WILD LIFE | 10.09.18

Open Wide

Their prey may be tiny, but these Indian mackerel need both gaping mouths and an assist from their school-mates to successfully snag a meal.

Photograph by Alex Tattersall

SHARE

Imagine for a moment that you’re a copepod—a pinhead-sized, torpedo-shaped crustacean drifting along in the warm currents of the Indian Ocean. You’re a favored menu item for many other ocean dwellers, so you need to be on high alert. You spread your two long antennae wide, ready to detect the pressure wave of an approaching predator. At the first sign of danger, you can rapidly propel yourself an astonishing distance with a single flap of your 8–10 jumping legs, a feat that has made you and your relatives some of the most successful creatures in the ocean. Still, there are dangers in these waters you’re unlikely to escape. If you could sense more than just light with your one compound eye, few things would alarm you more than the sight of this mouthy scene captured by photographer Alex Tattersall.

Indian mackerel (

Rastrelliger kanagurta

) have a widely varied planktonic diet, but a 2009 study revealed that copepods are their most frequent prey. While a single mackerel would be hard pressed to catch many copepods on its own, a large school of these streamlined fish working together can dramatically increase their chances of success. Whenever a group of mackerel encounter a dense aggregation of copepods, they begin pursuing their prey using a strategy called ram feeding. Aligning themselves in a tight-knit grid in which the gap between each fish is equivalent to the copepods’ average escape distance, the mackerel swim forward with their mouths agape. Long gill rakers—stiff projections that catch food while allowing large volumes of water to pass through—help the fish approach prey with as little disturbance to the water ahead of them as possible.

Copepods, which are normally sensitive enough to detect the mackerel coming despite this adaptation, can make multiple jumps before they exhaust themselves. But it takes a moment for them to reset their antennae after executing each jump, a pause that can be deadly. And if they don’t get swallowed during this downtime, it’s often just a matter of time before their escape jump lands them squarely in front of the waiting mouth of another fish. The mackerel close their mouths every few feet during ram feeding to swallow any copepods and other prey they’ve caught, then open wide in tandem once more to continue hunting. As they do, they reinforce a key link in their marine food web, amassing nutrients that can then be accessed by other species. They themselves are a favored food source for many larger animals—including humans.

Marsa Nakari Bay, Red Sea, Egypt

SHARE

ABOUT THE Photographer

Alex Tattersall is an award-winning UK-based marine photographer with interests in all aspects of ocean life. His boundless enthusiasm for creatively capturing the underwater world and sharing these ideas and techniques with others has become the signature of the photography workshop he leads.

Alex Tattersall

RELATED

TOPICS

ARTICLES

Argentina’s vast Iberá wetlands lost many of their largest species decades ago. Can an audacious rewilding plan rebuild a bygone world?

article | 03.14.17

The Mending

Agricultural entrepreneurs want to solve the planet’s livestock-feed crisis by farming insect larvae. Will their scheme fly?

article | 01.18.17

Maggot Revolution

Successfully raising a single infant is challenging enough that gorillas rarely have twins. But both of these babies are thriving, thanks to a few extra helping hands.

spotlight | 05.13.19

Hands Full

bioGraphic

is powered by the California Academy of Sciences, a renowned scientific and educational institution dedicated to exploring, explaining, and sustaining life on Earth.

©2018 California Academy of Sciences. All rights reserved.