Habitat use of Striped Bass (Morone saxatilis), estimated from otolith microchemistry, in San Francisco Bay and the Sacramento Delta estuary, and their relation to total mercury body burden upon capture

M.S. Thesis Project:   

Striped bass (Morone saxatilis) is a nearshore, anadromous species that is the most popular sport fish in the San Francisco Bay estuary and Sacramento-San Joaquin Delta. Because striped bass spend their entire lives in either estuarine or nearshore environments, they encounter contaminants, like mercury. 

Mercury, a known health hazard in high doses to consumers of fish, is only biologically available to striped bass in a form known as methylmercury (Wiener and Spry 1996). Methylmercury is a product of complex processes, known as methylization, performed by sulfate-reducing bacteria in anoxic sediments that transform inorganic mercury. High rates of methylization are known to be favored if turbid conditions persist, pH is low, and the level of dissolved organic carbon are high. These conditions are normally seen in coastal wetlands, like localized areas in the San Francisco Bay estuary and Sacramento Delta, where striped bass spend a great deal of their lives. 

There has been much research in the past decade to learn if striped bass are acquiring mercury from specific areas in the Delta and San Francisco Bay since methylization is thought to be localized (Snodgrass et al 2000) and mercury content in striped bass varies annually (Greenfield et al 2005). Recent techniques in analyzing the microchemistry of otoliths have shown promise in evaluating habitat use of striped bass over their entire lifespan (Secor 1992; Secor 1999; Kraus & Secor 2003; Zlokovitz et al 2003). If presence in specific locations were found to correlate with high body burdens of mercury contamination, management strategies for striped bass and the associated public health risks with their consumption could be focused much more efficiently. 

Other research projects:

Systematics of Western North Pacific Squatinids.
David A. Ebert (debert@mlml.calstate.edu) of the Pacific Shark Research Center (PSRC).

Squatinids are quite distinct from other shark-like fishes, but are difficult to differentiate amongst each other. Four of the 16 known valid squatinid species reported occur in the western North Pacific (WNP). Differences among the WNP species complex have traditionally relied upon the nasal barbel shape, interorbital and interspiracle distances, ocelli patterns, number of dermal folds about the mouth, and the presence of midback thorns. Unfortunately, many of these characters are difficult to distinguish, hindering identification of individuals. Using WNP squatinid specimens and photographs, both from field expeditions and museums, we confirm the validity of four species in the area. Additionally, the resulting information obtained also corrects mistakes present in S. formosa type material, clarifies differences in the particularly challenging distinction between S. formosa and S. nebulosa, and is the basis for a revised dichotomous key for the region that includes all four known valid WNP squatinid species.

Funding provided by PSRC

Publications & Presentations:

Walsh, J. & Ebert, D. (2007). A review of the systematics of western North Pacific angel sharks, genus Squatina, with redescriptions of Squatina formosa, S. japonica, and S. nebulosa (Chondrichthyes: Squatiniformes, Squatinidae). Zootaxa (1551): 31-47.

Presented the above paper orally at the Western Society of Naturalists conference (Seattle WA, October 2006) and the American Elasmobranch Society conference (St Louis MO, July 2007).

Awards Received:

Honorable Mention for Best Student Paper in Genetics and Population Biology (Western Society of Naturalists, October 2006).

Funding:

My MS Thesis study was made possible through funds provided by the San Francisco Estuary Institute.

Literature cited:

To be added