Scientists working from the University of Florida have been attempting to establish the basis for increased shark attacks around the main Hawaiian islands. According to their findings, observed patterns in the migration of tiger sharks could hold the key to explaining some of these deadly attacks.
The study was seven years in duration and used innovative techniques to investigate the movement of the life-threatening predators around the Hawaiian archipelago. This is a region well known for its frequent shark attacks.
As recently as August, a 20-year-old female experienced the ruthless nature of sharks, whilst snorkeling in a typical tourist destination of Hawaii. During the incident, her entire right arm was severed, and she died a week later from her injuries. The horrendous attack prompted authorities to immediately close several beaches, stretching one mile in either direction from the location of attack.
For this year, eight shark attacks have been recorded in Hawaii, most of which involved surfers, swimmers and snorkelers in highly turbid waters.
According to the team of researchers, most of the inter-island migration was demonstrated in female tiger sharks; the group report, during a summer-fall period, that 25 percent of mature female sharks upped sticks and headed for the main Hawaiian Islands from the more secluded French Frigate Shoals, which is one of the largest atolls in the area, with an enormous, crescent-shaped coral reef that encloses a lagoon.
According to Yannis Papastamatiou, a marine biologist working from the Florida Museum of Natural History, the group witnessed a surprisingly high number of tiger sharks when monitoring those that were found “hanging around” shark tours on Oahu. The spike occurred during the month of October, substantiating their existing model, that large numbers of pregnant females flock to the Hawaiian Islands during this period. He also drew a correlation between the number of shark attacks reported at this time, and their apparent migration patterns.
The study did not analyze the interaction between humans and tiger sharks directly and primarily focused upon monitoring their migration patterns. However, data from the International Shark Attack File from the Florida Museum did offer some insight into historical reports of deadly shark attacks. Since 1926, October, November and December are the months most associated with shark attacks, with the highest number of cases being reported during this stretch.
When describing the pattern of movement in tiger sharks, Papastamatiou equates it to a “free-for-all.” He explained that one would naturally imagine all members of an animal population to migrate in unison; however, due to environmental factors, this is not how it works in tiger sharks. The team were able to overcome these complexities by investigating migration over a total period of seven years.
The data modeling was executed by Felipe Carvalho, a co-author on the study. Over a hundred sharks were tagged and tracked, since 2004, using a technique called passive acoustic telemetry. In essence, a series of receivers were positioned across the area of interest, constituting the Hawaiian archipelago, extending some 1,500 miles. The receivers work to record the presence of the tagged shark subjects, without the need for direct interference, helping to yield more reliable results.
As discussed, a quarter of all mature females moved towards the Hawaiian Islands from the French Frigate Shoals, quite plausibly to give birth. Papastamatiou also conjectures that some tiger sharks may have decided to migrate to source more amenable conditions, searching for food or the correct thermal environment. Yannis summarized his thoughts on the perceived patterns of migration:
“So, what you see is this complex pattern of partial migration that can be explained by somewhat fixed factors, like a pregnant female migrating to give birth in a particular area, and more flexible factors such as finding food.”
The team also elected to investigate these environmental factors, including the accessibility of certain resources, and compared their collected datasets to other previous research studies. Christopher Lowe, a biological sciences professor of California State University Long Beach, remarked upon the applicability of the study’s results, which could provide authorities with a better opportunity to react to tiger shark movements, based upon seasonal changes. This may, in turn, help to reduce the number of shark bites through implementation of certain safety precautions.
However, according to KHON2 News, another co-author for the project, Dr. Carl Meyer of the University of Hawaii, cautions against people misinterpreting the results of their study, stating that they “… don’t have conclusive proof…” that seasonal pupping is definitely causing the elevation in shark attacks.
Ultimately, it at least seems likely that environmental factors, resources and pupping may at least serve as contributory factors in influencing migration of tiger sharks. This migration pattern, in turn, may or may not explain why there is an increase in the number of shark attacks during the latter months of the year.
By: James Fenner
University of Florida Link