119
chapter six
Diet and nutrition
Mark A. Hindell and Andrea Walters
6.1 Introduction
Diet and nutrition are fundamental in shaping the life histories and reproductive strategies of all animals but particularly so for marine mammals. This is because, despite their
diverse evolutionary origins, all marine mammals returned to the sea from terrestrial antecedents to exploit the abundant resources available in the marine environment. In so doing,
they have retained some of the traits of their land-based predecessors which dictate many
aspects of their feeding biology. Primary among these is their need to breathe air, requiring them to spend time on the surface away from the prey fields. The tension between the
need to obtain oxygen at the surface but to feed, hunt, and even digest food underwater in
the absence of available oxygen is a fundamental challenge for marine mammals. Further,
while cetaceans and sirenians can give birth and nurse young at sea, pinnipeds need to be
on land (or ice) for reproduction, further influencing their relationship with marine-based
food resources. During breeding and lactation pinnipeds either do not forage at all (many
of the phocids) or they forage close to the breeding sites (many of the ottariids); both strategies have their own implications for diet.
Contents
6.1 Introduction ........................................................................................................................ 119
6.2 Life history and diet .......................................................................................................... 120
6.3 Feeding mechanisms ......................................................................................................... 121
6.3.1 Filter feeding ........................................................................................................... 121
6.3.2 Pierce feeding ......................................................................................................... 124
6.3.3 Suction feeding ....................................................................................................... 126
6.3.4 Herbivory ................................................................................................................ 126
6.4 Methods for studying diet in marine mammals ........................................................... 127
6.4.1 Direct observation of feeding .............................................................................. 127
6.4.1.1 Traditional methods ............................................................................... 128
6.4.2 Novel, new techniques to investigate the feeding ecology of marine
mammals................................................................................................................. 129
6.4.2.1 Stable isotope ratios ................................................................................ 129
6.4.2.2 Fatty acids ................................................................................................ 130
6.4.2.3 Molecular analysis of prey ..................................................................... 132
6.4.2.4 Video and digital recording .................................................................. 133
Glossary ........................................................................................................................................ 133
References ..................................................................................................................................... 134
chapter six
Diet and nutrition
Mark A. Hindell and Andrea Walters
6.1 Introduction
Diet and nutrition are fundamental in shaping the life histories and reproductive strategies of all animals but particularly so for marine mammals. This is because, despite their
diverse evolutionary origins, all marine mammals returned to the sea from terrestrial antecedents to exploit the abundant resources available in the marine environment. In so doing,
they have retained some of the traits of their land-based predecessors which dictate many
aspects of their feeding biology. Primary among these is their need to breathe air, requiring them to spend time on the surface away from the prey fields. The tension between the
need to obtain oxygen at the surface but to feed, hunt, and even digest food underwater in
the absence of available oxygen is a fundamental challenge for marine mammals. Further,
while cetaceans and sirenians can give birth and nurse young at sea, pinnipeds need to be
on land (or ice) for reproduction, further influencing their relationship with marine-based
food resources. During breeding and lactation pinnipeds either do not forage at all (many
of the phocids) or they forage close to the breeding sites (many of the ottariids); both strategies have their own implications for diet.
Contents
6.1 Introduction ........................................................................................................................ 119
6.2 Life history and diet .......................................................................................................... 120
6.3 Feeding mechanisms ......................................................................................................... 121
6.3.1 Filter feeding ........................................................................................................... 121
6.3.2 Pierce feeding ......................................................................................................... 124
6.3.3 Suction feeding ....................................................................................................... 126
6.3.4 Herbivory ................................................................................................................ 126
6.4 Methods for studying diet in marine mammals ........................................................... 127
6.4.1 Direct observation of feeding .............................................................................. 127
6.4.1.1 Traditional methods ............................................................................... 128
6.4.2 Novel, new techniques to investigate the feeding ecology of marine
mammals................................................................................................................. 129
6.4.2.1 Stable isotope ratios ................................................................................ 129
6.4.2.2 Fatty acids ................................................................................................ 130
6.4.2.3 Molecular analysis of prey ..................................................................... 132
6.4.2.4 Video and digital recording .................................................................. 133
Glossary ........................................................................................................................................ 133
References ..................................................................................................................................... 134