a1 The Laboratory, Marine Biological Association, Citadel Hill, Plymouth PL1 2PB
Scientific data from the last 100 years are combined with primary and secondary historical information on the fisheries to summarize changes in the relative abundance of pilchards and herrings in the south-west in the last 400 years. The fluctuations in the two species are compared with recorded and inferred annual mean temperatures over the period. Pilchards are more abundant and extend farther to the east when the climate is warmer, as from 1590 to 1640 and from 1930 to 1960. In cooler times, as in the second half of the seventeenth century, herrings are more abundant while the pilchard fishery occurs later in the year and is restricted to west Cornwall. Lesser changes in the relative abundance of the two species and the timing of the fishery along the south coast of Devon and Cornwall in the intervening periods between these extremes accord fairly well with smaller fluctuations in climate. It is presumed that in addition to direct effects on reproduction and behaviour, changes in climate can indirectly influence the relative competitive advantage of the species through alterations in the associated ecosystem.