//
you're reading...

Biology

Facing the music: calls from one of the worlds most endangered dolphins

Amazon river dolphin. https://commons.wikimedia.org/wiki/File:Amazon_river_dolphin_5.jpg

The Study: Melo-Santos, G., Figueiredo Rodrigues, A.L., Tardin, R.H., de Sá Maciel, I., Marmontel, M., Da Silva, M.L., May-Collado, L.J. 2019. The newly described Araguaian river dolphins, Inia araguaiaensis (Cetartiodactyla, Iniidae), produce a diverse repertoire of acoustic signals. PeerJ: e6670. https://doi.org/10.7717/peerj.6670

 

River Dolphins

Figure 1. Images of Araguaian river dolphins depicting the two forms of behaviour examined in this study; socializing (A,B) and feeding (C,D) (Melo-Santos et al., 2019)

Inia araguaiaensis was first discovered in 2014 and is one of only five extant species of “true” river dolphins, four of which have “threatened” status (under IUCN). True river dolphins, also known as botos, are genetically distinct from other river-dwelling and marine dolphin species. Botos have flexible necks and backbones, large low dorsal fins, and a long slender rostrum (beak/snout). Exclusive to the Amazon, Orinoco, and Tocantins, these evolutionary relics are some of the rarest and most endangered dolphins in the world. Unfortunately, much less is known about botos than other dolphin species, partly due to the complexities associated with studying them. In a murky and complex habitat, these solitary cetaceans are difficult to detect. Our limited knowledge, coupled with their imminent extinction, makes boto research an urgent priority.

Figure 2. A spectrogram of dolphin vocalizations. Source: https://en.wikipedia.org/wiki/Spectrogram

Dolphin Vocalizations

Traditional vocalization studies, conducted on captive river dolphins, used spectrograms. Spectrograms are a visual representation of sound, graphed as frequency versus time (Fig. 2). These methods lack the ability to provide characteristic or quantitative information without further analytical tools. Previous research recognized few sound types in river dolphins, with many studies reporting only three sounds, and others even suggesting that Inia are silent. Later studies found up to six different types of sounds, but the number and type of sounds have caused contention in the scientific community.

 

 

Despite controversy over this topic, one thing is certain:

boto communication is vastly understudied.

 

The Study was cleverly designed to take advantage of a population of botos that regularly visit a fish market in the Tocantins River town Mocajuba, Northern Brazil. This sampling method reduced the difficulty associated with finding them while ensuring they remained free-rangeing. Throughout 2013-2016 boto acoustics and behaviors were monitored for three to fifteen days at a time. Sound recordings were taken using hydrophones (underwater microphones); video recordings were taken using GoPro’s (action cameras). Video recordings were used to acquire visual data including the number of individuals, age class, sex, individual identification (based on markings), and behavior. Two types of behavior were studied: socializing (physical contact or swimming alongside) and feeding (open-mouthed food soliciting, poking humans with snout) (Fig. 1).

 

To analyze the data the authors utilized the following acoustic programs and ecological principles:

  • ARTwarp program written in MATLAB
    • Categorize acoustic signals
  • Raven Pro software from Cornell Lab of Ornithology
    • Measures and analyzes sounds
  • Beluga program written in MATLAB
    • Further sound analysis
      • Call duration
      • Contours (pitch shifts)
      • subharmonics (frequency oscillation)
      • biphonation (two pitches at the same time).
    • Whittaker rank-abundance curve (Fig. 3)
      • Shows frequency of expression of each call
    • Rarefaction curve (Fig. 4)
      • Shows whether sampling efforts have saturated (i.e. further sampling would not be expected to find new features)


Figure 3. Whittaker rank-abundance plot of 237 unique sound-types ranked by abundance. (Melo-Santos et al., 2019)

Figure 4. Rarefaction curve of all call types discovered over the total cumulative 15.75 hours of acoustic recording (Melo-Santos et al., 2019)

 

 

 

 

 

 

 

 

 

 

What does it all mean?

Figure 5. Frequency contours showing 237 sound-type resulting from ARTwarp analysis of Araguaian botos from Mocajuba, Tocantins River.

From 727 sound clips, the ARTwarp analysis found 237 unique sound-types (calls), showing that Inia araguaiaensis have a significantly more diverse acoustic repertoire than ever before reported for the entire genus (Fig. 4). The Beluga and Raven programs showed that the majority of sounds were complex and non-linear, suggesting that calls contain information about individual identity, emotional state, and social dynamics (as previously shown in whales). Similar to Pontoporia (sister genus), call lengths were short and of intermediate bandwidth. Short, low-frequency calls have likely been selected for to avoid obstacles in a complex riverine habitat, while travelling father than calls of more gregarious cetaceans. The Whittaker plot showed that few calls were highly abundant (calf-mother interactions), while the majority were rare. This finding agrees with expectation since botos are typically solitary species with the exception of mother-calf interaction. In a complex, murky river mother-calf recognition may be facilitated by vocalizations. The rarefaction curve showed no asymptotic behavior, indicating that the 237 calls are likely not a full representation of the boto language.

 

Previous studies have shown that dolphins are highly intelligent and communicative animals, but little research has focused on out-groups, such as river dolphins. This work begins to untangle a possible link in the evolutionary development of cetacean communication. Gaining insight into both evolutionary linkages and animal behavior can be extremely beneficial in terms of conservation and management.

 

 

Video clip: https://www.eurekalert.org/pub_releases/2019-04/uov-mrd041619.php

Sound clips: https://peerj.com/articles/6670/#supplemental-information

 

 

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 5 days ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 2 weeks ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 3 weeks ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 1 month ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 3 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 3 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 4 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 4 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 5 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 5 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 6 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 6 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
  • by oceanbites 7 months ago
    Feeling a bit flattened by the week? So are these summer flounder larvae. Fun fact: flounder larvae start out with their eyes set like normal fish, but as they grow one of their eyes migrates to meet the other and
  • by oceanbites 7 months ago
    Have you seen a remote working setup like this? This is a photo from one of our Oceanbites team members Anne Hartwell. “A view from inside the control can of an underwater robot we used to explore the deep parts
  • by oceanbites 8 months ago
    Today is the day of  #shutdownacademia  and  #shutdownstem  and many of us at the Oceanbites team are taking the day to plan solid actions for how we can make our organization and the institutions we work at a better place
  • by oceanbites 8 months ago
    Black lives matter. The recent murders of Ahmaud Arbery, Breonna Taylor, and George Floyd have once again brought to light the racism in our country. All of us at Oceanbites stand with our Black colleagues, friends, readers, and family. The
WP2Social Auto Publish Powered By : XYZScripts.com