Publicação
Contribution to the diet evaluation of the harbour porpoise (Phocoena phocoena) in Portugal
| Resumo: | The harbour porpoise (Phocoena phocoena) is currently categorized as Critically Endangered in Portugal. Despite its concerning conservation status, there is a knowledge gap regarding its dietary habits in Portugal. Therefore, this study aims to elucidate about the feeding ecology of harbour porpoises along the continental Portuguese coast. To achieve this objective, the stomach contents of 42 harbour porpoises stranded on the northern coast of Portugal were analysed. The diet was qualitatively and quantitatively assessed and the relative importance of each prey species in the diet of the harbour porpoise was determined through occurrence, numerical, and biomass indices. The results of this study reveal that fish, particularly species targeted by commercial fisheries, constitute the main component of the harbour porpoise diet, complemented by cephalopods. Pouting (Trisopterus sp.) emerged as the predominant prey, followed by the common dragonet (Callionymus lyra) and species from the Soleidae family (Solea sp. and Solea solea). Overall, no significant differences were observed in the consumption of the predominant species (Trisopterus sp.) in relation to the sex or maturity of the porpoises. Regarding the nutritional quality of the prey, harbour porpoises consumed more prey species of medium nutritional quality (%N=91,75, %W=79,58), followed by species of high nutritional quality (%N=10,87, %W=20,40), while species of low nutritional quality were consumed in small quantities (%N=2,51, %W=0,09). No variations were observed in the consumption of prey species of different nutritional categories, according to the sex of the animals. In turn, mature harbour porpoises consumed a significantly higher number of medium nutritional quality prey compared to immature individuals. The results of the present study suggest that harbour porpoises exhibit opportunistic feeding strategies, given the diversity of their diet. However, harbour porpoises seem to show some level of selectivity towards the consumption of medium and high nutritional quality prey, to support their metabolic and energy needs. Although most of the fish prey species ingested by the harbour porpoises showed an average size inferior to the legally required minimum capture size, it was observed that most of the high nutritional quality species showed mean length within the minimum capture size, highlighting the potential impact of fisheries on the feeding ecology of porpoises. Understanding the dietary habits of cetaceans provides information about the ecology and resilience of their populations. Additionally, it allows for the assessment of the impact of environmental changes and human activities. This knowledge supports conservation efforts and the development of effective management strategies for the long-term survival of these marine mammals. |
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| Autores principais: | Barros, Sofia Ferreira Alves Meireles de |
| Assunto: | Harbour porpoise Phocoena phocoena Cetacean conservation Diet Feeding ecology Portuguese continental coast |
| Ano: | 2024 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso embargado |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | The harbour porpoise (Phocoena phocoena) is currently categorized as Critically Endangered in Portugal. Despite its concerning conservation status, there is a knowledge gap regarding its dietary habits in Portugal. Therefore, this study aims to elucidate about the feeding ecology of harbour porpoises along the continental Portuguese coast. To achieve this objective, the stomach contents of 42 harbour porpoises stranded on the northern coast of Portugal were analysed. The diet was qualitatively and quantitatively assessed and the relative importance of each prey species in the diet of the harbour porpoise was determined through occurrence, numerical, and biomass indices. The results of this study reveal that fish, particularly species targeted by commercial fisheries, constitute the main component of the harbour porpoise diet, complemented by cephalopods. Pouting (Trisopterus sp.) emerged as the predominant prey, followed by the common dragonet (Callionymus lyra) and species from the Soleidae family (Solea sp. and Solea solea). Overall, no significant differences were observed in the consumption of the predominant species (Trisopterus sp.) in relation to the sex or maturity of the porpoises. Regarding the nutritional quality of the prey, harbour porpoises consumed more prey species of medium nutritional quality (%N=91,75, %W=79,58), followed by species of high nutritional quality (%N=10,87, %W=20,40), while species of low nutritional quality were consumed in small quantities (%N=2,51, %W=0,09). No variations were observed in the consumption of prey species of different nutritional categories, according to the sex of the animals. In turn, mature harbour porpoises consumed a significantly higher number of medium nutritional quality prey compared to immature individuals. The results of the present study suggest that harbour porpoises exhibit opportunistic feeding strategies, given the diversity of their diet. However, harbour porpoises seem to show some level of selectivity towards the consumption of medium and high nutritional quality prey, to support their metabolic and energy needs. Although most of the fish prey species ingested by the harbour porpoises showed an average size inferior to the legally required minimum capture size, it was observed that most of the high nutritional quality species showed mean length within the minimum capture size, highlighting the potential impact of fisheries on the feeding ecology of porpoises. Understanding the dietary habits of cetaceans provides information about the ecology and resilience of their populations. Additionally, it allows for the assessment of the impact of environmental changes and human activities. This knowledge supports conservation efforts and the development of effective management strategies for the long-term survival of these marine mammals. |
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