Assessment of the Aphia minuta stock (Pisces: Gobiidae) by acoustic methods from the Bay of Alcudia (Mallorca, Western Mediterranean)

Acoustic techniques have been used for the first time to evaluate the abundance and distribution of the Aphia minuta stock (Pisces: Gobiidae) from the Island of Mallorca (Baleares, Spain). Acoustic surveys have been carried out during three consecutive seasons (1993, 1994 and 1995) in the more important fishing zone of this island, the Bay of Alcudia. Indices were obtained for abundance (m3) of this goby at the beginning of the fishing season. The volume of A. minuta has decreased from 12,902,751 m3 in January 1993 to 1,161,248 m3 in January 1995. The catches obtained have gone from almost six tonnes in 1993 to be practically nil in 1995Publicado

Fishery and growth of Aphia minuta off Majorca island

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Life cycle of the pelagic goby Aphia minuta (Pisces: Gobiidae)

Reproductive aspects of the transparent goby Aphia minuta (n=2977, 14-45 mm total length (TL)) were studied in Majorcan waters, western Mediterranean, during the fishing season (December to April) from 1985 to 1993. Male:female sex ratio was 1:1. Size at first maturity was 38 mm TL for females and 34 mm TL for males. Oocyte size-frequency distribution indicated that A. minuta is a single spawner. Fecundity of A. minuta ranged from 935 to 2648 oocytes. The breeding season extended from December to April with a peak in March. After a single reproduction at 5-6 months of age, most of the specimens disappeared from the fishing areas. Recruitment to the fishing area occurred in late December and early January (14-24 mm TL, age 2-3 months). On the other hand, the hatch date back-calculated from the age in days and the date of capture of individuals of A. minuta during the fishing season, indicated a spawning peak in autumn (September-October), six months after the peak of observed spawning. Schools of A. minuta were detected by acoustic methods, during the fishing season (winter-spring) in fishing areas (5-40 m depth), principally inside bays, and during the rest of the year (summer and autumn) in deeper areas (40-90 m), outside bays, with water temperatures between 13 and 16ºC and a high seasonal productivity in each depth range. Therefore, we propose that A. minuta has two annual cohorts in the western Mediterranean, corresponding to two main spawning in spring and autumn, respectively. Life history pattern indicated that we only know the winter cohort resulting from the autumn spawning. Meanwhile the summer cohort (spring spawning) grows and reproduces in deeper areas not being targeted by the fishery. Indirect validation is provided from information from other areas. The relevance of the life cycle is discussed in relation to fishery managementPublicado

Anchovy (Engraulis encrasicolus) otoliths reveal growth differences between two areas of the Spanish Mediterranean Sea

In the Mediterranean, small pelagic provide the larger catches, based mainly on 2 species: anchovy and sardine (Sardina pilchardus). Although the Mediterranean Sea is considered oligotrophic, there are areas with increased production due to their unique conditions related to the bathymetry, hydrography and meteorology. In the Spanish Mediterranean Sea, there are two areas with increased production due to their environmental characteristics: the Ebro Delta continental shelf, due to the discharge of the Ebro River and the Alborán Sea that receives Atlantic water, rich in nutrients, through the Strait of Gibraltar. The amount of growth in the first year can be measured from the otolith (R1) and some cases may be suitable to use it as a tool for stocks separation. This study presents and analyses anchovy otolith R1 distributions from these two different areas, from samples collected during acoustic surveys in the Spanish Mediterranean in 2012 and 2013 during the months of June and July. In addition, the condition factor was estimated for the total number of individuals and for the sexes separately. Regression analysis, similarity analysis, principal components analysis (PCA) and the Wilcoxon-Mann Whitney test were undertaken in order to identify any different growth patterns. The results suggested that the differences may be characteristic of the existence of population groups, and these could be used as a tool for differentiating stocks

Aproximació a la determinació de la variabilitat de la relació DNA/RNA durant el desenvolupament larval del llobarro Dicentrarchus labrax

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Otolitos de anchoa (Engraulis encrasicolus) revelan diferencias de crecimiento entre dos áreas del Mediterráneo español

Anchovy is a commercial species that supports large fisheries in the Mediterranean Sea. In addition, anchovy is an essential element of the pelagic food web, playing a considerable role in connecting the lower and upper trophic levels. Comparisons made regarding length frequency distribution, demographic structure, growth during the first year inferred from otoliths, and the condition factor of anchovy inhabiting the Spanish Mediterranean Sea (General Fisheries Commission for the Mediterranean management units, GSA06-Ebro Delta and 01-Alboran Sea), based on five-year data, clearly showed significant growth differences between areas and evidenced the existence of two independent anchovy stocks in the Spanish Mediterranean Sea. The anchovies inhabiting the Alboran Sea had higher growth than the anchovies inhabiting the Ebro Delta for the same age (one year old). The dramatic decline of the Alboran Sea anchovy could be related to the current management legislation in the Spanish Mediterranean Sea, based mainly on a common minimum catch size (9 cm), which should be revised given that sustainable anchovy exploitation is crucial for the pelagic food web equilibriumLa anchoa es una especie de interés comercial sometida a gran explotación pesquera en el mar Mediterráneo. Asimismo, esta especie es un elemento esencial de la cadena trófica pelágica dado que actúa como nexo entre los niveles más altos y más bajos de ésta. En este trabajo se han llevado a cabo comparaciones, basadas en un conjunto de datos de 5 años, entre las distribuciones de frecuencias de tallas; la estructura demográfica; el crecimiento durante el primer año, inferido empleando otolitos y el factor de condición de individuos de anchoa recogidos en el Mediterráneo español (unidades de gestión de la General Fisheries Commission for the Mediterranean, GSA06-Delta del Ebro y GSA01-Mar de Alborán), mostrando diferencias significativas entre áreas y evidenciando la existencia de dos stocks de anchoa independientes en el Mediterráneo español. Las anchoas procedentes del mar de Alborán presentaron un mayor crecimiento que aquellas procedentes del Delta de Ebro para la misma edad (1 año). La dramática disminución de la población de anchoa del mar de Alborán podría estar relacionada con la aplicación de una única legislación para todo el Mediterráneo español basada, principalmente, en una misma talla de primera captura (9 cm), que debería ser revisada puesto que la explotación sostenible de la anchoa es de crucial importancia para el equilibrio de la cadena trófica pelágicaVersión del edito

Acoustic estimation of volume and distribution of Aphia minuta (Pisces: Gobiidae) in Alcudia bay (Majorca island, Spain)

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Spatio-temporal patterns and morphological characterisation of multispecies pelagic fish schools in the North-Western Mediterranean Sea

Echosounder data from four surveys (1992, 1993, 1995 and 1996) is used to investigate the spatio-temporal variability of school behaviour in North-Western Mediterranean waters. The schools are described using morphological, energetic, spatial and temporal descriptors. The variability in the morphological, positional and energetic parameters of the schools is attributable more to the size of the school's individuals (juveniles or adults) than to the relative composition (percentage) of pelagic species in the area. This fact made difficult the identification of species in the studied area. The concentration of schools in certain geographic zones is determined by local oceanographic characteristics that favour the trophic or reproductive activity of these species. The diurnal aggregative behaviour of pelagic species is typical of the zone and no schools were detected at night. The biomass of the pelagic species in the area under consideration has diminished during the 4-year study period and no relationship was found between the number of schools and the biomass evaluated. This is the first time that the schools of small pelagic fishes from the Spanish Mediterranean Sea have been described and the information could be useful to the management and exploitation of the fisheries in the areaPublicado