We are studying the pelagic food web in the central North Pacific with particular attention to deep living fishes and other animals. Throughout the world’s oceans there are dense layers of animals that live in deep water during the day, hiding out from predators like tunas, then migrate to the surface at night to feed. This diverse group of mostly small (2-20cm) fishes, shrimps, and squids are called mesopelagic micronekton. These animals consume zooplankton and are in turn are food for commercially important pelagic fishes including albacore tuna, bigeye tuna, and swordfish. We have been investigating the distribution and community composition of mesopelagic micronekton in the Pacific and the factors affecting it. This is a collaborative project with the National Marine Fisheries Service - Pacific Islands Fisheries Science Center.
Past research has focused on the trophic biology or feeding ecology of deep-sea macrourid fishes. Macrourids used to be called rattails but now that they are fished they have been renamed grenadiers. They are among the largest, most diverse and widespread of all the deep-sea fishes. Studies of their diet show that they are among the top predators in their ecosystems and that they have the potential to exert significant pressure on their prey populations. Many are scavengers, eating animals such as fish, squids, and whales which die at the surface of the ocean and sink to the deep seafloor. Using stable isotopes and fatty acid biomarkers we have shown that at least one species of abyssal rattail's most important food is carrion. Using data on their abundance collected over a 20 year time span shows that changes in their number reflect changing number of large surface dwelling fishes which, when they die, provide carrion to the deep sea.
With regards to their diets, we use diet analysis, stable isotopes, fatty acid biomarkers and trace metals to understand the trophic ecology of this system. Our results show that mercury is probably introduced to the marine food web in the deep ocean because deep living micronekton have several times more mercury in them than shallow living species like flying fishes. This is translated to mercury in our seafood. Those that dive deep like bigeye tuna and swordfish have much more mercury than surface dwellers like yellowfin tuna or mahimahi.
Rattail (C. acrolepis, Monterey Bay)
C. longicirrhus and hagfish eating bait
Figure from Drazen, J.C., De Forest, L.G., 2008. The influence of Hawaiian seamounts and islands on the forage base for oceanic predators. Pelagic Fisheries Research Program Newsletter 13 (3), 3-8.
Bradley CJ, Wallsgrove NJ, Choy CA, Drazen JC, Hetherington ED, Hoen, DK, Popp BN (2015) Trophic position estimates of marine teleosts using amino acid compound specific isotopic analysis. Limnology and Oceanography: Methods. pdf
Sackett DK, Drazen JC, Choy CA, Popp B, Pitz GL (2015) Mercury Sources and Trophic Ecology for Hawaiian Bottomfish. Environmental Science & Technology 49 (11): 6909-6918. pdf
Hoen DK, Kim SL, Hussey NE, Wallsgrove NJ, Drazen JC, Popp BN (2014) Amino acid 15N trophic enrichment factors of four large carnivorous fishes. Journal of Experimental Marine Biology and Ecology 453:76-83. pdf
Choy CA, Davison PC, Drazen JC, Flynn A, Gier EJ, Hoffman JC, McClain-Counts JP, Miller TW, Popp BN, Ross SW, Sutton TT (2012) Global trophic position comparison of two dominant mesopelagic fish families (Myctophidae, Stomiidae) using amino acid nitrogen isotopic analyses. PLoS One 7: e50133pdf
Laxson CJ, Condon NE, Drazen JC, Yancey PH (2011) Decreasing urea: trimethylamine N-oxide ratios with depth in chondrichthyes: a physiological depth limit? Physiological and Biochemical Zoology 84: 494-505pdf
Choy CA, Popp BN, Kaneko JJ, Drazen JC (2009) The influence of depth on mercury levels in pelagic fishes and their prey. Proceedings of the National Academy of Sciences of the United States of America 106:13865-13869pdf
Drazen JC, Popp BN, Choy CA, Clemente T, De Forest L, Smith KL, Jr. (2008c) Bypassing the abyssal benthic food-web: macrourid diet in the eastern North Pacific inferred from stomach content and stable isotopes analyses. Limnology and Oceanography 53: 2644-2654pdf
Drazen JC (2002b) A seasonal analysis of the nutritional condition of deep-sea macrourid fishes in the north-east Pacific. Journal of Fish Biology 60: 1280-1295pdf
Drazen JC, Buckley TW, Hoff GR (2001) The feeding habits of slope dwelling macrourid fishes in the eastern North Pacific. Deep Sea Research I 48: 909-935pdf