Overfishing, climate variability appear to be culprits, says
Rutgers marine biologist
(August 5, 2015) A
Rutgers marine biologist studying the rise and fall of fish populations
worldwide recently made a counterintuitive discovery: ocean species that grow
quickly and reproduce frequently, such as sardines, anchovies and flounder, are
more likely to experience dramatic plunges in population than larger, slower
growing fish such as sharks or tuna.
Why is this counterintuitive? Because for life on land, the
situation is in stark contrast.
“Rabbits are doing pretty well compared to rhinos,” said
Malin Pinsky, assistant professor of ecology and evolution in the School of
Environmental and Biological Sciences. “Mice thrive while lions, tigers and
elephants are endangered.”
After studying population changes in 154 species of fish
worldwide over 60 years, Pinsky was surprised to see marine equivalents of
rabbits and mice collapsing to low levels – still shy of extinction but serious
enough to disrupt ocean food chains or fishing-based societies.
In his research, published this week in the journal
Proceedings of the Royal Society B, Pinsky sought an answer to this riddle. In
nearly all of the cases, overfishing was the culprit.
Photo: Shonda Foster
Malin Pinsky,
assistant professor of ecology and evolution in
the School of
Environmental and Biological Sciences.
Climate variations or natural boom-and-bust cycles
contribute to population fluctuation in small fast-growing fish,” he noted,
“but when they are not overfished, our data showed that their populations
didn’t have any more tendency to collapse than other fish.”
For example, this effect is apparent in sardines off the
coast of southern California, whose populations have fluctuated naturally for
thousands of years. But these fluctuations are not enough to explain why so
many fast-growing fish species have collapsed in recent decades – meaning a
drop to less than 10 percent of historical levels. With the advent of efficient
fishing vessels and techniques after World War II, population collapses started
to occur much more frequently in sardines and anchovies, which are valued for
pet food and fish oil.