Cajun Invasion

by Glennis Waterman

If you hang around with old timers in the Ninth Ward of New Orleans, sooner or later you’re going to hear someone complain how people from all over the US are moving into the neighborhood and displacing folks who were born here. As a transplant from Southern California I’m pretty sensitive to this talk, but I understand how they feel.

Because I’ve experienced something similar. My old neighborhood in Topanga, California is being overrun by invaders from Louisiana.

Procambarus clarkii, the red swamp crawfish – or “crayfish” as they call it in California – is the crawfish native to Louisiana’s swamps and bayous. Louisiana produces up to 90% of the crawfish sold in the US (FAO).

Researchers in the Santa Monica Mountains, a transverse coastal range in Southern California, have identified the red swamp crawfish as an invasive species displacing native stream fauna. It preys on tadpoles, snails, young fish, and fish eggs. It competes for shelter with less aggressive fauna, consumes plants on the bottoms of streams, and causes stream bed erosion. One native species particularly vulnerable to crawfish predators is the California coastal range newt, or Taricha torosa toros (Gamradt, et al).

In years of heavy rainfall, mountain streams wash down to the Pacific Ocean. Crawfish are freshwater dwellers, so with each gully-washer scores of the little invaders are washed into the Pacific Ocean, where they are unable to survive. This normally keeps the invasion in check, but during drought years, these cleansing washes occur less frequently.

How did crawfish get into the streams in the first place? Humans have enabled the invasion. Sports fishermen use crawfish as bait, introducing them into freshwater lakes and streams. They may also be escapees from aquaculture or hobby aquariums. Kats’s research showed that land development in watershed areas also greatly enables invasive species (Sea Grant).

According to Dr. Lee Kats, a biologist at Pepperdine University, crawfish can dig as far as three feet deep into dry creek beds, survive and reproduce. They have no known predators in the Santa Monica Mountains, and reproduce quickly. With these great survival skills, they are very difficult to eradicate.

Research has shown the only way to stem the invasion is to remove the critters completely. In 2013, a group of 50 citizen-scientist volunteers for the Resource Conservation District of the Santa Monica Mountains caught 224 crawfish in a 100 meter stretch of Topanga Creek, in my former neighborhood. They used nets and chunks of hot dogs tied to strings, since traps might affect endangered trout species (RCDSMM "Coastal"). In 2015, the California Department of Fish and Wildlife awarded an $800,000 grant to the Mountains Restoration Trust to remove crawfish from the entire Malibu Creek Watershed, a 109 square mile area. They will search areas of one hundred yards at a time and will continue to monitor for returnees in future years (Kim).

Are the volunteers planning to serve up their catch up with corn on the cob and steamed potatoes? No, sorry, folks. These mudbugs will be donated to the California Wildlife Center to feed rehabbed raccoons and possums in animal shelters. Hope they give them some Dixie beer to go with!

Just goes to show you how one culture’s culinary delicacy is another culture’s pest.

Sources:

Food and Agriculture Organization of the United Nations, Fisheries and Aquaculture Department. Species Fact Sheets: Procambarus clarkia. http://www.fao.org/fishery/culturedspecies/Procambarus_clarkii/en  Accessed 3/28/2018

Gamradt, Seth C., Kats, Lee B., and Anzalone, Christopher B. “Agression by Non-Native Crayfish Deters Breeding in California Newts.” Conservation Biology, Vol 22 No 3, June 1997, pp 793-796.

Garcia, C., E. Montgomery, J. Krug and R. Dagit. 2015. “Removal efforts and ecosystem effects of invasive red swamp crayfish (Procambarus clarkii) in Topanga Creek, California.” Bulletin of the Southern California Academy of Sciences. Vol 114(1):12-21.

Kim, Jed. “Dr Lee Kats Discusses the Invasive Red Swamp Crayfish.” 89.3 KPCC, January 9, 2015. https://seaver.pepperdine.edu/news/2015/01/dr-lee-kats-discusses-invasive-red-swamp-crayfish-893-kpcc/  Accessed 3/28/2018.

“Red Swamp Crayfish (Procambarus clarkii) Ecological Risk Screening Summary.” US Fish and Wildlife Service February 2011 Revised May 2015.  https://www.fws.gov/fisheries/ans/erss/highrisk/Procambarus-clarkii-ERSS-revision-May2015.pdf Accessed 3/28/2018.

Resource Conservation District of the Santa Monica.  “Coastal Cleanup Day Crayfish Roundup.” Mountains, http://www.rcdsmm.org/sites/default/files/userfiles/file/SpecialEvents/2013-9%20crayfish%20roundup%20article%202.pdf  Accessed 3/28/2018.

Resource Conservation District of the Santa Monica Mountains. “Creature Features: Red Swamp Crawfish.” http://www.rcdsmm.org/resources/creature-feature/  Accessed 3/28/2018.

Washington Department of Fish and Wildlife. Conservation. “Aquatic Invasive Species: Procambarus clarkii (Red swamp crawfish).”  https://wdfw.wa.gov/ais/procambarus_clarkii/   Accessed 3/28/2018.