Increase In Fish Biomass Research Articles

Fish (Spinibarbus hollandi) dynamics in relation to changing hydrological conditions: physical modelling, individual‐based numerical modelling, and case study

ABSTRACTThe paper reports the development of an individual‐based fish dynamics model, of which the key components are the rules for the movement of individual fish and the definition of the habitat suitability. The distribution of the fish mainly depends on the flow conditions (velocity, depth, substrate) and life cycle of the fish. A major contribution is the refinement of the rules for fish movement, based on laboratory experiments under volitional swimming conditions, which also provided the ranges of preferential velocities and substrate size for the target fish, Spinibarbus hollandi. Moreover, they provided data on the fish trajectories and distribution patterns that allowed for validation of the movement rules. The validated fish dynamics model was applied to investigate the effect of discharge increase during the dry season by means of reservoir operation in the Lijiang River, which was the subject of field investigations in 2007 and 2008. The model results indicated that reservoir operation leads to an increase of fish biomass. According to the fish movement rules, fish cannot always escape from riverbed regions that dry during decreasing discharge events, which causes them to be trapped and die. Reservoir operation decreases the area of dry riverbed and reduces the travel distance for fish to escape from dry regions. Critical advantages of the individual fish model over global models defined on the population level are that they can account for the time that the fish needs to reach a region of suitable habitat and for the spatial pattern of suitable zones and their connectivity. Copyright © 2013 John Wiley & Sons, Ltd.

Spillover of fish naïveté from marine reserves

Spillover of adult fish biomass is an expected benefit from no-take marine reserves to adjacent fisheries. Here, we show fisher-naïve behaviour in reef fishes also spills over from marine reserves, potentially increasing access to fishery benefits by making fishes more susceptible to spearguns. The distance at which two targeted families of fishes began to flee a potential fisher [flight initiation distance (FID)] was lower inside reserves than in fished areas, and this reduction extended outside reserve boundaries. Reduced FID persisted further outside reserves than increases in fish biomass. This finding could help increase stakeholder support for marine reserves and improve current models of spillover by informing estimates for spatial changes in catchability. Behavioural changes of fish could help explain differences between underwater visual census and catch data in quantifying the spatial extent of spillover from marine reserves, and should be considered in the management of adjacent fisheries.

Treatment of wastewater from shrimp farms using a combination of fish, photosynthetic bacteria, and vegetation

An innovative system combining fish, photosynthetic bacteria, and vegetable cultivation was used to treat the wastewater discharged from the shrimp farms. The experiment was divided into three phases, starting with photosynthetic bacteria Rhodopseudomonas palustris which are added to shrimp aquaculture wastewater at concentrations of 0.5 × 106, 1.0 × 106, 2.0 × 106, 4.0 × 106, and 8.0 × 106 colony-forming units (CFU)/mL (treatment 1, 2 3, 4, and 5, respectively) for 4 days to determine the optimal bacteria level. In the second phase, silver carp (Hypophthalmichthys molitrix) were introduced at the biomass levels of 0.25, 0.50, 0.75, 1.00, and 1.25 kg/m3 (treatment 6, 7, 8, 9, 10, respectively) for 7 days. In phase 3, Ipomoea aquatica, Oenanthe javanica, Lactuca sativa, and Brassica pekinensis were introduced and cultivated (treatment 11, 12, 13, 14, respectively) for 7 days. The wastewater values of TP, TN, CODCr, NH4, NO3, and NO2 were analyzed after each phase of treatment. The results showed that the wastewater quality changed drastically after the completion of all wastewater treatments. The removal rates of TP, TN, CODCr, NH4, NO3, and NO2 increased with increasing photosynthetic bacterial concentrations in Phase I. The removal rates of TP, TN, CODCr, and NO3 increased with increasing fish biomass, while the removal rates of NH4 and NO2 decreased in Phase II. The removal rates of TP, TN, NO3, and NO2 were the highest for treatment 11, while the removal rate of CODCr reached the highest value in treatment 12, and NH4 in treatment 14. I. aquatica showed the best removal of nutrients from among the four vegetables in Phase III. It is suggested that a combination photosynthetic bacteria (4.0 × 106 CFU/mL)–fish (0.75 kg/m3 silver carp)–vegetable (1.00 kg/m2Ipomoea aquatica) system could be a practical system for nutrient recycling in shrimp aquaculture wastewater on a larger scale.

Feasibility of different harvesting strategies and economies of scale in ranching wild cod (Gadus morhua)

The effects of different harvesting strategies and increased fish biomass on the feasibility of ranching wild cod in ‘herds’ formed with anthropogenic feeding were studied. The five following scenarios using purse seine as the method of capture were considered: I. Basic harvesting, II. Harvesting with size-grading and selling the smaller cod for on-growing, III. Harvesting with size-grading and on-growing the smaller cod in sea cages within the company, IV. Intensive harvesting at the end of the growth period, and V. Ranching larger biomass with basic harvesting. For basic harvesting it is assumed that wild cod are fully fed at several feeding stations for 165 days per year and harvested three days a week from September 1 to November 5 without size-grading. It is also assumed that the ranching company owns a suitable fishing vessel and cod quota, 200 tons in Scenarios IAIV and 500 tons in Scenario V. For a 15 year operating period, the net present value (NPV) for the five scenarios is €754 000, €809 000, €819 000, €700 000 and €1 504 000, respectively. Cod ranching is viable in all scenarios but the size of the operation has much greater effect than the harvesting strategy on the feasibility. Although intensive aquaculture will continue to grow globally, well managed fish stocks will always be an important food source for mankind and thus ranching, which basically is a quota multiplier, can increase this food supply, potentially at competitive prices.

Description and Application of a NPZD Model to Forecast Hurricane Impacts to Secondary Production in Coastal Ecosystems

Abstract Increases in hurricane strength and frequency are forecast to occur in association with global climate changes. In coastal ecosystems the passage of a hurricane is associated with increases in nutrients that may cause subsequent increases in phytoplankton and zooplankton biomass. Zooplankton are an important food source for small fishes that are feed on by larger fishes, thus commercial and recreational fisheries could benefit from the passage of a hurricane. NPZD simulations of hurricane scenarios are used to assess the magnitude and resilience of secondary production after the passage of hurricanes with different wind speeds and directions of approach. Short-term increase and recovery of phytoplankton and zooplankton biomass after the passage of hurricanes suggests short-term increase in fish biomass, and a potential benefit to some commercial and recreational fisheries.

Large Recovery of Fish Biomass in a No-Take Marine Reserve

No-take marine reserves are effective management tools used to restore fish biomass and community structure in areas depleted by overfishing. Cabo Pulmo National Park (CPNP) was created in 1995 and is the only well enforced no-take area in the Gulf of California, Mexico, mostly because of widespread support from the local community. In 1999, four years after the establishment of the reserve, there were no significant differences in fish biomass between CPNP (0.75 t ha−1 on average) and other marine protected areas or open access areas in the Gulf of California. By 2009, total fish biomass at CPNP had increased to 4.24 t ha−1 (absolute biomass increase of 3.49 t ha−1, or 463%), and the biomass of top predators and carnivores increased by 11 and 4 times, respectively. However, fish biomass did not change significantly in other marine protected areas or open access areas over the same time period. The absolute increase in fish biomass at CPNP within a decade is the largest measured in a marine reserve worldwide, and it is likely due to a combination of social (strong community leadership, social cohesion, effective enforcement) and ecological factors. The recovery of fish biomass inside CPNP has resulted in significant economic benefits, indicating that community-managed marine reserves are a viable solution to unsustainable coastal development and fisheries collapse in the Gulf of California and elsewhere.

Spatial and temporal effects on the efficacy of marine protected areas: implications from an individual based model

We have developed a spatially explicit model that simulates the interaction between fish and fishers based on past fish location, abundance and fish dispersal. We have examined four scenarios for the design and management of Marine Protected Areas (MPA) and for each we simulated fish biomass and fish catches: (1) No MPA. (2) A single MPA located at a feeding area. (3) A single MPA designed to maximise its overlap with the predominant route of fish dispersal. (4) The use of two MPAs. Each scenario was replicated with two scenarios regarding the time that fish remains within the MPA and two grid map scenarios to account for time–space effects and map/coastline characteristics. Results showed that overall closing an area increased fish biomass. However, an MPA located in the open sea for a limited time may have adverse effects on fish biomass. MPAs increased fish catches when a single large MPA or two small MPAs were located in the open sea for a limited time. The effects of time that fish remains protected in closed areas vary in combination with the spatial design: When examining time effects on the efficacy of MPAs within each scenario with an MPA located in the open sea, fish biomass was always higher in the case where fish was protected for more calendar days during each year. When comparing between different spatial designs, proximity to the coast was a more predominant factor in the efficacy of MPAs rather than time that fish was protected. The scenario that gave the highest total fish biomass was the one that covered the largest part of the migration route, despite increased edge effects. Our results suggest that it is not per se the perimeter to surface ratio that matters, but the trade-off between edge effects and maximised MPA surface in the predominant dispersal direction. Our results also have implications for the design of terrestrial reserves.

Spatio-temporal variability in fish-induced predation mortality on plankton: A simulation approach using a coupled trophic model of the Benguela ecosystem

We investigate the potential predation pressure that would affect plankton communities spatially and seasonally using a coupled model, where fish-induced predation mortality is explicit. In the southern Benguela ecosystem, the fish model OSMOSE is forced by a biogeochemical model providing plankton prey fields. We analyse the resulting potential predation mortality rate on copepods. Spatially, this mortality rate is higher on the South coast (Agulhas bank) than on the West coast (upwelling zone), reflecting a lower plankton concentration compared to food requirement for fish. Temporally, fish-induced predation mortality decreases at the beginning of the upwelling season, due to a rapid increase of plankton concentration combined with a lag in the subsequent increase of fish biomass. Such strong spatio-temporal patterns in fish-induced predation mortality encourage the development of two-ways coupling between fish and plankton models for better representing the dynamics of the southern Benguela food web.

Reduced density of the herbivorous urchin Diadema antillarum inside a Caribbean marine reserve linked to increased predation pressure by fishes

Disease has dramatically reduced populations of the herbivorous urchin Diadema antillarum Philippi on Caribbean reefs, contributing to an increased abundance of macroalgae and reduction of coral cover. Therefore, recovery of D. antillarum populations is critically important, but densities are still low on many reefs. Among the many potential factors limiting these densities, the focus of this study is on predation pressure by fishes. Marine reserves provide opportunities to examine large-scale manipulations of predator–prey interactions and, therefore, D. antillarum densities were compared inside and outside a reserve in The Bahamas (Exuma Cays Land and Sea Park; ECLSP). Urchins and their fish predators were surveyed at nine sites inside and outside the ECLSP. Because of lower fishing effort, the total biomass of urchin predators, weighted by their dietary preferences for urchins, was significantly higher inside the ECLSP. Furthermore, fish community structure was significantly different inside the Park because of the increased biomass of the majority of species. No urchins were seen inside the ECLSP and this was significantly lower than the density of 0.04 urchin m−2 outside the Park. Regression analysis indicated that the relationship between the biomass of urchin predators and the proportion of transects containing urchins was non-linear, suggesting that small increases in fish biomass dramatically reduce urchin abundances. The link between lower density of urchins and higher density of their predators inside the ECLSP is strengthened by discounting five alternative primary mechanisms (variations in macroalgal cover, larval supply, environmental setting, density of other urchin species and abundance of predators not surveyed). Caribbean marine reserves have an important conservation role, but increased fish predation appears to reduce densities of D. antillarum. Urchins currently have limited functional significance on Bahamian reefs, but any future recovery of D. antillarum is likely to be limited in reserves, with potentially important ecological consequences.

Managing Fisheries Resources in Danajon Bank, Bohol, Philippines: An Ecosystem-Based Approach

The Danajon Bank double barrier reef, located off northern Bohol Island of central Philippines, is the focus of this case study on ecosystem-based management (EBM). Fisheries management is relatively new in the area, particularly the aspect of managing fish stocks with wide distribution patterns crossing jurisdictional boundaries. Nevertheless, stakeholders are taking bold steps toward improving fisheries management. The impetus to take action comes from the realization that coastal habitats can no longer sustain the level of exploitation to which they have been exposed. The initiative is facilitated by the USAID-funded Fisheries Improved for Sustainable Harvests (FISH) Project in collaboration with various partners. The EBM approach of the FISH Project is incremental and builds on existing management systems and utilizes existing legal and institutional frameworks while encouraging progress toward ecosystem-wide management. Fisheries management tools include coastal management, marine protected areas, limitations on fishing effort and gear, control of extraction of specific life stages of important species, licensing, zoning, and coastal law enforcement. One FISH Project goal is to increase fish biomass by at least 10% in 2010 over the 2004 baseline. Monitoring data collected in 2006 and 2008 to quantify changes against baseline data for key indicators have generally shown incremental improvements based on fisheries-independent surveys and MPA assessments. The Danajon Bank experience shows that there are three major components in working toward EBM: (1) fisheries management interventions should always consider a defined ecosystem boundary as resource management unit; (2) there is a need to understand the dynamics of marine ecosystems and how they respond to human-induced changes, particularly to changes resulting from fisheries; and (3), there is a need for a governance system that supports limits to fisheries resource exploitation activities. The match between the spatial range of the ecosystem and the governance system is the most important consideration and will play an important role in scaling up of fisheries management initiatives.

Reserve effects and natural variation in coral reef communities

Summary 1. No-take reserves are a common tool for fisheries management and biodiversity conservation in marine ecosystems. Despite much discussion of their benefits, data documenting many reserve effects are surprisingly scarce. Several studies have also been criticized for a lack of rigour so that changes within reserves cannot be separated from underlying natural variation and attributed unequivocally to protection. 2. We sampled both benthic (video quadrats) and associated fish communities (underwater visual censuses) in a well-enforced reserve in The Bahamas. Sampling was explicitly stratified by habitat (‘ Montastraea reef’ and ‘gorgonian plain’). To distinguish reserve effects from natural variation, we compared changes inside and outside the reserve with those seen at equivalent spatial scales in other reef systems in the Bahamian archipelago that lack reserves. Reserve-level differences in benthic or fish communities not documented in other reef systems are categorized as ‘robust’ effects. 3. Robust reserve effects were limited to Montastraea reefs. The reserve supported an average of ≈ 15% more fish species per site compared to outside the reserve. This pattern was particularly driven by more large-bodied grouper, damselfish, and butterflyfish species inside the reserve. Increases in fish biomass and differences in community structure inside the reserve were limited to large-bodied groupers. Increased grazing pressure by parrotfishes in the reserve has lowered macroalgal cover, and caused previously undocumented changes in benthic community structure compared to sites outside the reserve. 4. Some reserve-level differences in fish communities were categorized as ‘misleading’ because equivalent differences were seen in other reef systems, and are likely to be caused by natural intra-habitat variation. Separation of robust and misleading results was only possible because of archipelago-scale sampling. 5. Synthesis and applications . The Bahamas represents a relatively lightly fished system within the Caribbean. However, cessation of fishing has still increased the mean number of species, the abundance of the most highly prized fishes and, through trophic cascades, altered benthic community structure. In certain habitats, reserves are clearly important for conserving fisheries and biodiversity. However, reserve effects must be explicitly separated from confounding variables to ensure conservation benefits are accurately identified and reported, and not oversold to managers and local stakeholders.

Structure of Caribbean coral reef communities across a large gradient of fish biomass

The collapse of Caribbean coral reefs has been attributed in part to historic overfishing, but whether fish assemblages can recover and how such recovery might affect the benthic reef community has not been tested across appropriate scales. We surveyed the biomass of reef communities across a range in fish abundance from 14 to 593 g m(-2), a gradient exceeding that of any previously reported for coral reefs. Increased fish biomass was correlated with an increased proportion of apex predators, which were abundant only inside large marine reserves. Increased herbivorous fish biomass was correlated with a decrease in fleshy algal biomass but corals have not yet recovered.

A spatially explicit learning model of migratory fish and fishers for evaluating closed areas

Fisheries models usually characterise the concentrations of fish and the distribution of the fishing fleet by spatial averages over large areas assuming homogeneous spatial characteristics. Many important management questions, such as those related to the spatial effects of closed areas, cannot be addressed by such models. This paper presents a model which describes the spatial movement of individual fish schools and the spatial response of individual fishing boats, and which can be applied on a much finer scale and thus can be used to analyse the scale-dependent development of the fishery. The motion of the fish is based on assumptions about time-dependent gradients in the relative attractiveness of nearby grid cells which motivate migrations based on feeding and spawning factors. The motion of fishing boats is modelled in a similar fashion, with the attractiveness of neighbouring cells based on historical catch records as a function of position and time of year, as well as whether current catch rates are high enough to justify staying in the same cell. Our model showed that marine reserves increase fish biomass but decrease fish catches. It is also indicated that marine reserves are of limited use when not combined with quotas of catches. Our findings also point that transfer rates of fish increase the benefits of marine reserves in terms of fish biomass but decrease fish catches.

Analysis of mtDNA haplotypes of kelp bass tests for sibling-dominated recruitment near marine protected areas of the California Channel Islands

Marine protected areas (MPAs) have been heralded as the next important fisheries management tool. Predicted benefits include increased fish biomass, increased species diversity, and enhanced recruitment to the MPA itself, as well as to proximal areas. Whereas MPAs have in fact been shown to increase biomass and species diversity, evidence of enhanced recruitment has yet to be seen. If MPAs are significantly enhancing recruitment, one would expect to see the recruitment dominated by groups of siblings arising from highly productive females predicted to eventually reside in MPAs due to the protection afforded them. If occurring, such sibling-dominated recruitment could be identified by significantly fewer mtDNA haplotypes and significantly fewer singleton hap- lotypes in population samples of recruiting juveniles compared to adult populations. We investigated a new approach for potentially determining whether MPAs might be significantly enhancing recruit- ment to proximal areas of Santa Cruz and the Santa Catalina islands in the California Channel Islands, by seeking evidence of sibling-dominated juvenile recruitment in mitochondrial DNA haplo- type data of the kelp bass Paralabrax clathratus. Our analyses found largely genetically mixed recruitment from the plankton, suggesting that recruitment to the sampled areas was not being mea- surably enhanced from point sources such as the nearby MPAs.

Consequences and Correctives Related to Lake Acidification, Liming and Mercury in Fish – A Case-Study for Lake Huljesjön, Sweden, Using the LakeWeb-model

This work exemplifies how a given lake (Lake Huljesjon, Sweden) would likely respond to changes in pH-values and to liming (a standard measure against anthropogenic acidification). The basic questions are: How would a liming influence pH? How long would the changes last? How would the changes influence the structure and function of lake ecosystems? The work uses a comprehensive lake ecosystem model, LakeWeb, which accounts for production, biomasses, predation, abiotic/biotic interactions of nine key functional groups of organisms, phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), two types of fish (prey and predatory), zoobenthos, macrophytes and benthic algae. LakeWeb is a dynamic model and gives weekly variations. It has been critically tested using empirical data and regressions from many lakes. Those tests are not presented here but have shown that the model can capture typical functional and structural patterns in lakes very well. This gives credibility to the results presented in this work, which would be very costly to obtain in the traditional manner by extensive field studies in one or a few lakes. This work presents for the first time predictions at the ecosystem level of how functional groups of organisms (and not individual species) are likely to respond to acidification and liming. Two existing dynamic models, one for liming, the other for Hg-concentrations in fish, have been added to the LakeWeb-model. These two models have previously been tested and proven to yield good predictions. The results presented here indicate that there are several probable changes in the structure and function of the lake foodweb related to acidification and liming. The predicted changes in macrophyte cover will influence the predation pressure on fish, and thereby the fish biomass. Reductions in primary production at low pH-values will cause reductions in fish biomass. There are several interesting compensatory effects between factors that increase fish biomass and factors that tend to decrease the biomass. Such matters can be handled quantitatively by the LakeWeb-model.

Effects of Galaxias maculatus on Nutrient Dynamics and Phytoplankton Biomass in a North Patagonian Oligotrophic Lake

In this study we analysed the effects of Galaxias maculatus, a landlocked small fish species, on nutrient dynamics, and the consequent effects on phytoplankton biomass of an oligotrophic North Patagonian lake. We performed field and laboratory experiments in order to explore nutrient release by G. maculatus with increasing fish biomass and body size, and the resulting phytoplankton responses. Our results showed that phytoplankton biomass was strongly enhanced in the presence of fish, and that enhancement was greater with increasing fish biomass. These algal increments were associated with higher nutrient concentrations, due to the excretion/egestion processes of fish. In our two laboratory experiments we did not observe phytoplankton increase, probably due to light conditions, but we did observe significant effects of fish on nutrient concentrations. As was expected, mass-specific nutrient release rates were higher in smaller fish than in larger ones. So, the amount of nutrients supplied to phytoplankton would be influenced by the size structure of fish population. As a consequence of different N and P release rates, an increase in the \({\text{N}}_{{\text{NH}}_{\text{4}} } \):PTDP ratio was observed in the presence of fish. The fact that G. maculatus is a species that moves in schools would determine spatial heterogeneity in nutrient release, with important effects of reducing nutrient limitation and shifting \({\text{N}}_{{\text{NH}}_{\text{4}} } \):PTDP ratios.

The role of fish and fisheries in Baltic Sea nutrient dynamics

Many studies show that fish and fisheries management can be important to freshwater nutrient dynamics, but similar reports from marine environments are scarce. In the Baltic Sea, we estimate the removal of nutrients by the fishery to be 1.4% and 7% of the total nitrogen and phosphorus load to the Baltic Sea. Moreover, compared with the anthropogenic load of nutrients that reaches the open sea, the fishery removes 2.4% and 18% of the nitrogen and phosphorus. In addition, we show that the summer increase of fish biomass can explain up to one third of the summer decrease in “total phosphorus” in the upper 40 m of the water column. This suggests that fish may compete with primary producers (particularly cyanobacteria) for phosphorus. The fish and the fishery can thus influence nutrient dynamics in marine systems substantially, and this should be considered in ecosystem oriented fisheries management.

Experimental study of trophic cascade effect of silver carp (Hypophthalmichthys molitrixon) in a subtropical lake, Lake Donghu: on plankton community and underlying mechanisms of changes of crustacean community

An enclosure experiment was carried out to test trophic cascade effect of filter-feeding fish on the ecosystem: growth of crustacean zooplankton, and possible mechanism of changes of crustacean community structure. Four fish biomass levels were set as follows: 0, 116, 176 and 316 g m-2, and lake water (containing ca. 190 g m-2 of filter-feeding fishes) was comparatively monitored. Nutrient levels were high in all treatments during the experiment. Lowest algal biomass were measured in fishless treatment. Algal biomass decreased during days 21–56 as a function of fish biomass in treatments of low (LF), medium (MF) and high (HF) fish biomass. Crustaceans biomass decreased with increasing fish biomass. Small-bodied cladocerans, Moina micrura, Diaphanosoma brachyurum and Scapholeberis kingii survived when fish biomass was high whilst, large-bodied cladocerans Daphnia spp. and the cyclopoids Theromcyclops taihokuensis, T. brevifuratus, Mescyclops notius and Cyclops vicinus were abundant only in NF enclosures. Evasive calanoid Sinodiaptomus sarsi was significantly enhanced in LF, but decreased significantly with further increase of fish biomass. Demographic data indicated that M. micrura was well developed in all treatments. Our study indicates that algal biomass might be controlled by silver carp biomass in eutrophic environment. Changes of crustacean community are probably affected by the age of the first generation of species. Species with short generation time were dominant and species with long generation time survived less with high fish biomass. Evasive calanoids hardly developed in treatments with high fish biomass because of the (bottle neck) effect of nauplii. Species abundance were positively related to fish predation avoidance. Other than direct predation, zooplankton might also be suppressed by filter-feeding fish via competition.

Studies on the Effects of Silver Carp (Hypophthalmichthys molitrix) on the Phytoplankton in a Shallow Hypereutrophic Lake through an Enclosure Experiment

The responses of nutrients, water transparency, zooplankton and phytoplankton to a gradient of silver carp biomass were assessed using enclosure methods. The gradient of four silver carp biomass levels was set as follows: 0, 116, 176 and 316 g m—2. Nutrients did not show any statistically significant differences among the treatments. An outburst of Daphnia only occurred in fishless enclosures where phytoplankton biomass was the lowest and water clarity significantly increased. While among fish enclosures, the small-sized Moina micrura dominated throughout the experiment and both zooplankton and phytoplankton biomasses decreased with increased fish biomass. No large colonial cyanobacterial blooms occurred in the fishless enclosures as predicted. This might be due to low water temperature, short experiment time and the occurrence of large bodied Daphnia in our experiment. Cryptophyta was the most dominant group in most of the enclosures and the lake water throughout the experiment. The fishless enclosure had much lower proportion of Cyanophyta but higher proportion of Trachelomonas sp.

A dynamic landscape model for fish in the Everglades and its application to restoration

A model (ALFISH) for fish functional groups in freshwater marshes of the greater Everglades area of southern Florida has been developed. Its main objective is to assess the spatial pattern of fish densities through time across freshwater marshes. This model has the capability of providing a dynamic measure of the spatially-explicit food resources available to wading birds. ALFISH simulates two functional groups, large and small fish, where the larger ones can prey on the small fish type. Both functional groups are size-structured. The marsh landscape is modeled as 500×500 m spatial cells on a grid across southern Florida. A hydrology model predicts water levels in the spatial cells on 5-day time steps. Fish populations spread across the marsh during flooded conditions and either retreat into refugia (alligator ponds), move to other spatial cells, or die if their cell dries out. ALFISH has been applied to the evaluation of alternative water regulation scenarios under the Central and South Florida Comprehensive Project Review Study. The objective of this Review Study is to compare alternative methods for restoring historical ecological conditions in southern Florida. ALFISH has provided information on which plans are most are likely to increase fish biomass and its availability to wading bird populations.