Effects of Spawning Location on Transport to Juvenile Nursery Areas: Animated Results of a Biophysical Model

S. Hinckley, AFSC & A.J. Hermann, PMEL/JISAO

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Why does a population of walleye pollock spawn at the exit of Shelikof Strait each spring? One hypothesis is that this population evolved to optimize physical transport to the juvenile nursery area near the Shumagin Islands 375 km to the southwest. Alternatively, factors other than physical transport (e.g. density of prey) may be significant.

We addressed these hypotheses with the coupled suite of physical and biological models, driven by winds and runoff appropriate to two years of good recruitment, 1978 and 1994. Five spawning regions and four spawning times were considered. Spawning regions 1-5 are indicated on the figure; spawning times are Early (mid-February), Middle (early April), Late (late May), and Very Late (mid-July). "1-Middle" represents the typical observed spawning time and location.
  • Click on map locations 1-5 to see how spawning location affects early life history for fish spawned in early April 1994
  • Click anywhere else on the map to view the modeled circulation during 1994
Initial locations of spawned populations in the experiment. Transport of fish to the juvenile nursery area promotes successful recruitment for a given year.

Results show that fish spawned to the south of Kodiak Island (e.g. 3-Middle) or much earlier or later than the observed spawning period (e.g. 1-Very Late) do not reach the Shumagin Island nursery area as juveniles by early September. However, the region and time of spawning which did allow successful transport to the nursery area (e.g. 4-Late) was much broader than the observed region and time. Hence factors other than physical transport alone must be considered to explain the spawning location and timing of this stock.
  • Click on individual images to watch selected regions and times:

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Funding support provided by NOAA Fisheries Oceanography Coordinated Investigations
and Coastal Ocean Programs