INTERANNUAL VARIABILITY OF HUMBOLDT SQUID (DOSIDICUS GIGAS) OFF OREGON AND SOUTHERN WASHINGTON

Previous studies have shown that oceanographic conditions influence the distribution of range-expanding Humboldt squid (Dosidicus gigas), but broad-scale temporal and spatial distribution analyses are limited. Interannual variability in Humboldt squid occurrence is largely undocumented north of California. We combined annual occurrences noted by fishermen with fisheries-dependent and fisheries-independent data between 2002–11 from 42.0080 ̊N, 131.0000 ̊W to 46.7008 ̊N, 131.0000 ̊W. Humboldt squid more frequently occurred at a sea surface temperature range of 10.5 ̊–13.0 ̊C, sea surface height anomalies from –4.0–1.0 m, 0.26–3.00 mg m–3 chlorophyll a, and sea surface salinity range of 32.2– 32.8 psu. Dissolved oxygen levels were bimodal, between 3.0–4.5 ml L–1 and 6.0–7.0 ml L–1 at 30 m depth. Maps of estimated likelihood of occurrence generated by nonparametric multiplicative regression were consistent with observations from fishermen. When Humboldt squid become abundant in northern California Current waters, research should include seasonal variability and oceanographic conditions at multiple depths. INTRODUCTION The Humboldt squid (Dosidicus gigas), also known as jumbo flying squid, is an opportunistic predator that has experienced episodic range expansions from the Eastern Tropical Pacific into South America and the California Current system. Humboldt squid sightings off of the South American coast have been documented since the 19th century and in 2002 they were seen as far south as Chiloe Island in southern Chile (AlarcónMuñoz et al. 2008). In the northern California Current system, Humboldt squid were documented in the 1930s off California with increasing occurrences since 2002 (Field et al. 2007; Litz et al. 2011). Humboldt squid have been seen as far north as Alaska (in 2004, Cosgrove 2005) and were first documented in southern Oregon in 1997 (Pearcy 2002). Peak density in Oregon occurred in 2009 (Litz et al. 2011); however, reported sightings in this area have decreased between 2009 and 2011 (Bjorkstedt et al. 2011; Marissa Litz, Oregon State University, pers. comm.). Humboldt squid live 1–2 years, have rapid growth rates, and high-energy demands (Nigmatullin et al. 2001; Zeidberg and Robison 2007). As a large predator, there is concern that future Humboldt squid expansion will result in a decline in valuable commercial fishery stocks and impact coastal food webs in the California Current (Field et al. 2007). Humboldt squid have the ability to alter food sources and foraging strategies based on varied environmental conditions (Bazzino et al. 2010). These squid have been known to prey on Pacific herring ( Clupea pallasii) (Field et al. 2007), mackerel (Scomber japonicas) (Sato 1976; Ehrhardt et al. 1983), sardines (Sardinops sagax) (Ehrhardt et al. 1983; Markaida and Sosa-Nishizaki 2003), hake (Merluccius productus) (Markaida and Sosa-Nishizaki 2003), rockfish (Sebastes spp.) (Field et al. 2007), and salmon (Oncorhynchus spp.). The valuable Pacific hake (Merluccius productus) fishery is of particular concern, as Humboldt squid are known to associate with hake schools and a decline in Chilean hake (M. gayi) biomass was attributed to an increase in Humboldt squid off the Chilean coast in 2001–06 ( Alarcón-Muñoz et al. 2008). In Oregon, Humboldt squid presence coincided with a decline in juvenile Pacific hake, which was in contrast to recent abundance trends (Litz et al. 2011). Previous research has indicated that oceanographic factors may contribute to the variable temporal and spatial population range of Humboldt squid (Gilly et al. 2006; Field et al. 2007; Zeidberg and Robison 2007), CHESNEY ET AL.: INTERANNUAL VARIABILITY OF HUMBOLT SQUID (DOSIDICUS GIGAS) CalCOFI Rep., Vol. 54, 2013 181 tration (NOAA) Fisheries Predator and Stock Assessment Improvement Plan (SAIP) from 2004–09 off Oregon and Washington. Litz et al. 2011 found Humboldt squid present in 60 of the 947 total trawls, and established that Humboldt squid abundance corresponded best with a station depth of 1000 m, 11 ̊–13 ̊C subsurface water temperature, 32.4–32.8 psu, and a density of 24.5–25.0 kg m–3 at 20 m. While their results provided significant baseline information for Humboldt squid monitoring in the Pacific Northwest, Litz et al. 2011 expressed need for broader scale distribution data analysis. The goal of this study is to establish distribution data and explore the relationship between broad-scale temporal and spatial oceanographic conditions and Humboldt squid occurrence off Oregon and southern Washington so as to contribute to baseline information on Humboldt squid interannual variability. Due to the coarse-scale of our data, we did not seek to explain squid behavior or migratory patterns. This study analyzes aggregate Humboldt squid occurrence information from three fishery-independent surveys, fisheries-dependent data from one observer program, and sightings by fishermen with annual remote sensing and field oceanographic data from 2002–11.