Conference at TCD Highlights How Good Management Helps Ocean Life to Recover – Message from Oceans Past

Posted on: 30 November 2010

Human life on the planet Earth depends on its oceans.  Since 1990, the output of fisheries has stagnated below 100 million tonnes per year in spite of the massive investment in high-tech vessels and equipment, and the opening up of distant and deep waters in the southern hemisphere.  The Earth’s oceans simply will not yield more.  Marine habitats are under severe pressure from exploitation, the torment of offshore structures, and nutrient run-offs from land use.  But what is the scale of change?  What used to be in the sea before humans began impacting on marine ecosystems and habitats?

How historical research can inform us of the scale of human impact through time was the focus of discussion at a major conference held in the Trinity Long Room Hub recently.  Oceans Past III is the third in a series of organised conferences as part of the Census of Marine Life’s History of Marine Animal Populations (HMAP) project.  HMAP provides baselines of marine life abundance and species distribution during past periods, against which present stocks can be compared.  Researchers in natural sciences and humanities from around the world participated in the conference.

TCD’s Professor of Environmental History, Academic Director of the Trinity Long Room Hub and chair of HMAP, Professor Poul Holm explained: “Historical research informs us of how much mankind depended on ocean resources for economic, social and cultural needs, and we need this knowledge to manage life in the oceans wisely.  Fortunately, only a few species have gone extinct.  The oceans are wide and deep, and many species may rebuild their own stocks if we let them.  Knowing what used to live in the sea, therefore, informs us about what might again live there if we allow the populations to grow.”

The History of Marine Animal Populations was designed to enhance the knowledge and understanding of how and why the diversity, distribution and abundance of marine life in the world’s oceans have changed over the long term. Over 100 researchers have engaged in this interdisciplinary research program since 2000. Generating historical evidence from sources that range from monastic ledgers and harbour records to kitchen middens, fishbones and whale teeth, the HMAP team has substantially increased our knowledge of the impact of humans on the marine environment, and the influence of natural factors on human welfare.  HMAP forms the historical component of the Census of Marine Life.  The first Census of Marine Life produced the most comprehensive inventory of known marine life ever compiled and catalogued it as a basis for future research, the findings of which were announced earlier this year by Professor Poul Holm.  This first baseline picture of ocean life – past, present, and future – can be used to forecast, measure, and understand changes in the global marine environment, as well as inform the management and conservation of marine resources. During the conference, international scientists presented new evidence of historical change in marine animal populations and ecosystems.  Other themes explored included data management, modelling and visualisation in marine historical ecology; linking history and science to policy and management, and investigating the long-term changes in interactions between human and marine animal communities.  Some of the case studies presented are summarised below.

Turtles and Sharks, Oaxaca, Mexico:

The global demand for turtle leather in the second half of the twentieth century led to a rapid depletion of Olive Ridley sea turtle stocks in the southern Mexican state of Oaxaca.  The Mexican federal government banned all sea turtle captures in 1990.  This, coupled with previous conservation measures during the fishery years, led to a speedy recovery of sea turtle populations.  As part of the fishery conservation efforts, eggs from slaughtered females were incubated, and the resulting hatchlings were released into the sea.  The Olive Ridley takes 12-15 years to reach reproductive age, so the recovery time coincides with the maturation time of the hatchlings released a generation earlier.  Today, the population of Olive Ridley turtles on the coast of Oaxaca has recovered and continues to grow.  Yet, due to an increase in demand for shark fins in East Asian markets, shark fishing quickly replaced turtle captures as an important source of income.  And history soon repeated itself, as the shark populations rapidly declined.  Michelle María Early Capistrán who conducted the research said: “The turtles are out of danger, but their safety was achieved at the expense of the sharks.”  The fishing efforts for both sharks and turtles in the region grew as a result of growing demands from a global market.  This is a clear example of how changes in global and local economic priorities can have a direct impact on marine animal populations, and how marine animal conservation is, at its very root, a political and economic problem.

Sharks, Northern Adriatic Sea:

In Chioggia’s fish market, in the Northern Adriatic Sea, elasmobranch landing greatly declined in the last 50 years.  Elasmobranchs are sharks, skates and rays, whose bodies have a cartilage structure instead of a skeleton, and are among the most vulnerable species of the oceans.  Their populations are on a worldwide decline.  Thirteen species are currently landed, but one shark, the common smooth-hound: Mustelus mustelus, represents more than 60% of the total elasmobranch landing. Researchers develop models by using historical and present data to predict population trends under different management scenarios.  These models predict that without proper management, the common smooth-hound population will decrease by approximately 80% in the next 50 years. Considering the elasmobranch’s high survival rates when released at sea after being caught, the models demonstrate that protection of juveniles proved to work far better than just reducing the fishing effort.  The combination of historical and present data and modelling makes this management scenario realistic and feasible.

Coral Reef, Hawai’i:

Coral reef ecosystems are among the most diverse coastal ecosystems in the world.  Researchers have reconstructed coral reef ecosystem conditions over the past 700 years, in the Hawaiian archipelago by integrating archaeological data, anecdotal and ethnographic information, and modern ecological, and fisheries data on marine species.  The researchers discovered that humans, in at least two cases, played a positive role in the recovery of coral reefs.  Prior to western contact, Native Hawaiian societies developed large-scale aquaculture systems and implemented effective management practices that sustained communities and coral reef ecosystems in the main Hawaiian Islands.  After western contact, the remote northwestern Hawaiian Islands have benefited from over a century of conservation and ecosystem protections, including the recent designation of this region as the fully protected Papah?naumoku?kea marine national monument.  The results challenge conventional assumptions and reported findings that human impacts to ecosystems are cumulative and lead only to a long-term path of environmental decline.  In contrast, recovery periods reveal that human societies have interacted sustainably with coral reef environments over long time periods and that degraded ecosystems may still retain the adaptive capacity to be resilient to human impacts.  Understanding environmental challenges of the past provides promise for contemporary efforts to manage ecosystems and societies toward social-ecological sustainability.