Range expansion events of the Humboldt squid reveal our inadequate understanding of populations of this species. Despite recent hatching, reproductive, tagging, genetic and dietary studies of Dosidicus gigas, much speculation remains concerning geographic migration, stock assessment and habitat preferences. This study provides evidence that statolith trace elemental variations can be useful in distinguishing among geographic populations. Specimens were collected from the Galapagos Islands, southern California, and Washington State. A dissection method was recorded and published. By using laser ablation methods, discrete measurements of 10 elements were collected at 6 to 7 ablation sites covering embryonic, paralarval, juvenile and adult stages. Analysis of Variance revealed important ontogenic elemental variations among ablation locations. Multivariate Analysis of Variance, ordination techniques and discriminant function analysis with permutation testing were all utilized to compare and characterize the variations found in elemental concentrations. Significant ontogenic variations were found for 8 out of the 10 focus elements; this is the first report for 5 of these elements for this species. The geographic populations were effectively classified as distinct group for the first time using these methods. Elemental fingerprint signatures were found to be significantly different at multiple ontogenic growth regions of the statolith. Seattle and California paralarvae exhibited similar elemental signatures despite significant differences in those found in the embryonic core and juvenile regions of the statolith. These methods are a useful tool in providing stock assessment and can be improved for use in future population dynamics models.

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Le nord du système du Courant de Humboldt (NHCS), le long des côtes péruviennes, est l'une des régions océanique les plus productives au monde. Il représente moins de 0.1% de la surface des océans mondiaux mais contribue actuellement à plus de 10% des captures mondiales en poissons, avec l’anchois Engraulis ringens comme espèce emblématique. Comparé aux autres systèmes d’upwelling de bord Est, la forte productivité en poissons ne peut être expliquée par une productivité primaire plus élevée. Par contre, le NCHS est la région où El Niño, et la variabilité climatique en général est la plus notable. D’autre part, les eaux de surface oxygénées recouvrent une zone de minimum d’oxygène extrêmement intense et superficielle. L’objectif principal de ce travail est de mieux comprendre les relations trophiques au sein du NHCS en combinant l'analyse de contenus stomacaux et d'isotopes stables. Cette étude se focalise sur une variété d’organismes allant des bas niveaux trophiques comme le zooplancton aux prédateurs supérieurs (oiseaux et les otaries à fourrure). Elle combine des études de contenus stomacaux ponctuelles et sur le long terme d’espèces clés telles que l’anchois et la sardine Sardinops sagax et une analyse plus globale, basée sur l'utilisation d'isotopes stables et considérant l’ensemble du réseau trophique dans les années récentes (2008 – 2012). Les analyses des contenus stomacaux d'anchois et de sardine ont permis de revisiter l'écologie de ces espèces. En effet, bien que le phytoplancton domine largement les contenus stomacaux en termes d’abondance numérique, le zooplancton est de loin la composante alimentaire la plus importante pour ces deux espèces en termes de carbone. Dans le cas de l’anchois, les euphausiacés contribuent à plus de 67.5% du carbone ingéré, suivis par les copépodes (26.3%). Sélectionner les proies les plus grandes telles que les euphausiacés procure un avantage énergétique pour l’anchois dans cet écosystème où les carences en oxygène imposent de fortes contraintes métaboliques aux poissons pélagiques. La sardine se nourrit de zooplancton plus petit que l’anchois (copépodes plus petits et moins d’euphausiacés). Ainsi, la compétition trophique entre les sardines et les anchois est minimisée dans le NSCH par le partage de la ressource zooplancton selon sa taille, comme cela a déjà été montré dans d’autres écosystèmes. Ces résultats remettent en question la compréhension première de la position des petits poissons pélagiques (zooplanctonophage et non phytoplanctonophage) dans la chaine trophique ce qui implique de reconsidérer le fonctionnement et les modèles trophiques du NCHS. Afin d’obtenir une compréhension plus globale de la position trophique relative des principaux composants du NHCS une approche basée sur des analyses d’isotopes stables (δ13C et δ15N) a été utilisée. Pour ce faire, la signature isotopique d'échantillons de 13 groupes taxonomiques (zooplancton, poissons, calmars et prédateurs supérieurs) prélevés entre 2008 et 2011 a été déterminée. Les valeurs de δ15N obtenues sont fortement impactées par l’espèce, la taille et la latitude. Le long de la cote péruvienne, la zone de minimum d’oxygène devient en effet plus intense et plus superficielle au sud de ~7.5ºS impactant fortement la valeur de δ15N de la ligne de base. Nous avons donc utilisé un modèle linéaire à effet mixte prenant en compte les effets latitude et taille afin de prédire la position trophique relative des composants clés de l’écosystème. Ces analyses isotopiques confirment les résultats issus des contenus stomacaux sur le régime alimentaire de l’anchois et mettent en évidence l’importance potentielle d’une composante souvent négligée de l’écosystème, la galathée pélagique Pleuroncodes monodon. En effet, nos résultats supportent l’hypothèse selon laquelle cette espèce s’alimenterait en partie sur les oeufs et larves d’anchois, menaçant ainsi les premiers stades de vie des espèces exploitées. [...] / The northern Humboldt Current system (NHCS) off Peru is one of the most productive world marine regions. It represents less than 0.1% of the world ocean surface but presently sustains about 10% of the world fish catch, with the Peruvian anchovy or anchoveta Engraulis ringens as emblematic fish resource. Compared with other eastern boundary upwelling systems, the higher fish productivity of the NHCS cannot be explained by a corresponding higher primary productivity. On another hand, the NHCS is the region where El Niño, and climate variability in general, is most notable. Also, surface oxygenated waters overlie an intense and extremely shallow Oxygen Minimum Zone (OMZ). In this context, the main objective of this study is to better understand the trophic flows in the NHCS using both stomach content and stable isotope analyses. The study focuses on a variety of organisms from low trophic levels such as zooplankton to top predators (seabirds and fur seals). The approach combines both long-term and specific studies on emblematic species such as anchoveta, and sardine Sardinops sagax and a more inclusive analysis considering the 'global' food web in the recent years (2008 –2012) using stable isotope analysis.Revisiting anchovy and sardine we show that whereas phytoplankton largely dominated anchoveta and sardine diets in terms of numerical abundance, the carbon content of prey items indicated that zooplankton was by far the most important dietary component. Indeed for anchovy euphausiids contributed 67.5% of dietary carbon, followed by copepods (26.3%).Selecting the largest prey, the euphausiids, provide an energetic advantage for anchoveta in its ecosystem where oxygen depletion imposes strong metabolic constrain to pelagic fish. Sardine feed on smaller zooplankton than do anchoveta, with sardine diet consisting of smaller copepods and fewer euphausiids than anchoveta diet. Hence, trophic competition between sardine and anchovy in the northern Humboldt Current system is minimized by their partitioning of the zooplankton food resource based on prey size, as has been reported in other systems.These results suggest an ecological role for pelagic fish that challenges previous understanding of their position in the foodweb (zooplanktophagous instead of phytophagous), the functioning and the trophic models of the NHCS.Finally to obtain a more comprehensive vision of the relative trophic position of NHCS main components we used stable isotope analyses. For that purpose we analyzed the δ13C and δ15N stable isotope values of thirteen taxonomic categories collected off Peru from 2008 - 2011, i.e., zooplankton, fish, squids and air-breathing top predators. The δ15N isotope signature was strongly impacted by the species, the body length and the latitude. Along the Peruvian coast, the OMZ get more intense and shallow south of ~7.5ºS impacting the baseline nitrogen stable isotopes. Employing a linear mixed-effects modelling approach taking into account the latitudinal and body length effects, we provide a new vision of the relative trophic position of key ecosystem components. Also we confirm stomach content-based results on anchoveta Engraulis ringens and highlight the potential remarkable importance of an often neglected ecosystem component, the squat lobster Pleuroncodes monodon. Indeed, our results support the hypothesis according to which this species forage to some extent on fish eggs and larvae and can thus predate on the first life stages of exploited species. However, the δ13C values of these two species suggest that anchoveta and squat lobster do not exactly share the same habitat. This would potentially reduce some direct competition and/or predation.

Interannual variability of Humboldt squid (Dosidicus gigas) occurrence in the northern California Current System is largely unknown. In Oregon, the distribution of this versatile predator and what is influencing their range expansion from Mexico is poorly understood due to the recent nature of their "invasion" and a lack of monitoring. Humboldt squid are large predators that have the potential to affect ecosystem structure and fisheries because of their high-energy demands and ability to exploit a variety of oceanographic conditions and prey sources. Developing baseline distribution information is a critical first step to assess their potential ecological, social, and economic impacts, and to develop models to predict future range expansion. This study has two main objectives: (1) to document where and when Humboldt squid have been present in Oregon through cooperative fisheries research, and (2) to correlate the sightings with oceanographic conditions using a geographic information system (GIS) and species distribution modeling (SDM). I conducted 54 interviews with local fishermen and aggregated their squid sightings with available fishery-independent survey and fishery-dependent observer data from the National Marine Fisheries Service. I compiled a total of 339 Humboldt squid sightings, reported for the years 2002-2011 from the Oregon coast to 131�� west longitude. Correlation analyses were performed for Humboldt squid sightings and sea surface temperature (SST), chlorophyll a content (chla), sea surface height anomalies (SSH), dissolved oxygen at 30 m depth (30 m DO), and sea surface salinity (SSS) using a GIS, nonparametric multiplicative regression (NPMR) habitat modeling, and maximum entropy modeling (Maxent). Results indicate that oceanographic conditions have the potential to influence Humboldt squid occurrence, and in Oregon, sightings vary temporally and spatially. Combining the sightings from fishermen and scientific surveys greatly enhanced the spatial extent of the data. Humboldt squid were most frequently observed between 124.4��W and 125��W in proximity to the shelf-break at the 200 m isobath, with peak sightings (116) recorded in 2009 and the fewest (6) reported in 2003 and 2011. The highest occurrence of Humboldt squid were observed at a SST of 10.5-13.0��C, 0.26-3.0 mg m����� chla content, -4.0-1.0 m SSH anomalies, 32.2-32.8 psu SSS, and at 3-4.5 ml L����� and 6-7 ml L����� 30 m depth DO. Maps of estimated likelihood of occurrence generated by NPMR were consistent with overlayed observations from fishermen, which were not used in the model because they were limited to presence-only information. An interdisciplinary approach that incorporates cooperative fisheries research and ecosystem-based management is necessary for monitoring Humboldt squid in Oregon. Traditional methods are insufficient because Humboldt squid are data-poor, highly migratory, and are main predators of many commercially important fisheries in Oregon. Based on my findings, sightings recorded by fishermen covered a much larger area over a longer time frame than the scientific survey and observer data, and excluding their knowledge would have led to a different interpretation of Humboldt squid distribution and environmental tolerances. Although there is uncertainty in the data from potential map bias or misidentification of smaller Humboldt squid, incorporating sightings from fishermen with traditional fisheries research increases the quantity and quality of information. Cooperative monitoring for Humboldt squid could include training in species identification and sea condition reporting in logbooks. Future "invasions" are likely, and more eyes on the water will improve our understanding of the behavior and impacts of Humboldt squid on coastal resources. / Graduation date: 2013