HOLDERNESS — A decline in the number of successful loon nesting pairs on Squam Lake since 2005 has biologists and conservationists concerned.

The Loon Preservation Committee and Tufts University are studying the decline and say pollution could be partly to blame.

The common loon, a water bird that faced extinction in New Hampshire in the 1960s, is now protected by federal law. To increase the bird population, floating nests have been placed; the sale of lead fishing sinkers and jigs — as well as their use in fresh water — has been banned; and efforts have been made to educate boaters about the need to keep a safe distance from the birds and their young.

Between fall 2004 and spring 2005, Squam went from having 16 nesting pairs to having nine, a loss of 44 percent, according to Harry Vogel, senior biologist and executive director of the Loon Preservation Committee (LPC).

“This was unprecedented on Squam or any other large lake in LPC's 37-year history,” he said.

Between 1995 and 2004, an average of 6.2 chicks lived to adulthood, but from 2008 to 2012, the average was closer to three.

For each territorial pair, .48 chicks need to survive to maintain a viable population, according to LPC data. Squam's success per pair was .20 from 2007 to 2012. In 2007, only one chick survived on the lake.

Statewide, the story has been different. In 1975, there were fewer than 125 paired adult loons in the state, but by 2010, there were 542. During that same time period, the number of surviving chicks went from about 25 to about 125, according to the LPC.

In a 2011 study of eggs that did not hatch, researchers found evidence of stain guards, flame retardants, industrial insulation coatings and pesticides on the shells. The chemicals came from Squam, not the birds' wintering grounds, which are largely along the coast, Vogel said.

The Squam Lake Loon Initiative paid for the study.

Additionally, fungus was found in the lungs of two birds that died on the lake this summer. Dr. Mark Pokras of Tufts University has been working with the LPC for 23 years.

He said the presence of fungus, including new and unusual types, has been a growing problem for loons in recent years.

Usually, a fungus is a secondary condition in the birds, often associated with stress.

An LPC study of loon deaths statewide between 1992 and 2008 found 52 percent died from eating lead sinkers or jigs. About 12 percent of the birds died in boating and personal watercraft-related incidents; 7 percent died after getting tangled in fishing line, 6 percent died of disease, and about 6 percent died after fighting with other loons.

An estimated 2 percent were illegally shot. Last week, a loon was found to have been shot on Back Lake in the Great North Woods, and Fish and Game officials are investigating.

The website for the Squam Lakes Loon Initiative is loon.org.

- - - - - - - -

Paula Tracy may be reached at ptracy@unionleader.com.