DOES HABITAT ASSOCIATION OF DOLPHINS DIFFER BETWEEN ARTIFICIAL REEFS AND NATURAL REEFS?

 

Overview

Photo taken under the authority of NMFS LOC No. 15512.o.

Photo taken under the authority of NMFS LOC No. 15512.o.

The Eckerd College Dolphin Project (ECDP) is the longest running undergraduate-centered dolphin research program in the world, it was initiated in 1993 to conduct research on bottlenose dolphins (Tursiops truncatus) in Tampa Bay. The project was started by Dr. John Reynolds and is now led by Dr. Shannon Gowans and Dr. Peter Simard. Multiple students work year-round on a variety of projects investigating questions on the population, social structure, ecology, distribution and acoustic behavior of bottlenose dolphins.

Why is it important? 

It is important to investigate these basic questions in order to contribute to general knowledge regarding the biology, ecology, and behavior of dolphins, and to aid in the making of informed conservation and management decisions regarding dolphins and dolphin habitat.


Map of study area showing acoustic recorder stations.

DSG recorder deployed in the Gulf of Mexico. Photo taken under the authority of NMFS LOC No. 15512.o.

Research question

As a member of the ECDP, my research during the spring of 2016 was focused on comparing the relative abundance of dolphins at artificial reefs and natural reefs to test whether their associations differed between the two habitats (i.e. did the prefer one habitat over the other? Where they at one habitat more often than the other habitat?).   

Methods

  • Autonomous acoustic recorders were deployed at four artificial reefs and four nearby natural reefs from April 2013 to March 2015 in the eastern Gulf of Mexico.
  • DSG recorders operated on a 10 sec/10 min duty cycle (ex: record 10 seconds, stop for 10 minutes, record for another 10 seconds, etc.), resulting in 144 recordings per day. 

Analysis

  • Acoustic files were examined for dolphin sounds (whistles, echolocation, burst, jaw snaps, etc.) using Adobe Audition
  • Files were scored as dolphins present or absent
  • Dolphin relative abundance (detections / hour / km2) was calculated for each day using a detection range algorithm accounting for ambient noise and sound attenuation (Simard et al. 2015)
  • Differences in dolphin relative abundance between artificial and natural reefs within each pair were analyzed using t-tests

Figure 1: dolphin detections / hour / km2 for Clearwater artificial reef and 21 HS natural reef. Clearwater reef had significantly higher detection rates (t=4.194, p<0.001).

Preliminary Results

  • 9 days analyzed for Clearwater artificial reef and 21 HS natural reef (Figure 1)
  • 6 for Pinellas II artificial reef and Caves natural reef (Figure 2)

Figure 2: dolphin detections / hour / km2 for Pinellas II artificial reef and Caves natural reef. Pinellas II reef had significantly higher detection rates (t=6.518, p<0.001).  


Discussion

•This is the first study to investigate the relative abundance of dolphins at artificial reefs in comparison to natural reefs

•In both reef pairs investigated, the artificial reef site had significantly higher dolphin relative abundance than the natural limestone reef

•Previous studies have found high levels of association between delphinids and bathymetric variability (e.g., Atkins et al., 2004)

•Both artificial and natural reefs increase the local density of many fish species (Bohnsack, 1989)

•In our study area, artificial reefs may provide better foraging habitat for dolphins than natural reefs due to differences in prey species or abundance

•In both reef pairs, a seasonal peak occurred in June – July, corresponding to dolphin distribution patterns in the study area (Simard et al., 2015)

•These are preliminary results, refinements in analysis and additional days and stations will be included in final analysis

Acknowledgements & References

•Funding provided by the Florida Fish and Wildlife Artificial Reef Program, Eckerd College Natural Sciences Summer Research Program

•Field assistance from Pinellas Co. Dept. of Environment and Infrastructure, members of USF Fish Ecology Lab, and many others

Atkins et al. (2004) Spatial distribution of Indo-Pacific humpback dolphins (Sousa chinensis) at Richards Bay, South Africa: environmental influences and behavioural patterns. Aquatic Mammals 30: 84-93.

Bohnsack (1989) Are high densities of fishes at artificial reefs the result of habitat limitation or behavioral preference? Bulletin of Marine Science 44: 631-645.

Simard et al. (submitted)  Quantification of boat visitation rates at artificial and natural reefs in the eastern Gulf of Mexico using acoustic recorders. Ocean and Coastal Management.

Simard et al (2015) Dolphin Distribution on the West Florida Shelf Using Visual Surveys and Passive Acoustic Monitoring. Aquatic Mammals 41: 167-187.


Authors

Anjali Boyd(1)*, Catherine Gallagher(1)*, Brittany Evans(1), Emily Sullivan(1), Carly Olson(1), Nikki Szlamnik(1), David Mann(2), Christopher Stallings(3), and Peter Simard(1)

1: Eckerd College, St. Petersburg FL,

2: Loggerhead Instruments, Sarasota, FL,

3: University of South Florida College of Marine Science, St. Petersburg FL

*Primary/presenting authors

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