Nautilus Research - Palau 2015
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- Опубліковано 11 лют 2025
- Update: The results of this research have been published:
Carlson B., M. Awai, W.B. Saunders, E.C. Franklin. 2021. Nautilus belauensis population demographics and trap yields in Palau were similar between surveys in 1982 and 2015. Mar. Ecol. Progress Series, 670: 239-245.
We had two primary goals while conducting this research and producing this video.
1. We wanted to determine if the Nautilus population in Palau has changed since the last extensive surveys were conducted 30 years ago. This is particularly important now because many Nautilus populations in other countries are rapidly diminishing due to world-wide demand for the shells.
2. We wanted to provide a guide to future researchers conducting similar work by establishing methods and protocols, and also how to ensure the safety of the animals throughout the catch and release procedure.
May 18 - 29, 2015, Palau: Checking catch-per-unit effort today versus 30 years ago when Dr. Bruce Saunders conducted his pioneering Nautilus research in Palau. Has the Nautilus belauensis population changed in 30 years? The data presented here are statistically significant (i.e. "no difference"), and indicate that at this time the population is stable.
Two important take-home messages have resulted from this work:
1) The data imply that the Nautilus population is probably stable, unlike in many other countries that routinely harvest them for the shell trade BUT ALSO
2) The Titan triggerfish is an aggressive predator on animals released following trapping at Short Drop Off, implying these fish have learned where dive shops release the Nautilus after the SCUBA diver's Nautilus dive. Please keep reading for details...
During research in May 2015 to assess the Nautilus population in Palau, we encountered a disturbing incidence of predation when the Nautilus were released after collection. We tied up to the buoy at Short Drop Off (SDO) and took the Nautilus to a depth of 130 ft (40 m) to release them. Almost immediately upon entering the water we were followed by a large Titan triggerfish (Balistoides viridescens). We didnʻt realize what would happen next, but as we pulled a Nautilus from our bag, the triggefish snatched it and swam off with it back up to shallower water. It came back a few minutes later to grab another Nautilus. We had a video camera running and captured the entire event (see video).
The triggerfish killed the Nautilus by biting them through the hood. It then deposited them under a ledge at about 60 ft (18m) depth. It was clearly agitated when we tried to rescue these animals, although it didnʻt attack us (which this species is known to do when guarding eggs).
When we released Nautilus at other locations away from the mooring buoy we were NOT bothered by triggerfish. This led us to conclude that probably others are releasing Nautilus at this SDO mooring buoy, perhaps for photography. If Nautilus are released at this same location over and over, it is highly possible that the triggerfish have learned to recognize the sound of the shells when they hit each other in the mesh bag, or perhaps the triggerfish can see the Nautilus in the bags, or they may actually smell the Nautilus, or simply hear the boat. Regardless of the stimulus, the triggerfish were quick to appear when we swam down the reef slope and they obviously “knew” what we were carrying.
To minimize this kind of predation on Nautilus, we recommend that dive shops do not use the mooring buoy at Short Drop Off as a release location, and do not use any site over and over for release. Instead, VARY THE RELEASE LOCATIONS. Secondly, release the Nautilus as deep as possible on the reef. We chose 130 ft (40 m) because the temperature is usually cooler (their upper depth range is limited by temperature) and the Nautilus have a better chance of reaching deeper depths more quickly. Alternatively, Nautilus can be released in blue water away from the reef and predators. If this method is used, be sure the bottom depth is no deeper than 2,000 ft (~610 m). Nautilus cannot live below ~2,500 ft (762 m) or they will implode.
[taxonomy:binomial=Nautilus belauensis]
Bruce thank you for posting this from your MACNA banquet talk. It's was wonderful to see you again.
You are doing excellent work. It’s a shame that the trigger fish can’t be deterred by some natural stuff they don’t like to give the nautilus a chance.
Great work!
is possible to see the nautilus without diving? using just snorkell?
No, Nautilus prefer cool deep dark water so seeing them on a shallow reef while snorkeling in the daytime is next to impossible.
Lori and Pat are still in Palau?
yes
cool video!
The release technique (perhaps unintentionally) was not in favour of the animal, maybe you should have dispersed them in a greater range of depth?
You didn't follow the story. When we released the animals in areas not frequented by divers, there was no problem. We accidentally discovered that it is not good to release them where divers go; in this case we used a mooring buoy used by dive companies. The dive companies have apparently captured and released nautilus for their divers at that spot in the past and the titan triggerfish learned that divers might have nautilus with them. The depth was not the problem; the location was the problem. Never release nautilus anywhere near where divers have been photographing nautilus on a regular basis. Normally, at a depth of 130' we should have been well below the normal depth range for the titan triggerfish, and in fact at the other locations we were never bothered by them. But going deeper than 130' also isn't a good idea given the very limited no-decompression limits for divers and the time it takes to release the animals.
Ah okay! Hadn’t read this before I posted. Thankyou
Fucking savages killing such lovely animals for there shells. Thank you for helping