Feeding ecology of franciscana dolphin Pontoporia blainvillei (Cetacea)

Author(s)

Barbara Henning Silva

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2011-12-20

Examining board members

Sergio Rosso; Emygdio Leite de Araujo Monteiro Filho

• Advisor: Sergio Rosso

Abstract

Ecological niche theory is originally based on the assumption that individuals of a species use similar resources and therefore are ecologically equivalents. Under this framework, the niche of the species can be defined in terms of average resource use. However, factors such as quality and quantity of prey resources in the environment, consumer gender, age or morphotype may influence the individual feeding behavior. Considering that possible interindividual variation, recently studies under optimal foraging theory have variation among individuals as a focus of interest. The species P. blainvillei is partionated in populations along its range and probably, subpopulations can be found in the Sao Paulo state coast: northern, central and southern. Hence, my first goal was to investigate if there is diet variation among the three franciscana subpopulations from Sao Paulo coast. Additionally, I searched for which factors would be the diet structure defined within one of the subpopulations (the central one). I have considered the seasonality, individual gender and sex as possible factors influencing the diet structure within the central subpopulation. I had 58 franciscana specimens obtained from bycatch in the Sao Paulo coast, being them from northern, central and southern regions. They were juveniles and adults of both genders and bycaught in all the seasons. I identified the prey species from the gut contents with fish otholits and squid beaks. I estimated prey length and weight using regressions with that structures measures and I investigated the diet structure using a diet variation index. Within the central subpopulation I found no diet variation based on seasonality or individual gender, instead I found diet variation for individuals from different ages. Probably, most of the diet variation among subpopulations is due to prey availability spatial difference. The lack of diet variation based on seasonality may be due to little seasonal variation in the abundance of the main prey, P. harroweri. The lack of variation due to gender is probably related to the prey selection on soft body and easy digestion instead of prey size, being this type of selection common for both genders. Juveniles franciscana preyed on more species than the adults and that niche shift as an age effect can be consequence of forraging skills development. Enclosing, even discarding the effects of the spacial and temporal prey availability, individual gender and age, I found interindividual-level diet variation within the central subpopulation, which can points out to franciscana individual specialization, but isotopic studies are required to infer that specialization (AU)

• FAPESP's process: 09/06919-0 - Feeding habits of Pontoporia blainvillei (Gervais & D'Orbigny, 1844) and Sotalia guianensis (van Beneden, 1864)on São Paulo State Coast
• Grantee: Barbara Henning Silva
• Support Opportunities: Scholarships in Brazil - Master