Research Document - 2000/101

Short term fluctuations in the pelagic ecosystem of the Northwest Atlantic.

By E.L. Dalley, J.T. Anderson, and D.J. Davis

Abstract

patial and/or annual effects accounted for significant variation in all variables examined during a broad-scale survey of the marine pelagic environment carried out for the sixth consecutive year, late summer 1999, in NAFO Divisions (2J3KLNO). Area differences were generally larger and associated with latitudinal or inshore/offshore clines. A north to south cline in temperature characterizes the area. In 1999, biomass of the smallest zooplankton size fraction remained relatively high, ranking second following initial increases in biomass from 1994 to 1997. The mid size increased each year, ranking highest in 1999 whereas mean biomass of the largest size remained relatively constant following an initial increase in 1995. In 1999 capelin larvae were relatively large, abundant and widespread but did not extend to southern Labrador coast as they did in 1998. Mean total nekton biomass (including jellyfish) in 1998 and 1999 was significantly higher than earlier years. Capelin (age 1+) and sand lance continued to dominate total nekton, but redfish increased to rank third in overall abundance, increasing by 2 orders of magnitude since 1998 and 3 orders since 1997. Arctic cod, which decreased in abundance in early years, maintained a relatively low, stable abundance over the past 3-4 years. Mean catch of pelagic capelin ranked highest in 1999, but was significantly higher than 1998 and 1995 only. The mean catch rate of pelagic 0-group Atlantic cod increased for the third year in succession. It was significantly higher in 1999 as a result of increases in the inshore particularly, but also the Northern Grand Bank. Catch rates of American plaice were highest in the time series in 1999 and hake were 2 orders of magnitude more abundant than in 1998. Six northern taxa that decreased sharply in 1998, all increased again in 1999 but remained relatively low in comparison to 1994 - 1997 levels. Of twenty measures of the nekton community examined in 1999 all but two ranked higher (6 significantly) than 1998 indicating a growing nekton community.

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