492
overlap can change several components of behavior, including feeding behavior, and
may reduce competition (Begon et al. 1996). According to the definition of Pauly
et al. (1998), franciscana dolphins and Guiana dolphins occupy a similar trophic
level.
Direct observation of feeding behavior in marine mammals can be difficult, thus
analysis of stomach contents is the method typically used for diet studies (Barros
and Odell 1990). Analysis of stomach contents of franciscana and Guiana dolphins
in Babitonga Bay revealed that teleosts are the most common prey item for both
species (Cremer et al. 2011; Paitach 2015). The squid Lolliguncula brevis was also
found in the stomach contents of both species.
Twenty-one fish species belonging to six families were identified in the diet of
franciscana dolphins, representing 69.4% of the numerical frequency of prey. Fish
also had the highest frequency of occurrence among prey, accounting for 91.3%.
Cephalopod frequency of occurrence was estimated at 47.8%, and numeric
frequency was estimated at 30.6% (Paitach 2015). The number of prey species and
the numerical dominance of fish compared to cephalopods agree with other studies
throughout the species’ geographical ranges (Bassoi 1997; Di Beneditto 2000; Di
Beneditto and Ramos 2001; Rodríguez et al. 2002; Oliveira 2003; Silva 2011; PasoViola et al. 2014).
Among the prey species, the ‘cangoá’ (Stellifer rastrifer) is the most important
in the franciscana diet, with a 70% index of relative importance. When the second
most important prey is added (the sardine Pellona harroweri), the value is closer to
90%. This result indicates that only a few prey species sustain franciscana population, as observed in other studies (Oliveira 2003; Silva 2011). Physical characteristics of this species (e.g., long rostrum and numerous small teeth) favor small-sized
prey like the sardine and the cangoá (Pinedo 1982; Oliveira 2003; Bassoi 2005;
Silva 2011; Cremer et al. 2012).
Twenty-eight fish species from 13 families were identified in the Guiana dolphin
diet. Teleosts also had the highest frequency of occurrence (88.2%), but cephalopods had higher numerical frequency (53.1%) than teleosts (46.9%). The number of
prey species for the Guiana dolphin varies from 10 to 36 throughout its geographical range (Di Beneditto 2000; Zanelatto 2001; Santos et al. 2002; Oliveira 2003; Di
Beneditto and Siciliano 2006; Daura-Jorge et al. 2011). Guiana dolphin population
sizes, behavior, habitat use, and social dynamics vary geographically, and variation
in prey richness may reflect the different ways that populations explore their respective environments (Daura-Jorge et al. 2007; Wedekin et al. 2007; Cantor et al. 2012;
Schulze 2012).
For Guiana dolphins, five prey species together had a 70% relative importance
value: Mugil curema, Pellona harroweri, Stellifer rastrifer, Micropogonias furnieri
and Trichiurus lepturus. The Guiana dolphin diet is composed of many prey species
with similar importance values and gradual reduction, including up to six species
with a combined importance value of 75%; this pattern agrees with other studies
(Zanelatto 2001; Oliveira 2003; Daura-Jorge et al. 2011).
M.J. Cremer et al.
overlap can change several components of behavior, including feeding behavior, and
may reduce competition (Begon et al. 1996). According to the definition of Pauly
et al. (1998), franciscana dolphins and Guiana dolphins occupy a similar trophic
level.
Direct observation of feeding behavior in marine mammals can be difficult, thus
analysis of stomach contents is the method typically used for diet studies (Barros
and Odell 1990). Analysis of stomach contents of franciscana and Guiana dolphins
in Babitonga Bay revealed that teleosts are the most common prey item for both
species (Cremer et al. 2011; Paitach 2015). The squid Lolliguncula brevis was also
found in the stomach contents of both species.
Twenty-one fish species belonging to six families were identified in the diet of
franciscana dolphins, representing 69.4% of the numerical frequency of prey. Fish
also had the highest frequency of occurrence among prey, accounting for 91.3%.
Cephalopod frequency of occurrence was estimated at 47.8%, and numeric
frequency was estimated at 30.6% (Paitach 2015). The number of prey species and
the numerical dominance of fish compared to cephalopods agree with other studies
throughout the species’ geographical ranges (Bassoi 1997; Di Beneditto 2000; Di
Beneditto and Ramos 2001; Rodríguez et al. 2002; Oliveira 2003; Silva 2011; PasoViola et al. 2014).
Among the prey species, the ‘cangoá’ (Stellifer rastrifer) is the most important
in the franciscana diet, with a 70% index of relative importance. When the second
most important prey is added (the sardine Pellona harroweri), the value is closer to
90%. This result indicates that only a few prey species sustain franciscana population, as observed in other studies (Oliveira 2003; Silva 2011). Physical characteristics of this species (e.g., long rostrum and numerous small teeth) favor small-sized
prey like the sardine and the cangoá (Pinedo 1982; Oliveira 2003; Bassoi 2005;
Silva 2011; Cremer et al. 2012).
Twenty-eight fish species from 13 families were identified in the Guiana dolphin
diet. Teleosts also had the highest frequency of occurrence (88.2%), but cephalopods had higher numerical frequency (53.1%) than teleosts (46.9%). The number of
prey species for the Guiana dolphin varies from 10 to 36 throughout its geographical range (Di Beneditto 2000; Zanelatto 2001; Santos et al. 2002; Oliveira 2003; Di
Beneditto and Siciliano 2006; Daura-Jorge et al. 2011). Guiana dolphin population
sizes, behavior, habitat use, and social dynamics vary geographically, and variation
in prey richness may reflect the different ways that populations explore their respective environments (Daura-Jorge et al. 2007; Wedekin et al. 2007; Cantor et al. 2012;
Schulze 2012).
For Guiana dolphins, five prey species together had a 70% relative importance
value: Mugil curema, Pellona harroweri, Stellifer rastrifer, Micropogonias furnieri
and Trichiurus lepturus. The Guiana dolphin diet is composed of many prey species
with similar importance values and gradual reduction, including up to six species
with a combined importance value of 75%; this pattern agrees with other studies
(Zanelatto 2001; Oliveira 2003; Daura-Jorge et al. 2011).
M.J. Cremer et al.