Effects of coastal circulation on the distributional patterns of pelagic juvenile fishes and otolith chemistry, and on the timing of juvenile reef fish settlement.

摘要

In three studies, I examined water masses and ocean current variability to elucidate some effects of coastal circulation on the distributional patterns of pelagic juvenile fish and otolith chemistry, and on the timing of juvenile reef fish settlement. In the first study, I found a strong link between coastal mesoscale flows and the spatial abundance patterns of juvenile and late-stage larval fishes. Surface currents observed by high frequency radar and concurrent CTD sampling during midwater trawling surveys in the Santa Barbara Channel region suggest that interannual abundance variations were linked to circulation that produced significant retention of fishes in 1998, but not in 1999. Findings indicate that cyclonic eddy circulation, when persistent, retains small fishes within a local area. Such features may help offset large scale declines in populations. From an ecological perspective, these fishes are forage for seabirds, marine mammals, and piscivorous fishes. In the second study, I found that fish from distinct coastal water masses possessed unique otolith elemental signatures. I used in situ temperature and salinity measured at the time pelagic juvenile fish were sampled to identify water masses. Chemistry of the most recent growth zone in the otolith not only differentiated fish collected in different water masses from distant areas spanning nearly 500 km within the California Current System, but also discriminated individuals that resided in different water mass environments associated with eddy circulation within the Santa Barbara Channel (first study). I discuss how phenomena associated with the 1997-1998 El Nino and eddy circulation may have affected coastal ocean conditions and variation in otolith chemistry. In the final study, I used water mass dynamics and ocean current variability observed during the settlement of juvenile fishes at oil platforms in the eastern Santa Barbara Channel to reconstruct recent transport pathways taken by the recruits. Results indicate that currents from the Southern California Bight, rather than from Central California, supplied recruits to settlement habitat. I concluded that remote sources, particularly from the Bight, subsidized local fish populations in the eastern Channel given the broad spatial scale of ocean currents over the course of the pelagic early life history.