Line-Transect Survey, Dunbar Castle II
Despite the bad weather which has prevailed for the last 2 weeks, we managed to squeeze in a line-transect survey on Thursday 5th July. For our new volunteers, this was the first time they had been on a marine mammal survey and their first up close encounter with the Cardigan Bay bottlenose dolphins.
We left New Quay on our survey vessel the Dunbar Castle II and headed south towards Cemaes Head; the southernmost point of the Cardigan Bay Special Area of Conservation (SAC). This SAC was originally designated due to the large bottlenose dolphin population found in the area; however it has since been realised that this area also has significant populations of river lampreys, sea lampreys and Atlantic grey seals. Cardigan Bay is a very diverse region, and has a variety of important examples of marine habitats including reefs, sub-tidal sandbanks and sea caves, all of which have been included in the SAC designation. These marine habitats are home to thousands of plants and animals, such as the nationally rare mantis shrimp (Rissoides desmaresti); this complexity and variety of ecosystems makes Cardigan Bay a truly outstanding marine environment.
Over the course of the day we had several sightings including 4 Atlantic grey seals, 3 harbour porpoises, many lion’s mane and compass jellyfish drifting past, a sheep (which we suspected had wandered off the cliff and drowned) and a total of 16 bottlenose dolphins, 5 of which were calves.
Through photo identification opportunities, we have been able to match some of the individuals seen on survey with those in our existing catalogue, these include; Barry, Spot, Milkshake, Moneypenny and her calf Tuppence. We also saw our adoptable dolphins Bond and Chris, with her calf Tigger. During our encounters we saw many different types of behaviour such as, leaping, socialising- where individuals turn and mingle with each other at the surface, bow-riding and feeding- one of the calves popped up with a fish in its mouth!
Not only were we able to carry out photo identification on individuals, but we also used our hydrophone to record the nearby dolphin’s clicks and whistles- their way of communicating to each other underwater. We are collecting this data to determine whether boat activity has an impact on their behaviour, and to try and establish whether clicks and whistles of a different frequency result in a certain type of behaviour. Although we know a lot about dolphins, their communication still remains a mystery to us.