Sharks have long held an aura of mystery, danger, and fascination in popular culture. As apex predators who inhabit the often dark and obscured depths of the ocean, sharks seem cloaked in shadow which lends itself perfectly to tales of nocturnal feeding frenzies.
If you’re short on time, here’s the quick answer to whether sharks are more active at night: while some species of sharks are indeed more active and feed more at night, not all sharks necessarily exhibit increased nocturnal activity or feeding behavior.
In this approximately 3000 word article, we will examine multiple species of sharks and studies observing their activity patterns to definitively answer whether sharks as a whole tend to be more active and feed more often at night compared to daytime.
Diel Activity Patterns of Different Shark Species
Tiger sharks
Tiger sharks are known to be most active at night when hunting for prey. Studies using acoustic telemetry have found that tiger sharks increase their swimming speed and traverse larger areas during nighttime hours.
This nocturnal activity pattern allows them to take advantage of the daily vertical migration of many prey species that come closer to the surface at night. However, tiger sharks are not exclusively nocturnal – they have also been observed hunting during the day, especially in turbid water with low visibility.
Hammerhead sharks
The activity patterns of hammerhead sharks can vary by species, location, and even individual preferences. Great hammerheads and scalloped hammerheads generally show crepuscular activity peaks around dawn and dusk. This means they are most active during the transitional periods between day and night.
One study in the Bahamas found scalloped hammerheads formed large hunting schools at dawn. Smooth hammerheads demonstrate more variable diel patterns, with both diurnal and nocturnal hunting observed.
White sharks
White sharks are primarily diurnal hunters, meaning they are most active during the day. Research using tagging data has shown they spend more time near the surface and swim faster during daylight hours when hunting seals and other prey. However, they are not exclusively active during the day.
Studies have revealed white sharks will also hunt at night, especially when environmental conditions like lunar illumination provide enough light. There is individual variability as well, with some sharks being more nocturnal than others.
Bull sharks
Bull sharks exhibit wide variations in diel activity based on location, tidal patterns, and other environmental factors. In some areas, they have shown crepuscular peaks in activity coinciding with dawn and dusk.
Other acoustic telemetry data indicates bull sharks can be active at all times of day, with regular diurnal and nocturnal movement. Individual differences exist too. Juveniles tend to be more active during the day, while adults hunt at night more frequently.
Bull sharks are opportunistic predators and will hunt whenever prey is available.
Lemon sharks
Lemon sharks display strong patterns of diel activity related to the tidal cycle. They are most active during tidal peaks, either on rising high tides or dropping low tides, and exhibit decreased activity at intermediate tide levels.
This allows them to take advantage of increased prey availability in very shallow water during tidal extremes. Within tidal periods, lemon sharks can be active both day and night but many individuals show crepuscular peaks around dawn and dusk when hunting in shallow water nursery areas.
Impact of Lunar Cycles on Shark Behavior
The lunar cycle has long been hypothesized to influence shark behavior and activity levels. Though the exact mechanisms are still being studied, there are some clear patterns that have emerged from research:
Hunting and Feeding
Many species of sharks, including tiger sharks, bull sharks, and hammerheads, demonstrate increased hunting, feeding, and catch rates during full moons. It is theorized that the increased ambient light on full moon nights improves their ability to spot prey.
In addition, full moons often coincide with tidal changes, increasing food availability near shorelines.
Migrations and Movements
Some sharks make predictable, cyclical migrations that correlate with lunar cycles. For example, scalloped hammerheads in the Eastern Pacific have been documented migrating offshore during full moons and inshore during new moons.
Researchers believe the brighter nights may aid navigation for these migration events.
Reproduction
There is evidence that female sharks synchronize reproductive events with lunar cycles. Ovulation and mating frequently occur around the full moon. This timing may help facilitate getting together for mating when sharks are already more active.
Ecotourism Impacts
Shark ecotourism operators plan excursions around lunar cycles to maximize shark sightings for participants. Full moon nights usually offer prime shark viewing. Divers off the coast of Honduras reported a 13-fold increase in shark abundance around the full moon versus the new moon.
While lunar impacts are species-specific, it is clear the moon exerts some influence over shark ecology. Research into exact mechanisms and dynamics across habitats continues, offering insights into shark conservation and management.
Other Factors Influencing Nocturnal Activity
Prey availability
The availability of prey is a major factor that impacts whether sharks hunt more at night or during the day. Species such as bull sharks and tiger sharks that feed on a diverse array of prey tend to be more active at night when certain prey species are more abundant.
For example,bull sharks often hunt at night to feed on species that emerge in darkness such as octopuses, lobsters and reef fish that hide in crevices and caves during daylight hours.
In contrast, sharks like the great white that rely on seals and sea lions as their primary food source, tend to be more active hunters during the day when these prey species are more active and visible.
However, great white sharks have been recorded feeding on a wide variety of species at night as well from fish to squid when seals and sea lions are less accessible.
The migration patterns and life cycles of prey species also impact nocturnal activity. For instance, spawning events for fish, crustaceans and cephalopods often occur after dusk which leads to increased shark hunting behavior at night to target the spawn.
Shark age
A shark’s age and life stage affects whether it hunts more actively during the day or at night. Younger sharks tend to be more active at night as a survival mechanism to avoid larger daytime hunters. Smaller, juvenile sharks have a higher risk of predation from larger shark species, so hunting under the cover of darkness improves survival odds.
Additionally, younger sharks with smaller teeth and jaws rely more on soft-bodied prey like squid, octopuses and small fish which are often more accessible at night. In contrast, larger adult sharks have the size, speed and teeth to hunt seals, sea turtles and dolphins which are active during daylight hours.
There are always exceptions as some massive adult shark species like the bluntnose sixgill shark do most of their hunting at depths of over 200 meters during nighttime hours. Their prey source deep in the ocean is more plentiful after dark.
Putting It All Together: Synthesizing Shark Diel Cycles
When reviewing the available research on shark activity patterns throughout the day, some interesting trends emerge. Multiple studies have shown that many shark species do exhibit daily cycles, with higher activity levels at certain times of day.
However, there is variation between species and even within species depending on location and environmental factors.
Higher Activity at Dawn and Dusk
Numerous research projects on sharks around the world reveal spikes in activity during crepuscular periods – around dawn and dusk. This pattern has been documented in species such as blacktip reef sharks, Caribbean reef sharks, bull sharks, and great hammerhead sharks.
Possible explanations include taking advantage of low light levels to ambush prey, interacting with tidal cycles, or avoiding times when warmer water temperatures could cause overheating.
Variability Between Locations and Species
While the dawn and dusk activity pattern is common, some species buck the trend. For example, lemon sharks in Bimini, Bahamas are more active at midday. This highlights how local conditions shape behavior. In addition, different shark species can exhibit contrasting cycles even in the same area.
Research in Shark Bay, Australia found higher dusk shark abundance but lower activity levels at that time.
Cycle Disruption from Human Activity
There are also indications that human activity and shark provisioning are interfering with natural cycles. Analysis in Moorea, French Polynesia showed grey reef sharks had less defined activity peaks in areas with greater tourism.
Another study in Fiji found bull shark diel cycles disappeared after consistent feeding for ecotourism.
Gaps Remaining in Understanding
While progress has been made, there are still knowledge gaps about shark diel activity cycles. Many species have not been closely studied over 24-hour periods. There is also debate around what drives cycles – whether it is influenced more by sunlight, tides, or other factors.
Expanding research methods with technology like accelerometer tags could provide more insight.
Conclusion
In conclusion, while some sharks do exhibit pronounced nocturnal activity or feeding patterns, not all species follow this trend. Various factors like lunar phase, water temperature cycles, prey availability, and shark age may mediate the extent of nocturnal behaviors in different shark populations and contexts.
By examining the diel rhythms of various species, however, we can gain greater insight into the lives and evolutionary pressures shaping these mysterious predators of the deep.
