Forage Fish Research Articles

Whole-genome resequencing and bisulfite sequencing provide new insights into the feeding habit domestication in mandarin fish (Siniperca chuatsi).

Mandarin fish (Siniperca chuatsi) is one of the most economically important fish in China. However, it has the peculiar feeding habit that it feeds solely on live prey fish since first-feeding, while refuses dead prey fish or artificial diets. After the specific training procedure, partial individuals could accept dead prey fish and artificial diets. The genetic basis of individual difference in artificial diet feeding habit is still unknown. In the present study, the resequencing was performed between 10 individuals which could be domesticated to accept artificial diets and 10 individuals which could not. Through the selective sweep analysis based on heterozygosity (Hp) and population differentiation coefficient (Fst), 57 candidate windows were identified as the putative selected regions for feeding habit domestication of mandarin fish, involved in 149 genes. These genes were related to memory, vision and olfaction function, which could be potential targets of molecular marker assistant breeding of artificial diet feeding trait. Beside of the DNA sequence, we also explored the potential role of DNA methylation in feeding habit domestication in mandarin fish. Whole-genome bisulfite sequencing was performed between the individuals which could be domesticated to accept artificial diets and those could not. 5,976 differentially methylated regions were identified, referring to 3,522 genes, such as the genes involved in cAMP signaling pathway. The DNA methylation changes of these genes might contribute to the adaption of artificial diets in mandarin fish. In conclusion, the putative selected regions and the differentially methylated regions were identified in the whole genome, providing new insights into the feeding habit domestication from live prey fish to artificial diets in mandarin fish. And the involved genes were identified as the candidate genes for molecular breeding of artificial diet utilization in mandarin fish.

Optimal Automatic Wide-Area Discrimination of Fish Shoals from Seafloor Geology with Multi-Spectral Ocean Acoustic Waveguide Remote Sensing in the Gulf of Maine

Ocean Acoustic Waveguide Remote Sensing (OAWRS) enables fish population density distributions to be instantaneously quantified and continuously monitored over wide areas. Returns from seafloor geology can also be received as background or clutter by OAWRS when insufficient fish populations are present in any region. Given the large spatial regions that fish inhabit and roam over, it is important to develop automatic methods for determining whether fish are present at any pixel in an OAWRS image so that their population distributions, migrations and behaviour can be efficiently analyzed and monitored in large data sets. Here, a statistically optimal automated approach for distinguishing fish from seafloor geology in OAWRS imagery is demonstrated with Neyman–Pearson hypothesis testing which provides the highest true-positive classification rate for a given false-positive rate. Multispectral OAWRS images of large herring shoals during spawning migration to Georges Bank are analyzed. Automated Neyman-Pearson hypothesis testing is shown to accurately distinguish fish from seafloor geology through their differing spectral responses at any space and time pixel in OAWRS imagery. These spectral differences are most dramatic in the vicinity of swimbladder resonances of the fish probed by OAWRS. When such significantly different spectral dependencies exist between fish and geologic scattering, the approach presented provides an instantaneous, reliable and statistically optimal means of automatically distinguishing fish from seafloor geology at any spatial pixel in wide-area OAWRS images. Employing Kullback–Leibler divergence or the relative entropy in bits from Information Theory is shown to also enable automatic discrimination of fish from seafloor by their distinct statistical scattering properties across sensing frequency, but without the statistical optimal properties of the Neyman–Pearson approach.

Eight single nucleotide polymorphisms and their association with food habit domestication traits and growth traits in largemouth bass fry (Micropterus salmoides) based on PCR-RFLP method.

The largemouth bass (Micropterus salmoides), an economically important freshwater fish species widely farmed in China, is traditionally cultured using a diet of forage fish. However, given the global decline in forage fish fisheries and increasing rates of waterbody pollution and disease outbreaks during traditional culturing, there is a growing trend of replacing forage fish with formulated feed in the largemouth bass breeding industry. The specific molecular mechanisms associated with such dietary transition in this fish are, nevertheless, poorly understood. To identify single nucleotide polymorphisms (SNPs) related to food habit domestication traits and growth traits in largemouth bass fry, we initially genotyped fry using eight candidate SNPs based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method, with genetic parameters being determined using Popgen32 and Cervus 3.0. Subsequently, we assessed the associations between food habit domestication traits of largemouth bass fry and these SNPs using the Chi-square test or Fisher's exact test. Furthermore, we used a general linear model to assess the relationships between the growth traits of largemouth bass fry and these SNPs. The Pearson correlation coefficient between growth traits and the SNPs was also determined using bivariate correlation analysis in IBM SPSS Statistics 22. Finally, the phenotypic variation explained (PVE) by the SNPs was calculated by regression analysis in Microsoft Excel. The genotyping results obtained based on PCR-RFLP analysis were consistent with those of direct sequencing. Five SNPs (SNP01, SNP02, SNP04, SNP05, and SNP06) were found to be significantly correlated with the food habit domestication traits of fry (P < 0.05); SNP01 (P = 0.0011) and SNP04 (P = 0.0055) particularly, had showed highly significant associations. With respect to growth traits, we detected significant correlations with the two SNPs (SNP01 and SNP07) (P < 0.05), with SNP01 being significantly correlated with body length, and height (P < 0.05), and SNP07 being significantly correlated with body height only (P < 0.05). Our findings indicated that the PCR-RFLP can be used as a low-cost genotyping method to identify SNPs related to food habit domestication and growth traits in largemouth bass, and that these trait-related SNPs might provide a molecular basis for the future breeding of new varieties of largemouth bass.

Effects of two subtropical piscivorous fish species on sediment disturbance and water quality: Implication for restoration by stocking piscivores

Subtropical lakes are often dominated by benthi-omnivorous fish (e.g., crucian carp) that may substantially disturb sediments and thereby increase water turbidity and nutrient concentrations. Piscivores stocking is sometimes used to control these benthi-omnivores in the expectation that they will reduce their adverse effects on the water quality. However, in shallow subtropical lakes the benthic foraging activities of piscivorous fish may also disturb sediments, a topic that has not yet been well elucidated. Here, we conducted a 6-day mesocosm experiment to explore the bioturbation effects of two native subtropical piscivorous fish (i.e., snakehead,Channa argusand mandarin fish,Siniperca chuatsi) in prey fish (crucian carp,Carassius carassius) present and absent scenarios. Our results showed that in mesocosms without prey, both snakehead and mandarin fish greatly increased the concentrations of suspended solids. However, the concentrations of total, organic and inorganic suspended solids were significantly higher in the mesocosms with snakehead than in those with mandarin fish, suggesting that snakehead has higher bioturbation effects than mandarin fish. When crucian carp were present, we found that both snakehead and mandarin fish significantly reduced prey abundance, whereas piscivore stocking did not significantly decrease the suspended solids and nutrient concentrations. Our study revealed differential effects of two subtropical piscivorous fish species on sediment disturbance and water quality, and we suggest that for lake restoration with piscivores stocking, mandarin fish are a better option than snakehead fish as their predation effect was equal but the strength of sediment disturbance by mandarin fish was lower than that of snakehead.

Using predator diets to infer forage fish distribution and assess responses to climate variability in the eastern Bering Sea

Forage fishes comprise an integral part of marine food webs in the highly productive ecosystems of the North Pacific. However, significant knowledge gaps exist related to the status of forage fish, their life histories, and how populations may react to future climatic shifts. Standardized bottom trawl surveys are critical to the stock assessment of groundfish but lack the gear and protocols to quantitatively evaluate small pelagic forage fish. Where diet data are available, predators may be used as an indirect method of collecting data on forage fish distribution and relative abundance. We used stomach contents data to infer predator-prey interactions in the eastern Bering Sea and to analyze the distribution of 5 forage taxa over a 34 yr time series (1985-2019). Using 4 dominant groundfish predators, we constructed forage fish and predator depth and temperature habitat profiles and used center of gravity (COG) analysis and global index of collocation to examine predator-prey overlap. Results provide insight on the habitat partitioning and competitive interactions between forage species and the dynamics between predators and prey. Interannual COG analyses indicated recent periods of cooling (2007-2013) and warming (2014-2019) had significant effects on the distribution of forage fish, and suggest differences in the relative resilience of forage fish populations to climate change in this region. Population shifts were particularly evident in recent periods of anomalous warming, highlighting the need to understand how future periods of prolonged warming may affect predator-prey dynamics. Results also demonstrate the importance of predator diet time series and how these data might inform multi-species models and management strategies.

Assessing individual movement, habitat use, and behavior of non-breeding marine birds in relation to prey availability in the US Atlantic

Resource availability is a key factor driving marine bird movements and distributions, but direct information on prey availability is difficult to obtain at relevant scales. We present novel methods for describing multi-scale trophic associations, combining movement analyses of marine birds with estimates of forage fish surface aggregations from digital aerial survey data and species occupancy from bottom trawl survey data. We analyzed satellite telemetry data from northern gannets Morus bassanus, red-throated loons Gavia stellata, and long-tailed ducks Clangula hyemalis in the US Atlantic during the non-breeding period. Using discrete-time hidden Markov models to distinguish area-restricted (i.e. putative foraging) from transit movements, we examined how environmental factors influence movement, and how forage fish species distributions and surface aggregations influence habitat use by gannets and loons that have greater dietary reliance. Our results suggest that chlorophyll a concentration significantly affected movement behavior across species, highlighting the importance of higher-productivity areas around estuaries during colder months when regional productivity is low. Though variable across species and seasons, spatial cross-correlation analysis revealed that herring species (Family Clupeidae), including Atlantic menhaden Brevoortia tyrannus, may be important resources; it also showed positive spatial correlations with forage fish aggregations. This suggests that prey patch dynamics and factors driving aggregation formation may be as important as species composition. However, spatial patterns were generally low (&lt;0.3), suggesting a mismatch in spatiotemporal resolution, exemplifying the challenges in quantifying trophic relationships in marine systems. Disentangling predator-prey relationships is critical to understanding the mechanisms driving marine bird behavior in rapidly changing marine systems.

Design of single-electron information-processing circuit modeled on Boids algorithm of fish shoals

We designed an analog single-electron (SE) information-processing circuit that mimics the behavior of a fish shoal. Although SE circuits are functional, there is not yet an optimum information-processing method established for them. To tackle this issue, we take inspiration from the behavior of fish shoals, where each fish determines its behavior by interacting with other fish, as in a multi-agent system. We demonstrated our SE circuit to effectively mimic one of the three rules of the Boids algorithm regarding fish shoal behavior through computer simulation. We believe our approach is a strong candidate for SE circuits having optimum information processing.

Differences in the behavior and diet between shoaling and solitary surgeonfish (Acanthurus triostegus).

Variation in behavior within marine and terrestrial species can influence the functioning of the ecosystems they inhabit. However, the contribution of social behavior to ecosystem function remains underexplored. Many coral reef fish species provide potentially insightful models for exploring how social behavior shapes ecological function because they exhibit radical intraspecific variation in sociality within a shared habitat. Here, we provide an empirical exploration on how the ecological function of a shoaling surgeonfish (Acanthurus triostegus) may differ from that of solitary conspecifics on two Pacific coral reefs combining insight from behavioral observations, stable isotope analysis, and macronutrient analysis of gut and fecal matter. We detected important differences in how the social mode of A.triostegus affected its spatial and feeding ecology, as well as that of other reef fish species. Specifically, we found increased distance traveled and area covered by shoaling fish relative to solitary A.triostegus. Additionally, shoaling A.triostegus primarily grazed within territories of other herbivorous fish and had piscivorous and nonpiscivorous heterospecific fish associated with the shoal, while solitary A.triostegus grazed largely grazed outside of any territories and did not have any such interactions with heterospecific fish. Results from stable isotope analysis show a difference in δ15N isotopes between shoaling and solitary fish, which suggests that these different social modes are persistent. Further, we found a strong interaction between social behavior and site and carbohydrate and protein percentages in the macronutrient analysis, indicating that these differences in sociality are associated with measurable differences in both the feeding ecology and nutrient excretion patterns. Our study suggests that the social behavior of individuals may play an important and underappreciated role in mediating their ecological function.

Reduction in overwinter body condition and size of Pacific sand lance has implications for piscivorous predators during marine heatwaves

Acute anomalous ocean warming events, including marine heatwaves (MHWs), have significant effects on reproduction and survival of piscivorous seabirds. Additionally, MHWs have negative effects on seabird fish prey, exacerbating these consequences and resulting in population implications for seabirds. We evaluated the relative body condition of Pacific sand lance Ammodytes personatus, an important seabird forage species, in Haro Strait, a highly productive region of southern British Columbia, Canada. We compared body condition and length of fish cohorts that experienced the 2016 MHW year (MHW cohorts) with fish hatched during 3 subsequent post MHW years (2017-2019). Age-0 MHW cohorts had a seasonal decline in body condition in age-0 fish from 100% in the summer to 81% in the winter, while age-1 fish showed a decline from summer-fall highs of 93.5% to wintertime low of 79.5%. In comparison, post MHW cohorts had a winter body condition that was 2-4 times higher than their MHW cohorts. Similar to previous studies in Alaska during the MHW, age-1 fish failed to grow and reach the typical size that distinguishes them from age-0 fish. Poor sand lance condition and growth in winter may explain the ramifications of a warming ocean for top predators, including seabirds and Pacific salmon, which depend on these prey fish in Haro Strait. Our results support the idea that Haro Strait, which is influenced by estuarine circulation resulting in cooler temperatures than surrounding areas, serves as a climate refugium for sand lance populations in summer and provides buffering capacity to ocean climate warming events.

Evolution of fish community structure, cause analysis and implications for &lt;i&gt;ex-situ&lt;/i&gt; conservation of Yangtze finless porpoise in Tian-e-Zhou Oxbow of Yangtze River

长江天鹅洲故道是长江江豚首个迁地保护区，其中充足而适口的饵料鱼类资源是长江江豚种群健康发展的保障。为此，根据2017年10月-2021年4月对长江天鹅洲故道进行的7次鱼类调查数据，结合禁捕前的历史数据，对其鱼类群落结构演变进行了分析，并针对长江江豚饵料鱼的供应状况对天鹅洲故道内鱼类资源管理提出了建议。调查期间，共采集到鱼类57种，其中，蒙古鲌（Culter mongolicus）、鲢（Hypophthalmichthys molitrix）和鳙（Aristichthys nobilis）等大中型鱼类生物量明显增加，而䱗（Hemiculter leucisculus）和似鳊（Pseudobrama simoni）等小型鱼类生物量呈现下降趋势。鱼类群落优势种逐渐由太湖新银鱼（Neosalanx taihuensis）、短颌鲚（Coilia brachygnathus）和䱗等小型鱼类转变为鳙、蒙古鲌和拟尖头鲌（Culter oxycephaloides）等大中型鱼类，尤其是新近出现的拟尖头鲌种群发展迅速。同时，短颌鲚和䱗等小型鱼类的体重在减小，而鲢、鳙等大中型鱼类规格在持续提高。长江江豚以小型鱼类和大中型鱼类的幼鱼为食，其资源下降将威胁长江江豚种群的维持和发展。为保障天鹅洲故道内长江江豚的食物供应，建议适当地捕捞鲢、鳙、蒙古鲌和拟尖头鲌，减缓鲢、鳙对小型鱼类的食物竞争压力，以及降低蒙古鲌和拟尖头鲌对小型鱼类的捕食压力；同时丰水期加强故道与长江的连通，引入更多长江干流繁殖的小型鱼类资源；并通过建设人工鱼巢以改善故道内䱗等产粘性卵小型鱼类的繁殖条件，增加小型鱼类资源量。;Tian-e-Zhou Oxbow is the first habitats for the ex-situ reserve established for the Yangtze finless porpoise. The rich and abundant forage fish resources are the guarantee for the healthy development of the Yangtze finless porpoise population. Therefore, the change of fish community structure was analyzed with combined of seven fish surveys data in Tian-e-Zhou Oxbow of Yangtze River from October 2017 to April 2021 and historical data before the fishing ban. In view of forage fish of Yangtze finless porpoise, some suggestions were provided for the scientific management of fish resources in Tian-e-Zhou Oxbow. During the investigation, 57 fish species were collected. The biomass of large and medium-sized fish such as Culter mongolicus, silver carp and bighead carp increased significantly while the biomass of small-sized fish such as Hemiculter leucisculus and Pseudobrama Simoni showed a declining trend. The dominant fish species gradually changed from small-sized fish such as Neosalanx taihuensis, Coilia brachygnathus and Hemiculter leucisculus to large and medium-sized fish such as bighead carp, Culter mongolicus and Culter oxycephaloides, in particular, the newly emerged Culter oxycephaloides population developed rapidly. Meanwhile, the body-weight of small-sized fish such as Coilia brachygnathus and Hemiculter leucisculus was decreasing, but the body-weight of large and medium-sized fish was increasing. Because the Yangtze finless porpoise feeds on the small-sized fishes and juveniles of large and medium-sized fishes, the decline of their food resources would threaten the maintenance and growth of the Yangtze finless porpoise population. In order to ensure food supply for the Yangtze finless porpoises in Tian-e-Zhou Oxbow, it suggested that rational capture of silver carp, bighead carp, Culter mongolicus and Culter oxycephaloides should be taken into consideration in order to reduce the food competition pressure of silver carp and bighead carp and the predation pressure of Culter mongolicus and Culter oxycephaloides on small-sized fishes. Besides, another measures to increase the small-sized fish resources like strengthening the connectivity of the oxbow with Yangtze River in the wet season to introduce more small-sized fish resources from Yangtze River and laying artificial fish nests in the oxbow to improve the breeding conditions for the small-sized fish species with adhesive eggs such as sharply should be carried out.

Influence of climate-mediated shifts in wetland vegetation on prey fish habitat use and schooling dynamics

Intertidal wetlands provide vital habitat for numerous species by serving as a basal resource and refuge for shelter-seeking fauna. These environments are particularly important for transient nekton that trophically link marine and terrestrial food webs via migration into the intertidal during the flooding tide. Changes in coastal vegetation due to a warming climate, such as the replacement of temperate saltmarshes with tropical mangroves, may alter habitat use by transient species due to differences in food provisioning and the structural attributes of mangrove and saltmarsh vegetation. In northeast Florida (USA), Fundulus heteroclitus (mummichog) and F. majalis (striped killifish) are abundant, trophically important, transient fishes that may exhibit behavioral changes with coastal habitat shifts. We experimentally manipulated predator presence in a large-scale mesocosm containing an array of 4 habitats found at the mangrove-saltmarsh ecotone: marsh vegetation (smooth cordgrass Spartina alterniflora), 2 species of mangroves (red mangrove Rhizophora mangle and black mangrove Avicennia germinans), and sand, and measured prey fish habitat use and schooling dynamics. Mummichogs utilized black mangrove habitat to the same degree as cordgrass regardless of the presence of a predator, indicating that mummichogs perceive both habitats as providing equivalent protection. Killifish exhibited little affinity for any particular habitat and exhibited schooling behavior over seeking refugia for predator avoidance, suggesting that vegetation changes may have little effect on killifish behavior. Further research on how such patterns of habitat use combined with habitat-specific dietary constituents of fundulids will help to predict how saltmarsh loss at the ecotone will influence nutrient and energy flows in coastal food webs.

Environmental DNA metabarcoding reveals seasonal and spatial variation in the vertebrate fauna of Ilulissat Icefjord, Greenland

Ilulissat Icefjord in Greenland is experiencing the effects of climate change, with the Sermeq Kujalleq glacier being one of the fastest-moving and most productive ice streams in Greenland. This is likely affecting the distribution of species in the fjord, including those important to local fisheries. Due to heavy ice conditions, few studies on environmental and ecological conditions exist from the fjord. However, new techniques such as environmental DNA (eDNA) metabarcoding now allow deeper insight into the fjord system. Here, we combine local ecological knowledge with data on hydrographic conditions, stable isotopes (δ18O), and eDNA metabarcoding to investigate the spatial and seasonal distribution of marine fish and mammals inside Ilulissat Icefjord. Our eDNA results support local observations that Arctic char migrate to the southern fjord during summer, harp seals forage in large herds in the fjord system, polar cod is the dominant prey fish in the area, and Greenland shark likely does not reside in the fjord system. Lower predation pressure in the Icefjord, due to the absence of Greenland shark and polar bears as well as limited fishing/hunting, is presumably one of the reasons why ringed seals and Greenland halibut are larger in the Icefjord. Furthermore, our results indicate that in summer, the southern branch of the fjord system has a more diverse community of vertebrates and different water masses than the northern branch and main fjord, indicating a time lag between inflows to the different branches of the fjord system. Our approach highlights the value of combining local ecological knowledge with scientific research and represents a potential starting point for monitoring biological responses in Ilulissat Icefjord associated with climate-induced changes.

Increased foraging effort and reduced chick condition of razorbills under lower prey biomass in coastal Newfoundland, Canada

When resources are finite, individuals optimize energy allocation between survival and reproduction to maximize fitness. As food becomes more limited within foraging ranges of breeding colonies, long-lived seabirds are predicted to increase time spent foraging, and chick growth, breeding success and ultimately adult survival, will be reduced. Across 3 years (2017, 2019, 2020), we investigated responses of breeding razorbills Alca torda in coastal Newfoundland, Canada, to inter- and intra-annual variation in biomass of the primary forage fish, capelin Mallotus villosus, which migrate from offshore into coastal regions during the summer to spawn. We combined capelin biomass (hydroacoustic surveys) with chick-rearing razorbill foraging effort (GPS, temperature-depth recorders), dietary proportions (blood δ15N and δ13C) and adult/chick body condition. Peak capelin biomass was near the long-term average for the study area in 2017 (0.109 g m-2) and 2019 (0.098 g m-2) and the lowest on record in 2020 (0.002 g m-2). In 2017 and 2019, razorbill foraging effort decreased after spawning capelin arrived inshore, but this decrease was not observed in 2020 (mean ± SE trip distance: 12.8 ± 2.8 km in 2017, 14.3 ± 1.7 km in 2019, 150.4 ± 25.2 km in 2020; number of dives per trip: 48.4 ± 11.8 in 2017, 385.8 ± 67.4 in 2020). Increased foraging effort during 2020 was associated with lower chick and adult body condition, likely due to parental birds flying farther and diving more to capture capelin. Findings suggest that lower capelin biomass observed in recent years may have long-term population-level consequences for razorbills and other seabirds in this region.

From diatoms to killer whales: impacts of pink salmon on North Pacific ecosystems

In response to a climate regime shift in 1977 and general heating of the North Pacific Ocean, pink salmon Oncorhynchus gorbuscha abundance reached record highs during 2005-2021, comprising 70% of all Pacific salmon. Pink salmon are approximately 25 times more numerous in odd- than even-numbered calendar years in some major North Pacific ecosystems, a unique demographic pattern analogous to repeating whole ecosystem treatment-control experiments. We found compelling examples indicating that in odd years, predation by pink salmon can initiate pelagic trophic cascades by reducing herbivorous zooplankton abundance sufficiently that phytoplankton densities increase, with opposite patterns in even years. Widespread interspecific competition for common-pool prey resources can be dominated by pink salmon, as indicated by numerous biennial patterns in the diet, growth, survival, abundance, age-at-maturation, distribution, and/or phenology of ecologically, culturally, and economically important forage fishes, squid, Pacific salmon and steelhead trout Oncorhynchus spp., seabirds, humpback whales Megaptera novaeangliae, and endangered southern resident killer whales Orcinus orca. In aggregate, the evidence indicates that open-ocean marine carrying capacity in the northern North Pacific Ocean and Bering Sea can be mediated by top-down forcing by pink salmon and by ocean heating, and that large-scale hatchery production (~40% of the total adult and immature salmon biomass) likely has unintended consequences for wild salmon, including Chinook salmon O. tshawytscha, and many other marine species. Further investigation of the effects of pink salmon on other species will increase our knowledge of ecosystem function and the important role top-down forcing plays in the open ocean

Analysis of the Development of Snakehead (Channa argus) Industry in Shandong, China and Comparison with the Substitution of Forage Fish with Compound Feed

Analysis of the Development of Snakehead (Channa argus) Industry in Shandong, China and Comparison with the Substitution of Forage Fish with Compound Feed

Across the North Pacific, dietary-induced stress of breeding rhinoceros auklets increases with high summer Pacific Decadal Oscillation index

Multi-colony studies of breeding seabirds may provide insights into the mechanistic links between large-scale climate variability and local changes in prey availability. In the North Pacific, the Pacific Decadal Oscillation (PDO) is a dominant climate index characterized by contrasting patterns in sea surface temperature between the western and eastern North Pacific. To examine how inter-annual variability in the PDO affects rhinoceros auklets Cerorhinca monocerata across the North Pacific, we measured inter-annual changes in nutritional stress (as reflected in plasma levels of corticosterone) of adults breeding on 5 colonies (2 and 3 colonies from the western and eastern Pacific, respectively). We also examined concurrent changes in mass and energy content of food loads delivered to chicks. We found that higher summer PDO values were associated with increased corticosterone levels and lower mass and energy contents of the food loads in both the western and eastern North Pacific colonies. Results indicated that oceanographic conditions during higher PDO values induced local changes in forage fish communities, leading to reduced prey availability, which, in turn, increased the nutritional stress of breeding birds. We conclude that the higher summer PDO index in recent years was associated with food-poor conditions for breeding rhinoceros auklets across their reproductive range, and prolonged periods of high summer PDO may be detrimental to the populations of this seabird species. Our results highlight the complexity of the mechanisms of how large-scale climate variability affects seabirds with a large geographical distribution.

Distribution and geographic differences in stable isotope ratios of diamond squid Thysanoteuthis rhombus (Cephalopoda: Thysanoteuthidae) in Japanese waters

AbstractDiamond squid Thysanoteuthis rhombus (Troschel, 1857), which can grow to a dorsal mantle length of ~100 cm in 1 year, is an important fisheries resource in subtropical and temperate waters worldwide. Around Japan, it is an important resource in the East China Sea, Sea of Japan, and western North Pacific Subtropical Gyre, including the Kuroshio area. It is not known if linkages occur between these habitats. To clarify the species distribution, we estimated the habitat of young squid using a generalized additive model based on trawl surveys and analyzed carbon and nitrogen stable isotope ratios (δ13C and δ15N) in tissue samples. Based on trawl observations, young squid were distributed around northeastern Taiwan and the Okinawa Islands in June–July and in the Sea of Japan and the Kuroshio extension areas in August–September. We observed ontogenetic changes in the stable isotope ratios. The δ15N values in large diamond squid (dorsal mantle length &gt; 400 mm) were significantly lower in the Pacific than those in other areas. Considering that the δ15N of forage fish is low in the Pacific and high in the East China Sea and Sea of Japan, large diamond squid in the northwest Pacific presumably have two distinct habitats.

Transcriptome Analysis Provides an Overview of Genes Involved in the Peculiar Food Preference at First-Feeding Stage in Mandarin Fish (Siniperca chuatsi)

The mandarin fish (Siniperca chuatsi) is an important economic fish species in China. Many carnivorous fish larvae feed on zooplankton or microdiets. However, the mandarin fish larvae feed on live prey fish exclusively, while refusing zooplankton or microdiets. A stable supply of palatable live prey fish results in high costs. Moreover, the application of live prey fish might bring the risk of pathogens. However, little is known about the genes underlying the food preference of mandarin fish larvae. Partial offspring of the domesticated strain could feed brine shrimp from three days post-hatching (dph), the open mouth day. In the present study, the mandarin fish larvae were randomly divided into three groups, then treated differently at 3 dph: (1) unfed; (2) fed with live prey fish; (3) fed with brine shrimp (Artemia). Differentially expressed genes were identified by RNA-seq. The differential expression of the transcription factors involved in retinal photoreceptor development and differentiation might contribute to the intake of brine shrimp in mandarin fish larvae. Meanwhile, the digestive enzyme genes involved in protein, fat, and carbohydrate digestion have been expressed in mandarin fish larvae at 3 dph, contributing to the digestion of ingested food. Our study provides an overview of genes and biological processes involved in the peculiar food preference at the first-feeding stage in mandarin fish larvae and has critical importance to the future application of non-fish live feeds in the culture of mandarin fish larvae.

Trophic sources and pathways of mesozooplankton and fish larvae in the Kuroshio and its neighboring waters based on stable isotope ratios of carbon and nitrogen

Major forage fishes spend their vulnerable early life stages in the Kuroshio and its neighboring waters where phytoplankton standing stocks are much lower than in coastal areas. Nevertheless, little is known of how mesozooplankton and fish larvae with their high biodiversity are supported in the Kuroshio ecosystem. Here we report stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) for mesozooplankton and fish larvae from coastal to pelagic sites in the East China Sea to evaluate trophic sources and pathways at lower trophic levels in planktonic food webs under different environmental regimes. Although δ13C and δ15N in mesozooplankton and fish larvae varied among taxonomic groups and sites, mesozooplankton δ13C and δ15N tended to be lower for particle-feeders than carnivores and fish larvae and at more pelagic sites than in coastal waters. There were significant linear regressions between δ15N and δ13C of mesozooplankton communities, with the similar slopes among sites and lower intercepts at more pelagic sites. The δ15N and δ13C of small copepods, euphausiids, ostracods, appendicularians and fish larvae were aligned close to the regression line covering all regions, indicating that these were trophic sources and pathways to mesozooplankton and fish larvae. Our results suggest that trophic sources of mesozooplankton and fish larvae are supported through copepods and appendicularian-integrated microbial production and are more dependent on diazotrophic production in more pelagic waters.

Climate tracking by freshwater fishes suggests that fish diversity in temperate lakes may be increasingly threatened by climate warming

AbstractAimMany freshwater fishes are migrating poleward to more thermally suitable habitats in response to warming climates. In this study, we aimed to identify which freshwater fishes are most sensitive to climatic changes and asked: (i) how fast are lakes warming? (ii) how fast are fishes moving? and (iii) are freshwater fishes tracking climate?LocationOntario, Canada.MethodsWe assembled a database containing time series data on climate and species occurrence data from 10,732 lakes between 1986 and 2017. We calculated the rate of lake warming and climate velocity for these lakes. Climate velocities were compared with biotic velocities, specifically the rate at which the northernmost extent of each species shifted north.ResultsLakes in Ontario warmed by 0.2°C decade−1 on average, at a climate velocity of 9.4 km decade−1 between 1986 and 2017. In response, some freshwater fishes have shifted their northern range boundaries with considerable interspecific variation ranging from species moving southwards at a rate of −58.9 km decade−1 to species ranges moving northwards at a rate of 83.6 km decade−1 over the same time period. More freshwater fish species are moving into northern lakes in Ontario than those being lost. Generally, predators are moving their range edges northwards, whereas prey fishes are being lost from northern lakes.Main ConclusionsThe concurrent loss of cooler refugia, combined with antagonistic competitive and predatory interactions with the range expanding species, has resulted in many commercially important predators moving their range edges northwards, whereas prey species have contracted their northern range edge boundaries. Trophic partitioning of range shifts highlights a previously undocumented observation of the loss of freshwater fishes from lower trophic levels in response to climate‐driven migrations.