Written by Heather Christiansen
White sharks are one of the most protected shark species globally. However, unlike other well-known aggregations in the Northeastern Pacific Ocean, South Africa, and Australia, relatively little is known about white sharks in the Northwest Pacific Ocean. Unfortunately, this region also has little white shark specific protection measures in place.
White shark’s behavior can vary depending on where they live. In order to determine the best way to protect white sharks in the Northwest Pacific Ocean it is important to gather details on what habitat they are using, if habitat use varies seasonally, how large and fast individuals grow, migration patterns and information on reproduction (mating, birthing areas, number of young per mother etc).
In order to collect as much information as possible on white sharks in the Northwest Pacific Ocean we worked with regional scientists and gathered all records and observations of white sharks in the area since 1951. Records were obtained from a variety of sources including scientific literature, newspapers, news websites and museums. There were a total of 240 records of white shark occurrences from Russia in the north down to Vietnam in the south. Individual sharks weighed between 35 to 5578 lbs (about the weight of an average pickup truck!). The size of the white sharks were wide ranging from young of the year at just over 4′ total length (measured from it’s snout to the end of its tail) up to the largest white shark on record at 19′ 9″ total length!
Size of the largest and smallest white sharks in this study compared to the size of an average 10 year old girl.
We found that white sharks live in this region year round, but were absent from northern waters (near Russia and Republic of Korea) during autumn and early winter and southern waters (near China, Taiwan, Vietnam, and the Philippines) in July and August. White sharks have been recorded in a wide range of water temperatures, but this data indicates a preferred temperature range.
Based on the number of observations over the study period we estimated the trend in the relative abundance of white sharks in this region. We determined that the population was relatively stable until recently (approximately the last 10 years) where the relative abundance has started to decline slightly. We need to be careful interpreting these results though because they are based on reports from observers and not focused monitoring. These results indicate that there is a regional population of white sharks and further monitoring is required to estimate the number of animals living in the region.
One of the most interesting results of this study was the number of pregnant females recorded. There have only been 26 pregnant white shark females reported worldwide, 11 of which were found in this study. We were able to estimate females in this region are pregnant for 20 months and had up to 10 pups per litter. Pregnant females were also recorded in more southern waters around Taiwan and Okinawa early in their pregnancies and around mainland Japan towards the end of their pregnancies. We don’t know very much about the reproductive strategies of white sharks worldwide so this study gave us a unique look at what pregnant females are doing. Additionally, we recorded young of the year white sharks in four countries indicating they may be using multiple countries as nursery areas.
Left: ovary from early term pregnant white shark, Right: egg cases from same shark approx. 4″ long
This study provides important information that helps fill in gaps in our knowledge for white sharks in the Northwest Pacific Ocean. This study will be used to guide future research and determine what conservation measures are necessary to protect white sharks in the Northwest Pacific Ocean. Formal monitoring programs both nationally and internationally will help improve biological knowledge and assess future population trends.
If you would like more information on the observation records of white sharks in the Northwest Pacific Ocean you can look at the full publication here:
Christiansen HM, Lin V, Tanaka S, Velikanov A, Mollet HF, et al. (2014) The Last Frontier: Catch Records of White Sharks (Carcharodon carcharias) in the Northwest Pacific Ocean. PLoS ONE 9(4): e94407. doi:10.1371/journal.pone.0094407