MARINE MAMMALS
The dentition and GIT of odontocetes and pinnipeds are described in detail by Mead (2007) and Richardson and Gales (1987) respectively. The dentition, GIT and metabolism of common bottle-nosed dolphins (Tursiops trunca- tus) are detailed in Cozzi et al.
(2017). Marine carnivores have intestinal tracts at least twice as long as terrestrial carnivores, which is thought to increase nutrient digestibility to compensate for reduced visceral organ function during diving (Fig. 14.3) (Martensson et al. 1998; Sparling et al. 2007; McGrosky et al. 2016). It is common for otari- ids to have gastroliths in their stomachs, however their purpose is not fully understood. It is thought that they assist in the digestive process and buoyancy control despite their absence in phocids and cetaceans (Needham 1997). Otariids and odontocetes are considered generalist predators (Table 14.4). DNA-based techniques have increased our knowledge of prey species consumed in the wild, however the nutritional composition of wild diets is not well known, and to date, there are no precise guidelines for nutritional management of pinnipeds in managed care.With macronutrient data lacking for most whole prey, regular nutritional analysis of the fish species fed is recommended to ensure adequate energy, protein and lipid levels are being obtained. Recent findings show that the macronutrient (protein and fat) requirements are similar for both the Australian sea-lion (Neophoca cinerea) and long-nosed fur seal (Arctocephalus forsteri). Providing five or more prey species is advised to meet macronutrient targets for carnivores and ensure optimal growth and maintenance.
Supplementation is essential for piscivores with most fish species containing thiaminase that is activated postmortem. Thiamine should be supplemented at 25-35 mg kg-1 fish fed to prevent deficiency.
The antioxidant activity of vitamin E is essential in the high polyunsaturated fatty acid diets of pinnipeds. Vitamin E is also progressively oxidised during the storage period and should be provided at a minimum of 100 IU kg-1 fish fed (Dierenfeld et al. 1991).The effectiveness of dietary carotenoids to assist in treatment of ocular disease is largely anecdotal but it is thought that pinnipeds lack cholesterol esterases to hydrolyse lutein esters. If this is confirmed they may benefit from free lutein in the form of beadlets as a bioavail- able dietary source (Koutsos et al. 2013).
The gut microbiome of Australian fur seals (Arcto- cephalus pusillus doriferus) appears to be highly variable with age and environment in wild populations. Dominant phyla include Fusobacteria, Bacteroidetes, Firmicutes and Proteobacteria (Smith et al. 2013; DAgnese et al. 2023).
Gastrointestinal illness is a common morbidity in bottle-nosed dolphins in managed care, and has been attributed to gastrointestinal dysbiosis (Linnehan et al. 2024). Successful faecal microbiota transplantation via the rectum has shown resolution of clinical gastrointestinal signs in these dolphins. Prominent bacterial phyla transfaunated were Firmicutes, Proteobacteria, and Actinobacteria (Linnehan et al. 2024).
Dugongs (Dugong dugon) consume mostly seagrasses and are classified as hindgut fermenting herbivores (Table 14.4). Dugongs have developed different adaptations for assimilating nutrients from low density feeds including a colon ~10 times their body length (Fig. 14.1b). Their dentition is unusual for large herbivores, possessing less than six cheek teeth at any one time and a grinding plate rather than many strong enamelled molars and premolars (Berta et al. 2015). Eros et al. (2007) provides a comprehensive description of the gastrointestinal anatomy of the dugong.
Gross energy requirements of zoo-housed dugongs fed eelgrass (Zostera marina) at between 0.82-0.99% bodyweight per day is 10.4 MCal (Goto et al.
2008). Typical zoo diets of lettuce are expected to be deficient in a range of nutrients. Dugongs maintained on a diet of cos lettuce are reported to suffer from non-regenerative anaemia that can be managed by injectable vitamin and mineral supplementation (see Chapter 47).The hindgut microbiome of free-ranging dugongs is significantly different to dugongs in managed care. Families of Firmicutes and Bacteriodetes dominate the hindgut community in free-ranging dugongs. Oral transfaunation attempts in zoo-housed dugongs fed a diet of mainly cos lettuce have proven unsuccessful in establishing a near-wild microbiome (Eigeland et al. 2012). Transfaunation via enema may be more successful in hindgut fermenters (Table 14.3).
Marine mammal supplements are not appropriate for dugongs as they are designed for a fish-based diet. Data on the nutrient composition of seagrasses commonly consumed by free-ranging dugongs is essential to determining species-specific nutrient requirements for better nutritional management of those in managed care. A dilute diet that meets horse nutrient requirements on a dry matter basis appears appropriate.
ACKNOWLEDGMENTS
We thank Shannon Livingston and Brad Arsenault for their assistance in preparation and whose practical and thoughtful comments significantly improved the manuscript; and Drs Jim Atkinson, Michael Power, Kate Brandis and Valentina Mella for information provided from their unpublished research.