Why monitor litter on the seafloor? Large area Area of - - PowerPoint PPT Presentation

Why monitor litter on the seafloor?

• Large area
• Area of accumulation?
• Previous studies have

shown large quantities

• Required in the MSFD

How to monitor?

Collect litter in trawls/dredges Visual counts of litter using divers or video

The BITS (Baltic International Trawl Survey) programme

What is a trawl and how does it capture litter?

Geographical scope

Baltic Sub-regions Sediment types

Types of items recorded

Several different list used in the Baltic and elsewhere – still under development

Average amount of items in the (surveyed area of) the Baltic Sea

NUMBER 58.9± 20.9 items per km2

(average ± 95% confidence interval)

Weight 85.3±65.2 kg per km2 42 % of the hauls did not contain any litter items

Much or little?

• OSPAR area: 13.8-230 items/km2 depending on

region

• North Sea: 38 items/km2
• The Adriatic : 510 ± 517 items/km2
• Number of hauls containing litter in the OSPAR

Area: 59-100%, depending on region

Conclusion: Within the same order of magnitude as

• ther Europeans regions

Less than the Adriatic and the Bay of Biscayne, more than the North sea

Much or little?

Combined area of sub-regions 227000 km2 ➔Approximately 13.2 million items ➔ Approximately 19000 tons

Temporal trend?

Conclusion: Significant differences among years No temporal trend Confounded with changes in geographical domain?

Different sub-regions

Conclusion: Significant differences among sub-regions Confounded with temporal trends? OBS! Some extremely high values excluded

Representativity in sub-regions

Sub-basin Area of sub- basin (km2) No of Hauls 2012-2016 Area per haul Eastern Gotland Basin

75093 295 255

Bornholm Basin

42219 648 65

Northern Baltic Proper

39674 9 4408

Western Gotland Basin

27683 59 469

Arkona Basin

17616 315 56

Great Belt

10760 125 86

Gdansk Basin

5876 29 203

Bay of Mecklenburg

4620 58 80

Kiel Bay

3356 61 55

Conclusion: Significant differences among sub-regions Influnced by the need of fish stock assessments- not ML

Top X – frequently found items

Conclusion: Items from natural materials dominate

Litter in different sediment types

Conclusion: Significant differences among sediment types

Representativity in sediment types

Sediment type Sediment type area (km2) No of Hauls 2012-2016 Km2 per haul Non-photic mud and clay 238000 1066 223 Non-photic sand 50600 341 148 Non-photic hard bottom 41330 28 1476 Photic sand 37300 84 444 Photic hard bottom 30970 12 2581 Photic mud and clay 24430 68 359 Conclusion: Best representativity in most common (accumulation) sediment types

Items from natural materials

Material Proportion (%) by number

• f items

North Sea 2014

Plastic 30.6 79 Metal 7.5 3 Rubber 2.7 3 Glass and ceramics 8.6 2 Natural 44.6 12 Miscellaneous 6.1 5

Conclusion: Items made from natural materials more common in the Baltic than in other regions

Items from natural materials

Conclusion: “Non-natural” weak but significant increase Interpret with caution…

What to do about areas that do not participate in trawl surveys

• Accept limited geographical scope?
• Extend trawl surveys?
• Use other monitoring approaches (e.g.

video)?

Summary

• Amounts “similar” to other European sea areas
• Items made from natural items dominate –

different from other European sea areas

• No total time trend- but significant increase if

natural items are excluded

• Monitoring geographical scope changing/improving

Analyses should be interpreted with caution

• Large areas of the Baltic not yet covered