The saltwater basses (Paralabrax species) are an important recreational fishery in California. This state-managed fishery comprises three species that are managed as a single unit: barred sand bass, kelp bass and spotted sand bass. Over the last decade, fish catches of the two focal species, barred sand bass and kelp bass, have remained at all-time lows. Until recently, understanding how and why these fish populations have fluctuated was limited by the lack of long-term abundance data for each species.
This project successfully reconstructed 54 years of data from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) on Paralabrax species larvae. The researchers used morphological identification, including machine-learning techniques, to create a “taxonomic key” for Paralabrax, allowing researchers to distinguish between the larvae of each species based on pigmentation. Using this key, the researchers determined the number of larvae in CalCOFI samples back through 1963. Finally, the researchers created a “standard index of abundance,” using a model that accounts for sampling techniques and other variables that might impact the larval count in the samples. The index also allowed researchers to identify important environmental drivers of bass larval abundance and was discovered to be useful in predicting future catches.
These tools have revealed that both species show sporadic recruitment, but kelp bass populations remain strong. Barred sand bass recruitment rates are more closely tied to temperature. Extreme warm water events over the past decade resulted in near all-time highs of larval abundance for both species, suggesting recovery of these populations is imminent. The results from this project have strong implications for how these species should be managed in the future and provide context as researchers consider what a warming ocean may bring.