L17- Rebuilding Ocean Life

• major review structuring this lecture (grand challenge of rebuilding marine life)→

  

Where are we now?

• there are many pressures on marine ecosystems:

  • exploitation→

    • total global catch in fisheries→ bars go above reported, includes estimated unreported and illegal fishing too, 100mt by 1990s and has remained relatively constant since

      

      → we take a huge biomass out of fisheries every year

    • hunting of marine megafauna→ daily locations of american whaling vessels show a huge density of points when whales were sited or caught from, does not include data from other countries too

      

      • huge loss of whales, estimated using models:

  

  • habitat loss→ there is lots globally and lots around coastlines

  

  • plastic waste pollution→ increased massively and is continuing to increase

  

  • climate change→ ocean continues to warm, heat waves are driving coral bleaching, increase in sea surface temp and heat content of upper 2000m, increases year on year

  

• summary→ there are lots of human pressures that started a long time ago, lots have peaked (hunting, fishing, deforestation, habitat loss) but some are recovering whilst some are growing

  

What can we do?

• systematic reviews of evidence e.g. conservation evidence (website),

• learn from documented case studies and anecdotal experiences

• 4 categories of impactful interventions for marine ecosystems:

  • regulate hunting

    • whaling has occurred for centuries but the late 19th century had technological advances and processing capabilities that led to huge losses by the 20th century

    • scale of this→ 3million whales were killed and processed in this time, all major whales were hit:

      

    • since then, the International Whaling Commission decided commercial whaling needed to stop for 1985-1986, some countries did not listen, is still in place→ has ended commercial whaling:

      • fin whales population was reduced to 1-2% of its pre-exploitation size but recent surveys have reported huge returns to ancestral breeding grounds→ are a recovering population

      → global agreements to reduce/halt exploitation leads to recovery of hunted populations

  • manage fisheries

    • fish in NE Atlantic have been intensely commercially exploited for decades, primary driver of decline is fisheries

    • have been well monitored→ can understand the pressures on them:

      • below→ things we can’t control, influenced by environment, predation etc.

      • above→ things we can control, fisheries, can influence that through fisheries management

      

    • better management from 2000 had led to an increase in fish biomass

    • large scales fisheries can be managed sustainably- have the understandings

    • status of many of the world’s fish stocks are formally assessed→ have data on how they can be managed

    • global coverage of the RAM database (the largest database of fisheries stock assessments)-

      • proportion that have a scientific assessment, size of pie chart is how much is caught

      • there are many stocks that are well assessed, but there are certain areas where the stocks are barely assessed

      

    • fishing biomass and mortality:

      • above 1→ biomass is healthy and at maximum sustainable yield

      • below 1→ fishing mortality is within maximum sustainable yield

      • fishing biomass decreased (reached maximum) and fish mortality increased (went above maximum) since 1970

      • there was wide spread exploitation

      • management pattern has reversed these effects

      

    • lots of fish stocks that have been exploited since 2006 now have fishing pressures below the maximum sustainable yield but lots of other stocks have increased in fishing pressures

      → reducing fishing pressure promotes fish stock rebuilding

    • full recovery will take years

    • how actively and effectively managed fish stocks are→ increases in intensity of management will cause a decrease in fish mortality and an increase in biomass

      

      → fish stocks with robust scientific assessments are well managed and increasing in fish

  • improve water quality

    • there are many regulations/frameworks being developed to reduce sewage in oceans

      • Stockholm convention, MARPOL convention→ have reduced pollutants in the sea

    • e.g. the baltic sea→ ‘time machine’, is already affected by future impacts expected to be seen in other seas

      • is enclosed, need international agreements:

      

      • heat map of stresses in seas→ the baltic sea has the highest, with high to intermediate in all these stressors

      

      • there has been an effort to improve water quality in this sea e.g. nutrient pollution (agricultural and industrial runoff)

      • successful management has lead to a regional trend reversal in nutrient pollution→ both types of nutrient are above target loads but trends are downwards

      

      → can get substantial improvements in water quality by implementing easy solutions but full recovery is more costly and can cause conflict with other areas

  • protect and restore habitats

    • MPAs- has increased to over 8% today

      • well protected MPAs do work→ increase fish biomass by 3x, fish density increases by 40%, spillover benefits, habitat benefits

    • initiatives to restore habitats

      • direct restoration measures- number of measures have increased over time and in multiple habitats e.g. project seagrass

      

      → coastal and marine habitats can be protected and restored but the issue is how to scale them up

Roadblocks to recovery of marine life:

• natural variability, environmental extremes, natural/social events, increased pressures from the human population, failure to mitigate climate change, gaps/biases in understanding

  • managing data-limited fisheries:

    • only 50% of stocks are scientifically assessed

    • there are no scientific assessments on small scale fisheries in coral reef and mangrove habitats

    • these stocks need qualitatively different types of assessments e.g. species specific vs mixed-species

  • climate change:

    • are not on target to meet targets e.g. Paris Agreement

    • spatial and habitat based conservation can help e.g. habitat restoration and MPAs can improve carbon sequestration, protection, biodiversity, catch and incomes

    • meta analysis from 200 MPAs show how marine habitats can help mitigate climate change:

      • how much they contribute to different pathways, global extent of habitat (size of circle)

      • have different effects

      • sediments don’t have much effect, just a little carbon sequestration, but cover most of the planet so globally this will have an impact

    

    → MPAs alone cannot offset all carbon but are a useful tool for climate change mitigation

Beyond managing crises:

• Duarte et al. suggest a 2050 target of substantial to complete recovery for most oceans is realistic

• futures:

  • managing high seas as global commons

  • science fiction prototyping→ imagining what oceans will look life, stepping back and looking at what future we want, optimism