Biological response in a changing ocean environment in Newfoundland waters during the latter decades of the 1900s

Ocean temperatures on the Newfoundland Shelf during the past several decades have experienced near-decadal oscillations superimposed on a general downward trend. In particular, the decade of the 1990s has experienced some of the most significant variations since measurements began during the mid-1940s. Ocean temperatures, for example, have ranged from record low values during 1991 to record highs during 1999
in many areas, particularly on the Grand Bank of Newfoundland. Coincident with the trends in ocean climate many commercial fish species have shown changes in abundance, particularly during the decade of the 1990s. Recruitment in Newfoundland cod stocks, for example, has declined almost steadily since the 1960s, reaching historical low values by the early 1990s. During the cold early 1990s, with fishing moratoria in place, recruitment continued to decline. However, by 1995, ocean temperatures began to warm and the pelagic ecosystem responded, with the biomass of invertebrate zooplankton increasing by a factor of 2 from the early to late 1990s. This was followed by a sharp increase in the nekton biomass during the late 1990s, although this increase
lagged that observed in the zooplankton. We conclude that the observed decline in cod recruitment since the late 1960s was due to a declining spawning-stock biomass
caused in part by a deteriorating ocean environment. Furthermore, the subsequent increase in the abundance of pelagic organisms observed during the latter half of the
1990s is consistent with the expected biological response to changes in the physical ocean environment.

Article from Marine Science Symposia Vol. 219 - "Hydrobiological variability in the ICES Area, 1990-1999", symposium held in Edinburgh, 8-10 August 2001. To access  the remaining articles please click on the keyword "MSS Vol. 219".