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Science 12 September 2008:
Vol. 321. no. 5895, p. 1446
DOI: 10.1126/science.1157390
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Technical Comments

Comment on "A Global Map of Human Impact on Marine Ecosystems"

Michael R. Heath

Fisheries Research Services, Marine Laboratory, 375 Victoria Road, Aberdeen AB11 9DB, UK. E-mail: heathmr{at}marlab.ac.uk


Figure 1 Fig. 1. Quarterly distributions (1/2° latitude by 1° longitude) of catches from the northeast Atlantic mackerel stock for 2006 [data from (14)]. Total annual catch was 472,700 tonnes, exceeded in the northeast Atlantic only by catches of Norwegian Sea herring. Surveys of planktonic eggs show that the majority of spawning activity occurs in Q2 west and southwest of Ireland (14, 15). Tagging studies (16) show that after spawning, the majority of fish migrate ~2000 km northward into the Norwegian Sea to feed during Q3, with a southward return migration during Q4 and Q1. The stock is only lightly exploited during Q2 when fish are close to the sea surface and difficult to catch. Most of the catch is taken during Q4 and Q1 when the fish are aggregated into very large schools. In 2006, 300,000 tonnes (63% of the annual total) were taken from an area of ~5000 km2 off the northern United Kingdom. Although there must be local impacts due to bycatch and slippage from nets (~4% of catch), the principal ecological impacts on an annual time scale must be distributed over the spatial envelope of the stock as a whole, which exceeds 250,000 km2. [View Larger Version of this Image (48K GIF file)]
 

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Science. ISSN 0036-8075 (print), 1095-9203 (online)