NOAA Technical Memorandum
NMFS-AFSC-132
Aspects of the early life history of capelin (Mallotus villosus) in the northwest Gulf of Alaska: A historical perspective based on larval collections October 1977 - March 1979
Abstract
Analyses of historical ichthyoplankton data collected in the vicinity of Kodiak Island, Gulf of Alaska, provide new information on the spawning strategy and early life history characteristics of capelin (Mallotus villosus) in the northeast Pacific. Ichthyoplankton surveys have been conducted by the Alaska Fisheries Science Center (AFSC) in the northwest Gulf of Alaska from 1977 to the present, primarily during spring. Time series data (1977-98) from these cruises indicate that a peak in capelin larval abundance occurs in late summer and early autumn (September-October) on the continental shelf.
Capelin larvae occur in the plankton throughout the rest of the year in low numbers, with a minimum observed from March-May. The most intensive seasonal collections of larvae were made during a 17-month period from 1977 to 1979, within four Kodiak Island bays and over the adjacent continental shelf and slope. More extensive analyses of these data concur with observed long-term seasonal patterns of abundance on the shelf and also indicate a summer peak (July-August) in larval abundance in Kodiak Island bays. Seasonal variation in abundance, length, and distribution of capelin larvae from the 1977-79 collections indicates that in 1978, capelin populations in this area spawned during the summer and autumn in inshore waters, with a peak in spawning activity during June-July.
The distribution patterns for these years suggest that subsequent to hatching and emergence into the plankton, larvae are transported from the bays and coastal zone around Kodiak Island into adjacent shelf waters, probably by tidal flushing and wind-induced surface currents. Mixing processes on the shelf seaward of Kodiak Island, reflecting variable current patterns in this area, are likely to enhance the dispersal of larvae as indicated by the uniformity observed among distribution patterns of several length categories of larvae. A comparison of larval abundance and lengths between bongo and neuston samples suggests that capelin larvae, mostly greater than 30 mm standard length, actively migrate to the surface layer. Although enhanced net avoidance by the larvae during daylight hours is a confounding factor, the observed diel variation in abundance of capelin larvae in the neuston implies that the migration to the surface layer is largely nocturnal. Our observations represent a picture of capelin early life history during a period of high adult abundance that has been linked to a cold phase in the oceanographic environment of the Gulf of Alaska.
View Online (.pdf, 3.72MB).
|
