HYDROCARBON CONCENTRATIONS IN THE NORTHERN NORTH-SEA AND EFFECTS ON FISH LARVAE

Two surveys were carried out in 1993 and 1994 to measure the concentra tions of oil in water and the associated effects on fish larvae along two north-south sections (between 57.00 degrees N and 62.00 degrees N at longitude 0.0 degrees E and 1.5 degrees E) through the northern Nor th Sea. At each station occupied hydrocarbon concentrations were logge d continuously from a towed in situ fluorimeter attached to a MIKT net used to sample larvae and deployed on an oblique tow from surface to bottom. The results show a distinct north-south gradient in hydrocarbo n concentration peaking around installations associated with oil and g as exploration and production. Depth averaged data show that the mean concentration in the top 50 m was between 3 and 4 mu g l(-1) at latitu des between 56.00 and 59.00 degrees N falling to values as low as 0.2- 0.5 mu g l(-1) in the more pristine waters to the north and west. The hydrocarbon levels in the top 50 m between 56.00 and 59.00 degrees N w ere elevated compared to those in deeper water. 7-Ethoxyresorufin 0-de ethylase (EROD) activity was measured in pooled samples of both sandee l and gadoid larvae. For both species the range of EROD activities was large and variable and this is probably due to damage to larvae assoc iated with capture and subsequent denaturation of the enzyme. Despite this the results show elevated EROD activity in samples taken on the s outhern end of the transect where hydrocarbon fluorescence in the wate r was highest and there is a significant regression of EROD activity o n hydrocarbon concentration. The results therefore suggest a significa nt elevation of hydrocarbons in a large area of the northern North Sea (5-10 times the true background) and that these concentrations are ca pable of inducing biological responses associated with deleterious eff ects in fish larvae.