Graduate Thesis Or Dissertation
 

Using parasite community data and population genetics for assessing Pacific sardine (Sardinops sagax) population structure along the west coast of North America

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dj52w749p

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  • Pacific sardines (Sardinops sagax) are an economically and ecologically important forage fish which transfer energy from planktonic primary producers and secondary consumers to upper trophic predators. Previous genetics studies of Pacific sardine suggested a panmictic population with a shallow genetic structure. However, more than one subpopulation within the Central California Offshore management unit may exist based on recovering larger individuals at higher latitudes and a temporal difference in sardine spawning off Southern California and the Pacific Northwest. Potential for separate sardine subpopulations questions the long-standing paradigm of an annual migration of individuals to feeding grounds off the Pacific Northwest in the summer with migrants returning to Southern California in the fall to spawn the following spring. This study applied parasite community analyses and population genetics techniques to assess migration patterns and stock structure of Pacific sardine in the California Current from Vancouver Island, British Columbia, Canada to San Diego, California, USA. A coastwide sardine migration is supported by the geographical distribution of Myosaccium ecaude (Trematoda), but a second migration pattern was identified within the Pacific Northwest from the geographic distribution of Lecithaster gibbosus (Trematoda). Population genetics studies identified a panmictic distribution for: 1) the trematode M. ecaude using a 283bp portion of the NADH-dehydrogenase subunit 1 (ND1) mitochondrial DNA (mtDNA) gene; and 2) three species of Anisakis nematodes (A. simplex s.s., A. pegreffii, and A. simplex 'C') using a 524bp portion of the cytochrome c oxidase 2 (cox2) mtDNA gene. These results suggest that the extensive movement of all of the potential hosts utilized by these parasites, the limited oceanographic barriers, and complexity in the California Current are not preventing the mixing of M. ecaude or Anisakis species populations. The diversity and availability of fish and cetacean species that undergo extensive migrations along the full length of the California Current system may enable large geographically distributed population sizes of these parasite species. We thus cannot confirm the existence of separate Pacific sardine subpopulations within the California Current by the occurrence of parasite communities or the population genetics analyses of M. ecaude or the three Anisakis species.
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