Impact of freshwater input and wind on landings of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in shelf waters surrounding the Ebre (Ebro) River delta (north-western Mediterranean)

Time series analyses (Box–Jenkins models) were used to study the influence of river runoff and wind mixing index on the productivity of the two most abundant species of small pelagic fish exploited in waters surrounding the Ebre (Ebro) River continental shelf (north‐western Mediterranean): anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). River flow and wind were selected because they are known to enhance fertilization and local planktonic production, thus being crucial for the survival of fish larvae. Time series of the two environmental variables and landings of the two species were analysed to extract the trend and seasonality. All series displayed important seasonal and interannual fluctuations. In the long term, landings of anchovy declined while those of sardine increased. At the seasonal scale, landings of anchovy peaked during spring/summer while those of sardine peaked during spring and autumn. Seasonality in landings of anchovy was stronger than in sardine. Concerning the environmental series, monthly average Ebre runoff showed a progressive decline from 1960 until the late 1980s, and the wind mixing index was highest during 1994–96. Within the annual cycle, the minimum river flow occurs from July to October and the wind mixing peaks in winter (December–April, excluding January). The results of the analyses showed a significant correlation between monthly landings of anchovy and freshwater input of the Ebre River during the spawning season of this species (April–August), with a time lag of 12 months. In contrast, monthly landings of sardine were significantly positively correlated with the wind mixing index during the spawning season of this species (November–March), with a lag of 18 months. The results provide evidence of the influence of riverine inputs and wind mixing on the productivity of small pelagic fish in the north‐western Mediterranean. The time lags obtained in the relationships stress the importance of river runoff and wind mixing for the early stages of anchovy and sardine, respectively, and their impact on recruitment.     

Predicting summer fin whale distribution in the Pelagos Sanctuary (north-western Mediterranean Sea) to identify dynamic whale–vessel collision risk areas

1. Mediterranean fin whales aggregating in the Pelagos Sanctuary in summer to feed are exposed to vessel collision risk, particularly from high-speed ferries.
2. This study developed models to predict summer fin whale distribution using a generalized additive model (GAM) and MaxEnt, with the aim of providing a tool to identify potential high whale–ferry collision risk areas along ferry routes within the Pelagos Sanctuary during summertime.
3. Models were trained using sightings data collected in the summer months of 2009–2018 on board ferries crossing the central area of the Pelagos Sanctuary. Environmental predictors were bathymetry and mean sea surface chlorophyll concentration of the annual spring bloom period.
4. The predictive ability of GAM and MaxEnt was assessed using existing knowledge of summer fin whale distribution in the region. GAM (deviance explained = 20.2%) predictions matched documented distributions more closely than that of MaxEnt, with highest predicted fin whale occurrence in deep offshore waters (>2000 m) encompassing the central north-western and western regions, and in the south-eastern region, consistent with known fin whale habitats within the Pelagos Sanctuary. Inter-annual variability was evident, influencing collision risk areas.
5. Collision risk was estimated as a function of the overlap between the predicted probability of fin whale occurrence and ferry density estimated from Automated Identification System data. Ferry routes that cross the northern and eastern regions of the Pelagos Sanctuary presented relatively higher collision risk.
6. Areas with changes in risk intensity between the years were temporally and spatially dynamic: some appeared intermittently throughout the study period while others persisted over consecutive years or recurred in different years.
7. Due to the vastness of the Pelagos Sanctuary, vessel speed reduction maybe a more practical measure to manage collision risk than re-routing shipping lanes. A combination of Seasonal Management Areas and Dynamic Management Areas approaches could be adopted for high-risk areas.

     

Relationships between Octopus vulgaris landings and environmental factors in the northern Alboran Sea (Southwestern Mediterranean)

The relationships between environmental factors and fluctuations in Octopus vulgaris landings in the northern Alboran Sea are studied from 1987 to 2007. Landings during this period show both a long term decrease and a strong inter-annual variability. An exploratory phase revealed that local coastal temperatures and those averaged for the whole Alboran Sea during the previous year were the main factors controlling such variability. Warm anomalies have a detrimental effect on the octopus landings on the following year and this suggests that the decreasing trend in octopus landings could be partially linked to the long term warming observed in the Western Mediterranean. It is not yet clear which are the specific mechanisms linking warm anomalies to landing decrease. Nevertheless some hypotheses are proposed and a statistical model is developed for attempting to predict octopus landings one year ahead.     

A bio-economic indicators suite for the appraisal of the demersal trawl fishery in the Southern Adriatic Sea (Central Mediterranean)

The state of demersal fishery in the Southern Adriatic Sea (GFCM-GSA 18, Central Mediterranean), years 1996–2003, from a biological, social and economic point of view was analysed using 47 indicators: 22 biological indicators obtained from fishery-independent data through yearly experimental bottom trawl surveys (“Medits” Programme), and 25 socio-economic indicators estimated from fishery-dependent data, available from the monitoring system of the Italian Institute for Economic Research on Fisheries and Aquaculture (IREPA). Biological indicators were applied for “single-species” (Eledone cirrhosa, E. moschata, Illex coindetti, Merluccius merluccius, Mullus barbatus, Nephrops norvegicus, Parapenaeus longirostris, Raja clavata, Zeus faber) and for “multi-species” analysis. Economic indicators describing economic performance, productivity, costs and prices, and the overall economic sustainability of fishery were estimated. Social indicators and a general indicator summarising social sustainability were also considered. Indicators’ values were displayed using the Traffic Light system. Both fishery-independent and fishery-dependent indicators highlighted a progressive decline of the trawl fishery system in the GSA 18. This decline was mainly related to the ongoing depletion of the traditional fishery target species (mostly long-living, late-maturing species) partially replaced by the increase of traditional accessory species (generally short-living species), as well as to the reduction of productivity and increasing costs. The whole procedure was proposed as a contribution to the identification and applicability of bio-economic indicators for fishery management purposes.     

Modelling recruitment dynamics of hake, Merluccius merluccius, in the central Mediterranean in relation to key environmental variables

Hake recruitment has been examined in relation to environmental variables in two of the main reproductive areas of the central Mediterranean, the northern and central Tyrrhenian Sea. Seventeen years time series data from trawl surveys revealed high fluctuations in recruit abundance that could not be just explained by spawning biomass estimations. Generalized additive models were developed to investigate hake recruitment dynamics in the Tyrrhenian Sea in relation to spawner abundance and selected key oceanographic variables. Environmental data were explored in attempt to explain survival processes that could affect early life history stages of hake and that accounted for high fluctuations in its recruitment.Thermal anomalies in summer, characterised by high peaks in water temperature, revealed a negative effect on the abundance of recruits in autumn, probably due to a reduction in hake egg and larval survival rates. In the northern Tyrrhenian, recruitment was reduced when elevated sea-surface temperatures were coupled with lower levels of water circulation. Enhanced spring primary production, related to late winter low temperatures could affect water mass productivity in the following months, thus influencing spring recruitment. In the central Tyrrhenian a dome-shaped relationship between wind mixing in early spring and recruitment could be interpreted as an “optimal environmental window” in which intermediate water mixing level played a positive role in phytoplankton displacement, larval feeding rate and appropriate larval drift. Results are discussed in relation to the decline in hake stock biomass and within the present climate change and global warming context.     

Modeling environmental,temporal and spatial effects on twaite shad (Alosa fallax) by‐catches in the central Mediterranean Sea

Modeling the relationships between environmental factors and the distribution at sea of species of conservation interest can be useful in predicting their occurrence from a local to a regional scale. This information is essential for planning management and conservation initiatives. In this study, generalized additive models (GAMs) were applied to investigate the influence of environmental, temporal and spatial variables on the catch rates of the twaite shad Alosa fallax (Lacepède) by the pelagic trawl fishery in the north‐central Adriatic Sea. Presence/absence and abundance [catch per unit effort (CPUE)] data between 2006 and 2012 were separately modeled, and the two models were then validated using a test data set. The most important factor influencing the presence and abundance of adult twaite shads was the spatial predictor (latitude × longitude). Two areas of major shads aggregations were observed, the most important of which being located near the estuaries of three main river systems of northern Italy. The twaite shad presence was also significantly affected by season, the largest and lowest occurrences being observed in autumn and spring, respectively. Among the environmental variables tested, only sea surface temperature was included in both models. Alosa fallax showed a wide thermal tolerance (6–27°C) with preference for temperature around 23°C. The model developed from the abundance data showed a moderate predictive power, whereas the accuracy of the presence/absence model was rather low. Some conclusions on the ecological requirements of A. fallax at sea arising from this study are useful to orient future monitoring and research programs and to develop effective conservation actions.     

Influence of oceanographic conditions on abundance and distribution of post‐larval and juvenile carangid fishes in the northern Gulf of Mexico

Relationships between abundance of post‐larval and juvenile carangid (jacks) fishes and physical oceanographic conditions were examined in the northern Gulf of Mexico (GoM) in 2011 with high freshwater input from the Mississippi River. Generalized additive models (GAMs) were used to explore complex relationships between carangid abundance and physical oceanographic data of sea surface temperature (SST), sea surface height anomaly (SSHA) and salinity. The five most abundant carangid species collected were: Selene setapinnis (34%); Caranx crysos (30%); Caranx hippos (10%); Chloroscombrus chrysurus (9%) and Trachurus lathami (8%). Post‐larval carangids (median standard length [SL] = 10 mm) were less abundant during the spring and early summer, but more abundant during the late summer and fall, suggesting summer to fall spawning for most species. Juvenile carangid (median SL = 23 mm) abundance also increased between the mid‐summer and early fall. Most species showed increased abundance at lower salinities and higher temperatures, suggesting entrainment of post‐larval fishes or feeding aggregations of juveniles at frontal convergence zones between the expansive river plume and dynamic mesoscale eddy water masses. However, responses were species‐ and life‐stage specific, which may indicate fine‐scale habitat partitioning between species. Ordination methods also revealed higher carangid abundances at lower salinities for both post‐larval and juvenile life stages, with species‐ and life‐stage specific responses to SST and SSHA, further suggesting habitat separation between species. Results indicate strong links between physical oceanographic features and carangid distributions in the dynamic northern GoM.     

长江口及邻近水域渔业环境质量的现状及变化趋势研究

本文根据2000～2002年6个航次的调查资料,对长江口及邻近水域的渔业环境质量进行全面研究及变动趋势分析。研究结果表明,长江口及邻近水域营养盐含量十分丰富,约90％无机氮是以硝酸盐形态存在。该水域主要受营养盐、重金属及有机物的污染。其中杭州湾水域受污染程度最为严重。长江口及邻近水域浮游植物初级生产主要受磷营养盐的限制。总的来说,长江口及邻近水域渔业环境质量正呈逐步下降趋势。     

Occurrence of common dolphins (Delphinus delphis) in the Gulf of Trieste and the northern Adriatic Sea

1. The Mediterranean common dolphin (Delphinus delphis), considered to have been very common in the past, had undergone a dramatic decline across most of the basin by the end of 1970s. In the northern Adriatic Sea, one of the regions with most available historical information, the common dolphin is thought to have been the most common and abundant cetacean throughout most of the 20th century. However, by the end of 1970s, it had virtually disappeared from the region and is now considered generally absent from the entire Adriatic Sea.
2. This contribution summarizes the occurrence of common dolphins in the Gulf of Trieste and provides a brief review of published records in other parts of the Adriatic Sea.
3. Systematic boat surveys in the wider area of the Gulf of Trieste between 2002 and 2019 confirmed that the common bottlenose dolphin (Tursiops truncatus) is the only regularly occurring cetacean species in this area. Despite this, several records of common dolphins were documented in the Gulf of Trieste between 2009 and 2012, through sightings of live animals or recovery of dead stranded animals.
4. Dorsal fin markings allowed the photo-identification of some of these, suggesting that at least four different live individuals (three adults and one calf) occurred here in recent times. Most cases involved single adult individuals, but one included a mother-calf pair that was temporarily resident in a port for several months, a behaviour atypical for this species. Photo-identification showed that the presumed mother had previously been sighted in the Ionian Sea in Greece, over 1,000 km from the Gulf of Trieste, making this the longest documented movement for this species worldwide.
5. At present, the common dolphin continues to be rare in the region.

     

Changes in the fish catches during a trial opening of sluice gates on a run-of-the river reservoir in Thailand

Abstract  Changes in catch-per-unit-effort (CPUE) were evaluated when all the sluice gates on the Pak Mun Dam, Mun River, Thailand, were opened between July 2001 and June 2002. CPUE ranged from 0.38 to 1.70 and 0.61 to 2.71 kg fisherman⁻¹ night⁻¹, downstream and upstream of the dam, respectively. No statistical differences ( P  > 0.05) among months were observed in both areas. The monthly percentage index of relative importance (%IRI) of the fish species caught varied between months.     

Trends in NE Atlantic landings (southern Portugal): identifying the relative importance of fisheries and environmental variables

Time series of commercial landings from the Algarve (southern Portugal) from 1982 to 1999 were analyzed using min/max autocorrelation factor analysis (MAFA) and dynamic factor analysis (DFA). These techniques were used to identify trends and explore the relationships between the response variables (annual landings of 12 species) and explanatory variables [sea surface temperature, rainfall, an upwelling index, Guadiana river (south‐east Portugal) flow, the North Atlantic oscillation, the number of licensed fishing vessels and the number of commercial fishermen]. Landings were more highly correlated with non‐lagged environmental variables and in particular with Guadiana river flow. Both techniques gave coherent results, with the most important trend being a steady decline over time. A DFA model with two explanatory variables (Guadiana river flow and number of fishermen) and three common trends (smoothing functions over time) gave good fits to 10 of the 12 species. Results of other models indicated that river flow is the more important explanatory variable in this model. Changes in the mean flow and discharge regime of the Guadiana river resulting from the construction of the Alqueva dam, completed in 2002, are therefore likely to have a significant and deleterious impact on Algarve fisheries landings.     

A tale of two seas: a meta‐analysis of crustacean stocks in the NE Atlantic and the Mediterranean Sea

Meta‐analysis of marine biological resources can elucidate general trends and patterns to inform scientists and improve management. Crustacean stocks are indispensable for European and global fisheries; however, studies of their aggregate development have been rare and confined to smaller spatial and temporal scales compared to fish stocks. Here, we study the aggregate development of 63 NE Atlantic and Mediterranean crustacean stocks of six species (Nephrops norvegicus, Pandalus borealis, Parapenaeus longirostris, Aristeus antennatus, Aristaeomorpha foliacea and Squilla mantis) in 1990–2013 using biomass index data from official stock assessments. We implemented a dynamic factor analysis (DFA) to identify common underlying trends in biomass indices and investigate the correlation with the North Atlantic Oscillation (NAO) index. The analysis revealed increasing and decreasing trends in the northern and southern NE Atlantic, respectively, and stable or slowly increasing trends in the Mediterranean, which were not related to NAO. A separate meta‐analysis of the fishing mortality (F) and biomass (B) of 39 analytically assessed crustacean stocks was also carried out to explore their development relative to MSY. NE Atlantic crustacean stocks have been exploited on average close to F_MSY and remained well above B_MSY in 1995–2013, while Mediterranean stocks have been exploited 2–4 times above F_MSY in 2002–2012. Aggregate trends of European crustacean stocks are somewhat opposite to trends of fish stocks, suggesting possible cascading effects. This study highlights the two‐speed fisheries management performance in the northern and southern European seas, despite most stocks being managed in the context of the European Union's Common Fisheries Policy.     

Retrospective analysis of the influence of environmental drivers on commercial stocks and fishing opportunities in the Irish Sea

Irish Sea fisheries have undergone considerable change in recent years following the decline of commercially important finfish stocks and their slow response to management's recovery plans. In 2015, the fishing industry called for a holistic exploration into the impact of environmental change and food web effects to identify the drivers underpinning stock dynamics. In this study, we identify correlations between large‐scale climatic indicators, temperature, primary and secondary productivity, and fish recruitment in the Irish Sea and incorporate them into an Ecopath with Ecosim food web model co‐created by scientists and fishers. Negative correlations were found between the North Atlantic Oscillation winter index (NAOw) and large zooplankton abundance and between the Atlantic Multidecadal Oscillation (AMO) and the recruitment of cod (Gadus morhua) and whiting (Merlangius merlangus). Using correlation analyses to direct the addition of environmental drivers to the Irish Sea ecosystem model improved the models fit against observed biomass and catch data and revealed the indirect impacts of environmental change as mitigated through trophic interactions. Model simulations suggest that historic environmental change suppressed the overall production of commercial finfish, limiting opportunities for the fishing industry, whilst also dampening the rate of stock recovery despite marked reductions in fishing effort. These results suggest that failure to account for ecosystem information may lead to misconceived expectations and flawed fisheries management; therefore, there is a need to operationalize ecosystem information through management procedures to support fisheries advice.     

Diversity and distribution of early life stages of carangid fishes in the northwestern Mediterranean: responses to environmental drivers

The diversity and distribution of the early stages of carangid fishes were investigated in relation to environmental conditions off the Catalan Coast (NW Mediterranean). Data were obtained during four oceanographic cruises conducted in spring–summer 2003 and 2004. A total of 4743 larvae from seven species and five genera were identified. Most were thermophilic species very abundant in the warm waters of the south and eastern Mediterranean. The presence of larvae and juveniles of Caranx crysos, Caranx rhonchus, Seriola dumerili and Trachinotus ovatus in the northwestern Mediterranean is reported for the first time. Except for Trachurus trachurus, which spawns in winter–spring, all species reproduce in spring–summer with a temporal succession in their spawning peaks. On average, the spatial patterns of different species (except T. trachurus) showed common features: a clear preference for spawning in coastal areas, high abundance of larvae in the south warmer zone in relation to the surface productive waters of Ebro river runoff and relatively high larval concentrations south of the thermal front and its associated anticyclonic eddy. The presence of larvae of thermophilic species of carangids in the northwestern Mediterranean indicates successful reproduction and establishment of these species in the cold part of the basin.     

基于海洋环境因子和不同权重系数的南海中沙西沙海域鸢乌贼渔场分析

根据2014年"南锋"号调查船在南海中沙西沙海域的声学走航调查数据,结合遥感获得的海表温度(SST)、叶绿素a浓度(CHL)、海面盐度(SSS)、海面高度(SSH)等海洋环境数据,按不同季节不同因子分别建立栖息地适应性指数模型,对不同因子赋予不同权重系数,计算栖息地指数模型准确度,以此来确定不同季节各因子的权重系数。结果表明,各因子的最适值呈明显的季节变化,春季SST的权重系数为0.7,其余因子权重系数为0.1时模型准确度最高;夏季CHL的权重系数为1,其余因子权重系数为0时模型准确度最高;秋季CHL权重系数为0.7,其余因子系数为0.1时模型准确度最高;冬季SST权重系数为1,其余因子系数为0时模型准确度最高。研究认为,鸢乌贼(Sthenoteuthis oualaniensis)渔场不同季节对不同因子的响应程度不同,赋予各因子不同的权重系数可以有效提高模型准确率。     

Variability of oceanographic and meteorological conditions in the northern Alboran Sea at seasonal,inter‐annual and long‐term time scales and their influence on sardine (Sardina pilchardus Walbaum 1792) landings

Time series of European sardine (Sardina pilchardus) landings from 1962 and environmental variables from 1978 in the northern Alboran Sea are analysed. European sardine spawns in the northern Alboran Sea from mid‐autumn to late winter at a temperature range slightly higher than the one observed in the nearby Eastern North Atlantic and the North Western Mediterranean. Individuals hatched during autumn and winter are incorporated to the fishery during the following summer and autumn producing the maximum annual landings. These landings show both a decreasing long‐term trend and a strong inter‐annual variability. Although further research is needed, the warming trend of sea surface temperature and the decrease in upwelling intensity inferred from empirical orthogonal function (EOF) analyses could have some influence on the negative trends of sardine landings. The inter‐annual variability of sardine abundance seems to be related to the wind intensity at a local scale, the second principal component of the chlorophyll concentration and the sardine abundance during the preceding year. If the inter‐annual variability is considered, a linear model including these three variables with a one‐year time lag allows to explain 79% of the sardine landings variance. If the negative linear trend is also considered, the model explains 86% of the variance. These results indicate that the body condition of spawners, linked to the food availability during the preceding year, is the main factor controlling the recruitment success. The possibility of predicting sardine landings 1 year in advance could have important implications for fishery management.     

基于GAM的长江口鱼类资源时空分布及影响因素

根据2006至2017年长江口及其邻近海域鱼类资源调查,运用广义加性模型研究长江口鱼类资源密度与环境因子之间的关系,并对2017年鱼类资源密度的时空分布进行预测。结果显示,春夏秋冬四个季节最佳GAM偏差解释率分别为69.6%、55.9%、51.4%和47.4%,交叉验证回归线斜率的平均效应为0.62～0.88。盐度、水温和溶解氧是影响长江口鱼类资源密度的主要环境影响因子且在不同季节对鱼类资源密度有不同的影响机制。总体上,在春、夏、秋季,盐度与鱼类资源密度之间存在正向相关性;在夏、秋、冬季,水温对鱼类资源密度有显著影响,在秋季与鱼类资源密度之间存在正向相关性;在春、秋、冬季,溶解氧对鱼类资源密度有显著影响,在冬季与鱼类资源密度之间存在正向线性相关。研究表明,2017年夏季鱼类资源密度较高;在长江口南支的自然延伸水域存在鱼类资源密度的相对低值,在崇明岛向海自然延伸方向水域存在鱼类资源密度的相对高值。后续研究将对长江口鱼类资源进行不同生态类型区分,以期更加准确地掌握影响各生态类型鱼类时空分布的环境因素及其时空分布信息。     

东海北部和黄海南部Ti鱼卵和仔稚幼鱼数量、分布及其与环境条件的关系

1999年夏季鳀鱼卵和仔稚幼鱼主要分布于黄海南部,122°00′～123°45′E、34°00′～35°15′N与122°15′E以西海域分别为鳀鱼卵与鳀鱼仔稚幼鱼的密集分布中心,其表层水温和盐度分别为25.5～26.9℃和27.11～31.81与26.4～27.0℃和31.31～32.05。鳀鱼卵和仔稚幼鱼分布的最适表层水温分别为25.5～26.4℃和25.9～27.0℃;全长为20mm以上的鳀鱼稚鱼已初步形成广盐性分布的习性,鳀鱼卵和仔稚幼鱼的分布对盐度的要求并不非常严格,水温是影响鱼卵和仔稚幼鱼分布的主要原因之一。鳀鱼卵和仔稚幼鱼的分布与叶绿素a的分布也有密切的关系,鳀鱼卵和仔稚幼鱼的密集分布中心正是叶绿素a的高值区。随着季节的变化,黄海南部鳀鱼产卵场由青岛外海逐渐向深水区转移。黄海南部鳀鱼活卵所占的比例为45.76％,胚胎发育状况良好。     

环境因子对黄海鳀鱼亲体-补充量关系影响的初步研究

鱼类年际资源量的波动可以归因于年间环境条件的变化和该种鱼类亲体数量的变化。文章根据1990～2001年间黄海中南部鳀鱼声学调查评估结果,以及黄海千里岩海区在此年间的表层水温和营养盐统计数据,以Ricker模型（R=αSe^-βS）为基础对黄海鳀鱼（Engraulis japonicas）亲体-补充量关系进行了初步研究。结果表明,黄海千里岩水域表层水温、磷酸盐浓度等环境条件因素对补充量有重要影响。     

Condition and recruitment of Aristeus antennatus at great depths (to 2,300 m) in the Mediterranean: Relationship with environmental factors

Depth and seasonal trends in the biological condition and recruitment of the red shrimp (Aristeus antennatus) have been analyzed over the slope to 2,233 m in the western Mediterranean. The best biological condition of A. antennatus (gonadosomatic index [GSI]) for mating and spawning occurred at 800–1,300 m in summer, in areas deeper than the fishing grounds distributed between 500 and 800 m. Females moved shallower to feed on the upper slope during periods of water‐mass homogeneity (autumn–winter), increasing their hepatic gland weight (hepatosomatic index [HSI]). Females moved downslope (800–1,100 m) to spawn (high GSI) during periods of water mass stratification (late spring–summer). The HSI of females decreased with depth down the slope in autumn, after the reproductive period. Small juveniles were distributed deeper than 1,000 m, associated with high near‐bottom O₂ levels, low turbidity and high C:N in sediments, implying favorable trophic conditions. This confirms the importance in studying the biology of deep‐sea species over their entire depth range. The progressive warming and increasing salinity of deep Mediterranean waters could provoke a decrease of dissolved O₂ that would affect the life cycle of A. antennatus.