Pacific Fish Have Gotten Smaller
The size of fish living near the ocean floor along the Pacific coast of the United States has declined dramatically in two decades.
Between 1980 and 2001, the average weight of rockfish, flatfish and skates dropped by nearly half.
Flatfish, including sole, netted off the coast of California, Oregon and Washington in 2001 typically weighed in only 57% as heavy as the average flatfish caught in 1980. Cartilaginous fish such as skate caught in 2001 averaged two-thirds (67%) the weight of those landed in 1980.
These size decreases don't entirely account for the overall 45% reduction in the average weight of bottom-dwelling fish. The shrinking is also due to larger species of fish becoming much less prevalent.
Populations of the bigger rockfish species dropped by 5 to 17% a year between 1977 and 2001. For two species, the declines are particularly alarming. After 1977, numbers of canary rockfish along the US west coast plummeted by 85% and boccacio rockfish by 96%.
At the same time, populations have actually increased for most of the 31 groundfish species studied by scientists from the Northwest Fisheries Science Center in Seattle. Cartilaginous fish doubled in number between 1977 and 2001. Flatfish became eight times more plentiful during the same period. Small species of rockfish, such as greenstripped and splitnose, experienced similar population growth, generally increasing over 6% annually.
The species in decline can be distinguished by their life histories. They are generally long-lived fish, that grow large and reproduce slowly.
The radically different population trends among species have overturned the Pacific Ocean's bottom-dwelling fish communities. Rockfish have gone from making up 60% of the fish caught in 1977 surveys to only 17% in 2001. Flatfish that used to make up 34% of catches, more recently comprise 80% of the fish netted. Flatfish have overtaken rockfish to become the dominant type of fish living near the US Pacific coast seabed.
Scientists maintain that overfishing has restructured the mix of these west coast fish. But declines in the later-maturing rockfish are greater than can be attributed to fishing alone. The flip in fish communities may have created conditions where canary and boccacio rockfish can no longer thrive.
What's most disturbing about these results, the authors of this study point out, is the revelation that even after fishing is curtailed, long-lived species may never recover from heavy harvesting.
Phillip S. Levin, Elizabeth E. Holmes, Kevin R. Piner and Chris J. Harvey. 2006. Shifts in a Pacific Ocean Fish Assemblage: the Potential Influence of Exploitation. Conservation Biology. 20(4): 1181-1190.