Prudhoe Bay causeways and the summer coastal movements of arctic cisco andleast cisco

Catch-per-unit-effort and mark-recapture data collected by fyke net during the summers of 1985-93 near Prudhoe Bay, Alaska, were analyzed to determine whether two oil industry causeways constructed perpendicular to the Beaufo rt Sea coast, West Dock and the Endicott Causeway, affected the feeding and migratory patterns of least cisco (Coregonus sardinella) and arctic cisco (C. autumnalis). During two of the four years in which juvenile least cisco were abundant in the study area, catch rates were significantly lower (p l ess than or equal to 0.0005) east of West Dock, which suggested that small fish traveling eastward along the coast failed to bypass the causeway. Hydr ographic conditions were generally consistent with the hypothesis that caus eway-induced upwellings of saline marine water immediately west of West Doc k may affect alongshore movement. No such disparities in catch were observe d at the Endicott Causeway. We studied rates of return for subadult and adu lt (greater than or equal to 250 mm) arctic cisco and least cisco tagged in the Prudhoe Bay area and recovered in a commercial fishery that operates i n the Colville River, Alaska. The expected rate of return was compared with actual rates of return over five years (for least cisco) and six years (fo r arctic cisco). Rates of return were based upon three areas of release: ea st of the easternmost causeway, west of the westernmost causeway, and betwe en the two causeways. For both species, across the three regions and all ye ars, there was no significant difference (p = 0.25 for least cisco; p = 0.3 0 for arctic cisco) between the expected and actual rates of tag returns. T he contrasting effects of the two causeways are discussed in terms of their design and location.