In 2004 the IMO passed a convention to deal with ballast water treatment. The first countries to sign the agreement, together representing around a quarter of worldwide sea traffic, committed to installing ballast-water treatment systems in their seaports and to carrying out regular inspections of ballast water. From 2016 onwards such systems will also be mandatory on board ships. International cooperation is also strengthened through initiatives of the ICES, which agreed in the mid-1990s on a code of conduct for the handling of exotic species in aquaculture, and recommended quarantine procedures, among other measures. The existence of the European common market has made the exchange of species between member states easier. The commercial transport of oyster larvae, as an example, is now practically equal in significance to ballast water as a cause of species introduction within the EU. At the same time, the import of oysters from non-EU regions has largely been eliminated. International cooperation within the EU has, on the one hand, improved protections against the import of species from non-European bioregions, but on the other hand it has exacerbated the exchange of species between bioregions inside the EU.