Market Sampling of Landings of Commercial Fish Species in the Netherlands in 2002

This report contains information on the biological sampling for the market sampling program: which species are sampled, how they were caught, when and where the samples are taken (date and position), how many fish have been measured, how many fish have been aged, etc. The report gives an overview of all the biological sampling activities in 2002 by RIVO on the landings of the commercial important species of herring, mackerel, horse mackerel, blue whiting, greater argentine, sole, plaice, turbot, brill, dab, lemon sole, cod, whiting, Norway lobster and four different species of rays from all ICES areas. This biological sampling took place on landings by both the Dutch fleet as well as foreign fleets landing in the Netherlands. In addition this report contains information on the biological samples collected during research vessel surveys and discard trips both on commercial and non-commercial species

Horse mackerel fecundity in relation to lipid content

During the 2004 mackerel and horse mackerel triennial egg survey fecundity of horse mackerel (Trachurus trachurus L.) was estimated using a new gravimetric and image analysis system. The fecundity estimates and mean oocyte diameters showed great variation between and within different institutes. Horse mackerel fecundity increased during the spawning season and showed no decline at the end of the spawning season. This indicates that this species is likely to be an indeterminate spawner. The lipid content was estimated from whole horse mackerel collected during the three months prior and during the spawning season. Lipid content rapidly decreased during the period of ovary development prior to the onset of spawning, but remained rather constant during spawning. A relationship between fecundity and lipid content could not be found. A time series of lipid content estimates collected annually or triennially might provide an index for changes in fecundity over time. Sampling needs to be carried out prior to the onset of spawning, when fat content is at its highest. Annual stomach content estimates collected in successive years might provide an index for food availability and feeding success. The stomach analysis carried out in 2004 indicated that horse mackerel was feeding only at a low level during the spawning perio

Egg and larval distributions of seven fish species in north-east Atlantic waters

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. Mackerel, horse mackerel, and sardine eggs and larvae presented the widest distribution, whereas megrim and anchovy showed a limited distribution, restricted to the Celtic Sea and the Bay of Biscay respectively. Correspondingly mackerel, horse mackerel and sardine showed the highest aggregation indices. Blue whiting larvae were found at the lowest temperatures, whereas anchovy eggs and larvae were found in the warmest waters. The analysis is a basis for evaluation of ongoing changes in the pelagic ecosystem of the north-east Atlantic