New understanding of Hawaii white shark movement revealed
A study by Researcher Kevin Weng of the University of Hawaiʻi at Mānoa’s School of Ocean and Earth Science and Technology and Randy Honebrink of the Hawaiʻi Department of Land and Natural Resources’ Division of Aquatic Resources sheds new light on the relatively rare but occasionally recorded presence of white sharks in waters surrounding the Hawaiian Islands. The study also suggests a new method to help distinguish between white sharks and close relatives, such as mako sharks. “Occurrence of White Sharks in Hawaiian Waters,” was published in the Journal of Marine Biology.
Satellite tracking studies have previously shown that Hawaiʻi’s white sharks are migrants from population centers off California and Mexico. A relatively small proportion of those West Coast sharks migrate all the way to Hawaiʻi, which is why they are so rarely seen.
The authors reviewed all available sources of information relating to white sharks in Hawaiʻi, including newspaper accounts of shark attacks, shark control program catch records, photos and videos from various sources, and satellite tracking data. Only data that could be confirmed as pertaining to white sharks was included in the analysis.
“We learned that white sharks occur in Hawaiʻi across a broader part of the annual cycle than previously thought—we recorded observations from every month except November. This is important for our understanding of white shark life history and population,” said Weng.
Since all records of white sharks in Hawaiian waters are of individuals larger than 10 feet, and no juveniles have ever been reported, there is no evidence of white sharks being residents or pupping here.
“Male and female white sharks have different migration patterns,” explained Weng. “Males have been recorded in Hawaiʻi from December through June, but females have been observed here all year round.”
Female white shark visits to Hawaiʻi may be related to a two-year reproductive cycle, in which they return to coastal aggregation sites off California and Mexico on alternating years. That leaves them with more time to spend in Hawaiʻi, where warmer water temperatures may speed up fetal development.
Misidentification of similar looking sharks, such as makos, has been a recurring problem.
A recent example was the sighting of a shortfin mako shark off Kaʻena Point, Oʻahu, on January 12, 2012. This sighting, captured on a video that “went viral,” was reported around the world as a white shark by the news media, an error that continues to this day.
This study proposes a simple method to help distinguish between the two species based on the shape of the head. Mako sharks have a more acute head shape than white sharks.
Since many sightings only obtain photographs of the head, this method should be helpful for situations with limited information and no specimen.
—Adapted from a UH Mānoa news release