Age-Structured Spawning in Rockfishes Sheds Light on Conservation Strategies

April 9, 2007

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

Findings Point to Benefits of Marine Reserves

SANTA CRUZ –Pacific ocean perch, wldow and yellowtail rockfishes are strong candidates for marine reserves, while the chilipepper rockfish is perhaps not, according to a new California Sea Grant/California Department of Fish & Game study.

chilipepper larvae

Stage 4 chilipepper larvae. Credit: S. Berkeley

Steven Berkeley of the Long Marine Laboratory at UC Santa Cruz bases this conclusion on an analysis he has led on the timing of rockfish spawning, as a function of female rockfish age, and of larval quality, as measured by oil globule size.

This analysis has shown that for Pacific ocean perch, widow and yellowtail rockfishes, the oldest females spawn earliest in the season. They also produce larvae with the largest oil globules (the source of nutrition for the developing embryo). Larger oil globules are associated with higher rates of larval survivorship, and good recruitment is usually correlated with high survivorship in larvae produced during the earliest part of the spawning season.

Translation: “Older female rockfish just get better with age,” said Berkeley, whose research on rockfish reproduction has led to what is colloquially known as the “big-fat-mamma” hypothesis. He calls it more delicately “the maternal effect,” but the idea is the same: For many species of rockfish, the oldest, biggest females are the best reproducers.

For the chilipepper rockfish, a different pattern was observed. There was no appreciable difference in the size of oil globules or in the timing of spawning for older vs. younger females.

3 yellowtail rockfish larvae

Stage 3 yellowtail rockfish larvae Credit: S. Berkeley

The importance of this research is that “it tells us we need to protect the large adults of these three rockfishes,” Berkeley said, since they are the ones most likely to be contributing to the next generation.

Enter marine reserves.

With traditional fishery management tools, it is almost impossible to selectively protect older females, he said. “One of the real advantages of marine reserves is that they can protect older fishes. This is important because fishing, even at sustainable levels, removes the oldest fish from the population, and it does it very quickly.”