Do Sharks Prefer Fish Blood to Human Blood?

TL;DR

Sharks strongly preferred the fish blood mixture in this controlled test, making 134 approaches compared with eight approaches to mammal blood and zero to seawater. Three remotely pumped surfboard stations were anchored far from the boat and observed by drone for an hour, reducing the chance that the boat or the boards themselves explained the sharks’ behavior.

Transcript

• This is a specialized human-shaped shark cage I designed. And this is me in the middle of a shark feeding frenzy in that cage, which as it happens, doesn't actually keep the sharks out. They're in the freaking cage. But to understand how I ended up in the middle of The Bahamas with buckets of blood, surrounded by a butt ton of sharks, we've gotta... Read More

Key Insights

• The fish blood mixture attracted far more shark activity than mammal blood under the conditions tested. Drone footage recorded 134 approaches to the fish mixture, compared with eight approaches to mammal blood and zero approaches to the seawater control.
• The seawater station was a control for interest in the experimental equipment. Because no sharks approached that board, the observed activity around the other boards was associated with their released contents rather than simple attraction to the surfboards.
• The mammal blood station contained cow blood instead of five gallons of human blood. The substitution was made because obtaining that quantity of human blood legally was difficult, and shark scientists consulted for the experiment said mammal blood smells essentially the same to sharks.
• The experiment used equal five-gallon buckets and custom pumps to create a direct comparison. Fish mixture, mammal blood, and seawater were released from separate anchored surfboards over the same one-hour observation period.
• The surfboards were placed far from the boat to address a limitation of the earlier test. The team reasoned that sharks near the boat might ignore a blood source because they were waiting for food to be handed out from the vessel.
• The backup system preserved the experiment after the remote trigger failed. Code in each pump was designed to start it automatically if no remote signal arrived after one hour, and that untested redundancy activated at the planned time.
• The previous experiment challenged the movie myth that a small amount of human blood automatically causes sharks to attack. It released 15 drops of human blood per minute for an hour near multiple sharks, which showed little interest.
• The fish mixture was selected for the cage demonstration because it produced the strongest measured response. The team prepared large bags of the mixture for release near a specialized human-shaped cage, while the participant wore steel chainmail and a weighted vest.

Questions & Answers

Q: Do sharks prefer fish blood or human blood?

The sharks in this experiment showed a strong preference for the fish blood mixture over the tested mammal blood. Drone footage recorded 134 approaches to the fish mixture board and eight approaches to the mammal blood board during the one-hour test. The seawater control received zero approaches, indicating that the surfboards alone did not attract the observed activity.

Q: How was the shark blood preference experiment conducted?

Three surfboards were anchored to the ocean floor far from the boat. Each carried a five-gallon bucket containing either a fish blood mixture, mammal blood, or seawater. Custom pumps released the contents over one hour, and a drone recorded shark activity. The researchers then reviewed the footage and counted approaches to each separate board.

Q: Why was cow blood used instead of human blood?

Cow blood was used because legally obtaining five gallons of human blood was difficult. According to the account, shark scientists consulted before the test had experimentally shown that mammal blood essentially smells the same to sharks. On that basis, the team treated cow blood as a practical substitute for human blood in the controlled comparison with fish blood.

Q: How many sharks approached each blood station?

The final tally counted shark approaches rather than a stated number of unique individual sharks. The fish blood mixture board received 134 approaches during the observation period. The mammal blood board received eight approaches, while the seawater control received zero. These results created a clear difference among the three treatments under the experiment’s specific conditions.

Q: Why did the experiment include a seawater control?

The seawater control helped determine whether sharks were merely interested in the surfboards or experimental equipment. It used a board and pumping setup like the blood stations but contained seawater. Because that control received zero shark approaches, the results supported the conclusion that the released blood mixtures, especially the fish mixture, were responsible for attracting shark activity.

Q: Why were the surfboards placed far from the boat?

The boards were moved far from the boat to reduce a possible confounding variable identified in the previous experiment. Sharks near the vessel might have smelled the blood but chosen not to investigate because they were waiting for a handout from the boat. Placing the stations in open water made the released liquids a more isolated attraction source.

Q: What happened when the remote pump trigger failed?

The custom remote trigger did not send the signal needed to start the three pumps, apparently because it had been damaged during shipping. The system included redundant code that would automatically activate each pump if no remote start signal arrived after one hour. Although that feature had not been tested beforehand, it activated on schedule and saved the experiment.

Q: Does one drop of human blood make sharks attack?

The earlier test described in the account did not support that movie-style claim. It released 15 drops of human blood per minute for an hour near several sharks, yet the sharks showed little interest. The later comparison also recorded only eight approaches to mammal blood, while fish blood produced 134, suggesting that blood source mattered greatly in these tests.

Summary & Key Takeaways

• The experiment compared shark responses to equal five-gallon buckets placed on three surfboards. One contained a fish blood mixture, another contained cow blood as a substitute for human blood, and the control contained seawater. Custom pumps released each liquid over an hour while drone footage recorded sharks approaching the separate stations.

• The researchers positioned the surfboards far from the boat because proximity had been a limitation in the previous human-blood experiment. All three boards were anchored to the ocean floor. When the remote trigger failed, backup code automatically activated the pumps after one hour, allowing the planned comparison to proceed under consistent conditions.

• Drone footage showed a large difference among the treatments. The fish blood board received 134 shark approaches, the mammal blood board received eight, and the seawater control received none. Based on those observations, the team selected the fish mixture to attract sharks around a specialized cage during the following day’s feeding-frenzy demonstration.