Looking for Part 1 of this article? Click here!
Author's note: since we operate commercial whale watching trips supported by land-based lookouts,
there are several sources of bias potentially affecting our sighting data.
For this reason, the analysis below should be considered a work in progress - a simple, preliminary attempt to find patterns
in the data we collected.
Furthermore, the hypothesis we formulate here cannot be put to test based on our data alone, so that the main
goal here is to stimulate discussion and, hopefully, contribute to further studies on larger, more appropriate datasets.
Remember from Part 1:
if there is a lot of phytoplankton in March (for which we use chlorophyll concentration
proxy), you will find a lot of krill in April. With a high concentration
of phytoplankton in April, you will see a high abundance of krill in May, etc. For this reason, to achieve a better graphical
representation of the correlation between chlorophyll concentration and baleen whale sightings, the number of sightings for any month is
superimposed with the chlorophyll value referring to the month before.
How do baleen whales know in advance how much krill there is going be off the Azores on any particular season?
Probably, they don't!
However, whales do remember the spots that, historically, turned out to be good foraging grounds
and they keep visiting them year after year.
Baleen whales are aware there are yearly fluctuations in food availability in any particular spot and they can
definitely live with that.
In years where krill is relatively scarce in the Azores, they will not linger for long. However, they are not all
migrating at the same exact time, so that we never, ever had a spring without baleen whales!
A Whale migration is an unbelievably long journey, especially if you consider the round trip.
Baleen whales migrate because having two distinct habitats (one for breeding, one
for feeding) is an energetically favoured strategy, despite the high cost of moving between them.
Baleen whales leave the Azores some time in late spring when food here becomes scarce.
They know there will be more to eat in the summer at higher latitudes.
In other words, they do not go all the way to Norway, Iceland, Greenland, etc. to keep fit and they would be happy to stay
longer in the Azores if krill kept being plentiful.
In a world where climate change is such a serious issue, it is important to keep monitoring the migration routes of animals such
as baleen whales, as well as their timing.
The chlorophyll data used in this article were produced with the Giovanni online data system, developed and maintained by the NASA GES DISC.
J. G. Acker and G. Leptoukh, “Online Analysis Enhances Use of NASA Earth Science Data”, Eos, Trans. AGU, Vol. 88, No. 2 (9 January 2007), pages 14 and 17.