Quantifying the effects of lobster traps and set gillnets on benthic habitats off the Pacific coast of Baja California Sur, Mexico

Biogenic structures including corals, sponges, and macroalgae can create habitat for marine life and are known to be among the most sensitive habitats to fishing impacts.  Few studies have evaluated the effects of fixed fishing gears on such habitats, leaving managers uncertain about the need to mitigate potential adverse impacts.  Here, I quantify immediate damage and removals of gorgonian corals and macroalgae caused by normal deployment of set gillnets and lobster traps at depths from 5 to 25 m off the Pacific coast of Baja California Sur, Mexico.  For traps, I examined benthic cover using a Before-After, Control-Impact design and found no significant difference between treatments.  In addition, I conducted trap dragging and crushing treatments over live gorgonian corals to simulate effects of storms or heavy currents.  Here, I found negligible to minor (<5%) impacts in the form of tissue loss and skeleton damage.  These results suggest that normal use of lobster traps at the depths in this study has minimal immediate effects on benthic cover and gorgonian corals at the depths in this study.  For set gillnets, I quantified interactions with biogenic structures per meter of net and characterized the outcomes.  Relative to lobster traps, set gillnets cause greater damage to biogenic structures.  Interviews with fishermen corroborate these findings.  The methods developed here provide a standardized approach to evaluate the habitat effects of fixed fishing gears.  This study confirms previous hypotheses that lobster traps have minimal habitat impacts and suggests the use of set gillnet closures in areas of high biogenic habitat density.