An Exploration of Ecosystem-Based Approaches for the Management of Red Sea Fisheries

Abstract

The Ecopath with Ecosim (EwE) modelling tool was used to simulate trophic interactions in the Red Sea ecosystem, with emphasis on its fisheries. Time-dynamic simulations were run to quantify the impact of fisheries, which represent the main anthropogenic impact on the ecosystem. The model was fitted to a time series of observed catch and effort data to improve its ability to mimic changes in the Red Sea ecosystem. EwE was also used to predict the consequences of different fishing scenarios: maintaining the status quo, banning all fishing, and projecting into the future at the present growth rate of the fisheries. Monte Carlo simulations were used to examine the sensitivity of the predictions to changes in model input parameters and the risk of fish abundance falling below selected thresholds. Equilibrium surplus-yield analyses were carried out on the major groups affected by the fishery. Finally, the model was used to examine the conflict between artisanal and industrial fisheries in the Red Sea by running scenarios where the fishing effort of each of these sectors was doubled.

Appendix

Table 9.A1 Key data on fish groups of the Red Sea ecosystem model

Appendix B: Non-fish Taxa Groups Included in the Model

Cetaceans

This group includes the dolphins and whales of the Red Sea, whose list and distributions have been described in the literature (Schmitz and Lavigne 1984; Frazier et al. 1987; Notarbartolo di Sciara 2002). All the reported cetaceans are from the suborder Odontocetea (toothed whales) except Balaenoptera edeni (Eden’s whale) and Megaptera novaeangliae (humpback whale), which are from the suborder Mysticeti. The P/B values for cetaceans were calculated assuming r/2 (Schmitz and Lavigne 1984), where r is the average intrinsic rate of growth (0.088 year⁻¹) for the Red Sea cetaceans species Stenella attenuata, S. longirostris, S. coeruleoalba and Tursiops truncatus data were available. The estimated P/B for the group equals 0.044 year⁻¹. The r/2 method is commonly used to measure P/B of marine mammals (Guénette 2005; Ainsworth et al. 2007). The Q/B value was estimated based on the body weight of Red Sea cetaceans taken from Schmitz and Lavigne (1984) and Trites and Pauly (1998), from which the ration was determined using the relationship in Trites and Heise (1996). The average Q/B value, 5.91 year⁻¹ was used in the model. Biomass data were not available and were estimated by the model.

Dugongs

Dugongs are herbivore marine mammals whose abundance in the Red Sea is estimated to be about 4,000 animals (Gladstone et al. 2003). With an average weight of 320 kg (Frazier et al. 1987), the biomass is calculated to be 0.00292 t · km^-2. Similar to the cetaceans , P/B for dugong was calculated using the intrinsic growth rate which is estimated to be 5 % year⁻¹ (Marsh et al. 1997), with P/B = 0.025 year⁻¹. The Q/B ratio is taken to be 11 year⁻¹ as calculated by Ainsworth et al. (2007), based on body weight.

Birds

The sea birds covering the whole Red Sea are described in Evans (1987) and recent reviews on the status of the Red Sea birds by country are available (PERSGA /GEF 2003; Marchi et al. 2009). However, they are very brief with some list of species sighted and habitat distribution with no estimate of abundance. The P/B value of 0.38 year⁻¹ was used based on Russell (1999). Seabird biomass was not available, and was estimated by the model.

Turtles

Five species of sea turtles , hawksbill (Eretmochelys imbricata), green (Chelonia mydas), loggerhead (Caretta caretta), olive ridley (Lepidochelys olivacea) and leatherback (Dermochelys coriacea), are reported for the Red Sea (Frazier et al. 1987; Tesfamichael 1994). The first two are the most abundant, with known records of nesting on the Red Sea beaches (Frazier and Salas 1984; Frazier et al. 1987; Gladstone et al. 2003). The P/B value for turtles was estimated using the relationship M = −lnS, where M is an estimate of P/B and S is the survival rate, which was 0.948 year⁻¹ for green turtle (Mortimer et al. 2000) and 0.867 year⁻¹ for loggerhead (Chaloupka and Limpus 2002). This gives an average P/B value of 0.1 year⁻¹. P/B value for all turtles in the Caribbean reef was calculated to be 0.2 year⁻¹ (Opitz 1996). Since the P/B estimate using survival rate was only for two species, i.e., it does not include all the five species in the Red Sea, an average of the P/B calculated from survival and the Caribbean value, 0.15 year⁻¹, was used for the model. Q/B value of 3.5 year⁻¹ was used based on ecosystem models of the Caribbean reef (Opitz 1996) and west coast of Peninsular Malaysia (Alias 2003). Sea turtle biomass was not available and was estimated by the model.

Invertebrates

The invertebrates most important for the Red Sea fisheries are shrimps. Hence, they was given a separate functional group. The most common species caught are Penaeus semisulcatus, P. monodon, Marsupenaeus japonicus, Melicertus latisulcatus, Metapenaeus monoceros and Fenneropenaeus indicus. P/B value of 5 year⁻¹ and Q/B of 29 year⁻¹ based on Buchary (1999) were used as a starting parameters to balance the model.

The coral reef structure in the Red Sea is important ecologically and is also the main fishing ground for the artisanal fisheries. Thus, the reef forming corals are categorized as a separate functional group. The high and relatively stable temperature of the Red Sea is favourable for the formation of coral reefs. They are home to more than 200 species of corals (Head 1987). The Red Sea coral reef coverage area is estimated to be around 16,030 km² (Spalding et al. 2001). Coral reefs are more developed in the northern part starting from the tip of Sinai Peninsula going south parallel to the coast until the central part (Sheppard et al. 1992). The longest continuous fringing reef in the Red Sea extends from Gubal , at the mouth of the Gulf of Suez , to Halaib , at the Egyptian border with Sudan (Pilcher and Alsuhaibany 2000). In the south, more patchy reefs are observed as the turbid water of the shallow shelf does not allow the growth of extensive reefs. Sanganeb Atoll , located in Sudan near the border with Egypt , is the only atoll in the Red Sea. It is unique reef rising from 800 m depth to form an atoll that has been recognized as regionally important conservation area. It was proposed to UNESCO for World Heritage Status in the 1980s (Pilcher and Alsuhaibany 2000). The biomass of corals was calculated based on data from the southern Red Sea (Ateweberhan 2004; Tsehaye 2007) adjusted for the total area of the Red Sea and the north-south abundance gradient giving 2.75 t · km⁻². The P/B value of corals was calculated based on daily turnover rate of 0.003 day⁻¹ (Crossland et al. 1991), which equals to 1.095 year⁻¹. A Q/B value of 9 year⁻¹ was used based on the Caribbean reef model (Opitz 1996).

The other invertebrates included in the model are: non-coral sessile fauna such as sponges, sea anemones, and tunicates; cephalopods: squids, octopuses and cuttlefish; other molluscs; echinoderms: starfish , sea urchins and sea cucumber ; crustaceans: representing all crustaceans except shrimps (which have a group of their own); and meiobenthos: polychaetes and nematodes. The P/B and Q/B values of these groups were taken from an ecosystem model of the Eritrean coral reef (Tsehaye 2007) adjusted for the area of the Red Sea fine-tuned during balancing and time series fitting (Table 9.B1).

Table 9.B1 Input parameters of some invertebrates groups

Primary Producers

There are three functional groups of primary producers in the model: phytoplankton , seagrasses and algae. The phytoplankton biomass of 21.5 t · km⁻² and a P/B 110 year⁻¹ were used based on data in (Weikert 1987; Veldhuis et al. 1997) averaged over all the Red Sea. For seagrass, a biomass of 11 t · km⁻² and P/B value of 19 year⁻¹ were used, based on Wahbeh (1988) and Aleem (1979). The biomass estimate of algae was based on Ateweberhan (2004) and Walker (1987), and was averaged for the whole Red Sea, resulting in 38 t · km⁻². The P/B value of 14 year⁻¹ was used based on Ateweberhan (2004) and Wolanski (2001), which is similar to the value in other coral reef ecosystems: Caribbean (Opitz 1996) and Indonesia (Ainsworth et al. 2007).

Table 9.C1 Effort (megawatt · hours) of Red Sea fisheries by gear, 1950–2010