Setting biological reference points for sea scallops (Placopecten magellanicus) allowing for the spatial distribution of productivity and fishing effort

2017 ◽  
Vol 74 (5) ◽  
pp. 650-667 ◽  
Author(s):  
Stephen J. Smith ◽  
Jessica A. Sameoto ◽  
Craig J. Brown
Keyword(s):  
Spatial Distribution ◽  
Habitat Suitability ◽  
Spatial Model ◽  
Stock Assessment ◽  
Fishing Effort ◽  
Reference Points ◽  
Assessment Model ◽  
Fishing Mortality ◽  
Placopecten Magellanicus ◽  
Fishing Vessels

Management for the major sea scallop (Placopecten magellanicus) fisheries in Canada is based on maximum sustainable yield (MSY) biomass and fishing mortality reference points applied to the whole stock, under the assumption that fishing mortality is uniformly distributed in space. However, scallop fishing vessels concentrate fishing in areas that consistently exhibit high densities resulting in a nonuniform spatial distribution of fishing effort. This study applies a spatial model for fishing effort derived from satellite vessel monitoring system data, scallop habitat suitability maps, and relative scallop density from a spatial stock assessment model to evaluate precautionary approach reference points in support of sustainable management. Target harvest rates were evaluated in terms of MSY for the higher habitat suitability areas. The results indicated that although MSY for the spatial model were similar to those when assuming a uniform distribution of effort, the biomass and catch rates over all areas were higher. The spatial model predicted that the MSY would be taken with less fishing effort, potentially lessening the benthic impacts from the scallop fishery.

scholarly journals Effects of unequal capture probability on stock assessment abundance and mortality estimates: an example using the US Atlantic sea scallop fishery

2017 ◽  
Vol 74 (11) ◽  
pp. 1904-1917 ◽  
Author(s):  
Samuel B. Truesdell ◽  
Deborah R. Hart ◽  
Yong Chen
Keyword(s):  
Spatial Patterns ◽  
Size Structure ◽  
Stock Assessment ◽  
Model Performance ◽  
Fishing Effort ◽  
Assessment Model ◽  
Fishing Mortality ◽  
Placopecten Magellanicus ◽  
Sea Scallop ◽  
The Us

Most stock assessment models assume that the probability of capture for all individuals of the same size or age in the stock area is equal. However, this assumption is rarely, if ever, satisfied. We used spatially referenced simulations, based on the US Atlantic sea scallop (Placopecten magellanicus) fishery, to generate catch, survey index, fishing effort, and size structure data that we input into a (nonspatial) catch-at-size stock assessment model to estimate abundance and mortality rates. We show that spatial patterns in fishing mortality degrade model performance for sessile stocks. Fishing mortality tended to be overestimated and abundance underestimated because trends in fishing mortality were exaggerated and the model misestimated the numbers of larger individuals due to spatial fishing patterns. These results are particularly relevant to sedentary species such as scallops, but are applicable wherever strong spatial patterns exist in fishing mortality.

scholarly journals Stock assessment and projections incorporating discard estimates in some years: an application to the hake stock in ICES Divisions VIIIc and IXa

2010 ◽  
Vol 67 (6) ◽  
pp. 1185-1197 ◽  
Author(s):  
C. Fernández ◽  
S. Cerviño ◽  
N. Pérez ◽  
E. Jardim
Keyword(s):  
Time Series ◽  
Stock Assessment ◽  
Reference Points ◽  
Assessment Model ◽  
Marine Science ◽  
Fishing Mortality ◽  
Change Over Time ◽  
Age Structured ◽  
Available Information ◽  
Over Time

Abstract Fernández, C., Cerviño, S., Pérez, N., and Jardim, E. 2010. Stock assessment and projections incorporating discard estimates in some years: an application to the hake stock in ICES Divisions VIIIc and IXa. – ICES Journal of Marine Science, 67: 1185–1197. A Bayesian age-structured stock assessment model is developed to take into account available information on discards and to handle gaps in the time-series of discard estimates. The model incorporates mortality attributable to discarding, and appropriate assumptions about how this mortality may change over time are made. The result is a stock assessment that accounts for information on discards while, at the same time, producing a complete time-series of discard estimates. The method is applied to the hake stock in ICES Divisions VIIIc and IXa, for which the available data indicate that some 60% of the individuals caught are discarded. The stock is fished by Spain and Portugal, and for each country, there are discard estimates for recent years only. Moreover, the years for which Portuguese estimates are available are only a subset of those with Spanish estimates. Two runs of the model are performed; one assuming zero discards and another incorporating discards. When discards are incorporated, estimated recruitment and fishing mortality for young (discarded) ages increase, resulting in lower values of the biological reference points Fmax and F0.1 and, generally, more optimistic future stock trajectories under F-reduction scenarios.

scholarly journals Evidence of overfishing of geoduck clam Panopea globosa from a length-based stock assessment approach

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e9069
Author(s):  
Marlene A. Luquin-Covarrubias ◽  
Enrique Morales-Bojórquez ◽  
Juan A. García-Borbón ◽  
Sergio Amezcua-Castro ◽  
Sergio A. Pérez-Valencia ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Growth Patterns ◽  
Reference Points ◽  
Assessment Model ◽  
Individual Growth ◽  
Biological Traits ◽  
Total Biomass ◽  
Fishing Mortality ◽  
Harvest Rate ◽  
Assessment Approach

Stock assessment of the geoduck clam Panopea globosa in Mexico has been based on data-poor without consideration of the biological traits of the species, promoting a passive management strategy without biological reference points for its harvest and conservation, which results in limited advice regarding the sustainability of the fishery. The stock assessment was supported on an integrated catch-at-size assessment model. The model described the population changes, including recruitment, selectivity, fishing mortality, individual growth patterns and survival over time, providing management quantities for the geoduck clam fishery, such as biomass-at-length (total and vulnerable) and harvest rate-at-length. The results indicated overfishing of the geoduck clam population; the harvest rate exceeded the management tactics established for this fishery, even the individuals smaller than the minimum legal size (130 mm) were harvested. Thus, declines in the total biomass (from 3,262 to 1,130 t) and recruitment (representing an 86% decrease) were observed from 2010 to 2012. Although the results showed a recovery trend in recruitment and total biomass from 2014 to 2016, this trend may have been due to the spatial relocation of fishing mortality.

scholarly journals The advantage of explicitly incorporating predation mortality into age-structured stock assessment models: an application for Atlantic mackerel

2009 ◽  
Vol 66 (3) ◽  
pp. 445-454 ◽  
Author(s):  
H. Moustahfid ◽  
J. S. Link ◽  
W. J. Overholtz ◽  
M. C. Tyrrell
Keyword(s):  
Stock Assessment ◽  
Fish Predation ◽  
Reference Points ◽  
Assessment Model ◽  
Fishing Mortality ◽  
Atlantic Mackerel ◽  
Predation Mortality ◽  
Spawning Stock ◽  
Age Structured ◽  
The Impact

AbstractMoustahfid, H., Link, J. S., Overholtz, W. J., and Tyrrell, M. C. 2009. The advantage of explicitly incorporating predation mortality into age-structured stock assessment models: an application for Atlantic mackerel. – ICES Journal of Marine Science, 66: 445–454. An age-structured assessment programme (ASAP) that explicitly incorporates predation mortality was applied to Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic. Predatory removals were modelled in the same manner as fishing mortality, with a comparable set of time-series, to produce estimates of predation mortality at age and for each year. Results from the analysis showed that incorporating predation into a mackerel stock assessment model notably altered model outputs. When excluding explicitly modelled rates of predation, the model underestimated the magnitude and uncertainty in spawning-stock biomass (SSB) and recruitment. Further, the rates of predation mortality varied across time and were higher for younger fish. Predation mortality was higher than fishing mortality for fish aged 1 year, approximately equal for 2-year-olds, and lower for older fish (3 years and older). Biological reference points for Atlantic mackerel differed considerably when predation mortality was included. For example, SSBMSY was more than twice as high in the model where predation was incorporated than in the fisheries-only model. Although there are several caveats to the predation model outputs, chief of which is that the estimates are conservative because some mackerel predators were excluded, the results demonstrate the feasibility of executing such an approach with an extant tool. The approach presented here ultimately has the advantage of detecting, and upon detection parsing out, the impact of predators relative to fisheries and has the potential to provide useful information to those interested in small pelagic fish and their associated fisheries.

scholarly journals Implications of climate change for the management of North Sea cod (Gadus morhua)

2005 ◽  
Vol 62 (7) ◽  
pp. 1483-1491 ◽  
Author(s):  
Laurence T. Kell ◽  
Graham M. Pilling ◽  
Carl M. O'Brien
Keyword(s):  
Climate Change ◽  
North Sea ◽  
Gadus Morhua ◽  
Stock Assessment ◽  
Management Strategies ◽  
Fishing Effort ◽  
Reference Points ◽  
Fishing Mortality ◽  
Short Term ◽  
Management Procedures

Abstract Robustness of both short-term stock biomass recovery and longer-term sustainable management strategies to different plausible climatic change scenarios were evaluated for North Sea cod (Gadus morhua), where climate was assumed to impact growth and recruitment. In the short term, climate change had little effect on stock recovery, which depends instead upon reducing fishing effort to allow existing year classes to survive to maturity. In the longer term, climate change has greater effects on stock status, but higher yields and biomass can be expected if fishing mortality is reduced. Incorporating environmental covariates in stock assessment predictions will not achieve sustainable resource use. The implications of climate change for biological reference points depend upon the mechanism through which temperature acts on recruitment, i.e. on juvenile survival or carrying capacity. It is not possible to distinguish between these processes with stock assessment data sets alone. However, this study indicates that reference points based on fishing mortality appear more robust to uncertainty than those based on biomass. Ideally, simpler management procedures are required that meet pre-agreed management objectives and are robust to uncertainty about the true dynamics.

Detecting mortality variation to enhance forage fish population assessments

2018 ◽  
Vol 76 (1) ◽  
pp. 124-135 ◽  
Author(s):  
Nis S Jacobsen ◽  
James T Thorson ◽  
Timothy E Essington
Keyword(s):  
Test Performance ◽  
Size Structure ◽  
Stock Assessment ◽  
Reference Points ◽  
Forage Fish ◽  
Natural Mortality ◽  
Time Varying ◽  
Fishing Mortality ◽  
Catch Data ◽  
Over Time

Abstract Contemporary stock assessment models used by fisheries management often assume that natural mortality rates are constant over time for exploited fish stocks. This assumption results in biased estimates of fishing mortality and reference points when mortality changes over time. However, it is difficult to distinguish changes in natural mortality from changes in fishing mortality, selectivity, and recruitment. Because changes in size structure can be indicate changes in mortality, one potential solution is to use population size-structure and fisheries catch data to simultaneously estimate time-varying natural and fishing mortality. Here we test that hypothesis, using a simulation experiment to test performance for four alternative estimation models that estimate natural and fishing mortality from size structure and catch data. We show that it is possible to estimate time-varying natural mortality in a size-based model, even when fishing mortality, recruitment, and selectivity are changing over time. Finally, we apply the model to North Sea sprat, and show that estimates of recruitment and natural mortality are similar to estimates from an alternative multispecies population model fitted to additional data sources. We recommend exploring potential trends in natural mortality in forage fish assessments using tools such as the one presented here.

scholarly journals Fisheries for the future: greenhouse gas emission consequences of different fishery reference points

2020 ◽  
Vol 77 (5) ◽  
pp. 1666-1671
Author(s):  
Sara Hornborg ◽  
Anthony D M Smith
Keyword(s):  
Greenhouse Gas Emissions ◽  
Greenhouse Gas ◽  
Greenhouse Gas Emission ◽  
Fuel Efficiency ◽  
Fishing Effort ◽  
Reference Points ◽  
Production Model ◽  
Fuel Use ◽  
Gas Emissions ◽  
Fishing Vessels

Abstract Global fisheries have for long been scrutinized in terms of ecosystem effects but only more recently for their greenhouse gas emissions. These emissions are dominated by fuel use on fishing vessels and the levels are often neglected side effects of resource overexploitation. Using a simple production model, Pella-Tomlinson, we illustrate how fuel efficiency (fuel use per unit of catch) varies with the level of exploitation and biomass depletion. For this model, fuel use per unit catch rises hyperbolically with fishing effort—it is relatively flat at low levels of effort but rises steeply as effort increases and biomass and catch decline. In light of these findings, the general fuel efficiency relationship with common fishery reference points on stock status is discussed, as well as other means of reducing fuel use and thus greenhouse gas emissions. We conclude that much may be gained by considering fuel efficiency in setting reference points for target stock biomass in fisheries and encourage further investigations.

scholarly journals Time-varying natural mortality in fisheries stock assessment models: identifying a default approach

2014 ◽  
Vol 72 (1) ◽  
pp. 137-150 ◽  
Author(s):  
Kelli F. Johnson ◽  
Cole C. Monnahan ◽  
Carey R. McGilliard ◽  
Katyana A. Vert-pre ◽  
Sean C. Anderson ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Assessment Method ◽  
Reference Points ◽  
Natural Mortality ◽  
Time Varying ◽  
Fishing Mortality ◽  
Total Allowable Catch ◽  
Robust Approach ◽  
Structured Population Models ◽  
Trade Offs

Abstract A typical assumption used in most fishery stock assessments is that natural mortality (M) is constant across time and age. However, M is rarely constant in reality as a result of the combined impacts of exploitation history, predation, environmental factors, and physiological trade-offs. Misspecification or poor estimation of M can lead to bias in quantities estimated using stock assessment methods, potentially resulting in biased estimates of fishery reference points and catch limits, with the magnitude of bias being influenced by life history and trends in fishing mortality. Monte Carlo simulations were used to evaluate the ability of statistical age-structured population models to estimate spawning-stock biomass, fishing mortality, and total allowable catch when the true M was age-invariant, but time-varying. Configurations of the stock assessment method, implemented in Stock Synthesis, included a single age- and time-invariant M parameter, specified at one of the three levels (high, medium, and low) or an estimated M. The min–max (i.e. most robust) approach to specifying M when it is thought to vary across time was to estimate M. The least robust approach for most scenarios examined was to fix M at a high value, suggesting that the consequences of misspecifying M are asymmetric.

scholarly journals Ecological Reference Points for Atlantic Menhaden Established Using an Ecosystem Model of Intermediate Complexity

2020 ◽  
Vol 7 ◽  
Author(s):  
David Chagaris ◽  
Katie Drew ◽  
Amy Schueller ◽  
Matt Cieri ◽  
Joana Brito ◽  
...  
Keyword(s):  
Striped Bass ◽  
Fishery Management ◽  
Stock Assessment ◽  
Reference Points ◽  
Atlantic Menhaden ◽  
Assessment Model ◽  
Total Allowable Catch ◽  
Important Species ◽  
Ecosystem Impacts ◽  
Intermediate Complexity

Atlantic menhaden (Brevoortia tyrannus) are an important forage fish for many predators, and they also support the largest commercial fishery by weight on the U.S. East Coast. Menhaden management has been working toward ecological reference points (ERPs) that account for menhaden’s role in the ecosystem. The goal of this work was to develop menhaden ERPs using ecosystem models. An existing Ecopath with Ecosim model of the Northwest Atlantic Continental Shelf (NWACS) was reduced in complexity from 61 to 17 species/functional groups. The new NWACS model of intermediate complexity for ecosystems (NWACS-MICE) serves to link the dynamics of menhaden with key managed predators. Striped bass (Morone saxatilis) were determined to be most sensitive to menhaden harvest and therefore served as an indicator of ecosystem impacts. ERPs were based on the tradeoff relationship between the equilibrium biomass of striped bass and menhaden fishing mortality (F). The ERPs were defined as the menhaden F rates that maintain striped bass at their biomass target and threshold when striped bass are fished at their Ftarget, and all other modeled species were fished at status quo levels. These correspond to an ERP Ftarget of 0.19 and an ERP Fthreshold of 0.57, which are lower than the single species reference points by 30–40%, but higher than current (2017) menhaden F. The ERPs were then fed back into the age-structured stock assessment model projections to provide information on total allowable catch. The ERPs developed in this study were adopted by the Atlantic menhaden Management Board, marking a shift toward ecosystem-based fishery management for this economically and ecologically important species.

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

2012 ◽  
Vol 69 (4) ◽  
pp. 770-783 ◽  
Author(s):  
Hilaire Drouineau ◽  
Louise Savard ◽  
Mathieu Desgagnés ◽  
Daniel Duplisea
Keyword(s):  
Stock Assessment ◽  
Sex Change ◽  
Assessment Model ◽  
Natural Mortality ◽  
The Novel ◽  
Fishing Mortality ◽  
Novel Structure ◽  
Shrimp Fisheries ◽  
Analytical Tools ◽  
Mortality Estimates

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.

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