Jim Steele/What’s Natural?
Two decades ago, fishery managers closed large areas of the eastern Pacific Ocean to bottom trawling because the targeted species like rockfish, sole, Pacific Ocean perch and other deep-dwelling fish were rapidly declining. However, much sooner than anticipated, fish abundance recovered. Thus, in January 2020, an area off Oregon and California, three times the size of Rhode Island, reopened to sustainable fishing with the blessings of both fishery managers and concerned environmentalists.
Likewise, despite widespread fears of fishery collapses in the 1990s, NOAA’s Fish Stock Sustainability Index has reported steady increases in the abundance of the most heavily fished species over the past 2 decades. Declining critical “forage fish” like Pacific anchovies and jack mackerel were now increasing since 2000 and accordingly, the abundance of humpback whales and California sea lions that feed on those forage fish steadily increased also. This change in good fortune is due to both wiser fishery management and beneficial natural climate variability.
To protect species from overfishing, the standard management response had been to limit the fishing season to fewer days. However, the unintended consequence was fishermen competed to catch as many fish as possible before the “season” closed. So, fishermen invested in bigger boats, worked longer days and risked fishing in severe weather that often resulted in lost nets and traps that further harmed the ecosystems.
New management policies have now developed “catch shares” and “individual transferable quotas”. Scientific assessments determine a sustainable number of “allowable catches”, and then fishermen “own” a share of that allowable catch. That share can be sold or traded. If a species’ abundance increases, the allowable catch increases, making the fishermen’s share more valuable. Thus, catch shares creates an economic incentive to maintain or increase a species abundance.
However, despite a fisherman’s best intentions to not overfish, natural climate variability causes fish species to boom and bust. A visit to Monterey California’s Cannery Row speaks to a time when the sardine fishery boomed in the 1930s but then collapsed when ocean conditions naturally changed. The human impact of this natural disaster was immortalized in John Steinbeck’s novel “Cannery Row”.
Upwelling is a key ocean dynamic that determines ocean productivity. Upwelling brings sunken nutrients from the ocean’s dark depths back to the sunlit waters promoting plentiful photosynthesis and the greatest concentrations of diverse marine life. Vigorous upwelling fosters larger algae fed upon by larger zooplankton, and forage fish like anchovies evolved to feed upon those larger plankton. Enhanced upwelling during La Ninas and the Pacific Decadal Oscillation’s cool phase promote anchovy booms along the California and Oregon Coast.
In contrast when El Ninos weaken upwelling, smaller algae and smaller zooplankton dominate coastal ecosystems. Sardines specialize on those smaller plankton. Decades with more El Ninos favor sardine abundance, while decades with more La Ninas favor more anchovies, but to the detriment of sardine abundance. So marine predators and fishermen alike must be flexible regarding which forage fish they target.
The ocean food supply enabled by upwelling and photosynthesis doesn’t just feed coastal fish. Open ocean ecosystems are nurtured as food is transported offshore, while sinking food supports rich ecosystems at darker depths.
The good news is warming climates increase vital upwelling. Upwelling and ocean productivity were reduced during the ice ages. Likewise, upwelling was reduced during the Little Ice Age that spanned 1200 to1850 AD. In contrast Dr. Francisco Chavez, Monterey Bay Aquarium Research Institutes’ senior researcher, determined upwelling and fish abundance increased along Peru’s coast with 20th century warming.
The collapse of the cod fishery off Canada’s east coast in the 1990s is the iconic example of how overfishing and unfavorable climate combined will court disaster. In the1990s, intruding cold Arctic waters pushed Newfoundland cod southward and concentrated them in the southern limits of their range. Because fishery managers estimate sustainable abundances by how easily fishermen maximize their catch, the concentration of cod in the south created an illusion of abundance. Not realizing those patches of high cod concentrations were the last refuges of a dwindling regional population, cod continued to be overfished. Historic fishery data reveal managers must be more alert to natural cycles of changing currents. Despite less fishing pressure in the 1800s, cold Arctic waters similarly flowed southward causing a comparable crash in cod abundance.
With advances in acoustical technology, fishery managers can now survey wider regions and better determine a species overall abundance. With a greater understanding of ocean oscillations and how fish aggregate, fishery managers are developing more fluid regulations that allow fishermen to increase their catch during boom times but reduce their catch during downturns. By protecting “refuges” during natural bust times, each species more rapidly rebounds when natural climate variability again favors their increase. With wiser management, we are rebuilding the oceans.
(Jim Steele is the retired director of San Francisco State University’s Sierra Nevada Field Campus and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism. Contact: naturalclimatechange@earthlink.net .)
Leave a Reply