Post 3. Ferry surveys from Cristina Munilla!

So our ace cruncher of numbers and expert statistician Cristina, is continuing with her series on her analysis of our Stena Ferry Data. She has spiced the introduction with a bit of tongue in cheek observation and a mini cryptic quiz hidden within it...all in a second language Here we go!...

Post 3. Ferry surveys – But I would sail 63 miles and I would sail 63 miles more (The surveyors)...

Please allow me to introduce this thing. Is a system that we all get. It’s been around for a long long year, so why don’t we use it then?
The birth of the decimal metric system (XVIII century) sought to facilitate the scientific, cultural, and commercial interchange across all the globe. As a matter of curiosity and to illustrate my point, although not strictly marine or Sea Trust related.

Back in 1988 NASA sent a spacecraft to Mars where it was supposed to orbit during a whole Mars’ year (687 days) to study the climate, atmosphere and surface of this planet. This project had a budget of $125.000.000. But the spacecraft never fulfilled its mission, after 10 months of travel to Mars, the Mars Climate Orbiter burned and broke into pieces. So why did this happen? The spacecraft navigation system was built by engineers using the English metric system (inches, feet, and pounds) while the scientists of the navigation team in the Earth who were guiding it were using the decimal metric system, so they thought the spaceship knew which way to go. As a result, they mistook acceleration readings measured in English units of pound-force seconds for a metric measure of force called newton-seconds. Consequently, the poor confused spaceship wobbled about and then shot off and crashed and burned as it hit the Martian atmosphere! To date, the Mars Climate Orbiter remains the most absurd error of the history of space exploration.

So for simplicity, clarity and peace of mind, it is always preferred to use the decimal metric system. This way the 63 miles that separate Rosslare and Fishguard are converted to 101 km.

Unfortunately, this system is not free of flaws. For example, the word kilometres has definitely too many syllables to fit in any future “The surveyors” hit record title, that might be a plagiarized effort based on the Proclaimers preoccupation with walking 500 miles to wake up with someone. But it did give us the opportunity to introduce this fun fact about the importance of consistent measurement!

But let’s get back to the maps we posted last week. Back then we mentioned that only by mapping the records, we were able to extract some interesting information about the behaviour of the cetaceans that we recorded. We then focused on the analysis of the number of sightings vs the number of individuals concluding that the most common species in the area (Harbour porpoise, Common dolphin, Risso’s dolphin and Minke whale) presented substantial differences with regards to their social habits

This week we are focusing on the minimum distance to the coast. Through the maps we presented last week we could already guess a preference of some species for more coastal environments whereas others tend to inhabit oceanic environments. For illustrative purposes, we have randomly selected a small subsample of the dataset (August and September for the years 2007 and 2008) , we have extracted records belonging to Common dolphins and Harbour porpoises and generated a heat-map for both species. For those of you who haven’t heard this term before, a heat-map is simply a representation of the data that uses a warm-to-cool color spectrum providing and immediate visual summary of the information. As the colours in the map gets closer to green-blue, the number of sightings in the area diminishes, while warmer colours such as red, indicate a high number of sightings in that area.

The differences are much clearer and more evident in these maps when we compare Common dolphins and Harbour porpoises. The latter tend to present hot-spots in coastal areas, while the former, tend to distribute further offshore.

These heat-maps are indeed very useful as a first approach but possibly not the best option to analyse all the information at the same time. Now that we have some hints, we are going to plot the distribution of the sightings based on the distance to the coast (in km of course) using the whole data-set for Common dolphins, Harbour porpoises, Risso’s dolphin and Minke whales. For those who are not used to looking at these graphs, I have created a second version of the same plot, but this time including some markers and flags to help understanding.

This graph is very revealing. As expected from the heat.maps, most of the sightings for Common dolphins occurred at more than 10 km from the coast, whereas in contrast, most of the Harbour porpoise sightings were recorded within 10 km away from the coast. As this distance increases, the number of porpoise sightings gradually decreases.

If we consider that the distance from Fishguard to Rosslare is 101 km approximately, we can deduce that the maximum recorded distance from the coast would be around 50 km. Thus, somehow, we would expect that either the species prefer coastal habitats like the porpoises, or oceanic habitats like the Common dolphins. Interestingly, the Minke whale, seems to prefer an in-between area, and most of the sightings were recorded at 10-30 km from the coast. Equally curious, the Risso’s dolphin seem to present a bimodal distribution, that means, the purple curve in the graph presents two “bumps” (one of them at around 5 km from the coast and a second one at around 30 km from the coast).

Why those distances? Is the distribution of these species only dependent on the distance to the coast? Or are there other features or variables that are driving these curious shapes? We will talk about it next week!
As always, we always welcome your ideas and inputs!

Hasta la vista! ... more next week... Cristina!

(By the way this post contains references to 3 songs that are superbly hidden in the text. Have you found them?)

All maps diagrams text and images © Copyright Sea Trust/Cristina Munilla unless other wise stated. Permission to use any of these Materials must be requested- email: seatrustwales@gmail.com