The population biology of horse mackerel (Trachurus trachurus L.) in the North-East Atlantic.
This study investigates the population biology of horse mackerel
inhabiting the Northeast Atlantic, their spawning grounds and migrations, and the degree of stock separation, with emphasis on the Southern and Western areas of the European shelf. The investigations involved the use of a wide range of
methodologies and techniques, including age determination techniques, tagging experiments, the analysis and evaluation of commercial catch data, egg survey data, bottom trawl survey data, biochemical methods, morphometric methods, survey sampling methodology, and associated statistical analysis.
Multivariate analysis of morphometric measurements, indicate that the horse mackerel that spawn on the Portuguese shelf (Southern area) are distinct from those that spawn on the Irish shelf (Western area). A distinction can also be made between the Portuguese horse mackerel and those from the Celtic Sea, English Channel and Northern Bay of Biscay. These findings are further supported by a study of otolith first ring distance, which also indicates that the Western and the North Sea horse
mackerel are not significantly different from each other.
Growth parameters of horse mackerel from the Western and
Southern areas were estimated using length and age data and the resulting growth curves for the two areas are different. This result is primarily due to differences in the growth of the younger fish. In the Southern area the fish grow faster than in the Western area. These results provide evidence for the existence of a separate unit stock of horse mackerel off the Portuguese coast, which is reproductively distinct from other populations in the north-east Atlantic. The results froma study of plasma transferrin polymorphisms did not provide any evidence
in support of these findings. The population structure and stock separation of horse mackerel in the north-east Atlantic are described and the implications for future management are discussed