A simulation model to explore the relative value of stock enhancement versus harvest regulations for fishery sustainability

Harvest restrictions and stock enhancement are commonly proposed management responses for sustaining degraded fisheries, but comparisons of their relative effectiveness have seldom been considered prior to making policy choices. We built a population model that incorporated both size-dependent harvest restrictions and stock enhancement contributions to explore trade-offs between minimum length limits and stock enhancement for improving population sustainability and fishery metrics (e.g., catch). We used a Murray cod Maccullochella peelii peelii population as a test case, and the model incorporated density-dependent recruitment processes for both hatchery and wild fish. We estimated the spawning potential ratio (SPR) and fishery metrics (e.g., angler catch) across a range of minimum length limits and stocking rates. Model estimates showed that increased minimum length limits were much more effective than stock enhancement for increasing SPR and angler catches in exploited populations, but length limits resulted in reduced harvest. Stocking was predicted to significantly increase total recruitment, population sustainability, and fishery metrics only in systems where natural reproduction had been greatly reduced via habitat loss, fishing mortality was high, or both. If angler fishing effort increased with increased fish abundance from stocking efforts, fishing mortality was predicted to increase and reduce the benefits realized from stocking. The model also indicated that benefits from stock enhancement would be reduced if reproductive efficiency of hatchery-origin fish was compromised. The simulations indicated that stock enhancement was a less effective method to improve fishery sustainability than measures designed to reduce fishing mortality (e.g., length limits).     

A stochastic simulation model of brown shrimp (Penaeus aztecus ives) growth,movement, and survival in Galveston Bay,Texas

A stochastic simulation model of brown shrimp (Penaeus aztecus Ives) population dynamics in Galveston Bay, Texas, is described, validated, and used to evaluate the effects of management alternatives and changing environmental conditions on shrimp dynamics. The model is composed of submodels representing: (1) recruitment, (2) growth, (3) natural mortality, (4) fishing mortality, and (5) emigration of brown shrimp. The model predicts significant changes in total annual harvest from the food shrimp, bait, and recreational fisheries resulting from (1) closure of the bay system to all fishing except during the spring and fall open seasons, (2) two-week postponement of the opening and closing of the open seasons for the food shrimp fishery, (3) a 2.5°C increase and (4) a 2.5°C decrease in mean water temperature, (5) an 80% increase and (6) an 80% decrease in fishing effort. No significant change in the total annual harvest is predicted when the food shrimp fishing season is extended from May 15 through December 15. Sensitivity analysis suggests that field experimentation designed specifically to test the hypothesis of a 60-day time lag between brown shrimp recruitment into the bays and exposure to the fishery should receive high priority. Simulation results are discussed within a management framework.     

Contribution of fishery discards to the diet of the Black-browed albatross (Thalassarche melanophris) during the non-breeding season: an assessment through stable isotope analysis

Black-browed albatrosses (Thalassarche melanophris) disperse over the Argentinean Continental Shelf and neighboring waters during their non-breeding season. It is one of the most frequent seabirds attending fishing vessels and also the most common Procellariform in the bycatch of longliners and trawlers in the area. Understanding the use of fishery discards by this species is an important issue when assessing the potential effect of strategic discard management in decreasing the abundance, interactions, and mitigating mortality. In the present study, we analyzed carbon and nitrogen stable isotope compositions in the blood of Black-browed albatrosses to assess the relative contribution of discards from different fisheries to the diet of this species in winter. Samples were obtained in winter 2011 from fishing vessels operating between 41–43°S and 57–59°W. No sex differences in δ¹³C and δ¹⁵N were observed. Results indicate that during their non-breeding season, isotopic signatures of Black-browed albatrosses are closer to discards and offal generated by fisheries and in particular by trawlers. The large fishing effort of trawl fisheries in Argentina highlights the urgency of an exhaustive analysis to find practical and effective ways to reduce the number of seabirds attending trawlers.     

A Comparison of Linear Demographic Models and Fraction of Lifetime Egg Production for Assessing Sustainability in Sharks

Conventional methods for management of data‐rich fisheries maintain sustainable populations by assuring that lifetime reproduction is adequate for individuals to replace themselves and accounting for density‐dependent recruitment. Fishing is not allowed to reduce relative lifetime reproduction, the fraction of current egg production relative to unfished egg production (FLEP), below a sustainable level. Because most shark fisheries are data poor, other representations of persistence status have been used, including linear demographic models, which incorporate life‐history characteristics in age‐structured models with no density dependence. We tested how well measures of sustainability from 3 linear demographic methods (rebound potential, stochastic growth rate, and potential population increase) reflect actual population persistence by comparing values of these measures with FLEP for 26 shark species. We also calculated the value of fishing mortality (F) that would allow all 26 species to maintain an accepted precautionary threshold for sharks of FLEP = 60%, expressing F as a fraction of natural mortality (M). Values of stochastic growth rate and potential population growth did not covary in rank order with FLEP (p = 0.057 and p = 0.077, respectively) and neither was significantly correlated with FLEP. Ordinal ranking of rebound potential positively covaried with FLEP (p = 0.00013), but the relative rankings of some species were substantially out of order. Adopting a sustainable limit of F = 0.16M would maintain all 26 species above the precautionary minimum value of FLEP (60%). We concluded that shark‐fishery and conservation policies should rely on calculation of replacement (i.e., FLEP), and that sharks should be fished at a precautionary level that would protect all stocks (i.e., F< 0.16M). Comparación entre Modelos Demográficos Lineales y la Fracción de Producción de Huevos a lo Largo de la Vida para Estudiar la Sustentabilidad en Tiburones Resumen     

A general model for tagging on multiple component fisheries: an integration of age-dependent reporting rates and mortality estimation

A major objective of analyzing multiple year tag return data in fisheries is to estimate fishing and natural mortality rates which may vary by age class and calendar year. To do this one needs to be able to estimate the reporting rates for the tags recovered. Some fisheries such as that for Southern Bluefin Tuna (Thunnus maccoyii) have multiple components with potentially different reporting rates for the tag returns. In this paper we develop a general model for multi-cohort, multi-year tag return analyses where there are multiple components to the fishery with potentially different reporting rates. We require the assumption that one component has a reporting rate of 100% (i.e., this could be the component of a boat based fishery where scientific observers are present). We show further how it is possible to partition the overall likelihood developed into two conditionally independent components. The first component of the likelihood is the standard multinomial likelihood that allows estimation of fishing and natural mortality rates. It uses the tag return matrix summed over all the components of the fishery. It requires an average reporting rate for the tag returns (where the average reporting rate is a weighted average of the individual reporting rates of the different components). The second component is also multinomial for the individual component tag returns and allows us to estimate individual component reporting rates. However, this requires that we augment our second component tag return likelihood with a catch data likelihood for the corresponding components. The methodology is illustrated on some Southern Bluefin Tuna tagging and catch data. We also discuss important model assumptions and give suggestions for future research including the integration of tag-return and catch at age data analyses.     

Discard analysis and damage to non-target species in the "rapido" trawl fishery

This paper describes the catch composition in the rapido trawl fishery and the direct effects on non-target species. All data were collected on commercial fishing vessels so as to reflect commercial rapido-trawling practice. The effects on non-target species were measured using two different damage scales (three- and seven-level scales) depending on the morphology of the taxa. Damage assessment was performed taking into account the whole fishing process by collecting individuals that passed through the cod-end, individuals that were retained in the cod-end and dropped onto the deck and individuals that were collected at the end of the sorting operation just before their return to the sea. Due to differences in the habitat and spatial distribution of target species, discard/commercial ratio was very different among the three different target species fisheries: 1:6 in the queen scallop (Aequipecten opercularis) fishery, 2:1 in the flatfish (Solea spp., Platichthys flesus, Psetta maximus and Scophthalmus rhombus) fishery and 9:1 in the scallop (Pecten jacobaeus) fishery. Damage sustained by non-target species was species-specific and related to the morphology of different organisms. The sorting operation produced similar levels of injury to those of the gear itself: all discarded animals showed higher levels of damage after the sorting than before. Damage to animals that had passed through the cod-end followed the same pattern, and these data could give an estimate of the "unobserved mortality". Our observations indicated a higher impact on non-target species caused by the queen scallop fishery than that caused by the flatfish fishery. This could be due to the total amount of hard-shelled species (in the queen scallop fishery, A. opercularis accounted for 87% of the total catch biomass) in any given haul, since shells macerated the catch during towing. Discarded animals from the queen scallop fishery showed higher levels of damage than those collected in the flatfish fishery. The rapido trawl fishery seemed to exert a strong selective pressure on the macrobenthic community, being able to modify the epibenthic fauna structure which, in heavily exploited fishing grounds, was dominated by bivalves, gastropods, crabs, starfish and brittlestars.     

Modeling spawning dates of Hucho taimen in Mongolia to establish fishery management zones.

The ecological impacts of recreational fisheries are of growing concern and pose a number of unique management challenges. Here we report on our efforts to provide guidance for managing a recreational fishery for taimen, the giant Eurasian trout (Hucho taimen) in Mongolia. This species has declined dramatically across its range of Siberia and Central Asia, and is currently listed as endangered in Mongolia. Strong populations persist in remote regions of Mongolia because of limited anthropogenic impacts and harvest, though interest in the fishery is expanding rapidly. Current fishing regulations list the spring "opening date" for taimen fishing as 15 June, although regulations have not been consistently enforced, partially because taimen spawn much earlier than 15 June in much of the country. Through a combination of statistical models, climate data, knowledge of taimen biology, and geographic information systems (GIS), we model taimen spawning dates for potential habitat in Mongolia. A parametric bootstrap procedure was used to simulate variability in spawning date derived from inter-annual climate variability and model error, from which we estimated the date in which taimen spawning is predicted to occur with 90% confidence. We recommend the designation of three fisheries management zones, with corresponding opening dates of 20 May, 1 June, and 15 June. Our fishery opening date recommendations are less restrictive than existing regulations. Provided there is little or no catch-and-release fishing mortality, this approach serves both environmental and human needs by protecting taimen during the reproductive period, while still allowing a post-spawning catch-and-release fishery that benefits local economies and generates revenue (through fishing concession fees) for local conservation efforts.     

Management and exploitation dynamics of small-scale fisheries in the Bay of Biafra: An integrative analysis of purse seine fishing activity

For many decades, fisheries research has focused on stock assessment and the impact of the fishery effort on resources. Although this knowledge remains necessary, a more integrated analysis of the joint dynamics of resource and operational activities is needed to provide more useful advice for the management of fishery systems. Since 1994 a new approach to fishery science has been carried out for Cameroonian small-scale fisheries, the aim being the incorporation into fishery science of research on fishery management, fishing processes and fishermen's behaviour. This paper presents a more systemic data approach which combines biological parameters and operational factor analyses with the goal of sustainable development. From two years of data collected on the purse seine fishing units operating in the Bay of Biafra (2002 and 2003), a set of three correspondence analyses is applied: (1) to the length frequency distribution of Ethmalosa fimbriata, (2) to the number of visits per fishing ground, and (3) to the species appearance frequency in the landings. These three analyses were plotted per month-year period. The results are presented in the form of an annual exploitation cycle, linking fishing grounds, the main species caught, and corresponding fishing period.     

Ecological and economic considerations on fishing and rearing of Tapes phillipinarum in the lagoon of Venice

A population dynamic model for Tapes philippinarum has been developed, using experimental data for the estimation of mortality, and literature information for recruitment. The population dynamic model has been coupled to a eco-physiological model of T. philippinarum previously developed, in order to simulate the evolution of individual size and number of individuals in each age class.The resulting age-size class model has been used to analyse the implication of different scenarios of fishing/harvesting of the bivalve in the lagoons of the Northern Adriatic Sea, where fishery and aquaculture represent important economic activities.Ten years long simulations have been performed, in which initial density, harvesting efficiency, minimum harvested size, were varied. Comparisons between the different strategies are made in term of total yields and bio-economic income. The model gives suggestions on the optimal fishing effort, in case of fishery, and on optimal seeding size and seeding moment, in case of aquaculture.A discussion of model results provides indications on harvesting policies which are appropriate from ecological-economical point of view. The final result is that economically more profitable strategies coincide with ecologically more conservative policies.     

Quantifying the squeezing or stretching of fisheries as they adapt to displacement by marine reserves

The designation of no‐take marine reserves involves social and economic concerns due to the resulting displacement of fishing effort, when fishing rights are removed from those who traditionally fished within an area. Displacement can influence the functioning of the fishery and success of the reserve, yet levels of displacement are seldom quantified after reserve implementation and very rarely before that. We devised a simple analytical framework based on set theory to facilitate reserve placement. Implementation of the framework requires maps of fishing grounds, fishing effort, or catch per unit effort for at least 2 years. The framework quantifies the level of conflict that a reserve designation might cause in the fishing sector due to displacement and the opportunities to offset the conflict through fisher spatial mobility (i.e., ability of fishers to fish elsewhere). We also considered how the outputs of the framework can be used to identify targeted management interventions for each fishery. We applied the method in Honduras, where the largest marine protected area in Central America is being placed, for which spatial data on fishing effort were available for 6 fisheries over 3 years. The proposed closure had a greater negative impact on the shrimp and lobster scuba fisheries, which concentrated respectively 28% and 18% of their effort inside the reserve. These fisheries could not accommodate the displacement within existing fishing grounds. Both would be forced to stretch into new fishing grounds, which are available but are of unknown quality. These stakeholders will likely require compensation to offset costly exploratory fishing or to travel to fishing grounds farther away from port.     

Some biological interactions affecting intertidal populations of the kelp Egregia laevigata

Near Santa Barbara, California (USA), the large laminarian kelp Egregia laevigata (Setchell) occurred from the lower intertidal zone to subtidal depths. In the intertidal zone there was a large recruitment of E. laevigata in the spring. The kelp were largely excluded from a zone in the lowest intertidal zone where the surf grass Phyllospadix sp, grew, but were abundant on all other rock surfaces. Experiments demonstrated that, while neither grazers nor sessile organisms significantly reduced recruitment, E. laevigata of the previous year-class did so. There were also interactions among E. laevigata of the same year-class, expressed as a density-dependent mortality of very small algae, and as faster growth rates and greater number of branches of kelp at low densities. These processes tended to make both numbers and biomass of E. laevigata uniform. The mortality rates of large E. laevigata were so high that, in some locations, no kelp survived for more than 8 months. E. laevigata was, therefore, essentially an annual and opportunistic species in the intertidal zone.     

Commercial fisheries under price uncertainty

The deterministic models applied in economics of fisheries are extended to comprise price uncertainty and risk aversion among the fishing units. It is proved that in the open-access fishery both the total fishing effort and the number of fishing units are reduced as the variance of the price increases; that the total fishing effort may be smaller in the open-access fishery than in the optimal fishery at a high variance; that only a fixed producer price system can create a first-best optimum, and that a tax on revenue is more efficient than both fishing unit quotas or tax on catch.     

Ecological role of stomatopods (mantis shrimps) and potential impacts of trawling in a marine ecosystem of the southeast coast of India

Ecosystems are balanced by nature and each component in the system has a role in the sustenance of other components. A change in one component would invariably have an effect on others. Stomatopods (mantis shrimps) are common and ecologically important predatory crustaceans in tropical marine waters. The ecological role of mantis shrimps and potential impacts of trawling in a marine ecosystem were estimated using Ecopath with Ecosim (EwE) Version 5.0 software, by constructing a mass balanced Ecopath model of Parangipettai (Porto Novo) ecosystem. Based on fisheries information from the region, 17 ecological groups were defined including stomatopods. Both primary and secondary data on biomass, P/B, Q/B and diet composition were used as basic inputs. The mass balanced model gave a total system throughput of 14,756 t km⁻² year⁻¹. The gross efficiency of 0.000942 indicated higher contribution of lower food chain groups in the fishery though the mean trophic level was 3.08. The immature and developing stage of the ecosystem was indicated by the ratio of total primary production and total respiration (1.832) and the net system production (2643.30 t km⁻² year⁻¹). Key indices (flow to detritus, net efficiency and omnivory index), split mortality rates and mixed trophic impact of different ecological groups were obtained from the model. A flow diagram was constructed to illustrate the trophic interactions, which explained the biomass flows in the ecosystem with reference to stomatopods. Two temporal simulations were made, with 10 year durations in the mass balanced Ecopath model by using ecosim routine incorporated in EwE software. The effect of decrease in biomass of stomatopods in the ecosystem was well defined, in the first run with increase in stomatopod fishing mortality, and the group showed a high positive impact on benthopelagic fish biomass increase (129%). The simulation with increase in trawling efforts resulted in the biomass decline of different ecological groups as elasmobranchs to 1%, stomatopods to 2%, crabs and lobsters to 36%, cephalopods to 63%, mackerel to 78%, and shrimps to 89%. Present study warns stomatopod discards and further increase in trawling efforts in the region and it explained the need for ecosystem based fisheries management practices for the sustainability of marine fisheries.     

Analysis of modified model for commercial fishing with possible extinctive fishery resources

The solution properties of a modified commercial fishing model are investigated in this paper. The results imply that fishery resources may be extincted under certain conditions. The positive invariant region, that is, the nonextinctive region, R(δ₁, δ₂), is a monotonic increasing correspondence of exiting rate of the fishing industry, δ₂, and is a monotonic decreasing correspondence of the entering rate of the fishing industry, δ₁. Also, there exist limit cycles for the system of equations of the modified model under certain conditions.     

Optimal fishery policy with artificial enhancement through stocking: California's white sturgeon as an example

Although optimal fishery policy has been derived from different kinds of economic and biological models, the interaction of fishing policy with artificial stocking policy has not been explicitly considered. We here determine optimal size limits, fishing effort, and stocking rate for three cases of interest: (1) recruitment-limited population, pre-recruitment stocking; (2) adult biomass-limited population, post-recruitment stocking; and (3) adult biomass-limited and recruitment-limited population, post-recruitment stocking. Results show that lower size limits should be set at the size at which the current market value exceeds the total future value of an individual, both to the fishery and to reproduction. Imposition of upper size limits is rarely optimal. Stocking is advisable when the hatchery cost times the relative contribution of stocking to recruitment is less than the contribution to the value of the catch. Optimal policy ranges from infinite effort at a specific size limit with maximum stocking when the cost of stocking is zero, to lower values of size limit and effort as stocking costs increase, the amount of stocking decreases, and more natural reproduction is optimal. Thus, as hatchery costs decline (or value of captured fish increases), optimal stocking/fishery policy varies from an unstocked fishery to a “put and take” fishery. The results are applied to the sturgeon fishery in the San Francisco Bay Estuary as an example. They imply that a reduced lower size limit and greater fishing mortality together with stocking would be optimal, but that current levels are conservative. The stocking decision depends critically on the values of parameters that are currently poorly known, such as: hatchery costs, survival to the fishery and the mechanisms controlling the sturgeon population.     

Estimation of some parameters of large fish populations by capture-recapture experiments

A certain number of tagged fish is liberated and assumed to be distributed randomly among a natural fish population. The fish are subjected to a number of fishing experiments within relatively short periods, and lie between equal intervening periods of durationT. Untagged fish are retained, while tagged fish are released during the fishing experiments. Denoting the catchability of untagged fish byq _u and that for tagged fish byq _t , it is assumed that they are related by the equation “q _u =cq _t ” wherec is a constant. Denoting the survival rates of tagged fish and the effective fishing effort of commerical fisheries per unit time from the (k-1)^th to thek ^th experiments by _t S _k andf _k , respectively, it is assumed that they vary from period to period. Assuming that during thek ^th experiment, the number of untagged fish captured and the experimental fishing rate of tagged fish are denoted by _u X _k and _t P _k , respectively, then $$\begin{array}{*{20}c} {\frac{{(_u X_k )^2 }}{{[_u X_{(k - 1)} ][_u X_{(k + 1)} ]}} = \frac{{_t S_k }}{{_t S_{(k + 1)} }} \cdot \frac{{e^{ - (1 - c)q_t f_{(k + 1)} T} }}{{e^{ - (1 - c)q_t f_k T} }} \cdot } \\ {\frac{{1 - c_t P_{(k - 1)} }}{{1 - c_t P_k }} \cdot \frac{{(_t P_k )^2 }}{{[_t P_{(k - 1)} ][_t P_{(k + 1)} ]}}.} \\ \end{array}$$ The above equation containsc as a single unknown, while all other terms are supplied by the capture-recapture experiments, exceptf _k andf _(k+1) which may be obtained from fisheries statistics. A number of the above equations are obtained from several experiments and can be combined into a single equation to obtain an overall estimate forc which can be used to derive estimates for experimental fishing rates, abundance, and instantaneous natural and fishing mortality rates for natural fish populations. These estimates are free from type (A) tagging errors, and have the advantage of taking into consideration the probable different behaviour of tagged and untagged fish.     

Optimum size limit for a fishery with a limited fishing season

In the management of a fishery with many year-classes, a standard objective is to maximize the biomass yield. If the fishing effort is fixed, this objective can be attained by prescribing an optimum size limit. This implies that only fish which are larger than the optimum size limit should be caught. The theory for computing the optimum size limit when fishing is carried out continuously is well established. In contrast the theory for computing the optimum size limit when the fishing season is limited to the same period in each year has not been developed in spite of the fact that many fisheries are exploited in this manner. A fishing season may be limited because the weather or the migration patterns of the fish population permits fishing only during a certain period in the year. A fishing season may also be limited because it is necessary to reduce the fishing mortality in order to conserve the fish population.A theory for computing the optimum size limit when the fishing season is limited is developed in this paper. It is applied to a hypothetical fishery. The data for this example comes from the North Sea plaice fishery. It is found that for a given fishing effort the optimum size limit is 44.5 cm if fishing is carried out continuously, 41.3 cm if fishing is limited to 6 months in a year and 28.7 cm if fishing is limited to a period of one tenth of a year in each year.     

When are no-take zones an economically optimal fishery management strategy?

Discussions on the use of marine reserves (no-take zones) and, more generally, spatial management of fisheries are, for the most part, devoid of analyses that consider the ecological and economic effects simultaneously. To fill this gap, we develop a two-patch ecological-economic model to investigate the effects of spatial management on fishery profits. Because the fishery effects of spatial management depend critically on the nature of the ecological connectivity, our model includes both juvenile and adult movement, with density dependence in settlement differentiating the two types of dispersal. Rather than imposing a reserve on our system and measuring its effect on profits, we ask: "When does setting catch levels to maximize system-wide profits imply that a reserve should be created?" Closing areas to fishing is an economically optimal solution when the value derived from spillover from the reserve outweighs the value of fishing in the patch. The condition, while simple to state in summary form, is complex to interpret because it depends on the settlement success of the dispersing organisms, the nature of the costs of the fishing, the economic and ecological heterogeneity of the system, the discount rate, and growth characteristics of the fish population. The condition is more likely to be satisfied when the closed area is a net exporter of biomass and has higher costs of fishing, and for fish populations with density-independent settlement ("adult movement") than with density-dependent settlement ("larval dispersal"). Rather surprisingly, there are circumstances whereby closing low biological productivity areas, and even sometimes low cost areas to fish, can result in greater fishing profits than when both areas are open to fishing.     

Econometric modeling of fisheries with complex life histories: Avoiding biological management failures

Economics of the fishery has focused on the wastefulness of common pool resource exploitation. Pure open access fisheries dissipate economic rents and degrade biological stocks. Biologically managed fisheries also dissipate rents but are thought to hold biological stocks at desired levels. We develop and estimate an empirical bioeconomic model of the Gulf of Mexico gag fishery that questions the presumptive success of biological management. Unlike previous bioeconomic life history studies, we provide a way to circumvent calibration problems by embedding our estimation routine directly in the dynamic bioeconomic model. We nest a standard biological management model that accounts for complex life history characteristics of the gag. Biological intuition suggests that a spawning season closure will reduce fishing pressure and increase stocks, and simulations of the biological management model confirm this finding. However, simulations of the empirical bioeconomic model suggest that these intended outcomes of the spawning closure do not materialize. The behavioral response to the closure appears to be so pronounced that it offsets the restriction in allowable fishing days. Our results indicate that failure to account for fishing behavior may play an important role in fishery management failures.     

Mass balanced and dynamic simulations of trophic models of kelp ecosystems near the Mejillones Peninsula of northern Chile (SE Pacific): Comparative network structure and assessment of harvest strategies

Mass balanced trophic models for kelp ecosystems which include subsystems dominated by Macrocystis integrifolia, Lessonia trabeculata and areas of barren ground (BG) were constructed for subtidal areas near the Mejillones Peninsula (SE Pacific), Chile. Information on biomass, P/B ratios, catches, food spectrum, consumption and dynamics of commercial and non-commercial populations was obtained and examined using Ecopath with Ecosim software analyses. The biomass of blades of L. trabeculata and M. integrifolia represented the compartments most relevant to the subsystems studied. Within the herbivores, the sea urchin Tetrapigus niger was dominant, followed by the snails Turritella sp. and Tegula sp. The fishes Pinguipes chilensis and Cheilodactylus variegatus were the dominant predators, followed by the asteroids Heliaster helianthus and Meyenaster gelatinosus. The highest system throughput (72,512 g wet weight m⁻² year⁻¹) was calculated for the subsystem dominated by M. integrifolia. The mean trophic level of the catch ranged from 1.1 (subsystem dominated by L. trabeculata) to 1.3 (subsystem dominated by M. integrifolia) to 3.2 (barren ground subsystem), showing that harvesting in each system was concentrated either on primary producers (blades of kelp species) or top predator fishes. Although the values for the Relative Ascendency (A/C) fluctuated from 36.5 to 45%, suggesting that all the systems were immature, the subsystem dominated by M. integrifolia emerged as the least resistant to external disturbances (e.g. fisheries). This result agreed with the high value of the system recovery time (SRT) for the M. integrifolia subsystem as a response to combined fisheries scenarios. The results obtained using mixed trophic impact (MTI) and Ecosim [increasing the fishing mortality F_i by 4×] showed that in most of the cases the predictions had the same qualitative tendencies. One of the most important results obtained in this study was that exploitation of kelp blades as an alternative strategy to harvesting the whole plants appeared to be ecologically sustainable, since harvesting the blades propagated only small effects on the entire subsystem. The fish P. chilensis may be considered as a top predator species with a strong top-down control since an increase in its fishing mortality in the subsystem dominated by M. integrifolia produced a high SRT value, and the F_MSY was less than the originally entered F_i in Ecopath. Based on the results obtained, it was concluded that the trophic mass balanced models and simulated management scenarios offered good possibilities for the planning of interventions and manipulations or the planning of more sustainable management strategies in highly disturbed natural systems.