OceanSentinel: Hammerhead Tagging

Ethically deploy tags on hammerhead sharks to log position, depth and key environmental parameters—including salinity, dissolved oxygen, turbidity/TSS, temperature and pressure—while attached to the animal (see the practical guide below). Each tag continuously monitors its position relative to OceanPulse buoy locations and ensures that a minimum monitoring period has been completed before release. Once both conditions are met—minimum monitoring period elapsed and trigger conditions relative to buoy locations satisfied—the tag automatically releases, floats to the surface and transmits the stored data via LoRa/LoRaWAN, enabling reliable, autonomous data collection without manual retrieval.


OceanSentinel extends the Argo principle into the biological domain—rather than profiling static water columns with floating sensors, it uses the hammerhead shark as a mobile sampling platform, while static OceanPulse buoys provide reference points for navigation, monitoring and trigger-based data collection. While Argo provides coarse global coverage, OceanSentinel can reveal fine-scale, behaviorally contextualised environmental data from otherwise under-sampled regions. The two systems are complementary: Argo defines the ocean’s “macrostate,” while OceanSentinel reveals its "microdynamics" as experienced by living organisms.


Together, the two systems are complementary:

In other words, Argo paints the ocean’s big picture; OceanSentinel fills in the fine details — the microdynamics — that show how organisms respond to their environment in space and time.

Update — Added Oceanographic Sensors
Update
What's new: support for oceanographic sensors — salinity (conductivity), dissolved oxygen (optical optode), turbidity/TSS (optical turbidity), plus guidance on calibration, sampling, compression and power impact.
1) High-Level Design
  • Goal: continuous logging of timestamped depth, GNSS (on surface), and oceanographic sensors (conductivity → salinity, temperature, dissolved oxygen, turbidity/TSS) while attached; transmit summary/packets on surfacing.
  • Maintain existing low-power state while submerged and only power high-draw sensors/radio/GNSS when necessary.
  • Use depth/combo wet-dry to decide surfacing and GNSS enablement. On surfacing acquire prioritized fixes (1–3) then transmit summary; optionally continue transmitting more packets respecting duty cycle.
  • Carefully balance the cost of tags and sensors against retrieval efforts and potential environmental impacts.
2) Mechanical / Attachment Considerations
  • Attachment, hydrodynamics, release mechanism recommendations unchanged — note additional sensors will require small sensor ports or cable exit points; keep tether/housing streamlined. Place sensor faces away from tether shadowing where possible.
  • For salinity/DO/turbidity probes prefer short rigid/arm-mounted probes that protrude slightly from the housing to reduce boundary-layer contamination from the housing during logging and to help flushing while the animal is moving.
  • Protect sensors during deployment with sprung caps or quick-release protective shrouds that expose the sensor after tagging (optional).
3) Electronics & Sensors — Recommended Additions

Core idea: add an embedded CTD/conductivity probe for salinity (or small conductivity sensor + temperature), an optical dissolved oxygen optode, and a compact turbidity/TSS optical sensor.

Suggested sensors (examples)

  • Conductivity / Salinity: mini conductivity probes or small CTD modules.
  • Dissolved Oxygen (DO): optical DO optodes (low drift, long-term stability).
  • Turbidity / TSS: optical turbidity meters that can be converted to TSS with calibration.
  • Temperature: precision thermistor or PT1000 (part of CTD stack).
  • Pressure / Depth: MS5803-14BA or equivalent remains recommended.

Updated BOM Highlights

  • Conductivity probe (mini CTD or discrete conductivity probe + temp sensor)
  • Optical DO optode (low-drift optode)
  • Optical turbidity sensor (small Nephelometer)
  • Low-noise analog front-end or digital interface for probes
  • Sensor mounting hardware & protective shrouds

Prototype cost varies: maker sensors (hundreds GBP) → scientific CTD/optode/turbidity (thousands GBP).

4) Firmware & Logic (Changes for Ocean Sensors)

Key changes: poll additional sensors on the logging loop, store calibrated values, manage per-sensor warm-up and calibration cycles to avoid long power-on times.

// simplified pseudocode
State = ATTACHED
Loop:
  read depth, wet_dry, accel
  if depth > DEPTH_THRESHOLD:
    if time_to_sample(CTD): wake_cond(); read_cond_temp(); compute_salinity(); sleep_cond();
    if time_to_sample(DO): wake_DO(); read_DO(); sleep_DO();
    if time_to_sample(TURB): wake_turbidity(); read_turbidity(); sleep_turb();
    log_point(timestamp, depth, accel_summary, temp, salinity, DO, turbidity)
    sleep(SLEEP_INTERVAL)
  else if surface_event_detected():
    enable_gnss(); get_fix(); store_fix()
  if release_detected(): State = SURFACED

Sampling Strategy & Calibration

  • CTD: short warm-up, 2–3 rapid consecutive samples averaged.
  • DO: brief stabilization period after power-on.
  • Turbidity: short averaging window; manage biofouling.
  • Metadata: store calibration coefficients and timestamps.
5) Data Format & Compression (Extended)

Keep compact binary format but extend to include new parameters.

// Header (per packet)
TagID(4) | FWver(1) | PacketIdx(2) | TotalPkts(2)
// For each point:
t_delta(uint16) | lat_delta(signed24) | lon_delta(signed24) | depth(uint16 cm)
temp(int16 deci-degC) | salinity(uint16*0.01 PSU) | DO(uint16*0.01 mg/L) | turb(uint16*0.1 NTU) | accel8
// CRC(2)
  • Quantize carefully; transmit full-fix once, then deltas.
  • Include calibration block with coefficients and sensor IDs.
6) LoRa Transmission Strategy
  • Send summary-first packets with key metrics, then additional packets if airtime allows.
  • Respect EU868 duty cycle; use confirmed uplinks sparingly.
7) Power Budget (Impact of New Sensors)

Rule of thumb: conductivity and turbidity sensors have modest impact; DO optodes can draw more depending on type.

  • Estimate per-sample energy including MCU wake, warm-up, and flash write.
  • Adjust battery capacity or reduce sampling rate as required.
8) Testing & Validation
  • Bench calibration: conductivity vs reference CTD; DO vs Winkler titration; turbidity vs TSS lab samples.
  • Saltwater tank tests: verify drift, fouling resistance, corrosion.
9) Permits, Ethics & Safety

Permits and animal-ethics approval remain required. Additional sensors may affect weight and buoyancy; confirm with review boards.

10) Server / Backend & Decoding
  • Decoder updates: handle new fields and scaling factors.
  • Store calibration metadata; visualize parameters over time and depth.
  • Export GPX/KML and CSV for analysis.
11) Practical Recommendations / Tradeoffs
  • Prefer optical DO for long-term stability.
  • Use integrated CTD for compact low-power setups.
  • Rely on turbidity→TSS conversion with local calibration.
  • Recover tag when possible for full data retrieval.

Hammerhead Shark Sensor Deployment — Practical Guide

Hammerhead sharks are agile and wide-headed predators that present unique hydrodynamic challenges for tagging. The following guidance outlines which sensors are practical to deploy, what operational constraints apply, and a recommended sensor stack.

Sensor TypePracticalityNotes
Temperature (thermistor or CTD)★★★★★Robust, low power; standard for habitat profiling.
Pressure / Depth★★★★★Essential for vertical dive behavior studies.
Conductivity (for Salinity)★★★★☆Feasible with anti-fouling and good flow exposure.
Accelerometer / Magnetometer (IMU)★★★★★Common for motion and orientation tracking.
GNSS (surfacing only)★★★★☆Useful on floating or post-release tags.
Optical Turbidity / TSS★★★☆☆Possible for short deployments in clear water.
Dissolved Oxygen (Optode)★★★☆☆Feasible for recovered or high-end tags; high power draw.
Fluorescence / Chlorophyll-a★★☆☆☆Experimental; generally too bulky or complex for shark-mounted use.
  • Hydrodynamics: Tag profile must remain under 3–5% of body cross-section to minimize drag.
  • Attachment Duration: Typically weeks to months; fouling may affect optical sensors.
  • Power & Memory: Adequate for CTD + IMU at 1–2 Hz sampling over 1–3 months.
  • Biofouling: Mitigate using copper tape, anti-fouling coatings, or UV LEDs near sensors.
  • Recovery: For high-cost sensors, consider timed release or acoustic pop-up floats.
  1. Pressure / Depth sensor (for dive and surfacing behavior)
  2. Temperature sensor (thermistor or CTD stack)
  3. Conductivity sensor (to derive salinity)
  4. 3-axis accelerometer and magnetometer (IMU)
  5. Optional: Optical dissolved oxygen optode for pilot deployments

This configuration achieves a high data-to-weight and data-to-power ratio, suitable for hammerhead morphology and open-ocean tracking. When combined with real-time telemetry, it provides insight into habitat use, behavior, and local water quality dynamics.

Last updated: Nov 5, 2025 — core sensor recommendations and module examples referenced from manufacturer product pages and mini-CTD vendors.