FIRST EVER OMNIVOROUS SHARKS IDEN­TI­FIED

Focus-Science and Technology - - DISCOVERIES -

We’re go­ing to need a big­ger salad cart. Re­searchers at the Univer­sity of Cal­i­for­nia have found that bon­net­head sharks, smaller cousins of the more fa­mous ham­mer­heads, sup­ple­ment their diet of crabs, shrimp and squid with mouth­fuls of sea­grass. It is the first time sharks have ever been con­firmed to be omnivorous, they say.

Traces of sea­grass have of­ten been found in the guts of bon­net­head sharks but it was as­sumed that they were con­sum­ing it un­in­ten­tion­ally rather than seek­ing it out. To test this the team grew sea­grass in wa­ter laced with pow­dered sodium bi­car­bon­ate. As the sea­grass grew it ab­sorbed a dis­tinc­tive form of car­bon into its struc­ture that the team were able to de­tect the pres­ence of in the sharks liv­ers, plasma and red blood cells.

They then fed five cap­tive sharks a diet con­sist­ing of 90 per cent of the mod­i­fied sea­grass and ten per cent squid for three weeks. All of the sharks gained weight dur­ing this time. The re­sult­ing anal­y­sis of the sharks re­vealed that not only were the sharks de­lib­er­ately con­sum­ing the sea­grass but that they were also able to break it down and ab­sorb nu­tri­ents from it. It turns out that bon­net­heads have spe­cial en­zymes in their stom­ach acids that al­low them to break­down the cel­lu­lose found in the plant ma­te­rial. They were able to di­gest 45 per cent of the or­ganic mat­ter found in the sea­grass putting them on a par with ju­ve­nile green sea tur­tles.

Bon­net­head sharks get the nu­tri­tion they re­quire through a diet of veg­e­ta­tion and meat

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