Marine predator migration during range expansion: Humboldt squid Dosidicus gigas in the northern California Current System

Abstract

Humboldt squid Dosidicus gigas have undergone a major range expansion in the northern California Current System (CCS) during the last decade. These squid are thought to migrate annually from Mexican waters into the CCS where they prey on many species, including several that support lucrative fisheries; however, swimming capabilities and features of longdistance horizontal migrations are not well understood. In the present study, adult Humboldt squid were tagged off central California with pop-up archival transmitting (PAT) tags (n = 5). All squid ex hibited diel vertical migrations and swam south or offshore (west) during tag deployment (2.7 to 17.6 d). One squid swam south at least 34 km d-1 for >17 d and crossed into Mexican waters, which is the highest sustained velocity and the longest horizontal migration observed thus far for Humboldt squid. Results from a simple model to estimate the daily locations and velocities of each squid throughout the deployments suggest an average velocity of ~37 km d-1 and a maximum of ~50 km d -1. Additionally, the model suggests that one squid made a bidirectional movement (first north and then returning south) that was not evident from deployment and pop-up positions alone. This study provides insight into Humboldt squid migratory capabilities that are relevant to seasonal migrations and episodic range expansions, both of which are crucial to future inter - actions of this species with ecosystems and fisheries. © Inter-Research 2012.