The fate of eggs and larvae of three pelagic species, mackerel (Scomber scombrus), horse mackerel (Trachurus trachurus) and sardine (Sardina pilchardus) in relation to prevailing currents in the Bay of Biscay: Could they affect larval survival? (original) (raw)
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Fisheries Oceanography, 2011
We investigate the effect of strong meteorological perturbations in early spring on the success of mackerel (Scomber scombrus) recruitment in the N ⁄ NW Iberian area (southern Bay of Biscay) for the period 1999-2008. In 2000, the year of the most pronounced recruitment failure on record, two consecutive multidisciplinary surveys sampled hydrographic conditions and mackerel eggs, larvae and post-larvae over the main mackerel spawning grounds of the north and northwest coast of the Iberian Peninsula. Analysis of egg and larval abundance and birthdates based on the otoliths of mackerel juveniles caught between July and October 2000 showed that there were no survivors from the early spring spawns, indicating a massive loss of early spawning effort. Moreover, the abundance of 1-year-old mackerel estimated from an acoustic survey carried out in 2001 was the lowest observed within the 1999-2008 time series. This low or null survival from the early spawns in 2000 could be due to the meteorological and oceanographic conditions of that spring, in particular two storm events in April after a relatively calm March. The first storm event from the north caused strong local wind in the southern Bay of Biscay but a weak oceanographic response. The second storm event from the southwest was mainly felt west of Galicia and caused a notable increase in shelf currents and a shift of the hydrographical structure along the shelf. Detailed analysis of strong wind pulses in early spring within the historical recruitment record suggests that strong local turbulence generated by high wind speeds and advection of larvae caused by the enhancement of shelf currents can contribute to reduced recruitment. Our observations indicate that, in 2000, both mechanisms were present.
Growth of young-of-the-year mackerel in the Bay of Biscay
Journal of Fish Biology, 2003
The first growth season of young-of-the-year (0þ year) mackerel Scomber scombrus, sampled in the Bay of Biscay, was parameterized to determine growth patterns. Daily increments were identified on sagittae otoliths, for calculation of age and growth of 92 larvae and 54 juveniles over the range 3Á6-215Á0 mm standard length (L S ). A Gompertz curve was fitted to the lengthat-age data. At the end of the first year of growth L S was 194Á2 mm, with a maximum growth increment of c. 2 mm day À1 , observed 62 days after hatching. Backcalculated growth increments for mackerel juveniles, during their larval stage, were higher than those observed for sampled larvae; only 10Á9% of sampled larvae were estimated to survive. Growth for north-eastern Atlantic mackerel was slower than that published for north-western Atlantic mackerel. Backcalculated hatching dates for mackerel were consistent with the typical temporal distribution of mackerel spawning in the Bay of Biscay.
Larval fish distribution in two different hydrographic situations in the Gulf of Cádiz
Deep-sea Research Part Ii-topical Studies in Oceanography, 2006
Ichthyoplankton assemblages and individual larval distributions of several mesopelagic and shelf-associated species were studied in two consecutive spring surveys in the Gulf of Ca´diz (2001), covering both coastal and oceanic domains. The two surveys were characterised by markedly different hydrographical conditions, partly attributable to a shift from westerly to easterly winds. At the scale studied, larvae of coastal and shelf-dwelling species were always clearly separated from mesopelagic species, probably as a result of well-defined coastal-oceanic habitats related to a wide shelf and the prevailing currents. However, underlying these associations, short-term hydrographic changes induced by wind forcing seemed able to severely affect the distribution patterns of the early stages of some shelf-associated species. In particular, species like the European anchovy Engraulis encrasicolus were transported off the usual areas of maximal concentrations following a strengthened northwestern coastal countercurrent. r (I.A. Catala´n).
Fisheries Oceanography, 2007
Large amplitude variations in recruitment of small pelagic fish result from interactions between a fluctuating environment and population dynamics processes such as spawning. The spatial extent and location of spawning, which is critical to the fate of eggs and larvae, can vary strongly from year to year, as a result of changing population structure and environmental conditions. Spawning habitat can be divided into 'potential spawning habitat', defined as habitat where the hydrographic conditions are suitable for spawning, 'realized spawning habitat', defined as habitat where spawning actually occurs, and 'successful spawning habitat', defined as habitat from where successful recruitment has resulted. Using biological data collected during the period 2000-2004, as well as hydrographic data, we investigate the role of environmental parameters in controlling the potential spawning habitat of anchovy and sardine in the Bay of Biscay. Anchovy potential spawning habitat appears to be primarily related to bottom temperature followed by surface temperature and mixed-layer depth, whilst surface and bottom salinity appear to play a lesser role. The possible influence of hydrographic factors on the spawning habitat of sardine seems less clear than for anchovy. Modelled relationships between anchovy and sardine spawning are used to predict potential spawning habitat from hydrodynamical simulations. The results show that the seasonal patterns in spawning are well reproduced by the model, indicating that hydrographic changes may explain a large fraction of spawning spatial dynamics. Such models may prove useful in the context of forecasting potential impacts of future environmental changes on sardine and anchovy reproductive strategy in the north-east Atlantic.
Journal of Plankton Research, 2006
This study presents results of the vertical behaviour of the European sardine (Sardina pilchardus) larvae as observed at sea off the NW Iberian coast during an oceanographic cruise conducted in May 2002. Samples were taken in a grid of 38 stations (conductivity-temperature-depth [CTD] measurements and Longhurst Hardy Plankton Recorder [LHPR] plankton hauls); a 69-h fixed station study was also performed (hourly CTD measurements and LHPR/neuston hauls every 2 h). The horizontal distribution of larvae is closely related to the circulation patterns measured by a current metre-mooring array deployed during the cruise. Larvae were mainly distributed in the upper 20-25 m of the water column, in evident association with the waters of the Western Iberia Buoyant Plume (WIBP). Large (older) larvae are found mainly in the surface layers, and larval size decreases with depth. A diel rhythm of migration to the neuston layer was observed, correlated with the inflation/deflation activity of the swim bladder. Larvae with lengths greater than 12.5 mm and inflated swim bladders were only found in this layer. Considering the near surface stratification conditions for food availability and Ekman transport in the upper few metres, even small vertical migrations of larvae can be very important for their survival and subsequent recruitment success.
Fisheries Research, 2001
Within the frame-work of the Shelf Edge Fisheries Oceanography Study (EU AIR SEFOS Project), 10 000 mackerel were tagged in March and April 1994, off the Basque Country (Spain), at the eastern part of ICES Division VIIIc, close to the boundary between the, so-called, Southern and Western mackerel stocks in the north-east Atlantic. The purpose of this experiment was to outline the migration routes for mackerel spawning in the south-east corner of the Bay of Biscay and to examine the justi®cation for separating a Southern and Western stock. Recaptures were recorded along the western coasts of Europe, from the north-west of Spain to the Norwegian coast. These results connected the ®sheries of the southern and northwestern areas and put in doubt the existence of two separate stocks in these regions. The paper concludes that the ®shery on spawning mackerel that takes place in the east and central Cantabrian sea in the ®rst half of every year is made on mackerel coming from the north-western area extending their southward spawning migration through ICES Division VIIIc, before going back to north. This migration pattern provides a simple explanation for the strong seasonality of the southern ®sheries on adult mackerel and for the disappearance of those adults from that area during the second half of the year. #
Fisheries Oceanography, 2008
In this study the spatial distribution of eggs, larvae and juveniles of European anchovy (Engraulis encrasicolus) was followed in 2004 and 2005 during three consecutive cruises each year in spring–summer to test what the limits of retention are in a non-upwelling area. Eggs, small larvae and large juveniles were mainly distributed over the shelf, whereas large larvae and small juveniles were found mainly off the shelf. Although overall distributions were similar, the 2 yr differed in that there was more of a coastal distribution of individuals in 2004, whereas in 2005 more individuals were found off the shelf. There were no significant differences in the length–weight relationships for individuals found on and off the shelf or between years. The correspondence in circulation patterns and the lack of difference in the length–weight relationships suggest that a single population is present, larvae drifting off the shelf due to currents and returning as mobile juveniles. Quantile regression analysis of the long-term recruitment index suggests that transport off the shelf may favour good recruitments. This would suggest that in non-upwelling regions the retention area resulting in good recruitment may not be restricted to the shelf.
Egg and larval distributions of seven fish species in north-east Atlantic waters
Fisheries Oceanography, 2007
The distribution of egg and larvae of mackerel, horse mackerel, sardine, hake, megrim, blue whiting and anchovy along the European Atlantic waters (south Portugal to Scotland) during 1998 is described. Time of the year, sea surface temperature and bottom depth are used to define the spawning habitat of the different species. Mackerel, horse mackerel, and sardine eggs and larvae presented the widest distribution, whereas megrim and anchovy showed a limited distribution, restricted to the Celtic Sea and the Bay of Biscay respectively. Correspondingly mackerel, horse mackerel and sardine showed the highest aggregation indices. Blue whiting larvae were found at the lowest temperatures, whereas anchovy eggs and larvae were found in the warmest waters. The analysis is a basis for evaluation of ongoing changes in the pelagic ecosystem of the north-east Atlantic.
Larval fish distribution in shallow coastal waters off North Western Iberia (NE Atlantic
Estuarine Coastal and Shelf Science, 2006
Monthly sampling for ichthyoplankton was conducted at three stations very near to the coast (near to shore shallow stations before the surf zone in direction to the shoreline) of Atlantic northwestern Portugal within contrasting localities: rocky shore, in front of a sandy beach receiving an estuary and a fishing port with heavy anthropogenic impact. Sampling was conducted from August 2002 to October 2003, always at full moon, at low tide and high tide in daylight hours, at the water column using a 48 cm diameter plankton net with 335 mm mesh. Analysis of the physico-chemical parameters pointed out the spatial (horizontal) homogeneity of the sampling area. Fish larvae from 41 taxa belonging to 17 families were identified; Blenniidae, Labridae, Ammodytidae, Clupeidae, Gobiidae, Soleidae and Gobiesocidae were the most representative during the study period. Parablennius gattorugine, Ammodytes tobianus, Symphodus melops, Sardina pilchardus, Lipophrys pholis and Coryphoblennius galerita were the most representative species (percentage contribution to total abundance). Peak abundance of fish eggs ocwas a pronounced winter/early spring (March 2003) peak in larval abundance dominated by the small sandeel A. tobianus. This study identifies the occurrence of a conspicuous assemblage of larval fishes at very nearshore shallow environments of a variety of species with different adult habitats: the fish larvae assemblage was dominated by intertidal species. The present study has shown that temporal and spatial variations in the larval fish assemblage are related to environmental conditions and biological dynamics: the results suggest that abiotic conditions mediate biotic parameters, and that both abiotic and biotic characteristics regulated the larval fishes at very nearshore shallow environments.