Surplus Production Model Research Articles

Impacts of distorted fishery statistical data on assessments of three surplus production models

We evaluated the effect of various error sources in fishery harvest/effort data on the maximum sustainable yield (MSY) and corresponding fishing effort (EMSY) using Monte Carlo simulation analyses. A high coefficient of variation (CV) of the catch and effort values biased the estimates of MSY and EMSY. Thus, the state of the fisheries resource and its exploitation was overestimated. We compared the effect using three surplus production models, Hilborn-Waters (H-W), Schnute, and Prager models. The estimates generated using the H-W model were significantly affected by the CV. The Schnute model was least affected by errors in the underlying data. The CV of the catch data had a greater impact on the assessment than the CV of the fishing effort. Similarly, the changes in CV had a greater impact on the estimated maximum sustainable yield (MSY) than on the corresponding estimate of fishing effort (EMSY). We discuss the likely effect of these biases on management efforts and provide suggestions for the improvement of fishery evaluations.

Fishery trends, resource-use and management system in the Ungwana Bay fishery Kenya

The present study assessed trends in resource-use, partitioning and management in the Ungwana Bay fishery, Kenya, using surplus production models. The fishery is one of East Africa’s important marine fisheries sustaining a bottom trawl commercial fishery and a resident-migrant artisanal fishery. Two models: Schaefer (1954) and Gulland and Fox (1975) were applied to catch-effort data over a 21-year period to model maximum sustainable yield (MSY) and optimal effort ( f MSY) to examine the status of resource exploitation and provide reference points for sustainable management. In the artisanal fishery, model MSYs range from 392–446 t to 1283–1473 t for shrimps and fish respectively compared to mean annual landings of 60 t for shrimp and 758 t for fish. These landings represent <50% of the model MSYs suggesting under exploitation in the sub-sector. Moreover, current fishing effort applied stands at <0.5 f MSY. On the other hand, mean annual landings in bottom trawl commercial fishery, at about 330 t for shrimps and 583 t and fish represent about 90% of the model MSYs of 352–391 t and 499–602 t for shrimps and fish respectively. Therefore, the bottom trawl commercial fishery is likely under full exploitation. Similarly, the current effort is estimated at >0.7 f MSY. Resource management in the bay is faced with numerous problems including resource-use conflicts, poor economic conditions in artisanal fishery, poor legislation, and inadequate research augmented by poor reporting systems for catch-effort statistics. Thus, the fishery lacks clearly defined exploitation regimes. Fisheries research and assessment of the marine resources are important for sustainability of the fishery. Moreover, income diversification in the poverty ridden artisanal fishery would go a long way in addressing resource-use conflicts and use of deleterious fishing methods in the sub-sector. Borrowing from the successes of the Japanese community-based fisheries resource management (CBFRM) which has easily resolved numerous fisheries management issues in coastal small-scale commercial fisheries, and the beach management unit (BMU) system which has been applied to the artisanal fisheries of south coast Kenya with enormous benefits, it is envisaged that a hybrid CBFRM–BMU system presents the best approach to sustainable resource-use in the Ungwana Bay fishery.

Development of Bayesian production models for assessing the North Pacific swordfish population

Bayesian surplus production models were developed for assessing the North Pacific swordfish population under alternative scenarios: a single-stock scenario and a two-stock scenario with subareas that represented the western central and eastern Pacific Ocean regions. Biomass production was modeled with a three-parameter production model that allowed production to vary from the symmetric Schaefer curve using an estimated shape parameter. Lognormal prior distributions for intrinsic growth rate and carrying capacity were assumed. Goodness-of-fit diagnostics were developed for comparing the fits of alternative model configurations based on the root-mean squared error of catch per unit effort (CPUE) fits and the standardized CPUE residuals. Production model fits for 1952–2006 indicated that the Japanese longline CPUE numbers were influential under each stock scenario because these scenarios were the longest time series of relative abundance indices. Model results also indicated that assumptions about the prior means for intrinsic growth rate and carrying capacity may be important based on the model configuration.

Bioeconomic analysis of Maryland’s Chesapeake Bay oyster fishery with reference to the optimal utilization and management of the resource

The present paper deals with the surplus production models of Verhulst-Schaefer and Gompertz-Fox that are applied to the Maryland’s Chesapeake Bay oyster fishery to investigate the sustainability properties of the stock and management of the fishery. The basic objective of this paper is to illustrate the way in which long run sustainability can achieve an optimum exploitation of the fishery. For this purpose, conventional economic model is used along with biological population growth model to develop a bio-economic model. The parameters of the bioeconomic model are estimated using empirical data of catch, effort and price of the Maryland’s Chesapeake Bay oyster fishery. Standard reference points are analyzed and tax policies are introduced to achieve the standard reference points. In order to achieve maximum level of profit from the fishery optimal steady state solutions i.e., optimum levels of stock, harvest and effort are determined. Keywords: Bioeconomics, fisheries management, reference points, price function, tax

Role of sea surface temperature and rainfall in determining the stock and fishery of the common octopus (Octopus vulgaris, Mollusca, Cephalopoda) in Tunisia

AbstractOctopus (Octopus vulgaris, Mollusca, Cephalopoda) is an important and valuable fishery resource on the eastern and southern coasts of Tunisia, but its landings are highly variable. This paper explores the effect of environment on octopus catch per unit effort (CPUE) during a 12‐year period, through correlation analyses and the incorporation into surplus production models of sea surface temperature (SST) and rainfall data collected during cold (January–May) and hot (August–October) seasons. CLIMPROD software was used to select the appropriate model and fit it to the fishery and environment data. In both seasons, SST significantly contributed to CPUE variability; fishery production was influenced positively by cold season SST but negatively by hot season SST. Due to a poor fit with cold season data, the impact of rainfall was analysed only for the hot season, during which it has a positive effect on production. Results are discussed in view of the life‐cycle of octopus and the dynamics of the Tunisian fishery. This first study of octopus variability in Tunisia highlights the necessity to incorporate environmental influence into stock assessment and management advice.

Assessment of the status of the coastal groundfish assemblage exploited by the Viareggio fleet (Southern Ligurian Sea)

The coastal demersal fish assemblage exploited commercially by the Viareggio fleet was assessed in order to define its exploitation status and sustainability. A production model was used provided management benchmarks for the species for which available data are limited. The ASPIC Surplus production model was used. The results showed a depleted population for most of the species involved ( B 2008 /B 0 between 0.05 and 0.35) with high relative fishing mortality ( F 2008 /F MSY between 1.18 and 1.64). Population projections using ASPIC-P allowed the exploitation strategies to be evaluated for a 10-year period. None of the populations are predicted to recover to B MSY if fishing effort remains at the 2008 levels. A reduction in effort of about 40% should increase the biomass in the medium-term of most of the species to B MSY or over, with a fairly good increase in yields of the most valuable species.

Maximum Sustainable Yields and Non-linear Paths to Steady-state Equilibrium

AbstractTraditional surplus production models are based on restrictive assumptions of fish population dynamics and distribution, fish catch, and fishing effort, and can provide misleading guidelines for fisheries management. Following a review of two conventional models and later contributions, this article first reassesses the rationale for unique sustainable fishery equilibrium and its estimation, in light of complex responses associated with non-constant marginal returns, target switching, and stochastic variability. A new modelling approach is then formulated, with specifications estimated by classical or cointegration regression techniques accounting for possible switches in long-run equilibrium parameters and varying strengths of short-run readjustments. This approach is applied to marine fisheries in Indonesia (Java Sea) and Papua New Guinea, and results are compared with traditional model specifications. Parametric and nonparametric estimates highlight specific problems in the conventional approac...

Accounting Explicitly for Predation Mortality in Surplus Production Models: An Application to Longfin Inshore Squid

AbstractOne approach to better account for ecosystem considerations in fisheries science is to incorporate ecological interactions into conventional stock assessment models. The longfin inshore squid Loligo pealeii is one of two squid species of ecological and commercial significance in the northwest Atlantic Ocean. A surplus production model with quarterly time steps was fitted to longfin inshore squid total removal (fishing and predation removal) and tuned with fishery‐dependent, fishery‐independent, and predation‐dependent indices to examine the effect of incorporating predation into a single‐species model. Total consumption of squid by all predatory fish exceeded the landings in most years of this analysis. The model output indicated that biological reference points for longfin inshore squid differ considerably when predation removals are included. It appears that by not including predation, the model underestimates stock biomass and overestimates fishery surplus production. Short‐term stochastic projections of such estimates demonstrate that increasing predation mortality and fishing mortality will decrease the biomass of longfin inshore squid. Failing to account for predation when performing stock assessments for longfin inshore squid and other similar forage species may misrepresent reference point estimates and result in management advice that could lead to biomass declines. We envision that the approach presented here will provide requisite information and a useful example towards improving the current modeling practices for longfin inshore squid and similar forage species.

Simulation Model for Evaluating the Response of Management Options on the Demersal Resources of Tamil Nadu Coast

The response of different management options on demersal fish catch in Tamil Nadu was examined using simulation model and time series data on catch and effort of demersal resources in Tamil Nadu during 1989-2005. For the simulation study surplus, production model and spectral models were used to simulate effort, yield and biomass. Genetic algorithm was used to estimate parameters of surplus production model. Effort, biomass and yield were simulated for the period 2006 to 2015 under different levels of effort such as reducing by 25%, 50%, and 75% of present level increasing by 25%, 50%, 75% and 100% of present level and also for the present level. The simulation results revealed that when the level of exploitation is kept at 25%, 50%, 75%, and 100% of the present level, the yield falls below the maximum sustainable yield (MSY) level and the biomass is kept above its MSY level. When the exploitation level is increased by 25% of the present level of exploitation, the yield falls below the MSY level in the years up to 2013 and the biomass remains above that at MSY level. But at this level of exploitation, the yield falls above the MSY level and the biomass falls below its MSY level for the years 2014 and 2015. The optimum exploitation level was worked out as 91.25% of the present level of exploitation.

Graphical Evaluation of Fishery Status Using a Likelihood Inference Approach

AbstractWe present a graphical method that uses a statistical likelihood approach to summarize evidence and risk in fishery status evaluation. The graphical method is based on the surplus production model and shows the fishery status as regions and colors on graphs. Two fishery status graphs are used: one is based on the comparison between observed catch and catch at the fishing mortality level corresponding to maximum sustainable yield; the other one is based on the comparison between observed catch and catch at the surplus production level. The graphical statistical likelihood approach quantifies the strength of evidence in supporting different hypotheses of fishing status as regions in the status graphs. A simulated hypothetical fishery is given as an example. Results are graphically presented to show the exploitation status of the fishery, and they compare favorably with those from a composite risk assessment method. This graphical statistical likelihood approach may improve the communication of knowledge and evidence among scientists, fishery stakeholders, and management agencies and may provide a better understanding of current fishery status.

A surplus production model including environmental effects: Application to the Senegalese white shrimp stocks

In Senegal, two stocks of white shrimp ( Penaeus notialis) are intensively exploited, one in the north and another in the south. We used surplus production models including environmental effects to analyse their changes in abundance over the past 10 years and to estimate their Maximum Sustainable Yield (MSY) and the related fishing effort ( E MSY). First, yearly abundance indices were estimated from commercial statistics using GLM techniques. Then, two environmental indices were alternatively tested in the model: the coastal upwelling intensity from wind speeds provided by the SeaWifs database and the primary production derived from satellite infrared images of chlorophyll a. Models were fitted, with or without the environmental effect, to the 1996–2005 time series. They express stock abundance and catches as functions of the fishing effort and the environmental index (when considered). For the northern stock, fishing effort and abundance fluctuate over the period without any clear trends. The model based on the upwelling index explains 64.9% of the year-to-year variability. It shows that the stock was slightly overexploited in 2002–2003 and is now close to full exploitation. Stock abundance strongly depends on environmental conditions; consequently, the MSY estimate varies from 300 to 900 tons according to the upwelling intensity. For the southern stock, fishing effort has strongly increased over the past 10 years, while abundance has been reduced 4-fold. The environment has a significant effect on abundance but only explains a small part of the year-to-year variability. The best fit is obtained using the primary production index ( R 2 = 0.75), and the stock is now significantly overfished regardless of environmental conditions. MSY varies from 1200 to 1800 tons according to environmental conditions. Finally, in northern Senegal, the upwelling is highly variable from year to year and constitutes the major factor determining productivity. In the south, hydrodynamic processes seem to dominate and determine the primary production and the white shrimp stock productivity as well.

Stock assessment and fishery management of Henicorhynchus spp., Cyclocheilichthys enoplos and Channa micropeltes in Tonle Sap Great Lake, Cambodia

Tonle Sap Great Lake, in the lower Mekong River basin, contributes 60% of Cambodia's inland fisheries catch. There are four types of fisheries, including the middle-scale fishery. The major species comprising the middle-scale fishery are Henicorhynchus spp. (16%), a small-bodied fish caught mainly with small-mesh nets, and Cyclocheilichthys enoplos (13%), and Channa micropeltes (7%) which are caught with a variety of gear. Here we apply the Schaefer surplus production model to the middle-scale fisheries using monitoring data collected between 1995 and 1999. Model simulations determined that the maximum sustainable yield ( F MSY) for Henicorhynchus spp., was obtained with the use of 47,206 gillnets (mesh size < 50 mm) and 4269 and 1605 fishing boats for C. enoplos and C. microplestes, respectively. Over 1995–1999, there was a strong trend of increase in fishing effort and decrease of catch-per-unit-effort in the waters of Pursat, Siem Riep and Kampong Chnnang provinces. These provinces have large population centres located close to the fishing grounds; fishing in these areas should be more strictly regulated.

TAC assessment for single species and multiple gear fisheries with an application to the Korean hairtail fishery

This paper describes a Total Allowable Catch assessment model for a single species and multiple gear types as an improvement on TAC assessment based on a single species and a single gear type. A case study is included for a hairtail species caught mainly by the Korean pair trawl and large otter trawl gears. We use a surplus production model based on the exponential growth model to estimate biological reference points. Fishing effort for the two gears is standardized and used in a general linear model. The Fox bioeconomic model is then used to estimate economic reference points. In the Korean hairtail fishery, the TAC assessment model for a single species and multiple gear types yielded values for each reference point that were more conservative.

Corrigendum: An ecosystem-based hypothesis for climatic effects on surplus production in California sardine (Sardinops sagax) and environmentally dependent surplus production models

We used environmentally dependent surplus production (EDSP) models to test hypotheses linking changes in habitat area, carrying capacity and surplus production in California sardine (Sardinops saga...

HARVESTING AN AGE‐STRUCTURED POPULATION AS BIOMASS: DOES IT WORK?

AbstractThe economics of fisheries is based heavily on describing fish populations by the surplus production model. Both economists and ecologists have different opinions on whether this approach provides an adequate biological basis for economic analysis. This study takes an age‐structured population model and shows how, under equilibrium conditions, it determines the surplus production model. The surplus production model is then used to solve an optimal feedback policy for a generic optimal harvesting problem. Next, it is assumed that the fishery manager applies this feedback policy even though the fish population actually evolves according to the age‐structured model. This framework is applied to the widow rockfish, Atlantic menhaden, and Pacific halibut fisheries. Population age‐structure contains information on future harvest possibilities. The surplus production model neglects this information and may lead to major deviations between the expected and actual outcomes especially under multiple steady states and nonlinearities.

A surplus production model with latent truncation and species targeting, with an application to Papua New Guinean fisheries

This paper first reviews traditional bio-economic models of catch–effort equilibrium and later contributions based on augmented and revised specifications. To overcome some of the pitfalls in fisheries analysis, an approach is formulated which accounts for latent truncation in the fishing fleet, species targeting and non-linear long-term relationships among catch, effort and biomass. The procedure is applied to purse seine and longline offshore marine fisheries in Papua New Guinea, where tuna and other fish resources are believed to be under-exploited on the whole, but selective overfishing is reported to take place. Statistical evidence of incidental truncation is weak, with results being sensitive to the selection of variables. Based on regression diagnostics and expected signs/statistical significance of parameter estimates, non-linear surplus production specifications prove to be more suited than original and unrestricted versions of the conventional approach for modelling the dominant (purse seine) fishery in PNG over the period 1979–2007, with both main and secondary target fishing being found not to exceed the maximum sustainable yield. In either case, policy implications of these results should be pondered against underreporting of official fish catches.

Hierarchical Bayesian approach for population dynamics modelling of fish complexes without species-specific data

Abstract Jiao, Y., Hayes, C., and Cortés, E. 2009. Hierarchical Bayesian approach for population dynamics modelling of fish complexes without species-specific data. – ICES Journal of Marine Science, 66: 367–377. Modelling the population dynamics of fish complexes is challenging, and many species have been assessed and managed as a complex that was treated as a single species. Two Bayesian state-space surplus production models with multilevel priors (hierarchical models) were developed to simulate variability in population growth rates of species in a complex, using the hammerhead shark complex (Sphyrna spp.) of the Atlantic and Gulf of Mexico coasts of the US as an example. The complex consists of three species: scalloped (Sphyrna lewini), great (Sphyrna mokarran), and smooth hammerhead (Sphyrna zygaena). Bayesian state-space surplus production models with multilevel priors fitted the hammerhead data better than a model based on single-level priors. The hierarchical Bayesian approach represents an intermediate strategy between traditional models that do not include variability among species, and highly parameterized models that assign an estimate of parameters to each species. By ignoring the variability among species, confidence intervals of the estimates of stock status indicators can be unrealistically narrow, possibly leading to high-risk management strategies being adopted. Use of multilevel priors in a hierarchical Bayesian approach is suggested for future hammerhead shark stock assessments and for modelling fish complexes lacking species-specific data.

Redefining the maximum sustainable yield for the Schaefer population model including multiplicative environmental noise

The focus of this article is to investigate the biological reference points, such as the maximum sustainable yield (MSY), in a common Schaefer (logistic) surplus production model in the presence of a multiplicative environmental noise. This type of model is used in fisheries stock assessment as a first-hand tool for biomass modelling. Under the assumption that catches are proportional to the biomass, we derive new conditions on the environmental noise distribution such that stationarity exists and extinction is avoided. We then get new explicit results about the stationary behavior of the biomass distribution for a particular specification of the noise, namely the biomass distribution itself and a redefinition of the MSY and related quantities that now depend on the value of the variance of the noise. Consequently, we obtain a more precise vision of how less optimistic the stochastic version of the MSY can be than the traditionally used (deterministic) MSY. In addition, we give empirical conditions on the error variance to approximate our specific noise by a lognormal noise, the latter being more natural and leading to easier inference in this context. These conditions are mild enough to make the explicit results of this paper valid in a number of practical applications. The outcomes of two case-studies about northwest Atlantic haddock [Spencer, P.D., Collie, J.S., 1997. Effect of nonlinear predation rates on rebuilding the Georges Bank haddock ( Melanogrammus aeglefinus) stock. Can. J. Fish. Aquat. Sci. 54, 2920–2929] and South Atlantic albacore tuna [Millar, R.B., Meyer, R., 2000. Non-linear state space modelling of fisheries biomass dynamics by using Metropolis–Hastings within-Gibbs sampling. Appl. Stat. 49, 327–342] are used to illustrate the impact of our results in bioeconomic terms.

Assessment and bioeconomic analysis of the Majorca (NW Mediterranean) trammel net fishery

Trammel net is the main fishing gear used by artisanal fishers in Majorca Island (NW Mediterranean), and is representative of Mediterranean small-scale fisheries using static gear. The use of static gears close to the coast, where seasonal variability and spatial heterogeneity are high, promotes the diversification of fishing practices or metiers .W e analyze the seasonal dynamics of the nets used, target species (red and black scorpionfish, red mullet and cuttlefish) exploitation patterns and the socio-economic conditions under which this fishery takes place, based on General Fisheries Directorate daily sale records (2002-2006). Additional personal socioeconomic interviews allowed the characterization of the trammel net fishery, its fishing behaviour, cost structure and conflicts. Catch and effort data and market surveys are used to evaluate the level of exploitation of the target species and allowed describing Majorca trammel net fishery as an activity based on a sustainable resource. The main target species were found to be near their maximum sustainable yield both by means of a surplus production model (with parameters estimated by CEDA-Catch Effort Data Analysis, software) and an age structured assessment model based on yield-per-recruit analysis. Management actions currently debated by local administration and fishers focus on improving fishers' economic situation, rather than on protecting a threatened resource. One of the management actions proposed is a one day effort reduction, which was analyzed here with the help of a bioeconomic simulation model. A 15-year (2005-2020) simulation allows providing advice to local managers to focus on the commercialization aspects, in order to obtain a higher value to the fish production, rather than expecting to obtain higher profits only by a reduction of the offer.

Primary productivity and the carrying capacity for herring in NE Pacific marine ecosystems

The carrying capacity for Pacific herring ( Clupea pallasi) and its relationship to primary productivity was examined for eight populations in the NE Pacific and eastern Bering Sea. Data on biomass (ages 3 and older) and catches of herring in British Columbia (Georgia Strait, west coast Vancouver Island, Central Coast, Queen Charlotte Islands, Prince Rupert) and Alaska (Sitka, Prince William Sound, eastern Bering Sea) during the second half of the 20th Century derived from analytical stock assessments were used to calculate annual surplus production of herring. There was considerable interannual variability in herring productivity among all populations, however, only three (Georgia Strait, Prince Rupert, Prince William Sound) showed significant differences in mean productivity on decadal time scales (productivity regimes). Carrying capacity for the most recent productivity regime for each population was estimated using the Schaefer surplus production model. Mean annual primary productivity was estimated from remotely-sensed (SeaWiFS) chlorophyll data for British Columbia and Sitka ecosystems, and from in situ chlorophyll data for Prince William Sound and the eastern Bering Sea. The carrying capacity for herring populations in the NE Pacific ranged from 28,000 to 250,000 tonnes, and to 325,000 tonnes in the eastern Bering Sea. When considered on the basis of their distributional area, the west coast of Vancouver Island and Georgia Strait populations had the highest carrying capacity per unit area (9.3–13.8 tonnes km −2) and the eastern Bering Sea had the lowest (0.7 tonnes km −2). There is a significant positive linear relationship between the productivity of herring populations at carrying capacity and primary productivity on a per unit area basis. Although similar direct relationships have been observed between phytoplankton standing stock (as chlorophyll biomass) and total catches of resident fish populations from these regions, such a direct relationship was unexpected between primary productivity and herring carrying capacity because of multiple trophic pathways and other factors (e.g. spawning habitat) which should limit the carrying capacity for individual populations of particular species of fish. These results may be used to forecast potential responses of herring in NE Pacific ecosystems to global changes in ocean productivity.