Statistical Power of Trends in Fish Abundance

1987 ◽  
Vol 44 (11) ◽  
pp. 1879-1889 ◽  
Author(s):  
Randall M. Peterman ◽  
Michael J. Bradford
Keyword(s):  
Time Trends ◽  
Statistical Power ◽  
Stock Assessment ◽  
Cohort Analysis ◽  
Assessment Methods ◽  
Trawl Survey ◽  
Estimation Errors ◽  
Management Objectives ◽  
Fish Abundances ◽  
Parophrys Vetulus

Estimation errors inherent in stock assessment methods may make it difficult to estimate time trends in fish abundances correctly. Our objective was to quantify the probability that trends in abundance of recruits will be successfully identified. For this analysis, we used an empirically based simulation model of English sole (Parophrys vetulus) off the west coast of North America. The unique wealth of data and past analyses of this population permitted us to include deterministic and stochastic components of growth, mortality, and reproduction in a realistic manner. Errors were also included in two simulated stock assessment methods: a trawl survey and cohort analysis. Under various conditions, we calculated the probability (analogous to statistical power) that these methods will meet three management objectives concerning time trends in recruitment. Monte Carlo simulations showed that although power depends on the objective, under most realistic conditions the probability of correctly detecting recruitment time trends may be unacceptably low. These results suggest new management guidelines for fisheries.

Influence of environmental, spatial, and ontogenetic variables on habitat selection and management of spiny dogfish in the Northeast (US) shelf large marine ecosystem

2014 ◽  
Vol 71 (4) ◽  
pp. 567-580 ◽  
Author(s):  
Skyler R. Sagarese ◽  
Michael G. Frisk ◽  
Thomas J. Miller ◽  
Kathy A. Sosebee ◽  
John A. Musick ◽  
...  
Keyword(s):  
Habitat Selection ◽  
Environmental Conditions ◽  
Statistical Power ◽  
Stock Assessment ◽  
Marine Ecosystem ◽  
Spiny Dogfish ◽  
Trawl Survey ◽  
Science Center ◽  
Large Marine Ecosystem ◽  
Northeast Us

Declines in abundance of commercially valuable groundfish have highlighted the ecological and commercial importance of previously underutilized elasmobranchs in the Northeast (US) shelf large marine ecosystem (NES LME). Seasonal distributions and ontogenetic habitats of one such species, spiny dogfish (Squalus acanthias), were investigated using Northeast Fisheries Science Center (NEFSC) bottom trawl survey data (1963–2009). Neonate, immature, and mature dogfish all selected warmer, more saline, and more southerly locations during spring compared with available locations. During autumn, larger dogfish occupied relatively warmer, shallower, and less saline waters while neonates selected higher salinities. There were strong ontogenetic patterns in habitats occupied. Contrary to expectation, geographic range contracted as abundance increased during autumn. This suggests that niche constraints override density-dependent effects, although detection of relationships within stages was limited by low statistical power. The proportion of mature female survey catch within the Mid-Atlantic Bight was significantly related to temperature, suggesting that environmental conditions surveyed may impact population trends. Collectively, these results highlight critical habitats, suggest mechanisms behind ontogenetic habitat selection, and provide insight into how changing environmental conditions may impact stock assessment.

scholarly journals Evaluating the role of data quality when sharing information in hierarchical multistock assessment models, with an application to Dover sole

2019 ◽  
Vol 76 (10) ◽  
pp. 1819-1835
Author(s):  
Samuel D.N. Johnson ◽  
Sean P. Cox
Keyword(s):  
Statistical Power ◽  
Fishery Management ◽  
Stock Assessment ◽  
Simulated Data ◽  
Assessment Model ◽  
Production Model ◽  
Estimation Errors ◽  
Lower Estimation ◽  
Relative Errors ◽  
Dover Sole

An emerging approach to data-limited fisheries stock assessment uses hierarchical multistock assessment models to group stocks together, sharing information from data-rich to data-poor stocks. In this paper, we simulate data-rich and data-poor fishery and survey data scenarios for a complex of Dover sole (Microstomus pacificus) stocks. Simulated data for individual stocks were used to compare estimation performance for single-stock and hierarchical multistock versions of a Schaefer production model. The single-stock and best-performing multistock models were then used in stock assessments for the real Dover sole data. Multistock models often had lower estimation errors than single-stock models when assessment data had low statistical power. Relative errors for productivity and relative biomass parameters were lower for multistock assessment model configurations. In addition, multistock models that estimated hierarchical priors for survey catchability performed the best under data-poor scenarios. We conclude that hierarchical multistock assessment models are useful for data-limited stocks and could provide a more flexible alternative to data pooling and catch-only methods; however, these models are subject to nonlinear side effects of parameter shrinkage. Therefore, we recommend testing hierarchical multistock models in closed-loop simulations before application to real fishery management systems.

scholarly journals Correcting density-dependent effects in abundance estimates from bottom-trawl surveys

2014 ◽  
Vol 71 (5) ◽  
pp. 1107-1116 ◽  
Author(s):  
Stan Kotwicki ◽  
James N. Ianelli ◽  
André E. Punt
Keyword(s):  
Stock Assessment ◽  
Dead Zone ◽  
Walleye Pollock ◽  
Assessment Model ◽  
Bottom Trawl ◽  
Trawl Survey ◽  
Negative Consequences ◽  
Catch Per Unit Effort ◽  
Density Dependent ◽  
Index Of Abundance

Abstract Indices of abundance are important for estimating population trends in stock assessment and ideally should be based on fishery-independent surveys to avoid problems associated with the hyperstability of the commercial catch per unit effort (cpue) data. However, recent studies indicate that the efficiency of the survey bottom trawl (BT) for some species can be density-dependent, which could affect the reliability of survey-derived indices of abundance. A function qe∼f(u), where qe is the BT efficiency and u the catch rate, was derived using experimentally derived acoustic dead-zone correction and BT efficiency parameters obtained from combining a subset of BT catch data with synchronously collected acoustic data from walleye pollock (Theragra chalcogramma) in the eastern Bering Sea (EBS). We found that qe decreased with increasing BT catches resulting in hyperstability of the index of abundance derived from BT survey. Density-dependent qe resulted in spatially and temporarily variable bias in survey cpue and biased population age structure derived from survey data. We used the relationship qe∼f(u) to correct the EBS trawl survey index of abundance for density-dependence. We also obtained a variance–covariance matrix for a new index that accounted for sampling variability and the uncertainty associated with the qe. We found that incorporating estimates of the new index of abundance changed outputs from the walleye pollock stock assessment model. Although changes were minor, we advocate incorporating estimates of density-dependent qe into the walleye pollock stock assessment as a precautionary measure that should be undertaken to avoid negative consequences of the density-dependent qe.

Lessons learned from data-limited evaluations of data-rich reef fish species in the Gulf of Mexico: implications for providing fisheries management advice for data-poor stocks

2019 ◽  
Vol 76 (9) ◽  
pp. 1624-1639 ◽  
Author(s):  
Skyler R. Sagarese ◽  
William J. Harford ◽  
John F. Walter ◽  
Meaghan D. Bryan ◽  
J. Jeffery Isely ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Reef Fish ◽  
Fish Species ◽  
Stock Assessment ◽  
Lessons Learned ◽  
Management Objectives ◽  
Trade Offs ◽  
Data Limitations ◽  
Management Procedures ◽  
Reef Fish Species

Specifying annual catch limits for artisanal fisheries, low economic value stocks, or bycatch species is problematic due to data limitations. Many empirical management procedures (MPs) have been developed that provide catch advice based on achieving a stable catch or a historical target (i.e., instead of maximum sustainable yield). However, a thorough comparison of derived yield streams between empirical MPs and stock assessment models has not been explored. We first evaluate trade-offs in conservation and yield metrics for data-limited approaches through management strategy evaluation (MSE) of seven data-rich reef fish species in the Gulf of Mexico. We then apply data-limited approaches for each species and compare how catch advice differs from current age-based assessment models. MSEs identified empirical MPs (e.g., using relative abundance) as a compromise between data requirements and the ability to consistently achieve management objectives (e.g., prevent overfishing). Catch advice differed greatly among data-limited approaches and current assessments, likely due to data inputs and assumptions. Adaptive MPs become clearly viable options that can achieve management objectives while incorporating auxiliary data beyond catch-only approaches.

Exploitation status and stock assessment by pseudo-cohort analysis of the bluefish, Pomatomus saltatrix, in the Gulf of Gabes (Tunisia)

2007 ◽  
Vol 87 (5) ◽  
pp. 1315-1319 ◽  
Author(s):  
Khalifa Dhieb ◽  
Mohamed Ghorbel ◽  
Othman Jarboui ◽  
Abderrahmen Bouaïn
Keyword(s):  
Stock Assessment ◽  
Cohort Analysis ◽  
Fishing Effort ◽  
Individual Growth ◽  
Eastern Coast ◽  
Pomatomus Saltatrix ◽  
Gulf Of Gabes ◽  
Gulf Of Gabès ◽  
Exploitation Status ◽  
The One

The bluefish, Pomatomus saltatrix, is quite abundant in the Gulf of Gabes, off the south-eastern coast of Tunisia. It is commercially exploited by artisanal gears and trawlers all year round, and by purse seine nets from May to August (bluefish fishery season). Catches of bluefish, in the period 1996–2004 fluctuated between 365.6 t and 1240.1 t with an annual average of 805 t. This fluctuation, partially due to the migratory nature of the species, could be also attributed to the fleet activities that sometimes changed at the mercy of the operators. The analysis of the virtual population of bluefish in the Gulf of Gabes showed that, in 2002, the stock that had just recovered rightly after an excessive fishing in 1996–1997 was again subject to a fishing effort that passed its capacity (E=0.71; E>0.5). The biomass (B) estimated to be ~2178.9 t only tolerated the extraction of 713.4 t (more or less one-third of B). However, the three fleets in use removed 1029.1 t with a yield per recruit (Y/R) of 70.5 g. As a result of this over-fishing, the actual stock of bluefish in the Gulf of Gabes was characterized by individuals having a mean total length of 17.88 cm, a size which is much lower than the one at first sexual maturity (23.5 cm). The turnover (D/B) being of 75.23%, it did not allow the reconstitution of the stock. The total removals (~1639 t) due to both natural mortality (M=0.28) and fishing mortality (F=0.675) had to be compensated especially by individual growth (1534.2 t; 93.6%) because of the low weight of the recruits.

Using management strategy evaluation to establish indicators of changing fisheries

2019 ◽  
Vol 76 (9) ◽  
pp. 1653-1668 ◽  
Author(s):  
T.R. Carruthers ◽  
A.R. Hordyk
Keyword(s):  
Management Strategy ◽  
Statistical Power ◽  
Stock Assessment ◽  
Model Misspecification ◽  
Management Approach ◽  
Data Types ◽  
Quality Of Data ◽  
Management Strategy Evaluation ◽  
Strategy Evaluation ◽  
Management Procedures

A new indicator is described that uses multivariate posterior predictive data arising from management strategy evaluation (MSE) to detect operating model misspecification (exceptional circumstances) due to changing system dynamics. The statistical power of the indicator was calculated for five case studies for which fishery stock assessments have estimated changes in recruitment, natural mortality rate, growth, fishing efficiency, and size selectivity. The importance of the component data types that inform the indicator was also calculated. The indicator was tested for multiple types of management procedures (e.g., catch limits by stock assessment, size limits, spatial closures) given varying qualities of data. The statistical power of the indicator could be high even over short time periods and depended on the type of system change and quality of data. Statistical power depended strongly on the type of management approach, suggesting that indicators should be established that rigorously account for feedbacks between proposed management and observed data. MSE processes should use alternative operating models to evaluate protocols for exceptional circumstances to ensure they are of acceptable statistical power.

Grenadiers of the World Oceans: Biology, Stock Assessment, and Fisheries

2008 ◽  
Keyword(s):  
Stock Assessment ◽  
Distribution Patterns ◽  
Abundant Species ◽  
Trawl Survey ◽  
Bathymetric Range ◽  
Main Species ◽  
The World ◽  
Species Specific ◽  
Depth Ranges ◽  
Preanal Length

<em>Abstract</em>.—The objective of this study is to describe the distribution patterns of abundance and biomass, on a geographic and bathymetric basis, of the main macrourid species of Mozambique waters. Catch data from a demersal trawl survey (<EM>MOZAMBIQUE 07</EM>) were analyzed. The survey covered the continental shelf and upper-middle slope from 17°00’S to 26°50’S and from 100–700 m depth. Fourteen macrourid species were collected from 200 m and deeper. The most abundant species and the highest in biomass were <em>Coelorinchus braueri</em>, <em>C. trunovi, C. denticulatus</em>, <em>Ventrifossa nasuta</em>, and <em>Malacocephalus laevis</em>. Only those five species were analyzed in detail. The occurrence and yields by geographic and bathymetric range of these main species seem to reveal the existence of some species-specific preference for determinate depth ranges and/or geographic areas. Preanal length-weight relationships were estimated for <em>C. braueri, C. trunovi, </em>and <em>V. nasuta</em>: <em>a</em>= 0.00071; 0.00020; 0.00080; <em>b</em>= 2.50; 2.80; 2.76 and <em>r</em><sup>2</sup>= 0.93; 0.97; 0.78, respectively.

Grenadiers of the World Oceans: Biology, Stock Assessment, and Fisheries

2008 ◽  
Keyword(s):  
Continental Slope ◽  
Ross Sea ◽  
Stock Assessment ◽  
Trawl Survey ◽  
Factors Affecting ◽  
Year Effect ◽  
Macrourus Whitsoni ◽  
Catch Rates ◽  
Potential Methods ◽  
Major Factors

<em>Abstract</em>.—An exploratory longline fishery for toothfish (<em>Dissostichus </em>spp.) in the Ross Sea, Antarctica has been carried out since 1997. The main bycatch species in this fishery is the grenadier, <em>Macrourus whitsoni. </em>No assessments have been carried out of the impact of the fishery on grenadiers, although they have life history characteristics that make them vulnerable to overexploitation. The aims of this research were two-fold; firstly, to characterize the bycatch fishery and to determine factors affecting bycatch rates; and secondly to examine potential methods of monitoring its abundance. A standardized CPUE analysis was used to determine factors affecting bycatch rates of grenadiers in the fishery. The analysis was based on fine-scale haul-by-haul data from all vessels in the fishery from 1999 to 2005. The major factors influencing grenadier bycatch were vessel, area, and depth. Catch rates of grenadiers were highest along the continental slope of the Ross Sea in depths from 600 to 1000 m, and there was an order of magnitude difference in grenadier catch rates between different vessels. Examination of vessel characteristics showed that catch rates of grenadiers were significantly lower with the Spanish line system than with the autoline system. There are several plausible reasons for this difference, including hook location with respect to the seabed, bait type, and differences in levels of reporting of bycatch between vessels. Various approaches to monitoring and assessing grenadiers in the Ross Sea fishery were explored. We conclude that the year effect from the standardized CPUE analysis is unlikely to be monitoring abundance but instead probably reflect changes in gear characteristics, fisher behavior, and targeting of effort. Trends in the length composition of the catch are confounded with depth, and are also of limited value at present. We consider that the best approach to obtaining abundance estimates for grenadiers in the Ross Sea would be to carry out a random bottom trawl survey of the continental slope.

Density-Dependent Growth of Age 1 English Sole (Parophrys vetuls) in Oregon and Washington Coastal Waters

1987 ◽  
Vol 44 (1) ◽  
pp. 48-53 ◽  
Author(s):  
Randall M. Peterman ◽  
Michael J. Bradford
Keyword(s):  
Coastal Waters ◽  
Time Trends ◽  
Annual Growth Rate ◽  
English Sole ◽  
Density Dependent ◽  
Stock Assessments ◽  
Negative Effect ◽  
Dependent Growth ◽  
Parophrys Vetulus ◽  
The Impact

We tested whether English sole (Parophrys vetulus) in Oregon and Washington waters show density-dependent growth. We found that there is a significant negative effect of cohort abundance on annual growth rate of age 1 fish, but not on growth of ages 2–7. Unlike most similar studies of density dependence, this result was not confounded by time trends in abundance and growth. The multiple regression of age 1 growth on cohort abundance and temperature accounted for 91% of the interannual variation in growth, which was a significant increase in r2 over that of the previously published relation with temperature alone. However, stock assessments which take into account only the previously published temperature effect on growth for this stock will probably not seriously overestimate the impact of management regulations which increase cohort abundance.

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