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April 2002 Vol. 17, No. 4   RSS Feed for Undercurrent Issues
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When the Little Boy Comes, the Big Boys Leave

the coming effects of El Niño

from the April, 2002 issue of Undercurrent   Subscribe Now

If you’re planning that oncein- a-lifetime dive trip, you might ask, “Have I really thought of everything?” Did you remember the little boy? The Christ Child? In Spanish, El Niño. Because if you don’t understand what this “little” fellow can do to your search for schools of hammerheads and other big critters, you might be in for one substantial, and expensive, disappointment.

Fishermen along the coast of Peru coined the phrase “El Niño” in the late 1800s. Around Christmas, they often caught fewer fish. They didn’t know why then, but scientists later learned that the culprit was the seasonal invasion of a warm southward ocean current that displaced the north-flowing cold current in which the Peruvians normally fished. Although Peru is among the most severely affected areas, the undersea impact of an El Niño can extend from the Galapagos north to Costa Rica’s Cocos Island and as far as the Indian Ocean, the Maldives, and beyond. Its effects can spell a big letdown for divers.

Under normal circumstances, the rich and interdependent eastern Pacific marine food web is well nourished by the continual upward surging of cooler water. Flush with plankton, this upwelling is the mother of oceanic meals. However, when the nutrientrich waters are forced deep, there is big trouble.

Normally, ocean water heated by the tropical sun is pushed by trade winds to the western Pacific. The warm water then piles up around Indonesia and other regions west of the International Date Line. From time to time (the reasons why aren’t clear) the trade winds weaken and this water slides eastward across the Pacific to South America. When the warm water reaches the South American coast near Peru, it spreads far north and south, along the coast.

When this “big slosh” occurs, the fish are forced to either feed deeper or leave the warmer water, returning only when the water cools again. Dependent invertebrates, like hard and soft corals, sea anemones, giant clams, and zooxanthellae (the symbiotic algae that give the coral its color) are not so lucky. As they cannot move away from the warmer water, they must either weather El Niño or perish. Corals, with their narrow temperature tolerance, seem to be the most vulnerable of all.

Since the late 1950s, there have been seven major El Niño events. They have occurred as often as every two years, although an interval of four to five years is the norm. Expected to last about eight to ten months on average, they have lingered as long as eighteen years. Popular Eastern Pacific dive venues hard hit by the last El Niño, which spanned 1997 to 1998, include Cocos Island and the Galapagos, though the warm currents extended up the coast as far as California. According to the Australian Institute of Marine Science, that last El Niño significantly affected sea life in Australia, Thailand, the Maldives, and Indonesia. Even the Caribbean, particularly the Bahamas, Belize, and the Cayman Islands, experienced some coral bleaching.

Now, scientists believe that El Niño is returning. To show what effect this might have, we turned to the Undercurrent archives for divers’ reports from the critical areas.

We found that in non-El Niño seasons nearly all divers visiting the Galapagos commented on the outstanding pelagic life, particularly the abundance of hammerhead sharks. For example, Joseph Pomento (Redondo Beach, CA) remarked that in June 1995 he saw “Mantas every dive, schools of hammerheads too numerous to count, squadrons of spotted eagle rays flying across the reef . . .“

Divers in 1996 continued to rave about sharks. In November, Bob Viggers (Seattle, WA) reported “Diving mostly packed with lots of fish and sharks, [thousands] of hammerheads on each dive at Darwin and Wolf Islands.”

But from the middle through the end of 1997, divers pointedly noted the effects of El Niño. For example, in May 1997, David Stoll (NYC) found that “Water temperatures at times exceeded 80 degrees, including Darw i n Island, where the schooling hamm e rheads are supposed to be. Lucky to see two or three in the distance.” During a January 1998 trip, John Walker (Tampa, FL) noted, “Because of El Niño, water was 82 degrees . . . some wildlife may have moved to colder water, there was enough to satisfy me. Saw hammerheads, but only deep and far away.” However, by midyear, water temperatures had cooled. On a July 1998 trip, Dr. Zygmunt Dembek (Suffield, CT) found the water ranging from sixty to seventy-eight degrees, depending upon thermoclines. “Huge schools of hammerheads are back at easy diving levels.”

The remarkable schools of
hammerheads and Galapagos
sharks were out of range,
disappointing many divers.

The same was true for the Cocos Islands. In September 1997, Peter Hartlowe said, “most hammerheads at 120-140 feet . . . tough to shoot that deep and dark.” The following January, Ray Pettigrew (Napa, CA) said, “being an El Niño year, the sharks were at 200 feet.”

Nevertheless, in both areas divers reported seeing plenty of mantas, large schools of fish, rays, and other sharks; it was just that the remarkable schools of hammerheads and Galapagos sharks were out of range, disappointing many.

Lacking the mobility of the sharks, the corals of the central and western Pacific and Indian Oceans suffered mightily, and bleached coral still remains in the waters of Micronesia, especially off Palau.

The Maldives were renowned for splendid corals. However, the last El Niño affected them greatly. In November 1998, Max Herndon (Pismo Beach, CA) found that “El Niño currents warmed the water to 92 degrees Fahrenheit and that killed much of the hard coral. Reefs that on previous trips that were a kaleidoscope of color are now disappointingly gray.” This devastation carried over well into 2000, when on a May trip Gwen Hyatt (Houston, TX) “. . . really noticed coral bleaching of reefs.”

In fact, only recently have the hard corals started to recover significantly. Karen Uyeda (San Jose, CA) remarked that on her trip last August, “The coral is still very damaged, but is recovering in many areas. The soft corals are doing well.” Palau was also seriously hit. El Niño nearly wiped out the jellyfish in Jellyfish Lake, but they have since returned, although in smaller numbers.

NOAA scientists are now reporting that below-normal sea surface temperatures in the central equatorial Pacific off South America have given way to above-normal readings. Ocean temperatures increased more than four degrees Fahrenheit in February. The head of NOAA, Admiral Conrad Lautenbacher, says that an El Niño will almost certainly arrive by summer. Some researchers believe it will last well into 2003. However, it is still too soon to predict its persistence with any certainty. One Singapore meteorological center has also reported the gradual warming of surface temperatures in the Pacific and predicts the onset of a weak to moderate El Niño episode later in the year.

As you plan your dive trips, follow these climatological developments carefully and choose your destinations with prudence. El Niño status is updated monthly at http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ enso_advisory/

----Doc Vikingo

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