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This thesis aims to contribute to a better knowledge of several aspects of the biology of L. piscatorius, namely biometry, growth and reproduction. The different subjects in this thesis were studied by examining fresh material obtained from commercial landings and research vessel surveys. L. piscatorius presents significant biometric differences between sexes (at 99% level of confidence). Small males are heavier than females of the same size. Conversely, large females are heavier than males of the same size. Attempts to estimate L. piscatorius' age were made using otoliths. Three other hard structures were used to ascertain consistency of the age readings: vertebrae, illicia and teeth. All structures showed seasonal growth increments. However, these growth increments were easier to interpret in vertebrae. Illicia sections were the most difficult structure to interpret. Although all structures chosen presented many sub-annual checks, illicia displayed them more closely than the others; making age readings more difficult. Teeth were considered inadequate for age readings because they may not be permanent structures. The accuracy and precision of age readings in otoliths were not determined; firstly, the real age of each fish was unknown. Secondly, there was no other independent reader to test precision between readers. The age readings in sagittae were validated and indirectly by back calculation, edge formation and marginal growth. The results obtained from age readings in otoliths were used to directly estimate growth parameters for L. piscatorius by sex. The study of the general morphology and histology of the gonads showed that L. piscatorius have unusual gonads. The testes are tubular, and bean shaped in transverse section while ovaries are confluent and form a single, flattened tube.

A total of 6512 specimens of Loligo forbesi Steenstrup (Cephalopoda : Loliginidae), obtained from Scottish fishing ports and research vessels during 1984/86, was used to investigate aspects of fishery biology of the species in Scottish waters. L. forbesi exhibits sexual dimorphism in size, males had a larger overall mean size (DML, weight) than females, and for each sex the mean size was larger in those from the north-eastern Atlantic than in those from the North Sea. In length-weight relationship, females had a higher regression slope than males and this relationship for squids from Rockall was significantly different to those from the North Sea. Multivariate analyses on measurements of body parts showed that Rockall squid, also, exhibited less variation in body form but distinct differences from those of the west coast and North Sea. Recruitment of L. forbesi occurred during April/May and November/December, the monthly growth rate after recruitment varied between 12.5 to 28.6mm DML/month for males and 12.5 to 17.5mm DML/month for females; for each sex the November/December cohort had lower growth rate. The logistic growth model best fitted the progression of modes of monthly length frequencies. Age determinations estimated from statolith markings varied from under 3 months for 30mm DML individual to 28 months for 571mm DML male individual. Sex ratio in L. forbesi varied significantly from 1:1 throughout the year with males exceeding females except during winter when the number of females may be equal to/or more than males. Mean size at maturity was 205mm DML for males and 192mm DML for females. Spawning occurred during December to March and the peak spawning period occurred in February throughout the study area. In this species, maturity coefficient and gonad-somatic index were the best indices for identification of spawning season. Fecundity is related to size and the average number of eggs per female was 6500.High proportions of specimens with 'empty' stomach were observed during the winter. The prey of L. forbesi was fish, crustaceans, molluscs and polychaetes in decreasing order of incidence. Identified fish prey were Argentina sphryaena, Trisopterus esmakii, Merlangius merlangus and Ammodytes sp.

In 1971, the European Communities introduced a Common Fisheries Policy (CFP), which was more fully developed in 1983. Its success remains largely questionable because it has failed to conserve fish stocks, has been unable to tackle the problem of vessel overcapacity or to generate rents from the fishery resource. This thesis presents an overview of the main components of the CFP and assesses their impact on different aspects of the fishing industry. The economic and biological knowledge on which the fisheries management is based has been evaluated and a management scheme for reforming the CFP is proposed. The thesis initially surveys the literatures in fisheries economics and in fish population dynamics. These should provide the basis for efficient management, and their role is evaluated. European Community institutions and the procedures which are involved in the policy formation are examined. Particular attention is paid to the evolution of the legislative framework of the Common Fisheries Policy from its establishment to the latest developments. The work evaluates the main constituent parts of the CFP, whose objectives are the rational development of the production factors, a fair standard of living for the producers, a stable market and the availability of supplies for consumers. The main conclusions reached are that the policy has been consistent with a decline in fish stocks, an increase in vessel capacity, a failure to stabilise market prices and a decline in the average fisherman's income. These outcomes can be attributed largely to an inadequate policy framework, which ignores the main conclusions of fisheries economics, and to an inadequate system of information gathering and of policing the regulations.

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