Human Impacts on Cod-Dominated Trophic Cascades in the Gulf of Maine

Cod fish
Project Summary:

In a repeat of trials conducted in 1992, predation experiments were conducted using time-lapse imagery with a goal of documenting changes in fish populations and predation impacts on Cashes Ledge.

Location:

Cashes Ledge, April 2006 – December 2007

Significance

Repeating experiments run in the past gives important information on how an ecosystem has changed over time. Correlating these changes with human impacts and management actions helps us to understand the longer term ecosystem responses to human pressure and protection measures.

Development of novel remote monitoring methodologies provides important tools to managers and scientists alike.

  • Jon D. Witman, Brown University
  • Funded by: Census of Marine Life Gulf of Maine Area Program
Project Detail:

Tethered predation experiments and time-lapse photography were used in August 2007 to record changes in dominant species and predation on this isolated rocky feature in the central Gulf of Maine. The preliminary findings are that the community of large fish has shifted from dominance by cod (Gadus morhua), a large-mouthed bottom and demersal feeder, to pollock (Pollachius virens), a water column feeder. Early results show that benthic predation is now dominated by a small-mouthed wrasse/cunner (Tautogolabrus adspersushas), which exerts far smaller predation pressure and consumes smaller prey than cod do. The reduction of cod is part of a wide-spread phenomenon rooted in high exploitation and possibly a system shift that does not favor recruitment of this species at this time.