Interspecific comparisons of growth and diet among late larvae of three co-occurring clupeoid species in the Kii Channel,Japan

Growth and diet were compared among larvae of Japanese anchovy Engraulis japonicus, Japanese sardine Sardinops melanostictus and Pacific round herring Etrumeus teres. Compositions of prey items of the three species in the same month showed greater similarity than for the same species in different months. Prey size as well as prey taxa of the three species overlapped considerably with one another. Therefore, interspecific prey competition is likely in the case of limited food availability. The most abundant species tended to change from anchovy to round herring in early winter, from round herring to sardine in late winter and from sardine to anchovy in early spring, indicating a temporal segregation in use of the nursery grounds. Similar seasonal changes in growth rates were observed for the three species. Although interspecific prey competition is likely, the temporal segregation and similar temporal changes in growth rates could favor their coexistence.     

Interannual fluctuations in acoustic biomass estimates and in landings of small pelagic fish populations in relation to hydrology in the Strait of Sicily

The main results of research work carried out since 1998 with regard to the application of hydro-acoustic technologies for the evaluation of biomass and distribution of small pelagic fish species off the southern coast of Sicily are presented, taking into account information from hydrology and from ecology of the fish populations targeted. The biomass estimates and the population‐density charts presented concern the two main species, i.e. sardine Sardina pilchardus (Walbaum, 1792) and anchovy Engraulis encrasicolus (Linnaeus, 1758). Both the sardine and anchovy populations experienced large inter-annual fluctuations, with biomass estimates ranging from 6000 to over 36,000 tonnes (t) (sardine) and from about 7000 to 23,000 t (anchovy). Acoustic estimates are largely consistent with landings recorded in Sciacca (the main fishing port for small pelagic species in the study area) during the year following the evaluation surveys. In addition, trends in sardine and anchovy biomass estimates appears to be negatively correlated with the mean sea surface temperature calculated over the time intervals January–September (sardine) and June–November (anchovy) of the preceding year, which correspond to larval and juvenile growth periods of target species. Observed patterns would suggest the importance of enrichment processes relevant to the survival of early stages, so determining recruitment success and finally higher population sizes.     

Rapid changes in growth,condition, size and age of small pelagic fish in the Mediterranean

Since 2007, the ecosystem of the Gulf of Lions has shifted to a different regime, characterised by a low anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) biomass and a remarkably high sprat (Sprattus sprattus) biomass. Surprisingly, the abundance and recruitment of anchovy and sardine remained high. To understand which processes (bottom-up or top-down control, etc.) could have caused this shift, we studied the changes in body condition, growth and size and age of anchovy, sardine and sprat over 1984–1985 and 1992–2012, using data from scientific surveys. The annual age structure of anchovy and sardine was estimated using Bayesian mixture models based on size frequency data with priors on the age–length relationship derived from independent otolith readings. The results indicated periods during which anchovy and sardine were in an average (1992–2004), good (2005–2007) or poor (2008–2012) overall state of condition. For sardine, the shift towards smaller fish observed during these past 4 years was explained by a combination of slower growth and the disappearance of older individuals (ages 2+). Despite the increase in biomass of sprat since 2008, indications were found that sprat was also smaller than in the past. As growth and condition decreased and overexploitation has not been documented or suspected for those three species in this area, we propose that the current decline in sardine and anchovy biomass could be due to qualitative and/or quantitative modifications in the planktonic production (i.e. a bottom-up control) or mass mortalities of adults due to an epidemic disease.     

Size matters: variation in the diet of chick and adult crested terns

We investigated ontogenetic, temporal and spatial patterns in the composition and size of prey in the diet of crested terns, Sterna bergii. Diet analyses indicated that crested terns are a generalist predator on surface-schooling clupeids (Australian anchovy Engraulis australis, sardine Sardinops sagax and blue sprat Spratelloides robustus), Degens leatherjacket Thamnaconus degeni, southern sea garfish Hyporhamphus melanochir, Australian herring Arripis georgianus, slender bullseye Parapriacanthus elongatus and barracouta Thyrsites atun. Ontogenetic differences in prey size indicated that adults are constrained in their foraging behaviour during the early chick-provisioning period by the need to self feed and select smaller prey that can be ingested by their chicks. Chicks consumed significantly higher proportions of clupeids than adults, which consumed mainly Degens leatherjackets and barracouta, suggesting that adults may select higher quality prey for their chicks compared to what they consume themselves. Spatial differences in prey composition were driven by differing proportions of sardine, Australian anchovy and Degens leatherjacket and could reflect local differences in the abundances of these prey. The size of prey taxa consumed by adults also reflected a North–South gradient in prey size. The large component of juvenile sardine in the diet of crested terns suggests future dietary measures may inform fisheries managers about changes in local juvenile sardine abundance. These data could assist in highlighting any fishery-related decreases in sardine recruitment and help ensure commercial fishing practices address principals of Ecologically Sustainable Development developed for Australian fisheries.     

Length-structured analysis of the reproductive season of anchovy and common sardine off central southern Chile

The anchovy (Engraulis ringens) and common sardine (Strangomera bentincki) are two small pelagic fish which have a similar reproductive strategy off central southern Chile. The seasonal reproductive dynamics of both the species was investigated by taking into account the gonadosomatic index (GSI) and visual maturity data as a function of female size for the period 1993–1999, and also the seasonal pattern in condition factor per size classes. Larger females of common sardine (repeat spawners) have a reproductive peak earlier in the season than younger females at first maturity, while larger anchovy have a reproductive peak delayed as compared with first-time spawners. The condition factor of females exhibited an inverse cycle with the seasonal pattern of GSI, and delayed by approximately 6 months. Although larger females tend to present better and wider condition than smaller females, the condition of females seems to be delayed in larger females probably mediated by the seasonal pattern in food availability. This “energy storage strategy” in spring and summer time seems to be size-dependent and past energetic reserves could also affect the egg production and timing of reproduction. We concluded that the reproductive season of anchovy and common sardine is different and mediated by the length structure in the seasonal upwelling system off central southern Chile.     

Buoyancy measurements and vertical distribution of eggs of sardine (<Emphasis Type="Italic">Sardina pilchardus</Emphasis>) and anchovy (<Emphasis Type="Italic">Engraulis encrasicolus</Emphasis>)

Measurements were made of the density and settling velocity of eggs of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus), using a density-gradient column. These results were related to observed vertical distributions of eggs obtained from stratified vertical distribution sampling in the Bay of Biscay. Eggs of both species had slightly positive buoyancy in local seawater throughout most of their development until near hatching, when there was a marked increase in density and they became negatively buoyant. The settling velocity of anchovy eggs, which are shaped as prolate ellipsoids, was close to predictions for spherical particles of equivalent volume. An improved model was developed for prediction of the settling velocity of sardine eggs, which are spherical with a relatively large perivitelline volume; this incorporated permeability of the chorion and adjustment of the density of the perivitelline fluid to ambient seawater. Eggs of both species were located mostly in the top 20 m of the water column, in increasing abundance towards the surface. A sub-surface peak of egg abundance was sometimes observed at the pycnocline, particularly where this was pronounced and associated with a low-salinity surface layer. There was a progressive deepening of the depth distributions for successive stages of egg development. Results from this study can be applied for improved plankton sampling of sardine and anchovy eggs and in modelling studies of their vertical distribution.Communicated by J.P. Thorpe, Port Erin     

Experimental evaluation of the energy balance in Octopus vulgaris, fed ad libitum on a high-lipid diet

A complete energy balance equation was estimated for the common octopus Octopus vulgaris at a constant temperature of 20°C, fed ad libitum on anchovy fillet (Engraulis encrasicolus). Energy used for growth and respiration or lost with faeces and excreted ammonia was estimated, along with total energy consumption through food, for six specimens of O. vulgaris (with masses between 114 and 662 g). The energy balance equation was estimated for the specimens at 10-day intervals. During each 10-day interval, food consumed, body mass increase and quantity of faeces voided were measured. The calorific values of octopus flesh, anchovy flesh and faeces were measured by bomb calorimetry. Oxygen consumption and ammonia excretion rates were monitored for each specimen during three 24-h experiments and daily oxygen consumption and ammonia excretion were estimated. It was found that 58% of the energy consumed was used for respiration. The amount of energy invested in somatic and gonadal growth represented 26% of the total energy budget. The energy discarded through faeces was 13% of consumed energy. The estimated assimilation efficiency (AE) values of O. vulgaris feeding on anchovy (80.9–90.7%) were lower than the AE values estimated for other cephalopod species with different diets of lower lipid content such as crabs or mussels. Specific growth rates (SGR) ranged 0.43–0.95 and were similar to those reported for other high-lipid diets (bogue, sardine) and lower than SGR values found for low-lipid, high-protein diets (squid, crab, natural diet). Ammonia excretion peak (6 h after feeding) followed the one of oxygen consumption (1 h after feeding). The values of atomic oxygen-to-nitrogen (O:N) ratio indicated a protein-dominated metabolism for O. vulgaris.     

Interannual fluctuations in acoustic biomass estimates and in landings of small pelagic fish populations in relation to hydrology in the Strait of Sicily

The main results of research work carried out since 1998 with regard to the application of hydro-acoustic technologies for the evaluation of biomass and distribution of small pelagic fish species off the southern coast of Sicily are presented, taking into account information from hydrology and from ecology of the fish populations targeted. The biomass estimates and the population-density charts presented concern the two main species, i.e. sardine Sardina pilchardus (Walbaum, 1792) and anchovy Engraulis encrasicolus (Linnaeus, 1758). Both the sardine and anchovy populations experienced large inter-annual fluctuations, with biomass estimates ranging from 6000 to over 36,000 tonnes (t) (sardine) and from about 7000 to 23,000 t (anchovy). Acoustic estimates are largely consistent with landings recorded in Sciacca (the main fishing port for small pelagic species in the study area) during the year following the evaluation surveys. In addition, trends in sardine and anchovy biomass estimates appears to be negatively correlated with the mean sea surface temperature calculated over the time intervals January-September (sardine) and June-November (anchovy) of the preceding year, which correspond to larval and juvenile growth periods of target species. Observed patterns would suggest the importance of enrichment processes relevant to the survival of early stages, so determining recruitment success and finally higher population sizes.     

An attempt to determine growth and hatching dates of juvenile sardine,Sardina pilchardus,in the Western Mediterranean Sea

Juvenile sardine, Sardina pilchardus Walbaum, 1792, were collected off Mallorca, Balearic Islands, during April–July 1989, and were aged by means of daily otolith increments. Growth rates were in the range of values reported for other clupeoids, although lower than those for larvae of the Mediterranean anchovy Engraulis encrasicolus. Hatching dates were back-calculated from the age in days and the date of capture. The data indicated that hatching was continuous, but revealed a low peak in the last half of November 1988 and a second, higher peak in the first half of March of the following year, in accordance with the general cycle of secondary production in this oligotrophic area.     

Size-specific changes in amount of lipid and daily growth rate of early larval sardine, Sardinops melanostictus, in the main Kuroshio Current and its offshore waters off eastern Japan

The size-specific nutritional conditions of larval sardines, Sardinops melanostictus, from the main Kuroshio Current and its offshore waters off eastern Japan were assessed by lipid analysis. A rapid lipid analysis technique (diagnostic kits for human serum lipids) was used to measure the different lipid components of individual sardine larvae as indicators of their nutritional condition. Size-specific growth trajectories of individual larvae were estimated by the biological intercept method, and the recent daily growth rate of standard length (SL) was calculated from the 3 d outer increment width on the otolith. Relationships between the amount of larval phospholipid (PL; tissue weight indicator) and SL, and the recent daily growth rate of larva (Gr) and SL, could be expressed by the equations PL = 0.459 SL ^1.77 and Gr = 0.0809 SL − 0.341, respectively. There was no notable difference in these values between the two survey areas. The relationship between the amount of triglyceride (TG) and SL could be expressed allometrically (TG = 0.013 SL ^2.63). The relationship between the index of starvation tolerance (TG/PL) and SL could be expressed by the allometric equation TG/PL = 0.0288 SL ^0.865, suggesting that larger sardine have a higher starvation tolerance than smaller sardine. The TG of the 8 to 9 mm SL size-class larvae in the offshore area was higher than in the main Kuroshio Current. To test whether the TG for each larval sardine in the 8 to 9 mm SL size-class could be correlated with variables (temperature, chlorophyll a and distribution density of the sardine larvae) measured at the sampling stations, correlation analyses were performed. A highly significant negative correlation between TG and distribution density of the sardine larvae was found. A density-dependence effect seemed to influence the fluctuation of the larval storage energy component for short-term needs. Received: 12 March 1998 / Accepted: 26 March 1999     

Comparison of feeding habits of myctophid fishes and juvenile small epipelagic fishes in the western North Pacific

To examine the potential trophic competition between myctophids and small epipelagic fishes in the nursery grounds in spring, we compared the stomach contents of dominant myctophids (Symbolophorus californiensis, Ceratoscopelus warmingii and Myctophum asperum; n = 179) and juvenile epipelagic fishes (Japanese sardine, Sardinops melanostictus, Japanese anchovy, Engraulis japonicus, chub mackerel, Scomber japonicus, and spotted mackerel, S. australasicus; n = 78) that were simultaneously collected at nighttime with a midwater trawl net around the Kuroshio-Oyashio transition zone in the western North Pacific. It was clear that the neritic copepod Paracalanus parvus s.l. was the most abundant species in NORPAC samples (0.335 mm mesh size) taken at the same stations. Diets of dominant myctophid fishes differed from those of the juvenile epipelagic fishes; Japanese sardine and anchovy mostly preyed upon P. parvus s.l. (23.6% of stomach contents in volume) and Corycaeus affinis (16.1%), respectively. Both chub and spotted mackerels mainly preyed upon the seasonal vertical migrant copepod, Neocalanus cristatus (15.9 and 14.7%, respectively). On the contrary, myctophid fishes probably do not specifically select the abundant neritic copepods. Namely, S. californiensis mostly preyed upon a diel vertical migrating copepod, Pleuromamma piseki (22.7 and 30.6% in stomach of juvenile and adult, respectively), while C. warmingii and M. asperum preyed on Doliolida (43.0% in stomach of juvenile C. warmingii), appendicularians (11.0% in stomach of juvenile M. asperum), and Ostracoda (6.3% in stomach of adult C. warmingii). Feeding habits of myctophid fishes seem adapted to their prey animals; low rate of digested material (less than 30% in volume) in stomachs of S. californiensis may be linked to the movement of P. piseki, hence S. californiensis can easily consume this copepod at night since they are more concentrated at night than daytime. High rate of digested material (over 40%) of M. asperum and adult C. warmingii suggest that they feed not only at night but also during the daytime in the midwater layer. Thus, myctophid fishes actually fed in the surface layer but less actively than the small epipelagic fishes. These results suggest that the potential for direct food competition between myctophids and small epipelagic fishes is low in the nursery ground, but there remains a possibility of indirect effects through their prey items, since the above gelatinous animals feed on common prey items as juveniles of Japanese sardine and anchovy.     

Oceanographic habitat,growth and mortality of larval anchovy (<Emphasis Type="Italic">Engraulis encrasicolus</Emphasis>) in the northern Aegean Sea (eastern Mediterranean)

Data from two ichthyoplankton surveys carried out during June 1995 and June 1996 were used to study the broad scale distribution patterns of anchovy eggs and larvae over the northern Aegean Sea continental shelf and the regional/inter-annual variability in growth and mortality rates of larvae. Two major spawning grounds were identified. One in the east, located in the area influenced by the Samothraki gyre (SG), in which a large amount of enriched, modified Black Sea water (BSW) is entrapped and one in the west, associated with zooplankton-rich waters in the semi-enclosed Thermaikos gulf close to several river mouths. In the NE Aegean, anticyclonic gyres generated over the continental shelf and fed by the circulating stream of BSW (like the SG) may act as retention areas for larval anchovy. In the west, the high enclosure of the Thermaikos Gulf contributes to reducing offshore dispersal. Major changes were observed in egg and larval abundance as well as larval mortality between June 1995 and June 1996 in both the western and eastern part of the continental shelf. Mean abundance of eggs and early larvae was >5 times higher in 1996 than in 1995, when waters were significantly cooler, fresher and richer in mesozooplankton. Larval survival decreased from 79 to 69% day⁻¹ in the east and from 89 to 74% day⁻¹ in the west between 1995 and 1996. Hence increased egg production was coupled with higher larval mortality during June 1996. Furthermore, a highly significant positive relationship between larval mortality (Z) and mean egg abundance (A) emerged (Z = −0154 + 0.205 log[A], r ² = 0.96, n = 7) when data from this study and a similar study in the NW Mediterranean were regressed. Mean growth rate of anchovy larvae in the study area (∼0.5 mm day⁻¹) did not differ significantly between areas/years. A marked ontogenetic change was observed in the otolith size/recent otolith growth-on-fish size relationships, which exhibited significant inflection points at ∼6 mm formalin preserved length. This change seems to coincide with performance (e.g., catchability) and behavioral changes (e.g., onset of vertical migrations) in European anchovy associated with the development of the caudal fin (the flexion stage).     

Relationship between zooplankton distribution,geographic characteristics and hydrographic patterns off the Catalan coast (Western Mediterranean)

Astract Northern anchovy larvae, Engraulis mordax, were collected on five cruises covering the Southern California Bight, one cruise in April 1984, four cruises in January, February and May 1986. The amounts of triacylglycerol, cholesterol and polar lipid were measured in individual anchovy larvae as indicators of their nutritional condition. There was a significant difference in each of the size-specific lipid components between the stations for four of the five cruises. This indicates that all the ocean habitats within a cruise were not equal in promoting growth (and presumably survival) in the anchovy larvae. There were also differences between cruises, where the percentage of the larvae judged to be in poor condition varied from 8 to 27%. Canonical correlation analyses revealed a significant relationship in most cases between the larval fish parameters and the physical and biological data collected from each occupied station. Cholesterol and triacylglycerol were the most important larval components, and the short-term energy storage component in the copepod Calanus pacificus was the most important station component. The data, however, are not sufficient to identify and characterize stations in the field which produce anchovy larvae in good condition.     

Nutritional condition and growth rate of anchovy larvae (Engraulis mordax) in the California Current: two contrasting years

A large number of northern anchovy larvae, Engraulis mordax, were collected in the Southern California Bight on two CalCOFI cruises during spring 1987, and the amounts of triacylglycerol, cholesterol and polar lipids were measured in each individual larva using the latroscan TLC/FID (thin-layer chromatography/flame ionization detection) system. The 1987 larvae were compared to larvae taken in the Bight during the previous year. Canonical correlation analyses revealed a significant relationship between the larval lipid components and physical/biological data collected at each occupied station during the late 1987 spring cruise, similar to that recorded in 1986. The short-term nutritional condition of the copepod Calanus pacificus was the most important station variable in both cruises. Their triacylglycerol:cholesterol ratio indicated that few of the 1987 larvae had been starving, but their very low contents of length-specific cholesterol and polar lipid indicated that they had been growing very slowly. Otolith readings on defatted larvae confirmed that the 1987 larvae had been growing significantly more slowly than the 1986 larvae. Furthermore, the data suggested that in the 1986 population the faster growing larvae were also those with the highest lipid content. This situation was reversed for the 1987 larvae, when the faster growing larvae in the population seemed to achieve their faster growth only at the expense of a lowered lipid content. The abundance of anchovy larvae was much higher in spring 1987 than in spring 1986 but, despite this, the apparent recruitment (number of Age 0 fish in July of each year) was not higher in 1987.     

Importance of the Japanese anchovy (Engraulis japonicus) to breeding rhinoceros auklets (Cerorhinca monocerata) on Teuri Island, Sea of Japan

Temporal variation in the diet and chick growth of rhinoceros auklets (Cerorhinca monocerata), on Teuri Island, Sea of Japan, was studied to understand how local marine environmental changes affect the reproduction of this piscivorous seabird. The food delivered by parents to chicks was sampled every 1-2 weeks from late May to July, 1994-1998. Overall, the diet of nestling rhinoceros auklets consisted of (by mass) 61% Japanese anchovy (Engraulis japonicus), 18% Japanese sand lance (Ammodytes personatus), 18% Japan Sea greenling (Pleurogrammus azonus), 2% other fish and 1% squid. Among years, the contribution of anchovy ranged from 16% to 93%. Once anchovy occurred in the diet, it dominated (80% on average) thereafter. Accordingly, when anchovy appeared in the diet early in the chick-rearing season (1994, 1998), the contribution of anchovy overall was large. The first appearance of anchovy in the diet of auklets late in the summer of 1997 was possibly related to negatively anomalous sea-surface temperature. Food loads composed of anchovy (34.0 g) were heavier than those of sand lance (22.5 g) and greenling (28.5 g). The energy density of anchovies also was higher: 6.3 kJ g^-1 wet mass compared to 0+ greenling (4.78 kJ g^-1) and 0+ sand lance (3.78 kJ g^-1). Thus, a high proportion of anchovy in the diet resulted in high food load mass, high daily growth rates of chicks and high fledging success. This study highlighted the importance of the time of arrival of migratory high-lipid prey, which is influenced by local oceanographic conditions, to the reproductive performance of a piscivorous seabird.     

Growth of the rock lobster Jasus lalandii and its relationship to benthos

Growth increments of the male rock lobster Jasus lalandii vary systematically with location within a small (38 km²) fishing ground off the South African west coast. High growth rates were recorded from an area where the availability of benthos suitable as rock-lobster food was also high. Increments could also be shown to vary significantly in different years, but over the size range examined, growth did not appear to be a function of size. Benthic biomass was found to be inversely related to depth. However, comparisons between biomass values from the same depths in two different areas of the fishing ground suggested that biomass was higher in areas which were in proximity to shallow water, where extensive kelp beds were found. Mussels (Aulacomya magellanica) formed an important constituent of the rock lobster's diet; these were prevalent at depths between 20 and 40 m, and especially in areas where rock-lobster growth rates were high.     

Factors affecting the spawning period of sardine in two highly oligotrophic Seas

Ovarian histology and weight dynamics of reproductive and somatic tissues were used to investigate seasonality of spawning and factors affecting reproductive period in two E Mediterranean sardine, Sardina pilchardus, populations (central Aegean and Ionian Seas), between September 1999 and May 2001. Despite similarities in the general spawning pattern of the two populations, i.e. protracted spawning season during the colder months of the year, reproductive period in the Ionian was shorter and lagged behind the Aegean by 2–3 months. In both Seas, reproductive period was influenced by body size as smaller females tended to have both shorter and delayed spawning season. Whereas hepatosomatic index (HSI) was consistently higher in reproductively active females during the whole spawning period, seasonality of spawning did not match variations of HSI. In both Seas fluctuations of HSI matched the spring burst of primary productivity and were followed by fluctuations in somatic condition and mesenteric fat by a 2 months’ lag. Somatic condition and reproductive activity displayed inverse seasonal patterns, implying that egg production in sardine basically relies on visceral and muscular fat deposits, accumulated during the summer growing season. Reliance of egg production on past energetic reserves suggests that sardine is a capital breeder, which is a rather efficient strategy in such oligotrophic habitats as the E Mediterranean, where winter spawning is accompanied by a particular decline in adult preying fields.     

Geographical variations in the trophic ecology of Japanese anchovy, Engraulis japonicus, inferred from carbon and nitrogen stable isotope ratios

Carbon and nitrogen stable isotope ratios of Japanese anchovy (Engraulis japonicus) and their stomach contents were examined and compared among various regions around Japan. Geographical variations in the isotope ratios were found between inshore and Pacific offshore regions. While most of the anchovy samples had isotope ratios around −17.6‰ for δ¹³C and 10.0‰ for δ¹⁵N as median values, higher (more enriched) isotope values were found in the anchovy sampled from inshore regions. On the contrary, lower (more depleted) values were found mostly in the anchovy from the Pacific offshore region including the Kuroshio Extension and Kuroshio-Oyashio transition zones. Higher carbon isotope ratios in the inshore regions may reflect a carbon source from benthic primary producers in addition to phytoplankton possibly through the consumption of the larvae of benthic organisms such as bivalves or decapods, which were found in the stomach contents of the inshore anchovy. Variations in the nitrogen isotope ratio may reflect not only differences in the trophic level of prey species, but also variations in the baseline level of food webs. Stable isotope ratios are potentially a useful tool for understanding the stock/population structure and migration of anchovy. The present findings indicate the potential importance of the “inshore–offshore” variations in the biology of Japanese anchovy populations in the northwestern Pacific waters.     

Oxygen uptake and comparative energetics among eggs and larvae of three subtropical marine fishes

Oxygen uptake was measured and energy budgets were determined for eggs and larvae of bay anchovy (Anchoa mitchilli), sea bream (Archosargus rhomboidalis) and lined sole (Achirus lineatus). Using an energetics model, both minimum rations and prey levels were estimated. The Q_{O 2} [μl (mg dry wt)^-1 h^-1] increased approximately five-fold for all species during development from egg to feedingstage larvae. The weight exponents in power functions, R=aW^b, relating oxygen uptake (R) to dry weight (W) did not differ significantly among species. The exponents were: bay anchovy, 0.9770; sea bream, 0.8382; lined sole, 0.9416. Oxygen uptake was generally lower for bay achovy than for the other species. In the energy budgets issimilation efficiencies of all species were low (24–75%). Gross growth efficiencies ranged from 11–41%, and net growth efficiencies from 38–57%. An estimated 32–83% of ingested energy was excreted in feces and urine. The lavae used a relatively small proportion of ingested energy in metabolism (6–31%). The anchovy had the lowest assimilation and gross growth efficiencies, and the highest excretion rate. Consistent with the better growth and survival observed in previous experiments, sea bream were the most efficient assimilators and had the lowest required minimum rations. Required minimum prey levels for first-feeding larvae ranged from 400 copepod nauplii l^-1 for sea bream and bay anchovy to 1 000 l^-1 for lined sole. The estimated required prey levels were higher than levels at which significant survival had been observed.     

Transfer of the chlorinated hydrocarbon PCB in a laboratory marine food chain

The transfer of chlorinated hydrocarbons (CHC) in a laboratory simulation of a three trophic level marine food chain was studied. The food chain consisted of the algal flagellate Dunaliella sp., the rotifer Brachionus plicatilis, and the larva of the Northern anchovy Engraulis mordax. CHC were introduced into the seawater at concentrations representative of near-shore conditions off southern California without the use of dispersing agents. Each trophic level appeared to be in a steady-state at the time of first sampling, 5 days after inoculation. Apparent partition coefficients were calculated for each trophic level. The CHC contamination in the diet of the rotifers and anchovy larvae was also calculated. Unfed anchovy larvae accumulated the same amount of CHC as fed larvae and the final concentration appeared to be dependent on the CHC concentration in the seawater. The data in this report suggest that CHC accumulation is not a food-chain phenomenon but rather the result of direct partitioning of the compounds between the seawater and the test organisms.