Off California, Many Common Fish Now Spawn Earlier
Researcher:
Rebecca Asch
Scripps Institution of Oceanography
University of California,
San Diego
E.: rgasch@ucsd.edu
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Revised:
December 1, 2010
Pacific jack mackerel, a species spawning earlier off California.
Credit: NOAA Southwest Fisheries Science Center
November 30, 2010
Contact: Christina S. Johnson, senior writer, csjohnson@ucsd.edu, 858-822-5334
On land, among the most compelling pieces of evidence for ecosystem restructuring under climate change are the observed shifts in seasonal animal migrations, breeding cycles and home ranges. New findings from California Sea Grant show that life history characteristics of marine species in the California Current ecosystem are also in a state of flux.
In particular, California Sea Grant researchers report that 18 of the region's 43 most abundant fish species are now spawning between 14 days and 62 days earlier than in the early 1950s.
Some of the earlier-spawning species include: jack mackerel, chub mackerel, hake, Senoritas, medusafish and the aurora, split-nose and short-belly rockfishes.
A map of sardine egg abundance. The black contour lines show egg concentrations; the color shading indicates sea surface height. (Click to view larger image.) Credit: R. Asch/UCSD
Eight species are also spawning later – between 15 days and 35 days later. Among these are chilipepper rockfish, blacksmith, two species of flatfishes and three species of mid-water fishes.
The findings are based on counts of fish larvae in water samples collected during the California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises, which began in the early 50s.
"We don't know why there is this trend toward earlier spawning," says California Sea Grant Trainee Rebecca Asch, a doctoral student at Scripps Institution of Oceanography at UC San Diego. "But, it's likely related to temperature."
"Many marine organisms use temperature as a cue for when to initiate spawning, so the idea that changes in seasonal temperatures would affect spawning time shouldn’t come as too much of a surprise," she says. "Similar patterns of earlier reproduction have been observed in many terrestrial ecosystems and have been frequently attributed to climate change, in general, and the earlier arrival of spring more specifically."
Sea surface temperatures off California are now reaching their seasonal peak about 25 days earlier today than in the early 1950s. Compellingly, the fish species that are spawning earlier are doing so by, on average, 29 days.
Meanwhile, for the species that are spawning later, Asch notes that they are predominately coastal dwellers that spawn in winter and fall, when upwelling is weak and larvae are less likely to be swept offshore, where the fish would perish. The hypothesis Asch is now exploring is that these species are responding to changes in upwelling patterns and associated offshore flows.
Asch presented her findings at the North Pacific Marine Science Organization (PICES) conference on the effects of climate change on fishes and fisheries in Japan, April 2010 and is preparing a manuscript on this work, as well as including it in her doctoral dissertation.
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