• Leanne Rosser

Back to Aomori: Dolphin Season 2021

My hopes of being reunited with the Pacific white-sided dolphins of Mutsu Bay were waning as the ongoing pandemic continued to cause disruption in Osaka. Yet with a little persistence I managed to squeeze in some last-minute fieldwork with the help of a memorial grant (The Honoka Fund*) intended to assist early career scientists such as myself. Returning back to the peaceful fishing village in Aomori prefecture, where my husband and I lived last year, was a refreshing treat of cleansing sea air and lush green mountains soaked in the golden glow of the Pacific light. We quickly settled back into the routine of morning coastal drives to the port, prepped with fully-charged cameras ready to board our fisherman captain's boat for a research survey in the bay.

The first day we had to tackle the choppy seas and bracing winds as we headed towards the mouth of the bay in search of dolphins. Every whitecap and wave seemed to be taking the deceptive form of a fin or the splash of a dolphin. We passed the usual feeding hotspot without seeing any of the familiar indicators of dolphins, such as birds diving or flocking together in anticipation of stealing a fish. The search continued with a growing sense of disappointment that accompanies a ‘no sightings’ survey so we decided to turn the boat back around to retrace our path. A sudden excited shout from my husband jumped us all into action, positioning ourselves on the bow to record the dolphin group in the distance and capture valuable photos of the dorsal fins that can be used for identification of individual dolphins. The small group of around 10 dolphins were hard to keep track of, surfacing unpredictably, difficult to spot amongst the rising waves, but our joy of finally having a sighting overshadowed the adversities.

Day 2 began with an eerie mist looming over the coast-lined mountains. We were joined by a drone team in the hope of recording feeding behaviour footage for our study. After the first 45 minutes of grey sea and sky a bursting succession of splashes appeared on the horizon, followed by an oncoming stampede of porpoising dolphins approaching on all sides of the boat. The drone was released into the air, speeding along to try and catch up with their rapid rush through the waves only to uncover that the dolphins were not feeding but socialising together in a flurry of excitement. Multiple groups spanned the surface as I perched on the bow trying to snap the passing blur of each fin. As a pelagic species, Pacific white-sided dolphins often travel in large groups as a safety in numbers strategy to remain alert to predators. Group living also allows dolphins to rest safely and hunt cooperatively. Here in Mutsu Bay these open ocean dolphins can be seen close to shore, making it a rare place to easily observe this species.

Day 3 occurred much like the day before with dispersed groups porpoising through the bay, some stopping to bow ride, twisting around one another and rolling on their sides to reveal striking black and white colouration just beneath the surface. Bow riding, scientists believe, is a way for the dolphins to conserve their energy by hitching a ride on the boat's momentum. Trying to shoot the scattered surfacings of these highly speedy oceanic creatures whilst struggling to keep your footing as the boat bounces along the bumpy sea is no easy feat. Each encounter is a rush of excitement in which I'm always left wanting more but what I love about studying wild dolphins is observing their whims, out at sea the encounter is on their terms.

I returned to Osaka with photos to sort through for any familiar or new fins to add to our ID catalogue, along with more research to write up in hopes of publication. As I begin preparations to leave Japan and return home to the UK my trip to Aomori gave me the boost I needed to get through this challenging time. Although I am unsure when I will return to Aomori, I have plans to continue working with the Mutsu Bay Dolphin Research team so I remain hopeful that I will be back someday in the near future. There is still so much to uncover about this amazing understudied cetacean.

By Leanne Rosser

© Leanne Rosser - Mutsu Bay Dolphin Research

*The Honoka Fund was established in memory of Honoka Morikawa whose valuable data is still used in the Mutsu Bay Dolphin Research Photo-ID catalogue. She is still considered a member of the team to this day.

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