New Zealand's expanding fishing activities were again under fire Thursday with falling numbers reported in yet another of the country's endangered marine mammals. The government announced it would develop a threat management plan to review the risks to the New Zealand sea lion, which is the rarest sea lion breed in the world with numbers estimated at under 10,000. The 1,575 pups counted this year on the subantarctic Auckland Islands, where 70 percent of the species breeds, was down 18 percent on last year, Conservation Minister Nick Smith said in a statement. "It is the third lowest since monitoring began in the mid-1990s and shows an on-going trend of decline over the last decade. We need to step up our efforts to ensure these sea lions survive," Smith said, adding the cause of the decline was unclear. "A wider investigation was initiated in 2012 that indicated that environmental change and prey abundance were likely to have played a role in the population decline. There is also evidence that a bacterial disease has reduced pup survival rates over the last two decades." Primary Industries Minister Nathan Guy said in the statement that incidental captures in fishing nets had declined significantly over the last decade with the introduction of sea lion exclusion devices on fishing nets, but the effectiveness of the devices was still to be monitored. The threat management plan could recommend active intervention to reduce the several hundred deaths from "misadventure and disease," extending or creating new marine mammal sanctuaries, or additional measures to reduce impacts of fishing, Smith said. The ministers stressed that fisheries around the New Zealand sea lion breeding areas generated more than 100 million NZ dollars (84.21 million U.S. dollars) per year in export earnings. Conservation groups welcomed the move, but said fishing activities should be immediately curbed in the breeding grounds, with WWF-New Zealand and Forest and Bird calling for an immediate suspension of trawling and squid fishing around the Auckland Islands. Last month alone the bodies, of two mature females were hauled up in squid nets, Forest and Bird marine advocate Katrina Goddard said in a statement. "The way the fishery was run saw the squid fishing effort increase by 140 percent in 2012. Given the serious questions around how many sea lions survive passing through sea lion exclusion devices in trawl nets, this was clearly a grave mistake, " Goddard said. The New Zealand (or Hooker) sea lion once numbered in the hundreds of thousands, with their habitat extending throughout New Zealand, but they were hunted close to extinction in the 19th Century. Last year, the government moved to extend fishing restrictions off the west of the North Island after claims that the world's smallest and rarest dolphin, the Maui's dolphin, was reduced to a population of just 55 adults, although conservation groups argued it was too little too late.