PNUD-DNP, 2003.

The Committee on Biological Diversity in Marine Systems (1995) highlighted that marine biodiversity is changing, and unless there is a change in human attitudes it is likely human-mediated extinction of species in the sea will be similar to those on the

land. The loss of species has been part of the earth’s evolutionary history through natural events. Over time some changes were reversible, and others were integrated through a process of adaptation. Human mediated changes, however, are often

irreversible, affecting many different habitats, occurring within shorter time frames, and the order of magnitude of change is often higher (Thorne-Miller and Catena, 1991 pp. 14-16; the Committee on Biological Diversity in Marine Systems, 1995 pp. 5-7). Many marine ecosystems are already highly stressed and may not be able to cope with new and increased stresses, which may lead to further loss of biodiversity. In the past the rate of change has been slower, often allowing for adaptation. This may be a particular problem for the flora and fauna of the deep oceans, which have until recently

experienced relatively stable conditions and may not be able to respond to rapid changes (Thorne-Miller and Catena, 1991 p. 15). There are a number of human activities that can directly or indirectly impact marine ecosystems, which in turn may also affect commercial fisheries and aquaculture. Ecosystem-based management requires the consideration of both direct and indirect effects of commercial fishing as well as the inclusion of other impacts such as bycatch, and recreational fisheries. The combined effects of, fishing, environmental variation, and climate change increasingly threaten marine ecosystems, and complicates management (Crowder et al., 2008). The principal issues are climate change; coastal development and land-based impacts; and the direct and indirect impacts of fishing and these will be discussed below.

Climate change

The environmental and biophysical impacts of climate change include the warming of ocean waters, sea level rise and ocean acidification; changing weather patterns and rainfall with more extreme storm and cyclone events; changes in ocean currents and waves; chemistry changes in ocean waters; and in coastal areas erosion of the shoreline. Productivity patterns, ecosystem boundaries and species composition may also change (Voice et al., 2006). Climate change may affect aquatic ecosystems in many ways, although the capacity of fish species to adapt to such change is not fully understood. Changes in water temperatures and especially in wind patterns, however, suggest climate change can disturb fisheries, with potentially serious impacts on global fishery resources (United Nations Environment Programme (UNEP), 2007 p. 122). Concern with the projected rapidity of current climate change centres on whether, species and

ecosystems have time for adaptation. This is an emerging problem, which has already reached an irreversible turning point in terms of current human planning time frames. Stabilisation of greenhouse gas concentrations is yet to be achieved, and even when stabilised, warming is likely to continue for centuries, but at a slower rate, while sea levels will continue to rise unabated for many centuries (Pittock, 2003 pp. 3-4). As a consequence of ozone depletion, UV-B radiation is increasing which may reduce productivity of phytoplankton in surface waters in the open ocean (Gray, 1997p. 163). There is also the threat of global warming through the impact of increased greenhouse gases most notably, but not restricted to carbon dioxide CO2. This is due to industrial

processes such as the burning of fossil fuels, and the widespread clearing of tropical forests. Although it is difficult to predict outcomes, it is likely there will be changes in climate and weather patterns with more frequent storm events and changes to rainfall patterns. There will also be a rise in sea level through expansion of the oceans and increased melting of the ice caps. These changes pose risks to many species that have low temperature range tolerances, such as corals; and for those species where sea level rises will result in the loss of critical coastal habitats (United Nations Environment Programme (UNEP), 2007 p. 59). An outcome of the continued increase in levels of atmospheric CO2 will be a decrease in carbonate ion concentrations and an increase in

hydrogen ion concentration; this will reduce the ability of oceans to absorb CO2,

resulting in acidification of the oceans. Acidification will decrease planktonic and benthic habitat calcification rates for individual species and coral communities (Sabine et al., 2004; Feely et al., 2004).

Climatic factors can affect the spatial extent of marine populations by modifying the dynamics of the spawning or feeding areas, consequently changing recruitment success and migration patterns. The inter-annual environmental fluctuations such as El Nino events affect the structure of the plankton community, the spatial distribution of fish and invertebrates, the recruitment success of pelagic fish and the mortality of birds and mammals in the northern Pacific. Alternate patterns between two small pelagic fish species, sardines and anchovy, have been observed on a decadal basis in upwelling systems (Curry et al., 2003 pp. 104-110). Climate change will affect the ocean environment and its capacity to sustain fish stocks. The situation is likely to be made worse in conjunction with other stresses such as land-based activities and impacts from

fishing. According to the FAO (2009 pp. 87-87) in general the impact of climate change (which may be positive or negative) on fisheries, aquaculture and coastal communities will depend on the vulnerability of each community. The factors determining

vulnerability include the nature and degree of exposure to climate change and the degree to which communities are dependent upon fisheries and their sensitivity to changes in the fishing sectors, the potential impacts to fisheries and livelihoods, and the adaptive capacity of communities.

Coastal zone development and land-based impacts

Many of the major threats to marine biodiversity are in the coastal zones, as a result of increased population densities in coastal areas, together with coastal development and urbanisation. In developed countries this is driven by lifestyle choices, whereas in developing countries it is more from population pressures and economic necessity. The coastal zone is also subject to multiple uses and users such as: port infrastructure for shipping and transport; tourism and recreational activities; oil and gas production facilities; waste disposal; and fishing and aquaculture. These activities can modify or damage marine habitats. Pollution from land-based activities also effect water quality. The cumulative impacts resulting from these activities have the potential to affect marine biodiversity, ecosystems and fisheries production (Gray, 1997; Rosenberg, 2003 p. 189; Kay and Alder, 2005 pp. 21-44). Three key issues are habitat modification or loss; water quality and pollution; and the introduction of exotic marine species. Habitat loss and modification can occur directly through land reclamation as for

example the draining of coastal salt marshes or the removal of mangrove forests; or may occur indirectly through human activities and the associated consequences of coastal development, such as eutrophication. The coastal marine environment is particularly vulnerable to both these pressures. Some habitats are important to particular species during the different stages of their life history such as providing food, shelter, safety, suitable spawning sites and juvenile nursery grounds. Some habitats are associated with particular species, for example seagrass and dugongs, therefore the loss of critical habitat may threaten particular species (Martha et al., 2002 pp. 341-358).

Chemical pollution and eutrophication are a cause of water quality issues. Organic and inorganic wastes from land-based activities such as agricultural, industrial, and

domestic wastes particularly affect estuaries and coastal areas. Nutrient pollution can cause harmful algal blooms (Hughes and Goodall, 1992; Suchanek, 1993;

Suchanek,1994; Rosenberg, 2003). Many of these chemicals react with the chemistry of seawater, which in turn may affect organisms that live and feed in these waters, also allowing toxins to enter the food chain. The effects of contaminants may not cause direct mortality, but may have negative population effects on recruitment processes and larval viability, or cause abnormalities in growth and reproduction. For example, coral reproduction processes are highly sensitive to decreased water quality and persistent pollution. Some heavily polluted estuaries have already lost much of their flora and fauna. Deep sea habitats may also be altered by pollution as the sea continues to be used for waste disposal, some of which is highly toxic (Thorne-Miller and Catena, 1991 pp. 17-19; Kay and Alder, 2005 pp. 21-44; Kaiser et al., 2005 pp. 476-483; Harrison and Booth, 2007 p. 355). The damming or diversion of rivers for power generation, flood control or irrigation has resulted in significant reductions and/or changes in the timing and amount of freshwater flowing to the sea. Reduced sediment flows into deltas and wetlands, has in some cases resulted in the loss of fish spawning habitat. Other activities such as mining or deforestation have led to large increases in sediment loads, which can smother coral reefs and other coastal habitats important to fisheries production (McKay et al., 1999; Gray, 1997).

The translocation of exotic species has the potential to alter entire ecosystems and habitats which may cause highly specialised native species to become vulnerable through competition and predation. Exotic species may also introduce parasites and diseases that native species have no immunity to, in some cases this may prove fatal. The difficulty is that once exotic species have become established, it is virtually impossible to eradicate them. The primary vectors for introductions are through the ballast water from commercial ships, the hulls of boats, and the aquaculture industry. The effects of invasive species are considered one of the main threats to native biodiversity, together with habitat destruction and modification. Disturbed terrestrial environments can facilitate animal and plant invasions, the extent to which this may also be the case in marine environments, particularly in disturbed coastal zones, is only beginning to be investigated (Meffe and Carroll, 1994; Glasby and Creese, 2007). Genetically modified species from aquaculture may escape or be introduced to the wild and interact, compete or breed with its wild counterpart. For example, reared salmon for

aquaculture has caused issues for wild salmon fish stocks in several countries (Richardson, 2003 pp. 278-279).

Impacts of fishing on marine ecosystems

Fishing affects the targeted fish stocks and other ecosystem components, directly or indirectly (Holmlund and Hammer, 1999; Sissenwine and Mace, 2001). Marine fish stocks show evidence of declines from a combination of unsustainable fishing

pressures, habitat degradation and global climate change (United Nations Environment Programme (UNEP), 2007 p. 145). The potential for fishing to impact ecosystem components directly or indirectly is now recognised. The direct impacts of fishing include the mortality of target species; non-target species caught as bycatch; and

discarding and high grading practices. Total species mortality (both natural and fishing) can fluctuate considerably, and may be more extreme in one year than another due to environmental conditions, such as changes in water temperature; lack of food;

competition; population density; predation; pathogens and disease (Fulton et al., 2004 pp. 7-10).

Direct impacts of fishing

Fishery systems are complex and subject to natural variation, and perturbations from human activities (including fishing), therefore yields are not constant. If annual stock assessments do not account for these variations, over-exploitation may occur. If this situation continues some populations may not be able to recover, especially in the case of long-lived slow-growing species. The outcome is that stocks may fall below the minimum viable population level (pushed past the ecological threshold, the allee effect), so even when management reduces fishing pressure stocks are slow to recover, or in some cases may not recover (Barbier et al., 1995).

Exploitation of commercial target species may result in demographic changes such as reduced population size, changes in size and age structure of populations and

community changes. The direct impacts of total mortality (natural, targeted catch, and bycatch /discards) on species can impact communities, populations and species components within an ecosystem in the following manner. Declines in slow growing species with low fecundity may over time result in community changes within an

ecosystem, to one dominated by highly productive and fast growing species. Fishing usually selects the larger and older fish, which can affect productivity (fecundity), as the larger and older individuals, usually have a greater reproductive capacity. This selective pressure on populations may change the size and age structure of a species leading to a reduction in genetic fitness. This in turn reduces the ability of a population to withstand fluctuations due to natural variability or other human activities, which further stresses and weakens ecosystem components (Fulton et al., 2004 pp. 7-8; Kenchington, 2003 pp. 235-240). One effect of over-fishing on community composition is fishing down marine foods webs (Pauly et al., 1998). This can occur where fishing fleets switch to new target species at a lower trophic level, thus leading to sequential over-fishing. Fishing can also disrupt foraging behaviour and reproduction of some species. Reproductive potential may be reduced for some fish and invertebrate species, by removing individuals from spawning migrations or aggregations, but also by causing aggregations to disperse or decline to densities at which they are ineffective (Fulton et al., 2004 pp. 7-8).

Although commercial fishing targets particular fish species, many non-target species are also caught as bycatch – depending on the fishery method and gears, which may then be discarded. Quantifying actual amounts of discards may be difficult globally, as these statistics are not required in many fisheries, or may be difficult to verify where there are no observer programs. Therefore, mortality will be underestimated, and in some

fisheries bycatch and discards may be larger than the landed catch. Different fishing techniques and gear types can lead to distinct and different types of bycatch, including incidental mortality (Goni, 2000). For example, shrimp trawls have a high bycatch rate due to small mesh nets used, retaining a large variety of fish that are found in the same habitat (Cook, 2003 pp. 220-223). Bycatch species may include other non-target fish species, invertebrates, marine mammals, reptiles, and birds. The loss of species at one level of the food chain could dramatically affect species at another level, as marine food webs can be very complex. Bycatch mortality is a serious problem due to its magnitude in terms of the removal of biomass and the range of species affected. This can be a problem particularly for slow growing species with low fecundity, those that have a limited geographical range, or are dependent upon particular habitats during different stages of their life history (Kaiser and Jennings, 2002 pp. 342-361). Bycatch problems in a fishery can also be a symptom of resource over-exploitation. Bycatch resulting from technological constraints imposed by gear may be made worse by economic forces

that drive the process. For example, the process of reducing selectivity to catch smaller fish so that profitability can be maintained will result in greater bycatch of small non- target species. As abundance of target species becomes less, in order to maintain catch rates fishers will extend the range of species taken and the geographical areas fished (Cook, 2003 p. 228).

Discarding may occur because the species caught do not have any commercial value, or regulations may prohibit the landing of certain species. High grading is the discarding of marketable species in order to retain the same species at a larger size, or higher price (Hall, 1995). Discarding can impact energetic pathways and community structure by increasing opportunistic scavenging, which may change the foraging patterns of certain species, leading to changes in predator/prey strategies. Discarding may also increase susceptibility to disease of individuals damaged by gear interactions, as well as the spread and introductions of pathogens due to changing local environmental conditions. Discarding can change chemical and ecological conditions as discards form deposits of organic material with high oxygen demands, and may lead to anoxic conditions in benthic environments that receive poor circulation (Fulton et al., 2004 pp. 9-12).

Indirect impacts of fishing

It is only recently that the indirect effects of fishing activities on other species and exploited ecosystems have been recognised, and are now of concern to a wide range of stakeholders (Fulton et al., 2004; Goni, 2000). Indirect impacts of fishing may include ghost fishing, community changes, habitat modification, and an increased susceptibility to environmental fluctuations. Fishing may affect community structure, competition and predator prey interactions may be changed, and may cascade through the food chain either by bottom-up or top down controls. Fishing operators often accidentally lose gear (nets or traps) or dump other debris used by the fishery (plastics). Lost fishing gear may cause mortality by continuing to catch fish (ghost fishing) for a long time afterwards ranging from days, months to years depending upon the depth, habitat type, current speed, and the longevity of the materials of gear, such as gill nets and traps. Marine litter and debris such as damaged nets and plastics may cause mortality by entangling mammals such as seals or turtles, or by ingestion, for example seabird chicks and light sticks (Fulton et al., 2004 pp. 8-9).

Fishing occurs across most marine ecosystem types, and may be associated with particular habitats. The deployment of fishing gear on these habitats and destructive fishing practices modify habitats by disturbance or destruction. For example trawling or dredging on the sea bed can impact benthic species, topographical structures and

sediments. Blast fishing, poison, and drift can cause high indiscriminate mortality, affect coral reefs, and recovery may take a long time. These practices impact the complexity, structure, function and composition of these ecosystems (Hall, 1999). Different forms or aspects of habitat complexity can be important to different life history stages or species. Impacts to habitats and ecosystems may result in changes to the productivity of target and non-target species, as habitats become unsuitable for particular species. Sediment resuspension and disruptions to sediment based nutrient cycling and digenesis can affect the composition and productivity of the overlying water column community (Fulton et al., 2004 p. 9).