest the need for a larger sample size, as well as the habituation of some dolphins to the fishery interaction, possibly being these experienced dolphins that will pass; these dolphins would have to be photo-identified to determine their contribution in the effects on the behavior of the population, derived from their interaction with the artisanal fishery.
... Primero se registró su comportamiento siguiendo el método ad libitum (Altman, 1974) y procurando navegar de forma paralela en su dirección de nado a una distancia promedio de 30 m para reducir el riesgo de perturbarlos. Se usaron las categorías más comunes en estudios etológicos para la especie, que consisten en: alimentación, tránsito, juego, social/sexual, descanso, evasión, e indeterminado (Morteo, 2002;García-Vital et al., 2015;Morteo et al., 2004;Morales-Rincon, 2016). ...
... El tamaño de los grupos de delfines varía de acuerdo con el comportamiento de los individuos y puede reflejar un equilibrio entre el número de animales necesarios para la defensa contra los depredadores, el acoso intraespecífico y por otra parte fomentar la alimentación eficiente, las interacciones sociales/reproductivas, y la sobrevivencia de las crías (Würsig y Würsig, 1979;Shane, 1980;Ballance, 1992;Wells y Scott, 2002;García-Vital et al., 2015). En los ecosistemas marinos con aguas abiertas, el tamaño promedio de los grupos de tursiones costeros generalmente es mayor a 15 animales y los avistamientos de manadas de tursiones costeros con más de 25 animales son poco comunes (Morteo, 2002;Martínez-Serrano et al., 2011). ...
... Las diferencias en el tamaño de grupo entre ambos sitios de estudio pueden explicarse mediante un modelo simple de alimentación, en el que los grupos de depredadores se ajustan a la dispersión y abundancia de los recursos alimentarios disponibles o de sus depredadores/ competidores (Ballance, 1992); en otras palabras, si los delfines no exceden la capacidad del recurso, tendrán mejores posibilidades de alimentarse al usar sus habilidades de ecolocalización en conjunto para ubicar a sus presas, como posiblemente ocurre en Nautla; en contraste, si la especie en cuestión ha excedido la capacidad de su alimento, o es un competidor antagonista (de la pesquería), como ocurre en Alvarado (Morteo et al., 2012a;Rechimont et al., 2018), tendrá mejores posibilidades de alimentarse en grupos pequeños o en solitario (Morales-Rincon, 2016), con la ventaja adicional de reducir la probabilidad de ser lastimados o de morir, simplemente por ser menos conspicuos y más difíciles de ubicar para los humanos (García-Vital et al., 2015;Morteo et al., 2017b). ...
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The bottlenose dolphin (Tursiops truncatus) is possibly the best known dolphin worldwide and their ecology and biology has been widely documented; however, research on this species in Mexico is re- cent, and the populations of the Gulf of Mexico have been less studied. In this work, we documented the fundamental aspects of the population ecology (distribution, demography, and behavior, includ- ing migratory movements) of bottlenose dolphins within the coastal waters of two localities in the State of Veracruz, separated by 230 km (Nautla 48 km2 and Alvarado 54 km2). We carried out 52 photo-identification surveys between July 2002 and September 2003. Search effort was 204.5 h and there were 76.1 h of sightings, where 60 schools were located with a total of 703 dolphins (42 young, 38 calves). Group size was different between sites (Nautla x= 11.0 ± 14.1, Alvarado x= 9.3 ± 8.41) and the relative abundance (dolphins h-1) was very variable (Nautla x= 4.1 ± 3.7, Alvarado x= 3.5 ± 1.6). We obtained 2,085 useful photographs of the dorsal fins of these dolphins with low photo- graphic efficiency (31%); which produced 555 records of individuals with high photo-identification efficiency (89%); the latter corresponded to 160 dolphins from Nautla and 92 from Alvarado. Daily absolute abundances averaged 187.0 (± 132.4 d.e.) marked individuals in Nautla and 68.6 (± 35.4 d.e.) in Alvarado, with a maximum of 636 individuals in both sites combined. The exchange rate between localities was 5%, where eight dolphins emigrated permanently from the source locality within a few days (x= 42.1 ± 16.9 d.e.), and the rest (n = 4) had back and forth movements. Two individuals traveled the distance from Alvarado to Nautla in 5 and 6 days, with a minimum swim- ming speed between 38 and 46 km d-1. Our results show limited connectivity, but possibly enough to promote genetic flow between these sites. The smaller population size for dolphins in Alvarado is possibly due to the high level of competition with the fisheries, which can regulate the amount of animals present in the site, coupled with its complex social structure, which can limit the income of a high proportion of new dolphins.
... Por otra parte, la correspondencia entre los grupos de adultos con la alimentación y el tránsito ( Fig. 17) posiblemente reflejan el uso principal de la zona de estudio, al ser los grupos más representados en la muestra; esto se debe al desplazamiento y la agregación de los individuos en los sitios con mayor disponibilidad de recursos (García-Vital et al., 2015). La correspondencia entre los grupos con crías y el comportamiento evasivo ha sido descrito con anterioridad para muchas poblaciones de esta especie, ya que normalmente se trata de grupos pequeños donde las madres tienden a ser más cautas (Morteo et al., 2012;García-Vital et al., 2015;La Fauci, 2017). ...
... Por otra parte, la correspondencia entre los grupos de adultos con la alimentación y el tránsito ( Fig. 17) posiblemente reflejan el uso principal de la zona de estudio, al ser los grupos más representados en la muestra; esto se debe al desplazamiento y la agregación de los individuos en los sitios con mayor disponibilidad de recursos (García-Vital et al., 2015). La correspondencia entre los grupos con crías y el comportamiento evasivo ha sido descrito con anterioridad para muchas poblaciones de esta especie, ya que normalmente se trata de grupos pequeños donde las madres tienden a ser más cautas (Morteo et al., 2012;García-Vital et al., 2015;La Fauci, 2017). Adicionalmente, los grupos de jóvenes no mostraron asociación fuerte con alguna conducta específica, aunque se relacionaron con la conducta social, lo cual es consistente con las estrategias sociales de esta especie particularmente durante esa etapa de su desarrollo (García-Vital et al., 2015). ...
... La correspondencia entre los grupos con crías y el comportamiento evasivo ha sido descrito con anterioridad para muchas poblaciones de esta especie, ya que normalmente se trata de grupos pequeños donde las madres tienden a ser más cautas (Morteo et al., 2012;García-Vital et al., 2015;La Fauci, 2017). Adicionalmente, los grupos de jóvenes no mostraron asociación fuerte con alguna conducta específica, aunque se relacionaron con la conducta social, lo cual es consistente con las estrategias sociales de esta especie particularmente durante esa etapa de su desarrollo (García-Vital et al., 2015). ...
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The bottlenose dolphin (Tursiops truncatus) is one of the most common species of odontocetes in Mexican coastal waters. Its presence off Mazatlan, Sinaloa has been documented since 2006; however, studies on this species are scare in the region. The goal of this work was to characterize the main parameters of their population ecology. Data was obtained through standardized ecotourism navigations during 2006-2012. A total of 152 sightings in 302 surveys were recorded (x=3.56 dolphins ∙ h-1; s.d.=2.64). We found differences in the relative abundance (RA), group size, and behavioral trends within annual, monthly and seasonal (dry and rainy) periods. The RA values for 2008 and 2012 were higher than the rest of the years (p<0.05), and we observed a RA increase during the dry seasons (February-April), associated with the decrement of sea surface temperature (18.9-25.0 °C) and high chlorophyll-a concentration (2.8-8.9 mg ∙ m-3). The correlation between these hydrographic parameters and the RA was low but significant (r2<0.25; p<0.01), possibly due to the delay in the trophic response to upwellings. The average group size was 24.2 dolphins (SD=36.6; min=1; max=300; md=10), with larger group sizes in 2011 and 2012 (x=41.4 and 31.9 dolphins, respectively) (p<0.05). During dry season (upwellings), we registered larger group sizes and higher frequencies of feeding behavior (35-73%), compared to the rainy season (travel: 28-69%). A total of 1,697 dorsal fin photographs were analyzed, and 65.5% were useful to identify 210 different individuals. Site fidelity was low (x=0.04; SD=0.03) and only 3% of the photo-identified dolphins were classified as residents, 11% as occasional residents, and the remaining (86%) as transients. The results indicate that bottlenose dolphins inhabiting the waters off Mazatlan, Sinaloa, belong to an open population with a large distribution and home ranges, which uses the area for feeding and travelling. Also, higher RA values and larger group sizes along with the incursion of new individuals during dry season were associated with socialization and feeding behaviors due to the hydrographic conditions during the development of coastal upwellings. The later promoted higher food availability that fits basic needs of the bottlenose dolphin population in this area. Furthermore, we observed an intensification of these trends under “La Niña” hydrographic conditions.
... Los estudios sobre la formación de grupos y su estructura social se han realizado principalmente en especies sociales como hienas (Frank 1986), chimpancés (Goodall 1986), murciélagos (Kerth et al. 2011, delfines (Wells 2003), etc. Los grupos de estas especies se componen por individuos que, al asociarse recurrentemente crean interacciones entre ellos, tales como la comunicación y comportamientos coordinados (Connor et al. 2001, Lusseau et al. 2006, Quintana-Rizo 2006, Morteo y Hernández 2007, Morteo et al. 2012, García-Vital et al. 2015. ...
... El análisis de asociación se hizo a través del software SOCPROG 2.9 (Whitehead 2009), con los datos del periodo de navegaciones (2019-2021). Se utilizó la información de los individuos avistados al menos en 5 ocasiones, con el fin de evitar sesgos por individuos sub-muestreados (Felix 1997, Gero et al. 2005, Morteo et al. 2014, García-Vital et al. 2015. ...
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La Ensenada de La Paz forma parte del hábitat de tursiones (Tursiops truncatus), especie gregaria que forma grupos determinados por factores socio-demográficos. Los tursiones son el componente principal en la riqueza de odontocetos en la zona, por lo que es importante actualizar el conocimiento acerca de la especie y, con ello, generar herramientas útiles para su manejo y la conservación de su hábitat. El objetivo de este estudio fue determinar la dinámica grupal de los tursiones en la Ensenada de La Paz, durante el periodo 2016-2021. Los datos se obtuvieron de registros fotográficos (2016-2018) realizados durante 1as navegaciones mensuales en el periodo 2019-2021. En los muestreos se registró el número de individuos, etapas de desarrollo y el comportamiento de los delfines. Para la identificación de los individuos, se utilizó la técnica de foto-identificación usando las marcas únicas en su aleta dorsal, se seleccionaron, calificaron y clasificaron las mejores fotografías por el tipo de marca que presentó cada individuo. Se estimó el tamaño de los grupos a través de un cálculo visual mediante la regla de la cadena y se determinó el tipo de formación de los grupos (compacta y dispersa). La composición grupal etaria se realizó a través del tamaño de los individuos como proxi de las etapas de desarrollo (adultos, jóvenes, crías y recién nacidos). Una vez foto-identificados los delfines, se realizó el análisis de estructura social mediante el índice de fuerza de asociación (HWI por sus siglas en inglés) entre pares de individuos. Los tursiones conformaron dos tipos de grupos conforme a la distribución espacial: compactos (mediana = 14 delfines) y dispersos (mediana = 25 delfines). Así mismo se registraron grupos de sólo adultos (mediana = 5 delfines) y grupos mixtos (mediana = 20 delfines) con adultos, jóvenes, crías y/o recién nacidos. En cuanto al comportamiento, los tursiones utilizaron el área para navegar, alimentarse y socializar. El número de tursiones foto-identificados fue de 147 delfines distintos, de los cuales el 66% presentó al menos una recaptura. Los tursiones conformaron una sociedad diferenciada (0.38 ± 0.11 DE), sus asociaciones fueron ocasionales (CDA=0.23± 0.07 DE). El análisis de conglomerados mostró que la sociedad de los delfines se compone por cuatro grupos, con individuos asociados de manera regular a moderada (CDA=0.41- 0.61) y cinco parejas de individuos con asociaciones fuertes (CDA > 0.81). Este trabajo redujo la brecha de información sobre los tursiones de la zona y exhibió la dinámica de sus grupos; estructura social, composición etaria y las asociaciones entre los delfines.
... Hurtado-Mejorada (2021) already found that bottlenose dolphin echolocation trains were significantly more frequent during fishing manouvers in the Alvarado area. Also, Garcıá-Vital et al. (2015) found lower group sizes as a possible adaptative response to lower the risk of human retaliation during interactions with fisheris (Morales-Rincon et al., 2019). Therefore, hearing interference due to high marine traffic (e.g. ...
... In addition, as noted by Morteo et al. (2017) and Bolaños-Jimeńez et al. (2021), individual dolphins that are "new" to the area (the majority of which were presumed to be male; Morales-Rincon et al., 2019), have been found to have a higher tendency to interact with local artisanal fisheries than local residents. Furthermore, dolphins in the region reduce their group sizes and reduce their surface behaviors when interacting with gillnet fisheries (Garcıá-Vital et al., 2015;Morales-Rincon et al., 2019), presumably to lower the risk of being spotted, since they often face retaliation while interacting with local artisanal fisheries (Morteo et al., 2017;Rechimont et al., 2018). In addition, dolphin's groups may reduce their size possibly to lower intraspecific competition, and also because obtaining the resource in fishing nets is easier, so they do not need to employ cooperative hunting strategies, which also reduces interindividual competition (Methion and Dıáz Loṕez, 2020). ...
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Competition between fisheries and bottlenose dolphins is a globally relevant conflict given its socioeconomic and ecological implications. Understanding the factors driving the interactions between dolphins and fishery activities is key to the development of appropriate mitigation strategies. Our study aimed to assess whether these interactions are related to the ecological, trophic, and nutritional characteristics of the catch. We used 117 gillnet sets from 48 fishing trips during 2009 – 2010 and 2015 – 2019, which were classified based on the presence or absence of dolphin interactions. These interactions occurred year-round and were documented in 46.1% of the sets, with 14.5% of those showing signs of depredation. The passive acoustic predatory hypothesis, which states that fish species that generate sound are subject to a higher predation intensity by dolphins, was not supported by our data. Also, with the exception of species diversity, ecological parameters such as richness, biomass and CPUE were slightly higher, although not significant in sets with dolphin interaction. Furthermore, during 2015 – 2016, we sampled 123 organisms of 25 representative fish species in the catches and determined the whole fish isotopic composition (δ13C and δ15N), and estimated the nutritional value (i.e., lipid, protein, and energy content) of each species. Isotopic values showed no differences between net settings (with and without interaction), fish habitat, or prey type (potential prey, n= 11 species, vs. non-potential prey, n= 14). However, a preference towards fish from a certain range of thropic levels was evident. All the fish (N= 123) showed significantly higher protein values during the Rainy period, which may be attributed to their reproductive cycles and higher primary productivity. Interestingly, energy contents of the dolphins’ potential prey were also significantly higher during this period. Unexpectedly, protein and energy contents were significantly higher in the fishes caught in the sets without dolphin interaction, but only during the Dry and Windy periods, respectively. Opportunistic feeding habits are well known for bottlenose dolphins, and our results showed that “easy access” to prey will likely prompt interaction with gillnets, regardless of the species composition, biomass, seasonality, preferred habitat, sound production capacity, or nutritional value of the captured fish.
... Moreover, prey selection within the water column can be driven not only by the nutritional properties (Spitz et al. 2012) but also the soniferous properties of the fish themselves (McCabe et al. 2010, Dunshea et al. 2013) as well as the gape size of the predator's mouth in relation to prey size (MacLeod et al. 2007). Multiple foraging strategies have been documented acrossand even within -different bottlenose dolphin populations, clearly adapted to the availability of different resources (Pryor & Lindbergh 1990, Chilvers & Corkeron 2001, Kopps et al. 2014, García-Vital et al. 2015, Rossman et al. 2015. In the Mediterranean Sea, for instance, some dolphin groups are known to follow and interact with trawlers (Genov et al. 2019), while others spend more time in the proximity of gillnets (Díaz López 2006) or fish farms (Díaz López 2012). ...
Understanding the foraging strategies of marine megafauna that interact with fisheries is key to conflict mitigation. Bottlenose dolphins Tursiops truncatus in the northern Aegean Sea frequently depredate bottom-set nets, but whether they exhibit prey selection within depredation events remains unknown. We conducted 80 fishing trials over 2 seasons (2020 and 2021) using gillnets in the Thermaikos Gulf, and investigated patterns in the catch and gear damage to determine whether bottlenose dolphins target certain genera over others. A high preference index was calculated for demersal fish like Mullus and Trachurus , as well as less frequently occurring pelagic fishes like Sphyraena . We also found a strong indication that dolphins target certain sizes of fish in certain genera, namely the shorter specimens of larger fishes and the larger specimens of shorter fishes. In conjunction with the patterns in the vertical position of holes torn in the nets, our findings suggest that bottlenose dolphins take advantage of whichever fish are seasonally prevalent.
... The geographic and taxonomic patterns found here are likely due to the coastal distribution of the studied species, which are also somewhat common within Mexican waters. As their distribution and habits facilitate access to their study, some dolphin species are prone to interact with boats, which increases the chances of finding them during any type of marine endeavor (García-Vital et al., 2015). Whales can also be commonly observed from the beach during their migrations to their reproduction areas in Mexico (Urbán et al., 2021); for instance, in the Pacific these species are also the focus of the ever-growing touristic activities and the whale-watching industry, attracting the public attention and the government to get involved in conservation programs, as they also serve as indicators of environmental change (Isasi-Catalá, 2001). ...
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Marine mammals are very diverse because of the oceanographic conditions of Mexican waters (where 36% of the current species worldwide are found); however, scientific research on many of these taxa is still at the basic stages. The goal of this study was to assess the scientific information available for these species and to determine research priorities through a GAP (from the acronym "Good", "Average", and "Poor”) analysis. Information from the abstracts of the meetings held by the Mexican Society of Marine Mammalogy (SOMEMMA) and online databases (SCOPUS and Web of Science) between 1998 and 2021 was analyzed using temporal (years), geographic (oceans or states), taxonomic (species), and thematic (topics) classifications. On average, of the 44 species included in the Mexican legislation, only 16 - included in 14 families (with most of the records) - are studied every year, Delphinidae (n = 500; 25.9%), Balaenopteridae (n = 335; 17.4%), and Otariidae (n = 316; 16.4%). The Gulf of California was the most studied region (35.4%), followed by the Northeast Pacific (19.3%), the Gulf of Mexico (15.5%), and the Caribbean Sea (6.9%). The most frequent topics were population ecology (32.9%), conservation (16.7%), and animal health (10.4%). A significant decrease in the taxonomic and thematic diversity of such studies has been noted since SOMEMMA meetings began to be held on a biennial basis. It is noteworthy that marine mammals are protected by Mexican Federal laws. However, stock assessments are not mandatory, therefore biological aspects and trends of several (mostly oceanic) species remain unknown in many places, especially in regions where academic and scientific institutions are not involved in marine science.
... Los delfines nariz de botella, también conocidos como tursiones o toninas (Tursiops truncatus Montagu, 1821) son organismos altamente sociales, por lo que generalmente llevan a cabo sus actividades en grupos que varían de acuerdo con el tipo de hábitat, la distribución de los recursos y las estrategias para maximizar la obtención de éstos (Morteo et al. 2004;Martínez-Serrano et al. 2011;Morteo et al. 2014;García-Vital et al. 2015;La Fauci 2015). Aunque pueden desplazarse grandes distancias, las altas densidades de estos animales suelen asociarse con sitios específicos en donde la configuración de la costa, la profundidad, la temperatura superficial, la productividad, así como la abundancia y disponibilidad de sus presas les permiten llevar a cabo su alimentación, socialización, crianza y descanso (Kelly 1983;Cockcroft et al. 1990;Hansen y Defran 1990;Quinn y Brodeur 1991;Defran y Weller 1999;Cañadas et al. 2002;Chávez-Andrade 2006;Vázquez-Castán et al. 2007;Martínez-Serrano et al. 2011;Morteo et al. 2012). ...
Behavioural plasticity in animals is tested whenever competitive interactions for space and/or food resources occur between wildlife and human activities. This study uses the concepts of operational and non-operational interactions between bottlenose dolphins ( Tursiops truncatus ) and artisanal fisheries in Alvarado, to search for differences in behaviour, age structure and group size. We conducted 20 surveys between 2015 and 2016, and recorded 64 groups by means of scan sampling from either a research boat or a fixed vantage point. Average dolphin group size was small ( ${\bar{\rm x}}$ = 3.2, SD = 2.2 individuals) and fewer individuals were commonly present when interaction with fisheries occurred. Operational interactions were defined within the first 30 m and occurred mainly with lone individuals (54% recorded from the lighthouse and 82% during surveys); this benchmark also accounted for higher frequencies in locomotion and feeding (χ ² = 83.10; df = 7; P < 0.001). We found a higher rate of new behavioural events for dolphin groups furthest from human activities, as well as a decrease in behaviours that imply greater body exposure as dolphins approach the fishing spots. Age structure and dolphin group size were not different during and in the absence of interaction with fisheries, but most interactions involved male dolphins. Behavioural variations in the dolphins' repertoire are likely a strategy to reduce the risk of injuries or death when interacting with human activities; these dolphins seem to have habituated to or at least tolerate fishing activities within the study area, possibly constituting a sex-biased pressure.
Surveys for the occurrence, distribution, and individual identification of Indo-Pacific bottlenose dolphins Tursiops aduncus were conducted around Amami Oshima Island, Kagoshima Prefecture, Japan from 2007 to 2013. The dolphins were primarily distributed in the areas where the survey effort was concentrated, particularly in Oshima Strait and on the western coast of the Island. In total, 33 groups of dolphins were encountered with a median group size of 8 (range: 1-50 individuals). The group size in Oshima Strait was significantly smaller than that recorded off the western coast. A total of 100 individuals were identified from photographs taken by the survey cruise and local residents with the cumulative number of identified individuals increasing over time and with no indication of saturation being reached. Thus, the population size of Indo-Pacific bottlenose dolphins in the waters around Amami Oshima Island was probably larger than that indicated by the present study; hence, photo-identification needs to be continued to provide a more accurate population size estimate in the future.
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With the goal of gathering ecological data to develop future cetacean management and conservation plans, the distribution, home range, and residency of bottlenose dolphins (Tursiops truncatus) were studied in the central-north Mexican Gulf of Mexico. Between July 2005 and June 2008, 59 boat surveys were carried out for a total of 313 h of effort at sea. During these surveys, 471 individuals were observed in 88 different groups. Photographs of naturally marked animals resulted in 275 different individuals photo-identified. Their distribution was homogeneous throughout the study area at a mean distance from the coast of 2.5 km (SD = 2.9, n = 471) and depths less than 20 m. Of the total of dolphins identified, 202 (73%) had a low sighting rate and were considered transients, whereas 34 individuals (12%) had medium and high sighting rates and were considered resident animals. At the population level, home range estimates calculated using the minimum convex polygon method showed a mean of2771 ± 1116 km². Using the adaptive kernel method, the mean size of home range was 1199 ± 143 km², with five core areas identified. These areas decreased in size during the rainy season because dolphins remained close to the river plumes. At individual level, the mean home range was 129.2 km² (n = 66), concurring with other reports from the Gulf of Mexico (Texas and Florida) in spite of habitat differences. The main component determining the size of the home range was the presence of rivers, rather than the geomorphology of the coast.
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Bottlenose dolphins (Tursiops truncatus) in the Galveston Bay Estuary, Texas, have been studied continuously since 1990. Most of this research has taken place in the 'Galveston Bay' area at the northeastern end of Galveston Island. In September 1995 we began a project to examine bottlenose dolphin occurrence patterns, habitat use, site fidelity, and movements in the San Luis Pass area, a relatively undisturbed area at the southwestern end of Galveston Bay Estuary; and to compare findings to previous work in Galveston Bay, approximately 48 km away. Eighty-three boat-based photo-identification surveys were conducted during 12 months in 1995–1996, totaling 349.4 h of effort, of which 94.3 h were spent in direct observation of 102 dolphin groups. Seventy-one individuals were identified, including 37 'residents' (Bay) and 34 'transients' (Gulf). These individuals were com-pared with 63 individuals identified in the study area in 1990. Fourteen of 71 (19.7%) animals identified in 1995–1996 were present in 1990, sug-gesting that some dolphins exhibit long-term site fidelity to the area. Dolphins identified in San Luis Pass were compared to photographs taken during 1995 surveys of Galveston Bay. Three animals were sighted in both study areas, indicating coastal movements between sites do occur. The study area was divided into four sections based upon habitat characteristics. Season and study area section were not independent with regard to group sightings. During summer, animals were most frequently sighted in a shallow bay furthest inland, whereas during winter, they were most frequently sighted in the Gulf of Mexico. This study suggested that the San Luis Pass area, devoid of deep man-made channels and structures, is inadequate to support dolphins during winter. This is in contrast to Galveston Bay, where groups have been sighted regularly in bays and channels year-round. We suggest that food resources in Galveston Bay are present year-round due to deeper water provided by the Houston and Galveston Ship Channels, and that this habitat may therefore be more attractive to dolphins than before human restructuring of the underwater environment.
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Resightings of photographically identified bottlenose dolphins (Tursiops truncatus) were used to calculate association indices for a population of free-ranging individuals occurring in the Galveston Bay system, Texas, and the adjacent Gulf of Mexico. Thirty-five individual dolphins with four or more sightings per year were included in the analyses to ensure likelihood of identification and comparability in 1990 and 1991. The patterns of association were weak, with few strong associations between individuals. The average association indices for 1990 and 1991 were similar; however, the magnitude of individual association indices changed drastically between the years. The low number of detectable, long-term affiliations indicates high group fluidity.