Oregon State University



Event Details

Dr. Cassandra Glaspie, Department of Fisheries and Wildlife, OSU

Hypoxia alters prey availability and trophic interactions in the pelagic food web of the northern Gulf of Mexico

Thursday, December 14, 2017 3:30 PM - 4:30 PM

The northern Gulf of Mexico (NGOMEX) experiences an annually recurrent region of summer hypoxia (≤ 2 mg L-1). The occurrence of hypoxia in coastal waters may alter trophic interactions within the water column. We examined how hypoxia in the Northern Gulf of Mexico (NGOMEX) impacts the catch rate, diet composition, prey availability, and community interactions of fishes using zooplankton biomass and fish diet data from summers 2006 - 2008, and dual frequency split-beam acoustics from 2003-2010. Hypoxia influenced zooplankton distribution and abundance; small zooplankton (≤ 5 µg average dry mass) biomass was vertically compressed into the surface waters in hypoxic areas, whereas large zooplankton (> 5 µg average dry mass) resided in hypoxic bottom waters, possibly as refuge from fish predators. Small pelagic fish density increased with temperature and dissolved oxygen, and relatively smaller fish were dominant in the warmest waters with the most dissolved oxygen. Overall, fish diets from hypoxic sites and normoxic sites differed. The mean proportion of large, mobile prey items such as fish, shrimp and squid was higher in diets of fish caught in hypoxic regions than in fish caught in normoxic regions. Hypoxia-induced habitat compression of small zooplankton increased predation risk, with observations of increased small zooplankton in fish stomachs when dissolved oxygen was low. Catch per unit effort (CPUE) of many fish species was lower in hypoxic regions as compared to normoxic regions. Impacts of hypoxia on zooplankton distribution and fish diet may alter energy flow in the NGOMEX pelagic food web, and should be considered in fisheries management. Some implications for Pacific Northwest fishes, including Chinook salmon and albacore tuna, will also be discussed.

OSU Hatfield Marine Science Center
Guin Library Seminar Room
2030 SE Marine Science Drive
Tom Hurst
maryann.bozza at oregonstate.edu
Hatfield Marine Sci Ctr
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