Basal Metabolic Rate
Energy Calculations:
General Equation for mammalian BMR
W= 5-15lbs, 12lbs/6.2kg average ~BMR= 150kcal/kg
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Food Consumption in order to maintain energy requirements (Daily Energy Expendature/DEE) (Decker et al. 2010)
- 4738kJ/day for an otter with a body mass of 7842g - approximate resting energy requirement of 4.1(W)/kg (Pfeiffer and Culik 1998) 2. Hunting in water: -Takes about 6.3kJ/g on average of energy to catch a fish -the approximate energy requirement being 10.3 (W)/kg (Pfeiffer and Culik 1998) 3. Hunting on land - Takes about 3.7kJ/g on average of energy to catch crayfish (predominant diet in warmer months) - the approximate energy requirement being about 16% less than in water, possibly due to thermoregulatory and speed differences (Pfeiffer and Culik 1998) |
Thermoregulation
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Strategies to maintain core body temperature: (Kruuk 2006)
- increase activity on land before entering colder water, this increases the core body temperature
- decrease the foraging time spent in water during colder climates (In Eurasian otters with similar thermoregulatory mechanisms to river , spend an average of 15 minutes or less foraging, if remain in water the body temperature drops approximately 2.3 degrees Celcius every hour.
- Use different thermo-insulation methods including small layer of subcutaneous fat (about 13% fat in River Otters), to maintain body heat without decreasing the agility and speed otters require for hunting, and their fur which has approximately 60, 000 hairs per cm2 which is vigorously maintained by otters with frequent grooming after diving so the fur maintains the ability to produce air pockets with diving and protect the otter from soaking up water into their coats with each dive
Growth and Reproduction
- typically consuming at approximately 28% of their body weight, as opposed to the typical 20% (Decker et al. 2010) - in Lutra Lutra species typically the female increases consumption of food from 4.41lbs/day to 6.61lbs/day - females in general are also smaller than males meaning they have a higher energy demand per kg of body mass, in Lutra lutra species this has been an average of 738KJ/kg vs . 698kj/kg for males) (Henry et al. 2012)
- increased food intake necessary for growth and normal physiological development - In milk forumlas in the milk from the lactating mother, want a high protein and fat content and very low milk carbohydrates (sugars etc) - after weining fish with high fat content are reccommended for optimal growth |
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Survival Challenges
Nutrient Challenges
- Sometimes there is a Vitamin B1 deficiency seen in otters in areas with high thiaminase activity in fish (an enzyme that breaks down thiamine, is seen fairly consistently in the Great Lakes Area) (Henry et al 2012), however if there is a high variety in diet, due to the opportunistic nature of these carnivores typically nutrient deficiencies are rare
Pollution:
- human involvement is one of the main struggles for this species
- In Nova Scotia, Haines et al. 2010 found high levels of mercury in the brains of river otters and minks, which can have highly neurotoxic effects to any species, including river otters. It was found that high selenium levels could combat the high levels of mercury through antioxidant measures, but are necessary to consume these in the diet, freshwater fish having a higher Hg:Se ratio than marine, inferring there may be difficulties with toxicity from Hg poisoning depending on location and diet of the river otter species.
- hunting was also a major issue in the declining population of river otters before multiple rehabilitation efforts were derived in both canada and the United States (Boyle 2006)
Seasons and Temperature Changes
- as mentioned above, thermoregulatory mechanisms are very costly and with seasonal changes and food availbility changes this can pose an issue for river otters
- smaller animals such as river otters have a decreased thermoregulatory capacity (Kruuk 2006).
- in freshwater vs. saltwater there is also an increased difficulty with thermo-insulation, seawater fur absorbs water a lot more readily than freshwater, increasing the energy requirements for additional thermoregulation strategies (Kruuk 2006)
- ecological constraints including periods of drought and other environmental conditions that would limit an otters food supply (Decker et al. 2010)
- Sometimes there is a Vitamin B1 deficiency seen in otters in areas with high thiaminase activity in fish (an enzyme that breaks down thiamine, is seen fairly consistently in the Great Lakes Area) (Henry et al 2012), however if there is a high variety in diet, due to the opportunistic nature of these carnivores typically nutrient deficiencies are rare
Pollution:
- human involvement is one of the main struggles for this species
- In Nova Scotia, Haines et al. 2010 found high levels of mercury in the brains of river otters and minks, which can have highly neurotoxic effects to any species, including river otters. It was found that high selenium levels could combat the high levels of mercury through antioxidant measures, but are necessary to consume these in the diet, freshwater fish having a higher Hg:Se ratio than marine, inferring there may be difficulties with toxicity from Hg poisoning depending on location and diet of the river otter species.
- hunting was also a major issue in the declining population of river otters before multiple rehabilitation efforts were derived in both canada and the United States (Boyle 2006)
Seasons and Temperature Changes
- as mentioned above, thermoregulatory mechanisms are very costly and with seasonal changes and food availbility changes this can pose an issue for river otters
- smaller animals such as river otters have a decreased thermoregulatory capacity (Kruuk 2006).
- in freshwater vs. saltwater there is also an increased difficulty with thermo-insulation, seawater fur absorbs water a lot more readily than freshwater, increasing the energy requirements for additional thermoregulation strategies (Kruuk 2006)
- ecological constraints including periods of drought and other environmental conditions that would limit an otters food supply (Decker et al. 2010)
![Picture](/uploads/2/5/8/0/25801510/8933011.png?349)
- The graph represents how the amount of energy required to catch prey changes with temperature, a lower energy expenditure in the summer (691 KJ/kg BM0,75/d) than in winter (750 kJ/kg BM0,75/d) (Henry et al. 2012)
- If this fluctuates and correlates with a decrease in prey availability at lower temperatures, it might result in weight loss and decreased nutritional status of the River Otter
- If this fluctuates and correlates with a decrease in prey availability at lower temperatures, it might result in weight loss and decreased nutritional status of the River Otter
Main references used for this page
1. Dekar, M.P., Magoulick, D.D., Beringer, J. (2010) Bioenergetics assessment of fish and crayfish consumption by river otter (Lontra canadensis): integrating prey availability, diet, and field metabolic rate. Fish Aqua Sci. 67: 1439-1448.
2. Henry, B., Maslanka, M., Heuer, K., Reed-Smith, J., and Nidasio, G. (2012) Otters in zoo, aquaria, rehabilitation and wildlife sanctuaries. IUCN River Otter Specialist. Available: http://www.otterspecialistgroup.org/Library/TaskForces/OCT.html [March 2, 2014].
3. Kruuk, H. (2006). Otters: ecology, behaviour and conservation. Great Clarendon St. NY: Oxford University Press
4. Pfeiffer, P., & Culik, B.M. (1998) Energy metabolism of under- water swimming in river otters (Lutra lutra L.). J. Comp. Physiol. 168B: 143–148.
1. Dekar, M.P., Magoulick, D.D., Beringer, J. (2010) Bioenergetics assessment of fish and crayfish consumption by river otter (Lontra canadensis): integrating prey availability, diet, and field metabolic rate. Fish Aqua Sci. 67: 1439-1448.
2. Henry, B., Maslanka, M., Heuer, K., Reed-Smith, J., and Nidasio, G. (2012) Otters in zoo, aquaria, rehabilitation and wildlife sanctuaries. IUCN River Otter Specialist. Available: http://www.otterspecialistgroup.org/Library/TaskForces/OCT.html [March 2, 2014].
3. Kruuk, H. (2006). Otters: ecology, behaviour and conservation. Great Clarendon St. NY: Oxford University Press
4. Pfeiffer, P., & Culik, B.M. (1998) Energy metabolism of under- water swimming in river otters (Lutra lutra L.). J. Comp. Physiol. 168B: 143–148.