Introduction

1. Cannibalism in blue crabs, Callinectessapidus: with emphasis in varying stressors and differences between sexes By: Alex Crouse Mentor: Dr. Nolan Introduction Methods • The blue crab fishery is the largest fishery in the Chesapeake Bay and now accounts for $50 million a year in revenue for Chesapeake Crabbers. However, this fishery has slowly been declining and has dropped by 70% since 1990, mostly due to overfishing (Lee et al 2004). • Previous research had been done on cannibalism in blue crabs, but only in juveniles. Little has been done to observe cannibalism and its effects in adult blue crabs. No previous work was found that showed a difference in cannibalism between the sexes. • Reproduction and migration both require large energy expenditures by females. Females should thus require a higher food intake to fulfill these energy needs. • Studies have shown that blue crabs are sensitive to high salinities. This is especially true in males (Ryer et al. 1997). No studies have been done to see how environmental stressors may effect blue crab behavior, including their cannibalistic tendencies. • Pilot studies performed in conjuncture with this experiment in the fall of 2008 did show an overall higher aggressiveness in the female populations under normal conditions. Conclusion Results • The data showed no significant difference in cannibalistic tendencies either between the sexes under controlled conditions or in males under experimental conditions. • Time may have played a critical factor in the lack of results found in this experiment. • This experiment should be repeated on a shorter time interval without separation to observe initial stress. When running the pilot studies in the Fall of 2008 we did not isolate the crabs and saw increased levels of cannibalism (data not shown). This being said we believe the immediate stress of being moved could cause cannibalism. The separation in the current experiment was done to acclimate the crabs to the new environment and eliminate the weaker crabs. • This experiment should also be repeated on a longer time scale to see if long term exposure to environmental stressors will cause an increase energy demand and thus an increase in cannibalism. Figure 1. Male and female limb loss under control conditions. No significance was found between males and females or over the course of the experiment. Error bars in this graph and in the following graphs are representative of the standard error. Literature Cited R.F. Lee, M.E. Frischer. Ecology and the decline of the Blue Crab. American Scientist 2004 92:548 Ryer, C. H., J. vanMontfrans,K. E. Moody. 1997. Cannibalism, refugia and the molting blue crab. Marine Ecology-Progress Series 147(1-3):77-85. Figure 2. Male limb loss over a seven day period under stressful conditions. Significant difference was seen between high salinity and high temperature at days 3 & 4, p<0.05. Hypotheses • Ho - There will be no difference in the rates of cannibalism between the sexes • H1 – The females will show a higher rate of cannibalism compared to the males • Ho – There will be no difference in rates of cannibalism upon induction of stress • H1 – Males will show a higher rate of cannibalism in high stress situations Figure 3. Data shows cannibalism in control conditions for male and females. No significant difference was seen between treatments Figure 4. Data shows cannibalism in male control and stressful experimental conditions. No significant difference was seen between treatments. Acknowledgements I would like to thank Dr. Jessica Nolan and Dr. Karl Kleiner for their help and continued support in this project.