Anomalously High Recruitment of the 2010 Gulf Menhaden (Brevoortia patronus) Year Class: Evidence of Indirect Effects from the Deepwater Horizon Blowout in the Gulf of Mexico

Abstract

Gulf menhaden (Brevoortia patronus) exhibited unprecedented juvenile recruitment in 2010 during the year of the Deepwater Horizon well blowout, exceeding the prior 39-year mean by more than four standard deviations near the Mississippi River. Abundance of that cohort remained exceptionally high for two subsequent years as recruits moved into older age classes. Such changes in this dominant forage fish population can be most parsimoniously explained as consequences of release from predation. Contact with crude oil induced high mortality of piscivorous seabirds, bottlenose dolphin (Tursiops truncatus), waders, and other fish-eating marsh birds, all of which are substantial consumers of Gulf menhaden. Diversions of fresh water from the Mississippi River to protect coastal marshes from oiling depressed salinities, impairing access to juvenile Gulf menhaden by aquatic predators that avoid low-salinity estuarine waters. These releases from predation led to an increase of Gulf menhaden biomass in 2011 to 2.4 million t, or more than twice the average biomass of 1.1 million t for the decade prior to 2010. Biomass increases of this magnitude in a major forage fish species suggest additional trophically linked effects at the population-, trophic-level and ecosystem scales, reflecting an heretofore little appreciated indirect effect that may be associated with major oil spills in highly productive marine waters.

Ocean currents and coastal exposure to offshore releases of passively transported material in the Gulf of Mexico

“…The DWH release occurred in one of the most productive regions of the GoM due to the fertilizing role of nutrients originating from the Mississipi's mouth (Lohrenz et al 1997). The impact of oil on organisms, foodwebs and ecosystems is complex and includes multiple feedbacks (Joye et al 2016, Short et al 2017). The chlorophyll concentration in the upper ocean is directly related with the primary productivity and is simulated by GOLFO12 in a consistent way compared to observations as shown by Damien et al (2018).…”

Marine Environmental Emergencies in the North Pacific Ocean: Lessons Learned from Recent Oil Spills

“…Dubansky et al (2017) present new evidence of how fish were exposed to different crude oil components in the field following the 2010 Deepwater Horizon oil well blowout. Short et al (2017) present evidence for a strong indirect effect of this blowout indicated by unprecedented recruitment of forage fish that were released from predation after seabirds that prey on them were killed in large numbers. Kim et al (2017) …”

Connectivity corridor conservation: A conceptual model for the restoration of a changing Gulf of Mexico ecosystem

“…Connectivity from marshes and shore habitats to the offshore realm of the Gulf are clearly evidenced by the lifehistory transitions of the Gulf menhaden, perhaps the primary forage fish in the Gulf that supports widereaching pelagic and terrestrial food webs (Geers et al, 2014;Short et al, 2017). Larval and early juvenile menhaden utilize salt marsh habitat when the fish are small and benefit from marsh structure as protection from predators while the Gulf menhaden are consuming phytoplankton and marsh plant detritus.…”

“…The offshore transport phase of the Gulf menhaden life history depends on the large volumes of riverine outflow of rainfall runoff to achieve successful offshore transport of the small fish into the coastal ocean waters to grow on their zooplankton diet, thereby increasing their size and gaining in swimming ability. Earlier in their life history, these same menhaden had relied on passive transport in the opposite direction to bring the newly released Gulf menhaden larvae from the offshore oceanic location of the spawning adults into the coastal juvenile rearing habitat of the salt marsh (Short et al, 2017). Hence, all of these forms of physical transport interconnectivity that link estuarine to coastal and offshore habitats play a major role in preserving the integrity of ecosystem-wide habitat functions.…”