2019 is nearly over! As we reflect on our gratitude for all your support, you can check out new opportunities to join DCP that are right around the corner.
Plus, meet DCP's newest named dolphin - Kiwi, check out holiday gift ideas, help folks in The Bahamas & learn about our recent & upcoming publications & presentations.
This issue of the Dolphin Gazette is perfect for reading by the fire or under a palm tree, depending on where you live!
Thanks for reading - and sharing!
Long-term Bonds: Social Structure of Atlantic spotted dolphins (Stenella frontalis) off Bimini, The Bahamas (2003-2016) – WMMC & upcoming publication!
DCP is very excited about our poster presentation at the World Marine Mammal Conference in Barcelona, Spain. Lead author and long-time DCP assistant/student, Nicole presented our work on associations among the spotted dolphins off Bimini. If you saw the poster in person, thank you for your interest in learning more!
This study is the first to investigate the social patterns of a population of Atlantic spotted dolphins (Stenella frontalis) off Bimini, The Bahamas, during a 14-year period (2003-2016). We generated association indices and conducted cluster, network, and temporal analyses using SOCPROG 2.8. Dolphins in this group display long-term, year-round residency around Bimini, as well as long-term preferences in association with a combination of rapid disassociation, constant companions, and casual acquaintances. We found no evidence of distinct social clusters within the study group; however, we discovered at least one subgroup of males with higher association than the rest of the population. Despite strong relationships between males, we found no evidence for the existence of alliances or coalitions. Bimini spotted dolphins do not experience the same social forces thought to drive such supportive relationships in other study groups; they do not experience repeated aggressive interactions with sympatric bottlenose dolphins (Tursiops truncatus), nor are males limited in their access to females.
Over the course of this 14-year study, we completed 804 boat trips in search of dolphins. This resulted in 3,609 hours of search effort. On 628 (78.1%) of those boat trips (“surveys”), we saw dolphins from the boat and this resulted in 1,609 separate dolphin sightings. On 524 (65.2%) we were able to observe them under water at least once, and we actually had 873 underwater observations.
Take away lesson:
The Bimini Atlantic spotted dolphin social network is characterized by fission-fusion dynamics. Dyads form long-term preferential associations lasting years, especially between same-sex pairs.
A group of five male dolphins had the highest association throughout the study period (2003-2016). These males are similar in age and have been observed consistently since 2003. You might know them as Buster (#04), Split Jaw (#22), Prince William (#64), Tim (#69) and Speedy (#78). Split Jaw and Prince William have the highest strength of association over the full 14-year period (.68, where 1 would mean they were together all the time).
Another way of looking at things:
In this graph, you see the standardized lagged association rates for all individuals (2003-2016). Basically, this tells you the probability of seeing a pair together after a given amount of time. The technical stuff is: moving average was set to 50,000 associations; standard errors were calculated by jackknifing over 30-day periods. Best-fitted model was combination of “rapid disassociation” (within one sampling period), “constant companions” (social units that associate permanently), and “casual acquaintances” (social units disassociate but may preferentially re-associate). If this is interesting to you, make sure you grab a copy of the full paper when it’s published.
Why might dolphins form associations rather than just associate at random?
Preferred associations may improve foraging success or predator defense in deep Gulfstream waters. Or, preferences may have developed in early life from joint membership in mother-calf groups.
This work has just been published in the peer-reviewed journal, acta ethologica. Click here to access it or jot us an email.
Thanks for visiting our poster at the 2019 World Marine Mammal Conference. We're excited you wanted to learn more.
DCP has been studying bottlenose and Atlantic spotted dolphins off Bimini, The Bahamas since 2001. In 2014, we published a short note on the evidence of failed shark attacks on the spotted dolphins. Now, we've conducted a similar assessment on the sympatric bottlenose.
At least 28.7% of catalogued bottlenose dolphins had at least one injury or scar that could confidently be atttributed to a shark. Another 27.1% of catalogued individuals had injuries or scars that we couldn't be sure where they came from. This means that at a minimum almost 29% of catalogued dolphins survived at least one shark attack....but, it could be as high as 56%. This is higher than the 15% of spotteds with confirmed attacks and the 16% of spotteds with undetermined scars (for a maximum of 31% of the spotted catalog).
Plus - we don't get to see 100% of every individual's body. Only seven individuals (5.5% of the catalog) had images or video of 100% of the body. 21.7% we could see about 75%, 25.6% about 50%, 38.8% only 25% and 8.5% only the dorsal fin. This means that even our conservative estimates of how many dolphins have scars from sharks is likely an underestimation.
We also asked: "How many individuals had injuries or scars that could be confidently attributed to separate shark attacks?" This is at least 5.4% - but again, because we are conservative in declaring a scar shark-induced + we don't see every dolphin's entire body, this is a big underestimation. And, another 8.5% had scars that we could not say whether they came from the same or multiple attacks, bringing the potential, but still conservative estimate to nearly 14%.
Nearly all (97.3%) shark-induced scars were on the dorsal side of the body. Does this mean that sharks rarely attack the ventral side? That assumption is unlikely; what is more plausible is that the vental injuries are the most likely to be fatal.
When comparing the evidence of failed shark attacks on these two sympatric species (bottlenose 29%, spotteds 15%), or comparing dolphins off Bimini to dolphins elsewhere in the world, we cannot conclude that the bottlenose are actually attacked more (or less) often. Why? Because we do not have information on successful shark predation. The dolphins that do not survive, do not show up with scars for us to document.
Even with our conservative estimates, it's clear that sharks do prey on the dolphins off Bimini. Understanding this as best we can will shed light on behaviors we observe, from group formation to habitat selection.
Thanks again for your interest in our study. This study was presented as a poster at the 2019 WMMC in Barcelona, Spain. Stay tuned to see if it ends up as it's own short note, or a section on our larger bottlenose site fidelity assessment project.
It's baaaaaaack! Your chance to get a DCP shirt! This year, our adult short sleeve (5 colors) and adult long sleeve (white & gray) feature a throwback to DCP's original logo. 2020 is our 20th Anniversary!
Women's tanks (2 styles, 4 colors each) and UPF50 rashguards (4 colors) are also available featuring our current logo.
This special order period ends on Monday (Nov 18th). Shirts and bundles are expected to ship ~26 December. So, while they won't arrive for Christmas & Hanukkah, they will be worth the wait. By pre-ordering your shirt, you help DCP reduce the overhead of placing the shirt order with our printer (Thank you!!).
DCP is teaching several field courses at our Roatan field site. But, there is ONLY course with space available:
7 - 14 March 2020, Field Course in Animal Behavior & Psychology, in collaboration with St. Mary's University (StMU)
Remaining spaces are now open to non-StMU students. The course is taught by DCP's Dr. Kathleen Dudzinski and StMU Professor, Dr. Heather Hill. Tuition credits with StMU are not included, but are not required. Cost per student is $1550 (USD). This includes lodging, food, instruction and a dolphin swim and encounter. Tuition credits and airfare are not included. Email info[at]dcpmail[dot]org right away if you are interested! Remaining spaces will be filled on a first-come, first-serve basis. To learn more about Dr. Hill, find her among our collaborators under the About menu.