Management Reference Points Research Articles

표지방류 조사를 통한 거제 외포 주변해역 대구(Gadus macrocephalus) 자원량과 어획사망률 추정

We estimated the population size and fishing mortality of Pacific cod Gadus macrocephalus during the spawning season in waters off Woipo, Geoje Island, Korea, using a mark-recapture method. We marked and released 51 cod>50 cm in total length; six were recaptured by local fishermen during the period from December 15 to 31, 2009. The estimated population size was ca. 180,000 and the fishing mortality of the exploitable cod was 26%. Although we could assume a closed population due to the short survey period, we evaluated the uncertainty in the estimates by applying bootstrap resampling because the sample size was small. The estimated 95% confidence interval was 94,000-568,000 for the population size and 8-49% for fishing mortality. Our study demonstrated that the application of mark-recapture methods and bootstrap resampling can be useful in stock assessment for fisheries management in Korea, but requires a larger sample size, spatially extensive coverage, and sophisticated mark-recapture models based on a refined sampling design for reliable stock assessment and biological reference points in sustainable cod management.

Diet variability and reproductive performance of macaroni penguins Eudyptes chrysolophus at Bird Island, South Georgia

We analysed summer diet and fledging mass of macaroni penguins Eudyptes chrysolophus breeding at Bird Island, South Georgia, during the creche period (January and February) between 1989 and 2010. Crustaceans were the main prey accounting, for over 90% of the diet by mass. Antarctic krill Euphausia superba was the main prey, in 17 out of 22 years. Amphipods Themisto gaudichaudii were the main prey in 1994 and 2009, fish in 2004, and the euphausiids Thysanoessa spp. and Euphausia frigida in 2000. There was no clearly dominant prey group in 1999. Prey diversity and the frequency occurrence of T. gaudichaudii both increased with a decreasing proportion of E. superba in the diet. There was strong evidence that macaroni penguins have a sigmoidal functional response, indicating that this kind of response should be accounted for when devising ecosystem-based management reference points for seabirds. The energy and mass of all euphausiids combined (rather than E. superba in particular) in the diet were the most reliable predictors of chick fledging mass; the correlation between model-predicted and observed values was 0.84. The gross energy content of individual meals was often above average in years when the diets contained fewer euphausiids, but fledging mass was always below average in these years. Although macaroni penguins are able to feed on a variety of prey types, chick growth was always severely impacted by a shortage of euphausiids due to higher energy or time costs associated with feeding on alternative prey types. Given their reliance on euphausiids, macaroni penguins would be particularly vulnerable to potential climate-driven declines in krill stocks.

Management of cancer pain: ESMO Clinical Practice Guidelines

Management of cancer pain: ESMO Clinical Practice Guidelines

Management reference points to account for direct and indirect impacts of fishing on marine mammals

AbstractReference points can help implement an ecosystem approach to fisheries management (EAF), by establishing precautionary removal limits for nontarget species and target species of ecological importance. PBR (Potential Biological Removal), developed under the U.S. Marine Mammal Protection Act (MMPA), is a limit for direct mortality for marine mammals, but it does not account for indirect effects of fishing due to prey depletion. I propose a generalization of PBR (called PBR*) to account for plausible changes in marine mammal carrying capacity (ΔK) from prey biomass decline relative to two example benchmarks: SSBMSY (maximum sustainable yield biomass for all known prey species) or SSBK (unfished prey biomass). PBR* can help identify when indirect fishing effects (alone, or combination with direct mortality estimates) may stymie MMPA objectives, and could inform catch limit estimates for target species that are also important as marine mammal prey. As a case study, I applied PBR* estimates to evaluate the possible combined direct + indirect effects of fishing on cetaceans in northeastern U.S. waters. Estimated distributions for ΔK were based on fish stock assessments and meta‐analysis of predator‐prey relationships from the mammalian literature. Based on this analysis, increased risk of marine mammal depletion due to indirect fishing effects was not evident, although this result must be interpreted cautiously given our limited understanding of cetacean diets and marine trophic dynamics. This study is intended to illustrate a possible practical approach for incorporating indirect fisheries impacts on marine mammals into a comprehensive management framework, and it raises several scientific and policy issues that merit further investigation.

Using a stock assessment framework to examine circle hooks: exploring changes in catchability and implications for management

A presumed conservation benefit of circle hooks is that they reduce catchability (q) and therefore bycatch of non-target species. While these changes may benefit a fish stock, they are difficult to incorporate in a stock assessment context, particularly for models that rely on fishery-dependent data, because few experiments exist that quantify the effects of circle hooks for a given species over appropriately large spatial scales. Consequently, to develop management advice, it may be necessary to model assumed changes in q within the adopted stock assessment model framework. Here we present a case study of bigeye tuna (Thunnus obesus lowe, 1839), a highly migratory species managed by the international commission for the conservation of atlantic tunas (iccat), and explore the management implications of changes in q within a multi-fleet, age-structured assessment context. This study demonstrates that changes in q on the order of ±30% are sufficient to cause notable differences in the magnitude of common management reference points estimated by stock assessment models. Relative to a base model that assumed a constant q, models that incorporated a theoretical reduction in q produced higher estimates of spawning stock biomass and maximum sustainable yield, and lower estimates of fishing mortality while a theoretical increase in q had the opposite effect. The magnitude of the change was dependent on the number of fisheries affected. We conclude that carefully designed studies are essential to quantify the effects of a proposed gear change and to inform the appropriate parameterization of stock assessment models.

Effects of variable reproductive potential on reference points for fisheries management

Analytical and simulation results with hypothetical vectors of biological parameters were employed to demonstrate the impact of variable reproductive potential on reference points based on spawning potential ratio (SPR). Implications for stock recruit function parameterizations are also noted. For the range of variability explored in this illustration, skipped spawning had a negligible impact on reference points, while factors related to spawner condition or experience and density independent survival of recruits (i.e. slope at the origin) had greater effects. When estimating yield per recruit (YPR) associated with a specified SPR, the variability in the biological parameters was greatly dampened. Estimating correlations between the observed trends in maturity and fecundity, and developing models to forecast the probabilities associated with observing a biological state in the future, would be an important contribution to understanding uncertainty in rebuilding projections and future catch advice.

Assessing stock reproductive potential in species with indeterminate fecundity: Effects of age truncation and size-dependent reproductive timing

Annual fecundity has been increasingly advanced as a preferred measure of stock reproductive potential (SRP), yet estimates are methodologically challenging, particularly for species with indeterminate fecundity. Inherent variability due to energetic and environmental constraints increases the uncertainty of annual fecundity estimates, and this uncertainty may have important consequences for management guidance. In this study, we assessed how size-dependent reproductive timing interacts with age truncation to impact estimates of SRP in spotted seatrout (Cynoscion nebulosus), using a combination of modeling techniques. Positive size dependence in spawning frequency, or the number of spawning events in a season, had a substantial impact on both the SRP and estimates of stock status relative to management targets. The loss of the oldest age classes, even under relatively low fishing pressures, resulted in a significant decline in SRP due to the disproportionately large contribution by these age classes. Not surprisingly, the effect increased with the strength of the size-dependent relationship, which also resulted in reducing the proportionality between SRP and spawning stock biomass (SSB). The potential for erroneously classifying the health of a stock was amplified when the population approached the management target because of the uncertainty and inherent variability in SRP. For management, characterizing all of the size-dependent relationships with SRP (batch fecundity, reproductive timing, egg/larval quality) may be more critical than obtaining precise estimates of SRP when management reference points are relative to unexploited conditions, as in spawning potential ratios (SPRs).

Latitudinal and stock-specific variation in size- and age-at-maturity of female winter flounder, Pseudopleuronectes americanus, as determined with gonad histology

Female winter flounder were examined using gonad histology to determine the adequacy of routine macroscopic maturity classification methods and to determine the spatial variation in size and age of maturity in U.S. waters. Sampling occurred in spring and autumn, which was adequate to collect immature, mature, spawning-active, and non-active females. Females were collected in coastal waters from Delaware Bay, USA, to the Scotian Shelf, Canada, including in Long Island Sound and on Georges Bank, which covered all U.S. stock areas. Mature fish spawned in spring, when gonads comprised up to 30% of the total body weight. Direct comparisons of maturity assignment by macroscopic versus microscopic methods demonstrated that both schemes are compatible, but the more cost-effective macroscopic method had trouble distinguishing larger immature from smaller resting females. Spatial comparisons, using gonad histology only, supported the existence of three stocks in U.S. waters, but also revealed significant variation in age at maturity within the two coastal stocks. Age-at-maturity was more variable than size-at-maturity, which is consistent with known stock-specific patterns of growth rates and a postulated life history tradeoff to delay maturity until a size threshold is reached. The within-stock variation in median age at maturity, about one year for coastal stocks, recommends further investigation of using static, stock-specific maturity ogives to calculate reference points for management.

Krill space: a comparative assessment of mesoscale structuring in polar and temperate marine ecosystems

Abstract Santora, J. A., Sydeman, W. J., Schroeder, I. D., Reiss, C. S., Wells, B. K., Field, J. C, Cossio, A. M., and Loeb, V. J. 2012. Krill space: a comparative assessment of mesoscale structuring in polar and temperate marine ecosystems. – ICES Journal of Marine Science, 69: . The spatial organization, mesoscale variability, and habitat associations of krill within portions of the Antarctic Peninsula and California Current marine ecosystems are compared. Using a decade of acoustic observations and remotely sensed oceanography (2000–2009), the hypothesis that mesoscale spatial organization of krill in both systems closely relates to geospatial variability of the shelf break and is non-linearly related to geostrophic flow and positively related to chlorophyll a (Chl a) is tested. Directional-dependence analysis to measure spatial variability of krill is used along with spatially explicit generalized additive models to quantify and compare the spatial relationships among krill and habitat characteristics in both systems. The results suggest the following aspects of krill spatial organization: (i) areas of dense aggregation, i.e. hot spots, are present in both systems and are orientated in the direction of the shelf break, (ii) moderate levels of eddy kinetic energy seem to concentrate krill in favourable habitats and lessen the likelihood of advection away from the system, and (iii) variable responses to surface Chl a concentration suggest that real-time Chl a values may not be useful as a global predictor of important krill habitat. The results provide valuable reference points for marine spatial management of krill and for refining ecosystem and foodweb models.

Can steepness of the stock–recruitment relationship be estimated in fishery stock assessment models?

Steepness of the stock–recruitment relationship is one of the most uncertain and critical quantities in fishery stock assessment and management. Steepness is defined as the fraction of recruitment from a virgin population obtained when the spawners are at 20% of the virgin level. Steepness directly relates to productivity and yield and is an important element in the calculation of many management reference points. Stock–recruitment relationships have traditionally been estimated from time series of recruitment and spawning biomass, but recently interest has arisen regarding the ability to estimate steepness inside fishery stock assessment models. We evaluated the ability to estimate steepness of the Beverton–Holt stock–recruitment relationship using simulation analyses for twelve US Pacific Coast fish stocks. A high proportion of steepness estimates from the simulated data and the original data occur at the bounds for steepness and the proportion decreased as the true steepness decreased. The simulation results indicate that, in most cases, steepness was estimated with moderate to low precision and moderate to high bias. The poorly estimated steepness indicates that often there is little information in the data about this quantity. However, reliable estimation is attainable with a good contrast of spawning stock biomass for relatively unproductive stocks when the model is correctly specified.

Evaluating the stock–recruitment relationship and management reference points: Application to summer flounder (Paralichthys dentatus) in the U.S. mid-Atlantic

The stock–recruitment relationship is one of the most uncertain processes of fish population dynamics, and is highly influential with respect to fisheries management advice. The stock recruitment relationship has a direct impact on reference points commonly used in contemporary fisheries management. Simulation analysis has shown that the steepness of the Beverton–Holt stock–recruitment relationship is difficult to estimate for most fish stocks, which has led to the use of proxy reference points. Proxy maximum sustainable yield reference points based on spawning biomass-per-recruit, which are commonly used when the stock–recruitment relationship is uncertain, are a linear function of steepness. Risk in terms of lost yield is generally lower when steepness is underestimated compared to when steepness is overestimated because the yield curve is flat when steepness is high (close to one: recruitment is independent of stock size), indicating that using a lower value of steepness might be appropriate. Simulation analysis based on data for summer flounder in the US mid-Atlantic indicates that steepness can be estimated from the data. Steepness is estimated to be close to one and a high steepness is supported by estimates for related species and from life history theory. Current target (F35%) and threshold (F40%) spawning biomass-per-recruit reference points used for summer flounder imply steepness values of 0.73 and 0.66, respectively, for the Beverton–Holt stock–recruitment relationship.

Data-limited management reference points to avoid collapse of stocks dependent on learned migration behaviour

AbstractMacCall, A. D. 2012. Data-limited management reference points to avoid collapse of stocks dependent on learned migration behaviour. – ICES Journal of Marine Science, 69: 267–270. Risk of stock collapse associated with the loss of a stock's migrational knowledge may be underestimated by conventional reference points. In this paper, I describe three different approaches: a data-poor precautionary approach is to ensure that individuals spawn at least twice; a data-intermediate approach is to calculate a repeat spawning potential ratio (rSPR), which is analogous to the conventional SPR; and for data-rich cases, age-structured population simulations are recommended.

Implications of uncertainty in the spawner–recruitment relationship for fisheries management: An illustration using bigeye tuna (Thunnus obesus) in the eastern Pacific Ocean

The impacts of the steepness parameter of the Beverton–Holt spawner–recruitment curve on fisheries stock assessment and management performance were evaluated, using data for bigeye tuna (Thunnus obesus) in the eastern Pacific Ocean. The analysis was conducted using the Stock Synthesis model. The estimates of maximum sustainable yield (MSY) and related management reference points are sensitive to the value of steepness (ranging from 0.4 to 1.0) of the Beverton–Holt spawner–recruitment relationship assumed in the assessment model. Steepness also impacts the evaluation of stock status. A lesser value assumed for steepness leads to a more pessimistic evaluation of the stock status regarding whether the stock is overfished or overfishing is occurring. However, a lesser value does not reduce the estimates of MSY due to the interaction between steepness and the estimates of other model parameters. When managing the stock under effort limitation using MSY-based fishing mortality, a lower assumption of steepness yields less expected losses in catch than does a higher assumption. This is due to the flatness of the yield curve when the steepness is high. A lower assumption of steepness also maintains a higher level of spawning biomass and recruitment.

Stock assessment for the western winter-spring cohort of neon flying squid (<em>Ommastrephes bartramii</em>) using environmentally dependent surplus production models

The western winter-spring cohort of neon flying squid, Ommastrephes bartramii , is targeted by Chinese squidjigging fisheries in the northwest Pacific from August to November. Because this squid has a short lifespan and is an ecological opportunist, the dynamics of its stock is greatly influenced by the environmental conditions, which need to be considered in its assessment and management. In this study, an environmentally dependent surplus production (EDSP) model was developed to evaluate the stock dynamics of O. bartramii . Temporal variability of favourable spawning habitat with sea surface temperature (SST) of 21-25°C ( P s ) was assumed to influence carrying capacity ( K ), while temporal variability in favourable feeding habitat areas with different SST ranges in different months ( P f ) was assumed to influence intrinsic growth rate ( r ). The parameters K and r in the EDSP model were thus assumed to be linked to temporal variability in the proportion of Ps and Pf, respectively. According to Deviance Information Criterion values, the estimated EDSP model with Ps was considered to be better than the conventional surplus production model or other EDSP models. For this model, the maximum sustainable yield (MSY) varied from 210000 to 262500 t and biomass at MSY level varied from 360000 to 450000 t. The fishing mortality rates of O. bartramii from 2003 to 2013 were much lower than the fishing mortality at target level and MSY level (F tar and F MSY ) and stock biomass was higher than B MSY , suggesting that this squid was not in the status of overfishing and stock was not overfished. The management reference points in the EDSP model for O. bartramii were more conservative than those in the conventional model. This study suggests that the environmental conditions on the spawning grounds should be considered in squid stock assessment and management in the northwest Pacific Ocean.

Predicting species vulnerability with minimal data to support rapid risk assessment of fishing impacts on biodiversity

Summary1. Large‐bodied species are especially vulnerable to fishing in mixed fisheries. Their effective conservation requires predictions of sensitivity and exposure to fishing mortality, but such predictions are hard to make when the population dynamics of most of these species have not been described.2. We present a method for assessing sensitivity and conservation management reference points using widely available life‐history data. The method allows the sensitivity of all fish species in a community to be assessed in relation to conservation‐ and yield‐based fishery reference points.3. Knowledge of sensitivity is used to (i) rank species by sensitivity, (ii) conduct a risk assessment to identify species potentially vulnerable to current fishing pressure and (iii) examine potential trade‐offs between fishery catches and the conservation status of sensitive species.4. The method is applied to the Celtic Sea bottom‐dwelling fish community. For the species present, conservation threshold fishing mortalities ranged from 0·05 per year for the most sensitive large elasmobranchs to over 1 per year for small teleosts. The assessment predicts that current levels of fishing mortality may place all the elasmobranchs and over a quarter of the teleosts below conservation reference points.5. Depending on the relative mortality rates affecting commercially targeted species and species of conservation concern, up to 65% of the potential yield‐per‐recruit of commercially important species may have to be forgone to reduce fishing mortality below conservation limit reference points for the most sensitive species.6. Synthesis and applications.The method presented provides a clear objective procedure to construct ranked species sensitivity lists that can inform management, monitoring and research. The Celtic Sea case study demonstrated that limiting fishing pressure on key commercial stocks to meet fisheries production targets may be insufficient to guarantee the persistence of more sensitive species. Management actions that effectively decouple the mortality rates on commercial species and ‘conservation’ species are likely to be required to make progress in relation to conservation objectives. The method would support rapid assessment of sensitivity to fishing in many regions around the world as only taxonomic lists and estimates of body size are required.

Visualizing Plant Community Change Using Historical Records

Ecological data from land surveys from 1811 for the 100,000-acre Connecticut Tract in western New York were transcribed and then analyzed using ArcGIS and IDRISI GIS software. The surveys contained both witness tree data and line descriptions, which were analyzed for species composition and community type. Results illustrate that many changes have occurred in species composition. Possible causes of these changes to the mature forests may include introduced pests and diseases or anthropogenic land-use change. Comparisons to the National Wetlands Inventory Database reveal that while some of the wetlands that were present in 1811 still exist today, particularly in the Byron-Bergen Swamp and in the wetlands along the Lake Ontario shoreline, other original wetlands have been lost while new wetlands have replaced some upland forests. This study helps elucidate past causes of temporal and spatial variability, and it provides a reference point for land managers who need to understand the effects of land-use history for ongoing restoration efforts.

Critical thresholds and tangible targets for ecosystem-based management of coral reef fisheries

Sustainably managing ecosystems is challenging, especially for complex systems such as coral reefs. This study develops critical reference points for sustainable management by using a large empirical dataset on the coral reefs of the western Indian Ocean to investigate associations between levels of target fish biomass (as an indicator of fishing intensity) and eight metrics of ecosystem state. These eight ecological metrics each exhibited specific thresholds along a continuum of fishable biomass ranging from heavily fished sites to old fisheries closures. Three thresholds lay above and five below a hypothesized window of fishable biomass expected to produce a maximum multispecies sustainable yield (B(MMSY)). Evaluating three management systems in nine countries, we found that unregulated fisheries often operate below the B(MMSY), whereas fisheries closures and, less frequently, gear-restricted fisheries were within or above this window. These findings provide tangible management targets for multispecies coral reef fisheries and highlight key tradeoffs required to achieve different fisheries and conservation goals.

Depletion-Based Stock Reduction Analysis: A catch-based method for determining sustainable yields for data-poor fish stocks

We describe a method for determining reasonable yield and management reference points for data-poor fisheries in cases where approximate catches are known from the beginning of exploitation. The method, called Depletion-Based Stock Reduction Analysis (DB-SRA), merges stochastic Stock-Reduction Analysis with Depletion-Corrected Average Catch. Data requirements include estimates of historical annual catches, approximate natural mortality rate and age at maturity. A production function is specified based on general fishery knowledge of the relative location of maximum productivity and the relationship of MSY fishing rate to the natural mortality rate. This leaves unfished biomass as the only unknown parameter, which can be estimated given a designated relative depletion level near the end of the time series. The method produces probability distributions of management reference points concerning yield and biomass. Uncertainties in natural mortality, stock dynamics, optimal harvest rates, and recent stock status are incorporated using Monte Carlo exploration. Comparison of model outputs to data-rich stock assessments suggests that the method is effective for estimating sustainable yields for data-poor stocks.

The promises and pitfalls of including decadal-scale climate forcing of recruitment in groundfish stock assessment

Concurrent declines in demersal fish stock abundances and shifts in long-term average environmental conditions have been well documented in the Pacific. Management advice ignoring environmental forcing of recruitment may cause stocks to be over- or under-harvested, so it is important to consider including environmental forcing on recruitment in stock assessment models. Simulation testing is used to determine the statistical power of stock assessments to identify long-term, decadal-scale environmental forcing of recruitment and the ability to estimate management reference points when the duration of the fisheries time series is equal to or less than the period of the environmental cycle. Commonly used assessment methods generally lead to lower total type I (incorrectly rejecting the null hypothesis of no environmental impact) and type II (failing to detect an environmental impact when such a relationship exists) error rates. The promise of integrating environmental data with decadal-scale variability directly into stock assessments via the stock–recruitment relationship is outweighed by the pitfall of high type I error rates that are due to fishing-induced stock declines that coincide with directional environmental change. However, the impact of type I errors can be minimized by choosing an appropriate combination of assessment method and reference point estimators.

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.