Rockfish recruitment and Upwelling

SMURF Site Map, Pushpin color key, Yellow= Santa Cruz study region, Blue=Monterey study region, Green=San Luis study region, Teal=East Channel Islands (ECI) study region, Pink=West Channel Islands (WCI)study region

A recent paper written by PISCO researchers and colleagues investigates whether or not ocean events such as upwelling or primary productivity (chlorophyll ‘a’) can be used as proxies to measure the recruitment of rockfishes (genus Sebastes) to nearshore regions.

The utility of simple, cheap and readily accessible proxies to measure complex ecological processes, such as recruitment would be a great help to ocean managers to adjust their catch allowed proactively to better correspond with stock dynamics. A recruitment proxy would allow tremendous insight for managing fished species, providing easy access to very difficult to measure recruitment data, such as how many individuals will recruit to a reef year on year, and how those numbers change over time.

This study was based on a time series of rockfish recruitment using SMURF buoys (Standard Monitoring Unit for the Recruitment of Fishes) from PISCO and colleagues at Cal Poly San Luis Obispbo. Using this time series data, that in some cases reaches back a decade, recruitment was measured by SMURFs at 5 locations across the California coast, from the Channel islands (2 sites), Morro bay and Monterey bay (north and south). The study focused on the recruitment patterns of two groups of nearshore rockfishes (kelp, gopher, black and yellow and copper [KGBC] and olive, yellowtail, and black [OYTB]) so grouped because they have similar larval characteristics, such as the timing of larval release and the amount of time spent drifting in the ocean before settlement (pelagic duration).

 

Graphic A

 

Graphic B

Standardized number of rockfish per SMURF per day for A. KGBC (kelp, gopher, black and yellow and copper)and B. OYTB (olive, yellowtail, and black).

Kelp Rockfish

Kelp Rockfish (Sebastes atrovirens)
Photo Credit: Scott Gabara, PISCO

The results of this study indicate that simple indices of ocean conditions are useful proxies to predict the year to year variation of settlement in some rockfish species groups. These results are indicated by a simplified correlation between regional upwelling and strong rockfish recruitment, by the extreme decline in recruitment after an extremely late upwelling period in 2005, and further backed up by data gathered from PISCO’s kelp forest monitoring program. While upwelling was generally a good predictor of recruitment or ‘proxy’, the timing and exact nature of the correlations differed geographically and among the two species groupings.

Although this study doesn’t provide the exact mechanisms causing recruitment, work hasn’t finished. The growing time series of data used here combined with a greater understanding of ocean conditions will enable scientists to better understand the correlation between ocean events like upwelling and recruitment. In the face of declining fisheries worldwide, simple proxies that enable ocean managers to adjust the catch forecasts for settlement and recruitment of a fisheries stock, based on ocean conditions could become an extremely valuable tool in fisheries management.

  • Caselle, J. E., M. H. Carr, D. P. Malone, J. R. Wilson, and D. E. Wendt, 2010. Predictability of settlement of nearshore rockfishes (genus Sebastes) in central and southern California using simple proxies of ocean conditions. CalCOFI Report 51:1-16 (view paper online)

 

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