Evaluating Pacific cod migratory behavior and site fidelity in a fjord environment using acoustic telemetry

Abstract

Pacific cod (Gadus macrocephalus) inhabiting Prince William Sound (PWS) may constitute a localized population separate from Gulf of Alaska (GOA) populations; however, connectivity between these regions has not been previously explored. To address this knowledge gap, we investigated Pacific cod migratory behavior and site fidelity using passive acoustic telemetry techniques. Acoustic-tagged Pacific cod (n = 111) were monitored by Ocean Tracking Network acoustic arrays located at the straits and passages connecting PWS with the GOA and arrays deployed in two PWS fjords. Few Pacific cod tagged in PWS moved to the PWS–GOA boundary (1.8%), indicating that demographic connectivity with the GOA was low. Furthermore, 77% of tagged cod spent at least 90% of the time they were known to be alive within small (less than 30 km2) fjords. Cod were present at monitored fjords every month of the study, though some cod migrated away from the fjords during the summer and returned the following winter (11% in 2015 and 5% in 2016). Using continuous-time multistate Markov models, we determined that movement behavior was related to fish length. Larger fish tended to emigrate from monitored fjords more often and undergo longer duration migrations.