Distribution and community structure of ichthyoplankton from the northern and central California Current in May 2004–06

The distributions, concentrations, and community structure of pelagic larval fishes collected from the central and northern California Current in the northeast Pacific Ocean during May 2004, 2005, and 2006 were analyzed to investigate inter-annual, latitudinal, cross-shelf, and depth-stratified variability. The inter-annual climate-induced variability during the sampling period provided a unique opportunity to observe how larval fish communities adjust to rapidly changing environmental conditions. The 170 depth-stratified samples collected from three cruises yielded 14 819 fish larvae from 56 taxa representing 23 families. Dominant larval taxa were Engraulis mordax , Citharichthys spp., Sebastes spp., and Stenobrachius leucopsarus . Larval concentrations decreased significantly in 2006 from 2004 and 2005 levels following the anomalous oceanic conditions observed in 2005 and decreased water temperature in 2006. Larvae were generally found in higher concentrations at northern (>43°N) versus southern (<43°N) stations, with larval E. mordax and Citharichthys spp. found almost exclusively in the north during all sampled years. Inter-annual variability related to dynamic upwelling intensity was observed in cross-shelf larval distributions, although concentrations of S. leucopsarus larvae consistently increased in the offshore direction, while larval Sebastes spp. were generally found in highest concentrations at intermediate stations along the shelf. Multivariate analyses revealed that latitude, station depth, and sea-surface temperature were the most important factors explaining variability in larval concentrations. The present study shows that the ichthyoplankton community of the central and northern California Current changed dramatically in response to the variable environmental conditions of 2004–06.     

Influence of mesoscale eddies on ichthyoplankton assemblages in the Gulf of Alaska

Mesoscale eddies (100–200 km in diameter) propagating along the shelf‐break in the Gulf of Alaska are ubiquitous and have been shown to influence the ecosystem, but their influence on ichthyoplankton species composition and diversity has not been described. Evidence for larval fish entrainment in these eddies was examined using data from a cruise in 2005 that sampled three eastern Gulf of Alaska mesoscale eddies, and sampling that compared shelf to slope ichthyoplankton assemblages in the northern Gulf of Alaska (2002–2004). Hierarchical cluster analysis of oceanographic data showed that stations grouped according to location within an eddy. Species hierarchical cluster analysis revealed a latitudinal turnover in species composition, and an abundant species group. Species richness was correlated with distance from eddy center (P = 0.00025), and assemblages within eddies were significantly different (P < 0.05) from those in surrounding basin and shelf waters. These results suggest that mesoscale eddies propagating along the continental shelf‐break influence larval fish assemblages over the shelf and slope, which has implications for the timing and extent of larval fish distribution in the Gulf of Alaska.     

High-frequency patterns in abundance of larval Pacific hake, Merluccius productus, and rockfish, Sebastes spp., at a single fixed station off central California

Standard CalCOFI (California Cooperative Oceanic Fisheries Investigations) ichthyoplankton bongo net sampling was conducted every 2 h over 11 days at a single fixed station off central California in February 1995. A conductivity, temperature, and depth cast was completed after each tow to record corresponding hydrographic information. Larval Pacific hake, shortbelly rockfish, and other rockfish were enumerated and length measurements were recorded. Time–depth contours of water density showed a clear boundary, defining the mixed layer along the σ = 25.0 isopycnal, that appeared to fluctuate vertically on a 12‐h cycle centered around 50 m depth. Temperature–salinity plots showed a distinctly different pattern in the mixed layer when compared with water below the pycnocline. Length–frequency distributions plotted by survey day indicated a relatively continuous input of small rockfish larvae into the survey area rather than a resident population growing progressively larger each day. Catches of rockfish larvae were much higher in nighttime tows and varied by survey day, but were unaffected by the depth of the 25.0 isopycnal. In contrast, catches of Pacific hake did not vary significantly on a diel basis, but were significantly variable by survey day and were influenced by the depth of the mixed layer. Catches of Pacific hake larvae were significantly higher during warm‐saline periods (spicy water), while shortbelly rockfish were significantly less abundant under these conditions. Spectral analysis showed a clear 12‐h cycle in the depth of the 25.0 isopycnal and a 24‐h cycle in the catches of rockfish larvae, while Pacific hake catches and spiciness of the mixed layer appeared to have lower frequency cycles in excess of 48 h.     

Earlier migration and distribution changes of albacore in the Northeast Atlantic

Marine species have exhibited trends in their geographic distribution and phenology in recent decades, and these changes are triggered by climate variability or anthropogenic pressures. Northeast Atlantic albacore has recently been identified to show changes of this nature, although the underlying causes are still uncertain. The aim of this work was to analyse the Northeast Atlantic albacore distribution shifts and phenological changes during the trophic migration that juveniles undertake from late spring to autumn and to identify potential causes of such variability. Specifically, time series of albacore catches of the Basque trolling fleet were studied and compared with trends derived from a null ecological niche model using very large number of catch observations (27,982). The results showed an earlier albacore migration of 2.3 days per decade during the period of 1981–2017, which was partly associated with the recent warming of the sea. The trend analysis of the catch distribution also detected a significant north‐westward trend in catch observations and a northward trend in species habitat. In contrast, both latitudinal trends were uncorrelated. This result suggests that interannual species distribution shifts are mainly related to factors other than oceanic‐climatic variability, such as fleet behaviour or prey changes.     

中国大陆阿根廷滑柔鱼鱿钓渔业CPUE标准化

阿根廷滑柔鱼是我国重要的头足类渔业之一,单位捕捞努力量渔获量(CPUE)标准化是对其资源进行评估的重要内容.研究根据2000-2010年中国大陆在西南大西洋的鱿钓产量统计数据和卫星遥感获得的海洋环境数据(表温,表温水平梯度,海面高度,叶绿素浓度),利用广义线性模型(general linear model,GLM)和广义加性模型(generalized additive model,GAM)对中国大陆西南大西洋阿根廷滑柔鱼渔业CPUE标准化.GLM模型结果表明,年、纬度、表温以及交互项年与纬度对CPUE影响最大.GAM模型研究结果则表明年、月、经度、纬度、表温、海面高度以及交互项年与纬度、年与经度对CPUE影响较大.根据AIC准则,包含上述8个显著变量的GAM模型为最佳模型,对CPUE的解释率为49.20％.高CPUE出现在夏季表温为12～16℃、海面高度为-20 ～20 cm和46.5° ～48.5°S范围内.研究表明,GAM模型较GLM模型更适合用于西南大西洋阿根廷滑柔鱼渔业CPUE标准化.     

Intra‐annual patterns of coastal larval fish assemblages along environmental gradients in the northeastern Mediterranean

To date, little is known about the larval‐fish assemblages (LFAs) in the eastern Mediterranean. The purpose of this study is to investigate the intra‐annual variations of LFAs with an emphasis on the effects of physical, chemical, biological and meteorological conditions in the gulf of Iskenderun, which is a shallow (100 m maximum depth), semi‐enclosed bay located in the northeastern corner of the Mediterranean. The gulf is under the influence of offshore waters throughout the year. The study was based on an ichthyoplankton survey program performed at 28 stations over 12 months, between November 2009 and October 2010. During the study, a total of 11,411 larval individuals belonging to 177 taxa were sampled. The jackknife estimate of maximum species richness was 225 ± 19 for the study area. The maximum larval richness (84 species) and abundance (827 larvae/10 m²) values coincided with spring bloom in April. Gobiids dominated the ichthyoplankton of Iskenderun Bay by constituting 9% of species richness and 42% of total individuals. Four LFAs were identified which were in early winter (November to January), late winter (February and March), spring (April to June) and summer (July to October). The intra‐annual variations of richness, abundance and composition of ichthyoplankton were significantly correlated with the temperature and mesozooplankton biomass. The wind conditions and thermal stratification were also significantly correlated with the composition of LFAs. In conclusion, phenology of LFAs were formed under the influence of physical and tropho‐dynamic conditions in Iskenderun Bay, Northeastern Mediterranean.     

西南大西洋阿根廷滑柔鱼渔业中国大陆鱿钓船CPUE标准化

阿根廷滑柔鱼是我国重要的头足类渔业之一,对其单位捕捞努力量渔获量( CPUE)进行标准化是对其资源评估的重要内容。本研究根据2000～2010年我国在西南大西洋的产量统计数据和卫星遥感获得的海洋环境数据（表温,表温水平梯度,海面高度,叶绿素浓度）,利用广义线性模型（GLM,general linear model）和广义加性模型（GAM,generalized additive model）对其CPUE进行标准化。GLM模型结果表明,年、纬度、表温以及交互项年与纬度对CPUE影响最大。GAM模型研究结果表明,年、月、经度、纬度、表温、海面高度以及交互项年与纬度、年与经度对CPUE影响较大。根据AIC数值,包含上述8个显著变量的GAM模型为最佳模型,对CPUE的解释率为49.20%。高CPUE出现在夏季表温为12～16°C、海面高为-20~20cm、46.5°～48.5°S海域。研究表明,GAM模型较GLM模型更适合用于西南大西洋阿根廷滑柔鱼CPUE标准化。     

Investigating the ‘northern Humboldt paradox’ from model comparisons of small pelagic fish reproductive strategies in eastern boundary upwelling ecosystems

Eastern boundary upwelling ecosystems are highly productive and sustain the world’s largest fisheries, usually dominated by sardine and anchovy species. Stock size is highly variable from year to year due to the impact of the unstable physical environment on fish early stages. Biophysical models of early life‐stage dispersal of marine organisms have been built by coupling (i) hydrodynamic models and (ii) life history models (i.e. egg and larva stages), and are therefore useful tools to investigate physical–biological interactions. Here, we review biophysical models of anchovy and sardine ichthyoplankton dispersals developed in the Benguela, Humboldt and Canary Current upwelling ecosystems. We also include a similar study conducted in the California Current upwelling on zooplankton. We then integrate this information into a comparative analysis of sardine and anchovy reproductive strategies in the different systems. We found that the main spawning periods match the season of (i) maximal simulated ichthyoplankton retention over the continental shelf in the northern Benguela, southern Humboldt and Canary (for sardine); (ii) maximal food concentration in the southern Benguela, California and Canary (for anchovy); and (iii) maximal shelf retention of ichthyoplankton and food concentration in the northern Humboldt (for both anchovy and sardine). This specificity of the northern Humboldt ecosystem could explain why it sustains the largest small pelagic fish stock. Finally, the possible effects of climate change on these patterns are discussed.     

Putting the pieces together: Recent growth,nutritional condition,and mortality of Engraulis anchoita larvae in the Southwest Atlantic

Dynamics of clupeiform fish populations such as anchovy are frequently impacted by environmental variations which can affect the success of the species recruitment. Herein, we have analyzed recent otolith growth rate, RNA/DNA nutritional condition index (sRD), and mortality rate of argentine anchovy larvae Engraulis anchoita from three different nursery areas in the Southwest Atlantic. We have evaluated the relationship between the environmental variables (abundance of copepod nauplii, temperature, chlorophyll‐a concentration, and abundance of E. anchoita larvae) and larval endogenous variables (size, weight, age, and otolith radius) to sRD and recent growth rate. Fast larval growth rates were observed toward the northern sector of the studied area, characterized by higher temperature. High values of sRD were associated with higher nauplii abundance in the proximity of coastal fronts. The larvae with the lowest growths and lowest minimum values of nutritional condition coincided with the area where there was less abundance of nauplii and higher larval mortality. Larval size and nauplii abundance were positive explanatory factors for both recent growth rate and sRD index. Temperature had a positive effect on recent growth rate and a negative effect on sRD index. This condition index was poorly explained in terms of model fit in comparison with the growth model. The results herein provided could be significant to better understand the recruitment of the species, as to determining favorable areas for the growth and survival of anchovy larvae.     

Quantifying the influence of geography and environment on the northeast Atlantic mackerel spawning distribution

Mackerel (Scomber scombrus) in the northeast Atlantic have shown changes in distribution at certain times of the year, which have impacted their exploitation and management. In this study, mackerel spawning habitat over 21 recent years was characterised using generalised additive modelling, based on spatial egg density data collected every third year during targeted ichthyoplankton surveys. Mackerel spawning distribution was found to depend primarily on geographical variables (coordinates and bottom depth), with preferred spawning locations on the shelf‐edge from the north of the Iberian peninsula to the west of Scotland, with a maximum west of Ireland. Environmental drivers had a lesser influence on egg distribution. Dome shaped relationships were found with temperature and mixed layer depth, with respective optimum at 13°C and around –300 m. The model was used to reconstruct maps of the potential habitat (areas where conditions were suitable, but not necessarily used, for spawning). Little changes were observed over the years in the potential habitat, suggesting that the expansion of the egg distribution (realised habitat) was not triggered by changes in the environmental variables investigated. Little evidence was found for density‐dependent habitat selection. There was a tendency for mackerel to make more use of areas of lesser suitability in years with large stock size (1992 and 2010). This pattern, however, broke down in 2013, when stock size was the highest, as spawning occurred very south and concentrated in the most suitable habitat.     

Distribution patterns and population structure of the blue shark (Prionace glauca) in the Atlantic and Indian Oceans

The blue shark (Prionace glauca) is the most frequently captured shark in pelagic oceanic fisheries, especially pelagic longlines targeting swordfish and/or tunas. As part of cooperative scientific efforts for fisheries and biological data collection, information from fishery observers, scientific projects and surveys, and from recreational fisheries from several nations in the Atlantic and Indian Oceans was compiled. Data sets included information on location, size and sex, in a total of 478,220 blue shark records collected between 1966 and 2014. Sizes ranged from 36 to 394 cm fork length. Considerable variability was observed in the size distribution by region and season in both oceans. Larger blue sharks tend to occur in equatorial and tropical regions, and smaller specimens in higher latitudes in temperate waters. Differences in sex ratios were also detected spatially and seasonally. Nursery areas in the Atlantic seem to occur in the temperate south‐east off South Africa and Namibia, in the south‐west off southern Brazil and Uruguay, and in the north‐east off the Iberian Peninsula and the Azores. Parturition may occur in the tropical north‐east off West Africa. In the Indian Ocean, nursery areas also seem to occur in temperate waters, especially in the south‐west Indian Ocean off South Africa, and in the south‐east off south‐western Australia. The distributional patterns presented in this study provide a better understanding of how blue sharks segregate by size and sex, spatially and temporally, and improve the scientific advice to help adopt more informed and efficient management and conservation measures for this cosmopolitan species.     

GLMs, GAMs and GLMMs: an overview of theory for applications in fisheries research

This paper provides an overview of the modelling process using generalized linear models (GLMs), generalized additive models (GAMs) and generalized linear mixed models (GLMMs), especially as they are applied within fisheries research. We describe the essential aspect of model interpretation and construction so as to achieve its correct application. We start with the simplest models and show the progression from GLMs to either GAMs or GLMMs. Although this is not a comprehensive review, we emphasise topics relevant to fisheries science such as transformation options, link functions, adding model flexibility through splines, and using random and fixed effects. We finish by discussing the various aspects of these models and their variants, and provide a view on their relative benefits to fisheries research.     

Modelling the oceanic habitats of two pelagic species using recreational fisheries data

Defining the oceanic habitats of migratory marine species is important for both single species and ecosystem‐based fisheries management, particularly when the distribution of these habitats vary temporally. This can be achieved using species distribution models that include physical environmental predictors. In the present study, species distribution models that describe the seasonal habitats of two pelagic fish (dolphinfish, Coryphaena hippurus and yellowtail kingfish, Seriola lalandi), are developed using 19 yr of presence‐only data from a recreational angler‐based catch‐and‐release fishing programme. A Poisson point process model within a generalized additive modelling framework was used to determine the species distributions off the east coast of Australia as a function of several oceanographic covariates. This modelling framework uses presence‐only data to determine the intensity of fish (fish km^?2), rather than a probability of fish presence. Sea surface temperature (SST), sea level anomaly, SST frontal index and eddy kinetic energy were significant environmental predictors for both dolphinfish and kingfish distributions. Models for both species indicate a greater fish intensity off the east Australian coast during summer and autumn in response to the regional oceanography, namely shelf incursions by the East Australian Current. This study provides a framework for using presence‐only recreational fisheries data to create species distribution models that can contribute to the future dynamic spatial management of pelagic fisheries.     

Variability of preferred environmental conditions for Atlantic bluefin tuna (Thunnus thynnus) larvae in the Gulf of Mexico during 1993–2011

The Gulf of Mexico (GOM) is the primary spawning ground for western Atlantic bluefin tuna (Thunnus thynnus). In this work, information reported by previous studies about the preferred environmental conditions for the occurrence of bluefin tuna larvae in the GOM is integrated into a dimensionless index, the BFT_Index. This index is used to evaluate the spatial and temporal variability of areas with favorable environmental conditions for larvae within the GOM during 1993–2011. The main findings of this work are that: (i) the proposed index successfully captures the spatial and temporal variability in the in situ occurrence of bluefin tuna larvae; (ii) areas with favorable environmental conditions for larvae in the GOM exhibit year‐to‐year spatial and temporal variability linked with mesoscale ocean features and sea surface temperature; and (iii) comparison of the BFT_Index‐derived variability with recruitment of age‐0 fish estimated from recent stock assessment indicates that changes in environmental conditions may drive a relevant component (~58%) of the recruitment variability. The comparison with the recruitment dataset further revealed the existence of key regions linked with recruitment in the central/northern GOM, and that the Loop Current may function as a trap for larvae, possibly leading to low survival rates. Above (below) average conditions for occurrence of larvae in the GOM during spring were observed in 2000, 2001, 2002, 2006–2008, and 2011 (1994, 1996, 1998, 1999, 2003 and 2010). Results reported here have potential applications to assessment of bluefin tuna.     

瓯江口夏秋季渔场浮性鱼卵和仔鱼的时空分布

利用2007年6月和9月瓯江口海域鱼卵、仔鱼调查资料,分析瓯江口渔场鱼卵、仔鱼种类组成、数量分布、产卵场位置和产卵期特征.结果表明,调查期间瓯江口鱼卵、仔鱼共出现6目11科18种(包括1种未定种),其中鲈形目种类最多,鲱形目次之.6月是瓯江口鱼类的产卵期,产卵场位于洞头大门岛周围水域,主要是规格较小的地区性物种,也是大型经济鱼类的饵料,例如小公鱼和虾虎鱼等;9月产卵场主要位于洞头群岛水域外侧,主要是一些经济鱼类,如白姑鱼等.瓯江口海域所处纬度、海域地形地貌和水文环境特征以及瓯江径流的综合影响,使大门岛附近成为瓯江口海域的主要产卵场.     

Distribution and richness of diadromous fish assemblages in Western Europe: large-scale explanatory factors

Abstract –  The aim of this study was to analyse the distribution of 14 diadromous fish at the beginning of the 20th century in western Europe. This study was conducted on a set of 41 water basins. Five environmental variables were selected and we used generalised additive models for explaining the presence–absence of species. The richest basins were located in the centre of the study area. Six main assemblage types were identified along a latitudinal gradient; they were constituted of a common species basis but differed by the absence or presence of other species. The 10 single species models produced have moderate to very good discrimination level and they can correctly predict both absence and presence. Temperature is included in all but one model, response curves vary according to the species; surface area is included in six models.     

Modelling the effects of dietary methionine level and form on postprandial plasma essential amino acid profiles in rainbow trout (Oncorhynchus mykiss)

Aquafeed formulation is susceptible to affect amino acid (AA) availability for metabolic functions. Statistical models were applied to quantify the effect of dietary methionine level (from 6.01 to 16.17 g kg^?1 dry matter) and form (free, coated or bound) on postprandial concentrations of plasma essential amino acid (EAA) in rainbow trout. Twelve diets were formulated with pea and soya protein concentrate or fish meal as the main protein ingredients and were supplemented or not with increasing amount of either crystalline or agar‐coated methionine. Fish were acclimatized to one of the 12 diets for 6 weeks before postprandial plasma sampling (six sampling points up to 36 h, seven fish each time), further analysed for EAA content. Using generalized additive models, we show that (i) dietary methionine level and form explained 74% postprandial methionine plasma variations and that (ii) the methionine dietary form and plasma concentrations significantly affected the plasma concentrations of the other EAAs. Finally, linear model revealed a positive relationship (R² > 0.9) between plasma concentrations of the three branched‐chain AAs under the present experimental conditions. The results obtained add new information on the dietary effects on EAAs in the plasma availability and the interactions between them.     

象山港不同温度区围隔浮游生态系统营养盐迁移—转化的模拟对比

为评估象山港海域电厂温排水对水体富营养化影响,以生态系统中氮、磷营养盐循环为主线,建立了适用于海洋围隔浮游生态系统的多变量的营养盐迁移—转化动力学模型。该模型包括浮游植物、浮游动物、溶解无机态营养盐、溶解有机态营养盐和生物碎屑5 个模块,涉及溶解无机氮、磷酸盐、溶解有机氮、溶解有机磷、浮游植物、浮游动物和生物碎屑7 个状态变量。利用2010年10月象山港其中一个温度区的围隔生态实验数据成功地进行了模型的验证,确定了相关参数的量值,并用该参数同时模拟3个不同温度区围隔氮、磷营养盐生物化学迁移—转化过程,进而得出温度对围隔浮游生态系统氮、磷营养盐迁移—转化影响的结论。结果表明,象山港电厂温排水加剧了受纳水体的富营养化程度。     

Evidence for spatial coherence in time trends of marine life history traits of Atlantic salmon in the North Atlantic

A hierarchical Bayesian life cycle model is presented that considers spatial covariation of marine life history traits of Atlantic salmon (Salmo salar) populations in the North Atlantic. The model is based on a collective analysis of the dynamics of 13 stock units (SUs) from two continental stock groups (CSGs) in North America and Southern Europe in a single hierarchical model over the period 1971–2014. The model sets up a new assessment framework for Atlantic salmon stocks. It also provides a framework to investigate the drivers of changes in Atlantic salmon population dynamics including disentangling the effects of fisheries from those of environmental factors in a hierarchy of spatial scales. It is used to test the hypothesis of a strong spatial synchrony in marine life history dynamics of Atlantic salmon populations. The trends in two key parameters associated with the early marine phase of the life cycle are estimated: (i) the marine survival during the first summer–autumn spent at sea and (ii) the proportion of fish maturing after the first winter at sea. The results provide evidence of a decline in the marine survival together with an increase in the proportion of fish that mature after the first winter at sea, common to all SUs. Our results show an increased coherence in the covariations of trends in these two marine life history traits related to geographic proximity of SUs which support the hypothesis of a coherent response of geographically proximate Atlantic salmon populations that likely share similar migration routes.