THE AVERAGE KILLER WHALE, or orca, needs 400 pounds of flesh a day. The techniques of obtaining it are not pretty. In Orcas of the Gulf (Douglas & McIntyre, 199 pages, $12.95 paper) Gerard Gormley doesn`t let his readers avert their eyes. In his description of an attack on a minke whale, orcas peel off a continuous strip of skin and blubber the way we peel a mandarin orange. In another, 4 5 of them take turns immobilizing three finback whales while eating them alive: Even a badly mauled whale could take the better part of A day to die, so orcas probably have little choice but to eat large prey alive .... The juveniles bit off chunks of ... tongue, which yielded several tons of succulent meat. Such gruesome narrative may be salutary today, when much of the western world is giddy with adoration of whales and shielded from the realities of predation. Huge sections of the public rush to environmental judgement with little more than sentiment to guide them, and with whiplash consequences to the economy of hunters, trappers, and fishermen. The structure of this book is curious and fruitful. Primarily, it is a fictional portrait of an extended family of orcas who live off the coast of Maine. Yet each chapter ends with a page or two of non-fiction: a naturalist`s thoughts on the validity and import of what has just been depicted. it works, perhaps because the chunks of fiction are so rich in detail that a reader welcomes the chance to ponder their significance before proceeding. Orcas of the Gulf is a wonderful antidote to the Bambi school of natural history.