Question: What sport do both Isabel Letham and Duke Kahanamoku have in common?

Context paragraphs:
Eddie Aikau: Edward Ryon Makuahanai Aikau (Kahului, Hawaii, May 4, 1946 – March 17, 1978) was a well-known Hawaiian lifeguard and surfer.  The words "Makua Hanai" in Eddie Aikau's full name mean "feeding parent", an adoptive, nurturing, fostering parent, in the Hawaiian language.  As the first lifeguard at Waimea Bay on the island of Oahu, he saved over 500 people and became famous for surfing the big Hawaiian surf, winning several awards including the 1977 Duke Kahanamoku Invitational Surfing Championship.

International Surfing Museum: The International Surfing Museum is a non-profit, 501(c) museum in Huntington Beach, Orange County, California.  The museum's goal is to preserve the history of the surfing culture throughout the globe.  It is dedicated to Duke Kahanamoku, who is generally regarded as the person who popularized the modern sport of surfing.

Ellie Crowe: Ellie Crowe is an award-winning author of more than sixteen books.  She was born in South Africa and lives in Honolulu, Hawaii and Santa Barbara, California.  Her books on the culture and history of Hawaii include "Exploring Lost Hawaii, Places of Power, History, Mystery and Magic", "Kamehameha, the Boy who became a Warrior King", recipient of the HVCB Kahili Award for Literary Arts in 2004, and "Surfer of the Century, the Life of Duke Kahanamoku", recipient of the Simon Wiesenthal Museum of Tolerance Once Upon a World Award in Children's Literature in 2008.  Her first book, "The Little Princess Kaiulani", is included in a time capsule in the grounds of the Princess Victoria Kaiulani Elementary School, Honolulu.

Ken Bradshaw: Ken Bradshaw (born October 4, 1952) is an American professional surfer and winner of the 1982 Duke Kahanamoku Invitational Surfing Championship.

Lord Jim (1925 film): Lord Jim is a 1925 silent film starring Percy Marmont (in the title role), Noah Beery, and Duke Kahanamoku.  The movie was directed by Victor Fleming and based on the novel "Lord Jim" by Joseph Conrad.  A print is preserved at the Library of Congress and at UCLA Film and TV.

Duke Kahanamoku Invitational Surfing Championship: The Duke Kahanamoku Invitational Surfing Championship is named in honor of the "Father of Modern Surfing", Duke Paoa Kahinu Mokoe Hulikohola Kahanamoku.  The contest began in 1965 by invitation only at Sunset Beach on the North Shore of Oʻ ahu until it was replaced by the Billabong Pro in 1985.  The championship was the first surfing event to be broadcast on a regular basis by ABC's "Wide World of Sports".

Girl of the Port: Girl of the Port is a 1930 romantic film, directed by Bert Glennon, from a screenplay by Beulah Marie Dix with dialogue from Frank Reicher.  The film was based on a short story, entitled "The Fire-walker" by John Russell, and starred Sally O'Neil, Reginald Sharland, Mitchell Lewis, and Duke Kahanamoku.

Duke Kahanamoku: Duke Paoa Kahinu Mokoe Hulikohola Kahanamoku (August 24, 1890 – January 22, 1968) was a Native Hawaiian competition swimmer who popularized the ancient Hawaiian sport of surfing.  He was born towards the end of the Kingdom of Hawaii, just before the overthrow, living into statehood as a United States citizen.  He was a five-time Olympic medalist in swimming.  Duke was also a law enforcement officer, an actor, a beach volleyball player and businessman.

Isabel Letham: Isabel Letham (23 May 1899 – 11 March 1995) was an Australian pioneer surfboard rider and swimming instructor, renowned as 'the first Australian to ride a surfboard' (although she disputed that claim - Isma Amor of Manly is believed to be the first Australian Female Surfer and Tommy Walker of Manly is believed to be the first Australian Male Surfer).  A probably erroneous story has been repeated for years that on 10 January 1915 at Freshwater Beach, Sydney she experimented riding a board in the Hawaiian tradition in tandem with Duke Kahanamoku.  This story has been disputed by researchers who have investigated its roots and provenance, and the reality is probably that she did not do so until shortly after, at Dee Why beach in Sydney, on February 6, 1915.

Butch Van Artsdalen: Charles M. Van Artsdalen (January 31, 1941 – July 18, 1979) was a legendary surfer.  He moved to La Jolla, California, from his birthplace of Norfolk, Virginia, at age 14.  Van Artsdalen is best known as a pioneer of surfing 25-foot waves at such North Shore locations as Waimea Bay and Sunset Beach; and tube riding in Hawaii during the early 1960-1970s.  A member of the Duke Kahanamoku Surf Team, he appeared in several surf movies and remained a fixture of the international surfing community until his death from alcohol-related illness in 1979.

Supporting paragraphs: Isabel Letham Duke Kahanamoku
Answer: surfing