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Influence of Mesoscale Eddies

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Influence of coastal-origin mesoscale eddies on ichthyoplankton assemblages in the Gulf of Alaska

Liz Atwood

Ocean conditions can potentially impact fish species with drifting early life history stages. Mesoscale eddies formed along the continental shelf of the Gulf of Alaska (GOA) during winter and spring are large and ubiquitous, facilitating cross-shelf water exchange. These mesoscale eddies may facilitate transport of early larval stages of fish from shelf to slope.

I am examining the relationship between ichthyoplankton (eggs, larvae, juveniles) and mesoscale eddies propagating along the GOA shelf break. In a multi-faceted approach, I am first examining ichthyoplankton assemblages from three well-characterized eddies (Haida, Sitka, and Yakutat) that were sampled in 2005. I will compare ichthyoplankton indices from within eddy to shelf regions using data from spring 2003. These samples will be analyzed for relative indices of diversity and abundance of eggs, larvae, and juveniles of species within each eddy.

Using historical altimetry data (1993 – present), I propose to reconstruct a time series of eddy presence in the western GOA (particularly in the Kodiak Island – Shelikof Strait region) to characterize annual eddy seasonality, strength, frequency, and persistence in the western GOA. I will then look at correlations between eddy properties (timing, magnitude, frequency, propagation direction) and annual abundance estimates of ichthyoplankton collected over the continental shelf in the same region.

Resulting patterns will be modeled to describe the relationship between life history of shelf-spawning species and mesoscale eddy dynamics. Results will help determine whether eddies are a source of larval exchange between the continental shelf and slope, and elucidate mechanisms that could be applicable to other, less well characterized areas such as the Bering Sea.

Nets on Deck of the NOAA Ship Miller Freeman
Sea Level height Anomaly (SLA, in cm) from AVISO tracks over the northeastern corner of the Gulf of Alaska, during a cruise study in 2002. Sample locations are marked by black hatches, and an anti-cyclonic eddy is evidenced by the positive SLA in red.

This research is being conducted in collaboration with Dr. Janet Duffy-Anderson (RACE/NOAA) and Dr. Carol Ladd (PMEL/NOAA). The work is sponsored by research grants with North Pacific Research Board (NPRB) and Alaska Fisheries Science Center (AFSC), and a student scholarship from NPRB.

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