Fishing, abundance and life history traits of the anadromous sea lamprey (Petromyzon marinus) in Europe

Among the rivers along the European coast that are still colonized by the sea lamprey (Petromyzon marinus), the Garonne Basin have the largest population of this species. This basin supports the largest fisheries of sea lamprey in France and certainly in Europe. In this article we provide data on the exploitation, the abundance and some life history traits both on the Garonne basin and at the European scale.The mean catch of the Garonne basin, over the period 1985–2003, is 72 t, confirming the top rank of the Garonne Basin sea lampreys population and of its fisheries. Abundance is estimated using a generalized linear model (GLM) on catch per unit of effort (CPUE) for the 1943–2005 period. Sea lamprey abundance appears to have peaked strongly between 1952 and 1970. From 1973 onwards, the trend is stable and abundance was only 35–40% of the maximum level. Since the end of the 1990s, the CPUE has shown a strong increase—a sign of an upward trend in lamprey abundance. This recent trend is confirmed by three other European time series gathered for this study. However a review of the official status of sea lampreys in many European countries shows that this species is still considered to be in decline.A literature review is made and shows that European sea lamprey exhibit an unusual latitudinal variation, with longer animals in the south and an increasing trend of its length at maturity over the years. A focus on Garonne Basin shows stable and distinct life history traits of adult sea lampreys in the two main rivers of the basin, including length and weight at maturity, length–weight relationship, and female gonad weight. However, the sex ratio shows a slight excess of females in both rivers that seems to be typical of a well-established population of European sea lampreys. Hypotheses explaining differences in the life history traits are discussed, including the possibility of homing in the European sea lamprey, but none of them was fully adequate. We advocate fully addressing the issue of homing in the case of anadromous sea lampreys since this issue can have important consequences on the management of European stock(s).