Are Age-Structured Models Appropriate for Catch-Effort Data?

1985 ◽  
Vol 42 (6) ◽  
pp. 1066-1072 ◽  
Author(s):  
Donald Ludwig ◽  
Carl J. Walters
Keyword(s):  
Simulated Data ◽  
Fishing Effort ◽  
Production Model ◽  
Model Structure ◽  
Catch Per Unit Effort ◽  
Unit Effort ◽  
Production Models ◽  
Stock Assessments ◽  
Age Structured ◽  
Age Structured Model

Simulated data have been used to evaluate the performance of schemes for estimating optimum fishing effort using a simple stock-production model and R. B. Deriso's age-structured model Even when the data are generated using Deriso's model, the simpler production model generally gives as good or better estimates for the optimal effort. The only exception to this result is when data are provided with unrealistically large contrasts in effort and catch per unit effort over time. The implication of these findings is that simple production models should often be used in stock assessments based on catch/effort data, even when more realistic and structurally correct models are available to the analyst; the best choice depends on how much contrast has occurred in the historical effort and catch per unit effort data, rather than on prior knowledge about which model structure is biologically more realistic.

scholarly journals Analysis of juvenile North Atlantic albacore (Thunnus alalunga) catch per unit effort by surface gears in relation to environmental variables

2005 ◽  
Vol 62 (7) ◽  
pp. 1475-1482 ◽  
Author(s):  
Nicolas Goñi ◽  
Haritz Arrizabalaga
Keyword(s):  
North Atlantic ◽  
Environmental Variables ◽  
Negative Relationship ◽  
Generalized Least Squares ◽  
Catch Per Unit Effort ◽  
Seasonal Thermocline ◽  
Unit Effort ◽  
Negative Effect ◽  
Thunnus Alalunga ◽  
Age Structured

Abstract The relationship between the catch per unit effort (cpue) of trolling and baitboat fisheries targeting juvenile North Atlantic albacore (Thunnus alalunga, Bonnaterre, 1788) and several environmental variables was studied. A multiple linear regression and a generalized least squares model (GLS) showed a significant negative relationship between age 2 albacore trolling and baitboat cpue, and the average agitation of the sea and the duration of insolation. No clear relationship was found between the juvenile albacore cpue and sea surface temperature, precipitation, and NAO or Gulf Stream Index. Underlying processes that could explain the negative effect of agitation and insolation are discussed, especially relating to the habitat of age 2 albacore above the seasonal thermocline. Results highlight the necessity of considering environmental variables in the standardization of albacore cpue series used for calibrating age-structured stock assessments.

Short-term Forecasting in Marine Fish Stocks

1981 ◽  
Vol 38 (10) ◽  
pp. 1247-1254 ◽  
Author(s):  
Max Stocker ◽  
Ray Hilborn
Keyword(s):  
Time Series ◽  
Marine Fish ◽  
Management Practice ◽  
Model Fitting ◽  
Production Model ◽  
Catch Per Unit Effort ◽  
Short Term ◽  
Fish Stocks ◽  
Production Models ◽  
The Difference

The predictive power of stock production models and simple time series methods was considered for five marine fish stocks. The distinction between model fitting and forecasting future short-term catch is discussed, as is the difference between techniques to forecast short-term yield, and techniques to calculate long-term management practice. Fox's procedure for fitting Pella and Tomlinson's stock production model, Schnute's method for fitting Schaefer's model, and Gulland's method are all considered. We found that all methods except that of Gulland work well for some stocks, and the relative performance of the methods depends upon the exploitation history of the stock. In several instances one of the best forecasts of next year's catch per unit effort (CPUE) was the previous year's CPUE, emphasizing the fact that a good forecasting technique may have no utility in determining management policies.Key words: production models, catch and effort, fisheries, management, catch forecasting, time series

scholarly journals Pêche Et Caractéristiques Morphologiques D’un Poisson-Chat Endémique Synodontis Punctifer (Daget, 1964) Dans Le Barrage Électrique De Taabo (Côte d’Ivoire)

2018 ◽  
Vol 14 (15) ◽  
pp. 101
Author(s):  
Hervé Oussou Koffi ◽  
Diaha N’guessan Constance ◽  
Soro Yaya ◽  
N’Da Konan
Keyword(s):  
Sex Ratio ◽  
Condition Factor ◽  
Morphological Characteristics ◽  
Fishing Effort ◽  
Annual Production ◽  
Allometric Growth ◽  
Catch Per Unit Effort ◽  
Large Size ◽  
Unit Effort ◽  
Significant Difference

A study of Synodontis punctifer (family: Mochokidae) of Taabo Lake was conducted from October 2015 to September 2016. This was carried out so as to evaluate its quantity (biomass) caught by fishing and also its morphological characteristics. The fish were caught using gillnets at 4 sites of the lake and different measurements were made. The fishing effort was 23 to 11 fishermen / day in Taabo city, 17 to 11 fishermen / day in Courandjourou, 13 to 5 fishermen / day in Ahondo, and 8 to 3 fishermen / day in Taabo village. The catch per unit effort (CPUE) ranged from 17.7 to 3.7 g / fisherman / day, 9.2 to 1.2 g / fisherman / day, 8.3 to 0.7 g / fisherman /day, 8 to 1g / fisherman / day at Ahondo, Courandjourou, Taabo city and Taabo village, respectively. The overall annual production was estimated at 2199.3 kg, i.e. 817 kg (40%) at Ahondo, 788.3 kg (35%) at Courandjourou, 462.5 kg (20%) at Taabo, and 131.5 kg (5%) in Taabo village. The overall sex ratio (1: 1.33) was in favor of females. Individuals have negative allometric growth at all sites with values ranging from 1.72 to 2.89. The condition factor does not vary significantly between different categories of individuals (ANOVA, F = 2.79, p ˃ 0.05). A significant difference was observed between the average sizes of the individuals of the different sites (test, p˂0,05). The large size specimens were captured at Ahondo, mean (avg = 15.38 ± 1.68 cm FL). In Courandjourou, the sizes were intermediate (avg = 13.63 ± 1.64 cm LF). Smalls sizes have been observed in Taabo city (mean= 12.37 ± 1.24 cm FL) and Taabo village (mean= 15.58 ± 1.58 cm FL).

scholarly journals Effect of hook and bait type on catch per unit effort in the Aegean Sea demersal longline fishery

2021 ◽  
Vol 38 (2) ◽  
pp. 181-188
Author(s):  
Ozan Soykan ◽  
Cemil Sağlam ◽  
İlker Aydın ◽  
Hasan Tuncay Kınacıgil
Keyword(s):  
Sparus Aurata ◽  
Length Distribution ◽  
Aegean Sea ◽  
Fishing Effort ◽  
Longline Fishery ◽  
Total Catch ◽  
Catch Per Unit Effort ◽  
Unit Effort ◽  
Catch Composition ◽  
The Impact

This study aimed to determine the impact of hook and bait type on the catch composition and catch per unit effort. Effects of hook and bait types on catch composition, catch per unit effort (CPUE), length and weight distributions in demersal longline fishery were determined by experimental surveys on demersal longline sets in the Aegean Sea. A total of 12 samplings corresponding to 4800 hook fishing effort were performed between April 2014 and September 2014. Two bait types; sardine (Sardina pilchardus) and grooved razor shell (Solen marginatus) and two hook types; J-hook and C-hook were tested. CPUE values were calculated for each species and assessed between different hook-bait combinations. A total of 623 individuals were captured belonging to 3 families and 9 species. It was found that more than 60% of total catch was captured by grooved razor shell and more than 50% of the total catch was caught with J type hook. J hook was found to be close to significant (p=0.06) and grooved razor shell was found significant (p=0.02) for CPUE. The effect of bait type was found to be more significant than that of hook type for CPUE and length distribution. Hook-bait combination differed according to species and C hook baited with sardine was determined to be the best combination for Sparus aurata as the most targeted fish in the study area. Discard ratio was calculated to be 34% in terms of weight and 42.5% in terms of total number of individuals for pooled data. The condition value (K) of the species ranged from 1.05 to 1.68 and differed according to bait type. Most of the high commercial value species caught with any hook-bait combination experimented within this study are larger than minimum fishing length according to minimum landing size regulations of Turkish fishery and maturity studies.

scholarly journals Fishing Effort and Associated Catch per Unit Effort for Small-Scale Fisheries in the Mozambique Channel Region: 1950–2016

2021 ◽  
Vol 8 ◽  
Author(s):  
Dirk Zeller ◽  
Gabriel M. S. Vianna ◽  
Matthew Ansell ◽  
Angie Coulter ◽  
Brittany Derrick ◽  
...  
Keyword(s):  
Fishing Effort ◽  
Small Scale ◽  
Catch Per Unit Effort ◽  
Important Species ◽  
Small Scale Fisheries ◽  
Mozambique Channel ◽  
Fishing Vessels ◽  
Unit Effort ◽  
Fishing Capacity ◽  
Channel Region

The Mozambique Channel region in East Africa has diverse marine ecosystems and serves as a migratory corridor for economically important species. Local and foreign industrial fisheries operate in the Mozambique Channel, but regional small-scale fisheries are the crucially important fisheries that provide food security, livelihoods, and economic opportunities for rural coastal communities. This study reconstructed and investigated trends in the fishing effort and catch per unit effort (CPUE) of small-scale marine fisheries in four Exclusive Economic Zones (EEZ) that constitute the Mozambique Channel, i.e., Union of Comoros, Madagascar, Mayotte, and Mozambique, from 1950 to 2016. Effective fishing effort for small-scale fisheries in the form of fishing capacity in kWdays (i.e., kilowatt days) was derived using the number, length, motorization (engine power) by fishing vessels, as well as an approximate human-powered equivalent for shore-based fishers without vessels, as well as days of fishing per year. Effective small-scale fishing effort in the Mozambique Channel increased by nearly 60 times from just over 386,000 kWdays in 1950 to over 23 million kWdays in 2016. Correspondingly, the overall small-scale CPUE, based on previously and independently reconstructed catch data declined by 91% in the region as a whole, from just under 175 kg⋅kWday–1 in the early 1950s to just over 15 kg⋅kWday–1 in recent years. All four EEZs showed the strongest declines in the small-scale CPUE in the earlier decades, driven by motorization and growth in vessel numbers impacting effective fishing effort. Increased motorization combined with a substantial growth in overall vessel numbers were the drivers of the increasing fishing effort and decreasing CPUE, and clearly suggest that continuing to increase the fishing capacity of small-scale fisheries in the absence of effective and restrictive management actions may exacerbate overexploitation risk.

Utilization rate of fish resources in Banggai Laut waters

2020 ◽  
Vol 1 (2) ◽  
Author(s):  
Aswad Eka Putra
Keyword(s):  
Fishing Effort ◽  
Utilization Rate ◽  
Catch Per Unit Effort ◽  
Surplus Production ◽  
Fish Resources ◽  
Unit Effort ◽  
Rate Of Increase ◽  
Increasing Trend ◽  
Fish Group ◽  
Method Approach

Capture fisheries is one of the leading sectors that drive the economy of Banggai Laut Regency. Improved fishing technology is related to fishing efforts that will affect the sustainability of fish resource stocks in the waters of Banggai Laut Regency. This study aims to identify the rate of utilization of fish resources in an effort to develop a sustainable fisheries sector in Banggai Laut waters. The method approach used is "Surplus Production". This method serves as an estimator of the relative abundance of a fish resource in the waters of Banggai Laut Regency which is based on the catch per unit of fishing effort. The results showed that the capability of the fishing fleet in Banggai Laut Regency has not been able to reach potential fishing areas. The catch per unit effort (CPUE) of fish resources in Banggai Laut Regency still shows an increasing trend with the highest rate of increase by other fish group including crustaceans and mollusks, about 0.160 tons/unit in the 2014-2016 period. Meanwhile, the catch per unit effort of the large pelagic fish group showed an increasing trend with the lowest rate of increase, about 0.001 tons/unit in the 2014-2016 period. Therefore the utilization rate of fish resources in the waters of Banggai Laut Regency is still classified as under exploited.

scholarly journals Endogenous fishing mortalities: a state-space bioeconomic model

2017 ◽  
Vol 74 (9) ◽  
pp. 2437-2447 ◽  
Author(s):  
José-María Da-Rocha ◽  
Javier García-Cutrín ◽  
María-José Gutiérrez ◽  
Ernesto Jardim
Keyword(s):  
Total Mortality ◽  
Fishing Effort ◽  
Bioeconomic Model ◽  
Fishing Mortality ◽  
Northern Spain ◽  
Management Regime ◽  
Target Management ◽  
Age Structured ◽  
Age Structured Model ◽  
Stock Abundance

Abstract A methodology that endogenously determines catchability functions that link fishing mortality with contemporaneous stock abundance is presented. We consider a stochastic age-structured model for a fishery composed by a number of fishing units (fleets, vessels or métiers) that optimally select the level of fishing effort to be applied considering total mortalities as given. The introduction of a balance constrain which guarantees that total mortality is equal to the sum of individual fishing mortalities optimally selected, enables total fishing mortality to be determined as a combination of contemporaneous abundance and stochastic processes affecting the fishery. In this way, future abundance can be projected as a dynamic system that depends on contemporaneous abundance. The model is generic and can be applied to several issues of fisheries management. In particular, we illustrate how to apply the methodology to assess the floating band target management regime for controlling fishing mortalities which is inspired in the new multi-annual plans. Our results support this management regime for the Mediterranean demersal fishery in Northern Spain.

Separating recruitment and mortality time lags for a delay-difference production model

2015 ◽  
Vol 72 (2) ◽  
pp. 161-165 ◽  
Author(s):  
Emilius A. Aalto ◽  
E.J. Dick ◽  
Alec D. MacCall
Keyword(s):  
Stock Assessment ◽  
Recovery Period ◽  
Time Lag ◽  
Simulated Data ◽  
Assessment Method ◽  
Production Model ◽  
Time Lags ◽  
Age At Maturity ◽  
Production Models ◽  
Pacific Rockfish

Many fishery production models implicitly incorporate a single time lag for both recruitment and mortality despite the fact that in populations of breeding adults, deaths occur yearly while the entry of new adults comes from juveniles born potentially many years prior to adulthood. Models that do not account for this difference in timing will overestimate abundance for a decreasing stock and underestimate increases during a recovery period. We investigated the effect of incorporating unequal recruitment and mortality time lags into depletion-based stock reduction analysis (DB-SRA), a stock assessment method for data-poor species. Using both simulated data and catch series of Pacific rockfish (Sebastes spp.), we found that for declining stocks with no mortality delay and a recruitment time lag equal to age-at-maturity, estimated overfishing limits were up to 40% lower than those from the model with both time lags equal to age-at-maturity. Deviation between the two models’ predictions increases with age-at-maturity and natural mortality rate, suggesting that time lag separation is most important for long-lived species. We propose a correction factor for net production models that eliminates stock overestimation due to implicitly equal time lags.

Spatio-temporal distribution of longline catch per unit effort, sea surface temperature and Atlantic marlin

2003 ◽  
Vol 54 (4) ◽  
pp. 409 ◽  
Author(s):  
C. Phillip Goodyear
Keyword(s):  
Temporal Distribution ◽  
Fishing Effort ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Fishing Mortality ◽  
Catch Per Unit Effort ◽  
Surface Temperatures ◽  
Unit Effort ◽  
Spatio Temporal ◽  
Catch Rates

Atlantic blue and white marlin are currently overfished, primarily as a result of bycatch in pelagic longlines directed at other species. One possible management measure to reduce fishing mortality on these species would be to restrict fishing effort in times and places with exceptionally high marlin catch per unit effort (CPUE). The International Commission for the Conservation of Atlantic Tunas maintains a database of catch and catch-effort statistics of participating nations. These data were analysed to determine whether the distribution of CPUE is sufficiently heterogeneous in time and space that such measures might provide meaningful management alternatives. The resulting distributions of catch rates were also contrasted with monthly average sea surface temperatures to examine the possible association between temperature and CPUE. The results show spatio-temporal heterogeneity in catch rates that may be partly explained by seasonal changes in sea surface temperatures. The time–area concentrations of high CPUE differ between the species. This observed heterogeneity might be exploited to develop alternatives for reducing fishing mortality for future management of the fisheries, but additional research is needed to refine the spatial scale of the analysis and to more fully understand the factors contributing to the observed distribution.

Estimating and testing non-additivity in fishing mortality: implications for detecting a fisheries collapse

2002 ◽  
Vol 59 (4) ◽  
pp. 597-601 ◽  
Author(s):  
Ransom A Myers ◽  
Terrance J Quinn II
Keyword(s):  
Population Model ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Mortality ◽  
Catch Per Unit Effort ◽  
Structured Population Model ◽  
Structured Population ◽  
Powerful Approach ◽  
Age Structured ◽  
Age Structured Model

Common in many fisheries collapses is a disproportionate increase in fishing mortality at younger ages. One mechanism by which this increase could occur is sufficient depletion of the population at older ages due to strong overfishing, which leads to targeting of younger fish. Thus, it is essential for assessments to estimate and test for a change in selectivity in the fishery. We introduce a simple and powerful approach based upon Tukey's one degree of freedom test for non-additivity. This approach can be applied within any statistical age-structured population model that estimates selectivity. We illustrate the approach with data from Atlantic cod (Gadus morhua) from St. Pierre Bank, Canada. The results show significant non-additivity in fishing mortality that translates into an increase in selectivity on younger ages when fishing mortality is high. This approach also can be applied to the output of an age-structured model that assumes catch-at-age is known without error or to any survey or catch-per-unit-effort data for which estimates of abundance are made by year and age. We believe that this approach should be routinely applied in assessments, particularly when overfishing has led to depletion of the overall population or to truncation of the age structure.

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