Oxygen Deficient Zones (ODZs) are the largest pelagic sink of N containing nutrients in the ocean. The offshore Eastern Tropical North Pacific ODZ has been shown to be organic matter limited. We propose zooplankton/forage fish as a key source of organic matter for N₂ production that has previously been ignored. We examined datasets from four cruises (April 2012, Jan 2017, April 2018, Oct 2019) at a station in the central ETNP. Backscattering data was used to determine zooplankton vertical migration depths (250-450 m, maximum at 270-280 m). Metazoan DNA concentrations, as measured by quantitative PCR, had a reproducible maximum at 270-280 m, confirming that these signals indicate the presence of zooplankton/forage fish. Additionally, a large maximum in sinking pteropod shells was found at 270 m, indicating that pteropods were part of the migrating community. While crustacean zooplankton have been shown to reduce respiration and excretion of ammonium under anoxia, we found intermittently measurable ammonium concentrations at 270 m. Here we show signatures consistent with organic matter of zooplankton/forage fish origin in the C:N and \(\delta\)¹³C of suspended and sinking organic matter at the vertical migration depth that suggest transportation to these depths by migrating zooplankton/forage fish. Also coincident with the migration maximum was a reproducible-between-years maximum in the biological N₂ gas, and a tertiary nitrite maximum, which suggest that the migrating zooplankton are linked to N loss. Thus zooplankton/forage fish appear to be one source of organic matter which can fuel biological N₂ production in ODZs.