Tursiops truncatus, the Bottlenose Dolphin, is found worldwide in
temperate and tropical areas, ranging from inshore to oceanic zones. They have
been known to participate in many types of group hunting, and prey on mostly
squid and fish (Hammond et. al, 2008). Two particularly interesting hunting
techniques have been documented, one involving role specialization in dolphins
within their social groups, and the other involving cooperation with humans for
mutual benefits.
Image: Photogapher "FOTOLEN" sourced from Flickr.com [Accessed 12 April] |
Role specialization
is unusual in the animal kingdom, and even considered rare. It involves
individuals within a group dividing up roles in the hunting technique, and
specializing in that role whenever the hunt is initiated. It was suggested that
individual foraging specialization techniques are more common in marine mammals
than terrestrial mammals (Gazda 2005).
Dolphins observed off Cedar Key in
Florida were seen to have a specific ‘driver’ in each group. The driver
herded the fish in tight circles, which acted as a barrier for the fish. Other
dolphins in the group (named the ‘barrier’ or ‘non-driver’ dolphins in the
study) would lift their heads out of the water and wait for the confused fish
to leap out of the water, and straight into their mouths. Two separate groups
in Cedar key were seen to have specialised roles of ‘driver’ dolphins,
demonstrating this rare example of role specialisation (Gazda 2005). Other dolphins have also been
observed using this hunting technique, however with the additional use of
stirring up "mud rings" with their tails, that act as barriers to channel fish
towards the rest of dolphins group waiting. (See video at the end of the post!)
Image: Photographer Todd Pusser [Accessed 12 April 2014] |
In Laguna,
Brazil, local fishermen catch mullet on a small scale fishing level,
providing mostly for self-consumption, but sometimes selling to the nearby markets.
One of the main fish that are sought is mullet, which are fished all year
around but more intensively during their migration months, which are April to
June. This time of year is strongly anticipated by the locals, who
cooperatively fish with groups of resident bottlenose dolphins. The residents
are a population of approximately 51 individuals, around 20 of which are
involved in the fishing activities with humans. Knowledge of this technique is
passed down from the elders to the young in the humans, and the female dolphins
are thought to pass it to their calves (Peterson 2008).
Image: Photographer "Alberto" sourced from Flickr.com [Accessed 12 April] |
The dolphins
herd schools of fish towards the fishermen’s boats and nets, and signal to the
men by doing a distinctive dive, letting them know when to throw their nets. The
dolphins then collect any stray fish, to eat for themselves. This unusual
friendship is strongly valued by the fishermen, who have affectionately named
each dolphin, and are able to recognize them individually. A video filmed by
the BBC shows the bond between the men and the dolphins, and provides an
insight into a truly unique method of hunting.
Mud Net Fishing in Florida
Dolphin Assisted Fishing in Laguna, Brazil
References
Gazda, S. K., Connor, R.C., Edgar,
R.K., Cox, F. (2005). "A division of labour with role specialization in
group-hunting bottlenose dolphins (Tursiops truncatus) off Cedar Key,
Florida." Proceedings of the Royal Society B: Biological Sciences 272(1559): 135-140. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1634948/?tool=pmcentrez&report=abstract
[Accessed 12 April 2014]
Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K.A., Karkzmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y. , Wells, R.S. & Wilson, B. 2012. Tursiops truncatus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 12 April 2014.
Peterson, D., Hanazaki, N., Simões-Lopes P.C. (2008).
"Natural resource appropriation in cooperative artisana between fishermen
and dolphins (Tursiops truncatus) in
Laguna, Brazil." Ocean & Coastal Management 51(6): 469-475. Available at: http://dx.doi.org.elibrary.jcu.edu.au/10.1016/j.ocecoaman.2008.04.003 [Accessed 12 April 2014]
Do you know if the dolphins keep the same hunting job throughout their entire life or if they change at certain times? Also, it's really interesting how the dolphins are able to work so well with the humans and how the tradition is passed on to the calves each generation.
ReplyDeleteHi Courtney! The papers didn't really specify whether the dolphins specialised in different roles at various stages in their life, but it could be possible that they switch roles with other group members.
DeleteFantastic post! Role specialisation in dolphins seems to be quite unique. I am curious though, is there role reversal (i.e. more than one driver), so that the driver also gets a chance to lounge around with its mouth open eating fish? ;) I also think that the bond between those people and that group of dolphins is astounding! Thanks for the amazing videos!
ReplyDelete