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SEASONAL OCCURRENCES of HUMBOLDT SQUID (DOSIDICUS GIGAS) in the NORTHERN CALIFORNIA CURRENT SYSTEM Marisa N

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SEASONAL OCCURRENCES of HUMBOLDT SQUID (DOSIDICUS GIGAS) in the NORTHERN CALIFORNIA CURRENT SYSTEM Marisa N LITZ ET AL.: SEASONAL OCCURENCES OF HUMBOLDT SQUID CalCOFI Rep., Vol. 52, 2011 SEASONAL OCCURRENCES OF HUMBOLDT SQUID (DOSIDICUS GIGAS) IN THE NORTHERN CALIFORNIA CURRENT SYSTEM MARISA N. C. LITZ AND A. JASON PHILLIPS RICHARD D. BRODEUR AND ROBERT L. EMMETT Cooperative Institute for Marine Resources Studies Estuarine and Ocean Ecology Program Oregon State University NOAA Fisheries Northwest Fisheries Science Center 2030 Marine Science Drive Newport Research Station Newport, OR 97365 2032 SE OSU Drive Tel. 541-867-0148 Newport, OR 97365 Fax: 541-867-0389 Email: [email protected] ABSTRACT est absolute growth rates of any squid species. In recent Recent visits by Humboldt squid (Dosidicus gigas) to years off the U.S. West Coast, Humboldt squid appear to the northern California Current system (CCS) were overlap in time and space with commercially important suggested to be related to larger climatic events such as species such as Pacific hake (Merluccius productus), Pacific El Niño, global warming, and expansion and shoaling sardine (Sardinops sagax), and rockfish (Sebastes spp.), and of the oxygen minimum zone. Due to their plasticity in are of major interest because of their potential ecosystem foraging behavior, coupled with an increased availabil- impacts (Field et al. 2007; Holmes et al. 2008). ity of prey resources, these excursions may also represent Humboldt squid invaded waters off southern and cen- opportunistic foraging explorations. Fisheries-indepen- tral California in large numbers during the mid-1930s dent surveys initiated by the Northwest Fisheries Sci- (Clark and Phillips 1936) then were virtually or totally ence Center in 1998 first encountered Humboldt squid absent until a short period in the mid-1970s, then virtu- in coastal waters off central Oregon and Washington in ally absent again until the 1990s (Field et al. 2007). Off 2004. Squid ranging from 36–79 cm mantle length were Oregon, they were not observed until the 1997 El Niño, caught during the following six years of sampling (2004– when Humboldt squid and other warm water species 2009), with individuals generally increasing in abundance were documented over the continental shelf and slope shoreward in late summer. The highest observed densi- from June through November in sea surface temperatures ties were in 2009 and measured 1,671 squid (106 m3)–1. ranging from 13.4 to 14.3˚C (Pearcy 2002). Between Physical features associated with increased squid catch 2002 and 2009, Humboldt squid undertook seasonal for- included station depth, subsurface water temperature, aging visits to the northern CCS, with many reports of ocean salinity, ocean density, and dissolved oxygen. In summertime beach strandings/landings by commercial, addition, the arrival of Humboldt squid onto the shelf scientific, and recreational fisheries off Oregon, Washing- in late summer was coincident with declines of juvenile ton, and British Columbia (Cosgrove 2005; Brodeur et al. (10–30 cm total length) Pacific hake (Merluccius produc- 2006; Trudel et al. 2006). However, little is known about tus), in contrast to the typical increases of hake recorded the seasonal and interannual variability in the large-scale in late summer during recent years. Our results suggest distribution of Humboldt squid in the northern CCS. that predator-prey interactions and ocean conditions in Several environmental and ecological factors have the CCS epipelagic zone lead to seasonal expansions, yet been implicated as potential drivers of the appearance unsuccessful colonization attempts, by Humboldt squid of Humboldt squid in temperate waters of the northern populations. Identifying the economic and ecological CCS, including warming ocean temperatures, shoaling, impacts of this newly arrived predator should be a top or expansion of the oxygen minimum zone (OMZ), research priority. and overfishing of subtropical predators in the Eastern Tropical Pacific (Pearcy 2002; Gilly et al. 2006; Field et INTRODUCTION al. 2007; Zeidberg and Robison 2007; Rodhouse 2008). Humboldt squid (also known as jumbo flying squid We hypothesize that an abundance of potential prey in Dosidicus gigas) have recently visited the northern Cal- the CCS, namely juvenile (10–30 cm total length [TL]) ifornia Current system (CCS) and have been docu- Pacific hake, Pacific sardine, northern anchovy (Engrau- mented as far north as southeast Alaska (Pearcy 2002; lis mordax), rockfish, and myctophids, may be an equally Cosgrove 2005; Brodeur et al. 2006; Rodhouse et al important explanation for episodic appearances of Hum- 2006; Wing 2006; Field et al. 2007; 2008; Rodhouse boldt squid in the northern CCS. However, the bio- 2008). They are voracious predators that can grow to logical and environmental mechanisms driving seasonal 2 m and 50 kg within a year (Zeidberg and Robison Humboldt squid visits remain poorly understood. 2007), and Markaida et al. (2004) found that Humboldt Here we analyze fishery and oceanographic infor- squid in the Gulf of California have one of the high- mation collected by NOAA Fisheries Northwest Fish- 97 Litz paste.indd 97 11/7/11 9:57 AM LITZ ET AL.: SEASONAL OCCURENCES OF HUMBOLDT SQUID CalCOFI Rep., Vol. 52, 2011 eries Science Center (NWFSC) during recent surveys individuals of each species for length. In the event of a off Oregon and Washington (2004–2009) to examine very large catch, we counted and weighed a subsample the seasonal and interannual patterns in the occurrence of each species and used the measured weight of the of Humboldt squid. Records from these surveys repre- remaining catch to estimate the total number of indi- sent a limited, though valuable comprehensive seasonal viduals caught. In addition, we collected environmental and annual time series of Humboldt squid catches in the information, including temperature, salinity, and water Pacific Northwest to date.T he objectives of this study density from the surface down to 100 m (or within 5 were to explore recent catch data and find some con- m from the bottom at stations <100 m depth) prior to nectivity between physical oceanographic conditions and each trawl by deploying a Sea-Bird SBE SEALOGGER the observed sporadic spatial and temporal occurrence 25 (SAIP study) or SBE 19 SEACAT (Predator study) of Humboldt squid in the northern California Current CTD profiler. Beginning in September 2008, the SBE to provide important baseline monitoring information 25 SEALOGGER CTD was outfitted with a dissolved which will serve the research community when design- oxygen (DO) sensor to measure in situ concentrations ing new studies. We hypothesize that changes in physi- (ml L–1). All CTD sensors were calibrated annually prior cal oceanographic conditions play an important role in to the start of each cruise season. determining ecological habitat for Humboldt squid, but Because of a disproportionate amount of zero catches, also that the interactive processes of biology, prey avail- the relationship between environmental factors and ability, and fisheries could play a role. Humboldt squid caught in our trawls was examined by a two-step or conditional modeling approach, using METHODS exploratory Generalized Additive Models (GAMs) with The NWFSC surveyed spring-fall marine resources the mgcv-package (Wood 2006) available for R (v2.10.1) off Oregon and Washington (2004–2009) by fishing software (The R Foundation for Statistical Computing, at night in two separate studies: the Stock Assessment http://www.r-project.org). GAMs were chosen for habi- Improvement Program, or SAIP study, initiated in 2004 tat analysis because the relationship between Humboldt (see Phillips et al. 2009), and the Predator study, initiated squid and environmental variables was expected to be in 1998 (see Emmett et al. 2006). Both studies fished a of a complex form, not easily fitted by standard linear Nordic 264-rope trawl behind a chartered fishing ves- or nonlinear models. GAM fitting techniques have been sel, but the SAIP study fished the headrope at midwater employed to understand and predict variations in cepha- (30 m), while the Predator study fished the headrope at lopod abundance in many systems (Bellido et al. 2001; the surface. The SAIP study regularly sampled four tran- Denis et al. 2002; Tian et al. 2009). sects monthly during May–September (and in Novem- Both binomial and conditional Poisson GAMs were ber 2004 and October 2005), with stations ranging from fitted to filtered data sets gathered on Humboldt squid 5–100 nautical miles (nm) offshore.A total of 412 night- during the SAIP Study (2004-2009). Humboldt squid time midwater trawls were conducted between Hec- presence/absence was first modeled against environmen- ata Head, OR (44˚00N) and Willapa Bay, WA (46˚40N; tal data using (1) a binomial family fit with a logit-link table 1a.). The Predator study sampled 535 nighttime function, using only stations that were repeatedly sam- trawls along two transects (5–30 nm from shore) off the pled over the six years where Humboldt squid were mouth of the Columbia River, OR (46˚10N) and Wil- captured (n = 315 hauls). Next, Humboldt squid abun- lapa Bay, WA (46˚40N) biweekly from April–August in dance (count), was modeled using (2) a Poisson distri- 2004–2009 (table 1b). While SAIP study stations spanned the shelf break and slope (station depths ranged from 55 TABLE 1 to 3,150 m), Predator study stations were located pri- Abbreviations, descriptions, and sources marily on the shelf (depths ranged from 28 to 293 m). of the large-scale environmental variables used in the At each station, the trawl was towed astern of the Generalized Additive Models (GAMs). fishing vessel for 15–30 minutes at a vessel speed aver- Abbreviation Description and source aging 3.1 kts. The deployed trawl had a mouth opening MEI Multivariate El Niño-Southern Oscillation Index. of 12 m deep by 28 m wide (336 m2) based on previ- From the NOAA Earth System Research Laboratory Web site: http://www.cdc.noaa.gov/ENSO/enso. ous determinations using a third-wire Simrad FS3300 mei_index.html.
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