When something finally happens that you have been thinking and dreaming about for a very long time there is often a sense of surrealism, like it’s not really happening and only a more lurid and tangible extension of those dreams which you have been having for so long. This is certainly true for where I find myself currently – in the tranquil Sicilian town of Torretta Granitola and hosted by scientists at IAMC-CNR having brokered a collaboration between this institution and Durham University. Since the very earliest days of my PhD research it was clear that there was a gaping hole in the geographic spread of the samples of Tursiops truncatus, or Bottlenose Dolphin, to which I had access. This might have been overlooked were it not for that hole to be sat squarely over a region that was of fundamental interest to my research question – how do environmental boundaries influence population structure of marine vertebrates. The Siculo-Tunisian channel, on which Torretta Granitola stands on the northern edge, is just such a boundary and the principle one around which my PhD was formed. To the East lies the warm, salty and deep water of the East Mediterranean Basin, to the West: the generally shallower Western Mediterranean Basin with its cooler waters influenced by the Atlantic. Research conducted by Dr Ada Natoli showed that there was a distinct genetic difference between Bottlenose Dolphins found in the Western Mediterranean Basin and those from the Eastern Mediterranean Basin and that the Siculo-Tunisian channel was the geographic region in the middle of these two groups. Could it be that the different environmental conditions found in the two basins has led to the discovered genetic differentiation?
To understand this more clearly, I need tissue samples from dolphins found in this region. With these we can conduct genetic analysis to see if the population split between the EMB and WMB is abrupt, i.e. the dolphins found here fall easily into one group or the other, or if in fact the dolphins here represent a more transitional grouping with geneflow in either direction or potentially even both. To do this requires biopsy sampling which can be done in a number of ways; rifle, scrubber, crossbow or even with a pole. After much research, reading and speaking to other scientists I decided to go with the use of a crossbow for a number of reasons. My principle reason was that many fellow scientists suggested that using a crossbow provided a higher sample return rate (particularly compared to a pole or scrubber) and this was important to me as I didn’t want to subject the animals to any more interaction was absolutely necessary. For me it would be quite tragic to cause any stress to wild animals, no matter how little, and yet come away with no samples to support the science that will eventually help to protect the animals themselves. Secondly, it is far easier to transport the crossbow and associated biopsy equipment across international borders than other methods such as a biopsy rifle. Thirdly the crossbow is an order of magnitude less expensive than a rifle.
So how does the crossbow work? The crossbow itself is a standard sports crossbow with a 150lb draw weight. This is the standard power used for biopsy sampling marine mammals. It must be strong enough to penetrate the skin of the animal and for the molded polyethylene flotation to cause the bolt to bounce back from the animal but not powerful enough for the bolt to injure the animal beyond required. The bolt itself is a specially designed item from a company based in Denmark called Ceta-Dart. It is an aluminium-carbon fiber shaft with three vanes and a molded polyethylene flotation. On the front is a threaded bar onto which you attach the cutting tip. The tips are 25mm deep, with an internal diameter of 7mm, and contain three backward facing barbs that hold onto the sample once taken. The bolt will float in the water after striking the animal and can be easily retrieved with a landing net. I’ll talk about the processing of samples in a future post.
With animal safety and welfare being of highest priority for me it was essential that I was accompanied by an experienced cetacean biopsy sampler. For this we flew in Tilen Genov, an extremely experienced biopsy sampler from Slovenia. Tilen is the President of the Slovenian Marine Mammal Society – Morigenos and I urge you to check out the amazing scientific research that this organisation does. Tilen provided us an opportunity to shadow him during the first week of the expedition as well as providing lectures and practical training on biopsy sampling.
One of the main issues to consider when conducting biopsy sampling is to be very aware of potential dangers to calves. Our basic rule is to never target mothers with calves or groups that contain calves. The main reason for this is due to the surfacing pattern of bottlenose dolphin calves, they typically come to the surface on the flank of the accompanying adult – putting their head firmly in the firing line. The last thing we would want to do is harm a calf so it is best to simply avoid the possibility altogether. In addition we never want to sample an individual animal more than once, not only as such samples would be superfluous but also to limit stress to an individual, so we run concurrent Photo-ID allowing us to keep track of who has already been sampled and identify potential target animals.
Next time I’ll tell you a little more about how we have been getting on…