Area use and movements of the white croaker (Genyonemus lineatus) in the Los Angeles and Long Beach Harbors

Understanding the movements of fish in relation to areas of contaminated and urbanized habitats is crucial to fisheries management and habitat remediation. In this study, the movements of white croaker in the Los Angeles and Long Beach Harbors were examined using both active and passive acoustic telemetry tracking. Daily area use for 20 fish actively tracked over multiple days averaged 94,720 ± 78,720 m(2) (±SD), with daily activity spaces shifting over periods of up to 1 month. Long-term dispersal (up to 7 months) of 93 passively tracked white croaker followed significantly non-random patterns, with 55 individuals (59.1%) making inter-regional Harbor movements. Inter-regional movements took an average of 4.7 ± 4.1 weeks to complete. Dispersal was significantly faster than what was predicted by an individual-based random walk model generated from short-term white croaker movements recorded during active tracking within the Harbor. Longer-term dispersal is likely the result of intentional movements between patches of favorable habitat rather than random daily shifts in activity spaces, indicating that white croaker deliberately utilize different areas within the Harbor and over the course of a year utilize much of the favorable Harbor habitat.

Methods for assessment of short-term coral reef fish movements within an acoustic array

BACKGROUND

Arrays of passive receivers are a widely used tool for tracking the movements of acoustically-tagged fish in marine ecosystems; however, the spatial and temporal heterogeneity of coral reef environments pose challenges for the interpretation of tag detection data. To improve this situation for reef fishes, we introduced a novel response variable method that treats signal detections as proportions (i.e., percent transmissions detected or "detection rates") and compared this against prior approaches to examine the influence of array and transmitter performance, signal distance and environmental factors on detection rates. We applied this method to tagged snappers and groupers in the Florida reef ecosystem and controlled range-tests on static targets in Bayboro Harbor, Florida, to provide methodological guidance for the planning and evaluation of passive array studies for coral reef fishes.

RESULTS

Logistic regression analysis indicated detection rates were primarily a non-linear function of tag distance from receiver. A 'model-weighted' function was developed to incorporate the non-linear relationship between detection rate and distance to provide robust positioning estimates and allow for easy extension to tags with different ping rates.

CONCLUSIONS

Optimal acoustic array design requires balancing the interplay between receiver spacing, detection rates, and positioning error. Spacing receivers at twice the distance of the modeled 50% detection rate may be appropriate when quantification of overall space use is a priority, and would provide a minimum of 75% detection rate. However, for research where missing detections within the array is unacceptable or time-at-arrival based fine-scale positioning is needed, tighter receiver spacing may be required to maintain signal detection probability near 100%.