The Securities and Exchange Board of India ( Sebi) and the National Commodity & Derivatives Exchange ( NCDEX) are taking measures to improve improve surveillance after issuing restraining orders against 16 entities for manipulating castor seed futures. Castor seed futures prices on the NCDEX fell sharply in January in comparison to the spot market. Players holding long positions as high as 62.5 per cent of the total open positions were trapped and were unable to pay mark- to- market margins. To avoid systemic risk the NCDEX on January 27 suspended the contract and put the terminals of four brokers in square- off mode. On Wednesday, the Sebi restrained these four brokers and 12 of their clients, many of whom are big players in the oil seeds business, from acting in any form on any exchange in the securities market. “Sebi is dealing the issue with from all angles — market integrity, governance, investor protection as well as systemic,” a source said. Sebi initially focused on limit