Predation detection fish tracking tag

Abstract

A tracking tag for aquatic animals may detect the occurrence of a predation event. The tag may include a pH sensitive material that degrades in the environment of an animal's gut. The degradation of the pH sensitive material causes a change in a detectable characteristic of the tag, which allows the tag to detect the predation event and adjust its operation accordingly.

What is claimed is: 
     
         1 . A tag for tracking an aquatic animal comprising:
 a sensor for detecting a characteristic of the tag;   a pH sensitive material exposed to an external environment of the tag, the pH sensitive material degrading in the presence of an acidic environment, the degradation of the pH sensitive material causing a detectable change in a characteristic of the tag detected by the sensor indicative of occurrence of a predation event;   a transducer for transmitting an ultrasonic signal based on at least the detection of the characteristic of the tag by the sensor; and   a microprocessor coupled to the transducer and the sensor, the microprocessor controlling the transmission of the ultrasonic signal by the transducer to communicate the occurrence of the predation event.   
     
     
         2 . The tag of  claim 1 , wherein the acidic environment is a gut of a predator fish. 
     
     
         3 . The tag of  claim 1 , wherein the pH sensitive material does not degrade substantially in a neutral or basic environment. 
     
     
         4 . The tag of  claim 3 , wherein the neutral or basic environment is a coelomic cavity. 
     
     
         5 . The tag of  claim 4 , wherein the sensor for detecting the characteristic of the tag comprises a magnetic field sensor capable of sensing a presence or absence of a magnet, wherein the magnet is fastened to the tag by the pH sensitive material such that the magnet is released from the tag when the pH sensitive material degrades in the acidic environment and a change in the presence or absence of the magnet detected by the sensor when the magnet is released provides the indication of the occurrence of the predation event. 
     
     
         6 . The tag of  claim 1 , wherein the pH sensitive material comprises a chitosan. 
     
     
         7 . The tag of  claim 6 , wherein the pH sensitive material is cast from a slurry of the chitosan and a solvent. 
     
     
         8 . The tag of  claim 7 , wherein the solvent is selected from:
 L-ascorbic acid;   citric acid;   acetic acid; and   hydrochloric acid.   
     
     
         9 . The tag of  claim 6 , wherein the pH sensitive material comprises a film having a thickness of at least 0.05 mm. 
     
     
         10 . The tag of  claim 9 , wherein the pH sensitive material comprises a film having a thickness of at least 0.20 mm. 
     
     
         11 . The tag of  claim 6 , wherein the pH sensitive material comprises a plasticizing agent. 
     
     
         12 . The tag of  claim 11 , wherein the pH sensitive material was treated with a cross-linking agent. 
     
     
         13 . The tag of  claim 12 , wherein the cross-linking agent is selected from:
 sodium citrate;   sodium sulfate; and   calcium chloride.   
     
     
         14 . The tag of  claim 1 , wherein the microprocessor operates in at least one of a first mode or a second mode based on at least the detection of the characteristic of the tag by the sensor. 
     
     
         15 . The tag of  claim 14 , wherein the microprocessor switches from operating in the first mode to operating in the second mode when the detection of the characteristic of the tag by the sensor changes as a result of a degradation of the pH sensitive material in the presence of the acidic environment. 
     
     
         16 . The tag of  claim 1 , wherein the microprocessor operates in at least a configuration mode for transferring data to the tag to configure operation of the microprocessor. 
     
     
         17 . The tag of  claim 16 , wherein a varying magnetic field is used for transferring data to the tag when the microprocessor is in the configuration mode. 
     
     
         18 . The tag of  claim 17 , wherein the microprocessor further operates in at least a calibration mode for determining a value for a compensation magnetic field to allow detecting of the varying magnetic field used for transferring data in the presence of a constant magnetic field. 
     
     
         19 . The tag of  claim 18 , wherein the microprocessor calculates the value for the compensation magnetic field and transmits the calculated value for the compensation magnetic field to an activation device. 
     
     
         20 . The tag of  claim 18 , wherein the tag transmits an indication of detected magnetic field in order to allow an activation device to calculate the value for the compensation magnetic field.