Abundance Of Anchovy Eggs Research Articles

Spawning overlap of Japanese anchovy Engraulis japonicus and Japanese Spanish mackerel Scomberomorus niphonius in the coastal Yellow Sea: A prey–predator interaction

AbstractJapanese Spanish mackerel Scomberomorus niphonius and Japanese anchovy Engraulis japonicus are typical predator and prey species, respectively, with high commercial values in the China seas. However, the interspecific interaction, particularly the relationship between the two species during early life stages, is unclear. Here, based on ichthyoplankton surveys in the coastal Yellow Sea during 2013–2018, we analyzed the relationship between the two species based on egg occurrence and abundance in the context of species interaction. Spawning optimal temperature were examined for anchovy (13.0–18.0°C) and mackerel (15.0–20.0°C) based on egg occurrences and abundances in relation to sea surface temperature. We confirmed the peak spawning periods (May and June) and primary spawning areas (Haizhou Bay) for both mackerel and anchovy based on spatiotemporal distributions of two species eggs. Mackerel showed a high spawning overlap with anchovy, and anchovy egg abundance were also higher in overlap areas. Anchovy egg abundance may be more important for mackerel spawning than environmental variables, suggesting the significance of prey for predators during early recruitment. The temperature also has important effects on mackerel spawning and could be a threshold affecting mackerel spawning activity. Mackerel might have evolved a spawning strategy of short‐term spawning timed to coincide with the peak spawning of anchovy in the coastal Yellow Sea. These results highlight the effects of interspecific relationships on spawning strategy of anchovy and mackerel in the coastal Yellow Sea and may provide some insights for early recruitment studies of piscivorous fishes in the context of the match–mismatch hypothesis.

Historical trends and future distribution of anchovy spawning in the Bay of Biscay

Future scenarios of fish stocks and the impacts of climate variability and change on fisheries are critical to anticipate and minimize potential economic losses in this sector. In this study, we assessed the impact of recent sea warming and future climate change on anchovy in the Bay of Biscay, where sea surface temperature has increased in the last three decades. We analyzed the historical evolution of the anchovy spawning and built species distribution models that are projected under the RCP8.5 climate change scenario. The historical analysis of anchovy spawning showed that spawning peak advanced at a rate of 5.5 days/decade from 1987 to 2015, and the gonadosomatic index (as proxy of spawning activity) generally increased, which might be associated to changes in phytoplankton abundance. In addition, the spawning area expanded and contracted depending on the total egg production. In the future, the overall anchovy egg abundance in the Bay of Biscay is expected to increase between 1.05 and 2.66-fold under the RCP8.5 climate change scenario by the mid and end-of-the-21st-century, respectively. Projected environmental changes are expected to induce an expansion of the spawning area (7.8% and 16.4% for mid- and end-of-the-century) and higher egg densities.

Distribution and abundance of eggs and estimation of spawning stock biomass of anchovy,Engraulis encrasicolus(Linnaeus, 1758), in the south-eastern Adriatic Sea

Seasonal distribution and abundance of anchovy eggs were analysed during three scientific cruises carried out from summer 2006 to summer 2007 in the Boka Kotorska Bay, and one cruise in July 2008 in the open waters of the south-eastern Adriatic Sea. Daily egg production method (DEPM) was applied for the first time for estimation of the anchovy spawning stock biomass in the south-eastern Adriatic Sea. The daily egg production was 13–581 eggs day−1within the bay, and 42–110 eggs day−1in the open waters. Anchovy egg abundance was highest in spring inside the Bay of Kotor (one of the innermost and eutrophic sub-bays of the Boka Kotorska Bay), which indicates that the conditions for anchovy spawning are very favourable in this part of the Adriatic Sea, even when temperatures are below the optimum. This study has shown that the Boka Kotorska Bay is an area of very intensive spawning of anchovy, and that small-size anchovies live and spawn in the bay, and after spawning migrate towards open waters. The length at which 50% of anchovy were mature (L50) was calculated as 9.28 for females and 9.02 for males. Spawning stock biomass was at a stable level during the period of investigation.

Spatial distribution of sardine and anchovy early life stages along the eastern Adriatic Sea

Event Abstract Back to Event Spatial distribution of sardine and anchovy early life stages along the eastern Adriatic Sea Barbara Zorica1, Vanja Cikes Kec1*, Goran Brzulja1 and Viktor Kraljević1 1 Institute of Oceanography and Fisheries, Croatia Despite long-term investigations of the Adriatic Sea in general and extensive research on sardine and anchovy as ecologically and economically important fish species, knowledge concerning their spawning ecology, precisely their possible spawning grounds, is still incomplete. Therefore, two scientific surveys (January, July 2012) were performed, as target species spawn during different periods of the year (sardine - October to April (Sinovčić et al., 2007) and anchovy - April to September (Zorica et al., 2013)). Throughout these surveys, standard vertical plankton tows were made during the daylight at 72 stations in January and 60 stations in July using a WP2 sampler (mouth opening, 0.255 m2; mesh size, 0.200 mm). WP2 net was put vertically down during the calm sea to a depth of 100 m or to 5 m above the seabed in relatively shallow marine area (less than 100 m). Plankton samples were preserved in 4% buffered formalin and transported to the laboratory where they were analysed. Throughout ichtyoplankton analysis of samples collected during the winter survey a total of 506 sardine eggs and 348 larvae were sorted out. The mean sardine egg and larval abundance in the analysed period at positive stations was 57.8 +/- 77.4 eggs/m2 and 29 +/- 25.85 larvae/m2, with peaks of 396 eggs/m2 and 108 larvae/m2 at positive sampling stations. Concerning the summer survey and anchovy early life stages from obtained samples 1489 anchovy eggs and 1036 larvae were isolated. Average abundance of anchovy eggs and larvae was 145.26 +/- 201.27eggs/m2 and 115.11+/- 162.32 larvae/m2, respectively. The highest values of mentioned parameters at positive stations were 800 eggs/m2 and 952 larvae/m2. According to obtained results and their processing within Ocean Data View (odv.awi.de), revile that both species during 2012 spawn above the whole continental shelf and the areas of higher early life stages abundance overlap. Acknowledgements This study was supported by the Ministry of Agriculture of the Republic of Croatia, as a part of the research project “Defining the spatial and temporal periods of sardine and anchovy spawning in the Adriatic Sea". References Sinovčić, G., Zorica, B. and ČIKEŠ KEČ, V. (2007). Abundance and some biological characteristics of sardine, Sardina pilchardus (Walb.,1792), in the coastal and open sea waters of the Adriatic Sea (Croatia). In: I. Rožanić (Editor). Proceedings, Second Conference on Marine Technology, Rijeka, pp. 155-174. Zorica, B., Vilibić, I., Čikeš Keč, V. and Šepić, J. (2013). Environmental conditions conducive to anchovy spawning in the Adriatic Sea. Fish. Oceanogr. 22(1): 32-40. Keywords: Small pelagic, Eggs, Larvae, Adriatic sea, Mediterranean Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Poster Presentation Topic: Life Cycles, Migration and Connectivity Citation: Zorica B, Cikes Kec V, Brzulja G and Kraljević V (2015). Spatial distribution of sardine and anchovy early life stages along the eastern Adriatic Sea. Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.fmars.2015.03.00009 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Oct 2015; Published Online: 04 Nov 2015. * Correspondence: PhD. Vanja Cikes Kec, Institute of Oceanography and Fisheries, Split, Croatia, cikes@izor.hr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Barbara Zorica Vanja Cikes Kec Goran Brzulja Viktor Kraljević Google Barbara Zorica Vanja Cikes Kec Goran Brzulja Viktor Kraljević Google Scholar Barbara Zorica Vanja Cikes Kec Goran Brzulja Viktor Kraljević PubMed Barbara Zorica Vanja Cikes Kec Goran Brzulja Viktor Kraljević Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Modeling Fish Egg Production and Spatial Distribution from Acoustic Data: A Step Forward into the Analysis of Recruitment

To date, there are numerous transport simulation studies demonstrating the relevance of the hydrodynamics for the advection, dispersion and recruitment of early stages of marine organisms. However, the lack of data has conditioned the use of realistic locations for the model setup and configuration in transport studies. This work (I) demonstrates the key role played by the use of the realistic initial position of the eggs of small pelagic fishes in the analysis of late-larval recruitment in coastal nursery areas and (II) provides a general solution for deriving future egg positions and abundances from adult biomass obtained from acoustic surveys and available fecundity data. Using European anchovy in the NW Mediterranean as a case study, we first analyzed the impact of the initial location, timing, egg buoyancy and diel vertical migration of larvae on the potential late-larval recruitment to coastal areas. The results suggested that prior knowledge of the initial spawning grounds may substantially affect the estimates of potential recruitment. We then integrated biological and acoustics-derived data (the biomass and size structure, sex ratio, a weight-batch fecundity model, mean weight, number of fish and mean spawning) to build a predictive model for interannual egg production. This model was satisfactorily contrasted with field data for two years obtained with the Daily Egg Production Method (DEPM). We discuss our results in the context of the fluctuations of European anchovy egg abundance from 2003 through 2010 in the NW Mediterranean and in terms of the potential applicability of the acoustics-based spatial predictive egg production model.

Merging anchovy eggs abundance into a hydrodynamic model as an assessment tool for estuarine ecohydrological management

ABSTRACTThe impoundment of rivers by large dams is the biggest direct anthropogenic impact on the hydrological cycle. However, dams can help solving eutrophication in estuaries by controlling flow pulses, which in turn might enhance the advection of fish larval stages from their spawning and nursery areas. Thus, this work aimed to merge data on the abundance of anchovy eggs with MOHID hydrodynamic model for the Guadiana estuary, allowing dam/basin managers to set river discharge scenarios that might mitigate/prevent eutrophication, without compromising the presence of fish larval stages inside the estuary. Data on anchovy larval stages were assessed in the Guadiana estuary and adjacent coast and three simulation setups were developed. In Simulation A, anchovy eggs abundance was merged in the hydrodynamic model to compare the outputs with data on the abundance, distribution and development stage of anchovy eggs and larvae. In Simulation B, lagrangian particles were incorporated in the model to determine the percentage of particles released from the upper, middle and lower estuary that remain in the estuary along 10 days, in two tidal situations and in seven river discharge scenarios. In Simulation C, the abundance of anchovy eggs was merged in the model to select the discharge scenario(s) that do not compromise the presence of anchovy larval stages in the estuary. Results confirmed the spawning and nursery areas of anchovy and showed that scenarios B (Qmax = 20 m3 s−1) and C (Qmax = 50 m3 s−1) should be applied during neap tides. The choice between scenarios depends on the degree of eutrophication, the effectiveness of an inexistent monitoring program and on plankton response experiments to flushing and increased nutrient loading. This work produced an easy‐to‐use management tool for Guadiana managers, serving as an example to other estuarine sites around the world. Ultimately, this work suggests that river flow management must be guided by robust ecological studies, under an adequate sociological framework and adopting sustainable economic principles to maintain and improve the ecosystem services. Copyright © 2010 John Wiley & Sons, Ltd.

Changes in a temperate estuary during the filling of the biggest European dam

This study aimed to determine whether and how the disruption of river flow, during the filling of the Alqueva dam, influenced the variability of abiotic and biotic factors in the Guadiana estuary, particularly the abundance and distribution of anchovy eggs. River inflow was found to be the most important factor in determining abiotic and biotic variability in the Guadiana estuary. Seasonal patterns were obscured by long periods of low inflow (mid April to early December 2002), which caused marked changes in the estuary. The estuarine turbidity maximum zone was displaced towards the upper estuary, to at least 38 km from the river mouth, 8 to 16 km upstream from previous records. The dynamics of nutrient stoichiometry was also affected. In the upper and middle estuary, P was more potential limiting than N and potential Si limitation was only frequent on the coast, with direct and/or indirect influence in changing phytoplankton dynamics and composition. Previously, the upper estuary alternated between potential P limitation during winter, Si limitation during spring and mid summer and N limitation during mid summer and autumn. The flooding of vast areas in the catchment of the dam probably caused the increase of DSi concentrations, as well as maximal N and P loadings. The abundance of larval stages of anchovy decreased, putatively because estuarine productivity has also decreased. In April 2002 there was an uncontrolled discharge from the Alqueva dam, which reduced the abundance of anchovy eggs by 99.99%. It is suggested that dam managers should mimic, as much as possible, the natural river flow, in order to minimize the impact on downstream ecosystems. Management efforts should not be restricted to the areas upstream of the dam, but should also encompass the estuary and adjacent coastal area.

Occurrence and Distribution of the Eggs and Larvae of Anchovy, Engraulis japonicus, in Jeju Strait, Korea, with Descriptions of Environmental Characteristics

The occurrence and distribution of eggs and larvae of anchovy, Engraulis japonicus, in Jeju Strait, Korea from May to November 2002 were investigated, and the relationships between the abundances of anchovy eggs and larvae and the oceanographic conditions, including meteorological data, were analyzed. During the sampling periods, the anchovy eggs occurred from May to October and about 95% of total egg abundance occurred in only two months from July to August, suggesting that the main spawning season of anchovies is confirmed in summer from July and August in Jeju Strait. The spawning area of anchovies gradually moved to the southern part of the survey area with time. The predominant anchovy larvae collected in this study were mostly smaller than 16.0 mm TL. Correlation analysis and multiple regression analysis showed that the anchovy egg abundance in the study area depended strongly on the wind conditions, especially less than 10 m/s, and increasing water temperature. Salinity variations also had significant effects on the abundance of anchovy larvae.

Relative importance of gulf and shelf waters for spawning and recruitment of Australian anchovy, Engraulis australis, in South Australia

AbstractGonosomatic indices and egg and larval densities observed from 1986 to 2001 suggest that the peak spawning season of the Australian anchovy (Engraulis australis) in South Australia occurs during January to March (summer and autumn). This coincides with the spawning season of sardine (Sardinops sagax) and the period when productivity in shelf waters is enhanced by upwelling. Anchovy eggs were abundant throughout gulf and shelf waters, but the highest densities occurred in the northern parts of Spencer Gulf and Gulf St Vincent where sea surface temperatures (SST) were 24–26°C. In contrast, larvae >10 mm total length (TL) were found mainly in shelf waters near upwelling zones where SSTs were relatively low (<20°C) and levels of chlorophyll a (chl a) relatively high. Larvae >15 mm TL were collected only from shelf waters near upwelling zones. The high levels of larval abundance in the upwelling zones may reflect higher levels of recruitment to later stages in these areas compared with the gulfs. The sardine spawns mainly in shelf waters; few eggs and no larvae were collected from the northern gulfs. The abundance of anchovy eggs and larvae in shelf waters increased when sardine abundance was reduced by large‐scale mortality events, and decreased as the sardine numbers subsequently recovered. We hypothesize that the upwelling zones provide optimal conditions for the survival of larval anchovy in South Australia, but that anchovy can only utilize these zones effectively when the sardine population is low. At other times, northern gulf waters of South Australia may provide a refuge for the anchovy that the sardine cannot utilize.

Anchovy egg and larval distribution in relation to biological and physical oceanography in the Strait of Sicily

The European Anchovy (Engraulis encrasicolus, Linnaeus, 1758) represents one of the most important fishery resources in some areas of the Mediterranean. This short-lived, small pelagic fish is characterized by large interannual fluctuations, probably as a result of environmental variability. As part of the European Project Med 98-070, the main aim of which was the study of the anchovy population in the Strait of Sicily, icthyoplankton surveys were carried out between 1999 and 2001, during the peak spawning season for anchovy. Present work reports the relationship between meso-zooplankton biomass and the abundance of anchovy eggs and larvae in the Strait of Sicily. Data on anchovy egg abundance showed that the main spawning area was located in the north-western region of the study area. The branch of the Atlantic Ionian Stream, running parallel to the southern Sicilian coast, acts as a transport mechanism for anchovy eggs and larvae towards the southernmost end of the island, off Cape Passero. Observed distributions were largely consistent with local hydrographic features, which allow larvae to be retained in areas providing the necessary feeding conditions for recruitment success.

Zooplankton assemblages and hydrography in the spawning area of anchovy (Engraulis anchoita) off Río de la Plata estuary (Argentina - Uruguay)

The massive spawning of anchovy (Engraulis anchoita) in Argentine waters takes place in spring in the coastal sector off the Buenos Aires Province, with the highest concentrations of spawners occurring in front of the Río de la Plata mouth. In October 1995, the size structure, composition and abundance of the zooplankton community was analyzed and related to the hydrography and the abundance of anchovy eggs. Oceanographic conditions were different from the recorded means for the season. A higher proportion of the colder and more saline shelf waters were present in the coastal area and strong haloclines were not observed. High values of plankton biomass were observed in the estuarine frontal area and in the weakly stratified waters of the median shelf. The cluster analysis of the stations gave rise to the formation of coastal (CA), transitional (TA) and shelf (SA) faunistic areas. Mesozooplankton smaller than 1 mm total length (TL) dominated the whole area. The copepods, Paracalanus spp. and Oithona similis, and the cladocerans, Evadne nordmanni and Podon spp., constituted the bulk of this mesozooplankton fraction. Oithona similis was the dominant species in the SA. The copepod, Acartia tonsa (1–2 mm TL), was extremely abundant in the estuarine front (more than 17 600 individuals m–3) followed by appendicularians, members of Pseudocalanidae, anchovy eggs and decapod larvae. Species of Calanidae (Calanoides carinatus and Calanus simillimus), the amphipod hyperiid, Themisto gaudichaudii, and the euphausiid, Euphausia lucens, largely dominated the macrozooplankton (>2 mm TL) in the TA and SA. In the CA, significant positive correlations between the abundance of small copepods (size ranges <1 and 1–2 mm) and anchovy eggs were found. Trophic implications of these findings for first-feeding anchovy larvae were discussed. The adequacy of the TA and SA as feeding ground for adults of anchovy was evaluated.

Temporal resolution of biological and physical influences on bay anchovy Anchoa mitchilli egg abundance near a river-plume frontal zone

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 237:257-269 (2002) - doi:10.3354/meps237257 Temporal resolution of biological and physical influences on bay anchovy Anchoa mitchilli egg abundance near a river-plume frontal zone Ernst B. Peebles* College of Marine Science, University of South Florida, 140 Seventh Avenue SE, St. Petersburg, Florida 33701, USA *E-mail: epeebles@seas.marine.usf.edu ABSTRACT: Bay anchovy egg abundance in the Manatee River estuary, Florida, was compared with conditions in the spawning ground before and after spawning to distinguish prey-supply-based spawning responses from post-spawning advective effects. Plume fronts were a prominent feature of the spawning ground. Egg distribution, copepod distribution and front development were surveyed 25 times across a wide range of freshwater inflow conditions. Surface-front strength (maximum interpolated salinity slope) was strongly correlated with the size of the frontal zone, as defined by surface areas having slopes >1 psu km-1. Eggs were most abundant landward of the frontal zone at a location with consistently high abundance of the copepod Acartia tonsa, which is consumed by adult and larval bay anchovies. Large, significant changes in egg abundance were observed over both long (seasons) and short (<3 d) periods (Tukey 95% HSD multiple range tests). An El Niño-associated flood event caused the rapid evolution of a large, seaward-moving frontal system that initially had a negative effect on egg abundance. Spawning resumed in reduced salinity following passage of the front, demonstrating a level of plasticity in spawning response to salinity change. A stepwise regression model explained 92% of the variation in egg abundance and suggested that tidal amplitude was not a significant determinant of abundance. Instead, egg abundance appeared to be determined initially by pre-spawning prey supply and temperature, and subsequently by variable retention behind the frontal zone. KEY WORDS: Iteroparity · Egg development · Population dynamics · Stock recruitment · Life history strategy · Plankton patchiness · Estuarine retention · Tampa Bay Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 237. Online publication date: July 18, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Alternating dominance of postlarval sardine and anchovy caught by coastal fishery in relation to the Kuroshio meander in the Enshu‐nada Sea

In the mid 1970s, the fishery catch of postlarval Japanese anchovy (Engraulis japonica) in a shelf region of the Enshu‐nada Sea, off the central Pacific coast of Japan, started to decline corresponding to a rapid increase of postlarval sardine (Sardinops melanostictus). In late 1980s, sardine started to decline, and it was replaced by anchovy in the 1990s. This alternating dominance of postlarval sardine and anchovy corresponded to the alternation in egg abundance of these two species in the spawning habitat of this sea. It was also noteworthy that during the period of sardine decline, sardine spawning occurred in April–May, a delay of two months compared with spawning in the late 1970s.The implication of oceanographic changes in the spawning habitat for the alternating dominance of sardine and anchovy eggs was explored using time‐series data obtained in 1975–1998, focusing on the effect of the Kuroshio meander. Large meanders of the Kuroshio may have enhanced the onshore intrusion of the warm water into the shelf region and contributed to an increase in temperature in the spawning habitat. This might favour sardine, because its egg abundance in the shelf region was more dependent on the temperature in early spring than was that of anchovy. In addition, enhanced onshore intrusion could contribute to transport of sardine larvae from upstream spawning grounds of the Kuroshio region. On the other hand, anchovy egg abundance was more closely related to lower transparency at the shelf edge, which may indicate the prevalence and prolonged residence of the coastal water, and therefore higher food availability, frequently accompanying non‐meandering Kuroshio.The expansion/shrinkage of the spawning habitat of sardine and anchovy in the shelf region, apparently responding to the change in the Kuroshio, possibly makes the alternation in dominance of postlarval sardine and anchovy most prominent in the Enshu‐nada Sea, in combination with changes in the abundance of spawning adults, which occurred almost simultaneously in the overall Kuroshio region. The implication of this rather regional feature for the alternating dominance of sardine and anchovy populations on a larger spatial scale is also discussed.

Regional and Temporal Variability in Distribution and Abundance of Bay Anchovy (Anchoa mitchilli) Eggs, Larvae, and Adult Biomass in the Chesapeake Bay

Patterns and variability in reproductive output of pelagic fish are seldom determined at the ecosystem scale. We examined temporal and spatial variability in spawning by bay anchovy (Anchoa mitchilli), and in distribution and abundances of its pelagic early-life stages, throughout Chesapeake Bay. On two cruises in June and July 1993, ichthyoplankton and zooplankton were collected on 15 transects at 18.5-km (10 nautical mile) intervals over the 260-km length of the bay. Finer-scale sampling was carried out in a grid of stations between two transects on each cruise. Regional abundance patterns of bay anchovy eggs and larvae in the lower, mid, and upper Bay were compared with zooplankton abundances, environmental variables, and biovolumes of two gelatinous predators—the scyphomedusa Chrysaora quinquecirrha and the lobate ctenophore Mnemiopsis leidyi. Abundances of anchovy eggs, and, especially, larvae were higher in July than in June. Baywide daily egg production increased from 4.25×1012 in June to 8.43×1012 in July. Concentrations of zooplankton that are potential anchovy prey nearly doubled on a baywide basis between June and July, while biovolumes of the ctenophore declined. Except for scyphomedusan biovolumes, all analyzed organisms differed regionally in abundance and were patchily distributed at 1-km to 10-km sampling scales. Negative correlations between larval anchovy abundances and gelatinous predator biovolumes suggested that predation may have controlled abundances of bay anchovy early-life stages. Biomasses of adult anchovy, estimated from daily egg productions, were higher in the lower Bay and remarkably similar—23,433 tons in June and 23,194 tons in July. Most spawning by bay anchovy occurred during July in the seaward third of Chesapeake Bay, emphasizing the importance of this region for recruitment potential of the Bay's most abundant fish.

Forecasts of recruitment in South African anchovy from SARP field data using a simple deterministic expert system

A rule-based deterministic model is used to forecast recruitment of anchovy Engraulis capensis in the southern Benguela from field measurements of biological and environmental variables collected during two consecutive years. Field data were obtained on a monthly basis during the anchovy spawning season as part of the South African Sardine and Anchovy Recruitment Programme (SARP). A total of six indicator variables was considered for the analysis: distance offshore of the 16°C isotherm; southerly wind stress; anchovy egg abundance; incidence of oocyte atresia in adult females; an index of fish starvation; and oil : meal ratios obtained from commercial data (which were used as an index of fish condition). In the model, data for each variable were assessed against a threshold value. “Active” variables were assumed to contribute towards below-average recruitment by being either above or below their threshold values, as defiNed by the rules. The model was not based on the SARP field data, which were used to test the model. Predicted results from the expert system compared favourably with final estimates of recruitment strength for both 1994 and 1995 (years of below average recruitment), indicating that field measurements of biological and environmental variables may be used in a structured manner to obtain forecasts of anchovy recruitment to the fishery.

Sampling errors in anchovy egg abundance estimates using the PAIROVET net

A replicate haul experiment was carried out using the vertically towed PAIROVET net in an area of high abundance of anchovy eggs in the Bay of Biscay. The main aim of the experiment was to compare the performance of ships of different size working in the same area. In addition, we tested the performance of the PAIROVET net and the deployment methodology used to sample anchovy eggs for biomass assessment purposes. We concluded that under the experimental conditions experi- enced in this cruise, different ships yield similar performances of the vertically towed PAIROVET net if the methodology is kept similar. The ANOVA suggests that the systematic central sampling (SCS) scheme currently in use for the Bay of Biscay anchovy biomass estimations (one station out at 3 miles) adequately represents the surrounding area along the transect line. The among-station component of variance within the unit sampling area of the current SCS turned out to be comparable and, in some cases, smaller than the within-station variance. Consequently, the spatial design of the SCS adopted during routine surveys appears to be a reliable strategy for sampling anchovy eggs in areas of high egg abundance, as in this experiment. In addition, it ensures fairly independent data units. In the area of the experiment, the most disperse egg stages (like 2- and 3-day-old eggs) show a larger within- station component of variance than the spatial component of variance within the rectangles of the current SCS. This suggests that for these stages, the sampling can still be improved cheaply by increas- ing the precision of egg abundance estimates per station with larger sample sizes, without changing the spatial sampling scheme or the number of stations. However, the benefits of this strategy will hardly affect the precision of the 1-day-old egg estimates because of their patchy distribution.

Study of the spawning area of the Northern anchovy in the Gulf of California from 1990 to 1994, using satellite images of sea surface temperatures

The influence of the water temperature on the distribution and abundance of eggs of the Northern anchovy in the Gulf of California was analyzed. Data on sea surface temperatures (SST) were combined with the analyses of patterns of eggs of plankton collected on the five cruises carried out from 1990 through 1994, during the spawning season of the Northern anchovy. The principal spawning area of this species is between the northern point of Angel de la Guarda Island and -30 miles south of Tiburon Island, and the whole breadth of the Gulf of California. On the western coast of California, the Northern anchovy spawn in water temperatures between 11.5 and 17°C, while in the Gulf of California, they prefer to spawn in water temperatures between 15 and 17°C. From the satellite images, one could relate the patterns of water masses and temperature fronts to the distri- bution and abundance of anchovy eggs, as well as know their interannual variability.

Vertical distribution of eggs and larvae ofEngraulis encrasicolus in stratified waters of the western Mediterranean

The vertical distribution of the eggs and larvae of the European anchovy (Engraulis encrasicolus) in the western Mediterranean Sea in June 1984 and Agust 1985 was analyzed based on multiple plankton tows carried out at varying depths and using nets equipped with opening and closing mechanisms. Hydrographic parameters such as temperature, salinity, and chlorophylla were recorded simultaneously. Maximum abundance of anchovy eggs and larvae always occurred above the thermocline, even when maximum chlorophylla concentrations were located below the thermocline. Larval distribution appeared to be associated with the availability of suitable food organisms. As in other clupeoid species, the anchovy larvae carried out vertical migrations related to the photoperiod.

Distribution and abundance of eggs of the anchovy, Engraulis australis antipodum Gunther, in relation to temperature and salinity in the Gippsland Lakes

Observations on the abundance of anchovy eggs in the Gippsland Lakes were made. From these observations, the duration and extent of spawning were inferred. Ten stations along the main salinity gradient were sampled from November 1978 to March 1980. Egg densities ranged from 1 to 38 170 eggs per 100 m3, densities of over 1000 eggs per 100 m3 being recorded on 16 occasions. Larval densities were much lower, only five records being greater than 100 larvae per 100 m3. Spawning extended from October to March. Peak egg and larval densities occurred in January for the two spawning periods examined. Eggs were found from McLennans Strait to the Entrance, with a few also collected from Bass Strait. Limited spawning did occur in the La Trobe River and in Lake Wellington during the 1967-1968 drought, when salinities were considerably higher than normal. The mean 'bottom' to 'top' density ratio for eggs was 3.8 to 1, probably as a result of vertical differences in salinity. Eggs were collected over a temperature range of 14.8-24.2�C, although the main spawning occurred above 18�C. The observed range in salinity was 2.3-35.5, but egg numbers in water below 15.8 were very low.

Characterising and comparing the spawning habitats of anchovy Engraulis encrasicolus and sardine Sardinops sagax in the southern Benguela upwelling ecosystem

The spawning habitats of anchovy Engraulis encrasicolus and sardine Sardinops sagax in the southern Benguela upwelling ecosystem were characterised by comparing their egg abundances with environmental variables measured concomitantly during two different survey programmes: the South African Sardine and Anchovy Recruitment Programme (SARP), which comprised monthly surveys conducted during the austral summers of 1993/94 and 1994/95; and annual pelagic spawner biomass surveys conducted in early summer (November/December) from 1984 to 1999. Eggs were collected using a CalVET net. Physical variables measured included sea surface temperature (SST), surface salinity, water depth, mixed-layer depth, and current and wind speeds; biological variables measured included phytoplankton biomass, and zooplankton biomass and production. Spawning habitat was identified by construction of quotient curves derived from egg abundance data and individual environmental variables, and relationships between these variables were determined using multivariate co-inertia analysis. SARP data showed that anchovy spawning was associated with cool water and moderate wind and current speeds, whereas sardine spawning was related to warmer water and more turbulent and unstable conditions (i.e. high wind speeds and strong currents) than for anchovy. SARP data also showed significant differences in selection of spawning habitat of the two species for all environmental variables. The relationship between anchovy egg abundance and salinity was strongly positive, but strongly negative with water depth, phytoplankton biomass and zooplankton production. Sardine egg abundance was strongly positively related to current speed. The spawner biomass survey data demonstrated that the spawning habitat of anchovy was characterised by warm water and high salinity, whereas sardine spawning was associated with cool water and low salinity. The survey data showed significant differences in spawning habitat selection by anchovy and sardine for SST, salinity and zooplankton biomass, but not for the other environmental variables. There was a positive relationship between anchovy egg abundance and SST, salinity and mixed-layer depth, and a negative relationship with water depth, phytoplankton biomass and zooplankton production. For sardine there was a strong positive relationship between egg abundance and current speed and wind speed. Differences in the results between the two survey programmes could be attributable to differences in their spatio-temporal coverage. Spawning habitats of anchovy and sardine appear to be substantially different, with anchovy being more specific than sardine in their preference of various environmental conditions.