Hake Eggs Research Articles

Inter-annual and seasonal variations in the Outer and Inner Sea spawning zones of southern hake, Merluccius australis, inferred from early life stages distributions in Chilean Patagonia

Merluccius australis, known as southern hake, is a demersal fish that inhabits waters off the southern tip of South America. The main spawning area has historically been located in the Outer Sea off northern Chilean Patagonia, where these fish aggregate to reproduce during austral winter. An alternative spawning ground has been reported to occur within the Inner Sea of Chiloé, where eggs of a few days old have been found. Neither the relative importance of this spawning zone nor the main environmental features that make it suitable for spawning have been assessed. We analyzed ichthyoplankton samples and hydrographic data from oceanographic cruises (2003–2015) carried out in austral winter and spring to characterize both spawning zones. Field data showed, on average, 30 and four times more southern hake eggs in the Outer Sea than in the Inner Sea for winter and spring, respectively. Accordingly, the species mainly spawns during winter in the Outer Sea but during spring in the Inner Sea. Potential retention zones were identified, and the spawning seasons for both areas were associated with local oceanographic processes that enhanced retention in nursery areas. The development of different main reproductive seasons in different zones is apparently linked to the inter-annual variability of environmental conditions in the main offshore spawning zone. In this case, secondary spawning in the Inner Sea could be part of a reproductive strategy to ensure offspring survival given unfavorable conditions in the Outer Sea.

Effect of temperature on the development and mortality of European hake (Merluccius merluccius L.) eggs from southern stock under laboratory conditions

The effects of five temperatures (10, 13, 16, 19 and 22°C) on the survival, development and hatching time of fertilized hake eggs from a spontaneous spawning were studied. Significant differences (p<0.05) were found between egg development at each temperature. The power law model provided good fits for the relationship between temperature and development time, with r2 values higher than 0.96. Total egg mortality rates were high for all temperatures, with the lowest values observed at 12.7°C (59%). In contrast, eggs did not tolerate temperature above 22°C. The time to complete stages I, II, III and IV showed significant differences (p>0.05) between this study and previous result reported for hake eggs from northern stock. These differences could be related to the different thermal history of the eggs, experimental conditions or differences in the grouping of developmental stages. An extensive review of some hake species from the Merluccius genera showed a low variability in time to hatch at each temperature.

Lipids and fatty acids as indicators of egg condition, larval feeding and maternal effects in Cape hakes (Merluccius paradoxus and M. capensis)

Cape hakes, Merluccius paradoxus and M. capensis, are important gadoid fish that are commercially harvested in the Benguela Current system off Namibia and South Africa. The aim of this study was to elucidate the nutritional condition and feeding preferences of their larvae. Hake eggs and larvae were sampled in austral spring of two consecutive years, 2007 and 2008, off the west coast of South Africa. They were identified to species using genetics, and total lipid content and fatty acid (FA) composition were analysed for each individual egg and larva to compare the condition of different early life stages of both hake species. Higher abundances of M. paradoxus eggs and larvae were consistently found compared to M. capensis. In both species, eggs contained wax esters (WE) and had significantly higher lipid content per dry mass than larvae. Lipid content as well as FA composition changed with the developmental stage of larvae. Quantities of essential fatty acid (EFA) increased with feeding of larvae due to dietary lipid incorporation. In 2007, yolk-sac larvae contained significantly lower total lipids than in 2008. It is argued that this was due to reduced lipid transfer by the spawning females to the eggs. These findings indicate that maternal effects are important in determining condition of hake larvae and that this may have an effect on their survival and subsequent recruitment.

Drift routes of Cape hake eggs and larvae in the southern Benguela Current system

The aim of this study was to combine observed circulation pattern with data on distribution of hake eggs and larvae in the southern Benguela from a survey in September/October 2005 to investigate drift routes of hake eggs and larvae. Genetic information enabled species-specific information about drift routes of the two hake species (Merluccius capensis and M. paradoxus) to be established. The results showed that both species were transported from spawning areas to nursery areas in the jet current, but differential cross-shelf distribution would most likely lead to species-specific drift routes which could explain why the two species seem to have different nursery areas.

Effects of temperature and lipid droplet adherence on mortality of hatchery-reared southern hake Merluccius australis larvae

Effects of exogenous (water temperature) and endogenous (lipid droplet adherence) factors were experimentally tested on early survival of southern hake Merluccius australis reared under controlled conditions. Experiments to determine the effect of temperature (10, 12 and 14 °C) on larval growth rates and yolk-sac absorption rates of unfed southern hake were carried out under laboratory conditions. There was no significant differences in growth rates at the temperature range tested (ANCOVA, F = 0.164, p > 0.25), but yolk-sac absorption rates and mortality increased with temperature (ANCOVA, F = 53.84, p < 0.001). A high percentage (between 31 and 81%) of hake eggs showed a lipid droplet not adhered (i.e., freely moving in the yolk, and not located in the posteriormost portion of the yolk-sac). In a second experiment, fed southern hake larvae with the lipid droplet not adhered during embryonic development did not survive after yolk-sac absorption. This study provides the first data on the influence of the lipid droplet absorption on larval survival of cultured hake, and can be used as an early indication of the quality of the batch.

Passive tracer reconstruction as a least-squares problem with a semi-Lagrangian constraint: An application to fish eggs and larvae

A variational, data assimilation, algorithm was developed for reconstruction of a two-dimensional, nonstationary, passive tracer field in the ocean with open boundaries and a known velocity field. The observations, spatial smoothing terms and passive tracer conservation equation were included as weak constraints. The algorithm was tested with simulated, nonstationary, pseudo-oceanographic data integrated for a 7-day period. Simulations were run to determine the robustness of the algorithm and the effect of theoretical, simulated ‘sampling events,’ mimicking the standard oceanographic survey. We explored the sensitivity of the reconstructed tracer fields to the distribution of the pseudo-oceanographic sampling strategy, essentially an antenna problem, and to errors in the velocity field and the observations. The algorithm was applied to observations of silver hake (Merluccius bilinearis) eggs and larvae obtained in August 1998 on the Scotian Shelf. Finally, the evolution of fish eggs and larvae concentration was found. The corresponding mortality rate of fish eggs and larvae was determined to be 0.28 day 1 , with errors of 0.03 day 1 . The approach, which is quite general and could be applied to many different problems requiring minimization subject to constraints, allows for error analysis of the results. The volume and variety of data collected in the ocean has substantially increased during the last decade. Besides traditional measurements of temperature and salinity, new observational and sampling techniques have enabled the collection of large quantities of biological and hydrochemical data that can be treated as passive tracers as they are not strongly coupled with the ocean circulation. The collection of these new data raises the problem of how to transfer these data, usually sampled on irregular grids, onto a regular grid, necessary for numerical analysis. One of the key interpretive questions is how to relate the observed pattern of the scalar or tracer fields to the circulation field which may be determined from different observations or derived from a numerical model. Some of these

Distribution and abundance of European hake Merluccius merluccius (L.), eggs and larvae in the North East Atlantic waters in 1995 and 1998 in relation to hydrographic conditions

Plankton samples from surveys in 1995 and 1998 were analysed in order to study the spatial distribution of hake (Merluccius merluccius) eggs and larvae. The cruises covered an extensive area from the south of the Bay of Biscay to the north-west of Ireland. This spatial distribution has been interpreted in relation to the direction and intensity of the dominant winds. An important decrease of eggs (69%) and larvae (27%) was observed from 1995 to 1998. Hake showed continuous spawning from February to July in the area. The centroids of hake egg distribution indicated a northward displacement of the peak of spawning as the season progresses. Spawning of hake was located close to the 200 m depth isobath in the southern area (Bay of Biscay) and it spread over the shelf in the area of the Celtic Sea. Eggs were most abundant at 20 m depth temperatures between 12 and 12.5°C. The centroids of hake larvae distribution also showed a northward displacement although not as strong as that of hake eggs. The spatial distribution of hake larvae by size ranges showed important differences between years: in 1995 it suggested inshore transport of larvae, from the spawning areas (close to the 200 m depth isobath) to nursery areas (closer to the coast) while in 1998 it suggested offshore transport. This transport does not correspond with the general wind regimes during those years. Therefore it is concluded that the transport of the hake larvae to nursery areas must be controlled by different hydrographic mechanisms such as geostrophic currents in the Bay of Biscay and tidal currents in the northern areas.

Spatial and temporal distribution and abundance of European hake, Merluccius merluccius, eggs and larvae in the Catalan coast (NW Mediterranean)

Plankton hauls were conducted on five surveys from November 1998 to November 1999 to study the spatial distribution of eggs and larvae of European hake off Catalonia (NW Mediterranean Sea). Also CTD casts to record hydrographic parameters were carried out on a closely spaced station grid. Merluccius merluccius eggs and larvae appeared mainly in late spring, summer and autumn surveys and were very scarce in winter. Strong differences in terms of egg and larval densities were observed between the two November surveys, which could be attributed to the anomalous hydrographic situation during November 1998. M. merluccius egg and larvae were mainly distributed over the continental shelf, with peak abundances between the 100 m isobath and the edge of the shelf. On the evidence of larval size frequency distributions in the different sampling sectors and the closely overlapping distribution patterns for the eggs and the adult spawning stock, drifting of hake eggs and larvae was not a major factor. The larval distribution extended only slightly further offshore than the egg distribution. Using the hydrographic information and the larval distribution data, an attempt was made to relate the different seasonal productivity levels over the spawning period and the distribution of the larvae.

Spawning of the chilean hake (&lt;i&gt;Merluccius gayi&lt;/i&gt;) in the upwelling system off Talcahuano in relation to oceanographic features

Previous studies have shown that the upwelling area off Talcahuano, in central-south Chile, is an important spawning zone for the hake Merluccius gayi . We document the results of a study designed to assess the importance of oceanographic features on the horizontal and vertical distribution of hake eggs and larvae. Ichthyoplankton samples and oceanographic data (CTDO casts, and wind speed and direction) were collected during a cruise carried out off Talcahuano (36o22´S-37o10´S) in early spring (October 1996), which included a grid of 61 stations up to 60 nm offshore. The oceanographic information obtained revealed the presence of an upwelling plume at Lavapie Point (southern zone) extending northward over the shelf, and the presence of a warmer water parcel close to shore in the northern area. Peak egg densities occurred in this northern area over the shelf, in a nucleus located at the shoreward moving deeper layer (40-100 m deep) and associated with the upwelling front about 20-30 nm from shore. The highest larval abundance also occurred in the northern area over the shelf and in the deeper layer but closer to shore than the egg nucleus. Because the timing (early spring) and location of spawning (at depth, over the shelf and in association with frontal structures) are also shared by other hake species in upwelling areas, we propose that they may be part of a more commonly developed strategy to enhance offspring survival in coastal upwelling areas of eastern boundary currents.

Interaction between Cape hake spawning and the circulation in the northern Benguela upwelling ecosystem

Cape hake in Namibian waters are demersal and mesopelagic spawners, spawning peaking offshore between 100 and 400 m deep, depending on local environmental conditions. The cross-shelf circulation, low-oxygen layers and mesoscale gyres are three important environmental factors influencing hake spawning behaviour and subsequent transport of the spawning products. Normally, hake spawn offshore near the bottom at depths of 150–400 m. However, during one cruise, spawning was concentrated below several subsurface mesoscale gyres, resulting in reduced dispersion of the eggs and larvae. When the low-oxygen layer above the bottom is pronounced, hake spawning has been observed close to the top of the layer at oxygen concentrations as low as 0.2–0.3 ml l -1 . The relatively small size of the eggs and their high specific gravity make them ascend quite slowly from the spawning depths, 10–40 m per day. Consequently, hake eggs spawned deeper than 200 m hatch before they reach the upper mixed layer. The newly hatched larvae are relatively undeveloped, without functional eyes or mouth, and display little swimming activity during their first hours, but laboratory observations have revealed subsequent periods of downward swimming activity. Based on current field observations, on buoyancy measurements of eggs and larvae and on observed larval behaviour, it is concluded that hake eggs and larvae are transported onshore by features of the upwelling subsurface circulation that compensate for offshore movement of surface water. This may be the basic mechanism concentrating early juvenile hake nearshore. Spawning activity near the low-oxygen layer might be a behavioural adaptation to minimize egg predation, because few other species are expected to survive such low concentrations of oxygen. Keywords: buoyancy, eggs, larvae, recruitment processes, retention, vertical distribution African Journal of Marine Science 2001, 23: 317–336

Spatial and temporal distribution of European hake, Merluccius merluccius (L.), eggs and larvae in relation to hydrographical conditions in the Bay of Biscay

The distribution patterns for hake eggs and larvae were determined by analysing samples collected on 12 cruises in the Bay of Biscay from February to June both in 1983 and 1995. The majority of the eggs and larvae were found in late winter and early spring. The expected northern displacement of both hake eggs and larvae as the season progresses was observed only in the case of larvae. A particular spatial pattern of larval distribution was found. Small larvae (2–4 mm) were found close to the spawning grounds at the shelf break. Mid-size larvae (4–8 mm) showed a more widespread distribution from the continental shelf and to areas well beyond the shelf break. Finally, the biggest larvae sampled (>8 mm) were recorded only on the continental shelf. This pattern seems to be a consequence of the combined action of different mechanisms. Wind-induced transport in the Ekman layer favoured an onshore transfer in 1983, whereas prevalent wind and geostrophic circulation favoured a northern, onshore transfer in 1995.

Early life history and spawning ofMerluccius capensiscastelnau in the northern Benguela Current

The eggs and the larval development of hake Merluccius capensis from the Benguela Current are described. The abundance and distribution of hake eggs and larvae found during several surveys made to northern Namibia between 1979 and 1981 at different times of the year are also given. Hydrographic relationships are discussed. Temperature and dissolved oxygen were found to be the parameters most significantly influencing the distribution of hake eggs and larvae. It is apparent from the literature that hake tend to have fixed spawning areas and seasons and that they have fairly well defined migratory habits at spawning time.