This study examines how increased regulatory attention to portfolio pumping affects the trading behavior of U.S. mutual funds. Attention by regulators should increase the likelihood of fines and reputational damage, raising the cost of such last-minute price manipulation. Consistent with this assertion, we find that last-minute price spikes in aggregate fund indices, in fund holdings and in institutional trading around quarter-ends declined, the declines are largest around year-ends, for small-cap and better-performing funds, and occurred faster for funds headquartered near SEC regional offices. These findings suggest that increased regulatory attention reduced portfolio pumping by U.S. mutual funds.

Corporate insiders often become aware of hedge fund attention prior to a 13D filing. We find abnormal buying activity by insiders in the months leading up to hedge fund 13D filings. Whereas 13D announcement abnormal returns are 7.72 %, profits to insiders who buy average 12.09 %. Insider buying is not linked to common firm characteristics that predict activist targeting. Our findings indicate that insiders are benefiting from private knowledge that their firm has become the focus of hedge fund activism, and sometimes this knowledge comes directly from the activist. However, insiders largely refrain from trading when there is formal communication with the activist. Profits to insiders who buy when there are no talks prior to the 13D filing are 14.49 %, triple the amount for insiders who have had early talks with the hedge fund. Insider trading is linked to indicators of poor corporate culture, but not related to outcomes of activism campaigns.

Short sellers are known to have private information about security prices. Empirical evidence of short selling, however, is based on only half of short sellers’ trading activity; specifically, the opening of the position. Using disclosed large-short-position data from the Japanese stock market, we provide the first detailed evidence of covering trades and find a positive reaction to short covering that only partially reverses. Although these results are consistent with substantial transaction costs for closing large short positions, they also reveal that some short sellers are privately informed about positive future events and have timing ability in covering positions.

Abstract We find that higher stock lending fees predict significantly lower future returns after controlling for shorting demand for US stocks during the period 2007–10. These results suggest that active institutional investors on the supply side play an important role in the return predictability of fees and they not only respond to demand but also price in additional information around earnings news announcements. Overall, we find evidence that stock lenders are informed and, together with short sellers, contribute to the price discovery process.

In this study, we examine the impact of a market-wide mandatory disclosure policy on short selling on the Tokyo Stock Exchange. We find that average short selling slightly declined while investors’ shorting strategies changed significantly in response to the disclosure. Previously highly shorted stocks were shorted less and shorting activity shifted toward smaller and riskier stocks, suggesting that retail investors became the more likely short sellers. Short sales became more trend-chasing, prices became less informative, and short-term price volatility increased. Overall, the pricing efficiency benefits of short selling declined after the mandatory disclosure policy.