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A trophic ecosystem model of La Paz Bay, on the southern Baja California Peninsula, was improved from one previously constructed by adding 13 functional groups. In the bay, small-scale fisheries take place, which are aimed at finfish, shark and clams. Also there is a pilot shrimp trawl fishery. At the mouth of the bay, communicating with the Gulf o...
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Context 1
... Paz Bay (Figure 1) is located on the south of the Peninsula of Baja California (24°06’–24°47’ North and 110°16’–110°45’ West), with an area of 1934 km 2 . The Espiritu Santo Island partially closes the mouth of the bay, leaving a small opening to the south (about 6 km wide and 19 m deep) and a larger one to the north (27 km wide and 300 ...
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... on two previous models by Arreguín-Sánchez et al . (2004) and Díaz-Uribe et al . (2007), an improved trophic model for the ecosystem of La Paz Bay (Figure 1) was constructed by adding 13 functional groups to the former contribution. New information consists of species of demersal communities that were captured through a shrimp trawl net operated by small boats with out-board engines. Presently, the model consists of a total of 48 groups: 29 fish, 3 marine mammals, 2 sharks, 1 marine bird, 5 macroinvertebrates including clams, shrimp and cephalopods, 2 epifauna, 2 zooplankton, 3 primary producers and 1 detritus (see Appendix A for species added to previous models that represent the new functional groups). The improved model also includes 20 commercial stocks captured by 5 gears: gillnet, hook, diving, shark-targeting and small-scale potential shrimp trawling (Table 1). Present models corresponded to the ecosystem during the period of 2005 and ...
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Citations
... In the southeastern gulf, two models developed for the Huizache-Caimanero lagoon system and adjacent continental shelf were used to evaluate the influence of fisheries on the trophic structure and some management scenarios with emphasis on the shrimp trawling fishery (Zetina-Rejón et al., 2003 Salcido-Guevara, 2006). In the southwestern gulf, three models for La Paz Bay were used to evaluate some management strategies for small-scale fisheries and a recently established marine protected area (MPA) which includes some traditional fishing grounds ( Díaz-Uribe et al., 2007; Arreguín-Sánchez et al., 2007). As a first approach in this work the existing trophic models of the northern and central-eastern regions of the gulf (ArreguínSánchez et al., 2002; Morales-Zárate et al., 2004; Lercari-Bernier, 2006; Lozano, 2006) were integrated and new information from the central-western region was added. ...
a b s t r a c t Understanding of the intricate interactions of endemic species with anthropogenic impacts of diverse economic interests on ecosystems is of paramount importance to the implementation of effective con-servation programs. A trophic mass-balance model was used to analyze the structural properties of the North and Central Gulf of California (NC-GulfCal) ecosystem, the most important fishing area in Mexico and where conservation efforts for protecting the endangered endemic porpoise known as vaquita (Pho-coena sinus) have been carried out for the last two decades. Results allowed to discuss the role of fisheries in the ecosystem and its implications for conservation of the endangered endemic porpoise. The trophic model was constructed with 166 functional groups and 3 regional fishing fleets. Abundance and catch from the early 1980s were used for balancing the model. Maturity indices of ascendency and production to respiration ratio indicate this ecosystem had a relatively high resilience and a high potential for devel-opment; this is in accordance with the highly variable environment found in the NC-GulfCal ecosystem. Mixed trophic impacts analysis confirms that pelagic and plankton groups have the most generalized impacts in this ecosystem. The model also shows that fisheries in the NC-GulfCal ecosystem, by the early 80s, were already operating in multiple habitats and landing a great variety of species. However, the highest exploitation pressure was focused on a few species. Although vaquita, since then, has also been under a high incidental mortality by gillnet fisheries, results suggest that predation should also be con-sidered as a key factor on vaquita population dynamics and regulations focused exclusively on fisheries probably are not enough to achieve a successful vaquita recovery program.
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... On the other hand, the shrimp fishery in the central Gulf of California was well developed and yields were stable ( ), and simulation experiments have been conducted to support ecosystem based fisheries management (Sánchez and Martínez-Aguilar, 2003 ). Several models were constructed for the southern Gulf; those by Salcido-Guevara and Arreguín-Sánchez (2007) and Sánchez et al. (2004) detail the impact of the shrimp trawl fishery on the ecosystem, while others such as Arreguín-Sánchez et al. (2007) consider the impacts of different fleets. The simulation experiments were performed using the ecosystem trophic model representing the shrimp trawling fishery in the central Gulf of California. ...
We conducted a four year interdisciplinary collaborative project focused in the Gulf of California, the most important fishing region for Mexico. We reviewed published reports, collected and analyzed phys-ical, chemical and ecological data sets, and developed models for the physical (atmosphere and ocean) and ecological components of this large marine ecosystem, to examine prevalent scientific questions regarding climate variability and change in the region, covering three time scales (ENSO, decadal-to-interdecadal, and long-term trend). We were able to describe how the Gulf of California influences the northward propagation of coastal trapped Kelvin waves associated with El Niño (ENSO) events, and how this signal, together with changes in the atmospheric forcing, results in a ENSO signature inside the Gulf. For the decadal-to-multidecadal scales, we found coherent trends among series, and with the Pacific Decadal Oscillation (PDO). The long-term temperature signal for the Gulf of California shows a warming that occurred in the mid 20th century, approximately a decade before that in the California Current. This signal is coherent with fluctuations in the industrial fisheries catch records (sardine and shrimps). For the recent decades we found no significant sustained long-term trend in any of the time series of physical and ecological variables that we considered. Instead, variability seems to be fully dom-inated by the interaction of PDO and ENSO. We stress the urgent need for more modeling efforts and the establishment of interdisciplinary (physical and biological) observation platforms for the marine environment in the Gulf of California.
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We consider the integral characteristics of the Okhotsk Sea ecosystem based on the ecosystem model «Ecopath» that was developed for the time of integrated marine ecosystem research during the past more than 30 years. The model includes 530 quantify assessed trophic links between the 48 functional groups, including detritus and phytoplankton. The average biomass, production, food consumption are estimated for each group. In a year, all functional groups in the Okhotsk Sea ecosystem consumed 16.95 billion tons of organic matters, or 11.15 tons/km2. The amount of new production (excluding reproduction of detritus) totaled 19.09 billion tons. Basic parameters of ecosystem functioning (net exports and metabolism, flows to detritus, etc.) and ratios (total catch to primary production, primary production to net metabolism, primary production to the total biomass, etc.) were estimated, they characterize the biological productivity of the Okhotsk Sea ecosystem. Comparative analysis with similar indices for the Bering Sea ecosystem and other 34 World Ocean ecosystems, according to the literary sources, was performed. We discuss the phenomenon of high biological productivity of the Sea of Okhotsk and the western Bering Sea ecosystems, the role of matter transport with water advection from the adjacent water areas, climate variability, as well
as the applicability of the definition of «maturity» of marine ecosystems and their individual components
for the analysis of the causes and dynamics of the significant non-recurrent events in the far-eastern seas.
A trophic structure model of the rocky coastal ecosystem in Bahia Tortugas, Mexico was constructed using Ecopath software to represent the main biomass flows in the system. Data for the model came from field observations (biomass estimates, stomach contents, and ecological observations for sea snails, abalones, lobster, some demersal finfishes, and macroalgae) carried out through ten field trips from 2006 to 2008. The results provide a snapshot of how the ecosystem operates. The model considers 23 functional groups. The total system throughput was 553t/km2/year, 57% corresponds to internal consumption, 28% to respiration, 14% becomes detritus, and only 1% is removed through commercial fishing. The model suggests that even for exploited populations, predation and competition are heavier stresses than current fishing effort; however, because spiny lobster showed the second highest keystoneness’ index value, increasing fishing pressure on this group could strongly impact the entire ecosystem. We believe that this model has the potential to support management by allowing the exploration of the potential impacts of different fishing decisions at ecosystem level.
