As U.S. fishing regulators weigh stricter catch quotas to allow time for critical species to recover in the waters of New England, scientists say that changing ocean conditions may be a factor in historic fish declines, not just decades of overfishing. Warmer ocean temperatures and changing ecosystems are contributing to declining populations of cod and flounder in the northeastern U.S., government officials say. In the Gulf of Maine this year, water temperatures were the highest ever recorded, according to the Northeastern Regional Association of Coastal and Ocean Observing Systems. National Oceanic and Atmospheric Administration (NOAA) scientists say that about half of 36 fish stocks — including cod and flounder — have been shifting northward into deeper, cooler waters for four decades. And while some regulators say the only chance of restoring populations is for tougher quotas on bottom-dwelling “groundfish” species, the New England Fishery Management Council this week delayed a vote on such cuts after fishermen said the reductions would devastate their industry.