Today Cristina continues with her examination of the data we have harvested from our Stena Europe surveys and presents more amazing statistics! This week following on from Holly's posting, Cristina looks at Minke whales!
Borada ffrindiau!
Post 7 – The trip!
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Migration is an adaptive behaviour that confers competitive advantages to those who are willing to take the challenge. This behaviour does not only allow the different species to take advantage of seasonal peaks in resource abundance but also it allows the individuals to avoid competition with other species, predators or even parasites. It has been described that baleen whales tend to present migratory behaviours where they travel to high latitudes during the summer to feed, and then to warmer low latitude areas during winter where they breed.
Although there is plenty of literature on cetacean migration, the truth is that our understanding of their migration routes is still poor. The reason for this is that the study of these animals is limited by factors such as; the weather conditions; the daylight; their mobility; the very short amount of time that they spent in surface when compared to the time they spend under the water. For example, the typical diving profile of cetaceans, and more specifically of Minke whales, usually consists of 3-4 inter-surfacing intervals, followed by a long deep dive for 20 minutes. This means, it is difficult to visually survey for these marine mammals. This shows how important the collection of data is and how it can contribute towards our understanding of these species.
Although there is plenty of literature on cetacean migration, the truth is that our understanding of their migration routes is still poor. The reason for this is that the study of these animals is limited by factors such as; the weather conditions; the daylight; their mobility; the very short amount of time that they spent in surface when compared to the time they spend under the water. For example, the typical diving profile of cetaceans, and more specifically of Minke whales, usually consists of 3-4 inter-surfacing intervals, followed by a long deep dive for 20 minutes. This means, it is difficult to visually survey for these marine mammals. This shows how important the collection of data is and how it can contribute towards our understanding of these species.
During our surveys (2004-2017) we have recorded 75 sightings of Minke whales. In most cases, sightings took place during the period April – September while only 3 animals were recorded during other periods. When we had a closer look, we also detected that, even within these months (April to September), the chances of recording a Minke whale varied substantially depending on the month. For example, April remains the absolute winner with almost a 50/50 chance of recording one of these animals during our ferry surveys.
It is also true that April is closely followed by June and July in terms of average number of sightings per survey; however, this is largely driven by an interesting phenomenon. Throughout the years, we had an average number of 5 minke whale records per year for our ferry surveys but in 2011 we had 16 sightings only in July and an annual total of 21 !!!
That means the total number of sightings for July for the year 2011 was 16 but the total number of sightings for July for the period 2004-2015 excluding 2011 was only 4!!
I still remember the Sea Trust annual Dolphin-Othon in 2012. For those of you who are not familiar with this event, it consisted of continuous ferry surveys (2 per day) for 1 week, We had several Sea Trust monitors and invited members of our community to join us on the bridge wings each day to show them and record cetaceans. During that year´s Dolphin-Othon, the weather conditions were very consistent and favourable for the whole week and we were able to complete 11 surveys. I remember a specific one, where on the morning crossing from Rosslare to Fishguard, we had spectacular views of Risso´s dolphins, big common dolphins pods, our well-known Harbour porpoises and even a Humpback Whale! All of them where very active and were accompanied with lots of sea bird activity, throughout the survey
The next survey started just a couple of hours after this amazing trip, and, as you may imagine, all the team were super excited to go back on board expecting to have another mind-blowing survey, just like the one we had earlier in the day. Unfortunately, this was not to be the case and all the frenetic marine wildlife activity that we witnessed early in the morning, had suddenly vanished! It was as as if it had never happened. everything had moved on. This just goes to show how the sightings can hugely vary even within the same day!!
In conclusion, If you had only done one of the two surveys you would have either thought the Irish sea was rammed with wildlife or conversely an empty wilderness. This is the importance of long term consistent surveying throughout the seasons. rather than snapshots once every few years that might produce a totally misleading picture. Only by such consistent long term surveys can we generate a more accurate picture of what is going on in our oceans!
In conclusion, If you had only done one of the two surveys you would have either thought the Irish sea was rammed with wildlife or conversely an empty wilderness. This is the importance of long term consistent surveying throughout the seasons. rather than snapshots once every few years that might produce a totally misleading picture. Only by such consistent long term surveys can we generate a more accurate picture of what is going on in our oceans!
Hasta la vista, Cristina!