Light traps as a tool to sample pelagic larvae of American lobster (Homarus americanus)

Abstract

We built a simple and relatively inexpensive light trap and tested its efficacy at catching pelagic larvae of the American lobster Homarus americanus Milne Edwards, 1837 in the field and the laboratory. We were particularly interested in assessing the potential of using these traps to support research on pelagic-benthic coupling, and therefore contrasted the abundance of postlarvae in the light traps to spatial variability in postlarval settlement. In laboratory experiments, 55% of postlarvae placed in 1 m diameter tanks were caught by the light traps, and 24% of postlarvae placed inside the light traps escaped, over a 24-hour period. In the field, the light traps caught lobster larval stages I and IV (the postlarva), but no stage II or III larvae. Catches of lobster postlarvae were lower than in previously published larval tow studies when standardizing for the amount of time the sampling devices spent in the water, but were roughly similar to these when standardized for the number of work hours required to obtain the samples. The light traps also caught a suite of other invertebrates, such as northern krill and all larval stages of the green crab and Atlantic rock crab, as well as some fish, such as juvenile lumpfish. The abundance of stage IV lobster postlarvae was significantly related to spatial variability in settlement, but unsurprisingly that of stage I larvae was not. Our results suggest that light traps may eventually provide an additional tool to sample lobster larvae and postlarvae, which may be particularly useful to study pelagic-benthic coupling as this passive sampling device better lends itself to the simultaneous sampling of many areas than do larval tows. However, we believe further lab and field experiments investigating modified trap designs, optimal soak time, and effect of depth, should be conducted to improve the efficacy of this new tool in American lobster research.