Ecological consequences of fishing activity on aquatic habitat Fishermen and/or their gear always interact with the habitat to some degree regardless of the techniques they use. Such interaction is obvious and adverse when lost fishing lines entangle non-target species, when pots and traps land on top of benthic fauna, and when nets drag across the riverbed, marsh bed and seabed. There are two types of disturbances that result from the interaction of fishing gear with the environment: physical disturbance, in which the habitat is directly disturbed, and biological disturbance, in which the habitat is disturbed indirectly by removal of competitors and predators from the system (Hall, 1999).
Fishing gear that is deployed at the surface or in mid-water can itself cause environmental effects, as well as the direct and indirect consequences of removing bycatch and prey species. In contrast, methods of fishing for bottom-dwelling species can affect the riverbed, marsh bed, and seabed habitat and its inhabitants to some degree (Jennings et al., 2001).
There are two different groups of fishing techniques that affect the benthic fauna and habitats. The active methods usually involve towing trawls or dredges of all sizes across the seabed. Such techniques are in use in the marine habitat of lower Mesopotamia. However, artisanal fishermen operating in the rivers and marshlands also use a range of other active techniques such as drive netting, spearing and fishing with chemicals or explosives. The passive fishing techniques include the use of pots or traps, baited hooks on long-lines, gill nets, and drift nets. All these techniques are in operation in both the fresh and marine waters of lower Mesopotamia. The impact of each of these various types of gear on non-target biota and habitat will also vary between different habitats and according to the manner in which they are used. To solve these problems, Marsh Arabs usually come down in the water prior to the fishing operation and start to cut as much aquatic vegetation as possible in order to facilitate their fishing operation. They do this only when they use seine nets. Such action occurs everywhere in the marshlands where there is thick vegetation. The impact of such action is not severe on the aquatic plant communities because only a few fishermen do so at any one time.
Effects of towing fishing gears
Bottom fishing causes more serious damage to the benthic organisms and the habitat than surface or mid-water fishing. Accordingly, most research has centred on the environmental impacts of the former (Jennings et al., 2001). The fundamental question to be answered is “what happens when benthic fishing gear interacts with the river, marsh and seabed?” The straightforward answer is that bottom fishing gear will wreak havoc on animal and plant communities in its path.
Towed and static fishing gears also interact negatively with the environment, however. Towed fishing gear tends to be more effective and sweep large areas of the river, marsh and seabed. In soft sediments this will lead to the turbulent re-suspension of surface sediments, which may remobilise contaminants and expose the anoxic lower sediment layers. This case is evident in the marshlands, where the movement of the towing nets disturbs the soft bottom of the marsh that contains contaminants and silt. On hard substrata, boulders may be physically moved and biogenic structures may be destroyed (Auster et al., 1996). This situation is clear in the rivers and the marine habitat of lower Mesopotamia. The magnitude of the impact on the habitat bottom is determined by the towing speed, the physical dimensions and weight of the gear and the type of substratum. The resultant changes to the habitat may persist for various periods of time, ranging from several years in muddy sediments found in sheltered areas, to decades in the relatively undisturbed deep sea (Auster et al., 1996). In the case of the marshlands, the situation is different wherever the bottom is covered with soft muddy sediments and water movement is negligible. Thus, changes will persist longer here than in areas with continuous wave action or current flow. As to the marine habitat, changes might persist for shorter times. In some cases habitat degradation may be permanent due to the fragmentation of the bed formation. This could happen when big holes are dug in the bottom of the marsh or bedrock is removed from a riverbed or from the seafloor. Such incidences have been observed where heavy towing gear has been used in the marshland and the huge amount of silt lifted by the net has left a large hole in the bottom. Similarly, large boulders were seen in the small trawling gear of the artisanal fishing boats operating in the marine habitat of lower Mesopotamia. Those boulders appeared to be newly fragmented from the bedrock of the area (personal observations).
Towing fishing gear, no matter how heavy, inevitably reduces the surface roughness of the bottom of the aquatic habitat, and thus also the complexity of both the surface and internal structure of soft sediment habitats (Schwinghamer et al., 1996). The presence of micro-topographic relief of the sediment such as feeding pits, shell fragments and small rocks that protrude from the bottom are important to much sessile biota. As fishing gear is towed across the bottom, surface sediments are re-suspended. The heavier particles sink quickly, while the finer particles are winnowed away by currents (Kaiser and Spencer, 1996, Schwinghamer et al., 1996). Divers in the marine habitat often report a fairly smooth seabed in the towed experimental site where towing fishing used to operate (Personal observation), which indicates clearly the effect of towing fishing gear.
The non-target organisms that get disturbed through the use of towed fishing gear are the infauna and epifauna. Towed gear does not adversely affect deeper burrowing fauna (Posey et al., 1996). Kaiser and Spencer (1996) indicated that effects of fishing are much more noticeable in less disturbed areas than in highly disturbed habitat. Such differences are clear in the lower Mesopotamian plain. Due to the current and wave actions and ship traffic, mainly oil tankers, the marine habitat is more disturbed than the river and marsh beds.
Chironomid larvae, dragonfly larvae and worms dominate the benthic fauna of the marsh area. Stylaria and Tubifex species (Oligochaeta) occur in moderate quantities, and univalve and bivalve molluscs are also present (George and Savage, 1970; Al-Dabbagh and Daod, 1985). Aquatic insects such as water beetles are well represented in the marshlands (Ali, 1976, 1978). A globally threatened species of libellulid dragonfly (Brachythemis fuscopalliata), which is known only from Iraq, Israel and Turkey, has been collected in the marshes of lower Mesopotamia, but no recent information is available on its status there (Groombridge, 1993). Consecutive bottom samples from the marshlands during the period 1971-1989 revealed a decline in both infauna and epifauna of the greater marsh area near Basrah city, the decline in infauna being less than that of epifauna (personal observations).
Fishing in shallow water has impacted aquatic plant communities in the marshland areas of lower Mesopotamia. Throughout the marshlands, the emergent vegetation is dominated by common reed (Phragmites australis), reedmace (Typha angustifolia), papyrus (Cyperus papyrus), and occasionally Arundo donax (Thesiger, 1954; Akbar, 1985). The deeper, permanent lakes support rich submerged aquatic vegetation such as hornwort (Ceratophyllum demersum), the pondweeds Potamogeton lucens and P. pectinatus, water milfoil (Myriophyllum sp.), stonewort (Chara sp.), the naiads Najas marina and N. armata,and water fern, (Salvinia sp.) Water lilies (Nymphoides peltata, N. indica, Nymphaea caerulea and Nuphar sp.), water soldier (Pistia stratiotes) and duckweed, (Lemna gibba) cover the surface of the smaller lakes and quieter back waters. These aquatic plants act as breeding, nursery, and protective means for several aquatic invertebrates (George and Savage, 1970; Al-Dabbagh and Daod, 1985; Ali, 1976) and fishes both freshwater and marine (Al-Hassan and Hussain, 1985; Al-Hassan et al., 1989).
Bottom fishing gear usually tears up individual plants and reduces biomass by shearing off fronds. Towing fishing gear may locally increase water turbidity through sediment resuspension, leading to regression in the aquatic plant cover. The dense nature of the submerged plants encourages sedimentation and accumulation of organic matter. The roots and other plant structures help to stabilize sediment in the same way that the roots of trees bind soil.
Effects of static fishing gear
Static fishing gear has relatively little effect on the life at the bed of the aquatic habitat, although there are problems associated with bycatch. Rocks and organisms may be sheared off if ropes, netting or traps become snagged on them. Nevertheless, these effects are relatively minor in comparison with those associated with active fishing techniques. Potential effects on plankton communities fall under the long-term effects of bottom fishing activity.
Indirect effects on habitats
Transport and subsequent deposition of sediments re-suspended as a result of bottom fishing may affect the settlement and feeding of biota at sites remote from the fishing area. Sediment re-suspension may have a variety of effects such as release of nutrients held in the sediment, exposure of anoxic layers, release of contaminants, increased biological oxygen demand, and smothering of the feeding and respiratory organs of various aquatic animals (Kaiser et al., 1996). This situation is clear in the marshland areas near the large rivers such as Tigris and Shatt al-Arab. The re-suspended sediments from the marshlands carrying all sorts of materials will eventually re-settle in the nearby rivers and disrupt the benthic fauna there.
In the marine habitats of the lower Mesopotamian plain, coral reefs are probably indirectly affected by bottom fishing activities. The process of catching the target species will reduce the abundance of corals, which in turn increases the abundance of other organisms on which the target species live. Several species of parrotfish such as blue barred parrotfish (Scarus ghobban) and gulf parrotfish, (S. persicus) that live in the area graze on algae and erode the reef matrix. Other target fish species such as emperor fish, (Lethrinus sp.) feed on invertebrates such as sea urchins and starfishes. Heavy bottom fishing activities will clearly determine the rates of bio-erosion.
Suggested future management and conservation options It is clear from the information provided here that fisheries in the lower Mesopotamian plain need an urgent management plan in conjunction with conservation measures to ensure a regulated fishery in the area. Governments and local authorities usually instigate fisheries management because the biological, social and economic consequences of unregulated fishing are undesirable. In most cases, the aims of the management programme are to ensure the economic and social well being of future generations or to protect habitat and species of conservation concern. For such a management project, there must be clear objectives supported by scientific advice and appropriate management actions (AOAD, 1978).
To express the aims of the management plan as a management strategy is the first stage of the management process. A better understanding of ecosystem function will facilitate quantitative strategies. In this aspect, appropriate assessment techniques by fisheries scientists will be of key importance for implementing the strategy. The following steps of management action could be well implemented in the inland fisheries and in the marine habitat of lower Mesopotamia.
The three main steps in management action are catch controls; effort controls and technical measures (OECD 1997), and all have their advantages and disadvantages. Catch controls, also known as output controls, are intended to control fishing mortality by limiting the weight of catch that fishermen can take. These include total allowable catches (TAC) or quotas (Q), which are limits on the total catch to be taken from a specific stock, as well as individual quotas (IQ). Catch controls are amongst the most widely used management regulations (OECD 1997). Such systems can be easily controlled by well-known members of the tribes in communities that live deep in the marshlands, or by members of fishing cooperatives in communities at or near the big city centres and near the marine habitat.
Effort controls limit the number of boats or fishermen who work in a fishery, the amount, size and type of gear they use, and the time the gear can be left in the water. Among the aims of effort control is reduction of catching power of the fishermen and thus reduced fish mortality. The way that fishermen change their behaviour in response to the regulations has a direct effect on the response of fishing mortality to effort control. This is an important point especially for Marsh Arabs who operate in the interior marshland fishing areas, which are remote from government or local authority inspectors. Accordingly, it is important to deal with local fishermen on a tribal basis to ensure that control systems are working. Failure to involve individual tribes in marshlands fisheries management will lead to failure of licensing, vessel and gear restrictions, and effort controls. If the catch controls and technical measures are not imposed, control effort is unlikely to be effective.
Technical measures restrict several technical fisheries issues, including species-related matters (i.e. size and sex), others related to the gears used, fishing seasons, and areas where fishing is allowed. Controlling the size of the fished species is considered as the most useful conservation measure to protect individuals below the minimum landing size. In the lower Mesopotamian plain, fishermen usually make their own nets and seldom purchase legal fishing gear from governmental agents (Hadid and Al-Mahdawi, 1977). Thus, size control and gear are very difficult to regulate in the marshlands. Temporal and areal limits can protect fished species at specific phases of their life histories. Protection of juvenile nursery areas or adult spawning grounds is usually enacted in the lower reaches of the Tigris and Euphrates Rivers near the big city centres, while in the marshlands, the situation is more difficult to control. Marsh Arabs fish in all seasons even in the breeding season of most commercial fish species, such as members of the carp family Cyprinidae. They usually catch fish and sell the yield at the fishing ground to middlemen who usually market the catch in great secrecy (Jawad, personal observation).
Management of fisheries in the lower Mesopotamian plain could use optimisation measures to determine the combination of management actions that would provide the best means of achieving a strategy (Jawad, unpublished data). The best example of optimisation would be to determine the combinations of mesh size and fishing effort that would maximize the profit from a gill net fishery. An advanced statistical analysis could be involved when more than two management actions have to be optimised, for which 2-D and 3-D contour plots are a useful and accessible way of presenting the results. Such advanced activity should be borne in mind for future fisheries management in the area.
Management feedback is an important step in the fisheries management program, as it is needed to adjust management actions and to ensure that management objectives are met. For example, the management strategy for the marshlands’ main fish species (Carp family) is to leave thousands of individuals to spawn each year. This situation is similar to that of Icelandic capelin (Jacobsson and Stefanson, 1998). Management action in this case, is to control fishing mortality by periodic assessment to confirm the size of the spawning stock, with feedback from the assessment scientists to the managers. A team of experienced people would be required to perform a continuous cycle of setting management strategies, implementing management actions, assessing the impacts of those actions, and modifying the actions in accordance with strategies. Many fisheries in the marshlands and rivers are heavily over-exploited, and minor tinkering with existing management practices would be insufficient to realize long-term biological, social or economic benefits. Clearly, major structural readjustment is needed, which is likely to include extensive decommissioning of boats to remove excess capacity, bans on new entrants to the fisheries, and allocation of property rights. Change would have some undesirable consequences in the short term, notably reduction in income. Such difficulties will be complicated in the marshlands, especially if the governmental agencies or other authority try to implement the readjustment measure, which could lead to major conflict, since Marsh Arabs are highly vulnerable to income reduction. On the other hand, and in the long term, capacity reduction would produce more efficient industry and happier and wealthier fishermen, although the Marsh Arabs will take long to convince.
It is possible to implement the capacity reduction in the fisheries grounds at the marine habitat of the lower Mesopotamian plain due to the presence of different sectors of the society and different social life. Fishermen in this area will accept the idea, and most importantly, they are easily controlled by authority. This is due to their social background and level of education. Moreover, the fishing area in which they operate is a national waterway, and no one can claim sovereignty on any part of it and declare it a private fishing area. To the contrary, in the marshlands, the tribal influences are quite clear on the fishing grounds. Such conditions are aided by the remoteness of the marshlands and the dominance of the tribal laws.
Managing fisheries for conservation
Maximization of yield was the overriding objective of fishery management for the last few decades. As a reflection of public and scientific concerns about the broad effects of fishing, species and habitat conservation have become increasingly important objectives to fisheries managers and authorities in several parts of the world. In the lower Mesopotamian plain, fishing activities in one way or another impact various non-target species such as dolphins, sharks, birds, and mammals. In the future, therefore, the issues of species and habitat conservation will become the dominant management objectives in several fisheries grounds of the area. In many of the developed countries, fishing is currently seen as a threat to the environment rather than a source of protein and income (Jennings et al., 2001). In lower Mesopotamia, a number of measures have been taken to conserve fish species (Jawad, 2003a). A report by the Arabian Organization for Agricultural Development (AOAD) in 1975 considers the main conservation schemes in force in the region. The recommendations were also concerned with natural and artificial breeding, aquaculture processes, and feeding and fish pathology.
Among the future primary management objectives is protection of endangered species. Several fish species, mammals, birds and invertebrates have been identified as endangered by fishing activities (Norse, 1993; Hawkins et al., 2000; Musick, 2000). There is a growing approach to listing of endangered species in several countries. Such an approach is yet inapplicable for the fish fauna of Mesopotamia due to the lack of basic taxonomical information. Several commercially important barbel species such as Barbus esocinus, B. grypus, and B. rajanorum have vanished from the marshlands and the large rivers due to overfishing and changes in their habitat. Species are known only from their original descriptions based on a few specimens collected from one locality. Many may well prove to be synonyms with more widely distributed and better known species. Owing to the poor field data, several fish species presumed or known to be valid are known only from a single river system or lake. Habitat destruction and pollution act as extinction factors for those fish species that are restricted to a single river system or lake. The severe limitations of taxonomic and distributional data on Mesopotamian fish fauna means that it is currently quite impossible to classify fish population from a conservation standpoint (Jawad, 2003a). Some of the taxonomic problems relating to Mesopotamian fishes were discussed by Jawad (2003b), and several attempts were made by Coad (1991, 1996a, 1996b) to identify the fish species of the Tigris-Euphrates River basin. Until a complete and integrated picture of the fish fauna of Mesopotamia is available, plans to protect endangered species cannot be implemented.
In the present time, the marshlands ecosystem may not contribute to the conservation of the fish biodiversity. Factors such as introduction of some parasitic crustaceans, i.e. Macrobrachium rudi (Al-Daraji et al., 2005); fish pathogens, i.e. helminth parasites (Bannai et al., 2005); bacteria (Jarallah et al., 2005), and fungi (Muhsin, 2005) may have a direct effect on the health of individual fish in particular and the fish stock in general. The previous factors were observed recently in the post-reflooding period. On the other hand, competition between the native and introduced carp fish species on food items appeared not to be a significant issue to affect the fish biodiversity in the southern Iraqi marshes (Faddagh and Al-Mukhtar, 2005). The International Technical Advisory Panel (ITAP) expected that exotic species are likely to exist in the system because the system has been so disturbed in the past few decades. The recommendation that ITAP put forward regarding the exotic species is to monitor them to ensure they are not out-competing native species (Eden Again Program, 2003). With the absence of complete control by the new government in the different sectors of life in Iraq, fishermen took the opportunity to use whatever fishing methods were available to them and paid no concern about their side effects on the fish stock and the environment. Prohibited fishing methods such as electroshocking and use of chlordane are among the common fishing methods in use today in the marshlands. In both methods, fishes of different sizes are caught and small fish are usually thrown away. This action will have a direct impact on the future fish stock in the area.
Habitat conservation is another objective of management for conservation. It can be achieved using gear restrictions and protected areas, but is not feasible in the marshlands due to the particular behaviour of the Marsh Arab fishermen, who agree neither on the need for gear restriction nor on the need to maintain protected areas.
Another approach for habitat conservation is through providing the optimum environmental conditions for fish stock to thrive. At the present time, the environment of the marshlands needs a high level of restoration due to the presence of several types of toxicants such as pesticides that were used in illegal fishing operations and carcinogenic agents originating from residues of the chemical weapons used in the marshes during the Iraqi-Iranian war. The latter are characterised by low degradability and may transfer to man through the food chain. Other pollutants may contribute to the degradation of the present marshland environment, among which are dissolved chemicals of military origin and industrial and domestic effluent from locations upstream on the Tigris and Euphrates Rivers (Faddagh, 2005). In addition, Neghamish and Ali (2005) found that the sediments and most of the marsh areas have high rates of salinity and Na+ content.
Fisheries science must become the main factor in future trends of fisheries management in the lower Mesopotamian plain if there are to be desirable consequences. Fisheries science is changing rapidly, bioeconomic analyses are becoming increasingly important in the assessment and management of fisheries, and there is increasing concern about the impacts of fishing on the aquatic environment. More research on the ways in which fishing affects ecosystem processes such as productivity and stability, and how it alters the role of ecosystems as nutrient stores are needed in the near future. Such studies may eventually provide the basis for setting practical management strategies such as limits to the frequency and intensity of fishing.