Nutritional Requirements
Sea otters arriving at a rehabilitation center will vary in nutritional condition. Even healthy wild otters have very little body fat and must consume about 25% of their body weight daily in high protein prey items. This high level of consumption is necessary for the otter to maintain a metabolic rate, which is two to three times higher than a terrestrial mammal of the same size. Oil contamination of the fur requires a further increase in metabolism to offset the additional heat loss. This may cause the otter to go into negative caloric balance and to lose weight (Costa and Kooyman, 1982; Davis et al., 1988).
Complicating this scenario, sea otters may be unable to feed normally after an oil spill for several reasons. They may be preoccupied with grooming their contaminated fur and spend less time looking for food. Severe chilling when in the water may prevent normal foraging behavior or force them to go ashore where food is unavailable. Oil contamination of intertidal prey species and oil spill response activities may displace otters from their normal foraging areas (Doroff and Bodkin, 1994). Oil ingestion and stress may cause gastrointestinal inflammation, ulceration, and diarrhea, which interfere with the complete digestion and absorption of food.
Data from hospitalized domestic animals shows that they undergo a series of metabolic adaptations following severe illness or injury, (Donoghue, 1989). A lowered metabolic rate occurs during the first twenty-four to forty-eight hours after a life threatening stress, follow (by a period of elevated metabolism which peaks in about four days, and lasts for two to four weeks. The same metabolic changes appeared to occur in oiled sea otters during the Exxon Valdez oil spill (EVOS). Those arriving at the rehabilitation center often showed little interest in food. However, as they began to regain their health and normal appetite, they consumed 30-50% of their body weight in food daily
When sea otters arrive at the rehabilitation center, their body condition and immediate nutritional needs should be assessed during initial clinical evaluations (see Chapter 4). Serious health problems (hypoglycemia, dehydration, etc.) will occur in animals that have not eaten adequately. These otters will require immediate medical treatment (see Chapter 5). Animals that are not heavily oiled and who health is stable should be allowed to rest and should be fed for twelve to twenty-four hours prior to sedation and cleaning; this will lessen the stress of capture. During this period, they should be offered familiar food such as clams and crabs. Food should be withheld one to two hours before sedation to prevent vomiting or regurgitation.
Diet and Food Preparation
Sea otters should be fed a variety of seafoods including shrimp crabs, clams, fish, squid, mussels, sea urchins, and abalone (Tuomi 1990). The caloric value of foods frequently consumed by sea otters during the EVOS are presented in Table 7.3. The percentage of water in these foods is quite high (66-83%). Protein contributes more than 70% of the calories for all items except salmon. By comparison, cat food is typically 25-35% protein and dog food is 18-32%. Only 10- 20% of the calories in a sea otter’s diet are from fat and almost none from carbohydrates.
To estimate the daily food consumption of a healthy otter, multiply its body weight by 0.25 and then divide this amount into five feedings spaced about three hours apart. Food should not be offered late at night, allowing undisturbed rest time. Otters in a hypermetabolic state should be offered as much food as they are willing to consume at each feeding. Once they have regained their health, they should be placed on a normal maintenance diet, about 25% of their body weight daily. However, this should be adjusted for individual animals so that they maintain body weight.
Freezing seafood is thought to reduce the transmission of parasites (Sweene 1965) and is convenient for purchase and storage. Fresh seafoods may be used, if the quality can be assured and facilities available to properly hold and process these foods. Staff should be trained in the proper handling of seafoods (human food sanitation standards) to ensure that food remains nutritious and uncontaminated (Ferrante, 1990).
The rehabilitation facility should have adequate freezer space to store at least a three-day supply of frozen seafood (Chapter 12). For a facility with 200 adult sea otters, the freezer should be able to hold 9,000 pounds of seafood. Frozen seafood should be thawed in air or cold water and used within several hours to avoid spoilage. Seafood should never be thawed in hot water, as this promotes bacterial growth. The food should be preweighed (one pound portions are convenient), placed in plastic bags, and kept chilled on ice until used. Preweighing food into bags makes it easier for the animal caretakers to estimate amount eaten by each otter. Uneaten food should be discarded after six hours.
Vitamin supplementation should be attempted for all captive otters. However, otters are adept at locating vitamin tablets hidden in food, and will often refuse to accept food that has been altered by supplements. Muffins containing krill and vitamins have been used at the Seattle Aquarium (Qtten-Stanger, personal observation). SeaTabsTm vitamins are available commercially and tolerated well by most marine mammals.
Roughage
Even with good sanitation and attention to nutrition, recuperating otters often develop diarrhea. The causes are varied and difficult to determine. Sea otter feces is commonly mucoid and poorly formed, especially when the shells or carapace of food items are excluded from the diet. Because defecation usually takes place in the water, detecting true diarrhea can be difficult, especially for observers not accustomed to normal sea otter eliminations. Overfeeding may contribute to diarrhea. The passage of undigested pieces of food, straining during a bowel movement (occasionally resulting in a prolapsed rectum), and bloody or tarry stools should be reported to the veterinarian.
Increasing roughage in the form of shells or carapace from whole food items such as mussels, crabs, and shrimp produces a more formed stool (Figure 7.6). The indigestible portions act as binders in the feces and may contribute to the mineral nutrition of the otters. This roughage may be removed for animals with gastrointestinal hemorrhaging, but may result in unformed feces that cannot be distinguished from diarrhea.
Methods of Feeding
Sea otters in critical care cages or fiberglass pens. should be hand fed by offering individual pieces of food with long-handled tongs. Food should never be offered to an otter using the bare hands; this may introduce food-borne pathogens, and the otter’s sharp claws and strong jaws can inflict serious injury. Food may be placed (in preweighed portions) into stainless steel feeding bowls placed on haulout platforms in the pools and larger pens. Rehabilitated otters in floating pens should be fed by throwing food into the water, or by placing the food in a bucket or basket that is submerged. This will encourage the otters to swim and dive for their food and will reduce the perception of the husbandry staff as a food source.
An accurate record of the type and amount of food eaten by each otter (Appendix 2, Forms K and L Download PDF) is important for monitoring the animal’s recovery. Most otters will readily accept food and rapidly adapt to various feeding routines. A variety of seafood should be consumed to ensure adequate nutritional intake. Some otters develop a preference for certain foods and should be encouraged to eat other items. Subordinate otters may need additional food offered to them after other animals in the group have finished eating.
An otter refusing food for more than one feeding or eating less than 10% of it’s body weight each day may indicate serious health problems and warrants immediate attention by a veterinarian. In the large holding pens, it is not possible to determine the exact food consumption of each animal, but husbandry staff should note any animal that does not appear to be eating. An otter that does not feed adequately should be moved to a different pen or to a critical care cage for observation and clinical treatment. Tube feeding may be necessary for severely anorectic sea otters (see Chapter 5).
