Hot Spots

Edy Setyawan, 2019

Scott Sinton, 2019

The Manta Watch team define a hot spot as an area or specific location that has experienced consistent manta ray activity over time.

These potential hot spots are identified as we continually update our sightings records, which we gather through real time citizen science submissions and by conducting dedicated manta ray surveys.

All usable verified sightings data is Geo- referenced i.e. has a corresponding GPS (latitude and longitude) position that we can then use to create manta sightings maps.

Along with the location, each verified sighting includes additional information such as the time, date and observed manta ray behaviour.

We can filter this information to be shown on our sightings maps, which helps us better understand how and when mantas are using certain locations. For example during the summer months feeding behaviour dominates in certain areas, highlighting suspected manta ray foraging habitats.

Once a hot spot is confirmed, that area then becomes the focus of intensive survey effort so that our team can learn as much as possible about that location and the manta rays found there.

The chances of encountering manta rays at a “hot spot” are far from guaranteed. A key part of our ongoing research is to better understand the factors that drive these hot spots and learn how to predict when they are going to fire. From the little we do know about NZ hot spots, it’s safe to say that timing is everything and WHEN is just as important as WHERE.

Map showing distribution of manta rays and associated behaviours (1994-2021) between the Poor Knights and the Hauraki Gulf, New Zealand.


Our biggest challenge is the fact that manta rays do not need to come to the surface at all. So when they do decide to hang out in those top 5 meters (where we can see them) it is for a specific reason.

Our first job as researchers is to understand what factors bring mantas to the surface. The second, trickier job is being able to predict when and where this surface activity is going to take place and be ready to jump into action at a moments notice.

Mark Erdmann, 2021

To help answer these questions we record both biological (animal focused) and physical (environmental) information about our suspected hot spot, both when we successfully encounter manta rays as well as when we don’t. We can then start to identify what factors are associated with manta surface activity and use these insights to increase our chances of spotting more manta rays in the future.

Everything in the ocean is connected and nothing acts in isolation, so by connecting all these clues we can begin to understand what’s happening in the wider context of the ocean and how manta rays fit into these ecosystems.

Mark Erdmann, 2021

Hot Spot Drivers

Manta rays generally come to the surface for three main reasons: to warm up, feed and to mate.

Manta and devil rays are ectothermic, meaning that they can’t regulate their own body temperature so it fluctuates according to the surrounding water. Both species are known to perform deep dives and can handle single digit temperatures for finite periods of time. After spending a stint in cool water, it is commonly agreed that mantas and devil rays like to heat up and have been observed resting by slowing cruising on or just below the waters surface.

We see this behaviour a lot in NZ, however it’s hard to predict and even harder to spot. Calm, sunny days are prime sun basking conditions for mantas.

Surface feeding activity is the “easiest” driver to predict and these events often occur in associations with oceanographic processes, one of which is upwelling. Upwelling is when cool, nutrient rich ocean water rises from the deep and mixes with the warmer surface waters.

This water mixing essentially fertilises the surface waters promoting high biological productivity in those areas. Which put simply means an increase in food, both microscopic plants (phytoplankton) and the animals (zooplankton) that feed on them. The sheer abundance of these tiny organisms form the basis of most oceanic food webs.

Edy Setyawan, 2021

From late spring to late autumn, krill (small shrimp like animals) are highly abundant and are a common prey species for whales, sea birds, and many fish species in NZ including manta rays. During these warmer months krill swarms often travel to the surface, triggering large multi-species feeding events where numerous species of birds, fish and marine mammals gorge themselves on the fast moving krill.

Manta rays have an in-built zooplankton super sense and know exactly when krill swarms begin to form and concentrate near the surface. Under the right conditions huge krill swarms can form, often attracting large numbers of hungry manta rays. When lots of mantas are feeding in the same place it is called an aggregation.

Depending on the size and density of the krill swarms these feeding aggregations can last for hours. In other words, this is when manta hot spots FIRE and become red hot! One of our key research objectives is to better understand the movements and behaviour of krill in NZ.

The reasons why krill choose to swarm at the surface and what factors drive this behaviour? We hope that learning this will ultimately provide greater insight into manta-krill interactions, in addition to highlighting potential threats to hot spots such as habitat degradation and climate change.

Jochen Zaeschmar, 2021