The tendency of female blacktip sharks to congregate in shallow waters during the daytime was most strongly connected to water temperature. Other factors considered were tide height and moon phase. The behavior seemed to be for purposes of thermoregulation, not foraging for food.

An analysis of 16 bird and mammal species was conducted to determine if these carnivores were typically finding enough food to satisfy their hunger and energetic needs in the course of a day. The model concludes that the animals typically find all of the food that they need with time to spare that is instead spent digesting.

It has been well-established that prey follow certain schedules to reduce the risk that they could be captured by a predator. How quickly can these schedules change when the risk of predation is reduced? Scientists assumed that there would be a slow response, if any, when the number of predators was reduced, until Mccauley and colleagues put this idea to the test.

By observing fish behavior on reefs where predators had been mostly eradicated by human behavior, the researchers found that fish typically thought of as nocturnal were 6-8 times more likely to be active on the reef during the day, representing a drastic change in what was thought to be a fixed behavioral pattern.

The same authors studied the chemical and physical activity of the shark stomach. They found that gastric acid secretion was continuous, regardless of the timing of feedings. Although the size and type of food did have an impact on stomach activity, the daily temperature cycle seemed to have the greatest influence on activity.

This conclusion naturally lead to the current study which is examining temperature as a factor driving more aspects of the behavior of this shark.

The timing of activity for two predators (rockcod and dottyback, both reef fishes), and their common prey (the lemon damselfish) was compared. The behavior of the prey fish was determined to be a compromise between ideal times for efficient food capture and predator avoidance, with a particularly strong avoidance of the rockcod.

For the present study on blacktip reef sharks, considering the influence of prey activity allowed researchers to explore if factors other than temperature were driving the behavior of sharks.

This previous study of temperature-related shark behavior sought to study the feeding movements of dogfish: a relatively small shark that lives on the bottom of shallow marine environments. Researchers found that dogfish "avoided warmer water even when it was associated with greater food availability" showing a strong preference for colder waters when given the chance.

The similar title of this paper ("Hunt warm, rest cool...") with that of the present study (."..Hunt Warm, Rest Warmer?) suggests that Dr. Papastamatiou and colleagues used the dogfish study as an important source of inspiration for their own study on blacktip reef sharks.

The quintessential fishing method, which uses a hook with a lure or bait attached to entice fish to bite on to the hook. Ensnared fish are then pulled to the surface for capture or release. This targeted fishing method allows scientists to minimize the impact of their research on other non-target fish that could end up as by-catch in nets, cages, and other gear. Also called "pole and line" fishing, this method can be used to make commercial fishing more sustainable, as in the case of tuna-fishing in the maldives, which you can read more about at The Guardian: https://www.theguardian.com/sustainable-business/pole-line-fishing-sustainability-tuna-market

This network was established in 1903 and has since grown to include over 150,000,000 acres of land that are dedicated to wildlife conservation.

Read more at the website of the U.S. Fish and Wildlife Service: https://www.fws.gov/refuges/?ref=topbar

Many of the news articles written about this study compare the methods used here to study sharks to the black-box flight recorder technology that is used to continuously collect in-flight data on airplanes--information that becomes particularly important in the event of a plane malfunction/crash.

Although no mention of 'black-box technology' is made in this paper, interviews with the author typically relied on this comparison to communicate the methods of the study to the public. Read one such example at Engineering and Technology: https://eandt.theiet.org/content/articles/2015/06/black-box-technology-shines-light-on-shark-behaviour/

A pattern of temperatures

A 24-hour cycle, more commonly referred to as a "day".

Commonly called "cold-blooded", this term describes an animal that regulates its body temperature using external energy sources. For example, this is the reason why many reptiles sunbathe.

The search for food in the environment.

The period of time that viviparous animals (those that give live birth and do not lay eggs) will carry a developing embryo. The length of this period will vary depending on species; for example humans have a gestation period of 40 weeks, whereas rabbits only take about a month.

The original hypothesis that shark behavior would be solely tied to their own temperature (most active when warm and resting when cool, or some other binary relationship) is revised in light of the more nuanced pattern that the researchers observed in the data.

Here, the authors present a new hypothesis that also includes the temperature and behavior of prey, pointing out that the sharks may be most active when the temperature gap between predator and prey is the largest due to their differences in thermal inertia. When the shark is cooling, the fish upon which it preys will have cooled down even more, reducing their ability to escape from the still relatively warm shark.

Ecologists often use equations to try to describe animal behavior. A "scaling coefficient" is a number by which a variable is multiplied, which is used here to say that temperature (the variable in this case) will cause a larger change in the behavior of prey (large scaling coefficient) than predators (small scaling coefficient).

Caranx ignobilis, the "Giant trevally" is called out as an animal that has some key similarities and differences in behavior from the blacktip reef sharks at the center of this study.

While both are apex predators from the Phylum Chordata, the trevally is a bony fish (Class Actinopterygii) while the shark is a cartilaginous fish (Class Chondrichthyes)

Ambush predators which hunt using stealth or strategy (ex: house cat) rather than speed or strength (ex: cheetah).

This 2009 study built upon the ideas presented in the 2006 study that first proposed the ODBA method using data collected from cormorants. The same methodology was applied to a range of terrestrial animals (including humans, skunks, geese, penguins, chickens, and armadillos) to test the validity of the method across species.

The authors concluded that ODBA was a valid method to predict oxygen consumption and metabolic rate for all of the animals included in the study, so the authors of the present paper on shark activity can expect a similar finding for their own species of interest.

This link does not seem to work, but the data resources of the United States Naval Observatory Astronomical Applications Department can be found at this website.

Another term for a "variable" that was considered as part of the study as a factor that could potentially explain the behavior in question.

Also known as autocorrelation, this is a phenomenon that occurs within datasets such as a time series in which the data points are not independent of each other. For example, the temperature recorded one minute is very likely to be similar to the temperature that was recorded for the previous time point because these time points have a relationship to each other, as the temperature will only change as quickly between them as the underlying physics allow. This phenomenon has consequences for some statistical analyses that researchers must correct for to avoid generating spurious results.

Striped surgeonfish

Striated surgeonfish

Whitecheek surgeonfish

An infraclass of the class Actinopterygii, this classification includes most ray-finned fishes found in the world today, with only a few exceptions of ancient fish which branched off earlier in evolutionary history.

A device used to detect sounds underwater.

A 2006 study on cormorants introduced a major shift in thinking about how to study the way in which animals use and acquire energy. The two major methods that were used before this point were 1) monitoring heart-rate or 2) measuring carbon dioxide production using the doubly labeled water method. The ODBA method employs accelerometers (devices to measure the rate of change in the velocity of an object) to measure the rate of energy expenditure for specific animal activities.

Describes the movements of smooth muscle in the stomach that contract as part of the digestion process.

Many animals "play dead" in response to a stress or threat, but this trance-like state in sharks is thought to be connected to mating since they typically have few predators to feel threatened by. It typically takes 15 minutes for this effect to wear off and has little or no lasting health consequences for the shark.

The numbers refer to the diameter of the tag, with different sizes being better suited to a range of animal sizes and data types.

How many measurements are made over a period of time. A measurement is said to be continuous if it is being constantly tracked, whereas discrete measurements are taken periodically at a time interval that the scientists have determined is frequent enough to answer their research question.

This illustration of the anatomy of a barrier reef shows the relative position and depth of the backreef and forereef to the lagoon found at the center of an atoll:

Located in the Pacific, south of Hawaii: With no permanent residents, this is a United States Minor Outlying Island that is part of the largest marine protected area in the world: the Pacific Remote Islands Marine National Monument.

Behaviors performed to control the temperature of an organism such as basking in the sun or seeking shelter.

An example of turtles basking in the sun to increase their body temperature:

It is a common misconception that all sharks must constantly be in motion in order to breathe. While this is not true for all sharks, this is the case for the blacktip reef sharks at the center of this particular study!

There are several different methods that sharks can use for breathing, which you can read more about at How Stuff Works: https://animals.howstuffworks.com/fish/sharks/shark-drown.htm

The emptying of the stomach which occurs as food moves on to subsequent stages of digestion and the eventual excretion of wastes.

The temperature conditions within which an organism has the best chance of thriving. This is one of several factors that determine the ecological niche of an organism, which describes how its behavior and habitat choice play a specific role in the context of the larger ecosystem that it is a part of.

The classic "bell curve" that is used to describe a normal distribution of values.

Enzymes perform many important functions in our bodies (such as digestion) and have a temperature at which they can perform optimally. Temperatures that are higher or lower will require more energy to perform the same task. Keeping your body, and the enzymes that it contains, at an optimal temperatures is a way to maximize the efficient use of energy.

Refers to things that happen during the twilight hours (dawn and dusk). This is in contract to "nocturnal" things that happen at night or "diurnal" things that happen during the day. Crepuscular animals such as deer, bears, and housecats tend to be the most active during these time periods.

A measurement that can be used to infer the health status of an organism. This is typically calculated by comparing a measurement like length to another like weight, for which a healthy ratio is known.

The human body-mass-index (BMI) can be considered a measurement of body condition, as this is derived from a person's height and the range of weights that are considered to be healthy for that height.

A fish with a high body condition is likely to be on the plump side with excess energy stored as a buffer for times of low food intake or high energy use, while a fish with low body condition would be skinny for its length and have low energy reserves.

The energy required for an organism to perform an action. This includes constant needs such as the maintenance of cells or voluntary actions like the use of muscles for swimming. Organisms must balance all of these metabolic costs with the intake of energy from food, or they will run an unsustainable deficit in their energy budget.

Describes the resistance of an object (or, in this case, an animal) to changes in temperature, and the speed at which it approaches the temperature of its surroundings. A warm fish with high thermal inertia would maintain its heat relatively well in cold waters, whereas a fish with low thermal inertia would lose its heat quickly in cold water and is more likely to have a body temperature that is similar to its surroundings.

The period that follows the high point in the tidal cycle (high tide) as the ebb current pulls water back towards the ocean.

"Diurnal" refers to things that happen during the daytime. This is the opposite of its antonym "nocturnal", which appears much more often in common speech to refer to animals that are active at night. In this case, "diurnal prey" is used to refer to the daytime activity of fish that the sharks may be feeding on.

Divers would follow prey fish during the daytime and visually observe the number of times that the tracked fish would bite at the plants upon which they grazed within a five-minute window of time. This data was collected as a measurement of prey activity, the timing of which could be compared with the periods of activity for the blacktip reef sharks

An island formed when an extinct mid-ocean volcano surrounded by coral reefs is eroded and subsided beneath sea level, leaving only a coral reef ring visible above the ocean surface. These are found only in tropical and subtropical regions where corals can thrive and continue to build up a reef at a rate that keeps pace with the erosion and subsidence of the underlying volcano.

Devices were attached externally or internally to captured sharks, which were then released and tracked. The attached devices would record measurements of several data types periodically. Devices either transmit information as it is being collected, or scientists must retrieve a logging device from the shark to access the data at the end of the experiment.

Bio-logging allows scientists to observe some aspects of the behavior of animals in their natural environment, rather than within the constraints of a laboratory setting that may alter the behavior of the animal.