Effects of oil-laden sediments on behavior and growth of juvenile flatfishes

Abstract

Three species of juvenile Pacific flatfishes: yellowfin sole (Pleuronectes asper), rock sole (P. bilineatus), and Pacific halibut (Hippoglossus stenolepis) were exposed to sediments contaminated with Alaska North Slope crude oil to determine the behavior and growth of juveniles in polluted nursery grounds. Responses were correlated with known biomarkers of toxicant exposure. In the behavior experiments, fish exhibited a strong preference for fine grained sediments ($<$500 microns) when presented with eight different sediment types ranging from mud to pebble. Juvenile yellowfin sole showed a preference for mud and mixed mud substrate, rock sole preferred sand substrates and halibut chose both mud and sand sediments. Flatfishes were able to detect and avoid heavily oiled (1400 $\mu$g/g total petroleum hydrocarbons-TPH) sediments but did not avoid sediments at oil concentrations of 400 $\mu$g/g TPH. Among yellowfin sole and rock sole, sediment preference altered behavioral response to oil whereas halibut did or did not avoid oil irrespective of sediment type. If flatfish do not avoid oil concentrations of 1600 $\mu$g/g and higher on preferred sediment, growth reductions occur. Fish reared on oiled sediment grew slower than controls on non-oiled sediments. Growth reductions in all three species were significant following 30 days of exposure to 1600-1800 $\mu$g/g TPH and became more pronounced over time. As the toxicant concentration or the length of exposure increased, growth per day decreased. By 90 days of exposure, fish exposed to 1600-1800 $\mu$g/g TPH grew 38-57% slower than controls. Halibut had the greatest change in growth rate following oil exposure. Exposure of halibut to sand laden with 4700 $\mu$g/g total hydrocarbons resulted in an 93% reduction in growth in 30 days. Condition factor was also most reduced in halibut. Changes in tissues and parasites indicated a reduction in fish health for all three species. There was an increase in fin erosion, liver lipidosis, gill hyperplasia and hypertrophy, and gill ciliate infestation combined with a decline in macrophage aggregates and gut parasites. Chronic marine oil pollution that results in hydrocarbon concentrations of 1600 $\mu$g/g in nursery sediments has the potential to reduce growth and health of juvenile flatfishes. Recruitment of juveniles to the fishery would be reduced due to increased susceptibility to predation and slower growth to maturity.