Climate impacts on the landings of Indian oil sardine over the south‐eastern Arabian Sea

The landings of Indian oil sardine (Sardinella longiceps, Clupeidae) along the south‐eastern Arabian Sea are about 43.8% of total Indian oil sardine production. The annual landings of this species exhibit large‐scale variability with prolonged years of surplus or deficit landings without identified reason. Evaluating Indian oil sardine landings along the Kerala coast during 1961–2017 in relation to environmental variations, we have elucidated a putative link between variability in landings versus environmental parameters and climate indices. The variables examined in this study, such as salinity and temperature along with physical indices such as upwelling and mixed layer depth (MLD) of the ocean help to propose a mechanism to temporal variability in the landings of Indian oil sardine. Colder temperature and timely intense upwelling lead to nutrient enrichment in the surface water, which promotes the growth of phytoplankton (chl‐a) and thereby food availability to Indian oil sardine are found during years with surplus catch. Less saline surface waters and shoaling of MLD at these times could lead to the aggregation of fish at particular depths and thereby a good catches. The reverse mechanism, such as more surface saline water, warm temperature, downwelling or weak upwelling, and less nutrient enrichment, leads to deficit landings. Further, it was noticed that the Pacific decadal oscillation and Atlantic multidecadal oscillation have a more pronounced impact on Indian oil sardine landings over the coast of south‐eastern Arabian Sea than previously reported ENSO associated impacts. All these point towards climate change implications for the Indian oil sardine fishery.     

Variations in spawning ground area and egg density of the Japanese sardine in Pacific coastal and oceanic waters

The spawning ground of the Japanese sardine, Sardinops melanostictus (Schlegel), was distributed over the oceanic waters as well as the coastal waters along the Pacific coasts of western and eastern Japan during 1978–1992. The area of the spawning ground in the coastal waters on the continental shelf has ranged from 95 000 km² in 1992 to 143 000 km² in 1988, constituting 44–77% of the total area of the spawning ground. The area of the coastal spawning ground was relatively constant in spite of the large fluctuations in egg abundance, i.e. size of the spawning population, from 88 trillion (1987) to 668 trillion (1989) in the waters. Spawning adults seemed to extend over the coastal waters irrespective of the size of the spawning population. In contrast to the coastal waters, the spawning area in the oceanic waters offshore of the continental shelf increased from 31 000 km² in 1978 to 183 000 km² in 1988 and then shrank to 83 000 km² in 1992, as a function of the spawning population size. The egg distribution density in the coastal waters stayed less than 6000 m⁻² mo⁻¹, but it reached as high as 27 400 m⁻² mo⁻¹ in the expanded spawning ground in the oceanic waters. The oceanic waters seemed to function as a reserve spawning ground for the sardine in years of extremely high spawning population.     

A selective and low impacting traditional fishery,sustaining the economy of small coastal villages in central Mediterranean: Keep or replace the small‐scale driftnets?

Small‐scale driftnets (SSDs) have been historically used in the Mediterranean without major environmental concern. The introduction of large‐scale driftnets caused unwanted catches of protected species. Specific regulations were therefore issued in European waters, culminating in a proposed moratorium on SSDs. This study aimed to characterise the SSD fishery targeting anchovy (menaide), evaluating its environmental sustainability, economic performance and social relevance. In 2013, a survey by interviews, logbooks and observers on board assessed the order of magnitude of this fishery in terms of fishing capacity and activity, volume of landings and revenues. The menaide fleet consisted in 60 vessels <12 m overall length, moored in little harbours in southern Italy. These nets are highly selective: the target species, European anchovy, Engraulis encrasicholus (L.) and sardine, Sardina pilchardus (Walbaum), dominates the catches, while discards are negligible. The anchovies caught are of high quality and large size; the high prices support fish processing by local factories. Moreover, the results of a SWOT analysis demonstrated that replacing SSDs with a semi‐industrial fishery, like purse seining, would increase impacts on the ecosystem, and a loss of socio‐economic opportunities for several coastal villages. These findings support the option of keeping SSDs operating, in the framework of specifically oriented management measures.     

Environmental conditions, satellite imagery, and clupeoid recruitment in the northern Benguela upwelling system

The relationship between oceanographic conditions and clupeoid (pilchard, Sardinops sagax, and anchovy, Engraulis capensis ) recruitment in the northern Benguela upwelling system was investigated from 1981 to 1987 using a time-series of mean weekly SST images. Two approaches were taken. The first involved correlating recruitment success with the number of weekly coastal `SST events' above various cut-off temperatures during the main reproductive season. The second involved constructing a multiple regression model of recruitment success with two independent environmental variables: namely, the number of coastal `SST events' greater than 19°C, and an onshore retention index for the early life-history stages. The retention index was derived from a spatial time-series analysis of the SST images using principal components analysis. In general, pilchard recruitment showed a positive relationship with the `number of SST events' whilst anchovy recruitment had a negative relationship; 1987 was an outlier year, during which there were exceptionally high levels of both pilchard and anchovy recruitment. The multiple regression R ² values were high and significant for both species (pilchard R ² = 0.88, anchovy R ² = 0.96). The regression model also accounted for the 1987 outlier according to levels of onshore retention which, despite low inshore SSTs, were particularly high during the 1986/87 reproductive season. Although these results need to be validated with data from a longer time period, they show how satellite data might be used for predicting clupeoid recruitment success in the northern Benguela.     

Pelagic ecology of a northern boundary current system: effects of upwelling on the production and distribution of sardine (Sardinops sagax), anchovy (Engraulis australis) and southern bluefin tuna (Thunnus maccoyii) in the Great Australian Bight

Shelf waters of southern Australia support the world's only northern boundary current ecosystem. Although there are some indications of intense nitrate enrichment in the eastern Great Australian Bight (GAB) arising from upwelling of the Flinders Current, the biological consequences of these processes are poorly understood. We show that productivity in the eastern GAB is low during winter, but that coastal upwelling at several locations during the austral summer–autumn results in localized increases in surface chlorophyll a concentrations and downstream enhancement of zooplankton biomass. Sardine (Sardinops sagax) and anchovy (Engraulis australis) eggs and larvae are abundant and widely distributed in shelf waters of the eastern and central GAB during summer–autumn, with high densities of sardine eggs and larvae occurring in areas with high zooplankton biomass. Egg densities and distributions support previous evidence suggesting that the spawning biomass of sardine in the waters off South Australia is an order of magnitude higher than elsewhere in southern Australia. Sardine comprised >50% of the identified prey species of juvenile southern bluefin tuna (SBT, Thunnus maccoyii) collected during this study. Other studies have shown that the lipid content of sardine from the GAB is relatively high during summer and autumn. We suggest that juvenile SBT migrate into the eastern and central GAB during each summer–autumn to access the high densities of lipid‐rich sardines that are available in the region during the upwelling period. Levels of primary, secondary and fish production in the eastern GAB during summer–autumn are higher than those recorded in other parts of Australia, and within the lower portion of ranges observed during upwelling events in the productive eastern boundary current systems off California, Peru and southern Africa.     

Pre‐Columbian fisheries catch reconstruction for a subtropical estuary in South America

Small‐scale fisheries provide food and livelihoods for thousands of people along the Brazilian coastline. However, considerable uncertainties still surround the extent to which artisanal and subsistence fisheries contribute to the total of national landings and their historical ecological significance. Fisheries monitoring is deficient in Brazil, and historical records are limited to irregular accounts spanning the last few decades, while this coastline has supported human populations for at least 6,000 years. Here, we estimate pre‐Columbian subsistence catches for a large subtropical estuary in southern Brazil. Our results suggest that prehistoric populations may have extracted volumes of fish biomass higher than or comparable with historical subsistence fisheries in the region, and that the latter is likely underestimated. If a long‐term perspective is required to evaluate the current economic value and status of fisheries in subtropical and tropical South America, this should go beyond the historical time interval and integrate the contribution of pre‐Columbian archaeology.     

Age-related movement patterns and population structuring in southern garfish, Hyporhamphus melanochir, inferred from otolith chemistry

Abstract  The southern garfish, Hyporhamphus melanochir (Val.), is an important inshore fishery species in South Australia. Over the past few years there have been concerns with this fishery, which is now considered to be over-exploited. Currently, the fishery is assumed to consist of two separate stocks, but there is no understanding of movement patterns both within and between these two stocks to justify this assumption. Otolith chemistry was used to infer age-related patterns of movement, delineate potential sub-populations and determine the extent of mixing within South Australian coastal waters. Results indicated that the population structuring of garfish is more complex than previously assumed and it seems that stocks can be discriminated at a much finer spatial scale. Garfish collected from sites separated by <60 km displayed significantly different chemical signatures (relative concentrations of ⁷Li, ²⁴Mg, ⁵⁵Mn, ⁸⁸Sr and ¹³⁸Ba) in their otoliths, especially during their second year of growth, indicating that they had inhabited different water bodies. From a broader perspective, South Australian garfish can be partitioned into six regional components with various levels of inter-mixing. From these results, it was suggested that assessment and management of the fishery may have to be restructured to align with the smaller spatial units.     

Distribution and abundance of South-west Atlantic anchovy spawners (Engraulis anchoita) in relation to oceanographic processes in the southern Brazilian shelf

The reproductive environment of the South-west Atlantic anchovy, Engraulis anchoita , in the southern Brazilian coast was investigated using maritime weather reports from the US National Climatic Center. These reports were summarized to yield seasonal distributions of sea surface temperature, wind stress and Ekman transport for 2-month segments of the seasonal cycle. The vertical oceanographic structure and dynamics were studied using temperature and salinity data collected from oceanographic cruises. The seasonal distribution and biomass of South-west Atlantic anchovy spawners were estimated by acoustic surveys. Anchoita spawns intensively off southern Brazil during winter and early spring when the Ekman transport is directed onshore, and the combined effects of freshwater run-off and the flow of cold water near the bottom result in a strong vertical stability over the continental shelf. During this season, primary production peaks due to nutrient input from Sub-Antarctic waters and freshwater run-off. These conditions would avoid dispersal of eggs and larvae offshore and favour the production and maintenance of fine-scale food particle aggregations required for successful first feeding of newly hatched larvae. In summer, the conditions are almost reversed and anchoita spawners are virtually absent from the area. Thus, the spawning strategy of anchoita in southern Brazil seems to be tuned in a way to optimize larval retention, minimize exposure to turbulent mixing and take advantage of enhanced plankton productivity.     

Environmental effects on the spatio‐temporal patterns of abundance and distribution of Sardina pilchardus and sardinella off the Mauritanian coast (North‐West Africa)

From 1998 to 2011, the effects of environmental conditions on the spatial and temporal trends of sardine and sardinella catch rates in the Mauritanian waters were investigated using generalized additive models. Two models were used: a global model and an oceanographic model. The global models explained more of the variability in catch rates (60.4% for sardine and 40% for sardinella) than the oceanographic models (42% for sardine and 32.4% for sardinella). Both species showed clear and inverse seasonal variations in abundances corresponding to their main spawning activities and the hydrologic seasons off the Mauritanian waters. Sardine prefer colder waters and seem to occupy the ‘gap’ in the northern part of the Mauritanian waters as soon as sardinella has left the area because of to lower water temperatures. Unlike sardinella, sardine showed a gradual southward extension between 2002 and 2009. The oceanographic model revealed that a high proportion of catch variability for the two species could be explained by environmental variables. The main environmental parameters explaining the variability are sea surface temperature (SST) and the upwelling index for sardinella, and the chlorophyll‐a (Chl‐a) concentration, the upwelling index and SST for sardine. The sardinella spatio‐temporal variations off Mauritania seem to be more controlled by thermal than productivity gradients, probably linked to the species physiological constraints (thermal tolerance) whereas sardine seems to be more controlled by an ‘optimal upwelling and temperature’ windows. The results presented herein may be useful for understanding the movement of these species along the Mauritanian coast and hence their management under a changing climate.     

Management of selected Polish commercial and recreational lake fisheries activities

The objective of management of Polish lakes is to fulfil the needs of commercial and recreational fishermen that developed after the political changes of the last decade. The effectiveness of the policies and practices adopted has never been studied. Six lake enterprises were selected, two in each of the lake districts: Mazuria, Pomerania and Great Poland. The two Mazurian enterprises manage a total of 13 325 ha of lakes, the Pomeranian ones 6130 ha and those of Great Poland 4156 ha. All data on commercial fisheries were collected and studies of anglers' activities were carried out through 550 questionnaires. The six enterprises were analysed as a whole and separately, with attention being paid to commercial landings and stockings in 1995–1999, and anglers' catches in 1998. Two enterprises and lakes were chosen for closer analysis. It was estimated that an average lake angler caught 59.2 kg of fish in 1998, and the overall landings by anglers was 35.0 kg ha^–1 yr^–1. Fish yield from lakes was 50.0 kg ha^–1 yr^–1 without considering poachers' catches.     

Effects of marine climate variability on the relative abundance of Lutjanus purpureus (POEY, 1866) on the Amazon Continental Shelf

The aim of this study was to analyze the effects of climate and marine variability on the catches of Lutjanus purpureus in three sectors of the Amazon Continental Shelf. Remote sensing data were compared with landings (CPUE) between 1997 and 2007 and analyzed for partial influence obtained through the Generalized Additive Model. Additionally, significant variables were analyzed through Wavelet Cross-Spectrum, and periods of high correlation between variables in space and time were identified. The results indicated a high coherence between catch per unit effort (CPUE) and environmental variables on an interannual scale, suggesting that Red Snapper fishing is mainly influenced by the seasonal effects of oceanographic variables. These results suggest that fluctuations in Red Snapper catches between 1997 and 2007 may be the result of natural processes that occur in the Amazon Continental Shelf every year in synergy with environmental variables, which are also indirectly affected by the El Niño–Southern Oscillation (ENSO) pattern.     

Fisheries catches and the carrying capacity of marine ecosystems in southern Brazil

The carrying capacity of marine shelf ecosystems in southern Brazil for harvestable species is analyzed by (1) quantifying the amount of available primary production appropriated by fisheries catches, (2) evaluating the trend in the mean trophic level of fisheries, and (3) simulating the ecosystem effects of “fishing down the food web” in an intensively exploited shelf region. Fisheries utilize ca. 27 and 53% of total primary production in the southern and south-eastern shelf regions, respectively. Regional variation in the carrying capacity appropriated by fisheries results from differences in the primary production, catch volume and trophic transfer efficiencies. Overall, fisheries landings do not display a trend of decreasing trophic level with time due to the collapse of the sardine fishery and the recent increasing of offshore fishing for higher trophic level species, mainly tunas and sharks. However, the simulations show that fishing down the food web through fisheries that target small pelagic planktivorous fishes, while at first increasing catches in intensively exploited regions, has the potential of decreasing yields, by interrupting major energy pathways to exploited, high-trophic level species. The consequences of these results to the design of precautionary measures for future fishing policies are discussed.     

Study of sardine (Sardina pilchardus) regime shifts in the Iberian Atlantic shelf waters

Sardine fisheries in the Iberian Atlantic shelf (36°N–44.5°N) show decadal‐scale cycles. In the late 1990s, a positive phase in sardine stock was expected; on the contrary, catches have declined until now. Regime shifts in climatic and oceanographic variables on different scales (as forcing factor) and shifts in sardine stock (as result) have been used with the aim of identifying the physical variables that explain most of the sardine population variance in the region. Circa 1998, when last sardine regime shift was detected, the main patterns of large‐scale atmospheric circulation in the Northern Hemisphere with influence in the study area namely Northern Atlantic Oscillation (NAO) and East Atlantic (EA) pattern changed and coupled in a combination that led to a rise in sea surface temperature and a decline in the coastal upwelling intensity. Several years with a downwelling situation in average in the main spawning and feeding Iberian sardine areas would have affected the stock abundance, averting the return to the projected positive regime. The sardine negative regime shift was detected first in the regions of the study located further north. The regional variable latent heat flux that groups a set of environmental processes related to the ocean–atmosphere heat exchanges and so with the turbulence manages to explain the 72% of sardine recruitment.     

The zooplankton biomass in the Sea of Japan

We examined seasonal, annual variation and horizontal distribution of zooplankton in the Sea of Japan from 1966 to 1990. Zooplankton was most abundant in the spring. The spring maximum appeared in February–March and in April–May in the southern and eastern parts of the study areas, respectively. In the summer and autumn, a secondary peak was most conspicuous in the eastern part. The difference between the estimated biomass at night and day was large in the spring and small in summer and autumn. The biomass in the offshore southern area peaked about every 3 years between 1966 and 1983, and increased abruptly in 1990. The density in the area north of 39°N or 40°N was high. Total biomass estimated in the upper 150 m layer in the Sea of Japan (10⁶ km²) was 9.5 × 10⁶ t in the daytime and 16.6 × 10⁶ t at night.     

Seasonal and interannual variations of oceanographic conditions off Mangalore coast (Karnataka, India) in the Malabar upwelling system during 1995–2004 and their influences on the pelagic fishery

Mangalore coast is well known for its multi‐species and multi‐gear fisheries and the fishery and oceanographic features of this region is a true representation of the Malabar upwelling system. Ten years of study (1995–2004) of oceanographic parameters has been carried out from the inshore waters off Mangalore to understand their seasonal and interannual variations and influences on the pelagic fishery of the region. Attempt has been also made to understand the influence of local and global environmental conditions on the alternating patterns of abundance between the Indian mackerel and oil sardine from the area. Field‐ and satellite‐derived oceanographic data have shown that coastal upwelling occurs during July–September with a peak in August resulting in high nutrient concentrations and biological productivity along the coast. Nearly 70% of the pelagic fish catch, dominated by oil sardine and mackerel, was obtained during September–December, during or immediately after the upwelling season. Catches of scombroid fishes were significantly related to cold Sea Surface Temperature, while such relationships were not observed for sardines and anchovies. Significant positive correlations were observed between the ENSO events (MEI) and seawater temperature from the study area. The extreme oceanographic events associated with the cold La Niña, which preceded the exceptional 1997–98 El Niño event, were responsible for the collapse of the pelagic fishery, especially the mackerel fishery along the southwest coast of India (Malabar upwelling system). Coinciding with the collapse of the mackerel fishery, oil sardine populations revived during 1999–2000 all along the southwest coast of India. Tolerance of oil sardine to El Niño / La Niña events and the low predatory pressure experienced by their eggs and larvae due to the collapse of mackerel population might have resulted in its population revival.     

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.     

Climate change and abundance of the Atlantic-Iberian sardine (Sardina pilchardus)

Climatic warming is affecting oceanic circulation patterns in coastal upwelling areas, but the impact of this climatic change on pelagic fish populations remains unclear. From juvenile landings collected over 38 years, the thresholds of environmental factors were determined that limited the optimal environmental window (OEW) for sardine (Sardina pilchardus recruitment success in the northwestern Iberian peninsula. The environmental factors considered were: water column stability in February, offshore water transport in March–April (Q_xMA), upwelling intensity in the preceding year from May to August (Q_xMJJA), and the winter North Atlantic Oscillation (NAO) index. From 1875 to the mid‐1920s, the mean number of years within the OEW was relatively constant. However, since the mid‐1920s, there have been oscillations and alternating decades with high and low number of years within the OEW, which were related to oscillations in sardine landings. From 1906 to 2000, there were four record, low sardine catches in the 1920s, 1950s, 1970s and 1990s, related to a high number of successive years with prevailing conditions out of the OEW. From 1875 to the present, a high year‐to‐year variation of the NAO, Q_xMJJA and water stability in February was observed, although with mean values usually within the OEW. The collapse in the 1950s was related, partly, to successive years with low Q_xMJJA. Successive years with high NAO values may be related to the collapse of the sardine fishery in the 1990s. Q_xMA has been the most significant factor controlling SRS in this area, being the factor related to the low catches observed in the 1920s, 1950s and 1970s. Water stability was not responsible for any of the collapses observed, but since the 1920s, there has been a significant trend toward decreasing water column stability before the onset of the spring bloom.     

Fishery resources and economic gain in three mangrove areas on the south-east coast of India

Abstract The fishery resources and fishing income in three different mangrove areas were evaluated. The mangrove-rich area provided high catches of shellfish and finfish and yielded high fishery income, compared with the mangrove-poor areas. Luxuriant mangrove areas supported a catch of 11 kg shellfish ha⁻¹ day⁻¹ and 4.5 kg finfish ha⁻¹ day⁻¹, corresponding with an economic gain of US$ 14 (Rs 603.7) day⁻¹ for shellfish and US$ 3 (Rs 130.5) day⁻¹ for finfish. The value of maintaining mangroves to ensure better fishery resources and to support coastal economies was identified. Management practices for conserving and enhancing mangroves and associated fishery resources are suggested.     

Pacific sardine (Sardinops sagax, Jenyns 1842) landings prediction. A neural network ecosystemic approach

In this study the performances of computational neural networks (CNNs), multiple linear regressions (MLRs) and generalised additive models (GAMs) to predict Pacific sardine (Sardinops sagax) landings and to analyse their relationships with environmental factors in the north area off Chile were studied. For this purpose several local and global environmental variables and indexes (sea surface temperature, sea level and Ekman transport index in the Chilean coast and, sea surface temperature in the area Niño 3 + 4 and Niño 1 + 2, and the south oscillation index) were considered as inputs or independent variables. Additionally, several CNNs were calibrated and validated adding the anchovy (Engraulis ringens) landings in the same area as model inputs. The time lags of the variables considered were selected through analysis of the non-linear cross-correlation functions and an alternative form of sensitivity analysis based on the approach of the missing value problem. The analysis of error measures with validation data set showed that the best results were obtained when local and global variables were used separately and combined with anchovy landings. Globally, the best result was given by a CNN with 18 input variables (model CNN 6(II) which only considered global variables and anchovy landings) and 10 neurons in a hidden layer. For this configuration the explained variance was slightly higher to 86% which supposed a standard error of prediction of 7.66%. These results were significantly better than those obtained with MLRs and GAMs. The strong correlation between predicted and observed sardine landings suggests that CNNs captured the trend of the historical data. Also, the generalisation capacity together the sensitivity analysis allowed us to identify the variables with a high weight in the model and partially to interpret the statistical functional relationships between these environmental variables and sardine landings.     

Oil sardine (Sardinella longiceps) off the Malabar Coast: density dependence and environmental effects

Marine fish stocks are known for extensive variation in landings, with temporal fluctuations attributable to density-dependent as well as environmental effects. In this paper we analysed a 44-yr time-series of oil sardine Sardinella longiceps landings from the Arabian Sea off the Malabar Coast of India. Density dependence was detected in the landings of oil sardine, reinforcing the potential for sustainable yields. Significant environmental factors (precipitation and sea level reflecting the strength of upwelling) during the monsoon period (June–August) are hypothesized to affect the dynamics of landings by influencing spawning and recruitment success. Together, density dependence and environmental variability during the monsoon explained 80% of the among-years variance in landings. Our results have important consequences for understanding catch variability and are potentially useful for facilitating management of this commercially important fishery.