The study, published in the latest Royal Society Biology Letters, suggests that although killer whales may consume a variety of fish species and mammals, many are highly specialized hunters dependent on this single salmon species.

Lead author John Ford explained to Discovery News that “nutritional stress” probably leads to killer whale deaths because it can make the whales “susceptible to other factors leading to mortality, such as disease and parasitism,” and possibly also more vulnerable to the “immuno-suppressive effects of PCBs” and other ocean pollutants.

Ford, a research scientist at Fisheries and Oceans Canada, and his colleagues used 25 years of demographic data from two populations of fish-eating killer whales in the northeastern Pacific Ocean, along with data on numbers of chum and Chinook salmon, commonly known as king salmon.

The data consisted of annual photo ID censuses for the whales and Pacific Salmon Commission population estimates for the fish.

The scientists determined that from 1974 to the mid 1990′s, resident killer whale populations steadily grew in number at an increase of nearly 2.6 percent per year. That pattern abruptly ended in the mid 1990′s, when both analyzed populations of killer whales entered a period of prolonged decline, dropping by up to 17 percent as of 2001. By 2004, the populations began to recover and show growth again.

The killer whale population’s ups and downs mirror those of king salmon for the same periods. The researchers suspect El Nino-like conditions in the early 1990′s resulted in the deaths of juvenile salmon, which then brought down the entire king salmon population for the region.

It’s doubtful that the weather events directly impacted the whales.

“Killer whales are very adaptable to a remarkable range of water temperatures, being found in the tropics as well as ice-covered waters,” Ford said. “The range of temperatures associated with El Nino events would be unlikely to have any direct effect.”

Ford and his team instead believe some killer whale populations are dependent upon Chinook salmon as their primary year-round food resource, even though these enormous apex predators physically have the ability to eat different types of fish, walruses, other large whales and additional prey.

“Animals born to a particular population learn foraging tactics to efficiently exploit particular prey types, but this specialization seems to constrain their ability to effectively hunt alternative prey,” Ford said. “Specialists can often be more successful than generalists because they are more efficient at their specialization, as in the old adage, ‘A jack of all trades is a master of none.’”

In a separate study, bioacoustician Whitlow Au of the Hawaii Institute of Marine Biology, and his colleagues found that killer whales prefer king salmon to such a degree that they can identify these fish when the Chinooks are swimming alongside Coho and Sockeye salmon.

Au’s team determined that even in winter months when king salmon make up just 10 to 15 percent of the salmon swimming in water, killer whales will use echolocation to reveal differences in the fishes’ “swimbladder shape and volume” to pick out king salmon.

Ford’s group, which is studying killer whale hunting tactics now, has additionally found that killer whales then “target individual fish and often corral them against steep shorelines.”

Given that the fate of some killer whales seems tied to that of king salmon, Fisheries and Oceans Canada calls for strengthening killer whale populations by ensuring adequate availability of prey.

Ford said the Canadian agency also urges “minimizing the potential effects of anthropogenic impacts, such as disturbance and noise, and identifying and protecting critical habitat.”

In an instant, a bite. In another instant, Jennings jerked his rod for the hook, and he reeled him in with the help of buddy Nick Austin.

That’s what it’s all about. Like hitting that 6-iron from 175 yards to within feet of the hole.

Jennings held his 3 1/2 -pound largemouth bass and, at the prodding of his two buddies, he gave it a big kiss. And another. And another before tossing his trophy back where he found it.

This is what young men do who romanticize about the outdoors, and for Jennings, Austin and Mitchell Travis, fishing their spots around town is no summer passing fancy. The relationship they have with the outdoors is a lifelong love affair.

“It makes me feel free,” said Travis about fishing his favorite holes.

And as the summer rolls along, there are plenty of reasons for these teenagers to fish in addition to love of the game. A big one is cost. Who needs consumerism — especially in a recession — when Mother Nature provides such good entertainment?… for free.

“That’s the biggest thing for me,” said Travis, whose parents no doubt agree and who like Jennings, also hunts deer, birds and pigs. “It’s something to do that’s cheap.”

Amen. And it reinforces environmentally conscience thinking, too.

More and more programs are being advanced to promote environmental stewardship while serving as instructionals that nurture and inspire agents of conservation. The Texas Parks and Wildlife Department offers a variety of programs that teach both families and youngsters about every facet of eco-life. Many state parks offer fishing clinics for families, teaching everything from the basic to pencil poppers and wooly buggers. At the North Texas Education Center in Grand Prairie on Saturday, the TPWD is offering an Angler Education course for adults who want to teach the family basic fishing skills.

For the more advanced youth fishermen, the Parks and Wildlife Department also offers competitive events or “derbies” to show their skills.

Texas Tech University’s Outdoor School in Junction in the Hill Country has programs for teachers and students. Not to mention that the Llano River down there, by all accounts, is good fishing.

Texas Parks and Wildlife is also offering free fishing at all of its state parks. The department has waived fishing license and stamp requirements for anyone fishing inside a state park. Park entrance fees still apply, but as long as you’re in the state park, you’re free to fish to your heart’s content. Of course, bag limits, length limits, and other regulations apply.

That’s news that make these three poster boys for environmental stewardship salivate.

“We once caught 25 sand bass in two hours,” Austin remembers about a trip he took. “That’s what’s best, you never know what you’re going to reel in.”

And there’s no intention of ever stopping. Why would you consider, not even if they make that dream catch.

When you’re in love, it’s for life.

“There’s always something bigger to catch,” said the visionary Austin, and Jennings interjected, “I’m never going to stop fishing.”

Thomas P. Fote, a New Jersey conservationist who sits on the Atlantic States Marine Fisheries Commission, said the pollutants are damaging commercial fisheries. He told congressmen not to “study a problem to death and never do anything.”

Fote appeared in a lineup of witnesses efore the subcommittee on Insular Affairs, Oceans and Wildlife of the House Natural Resources Committee. The witnesses pointed to research showing damage to fish and other aquatic species from pharmaceuticals, pesticides and other industrial chemicals, especially those that alter growth-regulating endocrine systems. Some scientists worry about the potential of similar harm to humans.

“Hundreds of peer-reviewed publications … demonstrate that numerous ubiquitous chemicals in the environment can interfere with development via the endocrine system, but there appears to be no will or authority to remove those chemicals from the supply chain,” said zoologist Theo Colborn, a professor emeritus at the University of Florida, who founded the nonprofit Endocrine Disruption Exchange.

The witnesses appealed for Congress to promote consumer take-back programs for unused drugs, to encourage industry financing of disposal, and to do more to keep discards from waterways and landfills.

The hearing comes on the heels of an Associated Press investigation that reported pharmaceutical traces in drinking water supplies of at least 51 million Americans and in many waterways. The drugs range from antibiotics to psychiatric drugs to endocrine-disrupting sex hormones.

One witness, pharmacist Fred Massoomi from Nebraska Methodist Hospital in Omaha, broke his collarbone in a recent fall and sat stiffly during his testimony. Asked by a panel member if he was in pain, he said, “Not right now.” Then he lifted a plastic bottle and smiled. “If I need any pain medication, I’ll just drink some water,” he said.

Most cities and water providers don’t test for pharmaceutical contaminants. The biggest source is considered to be human excretion, but manufacturers and health care facilities also send millions of tons of unused drugs into rivers and streams every year.

Utilities say their drinking water is safe, and no human risks are confirmed from pharmaceutical pollution. However, research shows that the pharmaceuticals sometimes harm fish, frogs and other aquatic species. Also, researchers report that human cells fail to grow normally in the laboratory when exposed to trace concentrations of certain drugs.

The House has already passed legislation to study the problem and find solutions, and the Senate is considering such a bill. Delegate Madeleine Z. Bordallo, D-Guam, who chaired the hearing, said she has talked to colleagues about the need for more legislation.