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As the cli­mate changes and fish­eries trans­form the oceans, the world’s African pen­guins are in trou­ble, accord­ing to a recently pub­lished study. Young pen­guins aren’t able to take all the changes into account and are find­ing them­selves ‘trapped’ in parts of the sea that can no longer sup­port them even as bet­ter options are available.

“Our results show that juve­nile African pen­guins are stuck for­ag­ing for food in the wrong places due to fish­ing and cli­mate change,” says Richard Sher­ley of the Uni­ver­sity of Exeter and Uni­ver­sity of Cape Town. “When the young of this endan­gered species leave the colony for the first time, they travel long dis­tances, search­ing the ocean for cer­tain signs that should mean they have found an area with lots of plank­ton and plenty of the fish that feed on it. But rapid shifts caused by cli­mate change and fish­ing mean these signs can now lead them to places where these fish, the pen­guins’ main prey, are scarce with impacts on their sur­vival — a so-​called ‘eco­log­i­cal trap.’ The results are pub­lished on 9 Feb­ru­ary in the jour­nal Cur­rent Biol­ogy.

The study
Pen­guins’ eco­log­i­cal trap — a graph­i­cal abstract.
Image credit Sher­ley et al.: Metapop­u­la­tion Track­ing Juve­nile Pen­guins Reveals an Ecosystem-​wide Eco­log­i­cal Trap. Cre­ative Com­mons License (CC BY 4.0)Sher­ley and col­leagues, includ­ing Stephen Votier, also at the Uni­ver­sity of Exeter, and sci­en­tists from the Namib­ian and South African gov­ern­ments, made the dis­cov­ery after using satel­lites to track the dis­per­sal of newly fledged African pen­guins from eight sites across their breed­ing range. They wanted to find out whether the pen­guins were being trapped in what’s known as the Benguela Cur­rent Large Marine Ecosys­tem (BCLME). The BCLME is one of four major east­ern bound­ary upwelling ecosys­tems of the world, Sher­ley explains. This por­tion of the ocean stretches from near the Angola-​Benguela front in south­ern Angola in the north to Cape Point in South Africa’s West­ern Cape.

It has his­tor­i­cally also been one of the most pro­duc­tive ocean areas in the world, rife with anchovies and sar­dines, which make good food for pen­guins and for peo­ple. In recent decades, over­fish­ing off the coast of Namibia, heavy local­ized fish­ing, and sub­se­quent envi­ron­men­tal change have reduced the num­ber of sar­dines and changed the areas that the fish use. In addi­tion, fish and plank­ton are no longer reli­ably found together as they were in the past. The prob­lem is that no one told the penguins!

The researchers devel­oped mod­els to show that the pen­guins travel over thou­sands of kilo­me­tres to find areas where sea sur­face tem­per­a­tures are low and chloro­phyll con­cen­tra­tions are high, a sign that should mean plenty of plank­ton and the fish that go with them. The researchers don’t yet know for sure, but they sus­pect that the pen­guins are respond­ing to sub­stances given off by phy­to­plank­ton when they are under stress, as occurs when they are being grazed on by predators.

“These were once reli­able cues for prey-​rich waters, but cli­mate change and indus­trial fish­ing have depleted for­age fish stocks in this sys­tem,” Sher­ley says.

Young pen­guins that find them­selves in the degraded Benguela ecosys­tem today often fail to sur­vive. Their breed­ing num­bers are about 50% lower than they would be if they found their way to other waters, where the human impact has been less severe, the new study shows.

Pos­si­ble solu­tion
Sher­ley and Votier say it might be pos­si­ble to pro­tect the pen­guins by translo­cat­ing chicks to a place where it’s not pos­si­ble to get trapped. They say there is some evi­dence that fledg­lings from the colonies in South Africa’s East­ern Cape gen­er­ally don’t get caught in the trap, at least not yet. There are other options, too, such as build­ing spa­tial fish­ing clo­sures in key areas where the pen­guins feed or oth­er­wise increas­ing the num­ber of sar­dines in the area.

“Pro­tect­ing the pen­guins — and other species — from falling into sim­i­lar eco­log­i­cal traps will require bet­ter action to account of the needs of preda­tors in man­ag­ing fish­eries and con­certed action to tackle cli­mate change,” accord­ing to Sherley.

Sher­ley says the South African gov­ern­ment is work­ing to imple­ment spa­tially explicit catch lim­its and man­age­ment prac­tices in their sar­dine fish­ery, which will almost surely help. The researchers are help­ing to inform their deci­sions with the pen­guins in mind. Mean­while, their work to under­stand how fish­ing influ­ences the inter­ac­tions between seabirds and their prey at dif­fer­ent spa­tial scales and at dif­fer­ent phases of the birds’ life­cy­cle and how to pro­tect them continues.

(Source: Cell­Press press release via EurekAlert!, 09.02.2017; Uni­ver­sity of Exeter Research news, 09.02.2017)