Spatial and temporal variability in reproductive timing of Antarctic krill (Euphausia superba Dana)

Spawning dates of Antarctic krill, Euphausia superba Dana, were calculated from larval stage compositions, and corrected using data on maturity stage composition of the adult krill. Both original and literature data obtained from the Antarctic Peninsula-Bellingshausen Sea area and around the Antarctic continent were used. A time series (1975/76–1986/87) for several subareas of the Antarctic Peninsula-Bellingshausen Sea area indicates considerable variation in the krill spawning start, maxima and completion. In particular years (1975/76, 1980/81), krill spawning in the western Atlantic sector began relatively early, was intensive, and completed early. Some years (1977/78, 1981/82) were characterised by long and non-synchronised krill spawning. Compiled data sets for the Atlantic sector (1980/81), the entire Antarctic (1983/84) and the east Indian-west Pacific Antarctic waters (1981–85) reveal some spatial patterns in krill reproductive timing. In relation to spawning timing variation, the habitats of the krill population fall into five categories: (1) areas with an early beginning (late Novemberearly December) and a variable, but normally long, duration (3–3.5 months) of krill spawning; this is generally the southern boundary of the Antarctic Circumpolar Current, (2) areas with an early beginning, but a short duration of krill spawning (Gerlache Strait), (3) areas with a highly variable (within 1–1.5 months) beginning and a relatively long duration (ca. 3 months) of krill spawning (Bransfield Strait, Palmer Archipelago), (4) areas with a late beginning (late December–January) and a long duration of krill spawning (Bellingshausen Sea, D'Urville Sea, and Balleny Islands area), and (5) areas with a delayed beginning, but a very short duration (ca. 1.5 months) of krill spawning (Ross Sea slope, probably the Coastal Current area off the Lasarev Sea shelf and in the south-eastern Weddell Sea. These patterns can be partly explained by peculiarities of the ice regime in particular areas and by routes of krill movement within water circulation systems.