Effects of Meteorological Events on the Distribution of Spotted Seatrout in a Louisiana Estuary Determined by Acoustic Telemetry

Meteorological events cause abrupt changes in abiotic conditions that often elicit behavioral and distributional responses in aquatic organisms.  Understanding the responses to such events is important for resource management as changes in behavior and distribution affect the accessibility of fishery species to monitoring surveys conducted in support of stock assessment.  In this study, we employed a synoptic array of remote telemetry receivers (VEMCO VR2Ws, n=59) to investigate the movement patterns of adult spotted seatrout (n=172) in a Louisiana estuary (Calcasieu Lake).  During the course of this long-term (2.5 year) study, numerous cold fronts, tropical storms, and freshets impacted the project area.  Spotted seatrout exhibited clear responses to these weather events.  Interestingly, the response to freshet-induced low salinities was strongly sex-specific in that only females avoided regions of the estuary where salinities were considerably low (<5) due to freshets.  Logistic regression analyses indicated that across all freshet events, the presence of females (p <0.002), but not males (p > 0.3), was significantly lower when salinities in the upper bay were < 5.  Moreover, females displayed a shift to higher salinity regions (lower bay) during freshets, but no distribution shift was observed for males.  This sex-specific response may be associated with differences in energy optimization strategies between males and females.  During tropical storms and cold fronts, spotted seatrout primarily utilized deeper channel habitats.  These habitats appeared to be functioning as a deep-water refuge as evidenced by the movement of individuals into the channel (~15 m depth) from shallower waters (<2.5 m) coincident with storm passages and significant increase in the depth distribution of sensor-equipped individuals during peak storm conditions (Wilcoxon rank sum test, p<0.0001).  While clearly important from a single-species aspect, knowledge of the abiotic preferences of coastal fishes as obtained in this study can also support ecosystem-based management initiatives.  For example, such information may be particularly useful for predator-prey models by providing important bounds on the suite of environmental conditions under which species would be expected to co-occur and thus predate or compete with one another.