High PCO2 does not alter the thermal plasticity of developing Pacific herring embryos during a marine heatwave.

Forage fish tend to respond strongly to environmental variability and therefore may be particularly sensitive to marine climate stressors. We used controlled laboratory experiments to assess the vulnerability of Pacific herring (Clupea pallasii) embryos to the combined effects of high partial pressure of carbon dioxide (PCO2) and a simulated marine heatwave. The two PCO2 treatments reflected current conditions (∼550 µatm) and a future extreme level (∼2300 µatm). The dynamics of the heatwave (i.e. rate of onset: ∼0.85°C day-1; maximum intensity: +4.4°C) were modeled from the most extreme events detected by a long-term regional temperature dataset. Simultaneous exposure to these potential stressors did not affect embryo survival. However, the heatwave did elicit significant metabolic effects that included higher rates of routine metabolism (Q10=1.15-1.72), growth (Q10=1.87), rate of development to hatch (Q10=3.01) and yolk consumption (Q10=3.21), as well as a significant reduction in production efficiency (-10.8%) and a three-fold increase in the rate of developmental anomalies. By contrast, high PCO2 conditions produced comparatively small effects on vital rates, including a significant increase in time to hatch (+0.88 days) and a reduction in routine metabolic rate (-6.3%) under the ambient temperature regime only. We found no evidence that high PCO2 increased routine metabolic rate at either temperature. These results indicate that Pacific herring embryos possess sufficient physiological plasticity to cope with extreme seawater acidification under optimal and heatwave temperature conditions, although lingering metabolic inefficiencies induced by the heatwave may lead to important carryover effects in later life stages.

Structure of winter groundfish feeding guilds in Pacific herring Clupea pallasii and walleye pollock Gadus chalcogrammus nursery fjords.

The contents of 1056 stomachs were included in a trophic-guild analysis to document separation amongst 16 groundfish species inhabiting Pacific herring Clupea pallasii and walleye pollock Gadus chalcogrammus nursery fjords in Prince William Sound, Alaska and to determine the relative contribution of C. pallasii and G. chalcogrammus to that separation. A total of five multi-species feeding guilds and one outlier species were determined through multivariate analyses. Major gradients of trophic separation spanned from invertebrates (mostly shrimps, crabs and unidentified decapods) to fishes (mostly unidentified fishes, C. pallasii and G. chalcogrammus) a pattern that was influenced by intra and interspecific differences in predator lengths. While C. pallasii and G. chalcogrammus were important to the overall guild structure, within-guild similarities were consistently highest due to unidentified fishes. In general, larger predators consumed the largest C. pallasii and G. chalcogrammus, with the smaller-on-average predators consuming smaller C. pallasii and fewer or smaller G. chalcogrammus. Regardless of guild inclusion, groundfishes primarily consumed pre-recruit C. pallasii and G. chalcogrammus (i.e., younger than age 3 years fishes), which has the potential to negatively influence recruitment of these forage fishes to the adult, spawning population.

Analytical and diagnostic performance of a qPCR assay for Ichthyophonus spp. compared to the tissue culture 'gold standard'.

Parasites of the genus Ichthyophonus infect many fish species and have a non-uniform distribution within host tissues. Due in part to this uneven distribution, the comparative sensitivity and accuracy of using molecular-based detection methods versus culture to estimate parasite prevalence is under debate. We evaluated the analytical and diagnostic performance of an existing qPCR assay in comparison to the 'gold standard' culture method using Pacific herring Clupea pallasii with known exposure history. We determined that the assay is suitable for use in this host, and diagnostic specificity was consistently high (>98%) in both heart and liver tissues. Diagnostic sensitivity could not be fully assessed due to low infection rates, but our results suggest that qPCR is not as sensitive as culture under all circumstances. Diagnostic sensitivity of qPCR relative to culture is likely affected by the amount of sample processed. The prevalence values estimated by the 2 methods were not significantly different when sample amounts were equal (heart tissue), but when the assayed sample amounts were unequal (liver tissue), the culture method detected a significantly higher prevalence of the parasite than qPCR. Further, culture of liver also detected significantly more Ichthyophonus infections than culture of heart, suggesting that the density and distribution of parasites in tissues also plays a role in assay sensitivity. This sensitivity issue would be most problematic for fish with light infections. Although qPCR does not detect the presence of a live organism, DNA-based pathogen detection methods provide the opportunity for alternate testing strategies when culture is not possible.

Population diversity in Pacific herring of the Puget Sound, USA.

Demographic, functional, or habitat diversity can confer stability on populations via portfolio effects (PEs) that integrate across multiple ecological responses and buffer against environmental impacts. The prevalence of these PEs in aquatic organisms is as yet unknown, and can be difficult to quantify; however, understanding mechanisms that stabilize populations in the face of environmental change is a key concern in ecology. Here, we examine PEs in Pacific herring (Clupea pallasii) in Puget Sound (USA) using a 40-year time series of biomass data for 19 distinct spawning population units collected using two survey types. Multivariate auto-regressive state-space models show independent dynamics among spawning subpopulations, suggesting that variation in herring production is partially driven by local effects at spawning grounds or during the earliest life history stages. This independence at the subpopulation level confers a stabilizing effect on the overall Puget Sound spawning stock, with herring being as much as three times more stable in the face of environmental perturbation than a single population unit of the same size. Herring populations within Puget Sound are highly asynchronous but share a common negative growth rate and may be influenced by the Pacific Decadal Oscillation. The biocomplexity in the herring stock shown here demonstrates that preserving spatial and demographic diversity can increase the stability of this herring population and its availability as a resource for consumers.

Persistence of external signs in Pacific herring Clupea pallasii Valenciennes with ichthyophoniasis.

The progression of external signs of Ichthyophonus infection in Pacific herring Clupea pallasii Valenciennes was highly variable and asynchronous after intraperitoneal injection with pure parasite preparations; however, external signs generally persisted through the end of the study (429 days post-exposure). Observed signs included papules, erosions and ulcers. The prevalence of external signs plateaued 35 days post-exposure and persisted in 73-79% of exposed individuals through the end of the first experiment (147 days post-exposure). Among a second group of infected herring, external signs completely resolved in only 10% of the fish after 429 days. The onset of mortality preceded the appearance of external signs. Histological examination of infected skin and skeletal muscle tissues indicated an apparent affinity of the parasite for host red muscle. Host responses consisted primarily of granulomatous inflammation, fibrosis and necrosis in the skeletal muscle and other tissues. The persistence and asynchrony of external signs and host response indicated that they were neither a precursor to host mortality nor did they provide reliable metrics for hindcasting on the date of exposure. However, the long-term persistence of clinical signs in Pacific herring may be useful in ascertaining the population-level impacts of ichthyophoniasis in regularly observed populations.

Behavioural responses of wild Pacific salmon and herring to boat noise.

There is growing concern about impacts of ship and small boat noise on marine wildlife. Few studies have quantified impacts of anthropogenic noise on ecologically, economically, and culturally important fish. We conducted open net pen experiments to measure Pacific herring (Clupea pallasii) and juvenile salmon (pink, Oncorhynchus gorbuscha, and chum, Oncorhynchus keta) behavioural response to noise generated by three boats travelling at different speeds. Dose-response curves for herring and salmon estimated 50% probability of eliciting a response at broadband received levels of 123 and 140 dB (re 1 µPa), respectively. Composite responses (yes/no behaviour change) were evaluated. Both genera spent more time exhibiting behaviours consistent with anti-predator response during boat passings. Repeated elicitation of vigilance or anti-predatory responses could result in increased energy expenditure or decreased foraging. These experiments form an important step toward assessing population-level consequences of noise, and its ecological costs and benefits to predators and prey.

Genetic structure of marine and lake forms of Pacific herring Clupea pallasii.

The Pacific herring (Clupea pallasii) is one of the most important species in the commercial fisheries distributed in the North Pacific Ocean and the northeastern European seas. This teleost has marine and lake ecological forms a long its distribution in the Holarctic. However, the level of genetic differentiation between these two forms is not well known. In the present study, we used ddRAD-sequencing to genotype 54 specimens from twelve wild Pacific herring populations from the Kara Sea and the Russian part of the northwestern Pacific Ocean for unveiling the genetic structure of Pacific herring. We found that the Kara Sea population is significantly distinct from Pacific Ocean populations. It was demonstrated that lake populations of Pacific herring differ from one another as well as from marine specimens. Our results show that fresh and brackish water Pacific herring, which inhabit lakes, can be distinguished as a separate lake ecological form. Moreover, we demonstrate that each observed lake Pacific herring population has its own and unique genetic legacy.

Genetic distances and variations of three clupeid species determined by PCR technique.

In this study, seven oligonucleotides primers were shown to generate the shared loci, specific loci, unique shared loci to each species and shared loci by the three species which could be obviously calculated. Euclidean genetic distances within- and between-species were also calculated by complete linkage method with the sustenance of the hierarchical dendevrepogram program Systat version 13. The genomic DNA isolated from herring (Clupea pallasii), Korean anchovy (Coilia nasus) and large-eyed herring (Harengula zunashi), respectively, in the Yellow Sea, were amplified several times by PCR reaction. The hierarchical dendevrepogram shows three chief branches: cluster 1 (PALLASII 01, 02, 03, 04, 06 and 07), cluster 2 (NASUS 08, 09, 10, 11, 12, 13 and 14), and cluster 3 (ZUNASHI 15, 16, 17, 18, 19, 20, 21 and PALLASII 05). In three clupeid species, the shortest genetic distance displaying significant molecular difference was between individual PALLASII no. 03 and PALLASII no. 02 (0.018). Individual no. 06 of PALLASII was most distantly related to NASUS no. 11 (genetic distance = 0.318). Individuals from herring (C. pallasii) species (0.920) exhibited higher bandsharing values than did individuals from Korean anchovy (C. nasus) species (0.872) (P<0.05). As a result, this PCR analysis generated on the genetic data displayed that the herring (C. pallasii) species was widely separated from Korean anchovy (C. nasus) species. Reversely, individuals of Korean anchovy (C. nasus) species were a little closely related to those of large-eyed herring (H. zunashi) species.