2 March 2005
Cod Numbers Decline 96 Percent
by Kate Melville
The volume of cod on the Scotian Shelf has plunged 96 percent since the 1850s, say Census of Marine Life scientists. Their research, published in Frontier's in Ecology, is based on old schooner catch records and observations, coupled with modern modeling tools. To estimate long ago fish levels, the researchers used 1850s New England schooner records of daily catch locations and fleet activity on the fishing grounds. The researchers said that fishermen then had "negligible incentive to falsify records" and, combined with ancillary documents, their logs "provide a solid, reliable basis for stock assessment." The findings may have profound implications for contemporary policy makers trying to rebuild fishery "remnants" and restore marine ecosystems.
The researchers say evidence for what constitutes a healthy fish population remains controversial. In rebuilding fisheries, decisions should reflect real and realistic goals for management, not just recently observed catch levels, they said. "Our historical analyses indicate that recent levels of biomass and catch may grossly under-represent the productive potential of commercially important species," said researcher Andrew A. Rosenberg.
Using a mathematical formula, the researchers estimated cod biomass on the Scotian Shelf was 1.26 million metric tons in 1852, compared with less than 50,000 metric tons today, the adults within which represent 3,000 metric tons, or 6 percent. The study notes the estimate of 1850 cod biomass is "quite conservative" as the old fishing logs only record adult cod. "Prevalent hook sizes in this deepwater fishery made landing smaller juvenile cod very unlikely," said Rosenberg. "Despite stringent regulations for the last 6-10 years and a slight rebuilding of fish stocks, the best estimate of adult cod biomass on the Scotian Shelf today comprises a mere 38 percent of the catch brought home by 43 schooners in 1855. In other words, 16 small schooners from this mid 19th century fleet could contain all of the adult cod on the Scotian Shelf today."
The estimated abundance of cod in 1850 is consistent with earlier research led by fellow Census of Marine Life scientist Ransom Myers that estimated how much cod could be sustained in the North Atlantic ecosystem. "Biomasses for many key marine species that are also valuable economic commodities probably follow the pattern we have estimated for this cod population. That is, biomass of commercially important species today is only a small fraction of what existed before industrialized exploitation," the researchers concluded.