Issue 3, October 2006

Hawaii Institute of Marine Biology Tests VEMCO's New pH Transmitter

VEMCO, working with a team of researchers at the University of Hawaii, has successfully integrated a pH sensor produced by Earth & Ocean Technologies of Kiel, Germany, into a VEMCO continuous 2-channel sensor transmitter. The transmitter, which also contains a temperature sensor, can be detected and recorded by VEMCO's VR100 tracking receiver. The prototype units can also be modified to be a coded tag detectable by VEMCO's VR2 and VR3 receivers. This development is an example of VEMCO's long history of working with the research community to expand our collective knowledge of fish behaviour and environment. For more information on similar projects, check out VEMCO's web page on experimental sensor transmitter design.

The researchers at the University of Hawaii are using pH sensing to gather information regarding the feeding habits of large pelagic fish to gain insight into the frequency of feeding and the size of meals. Their previous research employed a pH data logger, however; in order to gain useful information about animals in the wild, it was determined that a transmitter was needed.

The pH transmitters are currently being tested on captive, free-swimming, black-tip reef sharks living in a lagoon at the Hawaii Institute of Marine Biology's research facilities on Coconut Island, Oahu, Hawaii. The work is being spearheaded by Yannis Papastamatiou, a graduate student with Dr. Kim Holland's group at HIMB. The tags are being developed as part of the "Smart FAD" project on which Dr. Kim Holland and Dr. Laurent Dagorn of IRD are co- Principal Investigators.

The transmitters are wrapped in a piece of squid and inserted into the shark's stomach through a plastic tube placed in the shark's mouth. After about 24 hours, the sharks resume feeding and are fed known amounts of different types of food. The acoustic signals, produced by the tags in the shark's stomach, are detected by a hydrophone submerged near one end of the lagoon.

Yannis Papastamatiou inserts a squid-wrapped tag into
a shark's stomach via a large plastic insertion tube.

Initial test results are consistent and show very low pH levels (high acidity) are normal in the stomachs of this species. Ingestion of food causes a temporary decrease in acidity related to meal size and type. The next phase of the research will involve deploying the transmitters in free-ranging wild sharks.

The pH device contains a vial of electrolyte solution. It works by having a continual outflow of electrolyte which prevents contaminating matter (i.e. stomach fluids) from diffusing into the electrode and causing the probe to drift. This is particularly important in diving animals as the increase in pressure can increase contamination of the probe. The device lasts for as long as the reservoir of electrolyte fluid. With the current design, there is enough fluid to last 16 days. It is feasible for a larger animal to carry a larger device with more electrolyte solution and, therefore, a device lasting several months could be developed. Investigations are also underway to look into the viability of extending the life of the current reservoir by reducing flow while still maintaining sufficient accuracy to properly measure feeding.

The prototype sensor comes in a titanium case measuring 25mm x 169mm, which can be opened to refill the electrolyte fluid and replace the batteries. VEMCO's pH Sensor transmitter is available as a custom order. Please contact VEMCO Sales for more information on pricing and delivery.