Ecology of larval fishes in the Independencia Bay, Pisco, Peru: Temporal and spatial relationships, taxonomic aspects

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Velez, J. (2005): Ecology of larval fishes in the Independencia Bay, Pisco, Peru: Temporal and spatial relationships, taxonomic aspects , PhD thesis, Universität Bremen.
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This study focuses on the identification, assemblage dynamics and distribution patterns of larval fish in the Independencia Bay, Pisco, Peru. The structure of the larval fish assemblages in the Bay was examined using a combination of univariate and multivariate techniques. The plankton of Independencia Bay was sampled monthly during the year 2000, to ascertain ichthyoplankton composition, abundance, and seasonality (Publication I); to determine diel abundance patterns and to assess the vertical variations of the dominant families in the area during a 24-hour cycle, and to relate observed variations to oceanographic parameters (Publication II). These data were used to assess the inferred function of the bay as a fish spawning and nursery ground.The morphological development of some ichthyoplankton groups from the bay is described. In total, 16,156 fish larvae, representing 34 families, 48 genera and 48 species were collected. Engraulidae, Normanichthyidae, Blenniidae, Gobiesocidae, Haemulidae, Labrisomidae, Pinguipedidae and Atherinidae numerically dominated the diverse larval fish fauna and comprised 96.8% of the larvae captured; the remaining 3.2% included fish from several different families. The monthly mean density of total fish larvae showed two peaks. A springtime peak was dominated by newly hatched mote sculpins (Normanichthyidae) and newly hatched and pre-flexion anchovies (Engraulidae). A second, smaller, peak in summer was dominated by preflexion-stage anchovies, followed by mote sculpins. Greatest mean larval fish densities were recorded between September and November, suggesting a major spawning period. The greatest mean density during the spring peak was 7,492 larvae/100 m3, recorded in October. The greatest mean density during summer was recorded in February (2,493 larvae/100 m3). Concerning total larval abundance, there were no statistically significant differences between stations. Abundance in October (spring time) at Santa Rosa was higher than at the other three stations, but abundance in those other 3 stations was higher in February (summer time). The spring and summer ichthyoplankton abundance peaks in Independencia Bay coincided with high zooplankton standing stocks and also coincided, approximately, with periods of increased upwelling in the area. The occurrence of high larval fish densities and the wide range of larval stages suggest that Independencia Bay is a regionally important spawning and nursery ground for marine fish. A Principal Component Analysis (PCA) showed that temperature and salinity accounted for the largest fraction (74.4%) of the variability in the observed larval fish assemblage patterns. These conditions varied over time, station and water depth, however, interaction terms could not be clearly identified. Fitting a multinomial logistic model showed that larval fish assemblages and environmental conditions were associated in a complex way.Vertical distribution patterns of ichthyoplankton were examined from two depths (surface and 10 m) at two stations (Panteón and Tunga). Blenniidae, Engraulidae, Gobiesocidae, Normanichthyidae, Atherinidae, and Labrisomidae numerically dominated the diverse larval fish fauna at Panteón, near La Vieja Island, and comprised 97.6% of the larvae captured. Gobiesocidae, Atherinidae, Pinguipedidae, Blenniidae, Engraulidae, and Labrisomidae were most abundant at Tunga, near the mainland coast, and comprised 77.6% of the larvae captured. The highest cumulative larval density and abundance in the water column was found at Panteón. The number of taxa (5) was the same at the surface at both stations, and was higher at 10 m depth at Tunga (26) than at Panteón (21). Two patterns of larval vertical distribution were observed. The larvae of most species were located mainly at 10 m, only the larvae of Odontesthes regia regia were found mainly at the surface. There were no statistically significant differences between nighttime and daytime densities of fish larvae at either depth. Nevertheless, a small degree of vertical redistribution was apparent for some species that could be interpreted as nocturnal dispersal.The morphological development of two of the most abundant species from the bay is described in detail. Developmental series for individuals (recently hatched through transformation) of Normanichthys crockeri (Publication III) and Prolatilus jugularis (Publication IV) are presented using morphological features and pigmentation patterns. A total of 5,387 larvae (5,155 and 232 larvae of N. crockeri and P. jugularis, respectively) were identified. Ontogeny of both species is described and illustrated based on a total of 104 specimens (66 and 40 for N. crockeri and P. jugularis, respectively) ranging from 1.9 to 25.9 mm: recently hatched larvae through transformation stage. Larvae hatch size, information concerning the different stages (preflexion, flexion, postflexion and transforming), main diagnostic features of the larvae and meristic information including fin ray accounts are given. Osteological analysis of N. crockeri was also performed (Publication III). A total of 49 specimens were illustrated (see Publications III, IV and Appendix 6) to show pigmentation and morphological features of the larvae from Independencia Bay. These illustrations will be used for a guide to the ichthyoplankton of the bay (in preparation), and will be completed with ecological and meristic information.

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