Consequences of bias in age estimation on assessment of the northern stock of European hake (Merluccius merluccius) and on management advice

Abstract Bertignac, M., and de Pontual, H. 2007. Consequences of bias in age estimation on assessment of the northern stock of European hake (Merluccius merluccius) and on management advice. – ICES Journal of Marine Science, 64: 981–988. The results of a pilot tagging study on hake (Merluccius merluccius), conducted in the northern part of the Bay of Biscay in 2002, indicate that growth rates for this stock may be currently underestimated because of biased estimates of age. The impact that such a bias may have on the stock dynamics and the trends of the key population parameters, recruitment, spawning-stock biomass (SSB), and mortality are investigated. Assuming new growth parameters, a new age–length key is derived and used to produce and catch-at-age data and abundance indices, which are then used to assess the stock. Bias in estimating age affects the absolute levels of fishing mortality and stock biomass estimates, and also impacts the trend in SSB. However, trends in fishing mortality and recruitment are comparable, and the stock status with respect to precautionary reference points is broadly the same. As expected, the simulation also shows that the stock may be more reactive to changes in fishing levels, which affect medium-term forecasts. Long-term sustainable yields may also be impacted.

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Evaluating management strategies to implement the recovery plan for Iberian hake (Merluccius merluccius); the impact of censored catch information

ICES Journal of Marine Science ◽

10.1093/icesjms/fsp233 ◽

2009 ◽

Vol 67 (2) ◽

pp. 258-269 ◽

Cited By ~ 7

Author(s):

Ernesto Jardim ◽

Santiago Cerviño ◽

Manuela Azevedo

Keyword(s):

Management Strategies ◽

Maximum Sustainable Yield ◽

Sustainable Yield ◽

Fishing Mortality ◽

Merluccius Merluccius ◽

Total Allowable Catch ◽

Recovery Plan ◽

Stock Biomass ◽

Spawning Stock ◽

The Impact

Abstract Jardim, E., Cerviño, S., and Azevedo, M. 2010. Evaluating management strategies to implement the recovery plan for Iberian hake (Merluccius merluccius); the impact of censored catch information. – ICES Journal of Marine Science, 67: 258–269. Iberian hake assessment revealed an increase in fishing mortality (F) despite enforcement of a recovery plan. Recent landings exceeded the total allowable catch and discarding rates were high. Alternative management strategies based on F control were evaluated with respect to the probability of recovering spawning-stock biomass (SSB), expected profits, and robustness to uncertainty on catch information and stock dynamics. Results showed that the use of censored catch data, i.e. excluding the Gulf of Cádiz or discards, may lead to inappropriate conclusions. Reducing fishing mortality was necessary for SSB to recover. An Fmax strategy with discard reduction showed the highest probability of rebuilding SSB and led the fishery to sustainable exploitation, with an expected %SPR of 30–40% in 2025, mean individual weight in the landings of 450 g in 2015, and yield increasing by >20%. Because of uncertainty in the estimates of maximum sustainable yield, management strategies based on FMSY were least robust, but all strategies were robust to alternative stock–recruit models.

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Age estimation, growth and maturity of the European hake (Merluccius merluccius (Linnaeus, 1758)) from Iberian Atlantic waters

ICES Journal of Marine Science ◽

10.1016/s1054-3139(03)00086-9 ◽

2003 ◽

Vol 60 (5) ◽

pp. 1086-1102 ◽

Cited By ~ 58

Author(s):

C Piñeiro ◽

M Saínza

Keyword(s):

Life History ◽

Age Estimation ◽

Growth Parameters ◽

Grey Literature ◽

Von Bertalanffy ◽

Merluccius Merluccius ◽

Consistent Manner ◽

The Mean ◽

First Maturity ◽

European Hake

Abstract Difficulties in age estimation for hake (Merluccius merluccius) have hampered the assessment of stocks. Here, we describe new, agreed ageing criteria based on the interpretation of the pattern of otolith growth. Improved estimates of von Bertalanffy growth parameters, and new estimates of maturity ogive parameters and length–weight relationships for European hake from Iberian Atlantic waters are presented. The results came from a study carried out during 1996–1997 and provide the first published account of the main life history traits of Southern stock hake. von Bertalanffy growth parameters of males were L∞ = 70cm, K = 0.18 year−1, and t0=−0.97 year, and those of females were L∞ = 89cm, K = 0.13 year−1, and t0 = −1.15 year. Growth of sexes differed from age 3 onwards, with females being on average larger and heavier than males. The estimated total length (L, cm)–total weight (W, g) relationships were W=0.0132135L2.8134246 for males and W=0.0086471L2.942563 for females. Spawning took place from December to May with a peak in February. The mean length and age at first maturity were 32.8 cm at 2.5 years for males and 45 cm at 4.4 years for females. Application of new ageing criteria showed that otolith sections may be used to determine ages up to 5 years in a consistent manner. These results indicate that hake of the Southern stock grow at higher rates and mature earlier than previously considered. Summaries of hake's life history parameters from other marine regions are also presented in order to make information that belongs largely to the grey literature available.

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An alternative reference point in the context of ecosystem-based fisheries management: maximum sustainable dead biomass

ICES Journal of Marine Science ◽

10.1093/icesjms/fsv089 ◽

2015 ◽

Vol 72 (8) ◽

pp. 2257-2268 ◽

Cited By ~ 4

Author(s):

Hans-Joachim Rätz ◽

John Casey ◽

Steven J. Holmes ◽

Josep Lloret ◽

Hendrik Dörner ◽

...

Keyword(s):

Fisheries Management ◽

Reference Points ◽

Production Model ◽

Fish Stock ◽

Compensatory Mechanism ◽

Fishing Mortality ◽

Dead Biomass ◽

Selection Pattern ◽

Stock Biomass ◽

Spawning Stock

Abstract Under the 2013 Reform of the European Union's Common Fisheries Policy (CFP), fisheries management aims to ensure that, within a reasonable time frame, the exploitation of marine biological resources restores and maintains populations of harvested stocks above levels that can produce the maximum sustainable yield (MSY). The CFP also calls for the implementation of an ecosystem-based approach to fisheries management (EBFM). In this paper, we present the concept of maximum sustainable dead biomass (MSDB) and its associated management reference points for fishing mortality and spawning-stock biomass as alternatives to those associated with MSY. The concept of MSDB is illustrated by a dynamic pool production model of a virtual fish stock which takes into account variations in natural mortality (M), fishing mortality (F), and exploitation pattern. Our approach implies a compensatory mechanism whereby survivors may benefit from compensatory density dependence and is implemented through progressive substitution of M with F for varying rates of total mortality (Z). We demonstrate that the reference points for fishing mortality and spawning-stock biomass associated with MSDB are less sensitive to increasing compensation of M with F than those associated with MSY and more sensitive to changes in selection pattern. MSDB-based reference points, which are consistent with maximum stock productivity, are also associated with lower fishing mortality rates and higher stock biomasses than their MSY-based counterparts. Given that selection pattern can be influenced through fishery input measures (e.g. technical gear measures, decisions on areas, and/or times of fishing), whereas variations of M in response to F are not controllable (indeed poorly understood), that the results of many fish stock assessments are imprecise, that maximum stock productivity corresponds to MSDB and that MSY-based reference points may best be considered as limits, we propose that MSDB-based reference points provide a more appropriate basis for management under an EBFM.

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

ICES Journal of Marine Science ◽

10.1093/icesjms/fsn217 ◽

2009 ◽

Vol 66 (3) ◽

pp. 445-454 ◽

Cited By ~ 30

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.

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Can fisheries-induced evolution shift reference points for fisheries management?

ICES Journal of Marine Science ◽

10.1093/icesjms/fst077 ◽

2013 ◽

Vol 70 (4) ◽

pp. 707-721 ◽

Cited By ~ 77

Author(s):

Mikko Heino ◽

Loїc Baulier ◽

David S. Boukal ◽

Bruno Ernande ◽

Fiona D. Johnston ◽

...

Keyword(s):

Fisheries Management ◽

Fish Population ◽

Reference Points ◽

Population Characteristics ◽

Biological Processes ◽

Fishing Mortality ◽

Intended Meaning ◽

Stock Biomass ◽

Spawning Stock ◽

Induced Changes

Abstract Heino, M., Baulier, L., Boukal, D. S., Ernande, B., Johnston, F. D., Mollet, F. M., Pardoe, H., Therkildsen, N. O., Uusi-Heikkilä, S., Vainikka, A., Arlinghaus, R., Dankel, D. J., Dunlop, E. S., Eikeset, A. M., Enberg, K., Engelhard G. H., Jørgensen, C., Laugen, A. T., Matsumura, S., Nusslé, S., Urbach, D., Whitlock, R., Rijnsdorp, A. D., and Dieckmann, U. 2013. Can fisheries-induced evolution shift reference points for fisheries management? – ICES Journal of Marine Science, 70: 707–721. Biological reference points are important tools for fisheries management. Reference points are not static, but may change when a population's environment or the population itself changes. Fisheries-induced evolution is one mechanism that can alter population characteristics, leading to “shifting” reference points by modifying the underlying biological processes or by changing the perception of a fishery system. The former causes changes in “true” reference points, whereas the latter is caused by changes in the yardsticks used to quantify a system's status. Unaccounted shifts of either kind imply that reference points gradually lose their intended meaning. This can lead to increased precaution, which is safe, but potentially costly. Shifts can also occur in more perilous directions, such that actual risks are greater than anticipated. Our qualitative analysis suggests that all commonly used reference points are susceptible to shifting through fisheries-induced evolution, including the limit and “precautionary” reference points for spawning-stock biomass, Blim and Bpa, and the target reference point for fishing mortality, F0.1. Our findings call for increased awareness of fisheries-induced changes and highlight the value of always basing reference points on adequately updated information, to capture all changes in the biological processes that drive fish population dynamics.

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Growth, mortality and spawning stock biomass of the striped red mullet Mullus surmuletus, in the Egyptian Mediterranean waters

Mediterranean Marine Science ◽

10.12681/mms.105 ◽

2009 ◽

Vol 10 (2) ◽

pp. 5 ◽

Cited By ~ 7

Author(s):

S.F. MEHANNA

Keyword(s):

Growth Parameters ◽

Growth Parameter ◽

Reference Points ◽

Age And Growth ◽

Parameter Estimates ◽

Red Mullet ◽

Stock Biomass ◽

Reading Technique ◽

Spawning Stock ◽

Mullus Surmuletus

Population parameters such as age, growth, mortality and maturity-at-age are crucial parameters for accurate stock assessment and management plans to ensure the sustainable development of fisheries. Also, they are essential for the calculation of spawning stock biomass (SSB) and equilibrium yield as well as biological reference points including Fmax, F0.1 and F30%SSB. Age and growth parameters were estimated for the striped red mullet, Mullus surmuletus, sampled from commercial landings of the trawl fishery in the Egyptian Mediterranean waters, using the otolith reading technique. M. surmuletus has a longevity of 5 years, but over 70% of fish were less than 2 years old. The growth parameter estimates were K= 0.47 yrs-1, L∞= 31.74 cm, and to= -0.3 yrs. Natural mortality (M) was 0.43 yrs-1, fishing mortality (F) was 0.73 yrs-1, survival rate (S) was 0.31 and exploitation ratio was 0.63 yr-1. Length-at-50% maturity was estimated at 15.1 cm TL, while the length at first capture was estimated at 11.6 cm TL. SSB analysis showed that effort reduction is strongly recommended such that F be reduced by 40% to rebuild spawner biomass to acceptable levels. Per-recruit analysis revealed that F should be reduced by about 27% to achieve the maximum Y/R. All approaches point to the need for drastic reduction in fishing pressure by about 30-40% in the Egyptian Mediterranean fisheries.

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A two-stage biomass model to assess the English Channel cuttlefish (Sepia officinalis L.) stock

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu081 ◽

2014 ◽

Vol 71 (9) ◽

pp. 2457-2468 ◽

Cited By ~ 12

Author(s):

Michaël Gras ◽

Beatriz A. Roel ◽

Franck Coppin ◽

Eric Foucher ◽

Jean-Paul Robin

Keyword(s):

Reference Points ◽

Sea Surface ◽

Sepia Officinalis ◽

Sustainable Utilization ◽

English Channel ◽

Two Stage ◽

Stock Biomass ◽

Exploitation Rate ◽

Spawning Stock ◽

Age Structured

Abstract The English Channel cuttlefish (Sepia officinalis) is the most abundant cephalopod resource in the Northeast Atlantic and one of the three most valuable resources for English Channel fishers. Depletion methods and age-structured models have been used to assess the stock, though they have shown limitations related to the model assumptions and data demand. A two-stage biomass model is, therefore, proposed here using, as input data, four abundance indices derived from survey and commercial trawl data collected by Ifremer and Cefas. The model suggests great interannual variability in abundance during the 17 years of the period considered and a decreasing trend in recent years. Model results suggest that recruitment strength is independent of spawning–stock biomass, but appears to be influenced by environmental conditions such as sea surface temperature at the start of the life cycle. Trends in exploitation rate do not reveal evidence of overexploitation. Reference points are proposed and suggestions for management of the sustainable utilization of cuttlefish in the English Channel are advanced.

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Modelling the effects of establishing a marine reserve for mobile fish species

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f02-018 ◽

2002 ◽

Vol 59 (3) ◽

pp. 405-415 ◽

Cited By ~ 92

Author(s):

P Apostolaki ◽

E J Milner-Gulland ◽

M K McAllister ◽

G P Kirkwood

Keyword(s):

Fish Species ◽

Marine Reserve ◽

High Mobility ◽

Merluccius Merluccius ◽

Seasonal Movements ◽

Stock Biomass ◽

Spawning Stock ◽

Short And Long Term ◽

Immature Fish

We present a model of the effects of a marine reserve on spawning stock biomass (SSB) and short- and long-term yield for a size-structured species that exhibits seasonal movements. The model considers the effects of protecting nursery and (or) spawning grounds under a range of fishing mortalities and fish mobility rates. We consider two extremes of effort redistribution following reserve establishment and analyze the effects of a reserve when the fishery targets either mature or immature fish. We apply the model to the Mediterranean hake (Merluccius merluccius) and show that a marine reserve could be highly beneficial for this species. We demonstrate benefits from reserves not just for overexploited stocks of low-mobility species, but also (to a lesser extent) for underexploited stocks and high-mobility species. Greatly increased resilience to overfishing is also found in the majority of cases. We show that a reserve provides benefits additional to those obtained from simple effort control. Benefits from reserves depend to a major extent on the amount of effort redistribution following reserve establishment and on fishing selectivity; hence, these factors should be key components of any evaluation of reserve effectiveness.

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Evidence of underestimation of European hake growth in the Bay of Biscay, and its relationship with bias in the agreed method of age estimation

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2006.07.007 ◽

2006 ◽

Vol 63 (9) ◽

pp. 1674-1681 ◽

Cited By ~ 88

Author(s):

Hélène de Pontual ◽

Anne Laure Groison ◽

Carmen Piñeiro ◽

Michel Bertignac

Keyword(s):

Age Estimation ◽

Good Condition ◽

Estimation Method ◽

Somatic Growth ◽

Biological Knowledge ◽

Data Sets ◽

Bay Of Biscay ◽

Age Validation ◽

Management Advice ◽

European Hake

Abstract In 2002, a pilot experiment on hake tagging was carried out using methodology specifically developed to catch and handle fish in good condition. By the end of 2005, 36 hake and five tags had been returned to the laboratory (a 3.1% return rate) with a maximum time at liberty of 1066 days. The somatic growth of the recoveries proved to be twofold higher than that expected from published von Bertalanffy growth functions for the species in the Bay of Biscay. The growth underestimation was related to age overestimation, as demonstrated by two independent analyses. The first was based on a blind interpretation of marked otoliths conducted independently by two European experts involved in the routine age estimation of hake. The result shows that the age estimates were neither accurate (inconsistent with oxytetracycline mark positions) nor precise. The second approach compared the predicted otolith growth with the observed growth, and the discrepancy between the two data sets was large. Both types of analyses invalidate the internationally agreed age estimation method and demonstrate a need for further research. Although based on limited data, the study highlights the need to improve biological knowledge of the species in order to improve assessment and management advice. It also strengthens the argument for age validation.

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Management options for the Blackwater herring, a local spring-spawning stock in the Thames Estuary

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2004.02.001 ◽

2004 ◽

Vol 61 (3) ◽

pp. 297-307 ◽

Cited By ~ 13

Author(s):

Beatriz A. Roel ◽

Carl M. O'Brien ◽

Marinelle Basson

Keyword(s):

Fishing Effort ◽

Current Approach ◽

Slight Reduction ◽

Trawl Survey ◽

Management Options ◽

Fishing Season ◽

Thames Estuary ◽

Spawning Stock ◽

Management Advice ◽

The Impact

Abstract Herring caught in the Thames Estuary sustain a small local commercial fishery (peak catch of 606 t during the 1972–1973 fishing season). Loss of local consumers' interest in the herring product has resulted in a gradual decline in catches and fishing effort for the stock. The stock is assessed using an age-structured model that relies on the information provided by a scientific trawl survey, and management advice is provided before the fishing season starts in October. Given its current low economic value, managers have requested evaluation of options for multi-annual Total Allowable Catches (TACs) in an attempt to reduce the frequency (and costs) of assessment and associated management advice. A tentative relationship between sea surface temperature and recruitment is used to predict the impact of increasing sea temperatures on future recruitment in the context of global warming. Hypotheses of auto-correlation and of an environmental effect on recruitment, together with trends in weight-at-age and the overestimation of spawning-stock biomass, form the basis for sensitivity tests of the management options considered. Implementation of a 3-year fixed TAC with 40% constraint in TAC variability and a slight reduction in target F would seem appropriate for the stock, given that it is within safe biological limits and compares well in terms of yield and risk with the current approach of annual TAC revision.

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