Fuel Economy

Mar - 29 2020 | By

Hello, welcome back to another week at my blog. I hope all is well. The topic of discussion last week centered on the Great White Shark’s dermal denticles, their origin, and how they help the Great White Shark in its natural habitat. Today’s topic will be focused more so on an aspect of the Great White Shark that can not be physically seen with the naked eye. Great White sharks are known to be warm-bodied, however, have you ever asked yourself if their temperature is at a constant level or if they are able to thermoregulation? Simply put, Great White Sharks are not able to thermoregulation however, scientists have found that they do something else as a response to their environment.

When studying animals, whether they are marine or terrestrial, and their energy input vs. output, scientists tend to look at their Basal Metabolic Rate or BMR. BMR  is the minimal rate of energy expenditure necessary for an organism to maintain life processes. For the longest time, though other species of sharks were able to be held in captivity and studied, the Great White had not had its BMR studied due to the fact that they do not cope well in captivity. It was not until the 1st of July 1979,  when a fisheries scientist by the name of Frank Carey was able to follow and study a Great White’s BMR and how their body temperature would react in response. Carey and some of his colleagues heard about Great White sharks in a town nearby that were in the area due to a  carcass of a large whale. They organized an expedition and were able to tag one of the sharks in order to study them. One of the things discovered was that the muscles of the Great White are indeed warm and they would, later on, be the first to demonstrate endothermy in this species.

During the experiment, the shark’s muscle temperature deviated, and slowly responded to changes in the water temperature. As the Great White Shark dove deeper into the water, the temperature of the water dropped. As the water temperature dropped, the shark’s muscles began to cool, however, it was not thermoregulation, because the change occurred slowly and several hours after the shark had dove deeper. Meaning that as the shark cooled off it would be releasing heat but the heat release was actually significantly lower than expected which was later on then attribute to the rete mirable. The rete mirable is a complex of arteries and veins that uses countercurrent blood flow to act as a countercurrent exchanger.

The experiment demonstrated that Great White sharks are excellent energy metabolizers.  “if the animal were perfectly insulated, the production of metabolic heat would cause its temperature to rise; the rate of temperature increase would be directly related to metabolism. The shark, of course, was not perfectly insulated, and thus its body temperature was the result of a dynamic equilibrium between heat production and heat loss ” (ReefQuest Centre for Shark Research).

Due to their managing of energy Great White sharks do not need to feed as often as other animals, though they feed more regularly than thought before. The latest study done by Semmens et al shows that the feeding gap for Great White sharks is about 14.8 days, meaning that Great White sharks are able to greatly space out their refeeding window. Which if you think about it is absolutely amazing that they can not only go so long without feeding but that their energy expenditure is well maintained and balanced. Shown below is a graph of the results from the mentioned study.

 

 

 

 

Figure 1

figure1

Movements, swimming speeds and metabolic rates of a white shark.

(a) 3.5 h track from a 3.5 m male white shark at the Neptune Islands fur seal colony, Australia, determined by a radio-acoustic positioning system. Inset. a white shark Carcharodon carcharias at the Neptune Islands. (b) Swimming speeds (U, TLs−1) were calculated from locations made at ≤5 s intervals in (a) and used to estimate routine metabolic rate (RMR) (MO2, gO2h−1 as per the figure axis label) (see Materials and Methods for details).

(https://www.nature.com/articles/srep01471)

 

 

Studying how exactly Great White sharks’ bodies adapt to their surroundings without thermoregulation,  and their energy consumption to expenditure ratio can be further studied by scientists in order to maybe one day create technology that would mirror not only energy input to energy output but also to the longevity of the periods of refueling. Perhaps using the research scientist will someday be able to create even better diving suits that mimic the shark’s temperature response in order for us as people to be able to go to even deeper depths of the ocean.

As the blog comes to an end for this week, I leave you with a question: What are some other ideas that you can come up with that scientist could possibly create from studying the fuel economy of the Great White shark and their gradual temperature change? Take your time to ponder and I hope to see you next week for a new topic.

 

 

Citations: 

http://www.elasmo-research.org/education/white_shark/metabolism.htm

https://www.nature.com/articles/srep01471

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