Mackerel (Scomber scombrus) eggs parasitized by Ichthyodinium chabelardi in the north-east Atlantic: an overlooked source of mortality (original) (raw)
Related papers
Egg and larval distributions of seven fish species in north‐east Atlantic waters
2007
ABSTRACT The distribution of egg and larvae of mackerel, horse mackerel, sardine, hake, megrim, blue whiting and anchovy along the European Atlantic waters (south Portugal to Scotland) during 1998 is described. Time of the year, sea surface temperature and bottom depth are used to define the spawning habitat of the different species.
Scientia Marina, 2012
The spatial distribution of eggs and larvae of three pelagic species, mackerel, horse mackerel and sardine, in the Bay of Biscay was studied in 1998, 2001 and 2004. The spatial distribution was clearly different between the years studied and corresponds quite precisely to different water circulation regimes. Mackerel and horse mackerel larvae are more affected by the prevailing currents than sardine, as their spawning grounds are located offshore, far from the shelf break where the current velocities are higher. Survival rates for mackerel and horse mackerel were higher in 2001, when the offshore larval transport was stronger. However, for sardine, the mortality rate hardly varied between years. The abundance of 25-day-old larvae, considered as an index of the survival rate, appears to be a good recruitment indicator, at least for 1998, 2001 and 2004. Our results did not support the hypothesis of Bakun (1996), which states that dispersion of early life stages towards open ocean waters should cause high larval mortality. At least under the conditions observed for the years studied, the retention of larvae offshore appears to have a positive effect on larval growth and/or survival.
Effects of temperature on development and mortality of Atlantic mackerel fish eggs
Fisheries Research, 2006
The development of Northeast Atlantic mackerel (Scomber scombrus) eggs, obtained from artificial fertilisation during the spawning season in the Biscay Bay area, was monitored at five temperatures (ranging from 8.6 to 17.8 • C). The times to intermediate stages (III-V) and total hatching, obtained in this study, agree with the results of previous studies undertaken some years ago. However, the times over stages IA, IB and 50% hatching indicate that development rates differed significantly between the studies; this could be related to an effect of the previous thermal history of the eggs, or to experimental biases. Daily mortality (Z) during the embryonic period was found to vary between 0.17 and 0.38, using traditional exponential decay models. The estimates of mortality rate were found to range consistently with those derived from previous studies on Northwest Atlantic mackerel eggs without predation. However, the shape of the survivorship-curve during the development pursued in this study has indicated that mortality is not constant in time. Similarly, the suitability of an exponential model to describe daily mortality should be considered.
Mackerel and horse mackerel egg surveys are carried out triennially since 1977 in the NE Atlantic with multinational participation. The principle of the survey is to relate the quantities of freshly spawned eggs in the water column to the number of parental animals, thus rendering a direct estimate of the spawning stock biomass. Since spawning in these species occurs over a long period of time and is distributed over a very large area, the northern and southern spawning areas have to be sampled sufficiently and repeatedly during the entire spawning period (Annual Egg Production Method). In spite of the great sampling effort some areas (transects) are sometimes not or not adequately covered. The question arises, whether sampling effort could be reduced in favour of modelling missing stations and/or transects instead. The accuracy of the forecast, however, depends on the initial sampling accuracy. To test this, the spatial structure of the egg concentrations was analysed and modelled ...
Helgoland Marine Research, 2001
Short-term variability in vertical distribution and feeding of Atlantic mackerel (Scomber scombrus L.) larvae was investigated while tracking a larval patch over a 48-h period. The patch was repeatedly sampled and a total of 12,462 mackerel larvae were caught within the upper 100 m of the water column. Physical parameters were monitored at the same time. Larval length distribution showed a mode in the 3.0 mm standard length (SL) class (mean abundance of 3.0 mm larvae x =75.34 per 100 m 3 , s=34.37). Highest densities occurred at 20-40 m depth. Larvae <5.0 mm SL were highly aggregated above the thermocline, while larvae ≥5.0 mm SL were more dispersed and tended to migrate below the thermocline. Gut contents of 1,177 mackerel larvae (2.9-9.7 mm SL) were analyzed. Feeding incidence, mean number (numerical intensity) and mean dry weight (weight-based intensity) of prey items per larval gut were significantly dependent on larval size. However, while weight-based feeding intensities continued to increase with larval length, numerical intensity peaked at 4-4.9 mm SL, indicating a shift in the larval diet. While first-feeding larvae relied most heavily on copepod nauplii and eggs, larvae ≥5.0 mm SL initiated piscivorous feeding. All identifiable fish larvae were Atlantic mackerel. Thus, the piscivory was cannibalism. Larval feeding incidence and numerical feeding intensities peaked during daytime and were reduced at night. Daily ration estimates for first-feeding mackerel larvae <4.0 mm SL were extremely low x =1.43% body dry weight, but increased dramatically at 5.0 mm SL, i.e., at the onset of cannibalism, reaching >50% body dry weight in larva ≥8.0 mm SL.
Bluefin tuna egg and larval survey in the Balearic Sea, June 2001 (TUNIBAL 06/01)
2001
At its 2000 meeting in Madrid (Spain), the SCRS endorsed s everal research activities considered essential to the future of the BYP. The SCRS recommended exploratory research sampling of larvae and spawning sized bluefin tuna and the associated oceanographic conditions in the central Atlantic as outlined in SCRS/00/125, as well as, in the Balearic Islands region. The present document outlines the research proposal formulated by the Instituto Español de Oceanografía (IEO) focused on a bluefin tuna egg and larval survey (TUNIBAL 06/01) to carry out off the Balearic archipelago during June of this year, together with associated research activities related to the characterization of the bluefin tuna spawning environment, as well as, on its fishing fleet activities. A discussion guide for certain standardizing elements is also provided. RÉSUMÉ Lors de sa réunion de 2000 à Madrid, Espagne, le SCRS a entériné plusieurs activités de recherche qui étaient jugées essentielles pour l=avenir du BYP. Le SCRS a recommandé la recherche par un échantillonnage expérimental de larves et de thons rouges de la taille de géniteurs, ainsi que des conditions océanographiques associées dans l =Atlantique central, comme l=exposait le document SCRS/00/125, ainsi que dans l=archipel des Baléares.
Canadian Journal of Fisheries and Aquatic Sciences, 2008
We provide evidence that variation in location and timing of spawning of Atlantic cod, Gadus morhua, has a major impact on occurrence, distribution, and development of eggs and larvae in a large embayment on the south coast of Newfoundland. Atlantic cod egg densities, measured with a series of ichthyoplankton surveys in Placentia Bay during the spawning and postspawning seasons of 1997 and 1998, were highest during the early spring of both years and decreased through the spring and summer. Egg development stages and larval size suggest that eggs and larvae were released from spawning locations within the bay and developed as they were transported in cyclonic flow from the southeast and around the bay towards the southwest, where late-stage eggs and larvae were found to be most abundant. Although egg densities were generally lower in 1998, late-season egg production during the summer of 1998 was elevated in relation to 1997, providing a possible explanation for the observation that larval total densities were more than an order of magnitude higher in 1998 than in 1997. In terms of larval production, late spawners may be particularly important to successful egg hatching in the coastal waters of Newfoundland.
Maturity and spawning of Atlantic chub mackerel Scomber colias in M’diq Bay, Morocco
2020
Knowledge of reproductive parameters is necessary to understand the ecology, the population dynamics and to enable rational management of fish of economic interest. This work is a contribution to the study of some aspects of the reproductive biology of the Atlantic mackerel Scomber colias (Gmelin, 1789) in the Mediterranean Moroccan coast. The study is based on samples taken from commercial catches in M’diq Bay. The spawning period was determined following both the monthly changes of the gonadosomatic index and the histological maturity stages. The Atlantic chub mackerel spawn between November and March, with maximum activity in December.
Continental Shelf Research, 2015
The value of the Continuous Plankton Recorder (CPR) fish larvae dataset, with its extensive spatiotemporal coverage, has been recently demonstrated with studies on long-term changes over decadal scales in the abundance and distribution of fish larvae in relation to physical and biological factors in the North Sea. We used a similar approach in the west and southwest area of the UK shelf and applied a principal component analysis (PCA) using 7 biotic and abiotic parameters, combined with Hierarchical Cluster Analysis (HCA), to investigate the impact of environmental changes in the west and southwest area of the UK shelf on mackerel larvae during the period 1960-2004. The analysis revealed 3 main periods of time () reflecting 3 different ecosystem states. The results suggest a transition from an ecosystem characterized by low temperature, high salinity, high abundances of zooplankton and the larger phytoplankton groups, to a system characterized by higher temperature, lower salinities, lower abundances of zooplankton and larger phytoplankton and higher abundances of the small phytoplankton species. Analysis revealed a very weak positive correlation between the Second principal component and mackerel larvae yearly abundance, attributed to the North Atlantic Oscillation (NAO). The results presented here are in broad accord with recent investigations that link climatic variability and dynamics of mackerel reproduction. However, the growing body of literature that documents statistical correlations between environment and mackerel needs to be supplemented by local process studies, to gain more insight and to be able to predict mackerel response to climate change scenarios. Utilising the strength of the CPR dataset, namely its unique temporal coverage, in an analysis where other data (such as egg surveys) are drawn in to compensate for the spatial issues could prove to be the way forward. Crown