The commercial exploitation of a protected anadromous species, the river lamprey (Lampetra fluviatilis (L.)), in the tidal River Ouse, north-east England

Abstract

1. Throughout Europe, populations of anadromous fish and lampreys have declined over the past centuries due to human activities. River lamprey Lampetra fluviatilis are representative of such species and are listed in international conservation agreements. 2. Historic (1908-09 to 1913-14) and modern (1995-96 to 2003-04) data were available on commercial catches of river lampreys in the tidal Ouse, north-east England. During 2003-04, additional traps were operated by the University of Durham, downstream of the commercial fishery. 3. Catch per unit effort (CPUE) in the modern commercial fishery showed considerable variation between fishing seasons, ranging from a median CPUE of 0.5 lampreys per trap per day in 2000-01 to a median of 22.3 lampreys per trap per day in 2003-04. 4. The estimated catch of adult river lampreys each season in the historic fishery ranged between 25 500 (1913-14) and 54 500 (1910-11). Recent catches tended to be smaller, with a minimum catch of 9083 lampreys (2000-01) and a maximum of 30 992 lampreys (2003-04). 5. CPUE increased with discharge, up to a point above which CPUE declined with further increase in discharge. Migratory activity may be reduced at high flows and not stimulated at low flows, although the fishing efficiency of the traps themselves was probably reduced during high flows. 6. Samples of river lampreys caught in the university's traps were marked and released. Based upon the number of recaptures, the absolute minimum relative exploitation level of the commercial traps, over the whole fishing season, was estimated as 9.9%. The effect of such a reduction in the spawning population upon future recruitment is at present unknown. 7. The population of river lampreys in the tidal Ouse is potentially threatened by an unregulated increase in fishing effort. Current legislation needs to be modified to allow effective fishery management.