Striving for captive breeding of whale sharks
Whale sharks are the world’s largest fish, however there is limited information about whale shark ecology, and this is especially true concerning their reproduction.
In an attempt to clarify the reproductive ecology of whale sharks, Okinawa Churaumi Aquarium and Churashima Research Center have decided to work towards the world’s first ever captive breeding of whale sharks. This will be done by conducting various surveys and research while collaborating with external agencies.
Sexual maturity of the male whale shark “Jinta”
Generally, male sharks (like rays) have two claspers that grow during maturation and have a reproductive function. This transformation has already occurred to Jinta.
Jinta’s claspers grew rapidly between August 2011 and July 2012.
From April 2012, he has begun to move the claspers and researchers have confirmed the presence of sperm cells.
Surveys of sexual maturity
- Okinawa Churaumi Aquarium conducts health checks every month, taking blood samples from the whale sharks. The concentration of hormones within the blood is very important as it allow researchers to know the maturity level of the whale sharks. Jinta’s hormone concentrations changed with maturity, and also change depending on the season.
We have also conducted the same surveys every month with the female whale sharks and are verifying the level of maturity along with seasonal changes.
Monitoring their behavior
From 2014, Jinta started to chase the females and began to cross his claspers frequently.
In order to know the frequency of this behavior, we increased observation by staff and installed a 24-hour monitoring device.
The growth of the whale sharks
- It is essential to be aware of conditions in the aquarium in order to understand the pace of growth of the whale sharks. We consistently measure their total length as well as their girth monthly at our aquarium. We obtain important information through stable husbandry to answer questions such as “Are they steadily growing?”, “In which season do they grow fastest?” and “Are they consuming the right amount of food?”
Surveys of whale sharks in the wild
- In Okinawa there are times when a whale shark is caught in a fixed shore net and with the cooperation of fisherman they are released back into the ocean. When this event occurs we collect blood samples and measure their total length and their girth, collecting samples of tissues and DNA for chemical analysis. We also use an electronic marker to monitor their behavior in their natural habitat. With this research, we can gain valuable information into whale shark reproduction and ecology.
Two whale sharks on display
It is believed that a female whale shark will be sexually mature when her total length exceeds 9m. We now display two whale sharks at the aquarium, Jinta and our largest female (total length 8m) in the main tank. Jinta has already increased the number of approaches towards the female (chasing behavior) and we presume that reproduction is close.
As this female grows she is expected to become Jinta’s bride.
From November 2016, the main tank has housed two rather than three whale sharks.
The extra space will hopefully encourage reproduction.
At Okinawa Churaumi Aquarium we don’t just raise animals for exhibition – we also carry out investigative research.
A large part of our research is animal breeding. By demonstrating the results of healthy captivity, and providing biological data for the animals concerned, breeding animals in captivity generates valuable data for the preservation of wild specimens. The Japanese Association of Zoos and Aquariums is an organization that supports the activities of zoos and aquariums in Japan.
The Breeding Award was set up in 1957 and is awarded to “the successful breeding of animals in captivity where the offspring survive for more than 6 months, and which has not been accomplished before in Japan.”
Okinawa Churaumi Aquarium has received the Breeding Award for 26 different species including manta rays and Indo-Pacific bottlenose dolphins. The high success rate for breeding large sharks and rays, something rarely seen at other facilities, is of particular note.
We will continue our research into breeding and rearing techniques, aiming for successful breeding and long-term captivity of a greater variety of animals, and promoting the preservation and flourishing of marine life.
The Koga Award
The Koga Award was first established in 1986 and is named in memory of Dr. Tadamichi Koga, former director of the Japanese Association of Zoos and Aquariums, who contributed greatly to the protection and propagation of rare animals and whose generous donation formed the basis of the award fund.
The award is given to those who have notably contributed to the improvemment of breeding know-how in zoos and aquariums by demonstrating excellence in any of the following areas.
- Breeding of a globally rare species and one that is difficult to breed in captivity
- Successful breeding over multiple generations
- Breeding achieved as a result of creative, unique and groundbreaking efforts
In the very first award ceremony (1987), Okinawa Churaumi Aquarium received an award for successfully breeding two generations of whitetip reef shark in captivity.