Cross-shelf ichthyoplankton distributions in relation to hydrography off Northern California, with special attention to larval rockfishes

Graduation Date

2008

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Natural Resources: Fisheries, 2008

Committee Chair Name

Eric P. Bjorkstedt

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Larval rockfish distribution, Humboldt State University -- Theses -- Fisheries, Survival rate, Oceanographic structure, Zooplankton distribution, Hydrographic structure, Ichthyoplankton distribution

Abstract

As a first step towards evaluating the influence of oceanographic structure on the survival of larval fishes during the fall, winter and spring months off northern California, I examined the distribution of larval fishes, including larval rockfishes (Sebastes) and zooplankton, in relation to hydrographic structure along a transect extending due west of Trinidad Head, California from April 2006 to April 2007. Dominant taxa included the deep-sea smelts (Bathylagidae), northern lampfish (Stenobrachius leucopsarus), righteye flounders (Pleuronectidae), rockfishes (Sebastes), and slipskin snailfish (Liparis fucensis). Cross-shelf ichthyoplankton diversity patterns reflected adult spawning seasons and locations, and the distribution of coastal and offshore species agreed with ichthyoplankton assemblages identified in previous studies off California and Oregon. Liparids, some pleuronectids, most cottids, and the osmerids were consistently in the coastal assemblage. Sebastes, bathylagids, and myctophids were consistently in the offshore assemblage. These assemblages were relatively persistent across seasons. Although cross-shelf distributions differed among taxa, hydrographic structure appeared to affect distributions of larval fishes. Larval Sebastes were commonly observed at their greatest densities in the vicinity of fronts, while larvae of inshore taxa, including some flatfish, were rarely encountered offshore of fronts. Cross-shelf advection associated with upwelling conditions appeared to drive a general offshore displacement of larval fishes, while cross-shelf advection associated with downwelling caused a nearshore displacement of larvae. Hydrographic structure appeared to affect distributions of potential zooplankton prey throughout the winter and spring, and ichthyoplankton and zooplankton distributions were correlated in April 2007. These results suggest that fronts and related structures might affect larval survival and recruitment success in fishes for which the early life history stages exist in the plankton during the winter and spring, when coastal upwelling is at a seasonal minimum.

https://scholarworks.calstate.edu/concern/theses/3484zk267

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