Neocalanus plumchrus/flemingeri time-series Inner Stations

Colored box above represents the 95% confidence interval on the long-term mean abundance for May, error bars are 95% CI for each year.

Neocalansu plumchus/flemingeri stages

Distribution of Neocalanus stages collected by the multinet sampler


The three species of Neocalanus present if the Gulf of Alaska, N. flemingeri, N. plumchrus and N. cristatus, dominate the community biomass during spring and early summer. These species spawn at depth offshore of the shelf break and their young arrive at the surface to feed coincident with the spring phytoplankton bloom to feed. They pass through several life-stages until reaching the final feeding stage "copepodite-5" in late spring through early summer in the northern Gulf. At that time these gorged animals descend to depth with large lipid stores to hibernate until spawning around winter solstice.

Success of the these species in any years is driven by a combination of food availability and water temperature which governs their potential growth rate. In cold years, development is delayed, but so is the spring bloom and animals typically do well and persist later into the summer maximizing their overlap with vertebrate predators such as fish, seabirds and marine mammals. In warmer years, development is accelerated, potentially more than the bring bloom, and the bloom itself is often smaller and shorter lived. In theory, the animals complete their life cycles sooner, but the population overall does less well because food was more limited. In warm years the overlap is less extensive with with vertebrate predators.

Seward Line May cruises examine not only the size of the Neocalanus population, but the proportion of animals at each life-history stage to see how fast they have been growing. Additional experiments have directly measured growth rates. It is clear that over the last dozen years Neocalanus have experienced good and bad years. Beginning in 2007-2009 a series of cold years have significantly slowed development, while during the warm 2003, stage development was much faster, particularly for the inner stations of the Seward Line where many vertebrate predators feed.