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We examined aspects of summer feeding in Pacific hake (Merluccius productus) and spiny dogfish (Squalus acanthias). Euphausiids (Thysanoessa spinifera, Euphausia pacifica) and Pacific herring (Ciupea harengus pallasi) accounted for almost all of the hake diet over all August sampling periods (1983, 1985–89) and the 1988 summer feeding period (June-...
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... rations f ~ r hake differed between and within years and between shelf and shelf-break feeding areas. Results from the adjusted August data ( feeding areas, respectively (Table 7). These mean summer rations were just insignificantly different (t = 2.59, 0.10 < p < 0.05). ...
Citations
... The proportion of cannibalism, by weight, in Pacific hake stomachs was sourced from the California Current Trophic Database (CCTD), which is comprised of stomachs collected from multiple sources in 1988-1991, 1995-1999, 2002, 2007. The hake diet data were primarily from two sources: collected as part of the Pacific Coast continental shelf and upper continental slope survey conducted by the NOAA's Alaska Fisheries Science Center from 1980 to 2001 Livingston 1997 , Buckley et al. 1999 ), and from the hake acoustic-trawl survey conducted by the NOAA's Northwest Fisheries Science Center (NWFSC) from 2005 to 2019. ...
By incorporating trophic interactions and temperature-dependent bioenergetics, multi-species models such as CEATTLE (climate-enhanced age-based model with temperature-specific trophic linkages and energetics) are a step towards ecosystem-based stock assessment and management of high-value commercial species such as Pacific hake (Merluccius productus). Hake are generalist predators and previous studies in the California Current Ecosystem have determined that their diet consists of ∼30% cannibalism. We used CEATTLE to include cannibalism in a model of hake population dynamics and reexamined hake diet data to determine the proportion by age that can attributed to cannibalism. The proportion was highly variable, ranging between 0 and 80% of stomach contents by weight. When included in the CEATTLE model, the estimated spawning biomass, total biomass, and recruitment increased by 15, 23, and 58%, on average, relative to the single-species model, due to the estimation of time-and age-varying predation mortality, primarily for age-1 hake. The effects of cannibalism varied over time, with further increases in total biomass and recruitment resulting from the age structure of the population following large cohorts in 1980 and 1984. Results from the cannibalism model could be used to inform the estimation of time-and age-varying mortality in the single-species assessment and as a pathway for including ecosystem information in management through environmental and trophic drivers of variability in mortality.
... Hake TL approached 4 only in the JDF region. Hake consume more herring as euphausiid densities decline (Tanasichuk et al. 1991) and, correspondingly, increase predation on herring in the JDF eddy region in the late summer, when euphausiid density is lower (Hamel et al. 2015). It is possible that this late season increase in piscivory was reflected in the high TL of JDF hake samples. ...
The pelagic food webs of British Columbia’s (BC) coastal oceans have never had a comprehensive review of their trophic structure. In this study, we analyzed carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios of pelagic food web components collected from four regions in southern BC: Juan de Fuca Strait, the Strait of Georgia, Queen Charlotte Strait, and Queen Charlotte Sound during an August 2019 survey. In addition, conductivity, temperature, and depth (CTD), chlorophyll, and nutrient data were collected to assess the oceanographic basis for regionalization. Between regions, we observed differences in the isotopic baseline driven by regional oceanography. Likewise, we also observed oceanography-driven differences in regional food chain length, carbon range, and isotopic overlap. Species-specific trophic level and isotopic niche were determined. For common pelagic species, we described how trophic level varied regionally, was not always in line with previously published dietary data, and instead largely tracked regional changes in food chain length. We conclude that variable food web properties and trophic ecology can manifest across the small spatial scales of the BC coast’s discrete regions.
... Alternatively, the vertical distribution of hake in the water column may vary by age. For instance, younger hake may be shallower in the water column, possibly due to smaller prey being more surface oriented during certain parts of the day (Nielson and Perry 1990;Tanasichuk et al. 1991;Pillar and Barange 1995). Understanding how the CU impacts the distribution of key hake diet items, e.g., euphausiids, would be a useful next step in determining the mechanisms underpinning the spatial and ontogenetic varying relationships observed here. ...
In the California Current Ecosystem, the California Undercurrent (CU) is the predominate subsurface current that transports nutrient-rich water from southern California poleward. In this study, we used a large dataset of spatially explicit in situ observations of Pacific hake (Merluccius productus) and the CU (36.5–48.3°N) to estimate relationships between northward undercurrent velocity and hake distribution and determine whether these relationships vary across space or life-history stage. We found that both hake occurrence and density had strong spatially complex relationships with the CU. In areas north of 44°N (central Oregon), the CU effect was spatially consistent and opposite for occurrence (negative) and density (positive), indicating that hake may aggregate in areas of high northward velocity in this region. In areas south of 44°N, the CU effect showed a cross-shelf gradient for both occurrence and density, indicating a more nearshore hake distribution when northward velocity is higher in this region. Together, our results suggest that future changes in the CU due to climate change are likely to impact hake differently in northern and southern areas.
... Specifically, larger, older hake typically migrate much further north, and the northward extent of the distribution is also highly variable from year to year in response to ocean conditions, extending farther north with increasing ocean temperature and, likely, forage availability (Ressler et al. 2007, Malick et al. 2020a. Pacific hake diets are generally narrower than those of Chinook salmon, with a substantial reliance on krill and a more limited number of forage fishes (Brodeur et al. 1987, Tanasichuk et al. 1991, Buckley & Livingston 1997. The total biomass of Pacific hake has ranged from 1−10 million metric tons over the past 50 yr, and hake are the most abundant finfish in the CCE (Edwards et al. 2022). ...
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Trophic interactions are proximate drivers of ecosystem function, including predator-prey dynamics, and their spatio-temporal variability may reflect ecosystem shifts and changes in trophic transfer. We investigated biogeographic structuring of trophic interactions by analyzing multi-decadal time series of diet for Pacific hake Merluccius productus and Chinook salmon Oncorhynchus tshawytscha from a large marine ecosystem. We compared our predictions for spatio-temporal variability of hake and salmon trophoscapes (i.e. spatially explicit predictions of trophic relationships) to inform ecosystem dynamics and fishery bycatch patterns. We have 3 inter-related findings pertaining to the spatial coherence of the trophoscapes and the potential consequences to juvenile and sub-adult (i.e. after the first year at sea but prior to maturation) salmon when sharing foraging areas with Pacific hake. First, the spatial scale of Pacific hake diet represents coastwide variability, and the spatial variability of Chinook salmon diets differs across regions and demonstrates a broad diet. Second, the expectation for increased diet and spatial overlap of Pacific hake and Chinook salmon during low productivity periods (e.g. periods with low krill biomass, suboptimal upwelling) can inform fishery management challenges. In this regard, we explore the role of shared foraging habitats on increased predation, and consequentially reduced recruitment, by Pacific hake on juvenile salmon during sub-optimal upwelling conditions. Third, we show that above-average bycatch of sub-adult Chinook salmon was associated with later spring transition, potentially as a result of both Pacific hake and salmon sharing foraging areas and prey species on the shelf and shelf break.
... Pseudocollinia sp. have been reported more extensively from euphausiids in the Pacific, Atlantic and Southern Oceans (Lynn et al., 2014;Cleary et al., 2019), including infections of P. oregonensis causing mass deaths in E. pacifica populations off the coast of Oregon, USA (Gómez-Gutiérrez et al., 2006). So, it is likely that Pseudocollinia parasites are also influencing the productivity of E. pacifica populations in the nearby Strait of Georgia, where euphausiids are one of the dominant groups of zooplankton and serve as important trophic links as they are directly consumed by animals including fish and marine mammals (Tanasichuk et al., 1991;Mackas et al., 2013;Nickels et al., 2019). ...
Protists (eukaryotic microorganisms) commonly form symbiotic associations with crustacean zooplankton, but their diversity, prevalence and ecological roles are underestimated due to the limited scope of previous investigations. Using metabarcoding of the V4 region of the 18S rRNA gene, we characterized the eukaryotic microbiomes of the dominant crustacean zooplankton, specifically copepods, euphausiids, amphipods and ostracods, from the Strait of Georgia, Canada. Sequence reads from the alveolates dominated all zooplankton examined, which mostly comprised ciliates and dinoflagellates of known symbiont lineages. These lineages included not only those of parasitoids but also those of uncharacterized species. Apostome ciliate reads were the most abundant in all hosts except for cyclopoid copepods, which were dominated by the parasitic Syndiniales. Most symbiont lineages showed some degree of host preference, particularly Pseudocolliniidae ciliate parasites with ostracods, but were often detected in all hosts indicating broad host specificity. Reads from free-living protists, including diatoms and surprisingly hydrozoans, were inferred to be part of their diet. Hydrozoans may have been ingested from free organic matter, such as detritus or marine snow, suggesting a likely underestimated pathway of carbon cycling. This investigation contributes to resolving the interactions between zooplankton and protists and the potential ecological significance of symbioses on zooplankton productivity.
... Understanding how lower trophic levels respond to environmental change is an important component of ecosystembased management. In the northeast Pacific Ocean, euphausiids are important prey for a wide range of marine predators, including whales and seabirds (Abraham and Sydeman, 2004;Hipfner, 2009;Nickels et al., 2019), and an array of commercially important fish species such as Pacific hake (Merluccius productus), Pacific herring (Clupea pallasii), sablefish (Anoplopoma fimbria) and Pacific salmon (Tanasichuk et al., 1991;Robinson, 2000;Beamish et al., 2004). Euphausiids form dense aggregations which are inherently patchily distributed through the marine environment. ...
Euphausiids form a critical component of oceanic food chains and individual species vary in their responses to perturbation events. We aimed to establish if patterns of fine scale oceanographic variability and larger-scale climate events such as marine heatwaves (MHWs) could be linked with spring variability in the biomass of two key forage species in the northeast Pacific Ocean, Euphausia pacifica and Thysanoessa spinifera. To achieve this, we used long-term datasets from the west coast of Vancouver Island Canada, an important commercial fishing area, to first quantify interannual signals of variability in fine-scale oceanographic conditions using multivariate analysis. We then used geostatistical spatiotemporal modelling to quantify the effects on species-specific euphausiid biomass. Oceanographic data showed that the effects of warm events are not always observable, and effects vary across small spatial scales. Warming due to the 2014-2016 MHW was relatively mild on the continental shelf during spring (<1°C above climatology). Spring biomass of euphausiids, particularly E. pacifica, peaked in 2015, and all euphausiid groups analysed (E. pacifica, T. spinifera and total euphausiids) exhibited significant correlations with positive phases of the Pacific Decadal Oscillation. These results have implications for marine predators as euphausiids may act as system stabilisers in the northeast Pacific, thereby potentially increasing ecosystem resilience during extreme events.
... Hake are generally thought to migrate north from offshore waters in southern California during spring, and form feeding aggregations throughout the CCE during summer, consuming euphausiids, or krill, as a key prey item (Methot & Dorn, 1995;Tanasichuk et al., 1991). ...
... While a number of krill species exist in the CCE, Euphausia pacifica and Thysanoessa spinifera dominate the community (Brinton, 1962(Brinton, , 1967Brinton & Townsend, 2003) and are the primary species consumed by hake (Tanasichuk et al., 1991). Despite the importance of krill in hake diets, little is known about how shifts in krill abundance may affect hake distribution, growth, and recruitment. ...
... These results have important implications for potential temperature-induced shifts in hake feeding, growth, and recruitment. The diet of hake is predominantly composed of krill (Tanasichuk, 1999;Tanasichuk et al., 1991), but during warm ocean conditions, hake may switch to alternative prey to meet energetic demands if krill are not encountered, which could negatively impact growth (Grover et al., 2002). Conversely, in cool years, hake may consume more krill and experience greater growth and recruitment. ...
Understanding the influence of ocean conditions on predator–prey relationships can provide insight for ecosystem‐based fisheries management. Pacific hake (Merluccius productus) are abundant and commercially important groundfish in the California Current Ecosystem (CCE) that consume euphausiids (krill) as a major prey item. We used data from the biennial joint U.S.‐Canada Integrated Ecosystem & Acoustic Trawl Survey for Pacific hake (2007–2019, n = 8 surveys) to quantify co‐occurrence of age 2+ hake with krill in relation to bottom depth, continental shelf break location, surface chlorophyll‐a, and 100‐m temperature. Vertical distributions of hake varied among years and were not correlated to krill depth. Hake hotspots occurred primarily off the Oregon coast and near Cape Mendocino, while most krill hotspots occurred in the northern CCE. The probability of co‐occurrence was greatest during cool ocean conditions (100‐m temperature 1°C below average), averaging 41.0% and extending throughout most of the CCE. During warm ocean conditions (100‐m temperature 1°C above average), predicted co‐occurrence averaged 17.0% and was concentrated near Cape Mendocino. These results indicate that hake‐krill co‐occurrence is a function of predator and prey spatial distributions and overall krill abundance. Furthermore, temperature influences hake‐krill co‐occurrence and may explain some of the variation in hake growth and recruitment to the fishery.
... Diet differences between habitats could be the consequence of exogenous factors such as prey availability in each layer, and could also be attributed to an endogenous factor related to the known ontogenetic diet shift exhibited by this species (Angelescu & Cousseau, 1969;Belleggia et al., 2014;Sánchez, 2009;Sánchez & García de la Rosa, 1999). In general, Merluccius species worldwide exhibit ontogenetic changes in diet associated with size, particularly from small zooplankton crustaceans to larger and more active prey not accessible to smaller predators (Buckley & Livingston, 1997;Carpentieri et al., 2005;Cartes et al., 2009;Garrison & Link, 2000;Mahe et al., 2007;Stagioni et al., 2011;Tanasichuk et al., 1991). Alvarez-Colombo, 2001), and this was in accordance with a bottomup effect on condition of YOY hake previously suggested, manifested as lower condition values in winter, the less productive season (Temperoni et al., 2020). ...
The young‐of‐the‐year (YOY) Argentina hake Merluccius hubbsi remained at particular distances off the seabed at pelagic habitat, in a nursery area located in the San Jorge Gulf off south‐western Atlantic. Older specimens were daylight distributed near the bottom in the demersal habitat. In this paper the authors show that the pelagic habitat is favourable for YOY hake compared to the surrounding demersal habitat by decreasing the probability of encounter with larger hake protecting the YOY against conspecific predation, and providing a better food supply. From 303 stomachs of pelagic YOY Argentine hake analysed (60–250 mm), 274 (90.43%) contained prey. Pelagic Argentine YOY hake fed almost exclusively on zooplanktonic crustaceans (Euphausia spp. and Themisto gaudichaudii). From 980 demersal specimens (14–82 cm), 572 (58.36%) contained prey, mainly the lobster krill Munida gregaria, followed by other hakes by cannibalism. The intensity of feeding was higher on pelagic layers. The allometric weight–length relationship revealed that the YOY Argentine hake find sufficient food in the pelagic habitat to live and develop, by increasing their relative body thickness. The cannibalism increases from close to zero when the YOY hake are c. 20 m off the seabed, to between 15% (cold season) and 20% (warm season) when they are 10 m off the seabed. These results suggest that the pelagic habitat is a feeding ground for YOY hake, and it is a favourable one compared to the surrounding demersal habitat by protecting the YOY from cannibalism. Pelagic YOY hakes were less abundant and more distant from the bottom during the cold season (14.3 m) than during warm one (11.4 m), probably because of natural mortality and progressive recruitment to demersal habits.
... Robinson et al. [80] attributed the rapid decline in euphausiid biomass over the mid-summer period to predation by Pacific Hake. This commercial fish predator migrates onto the southern BC continental shelf in June and are heavy consumers of euphausiids [81]. However, the lack of high biomass of T. spinifera requires further investigation. ...
Euphausiids are a keystone species in coastal food webs due to their high lipid content and seasonally high biomass. Understanding the habitat and environmental drivers that lead to areas of high biomass, or ‘hotspots’, and their seasonal persistence, will support the identification of important foraging regions for mid- and upper- trophic level predators. We quantify the distribution of hotspots of the two dominant species of euphausiid in the north-east Pacific Ocean: Euphausia pacifica and Thysanoessa spinifera , as well as euphausiid larvae (mixed species). The Canadian coast encompasses the northern California Current Ecosystem and the transition zone to the Alaska current, and is a highly productive region for fisheries, marine mammals, and seabirds. We used spatiotemporal modelling to predict the distribution of these three euphausiid groups in relation to geomorphic and environmental variables during the important spring-summer months (April through September) when euphausiid biomass is highest. We quantified the area, intensity, and persistence of biomass hotspots across months according to specific oceanographic ecosections developed for marine spatial planning purposes. Persistent hotspots of both adult species were predicted to occur along the 200 m depth contour of the continental slope; however, differences were predicted on the shallower Dixon shelf, which was a key area for T . spinifera , and within the Juan de Fuca Eddy system where E . pacifica hotspots occurred. The continental slope along the west coast of Vancouver Island was the only persistent hotspot region common between both adult species and euphausiid larvae. Larval distribution was more correlated with T . spinifera than E . pacifica biomass. Hotspots of adults were more persistent across months than hotspots of euphausiid larvae, which were seasonally patchy. The persistence of biomass hotspots of forage species through periods of low overall biomass could maintain trophic connectivity through perturbation events and increase ecosystem resilience to climate change.
... The first, presented by McFarlane et al. (1997) suggests that this typical summer spatial pattern might reflect a 'food-predation risk trade-off' for Pacific Herring, i.e., Pacific Herring preferentially occur at the margins of Euphausiid hotspots to avoid Pacific Hake predation. Previous studies have shown that the Euphausiid hotspots usually harbour high densities of Pacific Hake McFarlane et al., 1997), which is a migratory species that usually enters BC waters in spring (May/early June), and mainly feeds on Euphausiids and Pacific Herring off the WCVI (Tanasichuk et al., 1991). In the present study (Models #3 & #6), we found that the shelf-break regions harbour high densities of several predators such as Pacific Hake, Sablefish and Arrowtooth Flounder, which provides additional support to the 'food-predation risk trade-off' hypothesis). ...
... Multi-species model #5 found a negative correlation in spatiotemporal biomass patterns between Pacific Hake and Pacific Herring, suggesting that increases in Pacific Hake biomass are associated with declines in Pacific Herring density off the WCVI. This negative correlation might reflect different responses to environmental conditions or prey availability, but is consistent with previously-published studies suggesting that Pacific Hake is a main predator species that substantially contributes to Pacific Herring mortality off the WCVI (Ware andMcFarlane, 1986, 1995;Tanasichuk et al., 1991;McFarlane et al., 1997). For instance, McFarlane et al. (1997) attributed the reduction in Pacific Herring abundance during warmer years off the WCVI to a concomitant increase in Pacific Hake-associated predation pressure. ...
... Besides Pacific Hake, published literature and analyses of stomach content data suggest that Pacific Herring usually experience predation from several other groundfish including Lingcod, Pacific Cod, Spiny Dogfish, Sablefish, Arrowtooth Flounder and Pacific Halibut (Ware and McFarlane, 1986;Tanasichuk et al., 1991;Beaudreau and Essington, 2007;Brodeur et al., 2009) and some pelagic species (i.e., Coho Salmon and Chinook Salmon). However, the relative contribution of those species to total summer predation pressure experienced by Pacific Herring is not fully understood. ...
Determining how fish respond to variation in biotic and abiotic conditions is a crucial prerequisite to forecasting changes in productivity and spatial distribution of fish stocks and designing sustainable marine resource management strategies. In the present study, we investigated the physical and biological drivers of the spatio-temporal dynamics of Pacific Herring (Clupea pallasi), which is a marine forage fish species important for commercial fisheries and First Nations in the northeastern Pacific. We fit multivariate spatio-temporal models to fisheries-independent trawl- and acoustics-based data collected off the West Coast of Vancouver Island (WCVI), Canada, during summers over the period 2006–2014. We evaluated the effects of the main ocean environmental drivers of WCVI lower trophic level productivity, including sea surface temperature (SST), chlorophyll a, fluorescence, salinity, oxygen, transmissivity and zooplankton density on variation in Pacific Herring biomass. Models were also used to measure spatio-temporal covariation with other pelagic, semi-pelagic, and bottom-associated fish species occurring off the WCVI to address potential competitive and predation interactions. Through application of these spatio-temporal models we found: (i) Pacific Herring biomass off the WCVI increased during 2006–2014; the highest Pacific Herring biomass was repeatedly found on the continental shelf (depths < 185 m) while low densities were usually observed along the shelf break (depths > 185 m), where Euphausiids, Pacific Hake, Sablefish and Arrowtooth Flounder were more abundant, which could reflect predation avoidance behaviour; (ii), the local biomass of Pacific Herring was related quadratically to the average SST in May; (iii) a positive covariation in spatio-temporal densities between Pacific Herring and its common zooplankton prey, supporting a potential bottom-up control hypothesis; (iv) a negative covariation in spatio-temporal densities between Pacific Herring and both Pacific Hake and Pacific Sardine, which could reflect predation and competitive interactions, respectively; and (v) a positive covariation in spatio-temporal densities between Pacific Herring and several groundfish species (i.e., Arrowtooth Flounder, Sablefish, Pacific Halibut, Pacific Cod), which highlights the need for an accurate assessment of the relative contribution of those species to the total summer predation pressure experienced by Pacific Herring off the WCVI. The findings of this study contribute to a better understanding of the WCVI marine ecosystem.
