Trachurus Murphyi Research Articles

In situ target-strength measurements of Chilean jack mackerel (Trachurus symmetricus murphyi) collected with a scientific echosounder installed on a fishing vessel

Abstract Peña, H. 2008. In situ target-strength measurements of Chilean jack mackerel (Trachurus symmetricus murphyi) collected with a scientific echosounder installed on a fishing vessel. – ICES Journal of Marine Science 65: 594–604. The use of commercial fishing vessels for scientific purposes has increased worldwide in the past 10 years. Many such studies have involved the collection of acoustic data from both uncalibrated and calibrated echosounders. However, few studies have involved investigations of in situ target strength (TS). During August/September 2003, in situ TS data on Chilean jack mackerel (Trachurus symmetricus murphyi) were collected on board a commercial purse-seiner during normal fishing operations off Chile, using a 38 kHz, Simrad EK60 scientific echosounder. The single-target detections of Chilean jack mackerel were filtered by depth, off-axis beam angle, and beam-compensation criteria to improve the quality of the data used for the TS calculations. Two methods, using raw data and tracked data, were employed to calculate the mean acoustic-backscattering cross section (σbs) and mean TS of Chilean jack mackerel. The results of the two approaches gave similar results, with a strong mode in the mean TS distribution between −35 and −37 dB for fish lengths ranging from 26 to 34 cm, indicating a b20 value of −66 dB. These results agreed well with most results published for this species and others of the same genus (i.e. T. trachurus, Trachurus t. capensis, and T. japonicus).

Prey occurrence in the stomach contents of four small cetacean species in Peru

The diets of long-beaked common dolphins Delphinus capensis (n=117), dusky dolphins Lagenorhynchus obscurus (n=72), Burmeister's porpoises Phocoena spinipinnis (n=69) and offshore common bottlenose dolphins Tursiops truncatus (n=22) were determined based on the analysis of the stomach contents collected from animals landed in ports along the Peruvian central coast and from Marcona, in southern Peru, during 1987-1993. The number of prey ingested was obtained by counting the number of fish otoliths and cephalopod mandibles (beaks). Only fish could be identified to species level. Long-beaked common dolphins fed mainly on Peruvian anchovy Engraulis ringens (70.0% by number), Panama lightfish Vincigerria lucetia (7.8%) and slimtail lanternfish Lampanyctus parvicauda (6.7%). Dusky dolphins consumed mainly anchovies (49.7%, 16.8%), slimtail lanternfish (23.6%, 0.1%), Inca scad Trachurus murphyi (17.1%, 0%) and mote sculpin Normanichthys crockeri (0%, 76.0%) off the central Peruvian coast and Marcona, respectively. In the same areas, Burmeister's porpoises fed mainly on anchovy (88.9%, 77.6%), silverside Odontesthes regia (6.5%, 0%), mote sculpin (0%, 8.1%) and South Pacific hake Merluccius gayi (0.6%, 7.9%). Offshore common bottlenose dolphins consumed mainly slimtail lanternfish (39.2%), barracuda Sphyraena sp. (13.5%) and Peruvian pilchard Sardinops sagax (13.3%). The diversity indices of the diet and temporal shifts in the main prey suggest an opportunistic feeding strategy for the four cetacean species studied, which take advantage of the locally most available epipelagic and mesopelagic schooling fish. Cluster analysis shows high similarity in their diets, with these four marine top predators being able to optimally exploit the high productivity of the Peruvian upwelling ecosystem.

Mercury content in Chilean fish and estimated intake levels

The intake of fish products is a major public health concern due to possible methyl mercury exposure, which is especially toxic to the human nervous system. This pilot study (n = 46) was designed to determine mercury concentrations in fish products for national consumption (Chilean jack mackerel, hake, Chilean mussel, tuna) and for export (salmon, Patagonian toothfish, swordfish, southern hake), and to estimate the exposure of the general population. The fish products were collected from markets in Talcahuano, Puerto Montt and Santiago. Samples were analyzed at the National Environmental Center by cold vapor atomic absorption spectrophotometry. Mercury levels in swordfish and one canned tuna sample exceeded levels prescribed by national and international standards. The remaining two export products (Patagonian toothfish, also known as Chilean sea bass, and salmon) complied with international limits, which are more demanding than Chilean regulations. Theoretical estimates of mercury intake varied from 0.08 to 3.8 µg kg−1 bw day−1 for high fish consumers, exceeding the provisional tolerable intake for tuna, Chilean seabass, Chilean jack mackerel and swordfish. This group appears to be at the greatest risk from mercury contamination among the Chilean population.

Stable isotope analysis reveals pelagic foraging by the Southern sea lion in central Chile

The diet of Southern sea lion Otaria flavescens is poorly known along the coast of central Chile (32°–39°S), where a population of about 17,300 individuals occurs, in an ecosystem that sustains one of the world's most important fishing industries. The primary objective of this study was to reconstruct the diet and estimate Trophic Positions (TPs) of sea lions and their prey off central Chile using stable isotopes ( δ 13C and δ 15N). Our results showed that the diet of sea lions is primarily composed of pelagic prey, with the jack mackerel Trachurus murphyi as the principal prey item in the diet of sea lion (1–99th percentile: 20–66%), while demersal prey accounted for only 0–2.8%. We also found regional differences on the relative contribution of prey to the diet of sea lions. Animals that were sampled close to major fishing areas showed an increase in the relative contribution of jack mackerel to the diet as opposed to animals sampled away from these areas that displayed a relatively more heterogeneous diet. Trophic Positions (TPs) of sea lions prey items ranged between 3.39 for jack mackerel and 4.48 for pink cusk-eel ( Genypterus blacodes). The TP for sea lions was 4.57. Hence, our results showed a community composed by at least 5 trophic levels, with sea lion as the top predator. In summary, our study demonstrates that the Southern sea lion is displaying pelagic foraging off central Chile. We highlight the necessity of conducting further research on the trophic ecology and diving behavior of Southern sea lion to obtain a better understanding of their role as top predator.

Human Pseudoterranovosis, an Emerging Infection in Chile

Fifteen cases of human pseudoterranovosis are reported for Chile, representing an emerging parasitic infection in this country caused by larvae of the nematode Pseudoterranova sp. Our observations also included an outbreak of pseudoterranovosis in 3 of 4 individuals who shared the same raw fish dish (cebiche). Most of the cases occurred in adult patients. The main source of infection was from consumption raw or fried marine fish, including hakes (Merluccius australis or Merlucciuts gayi), pomfret (Brama australis), Inca scad (Trachurus murphvi), and corvina (Cilus gilberti). Seasonal distribution showed most of the cases to occur in fall and spring. Parasite larvae were isolated from the mouths of most of the patients after they reported a pharyngeal tickling sensation, coughing, vomiting, or a foreign body in the mouth or throat.

'El Niño' Effects and Biomass Endogeneity in a Harvest Function: The Chilean Jack Mackerel Fishery

The main goal of this paper consists in estimating the input parameters of an annual harvest function for the Chilean jack mackerel stock; particularly, the effects of biomass on catch. One of the main problems faced is that the biomass variable is possibly endogenous, which would bias the estimators if the problem remains unsolved. Our empirical strategy consists in estimating a per vessel harvest function using panel data, which allows us to control for vessels' unobserved heterogeneity, and episodes of 'El Nino' phenomenon as valid instrumental variable for biomass, which allows us to control for the potential biomass endogeneity. This strategy produces consistent estimates of the biomass coefficient. The results, using a panel of industrial vessels operating in the central-southern region of Chile during the period 1985-2002, show that the endogeneity of the biomass variable biases upwardly the magnitude of its coefficient in a Cobb-Douglas harvest function. In the case of our data, the endogeneity bias even changes the sign of the catch-to-biomass elasticity. A first contribution of the paper is to address the endogeneity of biomass in a harvest function, an issue often underestimated in the empirical literature. A second contribution is related to 'El Nino' effects on the Chilean jack mackerel stock. The results show that an oceanic 'El Nino' episode not only has negative contemporaneous effects on jack mackerel biomass but also negative biomass effects lasting for at least two additional years.

Extracción, Caracterización Parcial y Termoestabilidad de la Enzima Transglutaminasa en Surimi, en Músculo Blanco de Jurel y en Miofibrillas de Carne de Vacuno

The objective of this research was to carry out the extraction and characterization of surimi and jack mackerel white muscle (Trachurus murphyi) and of bovine meat and to determine the thermostability of transglutaminase. Kinetics parameters and thermostability are more relevant to project the utility of this tissue in new food products development. The activities of this enzyme were of 4.7 x 10 -3 , 13.0 x 10 -3 y 53.0 x 10 -3 UI/g tissue for surimi and white muscle of jack mackerel, and meat of bovine respectively. It characterized transglutaminase of bovine meat, finding values of optimal pH of 6.5 and 40o C of temperature. The existence of two transglutaminases was postulated in the white muscle of jack mackerel, with optimal pH values of 5.4 and 7.6, temperatures of 50 and 60o C, and calcium concentrations of 10 and 40 mM. Inactivation constants ranged between 3.3 x 10 -3 and 0.4 h -1 for different temperatures of preincubation. The activation energy of denaturation was about 12.46 y 39.37 KJ mol -1 oK -1 .

Determinism and plasticity of fish schooling behaviour as exemplified by the South Pacific jack mackerel Trachurus murphyi

Pelagic fish schools are thought to show a general pattern of dispersion at night and aggregation within schools during the day. This pattern is often accepted as the major rule driving most of the other physiological, biological and ecological processes. Foraging on mobile prey, for instance, is assumed to be enhanced by schooling behaviour. Current theory assumes then that foraging is only possible for obligatory gregarious predatory fish from dawn to dusk. However, offshore mesopelagic communities perform vertical migrations and are out of reach for most oceanic pelagic predators during the day (with the exception of some apex predators, e.g. swordfish or big-eye tuna). To investigate how fish may overcome this apparent contradiction, we studied the 3-dimensional spatial strategy of the South Pacific jack mackerel Trachurus murphyi according to the abiotic and biotic conditions of the habitat. Data came from acoustic surveys performed in central Chile in 1997, 1998 and 1999. Our results show that the jack mackerel distribution was driven by prey during the night when foraging, and related to the hydrology when resting during the day in the upper part of the oxycline. Fish were more aggregated at night than during the day, probably because jack mackerel cycles of schooling behaviour depend primarily on prey availability. This 'atypical' behaviour could be an adaptation of gregarious pelagic fish to an oceanic ecosystem. Fish schooling behaviour is not necessarily driven directly by the diel cycle; rather, it can be functional and depends on prey availability.

Transglutaminase effects on gelation capacity of thermally induced beef protein gels

Transglutaminase (TG) is an enzyme that catalyzes an acyl-transfer reaction between the γ-carboxyamide group of peptide or protein-bound glutaminyl residues, and primary amines. TG action on protein molecules, causes a cross-linking and polymerizing effect of these latter, through ε-(γ-glutamyl)lysine bonds. This TG-mediated protein cross-linking creates drastic physical changes in protein-rich foods. This research objective, was to evaluate the microbial transglutaminase (MTGase) effect on beef gel texture. Time and incubation temperature, enzyme concentration, and Chilean jack mackerel ( Trachurus murphyi) surimi addition effects, were studied. Beef gel quality, was assessed by measuring gel strength and cooking yield. Additionally, SDS-PAGE electrophoresis and ε-(γ-glutamyl)lysine bond analysis by HPLC were carried out on the gels. MTGase addition, significantly increased gel strength. The optimal attributes were observed at 60 °C after 2 h and 0.5% w/w of MTGase, with a gel strength 88% higher than the control-gel. Jack mackerel surimi and MTGase incorporation in beef gels, significantly increased gel strength and cooking yield. SDS-PAGE analysis revealed that the myosin heavy chain (MHC) content decreased and that the cross-linked protein amount, apparently increased with time and MTGase addition. Proteolysis was also observed. ε-(γ-Glutamyl)lysine bond production also increased as a function of incubation time and MTGase concentration. These results, suggest that it is possible to improve mechanical properties of beef gels by adding MTGase and jack mackerel surimi, thus increasing their potential utilization in minced based products.

The decay of similarity over geographical distance in parasite communities of marine fishes

AbstractAim We evaluate, for the first time, the decay of similarity over distance in four species of marine fishes with different vagility: Trachurus murphyi (pelagic, highly vagile), Merluccius gayi (demersal, highly vagile), Sebastes capensis (demersal, low vagility) and Hippoglossina macrops (benthic, non‐vagile).Location We use our own data of the species composition of parasite communities in four host species: T. murphyi (Perciformes), M. gayi (Gadiformes), H. macrops (Pleuronectiformes) and S. capensis (Scorpaeniformes), from the coast of Chile and southern Argentina. Trachurus murphyi, M. gayi and H. macrops in the area studied live closely associated with the cold waters of the Humboldt Current System, while S. capensis in southern Chile is associated with the fjord areas south of c. 43° S, and in Argentina this species lives in close association with the cold water of the Malvinas Current, which mixes with the warm water of the Brazilian Current in the sampled area. Thus, for all four host species there are no known geographical (oceanographic) barriers that interrupt their continuous distributions.Methods Fish were collected and frozen (−18 °C) until examination in the laboratory. After thawing, each visceral organ was dissected separately, washed in running water, filtered using a mesh of 0.25 mm, and examined under a stereomicroscope (20×). For S. capensis, only ectoparasites were included in this study because data on endoparasites for some locations are not available. The approach of Poulin [Journal of Biogeography30 (2003) 1609] was used. For each host species, we computed similarity in parasite composition using the Bray–Curtis distance on a presence/absence matrix. Similarity between each pair of localities was correlated (linear regression on raw and transformed data) with the distance (in nautical miles) among those sites.Results Among conspecific populations of host fish, there was no correlation between sample size and parasite species richness. The same pattern was evident when all host populations were pooled and treated as a single sample. Except for H. macrops, an important proportion of the geographical ranges of the host species was covered. The decay in similarity of parasite communities over distance was recorded in three of the four hosts analysed. For H. macrops, no relationship between distances and decay of similarity was evident. A linear regression on non‐transformed data provided a good fit, and the regression on log(n + 1) does not change significantly for both r2 and probability, but slopes are smaller for log‐transformed than for non‐transformed data.Main conclusions Three of the four fish parasite systems studied fit well with the expected decay of similarity over distance. The slopes of the relationship between distance and similarity in the marine fishes studied are lower, but significant (three orders of magnitude) than those recorded in freshwater fishes by Poulin (2003). In our case, Hippoglossina macrops (benthic, non‐vagile host) does not show any relationship, suggesting homogeneity over the geographical area studied for this species.

Histamine Production by Two Enterobacteriaceae Strains Isolated from Tuna (Thunnus thynnus) and Jack Mackerel (Trachurus murphyii)

Growth of Enterobacteriaceae in scombroids such as tuna (Thunnus thynnus) and jack mackerel (Trachurus murphyii) usually promotes aminoacid decarboxylation to biogenic amines. Among these compounds, histamine, produced by histidin-decarboxylase activity, is reported as toxic. The objective of this study was to compare histamine production by a strain, identified as Serratia liquefaciens, isolated from tuna (T. thynnus) caught in the Gulf of Mexico and Morganella morganii isolated from Chilean jack mackerel (T. murphyii). Morganella morganii had higher histamine producing ability in a synthetic medium than S. liquefaciens, presumably as a result of stressing conditions on M. morganii. However, in a medium formulated with muscle protein extracts obtained from tuna S. liquefaciens showed higher histamine production at similar microbial counts. In this medium, histidine was extracted together with proteins from tuna striated muscle, it was assumed that it acted as histamine production promoter.

Resolution of the taxonomic status of Chilean and Californian jack mackerels using mitochondrial DNA sequence

Phylogeographic reconstructions using mitochondrial DNA sequences from both the control region and the cytochrome b gene demonstrated that two disjunct populations be recognized as Trachurus murphyi and Trachurus symmetricus. The species have been isolated for at least 250 000 years.

Impact of El Niño events on pelagic fisheries in Peruvian waters

Using data from stock assesment surveys on pelagic resources during El Niño events of 1972/73, 1982/83, 1997/98, we analyze biological changes on pelagic ecosystems and pelagic fisheries during different stages of development of El Niño phenomenon: emergence, full, final and post-Niño. Results indicate changes in spatial distribution of resources, their concentration and size structure. In anchovy (Engraulis ringens) a decrease in biomass was observed, which was estimated at 1.2 million tons in September 1998, the lowest throughout the 1990s. This resource showed an asymmetric distribution towards the south of Peru. Other pelagic resources increased their biomass during or after Niño events, primarily sardine (Sardinops sagax), jack mackerel (Trachurus murphyi), pacific mackerel (Scomber japonicus), and longnose anchovy (Anchoa nasus). At the end of the El Niño phenomenon we found less productivity but more diversity in the pelagic ecosystem. During the 1997/98 El Niño, the diversity index (Manual de Ecologia, 1a Edition, Editorial Trillas, Mexico, 267pp) increased from 0.87 to 1.23–1.70. In both the emergence stage and fully developed stages of El Niño we found large numbers of sardine and longnose anchovy present simultaneously. Size structure of sardine, jack mackerel, and pacific mackerel showed an increase in juveniles. Anchovy during El Niño showed a single modal group composed of adults, but the post-Niño phase indicated an increase in juveniles with an average length of 6–7 cm. In El Niño conditions spawning among anchovy was low, but among sardine and pacific mackerel it was high. We observed, for the first time during full spawning, juvenile sardines with a total length of 18–20 cm. The anchovy spawning season during the post-Niño phase was considerably lengthened, from April to December 1998. Drastic change occurred in fisheries when monospecific fisheries, based on anchovy before El Niño, became multispecific fisheries based on sardine, jack mackerel, pacific mackerel, longnose anchovy and other species typical of tropical and warm oceans. Landings of anchovy decreased substantially, but those of longnose anchovy, jack mackerel, pacific mackerel, and sardine increased.

Impact of El Niño events on pelagic fisheries in Peruvian waters

Abstract Using data from stock assesment surveys on pelagic resources during El Nino events of 1972/73, 1982/83, 1997/98, we analyze biological changes on pelagic ecosystems and pelagic fisheries during different stages of development of El Nino phenomenon: emergence, full, final and post-Nino. Results indicate changes in spatial distribution of resources, their concentration and size structure. In anchovy (Engraulis ringens) a decrease in biomass was observed, which was estimated at 1.2 million tons in September 1998, the lowest throughout the 1990s. This resource showed an asymmetric distribution towards the south of Peru. Other pelagic resources increased their biomass during or after Nino events, primarily sardine (Sardinops sagax), jack mackerel (Trachurus murphyi), pacific mackerel (Scomber japonicus), and longnose anchovy (Anchoa nasus). At the end of the El Nino phenomenon we found less productivity but more diversity in the pelagic ecosystem. During the 1997/98 El Nino, the diversity index (Manual de Ecologia, 1a Edition, Editorial Trillas, Mexico, 267pp) increased from 0.87 to 1.23–1.70. In both the emergence stage and fully developed stages of El Nino we found large numbers of sardine and longnose anchovy present simultaneously. Size structure of sardine, jack mackerel, and pacific mackerel showed an increase in juveniles. Anchovy during El Nino showed a single modal group composed of adults, but the post-Nino phase indicated an increase in juveniles with an average length of 6–7 cm. In El Nino conditions spawning among anchovy was low, but among sardine and pacific mackerel it was high. We observed, for the first time during full spawning, juvenile sardines with a total length of 18–20 cm. The anchovy spawning season during the post-Nino phase was considerably lengthened, from April to December 1998. Drastic change occurred in fisheries when monospecific fisheries, based on anchovy before El Nino, became multispecific fisheries based on sardine, jack mackerel, pacific mackerel, longnose anchovy and other species typical of tropical and warm oceans. Landings of anchovy decreased substantially, but those of longnose anchovy, jack mackerel, pacific mackerel, and sardine increased.

Diel vertical behaviour, predator–prey relationships, and occupation of space by jack mackerel (Trachurus murphyi) off Chile

Abstract In the southeastern Pacific, jack mackerel (Trachurus murphyi, Carangidae) is a heavily exploited pelagic species, and its presence in Chilean waters in autumn and winter is assumed to be mainly due to an inshore feeding migration. Predator–prey relationships are known to depend on the spatial and temporal scale of observation, but they can also be strongly affected by factors such as diel vertical migration. In studying the case of jack mackerel in detail, we used data from three acoustic surveys carried out in central Chile in 1997, 1998, and 1999. In terms of spatial occupation, jack mackerel behaviour is “atypical” behaviour, i.e. more aggregated during the night than during the day. The patterns we observed can be related to their nocturnal active foraging behaviour. Diel feeding behaviour is therefore a key factor in the aggregating behaviour of jack mackerel and its vulnerability to the purse-seine fishery that targets these nocturnal aggregations. This particular fish diel feeding behaviour also affected predator–prey relationships in relation to the spatial scale. Positive correlations at a “small” spatial scale (<7–25 km) were observed during the night when jack mackerel foraged, but not during the day. Finally, we show that prey biomass was lower where jack mackerel were abundant, which could indicate a jack mackerel top–down control on prey communities.

DETECTION OF MESOSCALE OCEANIC FEATURES USING RADARSAT-1, AVHRR AND SEAWIFS IMAGES AND THE POSSIBLE LINK WITH JACK MACKEREL (TRACHURUS MURPHYI) DISTRIBUTION IN CENTRAL CHILE

In order to verify the ability of RADARSAT-1 images to detect mesoscale oceanic features and the possible link of these oceanographic patterns with jack mackerel (Trachurus murphyi) distribution in the waters off central Chile, a project was developed as part of the Canada Centre for Remote Sensing Globesar-2 program. The combined use of simultaneously acquired RADARSAT-1, AVHRR sea surface temperature (SST), SeaWiFS Chlorophyll a concentration (Chl), TOPEX/ERS altimeter and ERS-2 scatterometer wind data greatly enhanced SAR imaging capabilities for the detection of oceanic features. Results show that detection of coastal wind-driven upwellings, eddies, frontal boundaries and phytoplankton blooms is possible using SAR imagery, given the proper environmental conditions. Results also suggest that jack mackerel distribution coastal resources is mainly associated with frontal boundaries, upwelling waters and high chlorophyll concentrations detected by the remotely sensing images

RELATING SPATIAL DISTRIBUTION OF CHILEAN JACK MACKEREL EGGS AND ENVIRONMENTAL FACTORS IN THE OCEANIC WATERS OFF CHILE

Chilean jack mackerel (Trachurus murphyi) is a highly migratory pelagic species that inhabits the Southern Pacific Ocean, constituting the most important fishery for Chile. This species exhibits an onshore migration during the summer related to coastal food availability, and an offshore migration towards reproductive oceanic areas (beyond Chilean EEZ) in early spring. During the spawning peaks (November) of 1998, 1999, 2000 and 2001, jack mackerel eggs were collected from four systematic surveys using 8-10 fishing vessels, deployed in the spawning area (76-92 W) off central Chile. Spatial distribution of eggs was modeled by geostatistical techniques. Environmental information including SST, wind, sea level anomalies and chlorophyll-a, as well as SST gradients, turbulence and currents were calculated. Exploratory results suggest a higher egg density related to warmer waters (16-19 C), moderate winds (4-8 m s-1) and low currents (< 15 cm s-1) as well as SST gradients (< 0.3 C 10 km-1). Statistical analysis developed with the purpose of providing evidence of habitat-species association, reveal a significant relationship (p<0.05) between egg density and both SST and wind magnitude. The spatial coupling between eggs and environmental data was accomplished by using the spatial Empirical Orthogonal Functions method (EOF), showing that high amplitudes of the first mode were spatially coherent with high density of eggs, warm waters and low magnitudes of wind, suggesting a bio-physical coupling among these variables in the jack mackerel spawning area

Mathematical model development, experimental validation and process optimization: retortable pouches packed with seafood in cone frustum shape

The aim of this research was to develop and validate a mathematical model coupled with an optimization technique for thermal processing of conduction-heated foods in retortable pouches in order to: (a) search for variable retort temperature profiles to minimize process time, and (b) search for variable retort temperature profiles to minimize quality gradient (thiamine) within the product. The model was validated utilizing Jack mackerel ( Trachurus Murphyi) packed in retortable pouches. The conjugated gradient method was utilized as a search technique to find the best variable retort temperature profile to satisfy the specific objectives. The simulation results were in good agreement with the observed temperatures. The prediction errors obtained in the validation study were under 5%. Non-significant differences ( P<0.05) were found between the experimental and predicted values. Simulations showed that significant reduction in process time (20–30%) could be attained utilizing variable retort temperature profiles while maintaining product quality.

Stability of n-3 fatty acids in fish particles during processing by impingement jet

Impingement jet systems have been identified as an alternative to conventional drying and freezing methods. Due to a high gas-particle relative velocity, which enhance heat transfer, product quality is improved. Surface heat transfer coefficients, drying and freezing times of fish particles (mackerel, Trachurus murphyi) were determined under several operation conditions (gas velocity and temperature, particle geometry, material load) using impingement jet. Heat transfer coefficients were estimated in the range of 100–300 W/m 2 K and a correlation of Nusselt and Reynolds numbers were established. Drying and freezing time was significantly influenced by gas temperature and particle geometry. The susceptibility of n-3 fatty acids of fish particles to oxidation during drying and freezing was determined by GC analyses of methyl esters of fatty acids, and results were compared with those obtained by alternative conventional methods. As freezing and drying time increased, n-3 fatty acids losses increased. This suggests that a lower gas temperature with short freezing time would yield a higher quality of fish particle (i.e. with minimal n-3 fatty acids losses) and a higher gas temperature with short drying time would yield a higher quality of product.

An eco‐morphological explanation of individual variability in the shape of the fish otolith: comparison of the otolith of Hoplostethus atlanticus with other species by depth

Variation in otolith shape (otolith polymorphism) in Hoplostethus atlanticus, Hoplostethus mediterraneus, Paratrichichthys trailli, Pagrus major and Trachurus murphyi, quantified using principal components analysis based on Fourier transform decompositions of outlines of otolith shape, was particularly high among the samples of H. atlanticus from the North Atlantic, New Zealand, Australia and Namibia. The scatter was uniform, however, and did not show any significant differences among regions. The implication drawn from the high variability in otolith shape of H. atlanticus was that otolith shape polymorphism was maintained by some form of balancing selection across many small local environments which may result in k‐selection with consequent poor response by H. atlanticus to maximum sustainable yield harvesting strategies. The variation in otolith shape defined by the otolith morphospace of the five species that were measured, showed a decreasing trend in scatter (i.e. decreasing complexity of shape) proceeding from the species with the deepest habitat (H. atlanticus) to the most shallow (T. murphyi).