|Title||The European anchovy (Engraulis encrasicolus) increase in the North Sea|
|Source||University. Promotor(en): Adriaan Rijnsdorp, co-promotor(en): Mark Dickey-Collas; Leo Nagelkerke. - S.l. : s.n. - ISBN 9789461736826 - 207|
Aquaculture and Fisheries
|Publication type||Dissertation, internally prepared|
|Keyword(s)||ansjovissen - engraulis - voedingsgedrag - populatiegroei - populatiedynamica - visserijbiologie - mariene ecologie - noordzee - anchovies - feeding behaviour - population growth - population dynamics - fishery biology - marine ecology - north sea|
|Categories||Marine Ecology / Pisces|
Small pelagic fish such as anchovy are of high socio-economic importance worldwide. They are known for strong fluctuations in abundance, for which the mechanisms are not always understood. European anchovy (Engraulis encrasicolus) increased its population in the North Sea starting in the mid-1990s while previously it was found in more southern waters in Europe. Changed food availability (resulting from plankton changes) or changed habitat availability (due to warmer waters) seemed likely candidate explanations for this increase, based on understanding of the species’ general ecology.
In order to compare the two likely explanations, first, the food of anchovy in the North Sea had to be determined. Analysing the contents of anchovy stomachs and comparing the results with other similar fish (herring and sprat), it appeared that anchovy was a generalist feeder. Observed patterns of anchovy distribution in fisheries surveys were compared to relevant environmental factors related to food availability and temperature. This showed that temperatures experienced by anchovies in the first months after birth was a better explanation for how many anchovy were caught than any measure of food availability was. Modelling their body growth in those months showed that during the past decades, the conditions for juvenile growth improved, probably leading to better overwinter survival.
This doctoral thesis contributed to an increased understanding of the ecology of anchovy in the North Sea, and the insights gained can support studies of small pelagic fish in other systems of the world where fisheries scientists wish to integrate more ecological understanding into their management practice.