In the summers of 2024 and 2025, the New Zealand Department of Conservation conducted blue whale surveys (SAPPHIRE project) off the west coast. A concerning finding was very few sightings in 2024, while more were observed in 2025.

We are oceanographers and not whale experts, so we decided to look at physical differences between the two periods. Our speculation actually started because, as kite surfers, we had been complaining about the lack of good sessions during the summer of 2024…

Using the ERA5 from OCEANUM.IO, we rapidly computed the wind speed anomalies for January 2024 and January 2025 by comparing to the previous decade. The results showed notable shifts in wind speed intensity and distribution. January 2024 was significantly less windy.

Taking our analysis one step further,  we computed Lagrangian Coherent Structures (LCS) for both periods to assess zones of convergence and potential biological aggregation. See one of our earlier posts for our white paper on LCS methodology. The resulting LCS fields reveal very distinct differences between the years - zones of stronger attraction are shown in red while the weaker ones are blue on the plot.

Could such variations in ocean physics affect plankton distribution and, by extension, Blue Whale presence? LCS reveals key oceanic transport pathways, aiding marine biologists in understanding how flow patterns affect biomass distribution. Whales, for instance, likely use these structures to save energy during migration and foraging, as LCS highlight areas where prey concentrates due to converging waters and enhanced productivity.

It would be an interesting project to revisit previous years' survey data and re-run LCS using our high-resolution 3D hydrodynamic model. If you're working on Blue Whale ecology or interested in linking biological observations with physical ocean processes, please get in touch to discuss.

We are keen to collaborate and co-publish.

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