Bycatch Reduction Technologies & Net Illumination in Coastal Fisheries

Overview of Ocean Conservation and Bycatch Challenges

• Research Institution & Focus: The Senko Lab, led by researchers within the School of Ocean Futures at Arizona State University, investigates innovative technological solutions to protect marine megafauna while supporting coastal fishing livelihoods.

• Primary Study Site: Isla El Pardito, located near La Paz, Baja California Sur, Mexico in the Gulf of California.

• Baja Mexico Gillnet Crisis:

  • Baja Mexico's gillnet fisheries feature the highest known bycatch rates on the planet (Senko et al. 2017, Marine Policy).

  • Critical sea turtle foraging hotspots directly overlap with high-intensity gillnet fishing zones.

  • Thousands of sea turtles are killed annually as incidental bycatch across small-scale fleets.

• Quantified Bycatch Severity:

  • $1$ turtle caught per $100\,m$ net per $24\,h$.

  • $4$ to $8$ turtles caught per fishing vessel per day.

  • $100$\text{--}$400$ turtles caught per day across the entire fishing fleet.

  • $2,000$\text{--}$4,000$ turtles caught per month across the fleet.

Sensory-Based Gillnet Illumination Science

• Historical Precedent: Artificial illumination has been used by humans to attract fish species for thousands of years.

• Development of Gillnet Illumination:

  • Developed over the past decade specifically as a sensory-based method to mitigate sea turtle bycatch.

  • Vision serves as the primary sensory domain for sea turtles when navigating and foraging.

  • Applications have expanded recently to target multiple marine megafauna taxa, including elasmobranchs (sharks and rays) and marine mammals.

• Spectral Sensitivity of Elasmobranchs:

  • Sandbar shark (Carcharhinus plumbeus), Smooth dogfish (Mustelus canis), and Spiny dogfish (Squalus acanthias) display peak visual sensitivity within the blue-green spectral region ($470$\text{--}$500\,nm$ wavelength).

  • Electroretinography shows consistent day and night spectral sensitivity profiles across these target shark species, establishing the sensory basis for visual deterrents.

Case Study 1: LED Net Illumination

• Study Details: Field trials conducted in gillnet fisheries off the Baja California Peninsula evaluated the efficacy of green LED lights attached along net float lines (Senko et al. 2022, Current Biology).

• Sea Turtle Bycatch Reduction:

  • Sea turtle Bycatch Per Unit Effort (BPUE) decreased by $51\%$ in mean BPUE ($kg$ turtle bycatch caught per $100\,m$ net per $12\,h$ soak).

• Aggregate Bycatch Reduction:

  • Total aggregate Bycatch Per Unit Effort (BPUE) decreased by $63\%$ ($P < 0.001$).

  • Biomass reductions were achieved across non-target taxa, including sea turtles, elasmobranchs, non-target finfish, and Humboldt squid.

• Target Finfish Catch:

  • Target finfish Catch Per Unit Effort (CPUE) was maintained, exhibiting a statistically non-significant $6\%$ increase.

  • Catch rates remained stable for key commercial target species, including Halibut, Grouper, and other target finfish.

• Operational Efficiency Improvements:

  • Mean haulback time (retrieval and sorting duration per $100\,m$ of net) decreased by $57\%$ ($P < 0.001$).

  • Reduced entangled non-target biomass allows fishers to retrieve gear and sort catch significantly faster.

• Night-Set Field Experimental Results (Senko et al. In Submission):

  • Night deployment tests ($n = 28$ sets) resulted in a $50\%$ decrease in mean turtle bycatch, target catch, and market value.

  • Aggregate non-target bycatch biomass decreased by $56\%$ during night deployments.

• Operational Limitations of Conventional LED Lights:

  • High Battery Costs: A single boat operating $1\,km$ of net with LEDs spaced every $5$\text{--}$10\,m$ requires $200$\text{--}$400$ AA batteries every $3$\text{--}$4$ weeks.

  • Environmental Impact: Heavy battery consumption generates substantial hazardous solid waste.

  • Gear Interference: Individual light pods entangle easily in netting, add physical weight, and pull nets downward, altering fishing depth and performance.

Case Study 2: Solar-Powered Bycatch Reduction Technology

• Multi-Stakeholder Co-Design Network: Development involved active collaboration between:

  • Local fisher leaders in Mexico.

  • Arizona State University's Solar Power Lab and School of Electrical, Computer, and Energy Engineering.

  • NOAA Fisheries.

  • Local and international conservation non-governmental organizations (NGOs).

• Solar Light Buoy Engineering Features:

  • First solar-powered bycatch reduction light engineered through fisher co-design.

  • Integrated design functions directly as a float line buoy, removing the need for separate weight-adding attachments.

  • Self-charges in natural sunlight and operates continuously for $1$ week without sun exposure.

  • Herematically sealed housing runs for years without requiring battery replacements or opening.

• Generation 2 (V2) Solar Buoy Enhancements:

  • $50\%$ reduction in size with a hydrodynamic, streamlined shape.

  • Automatic water-activation system that triggers illumination upon immersion.

  • Maintains identical light intensity output and charge performance cycles as Generation 1 units.

• Key Solar Technology Findings:

  1. Fisheries bycatch can be reduced using renewable energy harvested from the sun.

  2. Involving commercial fishers directly in technology co-design increases operational feasibility and adoption.

  3. Flashing solar light configurations successfully deter megafauna while maintaining commercial target finfish catches.

Media Coverage and Global Recognition

• Bloomberg Green (January 25, 2022): Highlighted findings from Current Biology showing a $95\%$ reduction in shark and ray bycatch biomass when green LED lights were deployed along $16,000$ feet of fishing nets in Mexico's Pacific waters, contrasting with global shark population declines of $71\%$ since 1970.

• NPR / KJZZ (February 5, 2022): Covered green LED net illumination as an emerging solution to prevent incidental marine mammal and sea turtle entanglements.

• The Economist (January 22, 2022) & Reuters: Featured illuminated fishing nets as a technological breakthrough for sustainable seafood and marine megafauna conservation.