The egg production and spawning stock size of the North Sea mackerel and horse mackerel stocks in 1988

During the period 5 April to 28 July 1988 the spawning areas of North Sea mackerel and horse mackerel were investigated by research vessels from the Netherlands, Denmark and Norway. Based on the plankton samples and temperature observations obtained during this period the egg production and spawning stock size were estimated. The total egg production of mackerel represents a spawning stock biomass of 37 000 tonnes, which is about 20 % less than the 1986 estimate. The total egg production of horse mackerel represents a spawning stock size of 110 000 tonnes

The egg production and spawning stock size of the North Sea mackerel stock in 1990

During the period 12 March to 20 July 1990 the spawning area of the North Sea mackerel was investigated by research vessels from the Netherlands, Denmark and Norway. Based on the plankton samples and temperature observations obtained during this period the egg production and spawning stock size were estimated. The estimated total egg production of mackerel (53 x 10^12 eggs) represents a spawning stock biomass of 78 000 tonnes, which is about twice the estimate in 1988

The egg production and spawning stock size of the North Sea mackerel stock in 1984

During the period 22 May to 17 July the spawning area of North Sea mackerel was investigated by research vessels from Scotland, the Netherlands, Denmark and Norway. Based on the 629 plankton samples and temperature observations obtained during this period the egg production and spawning stock size were estimated

Aggressive Incidents in Residential Youth Care

It is assumed that group climate can have an effect on aggressive behavior in adolescents living in residential facilities, but it is largely unknown whether there are climate differences between the various types of residential institutions, and whether group climate differently affects aggression incidents among adolescents placed in institutions that differ in levels of security (and openness). In current research, the differences in perception of group climate between open, semi-secure, and secure residential youth care facilities were examined as well as the association between group climate and aggression. In total, 159 adolescents (96 males, 63 females) completed the Prison Group Climate Instrument (PGCI), and (aggressive) incidents were recorded during a period of 3 months. Perception of group climate-including support from staff, group atmosphere among adolescents, possibilities for growth, and repression-did not differ between the various types of residential care, except for possibilities for growth. Adolescents in open and semi-secure institutions experienced more possibilities for growth than their peers in secure institutions. A more positive perception of group climate in open institutions proved to be related to less aggressive incidents at the living group. For semi-secure and secure institutions, no relation between group climate and aggression was found. Also, the longer adolescents stayed in residential youth care, the more aggressive incidents occurred

Growth and reproduction of horse mackerel, Trachurus trachurus (Carangidae)

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