Behavioral responses of rorqual whales (Balaenopteridae) to experimental fishing gear in a coastal environment

Abstract:

Whale entanglement in fishing gear is a global problem yet limited information exists about causal mechanisms of the entanglements.  Most knowledge about causes of mysticete whale entanglements stems from long-term research on North Atlantic right whales (Eubalaena glacialis), rope scarring studies on humpback whales (Megaptera novaeangliae) and minke whales (Balaenoptera acutorostrata), and a published field experiment by the co-authors that tested for behavioral responses of minke whales to different color ropes.  Here we present results from a new experiment that comparatively tested for behavioral responses of three rorqual whale (Balaenopteridae) species to an experimental buoy rope design with 20 cm rope “whiskers” attached at 1 m intervals.  Photogrammetric methods tested for statistically significant differences (α = 0.05) in swimming trajectory and velocity during experiments with whisker ropes (trials), standard ropes (control), and absence of ropes (control).  Correlation tests between whale behavior and environmental conditions were also conducted using data from an underwater sensing system of video cameras, hydrophone arrays, a flow device, and a photometer.  Results demonstrated that minke whales (n=26) exhibited significantly stronger behavioral responses to ropes with whiskers than standard ropes, and that fin whales (B. physalus; n=4) and humpback whales (n=2) exhibited relatively moderate responses (significant changes in trajectory but not velocity).  Considering the mean distance (39.3 m) of initial response when individuals approached whisker ropes, and a positive correlation between response magnitude and tidal flow velocity, these results suggest that rorquals in this experiment may have first detected whisker ropes from passive acoustic cues (noise-generating turbulence) over visual cues.  Broader impacts of this research include contributions of new information about rorqual whale rope avoidance behavior in shallow water, and the development of an inexpensive rope design that fits standard pot haulers and shows evidence of improved sensory detection by some mysticete whale species in coastal habitats.