Russell Investments Group has upped its leading stake in Ardmore Shipping Company.

The Seattle-based firm now owns 3.6 million shares after a 500,000 buy, Securities and Exchange Commission filings show.

Russell was already New York-traded Ardmore's biggest shareholder with 9.4% of all outstanding shares. The company now owns 11.2%.

Ardmore shares were trading at $6.14 Friday afternoon, up from its open of $6.09.

In second place behind Russell is Donald Smith & Company with 3 million shares, good for 9.1% of the company. Boston Partners cones in third with 2.1 million or 6.5%.

Last month, Ardmore chief executive Anthony Gurnee told TradeWinds that the tanker owner was performing on par with its larger competitors, also traded in New York.

"We'd like to grow, but we're only interested in growing if we can do it accretively, so we’re proceeding with patience,” Gurnee said.

"There's nothing wrong with running a 25 to 30-ship fleet.

“Less than 10 ships is too small, and even 10 to 20 is probably too small. But we're comfortable at our current number and focusing on getting better at what we do.”