Stock assessment of eels in the Baltic: reconciling survey estimates to achieve quantitative analysis

• The data from two scientific surveys, where eel is part of the catch, have been studied to assess trends in recruitment and escapement to and from the Baltic. Abundance of juvenile eel was monitored in the Sound, between Sweden and Denmark, from 1992 to 2002. The total natural recruitment of new eels was estimated under the assumption that the number of juvenile eels observed in the surveys represented an accumulation of eels migrating into the Baltic. To assess the total recruitment, the stocking by imported glass eels, or transplanted juveniles from outside the Baltic, was added. Fish larvae monitoring at a nuclear power plant in the Kattegat gave an index of glass eel abundance which was well correlated with glass eel monitoring in the Sound. This was used to extrapolate the recruitment time-series to the full period from 1981 to the present. The main conclusions from the analysis were: (i) the recruitment to the Baltic region, including the contribution from stocking, has declined by 95% between 1981 and 2012. (ii) The stocking of glass eel and bootlace eel has been of the same order of magnitude as natural recruitment, averaging 25-30% of the total supply of glass eel to the Baltic, with a decreasing trend with time. (iii) The total landings in the Baltic countries have ranged from 5 to 15% of the estimated survival without anthropogenic mortality. This proportion has been stable and independent of a large decrease in potential escapement.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Fisk- och akvakulturforskning (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Fish and Aquacultural Science (hsv//eng)

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

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