A day out shark tagging with NSU

After a whole week of rain and dreary skies, we were definitely very lucky to have clear and sunny skies for a day out shark tagging with Dr Derek Burkholder and the Nova Southeastern University team. It was definitely an eye opener considering nothing like that is done in Singapore (apart from Dr Neil Hutchinson’s bamboo sharks project, of which I have yet to set out with him actually and should do so when I get back!).

So there are a number of methods for tagging sharks, all of which to gain more data in order to understand patterns in sharks so we can have better scientific backing for methods to saving them. The one that was used on this trip was number tagging, where you puncture a hole in the first dorsal fin of the shark using a leather hole punch tool (I know it sounds painful but the sharks’ fins are made out of cartilage and do not have pain receptors I was told) and then attach the number tag very quickly. Other data such as species, sex, total length and pre-caudal length of the shark is also quickly recorded, as well a small piece of tissue sample for lab isotope analysis of the shark’s feeding habit, snipped and saved in a marked alcohol vial, before the circle hook is cut away and the shark is released.

The method used to bait the shark was drumline fishing using bonito fish, of which this illustration by Save Our Seas and these pictures taken, do a better job of explaining the method:

Drumline

 

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bonito bait

 

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weight anchors

10 baited hooks are then left out at 10 different spots of varying depths and pulled back up again in about an hour’s time. The baited line is long enough to allow for the shark to swim in big enough circles so they can still get to breathe.

We managed to get a female lemon shark on the line on the first round, which struggled a fair bit (of course, no one wants to be taken out of a zone where they can breathe and have their tail tied up) and all required data was collected before the hook was cut and the shark released.

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The lines were re-baited a second time after one round of removing them to check for sharks and on the second round, a male nurse shark was found on one of the lines.

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Definitely a good day out on the boat with much learning done, and we were even rewarded further at some point, with a small pod of bottle nosed dolphins breaching the water a couple of times just because!

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I think shark tagging can go a long way in shark research but given the possible harm and mortality to the sharks, it should only be done by careful hands who know exactly how to handle a shark quickly enough. It definitely was not emotionally easy for me to see the sharks struggle so much with the hook in their mouths and caudal fin all tied up, but a little more information about sharks can go a long way. However, since number tags were used, it is also important to make sure that enough word goes around that sharks are getting tagged so that every recapture leads to a definite reporting.

Can shark tagging be done in Lombok as a way to incentivise the local shark fishermen? Perhaps, but I need to have the expertise to train them and get them to see the dollar value of doing it. Also, I don’t think number tagging, although cheaper a method, would be useful in Lombok as satellite tags would. Worth a deeper thought now that I have seen firsthand how it can be done with the drumline fishing method. Looking forward to learning more from the FSU graduate students who are using long line and gillnet fishing methods for their shark survey studies, as I make a visit to the Florida State University Coastal and Marine Laboratory for a couple of days!

Kathy Xu

Singapore (Broward County, Florida)

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