Recently a study was published in the Journal of Marine Biology which sheds new light on the relatively rare but occasionally recorded presence of white sharks in waters surrounding theHawaiian Islands. It suggests a new method to help distinguish between white sharks and close relatives, such as mako sharks. The paper, titled “Occurrence of White Sharks in Hawaiian Waters,” was written by Kevin Weng of theUniversityofHawai’iat Mānoa’sSchoolofOceanand Earth Science and Technology (SOEST) and Randy Honebrink of the Hawai’i DLNR Division of Aquatic Resources (DAR).
“This study is valuable in that it provides a better understanding of the biology and behavior of white sharks, which is very useful for management purposes. White sharks were caught by pre-contact Hawaiians, and their teeth used in weapons and other implements. But in many ways they continue to mystify us today,” says William Aila, chairperson of the State of Hawai’i Department of Land and Natural Resources.
The results of Satellite tracking have previously shown thatHawaii’s white sharks are migrants from population centers offCaliforniaandMexico. A relatively small proportion of those West Coast sharks migrate all the way toHawaii, which is why they are so rarely seen.
All the available sources of information relating to white sharks in Hawaii, which included newspaper accounts of shark attacks, shark control program catch records, photos and videos from various sources, and satellite tracking data was by the authors. Only data that could be confirmed as pertaining to white sharks was included in the analysis. In cases where information was insufficient for positive species identification, the sightings were eliminated.
“We learned that white sharks occur inHawai’iacross 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,” says Dr. Weng,
Since all records of white sharks in Hawaiian waters are of individuals larger than 3.3 meters (10.8 feet), and no juveniles have ever been reported, there is no evidence of white sharks being residents or breeding there.
Scientists have learned a great deal about the migratory patterns of white sharks in the Eastern Pacific since the advent of satellite tracking, but important questions remain. “Our satellite tracking studies have been conducted in places where we can get very close to the animals — seal colonies — but this means that we may be sampling a subset of the population, and thus obtaining biased results,” said Weng. “It is possible that there are individuals that do not aggregate around seal colonies.”
“Male and female white sharks have different migration patterns,” explained Weng. “Males have been recorded inHawai’ifrom December through June, but females have been observed here all year round.” Female white shark visits toHawai’imay be related to a two-year reproductive cycle, in which they return to coastal aggregation sites offCaliforniaandMexicoon alternating years. That leaves them with more time to spend inHawai’i, where warmer water temperatures may speed up fetal development. Our results are consistent with a very recent paper by Domeier and Nasby-Lucas in the journal Animal Biotelemetry.
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 Ka’ena Point, O’ahu, on Jan. 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.