Changes in North Sea gadoid stocks

Abstract

Abundance and biomass of the major gadoid species in the North Sea have undergone large changes in the present century. During the gadoid outburst of the 1960s and 1970s, cod, haddock, whiting, and Norway pout produced some of the largest (as well as some of the smallest) year classes on record. Food requirements of the enhanced populations may have been some three to four times as large as current and previous levels. Although growth rates of cod did not change, there is evidence that food for juvenile haddock, and possibly whiting, was in short supply during the periods of maximum population density. The environmental factors that led to this increase in reproductive success have not been identified. Indices of recruitment for the whole North Sea, as provided by VPA, represent the pooled contributions of separate spawning units and may not be the most appropriate data to use when modelling the relationship between stock, recruitment, and environmental variables. Analysis of historical data indicates that recent levels of spawning-stock biomass of cod and haddock are close to their historic minima and fishing mortality rates are at (cod) or near (haddock) an historic maximum. Measures to reduce fishing mortality and improve exploitation patterns should be given the highest priority.1996 British Crown

Evidence for impacts by jellyfish on North Sea herring recruitment

“…The Great Salinity Anomaly of the 1970s saw a huge volume of cold, low-salinity water travel around the North Atlantic gyre from 1968 to 1981 and invade the North Sea during the low NAOI period 1977 to 1979 (Dickson et al 1988, Belkin et al 1998). In addition, changes in the plankton community contributed to the Gadoid Outburst of the 1970s, which saw a dramatic rise in the abundance of gadoids in the North Sea (Hislop 1996, Beaugrand et al 2003.…”

A century of North Sea epibenthos and trawling: comparison between 1902–1912, 1982–1985 and 2000

“…Caution is required when interpreting landings data as an indicator for bottom fishing effort, as landings vary with effort as well as with stock size. Combining a range of species partly accounts for this, but not if species vary in synchrony, such as was the case for several roundfish species during the 1960s 'gadoid outburst' (Hislop 1996). However, while stock fluctuations may go up and down, resulting in noise when interpreting longterm landings data for effort, fishing efficiency will generally only improve over time.…”

“…Notably, the very high roundfish landings from the mid-1960s to mid-1980s are generally attributed not only to sustained high effort but particularly to the 'gadoid outburst'. In this period the North Sea cod, haddock and whiting stocks produced some of the largest yearclasses on record (Hislop 1996). The peak in roundfish landings from 1969 to 1970 specifically relates to the extremely strong haddock year-class of 1967 (Holden 1978).…”

Long-term increases in prevalence of North Sea fishes having southern biogeographic affinities

“…Similarly, demersal fish stocks have experienced population expansions followed by rapid collapses. In the mid-1960s the 'gadoid explosion' led to unusually high landings of cod, haddock and whiting (Cushing 1984, Hislop 1996 around British coasts, while in the mid-1990s the once prolific cod fisheries of the Grand Banks completely ceased to exist in many areas (deYoung & Rose 1993).…”