Shares of two beleaguered shopping-center owners soared this week, joining a broader rally among stocks that individual investors have powered higher in their battle with professional money managers.

The share price of

Macerich Co.

jumped as much as 57% this week before giving back some of those gains. Shares early Friday afternoon were up 18% since Monday morning to $16.76.

Tanger Factory Outlet Centers

’ share price has also risen 18% this week to $15.78.

Both mall owners were among the top 100 U.S. stocks in terms of short interest, according to an analysis by Dow Jones Market Data. Their shares popped this week after online traders identified the two companies as sell targets by hedge funds and other professional investors.

Legions of these individual investors are using Reddit and other social-media platforms to share their trading decisions in an effort to prop up certain stocks that are heavily-shorted and cause some big Wall Street firms and traders to lose money.

“This has been shorted down below fair value for years! Lets fix this injustice!”, said a post in Reddit’s popular WallStreetBets forum. One of Macerich’s mall tenants include videogame retailer

GameStop Corp

, whose stock is in the center of the current trading mania.

Short sales are bearish bets in which an investor borrows shares and quickly sells them, with the intention of buying shares later at lower prices to repay the loan, pocketing the difference. But if the share prices rise instead, it could result in a short squeeze where these bearish investors are compelled to buy back shares they had sold short to cut their losses, pushing the stocks even higher.

Shares of Macerich, the Santa Monica, Calif.-based mall landlord with properties in Arizona, California, Virginia and New York, had sold off in recent years against a backdrop of rising retail vacancies and as more shoppers bought products online.

Around the beginning of the pandemic last year, shares of Macerich were as low as $5.02, a drop of 92% since the start of 2018.

Mall owners started to rally off their lows even before the short squeeze, boosted by hopes that new vaccines will bring back more shoppers. Macerich shares rose 30% on Nov. 9 after

Pfizer Inc.

and

BioNTech SE

announced positive results from their Covid-19 vaccine trial.

Shares of Tanger, whose open-air shopping centers have attracted more business than enclosed malls during the pandemic and whose share price fell less, gained 18% after the November vaccine news.

But the short-squeeze rally has been volatile and at least one big investor is using the recent gains to exit its big mall position. Ontario Teachers’ Pension Plan, the largest shareholder in Macerich, dumped its entire stake of around 15% in the real-estate investment trust.

The pension plan sold 24.6 million shares at a range between $18.60 and $26.59 a share on Wednesday, according to a public filing on Thursday.

Some analysts viewed Ontario’s sale of Macerich as a worrisome development, though it wasn’t necessarily clear whether the exit was a statement about the industry or the company.

The pension funds’s decision “to hit the eject button on its Macerich investment at seemingly the first feasible opportunity post-Covid could be interpreted as a dire outlook” for top of the line malls, values of malls in general, or Macerich’s balance sheet, analysts at real-estate analytics firm Green Street said in a Thursday report.

In a statement, an Ontario Teachers’ Pension Plan spokesman said: “Moving forward, we are focused on scaling and diversifying our global real estate platform, and growing our existing Canadian real estate business.”

News of the pension plan’s sale was previously reported by Bloomberg News.

Wall Street is in an uproar over GameStop shares this week, after members of Reddit’s popular WallStreetBets forum encouraged bets on the video game retailer. WSJ explains how options trading is driving the action and what’s at stake.

Write to Esther Fung at [email protected]

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