OceansIQ

Are Tasmanian coastal areas a love niche for broadnose sevengill sharks?

A broadnose sevengill shark caught off the coast
of Tasmania, Australia.

An essential question to answer when scientists want to understand the ecological role on any species is to identify if animals use the habitat for reproduction. This information can be used to inform and improve conservation and management programmes. With this in mind, we wanted to understand if the broadnose sevengill sharks (Notorynchus cepedianus) use certain Tasmanian coastal areas for reproductive purposes. 

A non-lethal approach to studying shark reproduction

Female sharks don’t have any clear external features that tell us about their reproductive status so traditionally, researchers conduct an internal examination of their gonads to determine their reproductive status. Unfortunately this internal examination requires killing the shark.  To avoid this cost, recent studies have focussed on developing a new technique to determine a shark’s reproductive status - using their reproductive hormones from non-lethal blood tests instead of their gonads. While developing the technique, initial studies still required the sharks to be killed to examine the gonads. However, this validation step was essential in successfully linking the reproductive hormones with the reproductive status of the shark.  Our study is the first to use this completely non-lethal approach, with no need to validate the technique. Great news for the sharks and us!

Blood and scars – all in a days work

Adam and I taking blood from seven gill shark. 

We took blood from 69 females, and a small subsample of 15 males. It took only 2 min to take blood from the animal before each animal was released back into the water. Several hormones were analysed in the samples - testosterone, 17β-estradiol, and progesterone. These reproductive hormones act as triggers or modulators of all aspects of reproduction. By studying their levels in each shark, we can know the reproduction condition of the individual shark. Gather enough data from many individuals, and we develop an understanding of the reproductive status of broadnose sevengill shark population over time and space. 

Taking blood into a syringe.

We also examined the females for mating scars before we released them. Mating scars are created at the time of copulation when a male grasps the female around their body with their mouth (and teeth) to immobilise them. Fresh mating scars are common in females just after these encounters and are clear indications to researchers of recent mating activity.

This is not the love coast we are looking for…

After we take the blood, we store it on crushed ice until
we reach the lab where we process the samples

Despite the fact that females and males are mating between September to April, we only found a few females with mating scars. This indicates that our area of sampling in Tasmanian coastal water is not the main area used by broadnose seven gill sharks for mating. 

Females have a bi-tri annual reproductive cycle - they are pregnant for around one year and spend at least another year not pregnant. As found from the blood samples, females in Tasmanian coastal waters are either at initial stages of pregnancy, resting after giving birth, or starting the new ovulatory cycle where females are preparing the ovary for a new ovulation. No near-term pregnant females were observed. 

Clearly, broadnose sevengills sharks do not use these Tasmanian habitats as pupping ground.

Unfortunate for me - I wanted to see baby sharks!!!!

In short, this study found that Tasmanian coastal waters do not have any reproductive relevance for this species. But if not here then where? Future management and conservation planning programmes need to identify whether there are other areas in Australia that play a critical role for reproductive purposes in this species. 

Importantly, this was the first study on broadnose sevengill shark reproduction to use a hormone-based, non-lethal method to obtain essential information for management and conservation. Its success in this project has important implications for conservation programmes of threatened and endangered species worldwide where this non-lethal methodology can now be applied without the validation step.

Awruch CA, Jones SM, García Asorey M, Barnett A (2014) Non-lethal assessment of the reproductive status of sevengill sharks Notorynchus cepedianus to determine the significance of habitat use in coastal areas. Conservation Physiology 2: doi:10.1093/conphys/cou013.