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The man with a plan

PSI researcher, Andy Suhrbier helps shellfish growers adapt to changing ocean conditions.


Follow the South Sound Light Trap Team as we search for tiny Dungeness crabs!

Light Trap Monitoring

What is a Light Trap?

Our light trap is featured in the image below. It has a large float on top to keep the trap upright in the water and a weight at the very bottom to keep the large jug (yes that's a 5-gal water jug!) submerged in the water near the surface. Large funnels are attached to the sides of the jug that allow animals to swim in, but not out. At night, the timer inside the trap turns on a strip of led lights, attracting animals to the trap like a moth to your light at night! When we pull the trap out of the water, the sample drains through a filter attached to the bottom of the trap, called the cod end. The cod end helps filter the water out, but collects the tiny crabs we want to see and count!

Light Trap

This style of light trap was designed by marine scientist, Dr. Alan Shanks to study larval Dungeness crab on the outer coast of Oregon and Washington. Biologists from the Swinomish Tribe standardized the design for research purposes throughout Puget Sound. The collaboration of scientists using the light traps belong to the Pacific Northwest Crab Research Group, formed in 2018. Our trap represents the South Sound region, monitoring April - September at Zittel's marina. Photo credit: Debbie Preston

What are we looking for?

We have joined biologists throughout the Puget Sound region to participate in annual, long-term monitoring of juvenile stages of Dungeness crab, including megalopae (below) and instars. Data collected from April - September helps crab fishery biologists make decisions about how adult populations of Dungeness crab should be sustainably managed year to year.


A Dungeness crab in the megalopa stage. Relatively large compared to other crab species, their carapace width ranges from 3.5mm to 4.6mm.

Why is it so important?

Recent declines in adult Dungeness crabs throughout Puget Sound prompted the formation of the Pacific Northwest Crab Research Group (PCRG) in late 2018, led by treaty tribes and supported by state and federal agency biologists, university scientists and non-profit organizations to provide science-based information for adaptive planning and management of this species.

Fishing pressure and impacts of climate change, including low pH are among the drivers implicated in recent recruitment failures and smaller adult populations. Collecting information on the early life stages of the Dungeness crab will help inform and forecast how healthy adult populations are throughout Puget Sound. Monitoring a keystone species, such as the Dungeness crab, gives us a big picture view of how the rest of the ecosystem is doing. Changes in adult populations and fisheries management of this species has broad economic and cultural impacts. Many communities around Puget Sound rely on the Dungeness crab fishery for their livelihood and food security, valued at $12.5M in Washington state.

Meet the team!

Margaret Homerding, Shellfish Biologist, Nisqually Indian Tribe

Shannon Boldt, Biologist & Board Member, Nisqually Reach Nature Center

Allison Brownlee, Aquatic Reserves Specialist, WA DNR Aquatic Reserves

Katie Houle, Research Biologist, Pacific Shellfish Institute

Yvonne Shevalier, Volunteer, Pacific Shellfish Institute

QUESTIONS? Contact Us!


PCRG logo

Zittel's Marina, for hosting the South Sound light trap ('19-'23)

Nisqually Indian Tribe, funding support for PSI light trap monitoring ('22)

Squaxin Island Tribe, funding support for PSI light trap monitoring ('19-'23)

The Russell Family Foundation, funding support for educational programming and light trap materials ('20,'21)

Keta Legacy Foundation, funding support for community science program and middle school curriculum design ('20)

Boston Harbor Marina, for hosting the PSI light trap ('20)

Tiny Crabs, Big Impacts Curriculum Student Work

Fantastic work from Komachin Middle School 7&8th grade students working on, "Tiny Crabs, Big Impacts" curriculum! Thank you Katie Standlea for introducing your students to the Dungeness crab fishery and monitoring efforts in Puget Sound! We love seeing your students work! Photo: Katie Standlea


Megalopae Icon

Are you a Middle School Science Teacher that wants to bring REAL DATA into the classroom? Look no further! PSI developed the curriculum entitled, "Tiny Crabs, Big Impacts: Long-Term Monitoring for Healthy Dungeness Populations", for Grades 6-8 (WSSLS/NGSS). Students will work through South Sound light trap data to understand how scientists are collaboratively monitoring a critical Puget Sound fishery. Explore the info below!

Introductory Presentation (PDF)

Supplementary Notes (PDF)

WDFW Article (3/11/2020) (PDF)

Data Module (Graphing Activity)- Teacher Key (PDF)

Data Module (Graphing Activity)- Student Workbook (Fillable PDF)

Data Module (Virtual Classroom)- Teacher Key (PDF)

Data Module (Virtual Classroom)- Student Workbook (Fillable PDF)


Please contact PSI Biologist, Katie Houle for additional resources and curriculum support.



Collect your very own Critter Cards! Througout the season we'll feature new creatures we found in our light trap for you to learn more about. Save the cards in a "digital deck" or print at home! Stay tuned to collect the whole set!


Light Trap Common Species ID Guide

Crab ID Guide

Zooplankton ID Guide

Invertebrates of the Salish Sea

Kozloff, E. N. 1996. Marine Invertebrates of the Pacific Northwest. University of Washington Press. 552 Pp


Bizzarro, J.J., Selleck, J., Sherman, K., Drinkwin, J., Hare, V.C., and Fox, D.S. 2022. State of the knowledge: U.S. West Coast nearshore habitat use by fish assemblages and select invertebrates. Portland, OR: Pacific Marine & Estuarine Fish Habitat Partnership. **Summary from light trap study, pp. 39

PSEMP Marine Waters Workgroup. 2021. Puget Sound marine waters: 2020 overview. **Light trap study featured, pp. 42

Houle, K. Homerding, M., Brownlee, A. and Boldt, S. 2021. Light Trap Monitoring for Larval Dungeness Crab. Project Summary. South Sound Science Symposium. Web.

Dungeness Instar

A Dungeness instar, the stage directly after the larval megalopae, caught in our light trap. Photo: K. Houle