Trip Report for February 11th - 18th, 2012

Flukes splashed at the surface and bodies rolled over at the top. Several males in the encounter gave us easy gender ID as they layed with their ventral surfaces facing up at the surface with clear view of their bright red genitalia. The image below captured a moment of sociosexual interaction between several males.

Some time into the encounter the contexts of these interactions began to emerge. Several individuals, with at least two males, were vigorously pursuing a smaller individual. Ton (TA169), a heavily scarred male, and Blotch (TA172), a male with a prominent dark spot along the trailing edge of his dorsal fin, attempted to mount the smaller dolphin, at times flanking the smaller dolphin on each side as it seemed to attempt to evade its suitors. Male bottlenose dolphins are known for their competition for reproductive access to females, forming alliances with one another to potentially improve chances for access to reproductively ready females. In some populations pairs of males have even been known to "herd" females by preventing her escape for up to several weeks. Gender ID of the third individual at some point in the future will be needed to confirm whether this may have been a sexual encounter for reproduction or the sociosexual kind. 

Within an hour the vigorous socializing had ceased and five of the dolphins had departed leaving only Ton, Blotch, and another individual milling along the caye. A rare occurrence, assessing that there were no calves or intense activity in the water, Ginger and I were able to slip into the water with the dolphins. Once the data has been collected and condtiions are optimal it is sometimes possible to attempt to acquire gender ID of an animal by observing it's genital slit underwater. After kicking furiously to catch up to them we were able to get a glimpse of the group as they swam towards us, briefly inspecting before changing direction and slowly swimming forward. 

 

 

We remained a comfortable distance from them, highly aware that this was not our world we were in; it was an aquatic world who's denizens should be afforded respect. Though we were not able to identify the sex of the third member of the group, we were grateful to have a chance to see the dolphins in their habitat first-hand. Several minutes into our swim they vanished into the shallows and we returned to the boat. Returning to the station, the trio were left quietly swimming into Fishing Bogue in waters three feet deep.

 Ginger and I inched along at our snorkel site along the eastern entrance of Fishing Bogue (image to your left). Turbid waters encircling the mangroves become crystal clear walls when you come face-to-face with the edges of the cayes. Here we find veritable displays of the biodiversity of life embedded in the labyrinth of the mangrove's roots. We entertained ourselves with the sights of bright orange sponges mushrooming from branching mangrove roots. Sea anemones and brittle seastars occupied the innards of the sponges with small fish and crabs craftily sliping away into the caye at our passing shadows. A long-snout seahorse (Hippocampus reidi) in bright yellow with brown bands along its back fastened to a root with with tail wrapped tightly. This tiny creature is often cleverly camouflaged amidst the mangroves where it feeds on the zooplankton and small crustaceans abundant in this ecosystem, but at the time it seemed a rather vibrant and conspicuous sight in the murky water.

After a time snorkeling along the edge of the mangrove habitat we turned towards the boat to Alton’s calls that a dolphin was here. Swimming hurriedly back and boarding Miss Callie, we set off behind a lone individual as it swam into Harry Jones Cut.

Luckily the dolphin was surfacing and making slow and prolonged exposures of his dorsal fin and flukes while making deep dives. With some fortunate surfacings we were able to identify the animal as Propeller; a resident male dolphin who is one of the few dolphins I find roaming the atoll alone. Only with us for a couple of minutes, his movements prevented a good of what he may have been doing but from the underwater footage we were able to see him swim directed towards the boat, turning abruptly, and rubbing himself against the bottom before swimming off.

 

 

  Often when foraging and socializing the dolphins can be seen with parts of their body against the substrate, stirring up mud plumes where they make contact. With touch playing such a major role in dolphin sensory worlds, Propeller may have been simply engaging in a pleasureful activity, rubbing his sensitive skin against the silty substrate before continuing on his way east into Harry Jones Cut.

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Big thanks to Ginger and Liz for joining our trip and supporting the research. Thanks to all of our guests for the week for coming down and supporting the station! Our volunteers make the on-going research possible. 

More entries to come from this busy field season! 

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