Towards predicting recruitment success of anchovy<i>Engrauus capensis</i>Gilchrist in the southern Benguela system using environmental variables: a rule-based model

Bloomer, S. F.; Cochrane, Kevern L.; Field, J. G.

doi:10.2989/025776194784286897

Cited by 15 publications

(7 citation statements)

References 11 publications

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“…The relationship between turbulence and growth is a complex one. Fish larvae are known to benefit from prey patchiness (Cushing 1983) and larval growth in species like northern anchovy Engraulis mordax is heavily dependent on the stability of food patches, which are dispersed by turbulence (Bloomer et al 1994). Increasing turbulent velocity results in an increase in encounter rate between planktonic particles (Rothschild & Osborn 1988), counterbalancing the effect of patch dispersion on growth (Davis et al 1991).…”

Section: Discussionmentioning

confidence: 99%

Environmentally induced short-term variability in the growth rates of larval herring

Gallego¹,

Heath²,

McKenzie³

et al. 1996

Mar. Ecol. Prog. Ser.

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ABSTRACT. The growth of hernng Clupea harengus larvae w~thin a patch tracked for approximately 20 din the Orkney-Shetland area (north of Scotland) was ~nvest~gated using otollth microstructure and, in a supporting role, condition factor analyses. Daily otolith growth responded conservatively to external factors, there being significant autocorrelation within individual otolith increment sequences. Past growth history explained most of the variation of the data. Both otolith microstructure and condition factor analyses yielded consistent results, indicating that short term variations in growth rate were related to environmental factors such as wind-induced turbulence level, and changes in illumination and prey concentration A dome-shaped effect of wind-generated turbulence on larval growth was detected, which indicated a maximum response at a wind speed of approximately 14.5 m S-', a value very close to the speeds predicted by theoretical studies to generate maximum ingestion rates of larval fish.KEY \VORDS: Fish larvae. Growth Environment. Turbulence Otolith INTRODUCTIONThe survival of fish larvae under natural circumstances is largely dependent on stage-specific mortality rate, i.e. the interaction between growth and mortality (Houde 1994). These 2 processes are interrelated since survival over any development interval is the product of mortality rate (d-l) and stage duration (d). Mortality rate generally decreases with increasing body size due to a variety of size-related effects on predator-prey interactions (Fuiman 1994), and hence the cumulative mortality for a population of fast growing individuals is less than that for slow growing individuals subject to the same predation rate (Houde & Schekter 1980, Houde 1987.Early attempts to detect growth varlability in fish larvae and relate it to environmental features were, with a few exceptions, unsuccessful (Heath 1992). Investigators examined the mean growth of the population, usually averaged over time periods of days or weeks, in relation to large-scale spatial (10 to 100 km) differences in prey abundance or environmental characteristics. However, this large-scale variation in time a n d space may account for only a small part of the total variability in growth. Small-scale spatlal and temporal variability, which could be more important for larval survival, is not examined in this approach. For example, small-scale turbulence may vary on time scales of minutes to hours and over short distances, particularly in the vertical plane. It is now evident that small-scale turbulence may have a profound influence on the encounter rate and capture success of planktonic predators (MacKenzie e t al. 1994). Thus there is scope for considerable within-population variability in growth induced by ingestion rate variability, over and above additional sources of variation between individuals due to foraging experience, genetic differences, etc. Studies of the effect of individual variability in growth on larval survival have shown that this factor may be as, or more, important...

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Section: Discussionmentioning

confidence: 99%

Environmentally induced short-term variability in the growth rates of larval herring

Gallego¹,

Heath²,

McKenzie³

et al. 1996

Mar. Ecol. Prog. Ser.

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“…For the Benguela, several such studies have been performed (see e.g. Bloomer et al. , 1994; Waldron et al.…”

Section: Introductionmentioning

confidence: 99%

Clupeoid larval growth and plankton production in the Benguela upwelling system

Skogen¹

2004

Fisheries Oceanography

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Upwelling is a characteristic feature of the Benguela system. Strong upwelling leads to high primary production, which, in turn, supports large biomass of higher trophic levels. To analyse intra-, interannual and decadal variability of fish recruitment, growth, and distribution, different methods to quantify this upwelling have been used. In the present work, an upwelling index, modelled diatom primary production, based on outputs from a numerical model for the Benguela upwelling system, is proposed. Upwelled water brings large amounts of nutrients into the euphotic zone and this supports primary productivity, which can be considered a preconditioner for the zooplankton that clupeoid larvae feed on. Therefore, it is assumed that high upwelling gives the potential for good feeding conditions for these larvae. This fact has motivated the use of the modelled index for upwelling intensity as a proxy for food availability and an investigation of the interannual variability of observed mean individual weight of Cape anchovy (Engraulis capensis) and sardine (Sardinops sagax) recruits. The study shows that the mean Cape anchovy recruit weight has a linear relationship with upwelling activity along the transport route (from the spawning to the nursery areas) and inside the nursery areas, while sardine have an Optimal Environmental Window (OEW) relationship to the upwelling on the transport route. A possible explanation for these observed differences is the prey the larvae feed on and the change in the plankton community as a function of upwelling activity.

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“…The intention is later to apply a so-called rulebased model (Bloomer et al, 1994) to the same data set. Such models are constructed so that their output, recruitment (defined as the state variable), is predicted from a set of inputs known as driving variables (in this case, spawning stock biomass and environmental variables), using different weights derived from the correlation between state and driving variables.…”

Section: Introductionmentioning

confidence: 99%

Quantifying environmental effects on the recruitment of the Brazilian sardine (<i>Sardinella brasiliensis</i>), 1977-1993

Jablonski¹,

Legey²

2004

Sci. Mar.

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SUMMARY:The recruitment process for Brazilian sardine (Sardinella brasiliensis) from 1977 to 1993 was investigated by taking into account the effects of spawning stock biomass (SSB), the intensity of the wind and the sea surface temperature (SST). Nonparametric models were applied. Best fits resulted from relating recruitment to a combination of SSB and Ekman transport. Transformation of Ekman transport is nearly dome-shaped, with lower and upper limits of 520 and 700 kg s -1 m . SST transformations also follow an apparent dome-shaped curve optimising around 24.75 and 25.5ºC. Inclusion of SST as a third predictor variable led to the loss of the dome-shaped relationship, as shown by the transformations with two predictor variables. Biomass curves are almost logarithmic, their critical point oscillating around 200,000-250,000 t, below which value the stock becomes more dependent on recruitment. The biomass range is greater than previous estimates. [1977][1978][1979][1980][1981][1982][1983][1984][1985][1986][1987][1988][1989][1990][1991][1992][1993]. -El reclutamiento de la sardina brasileña (Sardinella brasiliensis) fue investigado, en el periodo de 1977 a 1993, teniendo en cuenta los efectos de la biomasa del stock frezante, la intensidad del viento y la temperatura de la superficie del mar (TSM). Se aplicaron modelos no parámetricos. Los mejores ajustes fueron obtenidos considerando las variables de biomasa frezante (SSB) y el transporte de Ekman. Para la transformada del transporte de Ekman fue observada una forma aproximada de "domo" con límites inferior y superior, respectivamente, de 520 y 700 kg s -1 m -1 . La fracción de la variabilidad del reclutamiento explicada por el ajuste fue de 94%. Fueron evidenciadas regiones de máximo con lími-tes, respectivamente, de 0,035 y 0,045 N m -2 para el "stress" del viento; y 30 y 45 m 3 s -3 para el índice de turbulencia. Esos valores corresponden a vientos con intensidad entre 3,0 y 4,5 m s -1 . Las transformadas para la TSM muestran, también, un efecto con forma de domo alrededor de 24,75 a 25,5ºC. La inclusión de la TSM como una tercera variable independiente llevó a la 'perdida' de la forma "domo", observada en las curvas de las transformadas para dos variables. Para la biomasa, se observan curvas próximas a la logarítmica, con un valor de cerca de 200 a 250 mil toneladas como límite por debajo del cual el stock pasa a depender mas estrictamente del suceso del reclutamiento. Ese intervalo es superior a las estimativas obtenidas en estimaciones anteriores.

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Towards predicting recruitment success of anchovyEngrauus capensisGilchrist in the southern Benguela system using environmental variables: a rule-based model

Cited by 15 publications

References 11 publications

Environmentally induced short-term variability in the growth rates of larval herring

Environmentally induced short-term variability in the growth rates of larval herring

Clupeoid larval growth and plankton production in the Benguela upwelling system

Quantifying environmental effects on the recruitment of the Brazilian sardine (<i>Sardinella brasiliensis</i>), 1977-1993

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