Rate of survival in the open sea is the most significant measure of the effectiveness of a marine fish stocking program. Since the mid-to-late 1980s, the Ocean Resources Enhancement and Hatchery Program (OREHP) has contracted with researchers to develop juvenile and adult sampling programs to assess the proportion of hatchery-raised fish to the wild population. From 1988 to 2008, researchers from California State University at Northridge, San Diego State University, and Hubbs-SeaWorld Research Institute (HSWRI) conducted a standardized gill net sampling survey designed to capture 1- to 4-year-old juvenile white seabass in shallow waters off southern California. Initially, the survey focused on determining the distribution of young fish but switched in 1996 to look at recruitment of 1-year-old fish and recovery of tagged fish. In the late 1990s, HSWRI researchers developed a sampling program to recover adult hatchery-raised white seabass from the commercial and recreational fisheries. This program, which is ongoing, scans white seabass heads for the presence of a coded-wire tag. Since the inception of both programs, 1,400 hatchery-raised juvenile white seabass have been recovered in the juvenile gill net studies while 156 tagged, adult white seabass (legal-sized) have been recovered from the recreational and commercial fisheries.
The information collected from both the juvenile and adult sampling programs is used to estimate growth rates, determine patterns of migration while the fish are at large, and estimate the success of the program as a whole. Survival rate calculations are based on the relative numbers of tagged fish caught over time. Differences in rates of survival among batches can be used to optimize the release protocols by selecting the conditions which produced the greatest number of tag recoveries.
When a tagged fish is recovered from either commercial or recreational fishermen, the tag is extracted by HSWRI scientists. The code on the tag identifies when the fish was spawned, the location where it was released, how long it has been in the open ocean, and how far from the release site it was captured.