Traditional Stock Assessment Research Articles

Empirical validation of integrated stock assessment models to ensuring risk equivalence: A pathway to resilient fisheries management.

The Precautionary Approach to Fisheries Management requires an assessment of the impact of uncertainty on the risk of achieving management objectives. However, the main quantities, such as spawning stock biomass (SSB) and fish mortality (F), used in management metrics cannot be directly observed. This requires the use of models to provide guidance, for which there are three paradigms: the best assessment, model ensemble, and Management Strategy Evaluation (MSE). It is important to validate the models used to provide advice. In this study, we demonstrate how stock assessment models can be validated using a diagnostic toolbox, with a specific focus on prediction skill. Prediction skill measures the precision of a predicted value, which is unknown to the model, in relation to its observed value. By evaluating the accuracy of model predictions against observed data, prediction skill establishes an objective framework for accepting or rejecting model hypotheses, as well as for assigning weights to models within an ensemble. Our analysis uncovers the limitations of traditional stock assessment methods. Through the quantification of uncertainties and the integration of multiple models, our objective is to improve the reliability of management advice considering the complex interplay of factors that influence the dynamics of fish stocks.

Assessing the Relative Vulnerability of Chondrichthyan Species as Bycatch Using Spatially Reported Catch Data Series

Fishery impacts pose threats not only to target species, but also to bycatch species. Nevertheless, choosing priorities for conservation or research in fisheries is often driven by economic value and most retained bycatch species such as sharks and rays have been historically of low profit. Traditional stock assessments usually require large quantities of data, financial support, and feasible study conditions. The multi-species nature of Chondrichthyan catch along with their relatively lower value and sparsity of fishery-independent data creates significant challenges to developing accurate impact predictions. This study introduces a novel technique to quantify the relative vulnerability of Chondrichthyan species taken as bycatch. The approach is based on spatial interactions between species and fishing activity (termed here the fishery interaction index, or FII) and is correlated to metrics of productivity. A database of 15 years of fisheries logbooks was used to apply the method to 20 bycatch sharks and target species in one of the largest fishing sectors of Australia’s EEZ. Overall vulnerability based on the FII-productivity combinations obtained was found to agree considerably with the IUCN status of the assessed species, with only a few exceptions that reflected the local status differing from the general global assessments.

Dorsal Fin Spines and Rays for Nonlethal Ageing of Goliath Grouper Epinephelus itajara

Atlantic Goliath Grouper, Epinephelus itajara, the largest grouper in the western North Atlantic, exhibits life history characteristics (e.g., it is slow-growing, long-lived, and late-maturing) that make it particularly susceptible to fishing pressure. Otoliths, the structure typically processed for age determination, are usually collected as part of fishery monitoring, but otoliths are not available from Goliath Grouper due to a harvest moratorium enacted in 1990 for United States waters. Alternative structures—such as dorsal fin rays or spines—can be acquired for ageing via nonlethal sampling and may provide reliable age estimates. Since 2006, the Florida Fish and Wildlife Conservation Commission (FWC) has been collecting incidental Goliath Grouper samples from mortality events including those from cold kills and red tides. Corresponding otolith, dorsal fin ray and dorsal fin spine samples were compared to determine the accuracy and precision of the external ageing structures. Marginal increment analyses indicated that annulus (translucent zone) deposition occurred primarily in March–June on spines and in April–June on rays. While ages determined from both rays and spines exhibited high precision, the accuracy compared to otolith ages was low as a result of systematic underageing of both external structures, particularly at the oldest age classes. A correction factor was applied to rays and spines that remedied the underageing, but the correction factor was more successful for spines. An analysis of ray and spine section accuracy based on nonlethal structure removal from the fish (i.e., comparing ages from sections at the base of the structure within the body to those sectioned from the external surface of the body) determined that spines can be accurately aged when sampled distal of the base of the structure, but that rays cannot. Nonlethal sampling and ageing of Goliath Grouper spines facilitated by public participation could address management goals and help determine the offshore population age structure. Simultaneously, it could contribute critical data needed for a traditional stock assessment, should such a path be warranted by the recovery or management of the species.

Marine protected areas provide unfished reference information to empirically assess fishery status

Fisheries stock assessments typically determine stock-status using estimates of unfished biomass generated from fisheries dependent data. Due to limitations and biases in these data, modelled unfished estimates are reliant on assumptions regarding stock ecology. This can lead to a high degree of uncertainty in estimates of unfished biomass and can compromise sustainable management. We propose using the biomass of exploited species in no-take marine protected areas (marine reserves) as a proxy for unfished biomass to empirically assess stock status. Marine reserves provide contemporary examples of exploited populations in the absence of fishing under current conditions. Using lobster (Jasus edwardsii) potting and diver-based survey data from 2018 and 2019 we calculated fisheries relevant metrics from inside and outside two north-eastern New Zealand marine reserves. Based on marine reserve reference points, we found spawning stock catch rates and biomass of lobster in adjacent fished areas were 3 % and 2 % of unfished levels. Comparability of potting and dive survey estimates validates using dive survey data to estimate stock status, while differences in population information between survey methods highlights the limited ability of catch data to accurately inform on sub-legal abundances. Overall, our fisheries-independent approach suggests the fished population is at lower levels than latest estimates for the wider fishery and demonstrates how marine reserves can provide information on key parameters which can be incorporated into traditional stock assessments. Planning for future marine reserves should consider the value of such areas as tools to help manage fisheries in addition to protecting exploited species.

A reproductive resilience index for pelagic fish in the southern Humboldt Current Large Marine Ecosystem

Efforts to manage small and medium-sized pelagic fishes (SMPF) using traditional stock assessment methods are hampered by the elusive relationship between spawning stock biomass and recruitment. We propose to compute a reproductive resilience index (RRI) in three steps: ( i) we selected 16 biological traits related to distinct aspects of SMPF reproductive biology and characterized by a continuous (e.g., growth rate) or ordinal variable (e.g., spawning site fidelity) scored from 1 to 5 (1 representing a low contribution of the trait to reproductive resilience); ( ii) an expert panel assigned the traits’ scores to five exploited species in the southern Humboldt Current Large Marine Ecosystem; ( iii) a Bayesian Belief Network (BBN) model was used to estimate an RRI based on the combination of the traits’ scores. The BBN was used to explore environmental effects on the species’ RRI, as some reproductive traits can show intraspecies variability under external forces (e.g., fishing pressure). Through proving the RRI application to detect variability in species’ resilience at local time series, we show how the resulting RRI can be interpreted by fishery managers to improve the current management of SMPF.

Evaluating methods for estimating shark natural mortality rate and management reference points using life‐history parameters

AbstractSharks (class Chondrichthyes, subclass Elasmobranchii) typically have a long lifespan, slow growth rate and low fecundity, leading to low productivity and hence relatively high vulnerability to fishing. Information for managing fisheries catches of elasmobranchs is often lacking, because elasmobranchs are usually non‐target species, often with low abundance. It is more feasible to develop management reference points for elasmobranchs based on their life‐history information than through traditional stock assessments. The natural mortality rate (M) is the leading life‐history parameter (LHP) required by many methods for developing reference points and is itself often derived indirectly from other LHPs. In this paper, we evaluate nineMestimators, using 15 shark stocks in the Western and Central Pacific Ocean as examples. We then compare four methods for developing fishing mortality reference pointsFmsy, including empirical modelling, the Euler‐Lotka equation, anM‐productivity‐based method and the spawning potential rate converted method. Our analyses show that popularMestimators developed mainly from teleost data resulted in large deviations from the average and were not suitable for elasmobranchs. All four methods for estimatingFmsyperformed similarly. However, the empirical method is very simple and cost‐effective and tended to produce smaller deviations from the average than the other three methods. Nonetheless, it is recommended that multiple methods should be used to minimize possible bias and reflect uncertainty, if the required LHPs are available.

Air‐breathing ecology of Arapaima sp.: Conservation implications for an imperilled fish

Abstract Arapaima (Arapaima sp.) are highly overexploited fish endemic to the Amazon basin. Because the fish are obligate air‐breathers, it is possible to use surface‐breathing events to count individuals visually for population censuses important for conservation, yet uncertainties remain about body size and environmental influences on air‐breathing intervals, and thus count accuracy. This study examined relationships between breathing intervals and environmental parameters (e.g. water temperature and transparency) and body size for radio‐tagged arapaima (n = 12) in an upland river‐floodplain (Lake Ayapuá, Amazonas, Brazil). Generalized additive mixed models were used to evaluate environmental, size, and behavioural correlates of breathing intervals. Temperature was the most influential predictor of air‐breathing intervals, followed by body size. The shortest breathing intervals were associated with consecutive ‘aggressive’ breaths while the longest breathing intervals had consecutive ‘calm’ breaths. Type of breath, size, and temperature predictors revealed that breathing intervals ranged from 4 to 46 min and were not significantly different among life stages ( = 15.9 min for sub‐adults and adults (>1 m); = 14.8 min for juveniles (<1 m)). Whereas the current population census method uses fish counts in 20‐min intervals, this study found that 15% of observed breaths, and two thirds of fish, took longer than 20 min to breathe. These findings were obtained in relatively cool‐water environments, so it is recommended that future population census methods consider water temperature (e.g. extend intervals used for counts in cooler waters), which may improve the accuracy of census counts and thus further enhance arapaima conservation efforts. This study demonstrated an effective method in which fundamental biological information is used to inform and improve population census methods for an imperilled fish in a region where traditional stock assessment is ineffective. Similar approaches for adaptive stock assessments could be applied to improve conservation of other air‐breathing fishes (e.g. lungfishes) globally.

Spatio-Temporal Assessment of the European Hake (Merluccius merluccius) Recruits in the Northern Iberian Peninsula

The protection of fish nurseries has been recognized as a useful tool to efficiently manage fisheries given that protected areas enhance the recruitment of target species. To identify and locate potential nursery areas, a solid understanding of species-environment relationships and their spatio-temporal dynamics is needed. Within this context, in this study we assess where European hake (Merluccius merluccius) recruits persistently aggregate in the northern continental shelf of the Iberian Peninsula. Hake recruit data collected during scientific trawl surveys between 2005 and 2016 were analyzed using Bayesian hurdle hierarchical spatio-temporal models, considering the environmental variables bathymetry, sea bottom temperature and salinity. Additionally, three different spatio-temporal structures (i.e., persistent, progressive, or opportunistic) were compared to assess the temporal persistence of nurseries over time. Among all the environmental variables analyzed, bathymetry was the most important. The preferential habitat of recruits was found to be within a bathymetric range of 120–200 m. Our findings clearly show that there is a temporally persistent main nursery located along the continental shelf of the Artabrian gulf (off La Coruña) in addition to several areas with high aggregations of hake recruits but with strong inter-annual variability. We argue that the analytical framework applied in this study allowed us to identify European hake nurseries in the northern continental shelf of the Iberian Peninsula, as well as their spatio-temporal fluctuations throughout the study period (2005–2016), and to assess which environmental factors, among bathymetry, sea bottom temperature and salinity, influence the occurrence and abundance of recruits in the study area. Results of our models also produce a new abundance index that could be useful for improving traditional stock assessment models.

Modeling Quantitative Value of Habitats for Marine and Estuarine Populations

Coastal habitats (e.g., seagrass beds, shallow mud, and sand flats) strongly influence survival, growth, and reproduction of marine fish and invertebrate species. Many of these species have declined over the past decades, coincident with widespread degradation of coastal habitats, such that an urgent need exists to model the quantitative value of coastal habitats to their population dynamics. For exploited species, demand for habitat considerations will increase as fisheries management contends with habitat issues in stock assessments andmanagement in generalmoves toward amore ecosystem-based approach. The modeling of habitat function has, to date, been done on a case-by-case basis involving diverse approaches and types of population models, which has made it difficult to generalize about methods for incorporating habitat into population models. In this review, we offer guiding concepts for how habitat effects can be incorporated in population models commonly used to simulate the population dynamics of fish and invertebrate species. Many marine species share a similar life-history strategy as long-lived adults with indeterminate growth, high fecundity, a planktonic larval form, and benthic juveniles and adults using coastal habitats. This suite of life-history traits unites the marine species across the case studies, such that the population models can be adapted for other marine species. We categorize population models based on whether they are static or dynamic representations of population status, and for dynamic, further into unstructured, age/size class structured, and individual-based. We then use examples, with an emphasis on exploited species, to illustrate how habitat has been incorporated, implicitly (correlative) and explicitly(mechanistically), into each of these categories. We describe the methods used and provide details on their implementation and utility to facilitate adaptation of the approaches for other species and systems. We anticipate that our review can serve as a stimulus for more widespread use of population models to quantify the value of coastal habitats, so that their importance can be accurately realized and to facilitate cross-species and cross-system comparisons. Quantitative evaluation of habitat effects in population dynamics will increasingly be needed for traditional stock assessments, ecosystem-based management, conservation of at-risk habitats, and recovery of overexploited stocks that rely on critical coastal habitats during their life cycle.

Performance of length-based data-limited methods in a multifleet context: application to small tunas, mackerels, and bonitos in the Atlantic Ocean

Abstract Large scombrids, commercial tuna species, are regularly assessed and managed. However, most of the small scombrids, many mackerels and bonitos, lack accurate catch data to implement traditional stock assessments despite their economic importance in many small-scale fisheries. In this study, we analysed different approaches using length composition data from multiple fleets with different gear selectivity to assess small scombrids in the Atlantic Ocean. Using simulated populations, we compared two length-based methods (length-based spawning potential ratio and length-based integrated mixed effects ), under different length data grouping scenarios. We found that using length data from the fleet targeting the broadest range of sizes resulted in the lowest bias in spawning potential ratio of all options tested. Based on these results, we used biological and length data to estimate a quantitative proxy of current stock status for ten small scombrid stocks in the Atlantic Ocean. We found that some stocks are likely to be overfished, such as little tunny (Euthynnus alletteratus) in the Southeast Atlantic and wahoo (Acanthocybium solandri) in the Northwest Atlantic. This is a starting point in the estimation of stock status for these species, but should not be thought of as a replacement for other more data-intensive assessments.

Revisiting daily age determination in juvenile anchoveta Engraulis ringens

Recent studies using otolith microstructure analysis have suggested that the duration of the juvenile stage in anchoveta (Engraulis ringens) is shorter than previously suspected, which suggests that the ages being entered into the traditional age-based stock assessment are incorrect. However, the interpretation of young pelagic fish otoliths remains problematic. To clarify the age interpretation of larval and juvenile E. ringens, newly hatched larvae were reared in a quasi-natural environment for periods of up to 103 days. The sagittal otoliths were subsequently examined and measured by international otolith experts in a double-blind workshop study. The young anchovy could be aged both accurately and precisely using otolith microstructure, after measures were taken to correct for unresolvable increments formed immediately after hatch. The presence of a fast-growth transition zone characterised by either considerable splitting or subdaily increments or both was confirmed. This study confirms the hypothesis of rapid growth and young age through the juvenile stage for anchoveta, suggesting that a critical appraisal of the annual age determinations used as the basis for anchoveta stock assessment is warranted. The otolith interpretation principles outlined in this study may apply broadly across many small pelagic fish species.

Recruitment in tuna RFMO stock assessment and management: A review of current approaches and challenges

We review recent approaches and challenges in monitoring and estimating recruitment for the main commercial tuna species managed under the auspices of the five tuna Regional Fisheries Management Organizations (tRFMOs), including: (i) the stock assessment and management context, (ii) fisheries-independent recruitment monitoring successes, failures and future options, (iii) recruitment estimation methods within statistical population models and (iv) recruitment in projections for traditional stock assessment and management strategy evaluation. Despite the diversity in tuna populations and tRFMO scientific processes, there are many common recruitment themes, including: (i) fisheries-independent recruitment monitoring is difficult and rare (the aerial surveys for juvenile southern bluefin tuna, Thunnus maccoyi, and juvenile eastern Atlantic bluefin tuna stocks, T. thynnus, are the only time series used in assessments), (ii) most statistical models estimate lognormal recruitment deviations around a stationary Beverton-Holt relationship using a penalized likelihood approach, (iii) the degree of compensation in the stock-recruitment relationship and the variance is difficult to estimate (steepness is usually fixed at 0.7 ≤ h ≤ 1.0, and the CV is most often fixed with σR = 0.6 for lognormal recruitment deviations), and (iv) estimated recruitment time series often deviate systematically from the mean relationship, but it is unclear the extent to which this reflects reality (e.g. environmental change) or estimation artefacts (e.g. incorrect model assumptions or biased data). There is a trend toward the use of model ensembles to represent recruitment (and other sources of) uncertainty, both in the context of traditional assessments and management strategy evaluation. Recommendations include: i) continued development of fisheries-independent recruitment monitoring methods, including adopting emerging technologies (e.g. genetics-based mark-recapture or abundance monitoring with a network of acoustic FADs), and (ii) the management paradigm should be designed to be robust to future recruitment uncertainties (e.g. recognize that recruitment compensation might be much lower than model-based estimates or assumptions, and be prepared to respond to substantial serially-correlated recruitment deviations, e.g. regime shifts). Following a history of over-exploitation and difficulties in reaching international scientific and management consensus, the CCSBT now provides a leading example of how tuna recruitment issues might be addressed through innovative monitoring, comprehensive modelling of uncertainty, and management with simulation-tested management procedures.

Working Towards a Framework for Stock Evaluations in Data‐Limited Fisheries

AbstractData‐limited approaches to managing fisheries are widespread in regions where insufficient data prevent traditional stock assessments from determining stock status with sufficient certainty to be useful for management. Where severe data limitations persist, a catch‐only approach is commonly employed, such as in the U.S. Caribbean region. This approach, however, has not received the level of scrutiny required to determine the potential long‐term risks (e.g., probability of overfishing) to fish stocks. In this study, we present a framework for comparison and implementation of data‐limited methods, including the static Status Quo approach, which uses average catch landings. Candidate species for stock evaluation were identified through a data triage and included Yellowtail Snapper Ocyurus chrysurus (Puerto Rico), Queen Triggerfish Balistes vetula (St. Thomas and St. John), and Stoplight Parrotfish Sparisoma viride (St. Croix). Feasible data‐limited methods, based on data availability and quality, included empirical indicator approaches using relative abundance (i.e., catch per unit effort) or mean length. Results from the management strategy evaluation support the use of adaptive data‐limited methods, which incorporate feedback in contrast to the static Status Quo approach. The proposed framework can help guide the development of catch advice for dynamic fisheries management in data‐limited regions.

Is the spawning frequency of Argentine hake, Merluccius hubbsi, affected by maternal attributes or physical variables?

Spawning frequency (SF) is a parameter that represents the number of spawning events per time unit, used to estimate the reproductive potential of many fish populations. We analyzed the relationship between SF and size and age of Argentine hake females from the Patagonian stock. We also studied the influence of female nutritional condition and physical variables on spawning and estimated the monthly egg production in relation to size structure. Samples were collected during the spawning season between 2000 and 2014. This study revealed that the size and age of spawners had a positive effect on the SF of the stock. During the reproductive season this parameter ranged between 13 and 3 days for females within a total length (TL) interval of 35–80 cm. A positive relationship between the spawning activity and the water temperature was also observed, suggesting that this variable could has an influence on the growth and maturation of oocytes. Towards the end of the reproductive period SF was higher than at the beginning of the spawning, but batch fecundity was lower. This could be associated with the poor nutritional condition of females at the end of seasonal spawning. Our results reinforce the hypothesis of a significant maternal effect in Argentine hake, characterized by a higher reproductive output in larger females (>50 cm TL), which in general is not considered in the traditional stock assessment.

Mapping fishing grounds, resource and fleet patterns to enhance management units in data-poor fisheries: The case of snappers and groupers in the Abrolhos Bank coral-reefs (South Atlantic)

In most small-scale fisheries, especially in developing countries, the collection of reliable fishing statistics is not regular, hampering traditional stock assessments. In those data-poor fisheries, a precise knowledge of resources co-occurrence at the ecosystem level, as well as the spatial mapping of fishing activities seem key to support management in a complex fishers-environment context. In the largest South Atlantic coralline reef, the Abrolhos Bank, fisheries are extremely diverse in terms of exploitation capacity, fishing gears, target stocks and operating areas, but any regional fisheries management is currently in place. The aim of this study was to assess, organize, and analyze fisheries of three snappers (Lutjanus jocu, L. synagris and Ocyurus chrysurus), and three groupers (Cephalopholis fulva, Epinephelus morio and Mycteroperca bonaci) along the Abrolhos Bank, with an ultimate goal of proposing useful management units. Surveys were conducted in the main fishing ports, including fishers' interviews and fish size measures in landings. Data analysis allowed a precise fishing characterization, a grouping of stocks co-occurrence, and the mapping of fishing spots and grounds. Three stocks and seven fishing areas clusters were obtained and defined statistically, suggesting useful management units. Specific fishers' groups per fleet were identified as the main stakeholders to be consulted in fisheries plans. Spatial units based on the occurrence of snappers and groupers stocks were defined, having the “Parcel das Paredes” the greatest number of fishing spots and the lower fish sizes. Overall, findings contain unprecedented fine scale resolution units that clarifies and simplifies the connections among species, fleets, fishing areas and fishers. They should also strength the call for action to implement fisheries management in a broader ecosystem-scale context.

TropFishR: an R package for fisheries analysis with length‐frequency data

Summary The R package TropFishR is a new analysis toolbox compiling single‐species stock assessment methods specifically designed for data‐limited fisheries analysis using length‐frequency data. It includes methods for (i) estimating biological stock characteristics such as growth and mortality parameters, (ii) exploring technical aspects of the fisheries (e.g. exploitation rate and selectivity characteristics), (iii) assessing size and composition of a fish stock by means of virtual population analysis (VPA), and (iv) assessing stock status with yield prediction and production models. This paper introduces the package and demonstrates the functionality of a selection of its core methods. TropFishR modernises traditional stock assessment methods by easing application and development and by combining it with advanced statistical approaches.

Vulnerability of teleosts caught by the pelagic tuna longline fleets in South Atlantic and Western Indian Oceans

Productivity and Susceptibility Analysis (PSA) is a methodology for evaluating the vulnerability of a stock based on its biological productivity and susceptibility to fishing. In this study, we evaluated the vulnerability of 60 stocks of tuna, billfishes and other teleosts caught by the tuna longline fleets operating in the South Atlantic and Indian Ocean using a semi-quantitative PSA. We (a) evaluated the vulnerability of the species in the study areas; (b) compared the vulnerability of target and non-target species and oceans; (c) analyzed the sensitivity of data entry; and (d) compared the results of the PSA to other fully quantitative assessment methods. Istiophoridae exhibited the highest scores for vulnerability. The top 10 species at risk were: Atlantic Istiophorus albicans; Indian Ocean Istiompax indica; Atlantic Makaira nigricans and Thunnus alalunga; Indian Ocean Xiphias gladius; Atlantic T. albacares, Gempylus serpens, Ranzania laevis and X. gladius; and Indian Ocean T. alalunga. All species considered at high risk were targeted or were commercialized bycatch, except for the Atlantic G. serpens and R. laevis which were discarded, and may be considered as a false positive. Those species and others at high risk should be prioritized for further assessment and/or data collection. Most species at moderate risk were bycatch species kept for sale. Conversely, species classified at low risk were mostly discarded. Overall, species at high risk were overfished and/or subjected to overfishing. Moreover, all species considered to be within extinction risk (Critically Endangered, Endangered and Vulnerable) were in the high-risk category. The good concordance between approaches corroborates the results of our analysis. PSA is not a replacement for traditional stock assessments, where a stock is assessed at regular intervals to provide management advice. It is of importance, however, where there is uncertainty about catches and life history parameters, since it can identify species at risk, and where management action and data collection is required, e.g. for many species at high and most at moderate risk in the South Atlantic and Indian oceans.

Informing Recovery Goals Based on Historical Population Size and Extant Habitat: A Case Study of the Gulf Sturgeon

AbstractConservation efforts under regulatory programs such as the U.S. Endangered Species Act and Magnuson–Stevens Fisheries Conservation and Management Act seek to restore species in decline to a level where the populations are no longer in jeopardy. Key to designing effective conservation plans for the more than 2,500 species currently managed by these two U.S. programs is the establishment of realistic restoration targets given changes in habitats and ecosystems. Accomplishing this is difficult, particularly for populations that have experienced significant habitat alterations. We developed and assessed an approach for establishing quantifiable goals for the recovery of a threatened species by (1) estimating historical population biomass prior to directed fishing, (2) identifying large‐scale habitat modifications that limit available critical habitat, (3) assessing the relationship between historical baselines, habitat characteristics, and extant available habitat, and (4) using these relationships to inform recovery efforts in rivers where traditional stock assessment methods are not possible. In our case study of Gulf Sturgeon Acipenser oxyrinchus desotoi, we found that the current population levels in four of the seven river systems in the recovery plan are likely at or exceeding the mean carrying capacity, given the current levels of available habitat. In the remaining three rivers, extant Gulf Sturgeon populations are likely below their estimated carrying capacity levels. Our approach is of management importance because it establishes realistic recovery criteria through the assessment of changes in habitat from historic to present levels and is widely applicable across a species' range. An important application of this approach is to assess the potential benefits to fish species from management actions, such as dam removal or spawning habitat restoration, that are designed to restore habitat and promote species recovery.Received March 25, 2014; accepted September 29, 2014

SPAM (Sex-Structured Pandalus Assessment Model): a stock assessment model for Pandalus stocks

Despite the economic importance of Pandalus shrimp fisheries, few analytical tools have been developed to assess their stocks, and traditional stock assessment models are not appropriate because of biological specificities of Pandalus species. In this context, we propose SPAM (Sex-Structured Pandalus Assessment Model), a model dedicated to protandric hermaphrodite pandalids stock assessment. Pandalids are difficult to assess because the cues affecting sex change, size at recruitment, and mortality variability are not well understood or characterized. The novel structure of the model makes it possible to adequately describe variability in natural mortality by stage and in time, as well as variability in size at sex change and recruitment. The model provides traditional stock assessment outputs, such as fishing mortality estimates and numbers of individuals, and provides in addition yearly natural mortality estimates. The model is applied to the exploited shrimp stock of Pandalus borealis in Sept-Îles (Québec, Canada) as an illustrative example of the utility of the approach.

Detecting and forecasting complex nonlinear dynamics in spatially structured catch-per-unit-effort time series for North Pacific albacore (Thunnus alalunga)

The presence of complex, nonlinear dynamics in fish populations, and uncertainty in the structure (functional form) of those dynamics, pose challenges to the accuracy of forecasts produced by traditional stock assessment models. We describe two nonlinear forecasting models that test for the hallmarks of complex behavior, avoid problems of structural uncertainty, and produce good forecasts of catch-per-unit-effort (CPUE) time series in both standardized and nominal (unprocessed) form. We analyze a spatially extensive, 40-year-long data set of annual CPUE time series of North Pacific albacore ( Thunnus alalunga ) from 1° × 1° cells from the eastern North Pacific Ocean. The use of spatially structured data in compositing techniques improves out-of-sample forecasts of CPUE and overcomes difficulties commonly encountered when using short, incomplete time series. These CPUE series display low-dimensional, nonlinear structure and significant predictability. Such characteristics have important implications for industry efficiency in terms of future planning and can inform formal stock assessments used for the management of fisheries.