Although the California Current has undergone substantial environmental shifts in the past few decades, the summer of 2005 exhibited highly anomalous conditions relative to all previous recorded summers in terms of late initiation of upwelling and the resulting elevated surface temperatures and depressed productivity through July. The response of pelagic nekton to these anomalous conditions was widespread and included onshore and poleward displacement of taxa to new geographic areas, population changes within the normal range, and reduced productivity of early life stages based on larval and juvenile surveys. Some nekton exhibited anomalous distributions in 2004. Many ecologically important species were affected. The response of the nektonic community off California was greater than during El Niño conditions.

The community structure of pelagic zooplankton and micronekton may be a sensitive indicator of changes in environmental conditions within the California Current ecosystem. Substantial oceanographic changes in 2015 and 2016, due to the anomalously warm ocean conditions associated with a large-scale marine heatwave perturbation, resulted in onshore and northward advection of warmer and more stratified surface waters resulting in reduced upwelling. Here we quantify changes in the macrozooplankton and micronekton community composition and structure based on five highly contrasting ocean conditions. Data from fine-mesh pelagic trawl surveys conducted off Oregon and Washington during early summer of 2011 and 2013-2016 were examined for interannual changes in spatial distribution and abundance of fish and invertebrate taxa. Overall species diversity was highest in 2015 and lowest in 2011, but 2016 was similar to the other years, although the evenness was somewhat lower. The community of taxa in both 2015 and 2016 was significantly different from the previously sampled years. Crustacean plankton densities (especially Euphausiidae) were extremely low in both of these years, and the invertebrate composition became dominated mostly by gelatinous zooplankton. Fishes and cephalopods showed mixed trends overall, but some species such as age-0 Pacific hake were found in relatively high abundances mainly along the shelf break in 2015 and 2016. These results suggest dramatically different pelagic communities were present during the recent warm years with a greater contribution from offshore taxa, especially gelatinous taxa, during 2015 and 2016. The substantial reorganization of the pelagic community has the potential to lead to major alterations in trophic functioning in this normally productive ecosystem.

Tarletonbeania crenularis specimens were collected off Oregon in 2006 and 2009 and aged by enumeration of growth increments in otoliths (sagittae). Three microstructural zones were evident in the otoliths of juvenile and adult fish: central, middle, and external. The number of increments in the central zone are thought to be deposited during the larval phase which is restricted to the uppermost 350 m water layer. The middle zone constituted of barely visible increments, most likely represented a non-migratory behavior of transforming larvae and early juvenile stages. Well defined growth increments were found in the external zone which was presumably formed during extensive vertical migrations of juvenile and adult fish. If the enumerated increments were deposited daily, as previously validated for other myctophid species, the examined individuals indicated a shorter life span than has been formerly reported on the basis of length frequency analysis. The otolith microstructure interpretation was supported by otolith size to fish length proportions and somatic growth of larvae and postlarval fish. Otolith length to standard length relation was described by linear regression models for larvae and postlarval migratory stages with an abrupt disruption between these two groups. The number of growth increments in otoliths plotted against standard length showed a curvilinear growth for larvae and for the postlarval fish. The lack of information on the size at age of transforming larvae and non-migratory early juveniles did not allow us to estimate a complete growth model for T. crenularis. However, a pronounced decrease in growth between larval and postlarval migratory phases was distinguished. The uncoupling of otolith and somatic growth was interpreted as a merged effect of downward migration of larvae to the mesopelagic transformation depth, prolonged stay of transforming larvae and early juveniles at this depth without performing diel vertical migrations, and shrinkage during metamorphosis. Back-calculated hatch dates suggests a prolonged spawning season of this species without any distinct peak.

This study investigated the spatial distribution of juvenile North Pacific albacore (Thunnus alalunga) in relation to local environmental variability [i.e. sea surface temperature (SST)], and two large-scale indices of climate variability, [the Pacific Decadal Oscillation (PDO) and the Multivariate El Niño/Southern Oscillation Index (MEI)]. Changes in local and climate variables were correlated with 48 years of albacore troll catch per unit effort (CPUE) in 1° latitude/longitude cells, using threshold Generalized Additive Mixed Models (tGAMMs). Model terms were included to account for non-stationary and spatially variable effects of the intervening covariates on albacore CPUE. Results indicate that SST had a positive and spatially variable effect on albacore CPUE, with increasingly positive effects to the North, while PDO had an overall negative effect. Although albacore CPUE increased with SST both before and after a threshold year of 1986, such effect geographically shifted north after 1986. This is the first study to demonstrate the non-stationary spatial dynamics of albacore tuna, linked with a major shift of the North Pacific. Results imply that if ocean temperatures continue to increase, US west coast fisher communities reliant on commercial albacore fisheries are likely to be negatively affected in the southern areas but positively affected in the northern areas, where current albacore landings are highest.

The Fukushima Daiichi power station released several radionuclides into the Pacific following the March 2011 earthquake and tsunami. A total of 26 Pacific albacore (Thunnus alalunga) caught off the Pacific Northwest U.S. coast between 2008 and 2012 were analyzed for (137)Cs and Fukushima-attributed (134)Cs. Both 2011 (2 of 2) and several 2012 (10 of 17) edible tissue samples exhibited increased activity concentrations of (137)Cs (234-824 mBq/kg of wet weight) and (134)Cs (18.2-356 mBq/kg of wet weight). The remaining 2012 samples and all pre-Fukushima (2008-2009) samples possessed lower (137)Cs activity concentrations (103-272 mBq/kg of wet weight) with no detectable (134)Cs activity. Age, as indicated by fork length, was a strong predictor for both the presence and concentration of (134)Cs (p< 0.001). Notably, many migration-aged fish did not exhibit any (134)Cs, suggesting that they had not recently migrated near Japan. None of the tested samples would represent a significant change in annual radiation dose if consumed by humans.

During the day, Dungeness crab (Cancer magister) megalopae from off the outer coasts of Vancouver Island and Washington are aggregated at about 25 m whereas those from the Strait of Georgia are at about 160 m. At night, both populations of megalopae seem to be mostly in the top metre of water. Juan de Fuca Strait, which connects the Strait of Georgia to the Pacific Ocean, typically has an estuarine circulation, with outflow in the top 50–100 m and deeper inflow. Because the daylight to dark ratio when megalopae are present is about 3:1, the Strait of Georgia and outer-coast megalopae are mostly retained within their own systems by currents at their daytime depths. Occasional intrusions of outer-coast megalopae into Juan de Fuca Strait may occur when estuarine flow in the Strait temporarily breaks down following sustained, strong, southwesterly winds; such intrusions are typically restricted to the south and head of Juan de Fuca Strait, and even extensive ones do not carry megalopae far into the Strait of Georgia. The daily movement of larval crab to cold (<10 °C), deep water in the Strait of Georgia may explain, at least partially, the delay in seasonal timing of settlement and their smaller physical size at settlement compared with outer-coast megalopae.

No abstract

Length-based models were developed for the male Dungeness crab (Cancer magister) population on the Fraser delta near Vancouver, British Columbia. The models incorporate the probability of moulting, moult increments, natural mortality during moulting and non-moulting periods, direct fishing mortality, and handling mortality that occurs when sublegal-sized crabs are caught and released. The models were used to investigate how long-term yield might be affected by the combination of handling mortality and an intensive fishery. The models were calibrated to survey data, and key biological parameters were estimated. The probability of moulting is near one for male crabs in the 130-to 150-mm carapace width range and decreases as crabs get larger. There is a 70.1% probability a crab will survive the 1-month period beginning with a moult. The non-moulting natural mortality rate is 0.97 year -1 . When handling mortality is incorporated into the model, yield per recruit increases with the exploitation rate until it reaches approximately 94%. F 0.1 is equivalent to 70%. An approach was developed to calculate the threshold ratio of discarded to retained crabs beyond which fishing would reduce the long-term yield.Résumé : Nous avons mis au point des modèles basés sur la longueur que nous avons appliqués à une population de crabes dormeurs mâles (Cancer magister) du delta du Fraser, près de Vancouver. Les modèles tiennent compte de la probabilité de la mue, de la croissance à la mue, de la mortalité naturelle durant les périodes de mue et en dehors de ces périodes, de la mortalité directe due à la pêche et de la mortalité due à la manipulation, lorsque des crabes de taille inférieure à la taille réglementaire sont capturés et relâchés. Les modèles ont servi à déterminer comment le rendement à long terme peut être affecté par la combinaison de la mortalité due à la manipulation et d'une intensité de pêche élevée. Nous avons calibré les modèles aux données d'inventaire et nous avons estimé les paramètres biologiques. La probabilité de la mue chez les crabes de largeur de carapace 130-150 mm est près de 1 et elle diminue en fonction de la taille chez les crabes plus grands. La probabilité qu'un crabe survive à la période d'un mois qui suit la mue est de 70,1 %. La mortalité naturelle est de 0,97·année -1 en l'absence de mue. Si la mortalité due à la manipulation est ajoutée au modèle, le rendement par recrue augmente en fonction du taux d'exploitation jusqu'à atteindre approximativement 94 %. F 0,1 équivaut à 70 %. Nous avons développé une méthodologie pour calculer le seuil du rapport des crabes rejetés sur les crabes retenus au-dessus duquel la pêche réduit le rendement à long terme.[Traduit par la Rédaction] Zhang et al. 2134