Evidence for predator-induced behavioral plasticity of juvenile red king crab (Paralithodes camtschaticus) Benjamin Daly University of Alaska Fairbanks
King Crabs in Alaska Many stocks depressed despite a lack of fishing Why is stock enhancement being considered? Commercially valuable Recruitment limitation (Blau, 1986) 1960s Russians introduced RKC to Barents Now: established reproductive pop Evidence to restore king crabs to historic range in AK?
AKCRRAB Alaska King Crab Research Rehabilitation and Biology Created in 2006 Partnership between the University of Alaska Fairbanks, Alaska Sea Grant, Chugach Regional Resources Commission (CRRC), NOAA, and community-based groups Begin to assess the feasibility of stock enhancement for king crabs in Alaska
Enhancement: Next Steps From a hatchery perspective: 1. Is large-scale culture possible? Yes! 2. How can we improve post-release survival?.. Predation: major source of mortality Period immediately after release likely very important
Hatchery-induced Deficiencies Behavioral and morphological Examples: fin fish, crabs, lobsters, conch Benefits of conditioning European lobster Improved predator response (shelter seeking behavior) Claw morphology Scissor, crusher claws blue crab Increased burial behavior Spine length Shell color
Conditioning Goal: Determine if juvenile red king crabs display signs of predator induced behavioral plasticity. Does exposure to predators impact crab behavior? Do potential behavioral modifications translate to increased survival?
Juvenile RKC Predator Defenses Age-0 crabs: Three dimensional structure Cryptic behavior Aggressive displays? Flaring arms, etc Older juveniles: Podding? Photos by Jodi Pirtle
Experimental Animals Juvenile red king crabs: 5-7.5 mm CL Fish Predators: Pacific halibut (180 mm) Pacific cod (200 mm)
Crab conditioning: caged methods Visual cues Chemical cues No direct physical contact
Crab conditioning: un-caged methods Visual cues Chemical cues Physical contact Observe predation
Methods: predation trials Mesocosm Island of substrate Fish pairs Social facilitation 1 week acclimation 3 treatments (naïve, cage, un-caged) 20 crabs Introduced in dark Allowed to acclimate Length: 1 hour Video recorded
Methods: Video analysis Crab Survival Crypsis index Proportion of crabs hiding Crabs not visible by video analysis (adjusted for predation) Fish behavior Activity index Proportion fish actively swimming: relative index Crabs eaten per target Crabs eaten per strike Strikes per target Way to evaluate feeding efficiency
Methods: Statistical analysis Repeated measures ANOVA (randomized block) Fish pairs exposed to all 3 treatments
Crab Survival 90 halibut b 80 p=0.038 ab % Survival 70 a 60 50 n=6 n=6 n=6 naive conditioned (caged) conditioned (uncaged)
Crab Crypsis 100 80 Crypsis index 60 40 20 0 0 10 20 30 40 50 60 Time conditioned (caged) naive conditioned (uncaged)
Crab Crypsis 100 80 Crypsis index 60 40 Crypsis index (initial) 100 80 60 40 20 0 p <0.001 a naive b conditioned (caged) b conditioned (uncaged) 20 0 0 10 20 30 40 50 60 20 10 No. crabs targeted Time conditioned (caged) naive conditioned (uncaged)
Crab Crypsis 100 80 Crypsis index 60 40 100 p=0.003 a ab b 20 0 0 10 20 30 40 50 60 Time conditioned (caged) naive conditioned (uncaged) Crypsis index (t=60) 80 60 40 20 0 naive conditioned (caged) conditioned (uncaged)
Fish Behavior: Strikes 60 Total number of strikes 50 40 30 20 10 0 0 10 20 30 40 50 60 Time (min)
Fish Behavior Fish activity index Crabs eaten per target Crabs eaten per strike Strikes per target No differences between crab treatments
naive only 25 Predation (dependent variable) is correlated with fish activity. Targets 20 15 10 5 0 0 20 40 60 80 100 caged only Activity index uncaged only 18 16 14 30 25 Targets 12 10 8 6 4 2 Tragets 20 15 10 5 0 0 20 40 60 80 100 0 0 20 40 60 80 100 Activity index Activity index
Conditioning Effects Conditioned crabs had slightly better survival Naïve vs Un-caged (p=0.038) Conditioned crabs had increased cryptic behavior Physical interaction with fish seems important Visual + chemical cues alone DO induce a response Crypsis improved over the course of trial Is this evidence of behavioral plasticity? Is predator exposure inducing a behavioral modification?
Conditioning Effects: Caveat Un-caged conditioning methods: Fish actively preying on some crabs Are crabs modifying behavior from physical interactions of predators? OR Are the fish eating behaviorally inferior crabs thereby preselecting for superior crabs? However, Naïve Caged comparisons significant in terms of crypsis
Implications for Hatchery Conditioning Goal: Determine if juvenile red king crabs display signs of predator induced behavioral plasticity Potential is there for hatchery conditioning May increase post release predator responses May increase survival Future research: What about conditioning duration? Conditioning with natural substrates Verification in field Hatchery - wild comparison is lacking
Acknowledgements NOAA - Fisheries Behavioral Ecology Program, HMSC, Newport OR Dr. Al Stoner Dr. Cliff Ryer Alutiiq Pride Shellfish Hatchery Jim Swingle Jeff Hetrick Funding by Sea Grant Aquaculture
Questions?