Incorporating Uncertainty into Fishery Models

2002 ◽  
Keyword(s):  
Fishery Management ◽  
Population Analysis ◽  
Management Plan ◽  
Atlantic Menhaden ◽  
Production Model ◽  
Fishing Mortality ◽  
Juvenile Abundance ◽  
Stock Assessments ◽  
Mortality Projections ◽  
Production Modeling

<em>Abstract.—</em>Stock assessments of Atlantic menhaden are conducted annually for the Atlantic States Marine Fisheries Commission, as required by the recently updated Fishery Management Plan, adopted in 1992. Uncertainties in stock assessments have been explored over the years from many perspectives. Two general areas of analysis are considered here. The first area is largely deterministic and concerns the virtual population analysis (VPA), including development and coherence of the catch-at-age matrix; historical retrospective problems; implications of assuming constant <EM>M </EM>at all ages analyzed; and reliability of recruitment estimates relative to fishery-independent juvenile abundance indices when used for calibrating the VPA. The second area of consideration comprises stochastic analyses, including stochastic projections based on biological benchmarks determined from yield-per-recruit and spawning-stockbiomass- per-recruit models; bootstrapped application of a surplus-production model; and projections from that production model. Nonetheless, the largest uncertainty in assessment of the stock stems not from modeling considerations, but is a biological question: Can the high stock levels observed in the 1950s be regained by reducing fishing mortality? Projections based on production modeling assume that they can, but if exogenous forces (for example, habitat loss or pollution) have affected the stock, it may be that they cannot. If the recent pattern of lower fishing mortality rates in response to social and economic factors continues, the fishery will in essence conduct an experiment that may answer the question.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

2001 ◽  
Keyword(s):  
North Atlantic ◽  
Fishery Management ◽  
Population Analysis ◽  
Mortality Rates ◽  
Fishing Mortality ◽  
Stock Biomass ◽  
The Status ◽  
Eastern North Atlantic ◽  
Charleston Bump ◽  
Definition Of

<em> Abstract.</em>—The status of the wreckfish <em> Polyprion americanus </em>stock caught on the Blake Plateau in the southeastern United States Atlantic was analyzed by calibrated virtual population analysis (VPA) to estimate trends in fishing mortality and population (or stock) biomass. Calibration of the FADAPT VPA program was to fishery-dependent catch-per-unit effort (CPUE) for a range in assumed values for natural mortality (M). Age-length keys were developed from two aging studies of wreckfish (1988– 1992 and 1995–1998). Keys were developed annually (pooled across seasons to create three “annual” age-length keys to represent 1988–1990, 1991–1993, and 1994–1998) and seasonally (pooled across years to create three seasonal age-length keys to represent April–June, July–September, and October to end of fishing year on 15 January). Analyses based on both annual and seasonal catch matrices showed similar patterns and values, with the seasonal catch matrix producing slightly lower estimates of fishing mortality rates (F) and higher estimates of biological reference points based on F. Fishing mortality rates peaked in 1989, as did the maximum annual U.S. landings (4.2 million pounds). Subsequently, both landings and fishing mortality rates have generally declined. Although stock biomass has generally declined over the study period, recruitment at age 7 has risen since about 1994. Meanwhile, annual estimates of static spawning potential ratio (SPR), which are inversely related to F, have risen since 1994. Fishing mortality rates from recent low landings are at or near the South Atlantic Fishery Management Council’s threshold definition of overfishing (static SPR of 30%), while the process of rebuilding with improving recruitment appears to be underway. Concern persists because the assessment is based on the underlying assumption that wreckfish from the Blake Plateau form a single stock separate from the eastern North Atlantic and genetic evidence suggests the stock encompasses the entire North Atlantic.

scholarly journals Measurement Error Affects Risk Estimates for Recruitment to the Hudson River Stock of Striped Bass

2002 ◽  
Vol 2 ◽  
pp. 238-253 ◽  
Author(s):  
Dennis J. Dunning ◽  
Quentin E. Ross ◽  
Stephan B. Munch ◽  
Lev R. Ginzburg
Keyword(s):  
Measurement Error ◽  
Mortality Rate ◽  
Striped Bass ◽  
Power Plants ◽  
Fishery Management ◽  
Hudson River ◽  
Management Plan ◽  
Fishing Mortality ◽  
Beach Seine ◽  
Indian Point

We examined the consequences of ignoring the distinction between measurement error and natural variability in an assessment of risk to the Hudson River stock of striped bass posed by entrainment at the Bowline Point, Indian Point, and Roseton power plants. Risk was defined as the probability that recruitment of age-1+ striped bass would decline by 80% or more, relative to the equilibrium value, at least once during the time periods examined (1, 5, 10, and 15 years). Measurement error, estimated using two abundance indices from independent beach seine surveys conducted on the Hudson River, accounted for 50% of the variability in one index and 56% of the variability in the other. If a measurement error of 50% was ignored and all of the variability in abundance was attributed to natural causes, the risk that recruitment of age-1+ striped bass would decline by 80% or more after 15 years was 0.308 at the current level of entrainment mortality (11%). However, the risk decreased almost tenfold (0.032) if a measurement error of 50% was considered. The change in risk attributable to decreasing the entrainment mortality rate from 11 to 0% was very small (0.009) and similar in magnitude to the change in risk associated with an action proposed in Amendment #5 to the Interstate Fishery Management Plan for Atlantic striped bass (0.006)— an increase in the instantaneous fishing mortality rate from 0.33 to 0.4. The proposed increase in fishing mortality was not considered an adverse environmental impact, which suggests that potentially costly efforts to reduce entrainment mortality on the Hudson River stock of striped bass are not warranted.

Ridge virtual population analysis to reduce the instability of fishing mortalities in the terminal year

2017 ◽  
Vol 74 (9) ◽  
pp. 2427-2436 ◽  
Author(s):  
Hiroshi Okamura ◽  
Yuuho Yamashita ◽  
Momoko Ichinokawa
Keyword(s):  
Ridge Regression ◽  
Population Analysis ◽  
Japan Sea ◽  
The Sea Of Japan ◽  
Fishing Mortality ◽  
Population Analyses ◽  
Virtual Population ◽  
Stock Assessments ◽  
Abundance Indices ◽  
Stable Estimation

Abstract Tuned virtual population analyses are widely used for fisheries stock assessments. However, accurately estimating abundances and fishing mortality coefficients in the terminal year using tuned virtual population analyses is generally difficult, particularly when there is a limited number of available abundance indices. We propose a new method of integrating the tuned virtual population analyses with a ridge regression approach. In our method, penalization in the ridge regression is applied to the age-specific fishing mortalities in the terminal year, and the penalty parameter is automatically selected by minimizing the retrospective bias. Therefore, our method is able to simultaneously obtain a stable estimation of fishing mortality coefficients in the terminal year and reduce retrospective bias. Simulation tests based on the northern Japan Sea stock of walleye pollock (Gadus chalcogrammus) in the Sea of Japan demonstrated that this method yielded less biased estimates of abundances and avoided overestimations of fishing mortality coefficients in the terminal year. In addition, despite limited abundance indices, our method can perform reliable abundance estimations even under hyperstability and hyperdepletion conditions.

From Catastrophe to Recovery: Stories of Fishery Management Success

2019 ◽  
Keyword(s):  
Striped Bass ◽  
Fishery Management ◽  
Hudson River ◽  
Management Plan ◽  
Lessons Learned ◽  
Juvenile Abundance ◽  
Spawning Stock ◽  
Long Term Monitoring ◽  
Term Monitoring

<i>Abstract</i>.—The Striped Bass <i>Morone saxatilis</i> is an extremely important commercial and recreational species with a coastal migratory stock in the United States referred to as “Atlantic Striped Bass” managed by the Atlantic States Marine Fisheries Commission (ASMFC). Atlantic Striped Bass has four major contributing stocks, including the Chesapeake Bay, which comprises 70–90%, and the Hudson River, the Delaware River, and the Albemarle Sound/Roanoke River (A/R). The collapse of Atlantic Striped Bass in the late 1970s precipitated federal funding and legislation like the Emergency Striped Bass Study for research on causative factors of the decline and potential management recommendations. The 1981 ASMFC Interstate Fishery Management Plan (ISFMP) for Atlantic Striped Bass was nonmandatory and mostly ineffective until the 1984 Atlantic Striped Bass Conservation Act provided regulatory authorities to the ASMFC and the federal government to close fisheries in states out of compliance with ISFMPs. Restrictions and moratoria on harvest imposed in several states reduced mortality, and under favorable environmental conditions and given Striped Bass life history, multiple years of good recruitment occurred. This allowed target thresholds for female spawning stock biomass to be achieved and the ASMFC to declare recoveries of Atlantic Striped Bass stocks from 1995 to 1998. Regulation of river flows was particularly important for the A/R stock recovery, and this stock is presented as a case study. During the 20+ years following recovery, long-term monitoring by states in support of adaptive management was primarily supported by the stable, nonappropriated funding of the Sport Fish Restoration Act. Monitoring includes spawning stock characterization and biomass estimation, juvenile abundance surveys, cooperative coastwide tagging, and harvest data collection. Future issues facing the recovered Atlantic Striped Bass include interspecies effects of relatively high abundance, management of stocks separately instead of as a single coastal stock, and ecosystem-based fisheries management. Key lessons learned in the Atlantic Striped Bass recovery are that high societal value of the species provided the political impetus to create and fund the recovery program, coordination of management and enforcement efforts among all jurisdictions was essential for this migratory species, and fully funded long-term monitoring programs are critical to adaptive population management.

Evaluation of effort reduction in the Florida Keys spiny lobster, Panulirus argus, fishery using an age-structured population analysis

1997 ◽  
Vol 48 (8) ◽  
pp. 1045 ◽  
Author(s):  
Robert G. Muller ◽  
John H. Hunt ◽  
Thomas R. Matthews ◽  
William C. Sharp
Keyword(s):  
Fishery Management ◽  
Population Analysis ◽  
Spiny Lobster ◽  
Florida Keys ◽  
Environmental Damage ◽  
Population Fluctuations ◽  
Fishing Mortality ◽  
Time Period ◽  
Effort Reduction ◽  
Age Structured

A management programme implemented in Florida in 1993 was designed to reduce the number of traps in the spiny lobster fishery in order to reduce gear conflicts, environmental damage and effort without reducing harvest. Traps in the commercial fishery were reduced from 939 000 in 1991 to 568 000 in 1995. Landings by fishing season, zone (upper Florida Keys and lower Florida Keys), sex, and time period (summer v. winter) were pro-rated into numbers by length that were assigned ages by using growth simulations. From tag–recapture data, moult interval was estimated by using a logistic regression with terms for zone, sex, time period, carapace length, and time at large. For lobsters that moulted, the moult increment was modelled with a multiple regression including the same terms. Standardized catch-per-trip and total landings increased as traps were reduced. Age-structured analysis of the catches-at-age indicated that fishing mortality decreased by 16%, even as landings increased. It is not known whether the increase in landings was due to natural population fluctuations or to positive results of trap reduction. Fishing mortality rates still exceed common benchmarks used in fishery management, and excessive traps remain in the fishery.

scholarly journals Among-stock comparisons for improving stock assessments of data-poor stocks: the “Robin Hood” approach

2011 ◽  
Vol 68 (5) ◽  
pp. 972-981 ◽  
Author(s):  
André E. Punt ◽  
David C. Smith ◽  
Anthony D. M. Smith
Keyword(s):  
Marine Science ◽  
Fishing Mortality ◽  
Robin Hood ◽  
Estimated Parameters ◽  
Stock Assessments ◽  
Time Information

Abstract Punt, A. E., Smith, D. C., and Smith, A. D. M. 2011. Among-stock comparisons for improving stock assessments of data-poor stocks: the “Robin Hood” approach. – ICES Journal of Marine Science, 68: 972–981. An approach is outlined for conducting stock assessments in which parameters are estimated for multiple stocks at the same time. Information from data-rich stock assessments, e.g. trends in fishing mortality, and values for parameters of selectivity functions are provided to data-poor assessments in the form of penalties on the estimated parameters, which leads to stock assessments for the most data-poor stocks being informed by those for the most data-rich stocks. The method is applied for example purposes to data for nine stocks in Australia's southern and eastern scalefish and shark fishery. The results of the application confirm that results for data-rich stocks are little impacted by being assessed in conjunction with data-poor stocks and that the results for data-poor stocks can be qualitatively different when information for data-rich stocks is taken into account.

scholarly journals Sustainable exploitation of temperate fish stocks

2009 ◽  
Vol 6 (1) ◽  
pp. 124-127 ◽  
Author(s):  
Henrik Sparholt ◽  
Robin M. Cook
Keyword(s):  
Species Interactions ◽  
Fishery Management ◽  
Regional Scale ◽  
Single Species ◽  
Fishing Effort ◽  
Theoretical Concept ◽  
Maximum Sustainable Yield ◽  
Production Model ◽  
The Status ◽  
Long Time

The theory of maximum sustainable yield (MSY) underpins many fishery management regimes and is applied principally as a single species concept. Using a simple dynamic biomass production model we show that MSY can be identified from a long time series of multi-stock data at a regional scale in the presence of species interactions and environmental change. It suggests that MSY is robust and calculable in a multispecies environment, offering a realistic reference point for fishery management. Furthermore, the demonstration of the existence of MSY shows that it is more than a purely theoretical concept. There has been an improvement in the status of stocks in the Northeast Atlantic, but our analysis suggests further reductions in fishing effort would improve long-term yields.

scholarly journals Essential habitat for sardine juveniles in Iberian waters

2017 ◽  
Vol 81 (3) ◽  
pp. 351 ◽  
Author(s):  
Sílvia Rodríguez-Climent ◽  
Maria Manuel Angélico ◽  
Vítor Marques ◽  
Paulo Oliveira ◽  
Laura Wise ◽  
...  
Keyword(s):  
Fishery Management ◽  
Generalized Additive Models ◽  
Management Strategies ◽  
Coastal Region ◽  
Additive Models ◽  
Spawning Grounds ◽  
Significant Relationships ◽  
Juvenile Abundance ◽  
Spatial Differences ◽  
Core Areas

In a period when the Iberian sardine stock abundance is at its historical minimum, knowledge of the sardine juvenile’s distribution is crucial for the development of fishery management strategies. Generalized additive models were used to relate juvenile sardine presence with geographical variables and spawning grounds (egg abundance) and to model juvenile abundance with the concurrent environmental conditions. Three core areas of juvenile distribution were identified: the Northern Portuguese shelf (centred off Aveiro), the coastal region in the vicinity of the Tagus estuary, and the eastern Gulf of Cadiz. Spatial differences in the relationship between juvenile presence and egg abundances suggest that essential juvenile habitat might partially differ from the prevailing spawning grounds. Models also depicted significant relationships between juvenile abundance, temperature and geographical variables in combination with salinity in the west and with zooplankton in the south. Results indicate that the sardine juvenile distribution along the Iberian Peninsula waters are an outcome of a combination of dynamic processes occurring early in life, such as egg and larva retention, reduced mortality and favourable feeding grounds for both larvae and juveniles.

scholarly journals North Sea cod recovery?

2006 ◽  
Vol 63 (6) ◽  
pp. 961-968 ◽  
Author(s):  
Joe Horwood ◽  
Carl O'Brien ◽  
Chris Darby
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Mortality Rates ◽  
Fishing Effort ◽  
Current Status ◽  
Fishing Mortality ◽  
Commercial Fish ◽  
Fish Stocks ◽  
Stock Assessments ◽  
Low Levels

AbstractRecovery of depleted marine, demersal, commercial fish stocks has proved elusive worldwide. As yet, just a few shared or highly migratory stocks have been restored. Here we review the current status of the depleted North Sea cod (Gadus morhua), the scientific advice to managers, and the recovery measures in place. Monitoring the progress of North Sea cod recovery is now hampered by considerable uncertainties in stock assessments associated with low stock size, variable survey indices, and inaccurate catch data. In addition, questions arise as to whether recovery targets are achievable in a changing natural environment. We show that current targets are achievable with fishing mortality rates that are compatible with international agreements even if recruitment levels remain at the current low levels. Furthermore, recent collations of data on international fishing effort have allowed estimation of the cuts in fishing mortality achieved by restrictions on North Sea effort. By the beginning of 2005, these restrictions are estimated to have reduced fishing mortality rates by about 37%. This is insufficient to ensure recovery of North Sea cod within the next decade.

Population dynamics and stock assessment of Hilsa shad, Tenualosa ilisha (Hamilton, 1822) along the coast of Bangladesh

2021 ◽  
Vol 48 (2) ◽  
pp. 231-241
Author(s):  
Md Khairul Islam ◽  
Md Humayun ◽  
Manmatha Nath Sarker ◽  
Md Sharifuddin ◽  
M Niamul Naser
Keyword(s):  
Growth Parameters ◽  
Stock Assessment ◽  
Population Analysis ◽  
Total Mortality ◽  
Maximum Sustainable Yield ◽  
Fishing Mortality ◽  
Recruitment Pattern ◽  
Weight Relationship ◽  
Tenualosa Ilisha ◽  
Highly Correlated

Stock Assessment of Tenualosa ilisha (Hamilton, 1822) were estimated using FiSAT-II software with length-frequency data collected from different landing centers. The Southeast Coast of Bay Of Bengal, Cox's Bazar. The Von Bertalanffy growth parameters Land K for the species were asymptotic length (L∞) was 51.41 cm, growth rate (K) was 0.75 year-1 and t0 = -0.2 year respectively. The estimated value of total mortality (Z) based on length converted catch curve using these growth parameters was 2.35 year-1.Natural mortality (M) based on growth parameters and mean environmental temperature (T = 27° C) was 1.00 year-1 and fishing mortality (F) was 1.35 year-1. Optimum length of hilsa at first capture (Lc=L50) was 28.36 cm TL. Growth performance indices (ϕ') was 3.30. The estimated value of the exploitation rate (E) using the length-converted catch curve was 0.57. The recruitment pattern of this species was continuous and two peaks per year. The present investigation clearly showed the over fishing (E > 0.50) condition for T. ilisha in Bangladesh. The estimated length-weight relationship for the combined sex was found to be W = 0.0109 L3. Virtual population analysis (VPA) showed that the maximum fishing mortality occurring in the length between 30 to 35 cm with a maximum value in the length of 32 cm that repeatedly indicate high fishing mortality in the T. ilisha. The generalized length-weight relationship was fitted with the pooled data of all monthly samples were BW = 0.029 TL2.718 (R2= 0.833) respectively. The results revealed that all length-weight relationships were highly correlated (r > 0.993). Maximum sustainable yield (MSY) was estimated as 435,554 t. Bangladesh J. Zool. 48(2): 231-241, 2020

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