January 22, 2015
Two new papers by Farallon Institute scientists are included in a special issue of Deep-Sea Research Part II: Topical Studies in Oceanography. The issue is titled "CCE-LTER: Responses to the California Current Ecosystem to climate forcing".
Bill Sydeman and co-authors include a paper investigating changes in upwelling and stratification in the Southern California region of the California Current Ecosystem and how they might affect seabird populations through changes in prey availability. The results show that there are seasonal trends in upwelling and stratification. Among the prey species examined, including krill and forage fish, no overall trend in krill abundance was found, while there were decreases in abundance seen for several fish species. The composition of the krill community, however, changed through time. Seabird density also decreased over the study period. Spring seabird density in the study area was found to be related to spring krill abundance and winter nearshore larval fish abundance, dominated by anchovy. Understanding predator-prey relationships such as these, and their relationship to environmental conditions is of great value when considering ecosystem-based management of upper trophic level organisms (fish, seabirds, and mammals).
In another paper, Farallon Institute post-doctoral researcher Pete Davison and co-authors describe mesopelagic fish biomass in the California Current Ecosystem. Mesopelagic fishes are an abundant group of fish that live at ocean depths of 200-1000 m and are a vital link between lower trophic levels and higher predators, as well as between the productivity of the ocean surface and the deep sea. Sampling these fish is difficult due to the depth of their habitat, and scientists assess the biomass of this group by either trawl sampling or acoustically-derived estimation. This study utilized and compared these methods while also addressing aspects of inaccuracy that warrant improvement. The authors provide a new estimate of mesopelagic fish biomass that is much larger than any previous estimate, and demonstrate a significant role of these species in regional ecosystem functions.