Life History Transmitters (LHX tags), were custom developed by Markus Horning in collaboration with Wildlife Computers specifically for research on the endangered Steller sea lion, see our project Life History Transmitters in Steller sea lions.

Life History Transmitters in Biology:

Data on survivorship is crucial for the effective monitoring and management of many species of marine endotherms, in particular endangered species and those potentially exposed to detrimental ecological and anthropogenic environmental changes, or climate related regime shifts. In addition, data on individual survivorship is needed to assess the efficacy of programs designed to ameliorate the impact of such changes and shifts.

Due to wide dispersal or migrations, and the open ocean ranging of marine endotherms, such data is extremely difficult to obtain. Survival of free-ranging animals is typically assessed through mark and recapture studies, or through the use of mortality transmitters. Mark and recapture studies are expensive and logistically complex to conduct, and highly disruptive in the rookeries of shy species such as Stellers. In addition, such studies cannot directly distinguish between dispersal / emigration, and mortality. Conventional mortality transmitters are externally attached VHF transmitters. Several problems are associated with such devices: on pinnipeds and seabirds, external units typically do not remain attached beyond the annual molt, limiting tracking to a maximum of one year. Battery-size and -capacity constraints also limit the life span of such units. Implanting mortality transmitters would avoid such problems. Implanted devices have been successfully used on a wide range of marine endotherms. However, reception range and thus area coverage from implants is reduced compared to external devices. Transmitting life span is still limited to 2-3 years.

A possible solution to extend coverage range for mortality transmitters is the use of satellite-linked devices. Satellite-linked data loggers, using the Argos system aboard NOAA satellites (accessible through Service Argos Inc.) for obtaining location fixes and transmission of stored data have been successfully and extensively used on oceanic vertebrates. At present however, transmission to a satellite from implanted devices is not feasible.

To circumvent this problem, the concept of implanted, delayed transmission, Satellite-linked Life History Transmitters (LHX) was developed by Markus Horning through the Laboratory for Applied Biotelemetry & Biotechnology (LABB) at Texas A&M University. Under seed funding from the North Pacific Marine Research Program, LHX devices were developed by the LABB in cooperation with Wildlife Computers. The LHX units consist of an ARGOS-compatible transmitter, a microprocessor driven controller, and five sensors for pressure, temperature, motion, light-level and conductivity. These LHX devices continuously monitor these built-in sensors to establish death of an instrumented animal, then store time and date of death in memory. Subsequently, the LHX devices will transmit this data to an orbiting ARGOS satellite, once the positively buoyant device has been released from the decomposing or consumed body. Through the absence of any transmissions, until after death, battery life is greatly extended to well beyond eight years.

An x-ray radiograph showing the intraperitoneally implanted LHX tag in the gut cavity, below the vertebral column and in front of the hip of the animal. The LHX tag is about the length of three vertebrae in this very small California sea lion.

The LHX tags were first deployed on rehabilitated California sea lions, at The Marine Mammal Center. These animals were relatively small, compared to the Steller sea lion the devices were developed for. On larger animals, such as this adult California sea lion that received dual tags, the devices are about the length of two vertebrae:

An x-ray radiograph showing two intraperitoneally implanted LHX tags adjacent to the vertebral column of an adult male California sea lion, and just anterior to the hip. The LHX tag is about the length of two vertebrae in this animal.

The LHX tags and their development are described in detail in this publication:

Markus Horning and Roger D. Hill (2005)
Designing an archival satellite transmitter for life-long deployments on oceanic vertebrates: The Life History Transmitter. IEEE Journal of Oceanic Engineering, Vol. 30 (4): 807-817.

One of the problems associated with this concept of "delayed-transmission" satellite-linked life history transmitters, is the impossibility of periodically transmitting an 'alive' signal, which is traditionally used to verify continued operation of the transmitter, and to guarantee the quality of the data obtained. In the absence of such transmissions of 'alive' signals, the accurate assessment of the transmission failure rate of implanted mortality transmitters becomes crucial. Mortality data obtained in form of positive 'deceased' signals needs to be corrected by estimates of failure rates. In the LHX project, the use of dual redundant implants is one of several approaches used to quantitatively assess instrument and transmission failure rates. Cumulative system failure rates are determined by comparing the ratio of dual versus single hits from two redundant LHX devices implanted into each study animal.

A required step before we can consider implanting LHX devices into free-ranging Steller sea lions - a declining and endangered species - is the validation of the LHX concept under highly controlled conditions, on captive animals.

This validation consists of two steps:

  1. Verification of the absence of post-surgical complications that could result from the procedures.
  2. Validation of proper operation of LHX devices, and at least a rough estimate of the failure rate of the system.

We will accomplish these validations through a combination of tests:

  1. Implanting dual LHX devices into rehabilitated California sea lions at The Marine Mammal Center (TMMC) at Sausalito, CA - a major marine mammal rehabilitation organization.
  2. Implantation of dual LHX devices into juvenile Steller sea lions under highly controlled conditions at the Alaska Sea Life Center (ASLC) in Seward, AK.
  3. Deployment of dual LHX devices on carcasses to simulate mortality events, along the Northern Pacific rim. The purpose of these carcass deployments is to assess the effects of non-independence of the two paired LHX tags on failure likelihood and thus on failure rate assessments.

We have now started all three of these tests. First results on some aspects of our validation studies are now available:

Mellish JE, Thomton J, Horning M (2007). Physiological and behavioral response to intra-abdominal transmitter implantation in Steller sea lions. Journal of Experimental Marine Biology and Ecology 351: 283-293.