Measures for coastal fish Lena Bergstrm, Patrik Kraufvelin, Ulf - - PowerPoint PPT Presentation

Measures for coastal fish

Lena Bergström, Patrik Kraufvelin, Ulf Bergström, Jens Olsson Department of Aquatic Resources, SLU, Sweden

SOM Fish WS 1-2019, Warszaw

Measu sures f s for c coastal f fish sh t to reduce mort

• rtali

ality

Measure name Link to major pressures Scientific support for effectiveness for fish in the Baltic Sea Permanent fisheries closures (no-take areas) Fishing Yes Partial fisheries closures Fishing Yes Regulation of fishing gears and catch Fishing Yes

Source: HELCOM Thematic Assessment of Coastal Fish 2018 (HELCOM Fish Pro III)

Mea easures es f for c coastal f fish to support t producti tivity

Measure name Link to major pressures Scientific support for effectiveness for fish in the Baltic Sea Stocking of young fish Fishing No Nutrient reduction Eutrophication No Habitat protection Physical exploitation Yes Habitat restoration (see next slide) Physical exploitation, Eutrophication Yes, but mainly local effects Reduction of harzardous substances Input of hazardous substances No Biomanipulation (extraction

• f e.g. Cyprinids/sticklebacks)

Fishing, Eutrophication No

Source: HELCOM Thematic Assessment of Coastal Fish 2018 (HELCOM Fish Pro III)

Supporting the productivity of fish

Restor

• ration
• n me

measures t that ma may s suppor

• rt p

productivity of coastal al f fish

Measure name Link to major pressures Scientific support for effectiveness for fish in BS Restoring eelgrass and freshwater angiosperms Eutrophication, Physical exploitation No Restoring unvegetated soft bottoms Eutrophication, Physical exploitation No Restoring hard bottom macroalgae Eutrophication No Restoring blue mussel reefs and blue mussel bottoms Eutrophication No Restoring stony reefs, placing

• ut artificial reefs

Physical exploitation, Eutrophication Yes Restoring wetlands (pike and perch factories) Agriculture and forestry, Food web measures, Physical exploitation, Eutrophication Yes

Source: Kraufvelin et al. In prep.

Mortality factors of fish

Gener eneral t trends ends i in n Sweden eden f for coast stal fish sh and its ts morta tality fact ctors

Perch Pike Pikeperch Commercial fisheries Recreational fisheries Cormorant Grey seal

Statements based on current studies

• Recreational fishing has strong effects on all three species
• Areas closed to fishing have 2-5 times higher abundances. Quick

responses

Fisheries Cormorant Grey seal

• May locally decrease predator populations, especially of perch
• Uncertain estimates. Pike seems prone to seal predation

The total picture affects the efficiency of fisheries regulation measures

Evidences? Methods for understanding mortality factors

• A. Comparison of fish removals
• B. Population modelling
• C. Experimental studies
• Large-scale manipulations, e.g no-take areas
• Natural experiments

Fish removals per year

• Recr. fishing
• Comm. fishing

Cormorant Grey seal

Perch Pike

• A. Comparison of fish removals

Based on fisheries statistics, and abundance + diet data Estimates per ICES SD, for all important species

Source: Hansson et al 2018. ICES Journal of Marine Science 75

• B. Population modelling

Parametrisation is difficult Conclusions on population effects differ between studies How do seals and cormorants affect fish stocks?

• Heated debate. Strong opinions
• Little evidence
• Weak interest from management

• C. Experimental studies

Case 1: Removal of fisheries with pr preda edators pr pres esen ent

• No-take zone established in 2010
• Test fishing in 2009-2016 in no-take zone and reference area
• Estimation of predator removals

Effects of fishing and predation

• Fishing: strong increase in no-take area
• Seal predation: negative effect on pike, perhaps also perch
• Cormorant predation: negative effect on perch

Grey seal

Increase in no-take area Initial increase, then decrease after seal came in No increase, possibly due to predation

Source: Bergström U et al In prep.

• No-take zone established already in 1980
• Test fishing in 2005, 2013 and 2018 in no-take area and reference
• Increasing seal abundances during period
• Cormorant colony since 2014
• C. Experimental studies

Case 2: Removal of fisheries + addition of predators

Effects of fishing and predation

• Fishing: 2-4 times higher abundance in no-take area
• Seal predation  decrease in pike
• Cormorant + seal predation  decrease in perch

5 10 15 20 25 30 2005 2013 2018

Perch

No-take Reference 0,0 0,2 0,4 0,6 0,8 1,0 2005 2013 2018 CPUE

Pike

Seal Seal + cormorant Source: Bergström U et al In prep.

Other effect sizes: Comparing effects of fishing and eutrophication (A)

Differences in species compositon Interannual variation in a referecence area Increasing nutrient enrichment No-take area close to reference area

Source: Bergström L et al 2019 Ambio

Differences in species Biomasses Piscivores Non-piscivores

Source: Bergström L et al 2019 Ambio

Other effect sizes: Comparing effects of fishing and eutrophication (B)

Conclusions

No-take areas are valuable management measures to restore fish Fishing, cormorants and seals all contribute to declines in coastal predatory fish. The impact of cormorants and seals is increasing To restore fish populations, we have to manage both fisheries and top predators