Rapid declines threaten the persistence of many marine fish. Data from more than 230 populations reveal a median reduction of 83% in breeding population size from known historic levels. Few populations recover rapidly; most exhibit little or no change in abundance up to 15 years after a collapse. Reductions in fishing pressure, although clearly necessary for population recovery, are often insufficient. Persistence and recovery are also influenced by life history, habitat alteration, changes to species assemblages, genetic responses to exploitation, and reductions in population growth attributable to the Allee effect, also known as depensation. Heightened extinction risks were highlighted recently when a Canadian population of Atlantic cod (Gadus morhua) was listed as endangered, on the basis of declines as high as 99.9% over 30 years. Unprecedented reductions in abundance and surprisingly low rates of recovery draw attention to scientists' limited understanding of how fish behavior, habitat, ecol...

/pdf/marine-fish-population-collapses-consequences-for-recovery-4t73ltufho.pdf

Marine Fish Population Collapses: Consequences for Recovery and Extinction Risk

Fishing affects the seabed habitat worldwide on the continental shelf. These impacts are patchily distributed according to the spatial and temporal variation in fishing effort that results from fishers' behaviour. As a consequence, the frequency and intensity of fishing disturbance varies among different habitat types. Different fishing methodologies vary in the degree to which they affect the seabed. Structurally complex habitats (e.g. seagrass meadows, biogenic reefs) and those that are relatively undisturbed by natural perturbations (e.g. deep-water mud substrata) are more adversely affected by fishing than unconsolidated sediment habitats that occur in shallow coastal waters. These habitats also have the longest recovery trajectories in terms of the recolonization of the habitat by the associated fauna. Comparative studies of areas of the seabed that have experienced different levels of fishing activity demonstrate that chronic fishing disturbance leads to the removal of high-biomass species that are composed mostly of emergent seabed organisms. Contrary to the belief of fishers that fishing enhances seabed production and generates food for target fish species, productivity is actually lowered as fishing intensity increases and high-biomass species are removed from the benthic habitat. These organisms also increase the topographic complexity of the seabed which has been shown to provide shelter for juvenile fishes, reducing their vulnerability to predation. Conversely, scavengers and small-bodied organisms, such as polychaete worms, dominate heavily fished areas. Major changes in habitat can lead to changes in the composition of the resident fish fauna. Fishing has indirect effects on habitat through the removal of predators that control bio-engineering organisms such as algal-grazing urchins. Fishing gear resuspend the upper layers of sedimentary seabed habitats and hence remobilize contaminants and fine particulate matter into the water column. The ecological significance of these fishing effects has not yet been determined but could have implications for eutrophication and biogeochemical cycling. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators. In contrast, high levels of trawling disturbance cause sediment systems to become unstable due to large carbon fluxes between oxic and anoxic carbon compartments. In low energy habitats, intensive trawling disturbance may destabilize benthic system chemical fluxes, which has the potential to propagate more widely through the marine ecosystem. Management regimes that aim to incorporate both fisheries and habitat conservation objectives can be achieved through the appropriate use of a number of approaches, including total and partial exclusion of towed bottom fishing gears, and seasonal and rotational closure techniques. However, the inappropriate use of closed areas may displace fishing activities into habitats that are more vulnerable to disturbance than those currently trawled by fishers. In many cases, the behaviour of fishers constrains the extent of the impact of their fishing activities. Management actions that force them to redistribute their effort may be more damaging in the longer term.

Modification of marine habitats by trawling activities: prognosis and solutions

Summary
1Global-scale environmental degradation and its links with non-renewable fossil fuels have led to an increasing interest in generating electricity from renewable energy resources. Much of this interest centres on offshore renewable energy developments (ORED). The large scale of proposed ORED will add to the existing human pressures on coastal ecosystems, therefore any ecological costs and benefits must be determined.
2The current pressures on coastal ecology set the context within which the potential impacts (both positive and negative) of offshore renewable energy generation are discussed.
3The number of published peer-review articles relating to renewable energy has increased dramatically since 1991. Significantly, only a small proportion of these articles relate to environmental impacts and none considers coastal ecology.
4Actual or potential environmental impact can occur during construction, operation and/or decommissioning of ORED.
5Construction and decommissioning are likely to cause significant physical disturbance to the local environment. There are both short- and long-term implications for the local biological communities. The significance of any effects is likely to depend on the natural disturbance regime and the stability and resilience of the communities.
6During day-to-day operation, underwater noise, emission of electromagnetic fields and collision or avoidance with the energy structures represent further potential impacts on coastal species, particularly large predators. The wider ecological implications of any direct and indirect effects are discussed.
7Synthesis and applications. This review demonstrates that offshore renewable energy developments will have direct and, potentially, indirect consequences for coastal ecology, with these effects occurring at different scales. Ecologists should be involved throughout all the phases of an ORED to ensure that appropriate assessments of the interaction of single and multiple developments with the coastal environment are undertaken.

/pdf/offshore-renewable-energy-ecological-implications-of-10m9p1d5k1.pdf

Offshore renewable energy - ecological implications of generating electricity in the coastal zone.

https://assets.wwf.org.uk/downloads/bycatch_paper.pdf

Defining and estimating global marine fisheries bycatch

Comparison of baited remote underwater video stations (BRUVS) and prawn (shrimp) trawls for assessments of fish biodiversity in inter-reefal areas of the Great Barrier Reef Marine Park

Introduction. Acknowledgements. Contributors. PART 1: Distribution of Fishing Effort and Physical Interaction with the Seabed. 1. Spatial and temporal patterns in North Sea fishing effort (S. Jennings, K.J. Warr, S.P.R. Greenstreet and A.J. R. Cotter). 2. Physical impact of beam trawls on seabed sediments (R. Fonteyne). 3. Is bottom traw3ling partly responsible for the regression of Posidonia oceanica meadows in the Mediterranean Sea (G.D. Ardizzone, P. Tucci, A. Somaschini and A. Belluscio). PART 2: Effects of Fishing on Benthic Fauna and Habitats. 4. Fishing mortality of populations of megafauna in sandy sediments (M.J.N. Bergman and J.W. van Santbrink). 5. Effects of otter trawling on the benthos and environment in muddy sediments (B.Ball, B. Munday and I. Tuck). 6. The effects of scallop dredging on gravelly seabed communities (C. Bradsaw, L.O. Veale, A.S. Hill and A.R. Brand). 7. Impact of scallop dredging on maerl grounds (J.M. Hall--Spencer and P.G. Moore). PART 3: Fishing As A Source of Energy Subsidies. 8. The behavioural response of benthic scavengers to otter--trawling disturbance in the Mediterranean (M. Demestre, P. Sanchez and M.J. Kaiser). 9. Food subsidies generated by the beam--trawl fisher in the southern North Sea (M. Fonds and S. Groenewold). 10. Impact of trawling on populations of the invertebrate scavenger Asterias rubens (K. Ramsay, M.J. Kaiser, A.D. Rijnsdorp, J.A. Craeymeersch and J. Ellis). 11. Seabirds and commercial fisheries: population trends of piscivorous seabirds explained (C.J. Camphysen and S. Garthe). PART 4: Long--Term Changes Associated with Fishing. 12. Distribution of macrofauna in relation to the micro--distribution of trawling effort (J.A. Craeymeersch, G.J. Piet, A.D. Rijnsdorp and J. Buijs). 13. Long--term changes in North Sea Benthos: Discerning the role of fisheries (C.L. J. Frid and R.A. Clark). 14. Effects of fishing on non--target fish species (S.P.R. Greenstreet and S.I. Rogers). 15. Impacts of fishing on diversity: from pattern to process (S. Jennings and J.D. Reynolds). PART 5: Conservation Methods, Issues and Implications for Biodiversity. 16. Technical modifications to reduce the by--catches and impacts of bottom--fishing gears (B.van Marlen). 17. Fishing and cetacean by--catches (N.J.C. Tregenza). 18. Effects of fishing on non--targeted species and habitats: identifying key nature conservation issues (M.L. Tasker, P.A. Knapman and D. Laffoley). 19. The need for closed areas as conservation tools (H.J. Lindeboom). 20. No--take zones: a management context (J.W. Horwood). PART 6: Socio--Economic Implications and Mechanisms for Reducing the Impacts of Fisheries. 21. Economic incentives to discard by--catch in unregulated and individual transferable quotas fisheries (S. Pascoe). 22. Options for the reduction of by--catches of harbour porpoises (Phocoena phocoena) in the North Sea (J.M. McGlade and K.I. Metuzals). 23. Economic and sociocultural priorities for marine conservation (P.J. S. Jones). 24. Integrated management: the implications of an ecosystem approach to fisheries management (D. Dymes). PART 7: Workshop Conclusions. 25. The implications of the effects of fishing on non--targeted species and habitats (M.J. Kaiser). Glossary. Index.

S.J. De Groot

Papers

The effects of fishing on non-target species and habitats: biological, conservation and socio-economic issues

The behavioural response of benthic scavengers to otter trawling disturbance in the Mediterranean

The implications of the effects of fishing on non-target species and habitats