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• W2112037822 abstract "Eleven ichthyoplankton surveys, conducted during the winter and spring quarters of 1978 and 1979, indicate that spawning of the northern anchovy, Engraulis rnordax, was contracted both spatially and temporally in 1978 relative to 1979. Larvae were farther offshore in 1979. Instantaneous daily larval mortality rate estimated from slope of the age-frequency distribution (yolk sac through 15 mm, ca. 25-30 days) varied insignificantly between 1978 and 1979 and averaged 0.168. Comparison to a simple model of spawning suggests that seasonal changes in the slopes are due solely to a systematic bias and not to real changes in the mortality rate. Seasonal larval production was compared with birthdate distributions of fish surviving to the juvenile stage. In both years March had the greatest larval production and was the commonest month of birth among the survivors of the larval stage. Larval survivorship tended to increase within the 1978 spawning season and decrease within the 1979 season. Low survivorship in winter 1978 is consistent with the hypothesis that winter storms disrupted aggregations of prey necessary for larval feeding, but does not explain why apparent recruitment was greater in 1978 than 1979. Variation in larval survivorship could not be attributed to larval mortality. The offshore distribution of larvae in 1979 may have contributed to the relatively low survival. RESUMEN Once estudios de ictioplancton realizados durante 10s trimestres de invierno y primavera en 1978 y 1979 indican que el desove de la anchoveta Engraulis mordax en 1978 se produjo relativo al de 1979, tanto espacialmente como temporalmente. Las larvas estaban mas lejos de la costa en 1979. El indice de mortalidad instantanea diaria de larvas que se estimo de la inclinacion de la distribucion de frecuencias de edades (vitelo hasta 15 mm, alrededor de 25-30 dias) vario insignificativamente entre 1978 y 1979, con un promedio de 0.168. Una comparacion con un modelo simple de desove sugiere que cambios temporales en las inclinaciones se deben unicamente a un sesgo sistematico y no a cambios verdaderos en el indice de mortalidad. [Manuncnp received March I , 1982 1 226 La produccion larval temporal fue comparada con distribuciones de fechas de nacimiento de peces que sobrevivieron hasta la etapa juvenil. En ambos aiios, la mayor produccion de larvas occurrio en marzo, y el haber nacido en este mes era mas comun entre 10s sobrevivientes de la etapa larval. La supervivencia larval tendia a aumentar en la epoca de desove de 1978 y a descender en la Cpoca de 1979. La supervivencia baja del invierno de 1978 es consistente con la h i ~ t e s i s de que tormentas de invierno interrumpieron conjuntos de presas necesarias para alimentar las larvas, pero no explica porque el reclutamiento era mayor en 1978 que en 1979. La variacion en la supervivencia larval no se pudo atribuir a la mortalidad larval. La distribucion de larvas fuera de la costa en 1979 pudo haber contribuido a la supervivencia relativamente baja. INTRODUCTION The planktonic phase of a schooling fish’s life history is considered the most amenable to quantitative sampling (Smith and Richardson 1977). Egg and larvae surveys have been used to estimate the number of adults responsible for their production (e.g., Sette and Ahlstrom 1948; Saville 1964; Smith 1972). Fish larvae are also of interest because they are the link between the present adult stock and some future recruitment to the adult stock. The lack of a clear relationship between stock and recruitment has focused attention on events during the larval stage and their ultimate effect on survival to the juvenile and adult stages. The literature on the pelagic fishes of the California Current is particularly rich. Smith (1981) summarized the influences on northern anchovy larval survival: ( I ) the availability of suitable prey for larvae exhausting their yolk sacs (Lasker 1978); (2) interspecific and intraspecific predation (Hunter 1976; Hunter and Kimbrell 1981); (3) starvation (Hunter 1976; O’Connell 1980); (4) effect of adult nutritional state on quality of eggs and fitness of larvae (Smith and Lasker 1978; Hunter and Leong 1981); (5) preschooling dispersal (Smith 1973; Hewitt 1981); and (6) larval transport to or from favorable areas (Sette 1950; Parrish et al. 1981). In this report we describe the results of ichthyoplankton surveys conducted in 1978 and 1979, and discuss what may be inferred about factors affecting larval anchovy survival during those 2 years. DistriHEWllT AND METHOT: DISTRIBUTION AND MORTALITY OF NORTHERN ANCHOVY LARVAE CalCOFl Rep., Vol. XXIII, 1982 bution maps, abundance estimates, and mortality are reported for each of 11 surveys. METHODS AND MATERIALS The data presented here were obtained during 11 cruises (Table 1) conducted off the coast of the Califomias (Figure 1) in 1978 and 1979, as part of the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Plankton samples were taken obliquely from a depth of 210 m with 0.505-mm mesh nylon nets mounted on a bongo frame (see Kramer et al. 1972, for detailed methodology). Samples were preserved in a buffered Formalin solution and an ethyl alcohol solution. A subsample of the alcoholpreserved specimens of anchovy larvae was aged using daily increments in the otoliths (Methot 1981). Anchovy larvae in Formalin-preserved samples were enumerated in I-mm classes of standard length. Preserved larval lengths were adjusted to live lengths using the shrinkage factors reported by Theilacker (1980). We use two different summarization procedures. The first will be presented on a fine spatial scale but will not take into account extrusion, avoidance, and growth that affect the relation between larval production and the catch in each I-mm size class. The results of this first summarization are used to describe the distribution and relative abundance of larvae. The second procedure incorporates factors affecting the relation between larval production and catch but requires a large sample size, so no withincruise stratification was possible. The age-specific larval productions resulting from the second summarization are used to calculate mortality rates of larvae. Only samples from the central population of anchovy are considered in the quantitative analyses. Electrophoretic and morphometric data indicate that anchovy along southern Baja California constitute a separate population (Vrooman and Smith 1971). We exclude samples collected south of CalCOFI line 110 (Figure 1). A third population occurs primarily along TABLE 1 CalCOFl Surveys 1977 through 1979" @default.
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• W2112037822 title "Distribution and Mortality of Northern Anchovy Larvae in 1978 and 1979" @default.
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