Ray Tagging with Helen Cadwallader

Photo Credit: Lucas Allen

The Fins United Initiative Founder Melissa has always been interested in #flatsharks, so when she came across another international scientist based in New Zealand studying them, they struck up a conversation and have been #majesticflapflap bff's since then. TFUI is proud to present close friend and colleague Helen Cadwallader, a PhD student at the University of Waikato Coastal Marine Field Station in Tauranga, New Zealand, studying the large population of stingrays that spend time in the Tauranga Harbour. She's also the creator of Apex Predators Project - check it out!

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The Fins United Initiative: First of all, thanks for taking time out of your busy schedule to chat with TFUI. Can you explain to the readers what your project is about?

Helen Cadwallader: New Zealand’s Rays, more specifically, two of the rays that inhabit Tauranga Harbour on the east coast of the North Island of New Zealand; the Short tail stingray (Bathytoshia brevicaudata) and the NZ Eagle ray (Myliobatis tenuicaudatus). Very little is known about either species, so I’m trying to work out where they feed, the habitats they use and whether the increasing urbanisation or New Zealand’s coastal areas might be having an effect on them.
 
TFUI: So you are tagging rays for your PhD! Can you explain what “tagging” is? 

HC: Tagging is attaching an identification device to an animal.

TFUI: What does the tagging data help show?

HC: Depending on the type of tag this can provide a lot of information from the most basic information such as whether the same animals inhabit the same areas from day to day or year to year and growth rates (comparing measurements taken when the animal is tagged and then when the animal is re-caught) to real-time complex fine-scale movement behavior including depth, speed and some nowadays can even record sound, to long term seasonal movements and migrations. Tags can be attached with darts or implanted into the animal, depending on what they’re being used for.

Photo Credit: Lucas Allen

TFUI: Do scientists need permissions to tag animals?

HC: Yes, all scientific tagging projects have to apply for ethics approval from their organization. To gain approval the scientists need to prove that they have thought about and know the risks involved for the animals and the researchers, and any alternatives. They also have to prove that they have adequate training, support and knowledge to reduce the risks to the animals as much as possible.
 
TFUI: So what are you tagging rays for? What type(s) of tag(s) are you using for your rays?

HC: I’m using visual tags, also known as conventional tags - both darts and Peterson discs to see where the Short tail stingrays are going within the harbour and whether individuals use multiple areas or are resident to one area.

TFUI: Why did you choose that specific tag type over others?

HC: In a nutshell, it is the best tag type for the data I need, counterbalanced with logistics and cost. Hi-tech tags are expensive and for a PhD project that is often restrictive. Tauranga Harbour is a difficult environment to use tags. It is a very urban, city harbor at the Southern end with strong currents, lots of recreational boat traffic and a large, busy container port. This means that acoustic tags (which ping out an ultrasonic signal picked up by fixed receivers) have a much lower detection range than in other areas. In addition, Short tails, being very large rays (they can regularly reach disc widths of over 2 metres) are very difficult to turn over, which is the common method of implantation of acoustic tags and so external tag attachment would be necessary, which could also prove a problem with snagging etc unless done in a certain way.
 
TFUI: What data do you hope to get from these tags?

HC: The data for my tagging program comes from re-sights of tagged animals by researchers and the public via a website (www.apexpredator.co.nz) this will tell me where individual rays are found and when. It might even tell me which other rays they are often seen with.

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Photo Credit: Lucas Allen

TFUI: So how have you found tagging rays to be like? Is it a challenge to tag rays?

HC: A challenge but great fun. They are big, like very big, so we gave up on catching on hooks them like you would a shark for this project. They’re caught with a tarpaulin and bait. The barbs prove a challenge as someone has to hold on to the tail (covered in a blanket) and they are VERY strong. We have to do all of this, tag measure and release in as short a time as possible to avoid stressing them out too much. Water visibility, weather, number of people available, all adds to the challenge!
 
TFUI: Does tagging hurt rays?

HC: There are debates on this, but it is thought that elasmobranchs and in particular ray species may lack the physiological apparatus to process pain stimuli. In mammals, it is unmyelinated nerve fibres (known as nociceptors) that detect and process pain and the lamina I of the spinal cord that transfers this information to the brain. Several studies have now shown a near absence of unmyelinated nerve fibres and an absence of the spinal cord lamina I in a wide variety of ray species suggesting an inability to process noxious stimulae as pain in these species (Reviewed in Rose et al 2012). So in a word, no. They may feel something similar, but not ‘pain’ in the same way that we do.
 
TFUI: What’s been the most interesting tagging event you’ve had?

HC: We’ve had a pregnant female, which we had to be more careful with so she wouldn’t abort her pregnancy, and a few that got a little bit whippy with their tails!
 
TFUI: Yeouch! Sounds like a handful. So why do we need to tag these animals?

HC: To find out where they go. In order to protect species and their habitats we need to find out what they’re doing, how long they spend in places etc, tagging helps us achieve this.
 
TFUI: Do the electronic tags interfere with their electro-magnetic senses?

HC: No, the electro-magnetic senses are a lot more distance limited than many people think – as little as 30 or 50 centimetres - so the distance a tag is situated from the ampullae of lorenzini (the electro-sensory mechanisms) means that its very unlikely to have an effect.
 
TFUI: Are there any other potential negative impacts of tags on these #flatsharks?

HC: Catching and tagging an animal always has the potential to negatively impact the animal. In the ocean tags can be fouled by encrusting organisms, which may add weight to the tags. In addition, there is always the risk of infections at the point of attachment and implantation. It is the job of the researchers to minimize these risks as much as possible, and the benefit always needs to outweigh the risks before a potentially invasive technique like tagging is used.

the fins united initiative would like to thank helen for her time 
and we wish her well on her current/future projects! 

say hello!

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