The Impact of Whaling on the Ocean Carbon Cycle: Why Bigger Was Better

Abstract

BackgroundHumans have reduced the abundance of many large marine vertebrates, including whales, large fish, and sharks, to only a small percentage of their pre-exploitation levels. Industrial fishing and whaling also tended to preferentially harvest the largest species and largest individuals within a population. We consider the consequences of removing these animals on the ocean's ability to store carbon.Methodology/Principal FindingsBecause body size is critical to our arguments, our analysis focuses on populations of baleen whales. Using reconstructions of pre-whaling and modern abundances, we consider the impact of whaling on the amount of carbon stored in living whales and on the amount of carbon exported to the deep sea by sinking whale carcasses. Populations of large baleen whales now store 9.1×106 tons less carbon than before whaling. Some of the lost storage has been offset by increases in smaller competitors; however, due to the relative metabolic efficiency of larger organisms, a shift toward smaller animals could decrease the total community biomass by 30% or more. Because of their large size and few predators, whales and other large marine vertebrates can efficiently export carbon from the surface waters to the deep sea. We estimate that rebuilding whale populations would remove 1.6×105 tons of carbon each year through sinking whale carcasses.Conclusions/SignificanceEven though fish and whales are only a small portion of the ocean's overall biomass, fishing and whaling have altered the ocean's ability to store and sequester carbon. Although these changes are small relative to the total ocean carbon sink, rebuilding populations of fish and whales would be comparable to other carbon management schemes, including ocean iron fertilization.

The Structuring Role of Marine Life in Open Ocean Habitat: Importance to International Policy

“…Emerging evidence suggests that mobile marine species can transform the environment as they move through it, transferring nutrients within the water column (deep to shallow and vice versa) and across oceans (Wilson et al, 2009;Pershing et al, 2010;Roman and McCarthy, 2010;Roman et al, 2014;St John et al, 2016). For example, depletion of whales due to commercial whaling resulted in substantial deep-sea habitat loss through a reduction in dead whale "falls" (Smith, 2007), declines in primary productivity due to reduced nutrient shuttling Roman and McCarthy, 2010), changes in food-web structure and biogeochemical cycles (Lavery et al, 2010;Roman and McCarthy, 2010), and reduced potential for organic carbon sequestration (Lavery et al, 2010;Pershing et al, 2010).…”

“…For example, depletion of whales due to commercial whaling resulted in substantial deep-sea habitat loss through a reduction in dead whale "falls" (Smith, 2007), declines in primary productivity due to reduced nutrient shuttling Roman and McCarthy, 2010), changes in food-web structure and biogeochemical cycles (Lavery et al, 2010;Roman and McCarthy, 2010), and reduced potential for organic carbon sequestration (Lavery et al, 2010;Pershing et al, 2010). The consequences of extraction therefore extended far beyond the decline of individual whale species.…”

An Ecosystem Services Perspective for the Oceanic Eastern Tropical Pacific: Commercial Fisheries, Carbon Storage, Recreational Fishing, and Biodiversity

“…Of course, this idea assumes that: (i) a reduction of fishing effort would increase those ES, and (ii) the corresponding increases in value would exceed the value lost by commercial fisheries. While studies have shown that reduced fishing pressure can lead to increases in biodiversity (Worm et al, 2006), carbon storage (Pershing et al, 2010), and the quality of recreational fishing (Hughes et al, 2005), these changes and their associated monetary values would require further study for the ETP prior to implementation of any policy based on this idea. Additionally, viewing the trade-off in this way does not consider societyspecific impacts of scaling back (e.g., economic impacts to Latin American fishers), which is a topic worth investigation.…”

“…The biological pump moves POC from the surface to deep ocean sediments through passive (e.g., sinking fecal pellets and ballasts) and active (e.g., vertical migrations by fish and zooplankton) transport (Eppley and Peterson, 1979;Ducklow et al, 2001;Henson et al, 2012;Davison et al, 2013). Additionally, carbon is stored in populations of large, long-lived vertebrates (e.g., apex predators), such as cetaceans and large fish; this is comparable to carbon being stored in large trees (Pershing et al, 2010). These important regulating services can be impacted by the use of provisioning services, particularly fisheries, which have the capacity to reduce populations of large consumer species and alter food web structure (Dayton et al, 1995;Jackson et al, 2001;Pauly et al, 2002).…”

“…These important regulating services can be impacted by the use of provisioning services, particularly fisheries, which have the capacity to reduce populations of large consumer species and alter food web structure (Dayton et al, 1995;Jackson et al, 2001;Pauly et al, 2002). Such changes may decrease the amount of carbon stored in megafauna populations and alter the magnitude and efficiency of the biological pump, which is strongly influenced by food web structure (Ducklow et al, 2001;Pershing et al, 2010).…”