Ocean sunfishes, Molidae, comprise the world’s heaviest bony fishes. They include the short mola,
Coral reefs in and around the islands of Nusa Lembongan and Nusa Penida in Bali, Indonesia, support a thriving tourism industry with more than 200,000 tourists visiting each year [
Seasonal sea surface temperature (SST) climatology of the region showing lower temperatures in the second half of the year when
(a) 1 m TL
Little is known about the long-term movements or behavior of any species of ocean sunfish in Bali or the potentially disruptive effects of the region’s growing dive tourism pressures. A 2015 survey conducted by researchers from Udayana University, Conservation International, and Oceans Initiative off Bali’s southern coast from 30 Oct to 5 Nov estimates the ocean sunfish population to be 204 individuals in a survey region of 1393 km2, which translates to a mean density of 1 individual per 6.8 km−2 (Rob Williams
In September 2004 and October 2008, 4 pop-up satellite tags (2 PAT-4 tags in 2004 and 2 MK-10 PAT tags in 2008) were deployed on 4
Fish deployment (green) and pop-off (red) locations. (a) Indonesian regions where fish traveled. (b) 2004 deployments and pop-offs for Fishes A and B. (c, d) Fishes C and D in 2008. Pop-off locations based on location codes ≥1. See Table
Tag deployment summary.
Fish | Tag ID |
Deploy |
Pop-off |
SST (°C) |
Deploy |
Pop-off |
LC | TL cm | Days |
---|---|---|---|---|---|---|---|---|---|
A | 04P0144 |
Sep 15, 2004 | Oct 9, |
24° |
−8.71 |
−9.599 |
2 | 150 | 24 |
|
|||||||||
B | 04P0158 |
Oct 6, |
Oct 13, 2004 | 23° |
8.71 |
−9.989 |
1 | 135 | 7 |
|
|||||||||
C | 08A076 |
Oct 9, |
Apr 15, 2009 | 22° |
8.66 |
−8.674 |
3 | 100 | 188 |
|
|||||||||
D | 08A078 |
Oct 11, 2008 | Jan 8, |
26° |
8.71 |
−10.581 |
3 | 100 | 89 |
Vertical data were analyzed using transmitted time at depth (TAD) and time at temperature (TAT) histograms and profiles of depth and temperature (PDT) data summarized at 12-hour intervals. The thermal habitat was characterized by creating a cross section of the water column traversed by the fish, while the habitat preferences were characterized by the amount of time spent in a range of depth and temperature bins. Analyses were performed in MatLab (The MathWorks, Inc., Natick, MA, USA).
To examine oceanographic variability in the greater region surrounding Bali, we examined satellite sea surface temperature (SST) data on 2 time scales: (1) a climatology based on 12 years (2004–2015) of data, binned to 3-month seasonal means, and (2) a single average for September-October 2004, when 2 tag deployments successfully returned water column data. Original SST data for these analyses were global monthly means of Advanced Very High Resolution Radiometer (AVHRR) data (
In 2004, Tag 52918 on Fish A popped off prematurely after 24 days of deployment and Tag 52943 on Fish B popped off after 7 days. Both tags provided pop-off locations roughly 150 km south of the deployment location in Nusa Penida. In 2008, Tag 89297 on Fish C popped off as scheduled after 188 days and surfaced less than 10 km from its initial deployment location, while Tag 89298 on Fish D popped off prematurely after 89 days, surfacing 747 km to the east. Both 2008 tags provided pop-off locations, but too little temperature and depth data to analyze (Table
Three of the four tags popped off in relatively close proximity to the deployment location on Nusa Penida (Figure
Sea surface temperature (SST) during September-October 2004, coincident with tagging period. Deployment (green) and pop-off (red) locations for Fishes A and B.
In 2008, Tag 89297 (Fish C) popped off on the north side of Nusa Penida, less than 10 km from the original deployment location, 188 days earlier. Only one of the tags, 89298 (Fish D), revealed significant movement away from the Nusa Penida region, popping up 747 km to the east of its deployment location, near the island of Savu after an 89-day deployment. Additional long-term tagging data are required to determine the degree of long-term site fidelity to the Nusa Penida region.
Combined 2004 data from Fish A and Fish B showed that the majority of time was spent in the upper 250 m south of Bali, ~45% in the upper 50 m and 50% between 50 and 250 m (Figure
Summaries of depth and temperature range occupation based on all 2004 data from Fish A and Fish B.
Following tagging, Fish A stayed in warm, shallow (<40 m) waters during the first few days and then began much deeper dives, to 200–400 m, consistent with its movement offshore into deep water (Figure
Depth occupation in relation to water column thermal structure for 2004 data from Fish A, tag 52918. (a) Thermal cross section of water column traversed by fish; each vertical bar represents a 12 hr time period, extending to the deepest point reached during the period and color-coded by temperature. Black contours define corresponding time at depth (TAD) >25%. (b) Corresponding TAD section.
Previous observations on
In comparison,
Additional site fidelity and behavioral data of
The short ocean sunfish
The authors declare that they have no competing interests.
Funders include Conservation International, AAAS Women’s International Science Collaboration (WISC) grant, and National Geographic Conservation Trust Grant C298-15. Special thanks are due to Brett Hobson, Michael Cortenbach, Sven Fautz, Bali Dive Academy, Aidah A. A. Husain, Tim Rock, Chris Paporakis, Ambo Tuwo, Iwan Dewantama, Jos and Lida Pet for logistics and tagging; Rob Williams for survey data; Marianne Nyegaard, Marthen Welly, Rili Djohani, Mohammad Erdi Lazuri, and Coral Triangle Center for continuing this research. Research was conducted under an Indonesian research visa IMT.2.GR.01.06.03.3349DG.315 to Tierney Thys.