He’s gone fishin’ — on the streets of New York.

For eight years, Eliel Santos has been using dental floss and mousetrap glue to reel in gold, jewelry, electronics and cash trapped beneath city sidewalk grates.

“If you drop it, I’m going to pick it up — so be careful,” advised Santos, 38, a Puerto Rico native who lives in The Bronx.

When The Post followed Santos on a fishing trip last week, he hauled in a green iPod Nano in Times Square, a fake gold necklace, and a pocket full of change along Broadway between 23rd and 47th streets.

He wastes no time, walking quickly from one side of the street to the other, his head cocked as he peers with laser focus into the darkness below.

Suddenly, like a heron zeroing in on a creek minnow, he freezes and stands over his target. He quickly lowers the sticky lure, which he controls with the precision of an archer.

With a fatal strike, his prey is snagged.

“Just a quarter,” he says, stuffing the coin in his pocket.

Santos fishes around Manhattan, Brooklyn and Queens seven days a week and remembers every grate like it’s a city landmark.

“This one here, I helped a guy get back his wedding ring,” he says in Times Square. “He was worried he was going to get in trouble — he was almost crying.”

He pays particular attention to areas where tourists are exchanging money with street vendors.

“They sit down to get a portrait and their money falls out,” he says.

Most items he catches are pawned — his biggest take was $1,800 for an 18k gold and diamond bracelet he caught in Harlem. Some items he leaves in their place. “I saw a bloody knife in Brooklyn on Franklin Avenue — I didn’t touch it.”

His white whale? “A woman told me she lost a $20,000 ring near Madison Square Garden,” he says. “I couldn’t find it.”

He got hooked on the urban trade entirely by happenstance.

“I saw a guy on 41st Street and Broadway who dropped his keys down a grate and he was looking for a locksmith.

I said, ‘I will help you if I can.’”

Santos ran to a store to buy a mouse trap — he guessed the tacky glue would do a better job than chewing gum. He affixed the glue to a rock, tied a string around it, and lowered the contraption down about 15 feet. In no time, the keys were secured.

“He said, ‘Oh man, that’s awesome!’ — and he gave me $50.”

“I thought, ‘Wow, this is a good way to make money!’” Santos said.

And it has been.

On good days, he’ll haul in about $150. On great days, he’ll find jewelry that he pawns for over $1,000.

“Sometimes I give jewelry to my wife — and she always asks, did you buy this or find it?”

Over the years, Santos has perfected his gear. He ditched the string because it was too fragile, experimented with fishing line but found it too inflexible, and now uses dental floss exclusively — 120 yards worth of Aim brand. “It’s only $1.19.”

The line is MacGyvered with black electrician’s tape to differed sized weights — found metallic objects — to accommodate even the narrowest grate.

He changes the Blue-Touch mouse glue about three times a shift, which spans generally from 9 am to about 2 pm.

To snag cash, he uses a tiny fishing hook that he’s straightened out like a spear. Heavy objects are hauled in using two or more glue weights, and a traditional fish hook is also used on occasion to grab hard-to-snag earrings or chains.

Sometimes he uses a pair of binoculars and a flashlight, and he’ll wear purple rubber gloves on occasion.

“In case it’s in toxic water,” he explains.

Lately, he’s been hauling in iPhones from the bowels of Times Square — three at one particular spot, he says, including one that had “dirty pictures” of the woman who owned it.

“When people text while they are standing on a grate, their phones fall in,” he shrugs.

Each day, he marks down on my map where he’s been, so as not to return too soon. “I leave time for people to drop stuff.”

Thursday to Sundays are best, especially in June and July. Mondays are unlucky.

The day after parades are windfalls — drunken St. Patty’s Day revelers earned him $73 dollars in just one hour’s work this year, he recalls.

“I have a lot of patience and optimism,” he says. “If I want something, I’m going to get it.”

Cash on the line

Eliel Santos has literally struck gold below New York City’s much-traveled streets.

Here are some of his biggest catches:

* Lexington Avenue/79th Street: $270 money order

* Lenox Avenue and 125th Street: 18K white gold and diamond bracelet—sold for $1,800

* Broadway and 45th Street: Three iPhones

* Duffy Square: iPod Nano