Variation in geographic stock area, catchability, and natural mortality of ocean shrimp (Pandalus jordani): some new evidence for a trophic interaction with Pacific hake (Merluccius productus)

1995 ◽  
Vol 52 (5) ◽  
pp. 1018-1029 ◽  
Author(s):  
Robert W. Hannah
Keyword(s):  
Mortality Rates ◽  
Fishing Effort ◽  
Trophic Interaction ◽  
Natural Mortality ◽  
Commercial Catch ◽  
Merluccius Productus ◽  
Shrimp Abundance ◽  
New Evidence ◽  
Incorrect Information ◽  
Logbook Data

Interannual variation in geographic stock area, catchability, and natural mortality of age 2 ocean shrimp (Pandalus jordani) was investigated for the years 1980–1990, using commercial catch and logbook data. Stock area changed gradually from 1980–1990, but showed wide variation, demonstrating that an assumption of constant catchability is not valid for ocean shrimp. Stock area was positively correlated with total catch, suggesting that stock area increases roughly in proportion to shrimp abundance. The time series of fishing effort and effort per unit stock area were quite different, showing that fishing effort probably gives incorrect information on time trends in ocean shrimp fishing mortality. Natural mortality rates varied widely over the study period also and were positively correlated with the abundance of age 2+ Pacific hake (Merluccius productus), a known shrimp predator. The best correlations were between natural mortality rates and the number of age 2–7 Pacific hake. Hake abundance indices that included only age 3+ fish were not significantly correlated with shrimp natural mortality rates, suggesting that if a trophic interaction exists between these two species, it may be influenced by hake recruitment events.

Dynamics and Exploitation of Lake Whitefish in Southern Georgian Bay

1966 ◽  
Vol 23 (2) ◽  
pp. 221-274 ◽  
Author(s):  
Daniel Cucin ◽  
Henry A. Regier
Keyword(s):  
Mortality Rates ◽  
Exponential Model ◽  
Fishing Effort ◽  
Natural Mortality ◽  
Coregonus Clupeaformis ◽  
Commercial Catch ◽  
Georgian Bay ◽  
Gill Nets ◽  
Size At Age ◽  
Mean Risk

Instability of the population of Coregonus clupeaformis (Mitchill) in southern Georgian Bay from 1948 to 1964 was evidently partly due to intensive fishing.The population was discrete at least from 1956 to 1964 as determined by extensive tagging. From 1948 to 1964, estimated effective fishing effort varied 10-fold and annual yields almost 20-fold, with two cycles of abundance and scarcity. Strength of 1951–59 year-classes, defined as population size at age III, varied 40-fold. In spite of the marked instability, the population was in recent years more stable than any other whitefish population in Georgian Bay or Lake Huron.Almost all the commercial catch was made with gill nets of [Formula: see text] mesh. In 1957, fishing depended largely on age VII–IX fish; by 1964, on those of age V and VI. Apparent growth rate increased during this period: in 1957 age XII fish weighed 3.4 lb; in 1964 age VI weighed 3.7 lb. From 1959 to 1964, reproduction depended largely on males age IV+ and older and longer than 17 inches, and on females age V+ and older and longer than 18 inches.Natural mortality coefficients (exponential model) averaged 0.41 for fish of the 1948–58 year-classes beyond age III. Gillnetting was largely restricted to 2 months in late spring and two in fall. In each fishing season these gill nets took about 40% of the survivors of a year-class after it became fully vulnerable, at ages V, VI, and VII during the early 1960s.Combining growth and natural mortality rates in a biomass curve indicated that individual year-classes would provide highest yields when fished intensively at age IV, or slightly earlier than they were fished in the early 1960s. Yet the only hypothesis that might explain the continued existence of a fishable population was that relatively large parts of the habitat were either legally closed or unsuitable for fishing. Evidently the fishing was intense and increasing the effort would mean risk of a population collapse.

scholarly journals Estimating natural and fishing mortality and tag reporting rate of southern rock lobster (Jasus edwardsii) from a multiyear tagging model

2001 ◽  
Vol 58 (12) ◽  
pp. 2490-2501 ◽  
Author(s):  
S D Frusher ◽  
J M Hoenig
Keyword(s):  
Mortality Rates ◽  
Fishing Effort ◽  
Reporting Rate ◽  
Standard Errors ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Rock Lobster ◽  
Relative Standard ◽  
Jasus Edwardsii ◽  
Mortality Estimates

Fishing and natural mortality rates and tag reporting rate for rock lobsters (Jasus edwardsii) in northwest Tasmania, Australia, were estimated using multiyear tagging models. These estimates are necessary for assessment of the resource. Several models were examined that had either two or three tagging events each year, and either combined sexes or kept sexes separate. The model that best described the dynamics of the fishery utilized three tagging events within a year. The year was divided into discrete periods and, within each year, fishing effort and duration of period were used to apportion fishing and natural mortalities, respectively, to the periods. The separation of fishing mortalities by sex was not found to improve the models. Although high (1.0–1.2·year–1), the instantaneous fishing mortality estimates were comparable to estimates obtained from other methods and the relative standard errors were low. Reporting rate estimates were also precise and indicated a lack of participation by the fishing industry. Estimates of natural mortality were low (0.00–0.02·year–1) but imprecise.

scholarly journals An integrated tagging model to estimate mortality rates of Albemarle Sound – Roanoke River striped bass

2017 ◽  
Vol 74 (7) ◽  
pp. 1061-1076 ◽  
Author(s):  
Julianne E. Harris ◽  
Joseph E. Hightower
Keyword(s):  
Striped Bass ◽  
Stock Assessment ◽  
Mortality Rates ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Albemarle Sound ◽  
High Reward ◽  
Accuracy And Precision ◽  
Summer Mortality ◽  
Roanoke River

We developed an integrated tagging model to estimate mortality rates and run sizes of Albemarle Sound – Roanoke River striped bass (Morone saxatilis), including (i) a multistate component for telemetered fish with a high reward external tag; (ii) tag return components for fish with a low reward external or PIT tag; and (iii) catch-at-age data. Total annual instantaneous mortality was 1.08 for resident (458–899 mm total length, TL) and 0.45 for anadromous (≥900 mm TL) individuals. Annual instantaneous natural mortality was higher for resident (0.70) than for anadromous (0.21) fish due to high summer mortality in Albemarle Sound. Natural mortality for residents was substantially higher than currently assumed for stock assessment. Monthly fishing mortality from multiple sectors (including catch-and-release) corresponded to seasonal periods of legal harvest. Run size estimates were 499 000–715 000. Results and simulation suggest increasing sample size for the multistate component increases accuracy and precision of annual estimates and low reward tags are valuable for estimating monthly fishing mortality rates among sectors. Our results suggest that integrated tagging models can produce seasonal and annual mortality estimates needed for stock assessment and management.

scholarly journals Numerical Model of Fish Exploitation – structure and application

2019 ◽  
Vol 27 (2) ◽  
pp. 86-101
Author(s):  
Paweł Buras ◽  
Wiesław Wiśniewolski
Keyword(s):  
Numerical Model ◽  
Simulation Models ◽  
Fishing Effort ◽  
Natural Mortality ◽  
Recreational Fisheries ◽  
Fisheries Resources ◽  
Fish Exploitation ◽  
The Common ◽  
Common Bream ◽  
The Impact

Abstract Fisheries simulation models are tools used for forecasting the effects of exploitation and determining the directions of managing fisheries resources. The Numerical Model of Fish Exploitation (NMFE) and its capabilities were tested on a population of common bream, Abramis brama (L.) in a dam reservoir that is exploited by commercial and recreational fisheries. Based on the designated population parameters of N0, Fij, Mi, and ei and the size and structure of the common bream population in the reservoir, the model was used to examine hypothetical simulation variants of changes in fishing intensity E1 with nets and rods, changes in fishing intensity based on actual fishing effort with nets, changes in natural mortality, changes in the size of fish caught, and the impact of this on the size of the resources. Initial catches with nets and rods were calculated. Increasing fishing effort did not translate proportionally to increased catches, and the function was curvilinear. The results of simulations that reduced the intensity of fishing with nets and decreased catch sizes concurred with data from actual catches. Simulations of changes in natural mortality had various effects on the size of catches. Reducing parameter M did not impact the level of catches, while increasing parameter M reduced the size of catches significantly.

scholarly journals Optimal fishing mortality assignment for southern hake Merluccius australis in Chile

2020 ◽  
Vol 48 (4) ◽  
pp. 613-625
Author(s):  
Felipe Lopez ◽  
Jorge Jimenez ◽  
Cristian Canales
Keyword(s):  
Mortality Rate ◽  
Economic Benefit ◽  
Mortality Rates ◽  
Fish Population ◽  
Fishing Effort ◽  
Economic Benefits ◽  
Historical Background ◽  
Total Catch ◽  
Fishing Mortality ◽  
Objective Functions

Since 1979, southern hake (Merluccius australis) has been exploited in Chile from the Bio Bio to the Magallanes regions, between the parallels 41°28.6'S and 57°S. There is evidence of a constant fishing effort and a sustained reduction of the fish population, consistent with a progressive decrease in total annual catches. Management strategies based on the maximum sustainable yield (MSY) and quota assignment/ distribution criteria have not been able to sustain acceptable biomass levels. A non-linear optimization model with two objective functions was proposed to determine an optimal total catch quota for more sustainable exploitation of this fishery. The first function maximizes the total catch over time in response to an optimal assignment of fishing mortality rates per fleet; the second function maximizes the total economic benefit associated with the total catch. The dynamics of the fish population were represented with the equations of a predictive age-structured model. Decision variables were fishing mortality rates and annual catch quotas per fleet, subject to constraints that guarantee a minimum level of biomass escape over a long-term period. The input parameters were obtained from the last stock evaluation report carried out by the Instituto de Fomento Pesquero (IFOP) of Chile. The historical background data of the fishery and the regulatory framework were relevant aspects of the methodology. Five scenarios were evaluated with the two objective functions, including a base scenario, which considered the referential mortality rate as input data as the average mortality rate per fleet from 2007 to 2012. Total economic benefits fluctuate between 102 and USD 442 million for total catches in the range of 108 to 421 thousand tons, which were obtained from maximizing the economic and biological objective functions. Economic benefit/catch ratios were reduced for scenarios with higher constraints on catch limits, and they were more efficient from a biological point of view. Situations with lighter constraints showed in general higher economic benefits and better performance ratios than those with stronger restrictions. The use of optimization models may provide a useful tool to evaluate the effect of regulations for adequate conservation and economical utilization of a limited resource.

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.

scholarly journals Stalked barnacle (Pollicipes pollicipes) harvesting in the Berlengas Nature Reserve, Portugal: temporal variation and validation of logbook data

2009 ◽  
Vol 67 (1) ◽  
pp. 19-25 ◽  
Author(s):  
David Jacinto ◽  
Teresa Cruz ◽  
Teresa Silva ◽  
João J. Castro
Keyword(s):  
Temporal Variation ◽  
Nature Reserve ◽  
Marine Protected Area ◽  
Temporal Patterns ◽  
Fishing Effort ◽  
Tidal Range ◽  
Systematic Bias ◽  
Pollicipes Pollicipes ◽  
Specific Regulation ◽  
Logbook Data

Abstract Jacinto, D., Cruz, T., Silva, T., and Castro, J. J. 2010. Stalked barnacle (Pollicipes pollicipes) harvesting in the Berlengas Nature Reserve, Portugal: temporal variation and validation of logbook data. – ICES Journal of Marine Science, 67: 19–25. Stalked barnacle (Pollicipes pollicipes) exploitation at the Berlengas Nature Reserve, Portugal, by professional harvesters has been subject to specific regulation since 2000. The only available information on barnacle exploitation there comes from catch reports (logbooks) provided by the harvesters. We evaluated the quality of the logbook information, described the temporal patterns of P. pollicipes fishing effort from 2000 to 2006 based on the logbook data, and modelled the daily fishing effort in relation to variability in oceanographic conditions. Results suggest different levels of reliability for the information contained in the logbooks: (i) information on the date of harvest seems to be reliable because 83% of the observed harvest dates were also declared; (ii) information on the quantity harvested shows a large discrepancy (mean = 31.8%) between declared and observed amounts, but we believe it can be used to analyse temporal patterns of exploitation, because there was no systematic bias (under- and overreporting was to the same extent). The total quantity of barnacles harvested between 2000 and 2006 (∼16 t year−1) was closely related to the effort applied. Daily harvesting effort was considered a function of two predictive variables (significant wave height and tidal range) and of their interaction. Neither the harvesting activity nor the resource itself seems to be at risk of collapse if such levels of pressure are maintained, but efforts should be made to increase surveillance and monitoring within the marine protected area.

Contrasting decadal trends in mortality between large and small individuals in skate populations in Atlantic Canada

2013 ◽  
Vol 70 (1) ◽  
pp. 74-89 ◽  
Author(s):  
Douglas P. Swain ◽  
Ian D. Jonsen ◽  
James E. Simon ◽  
Trevor D. Davies
Keyword(s):  
State Space ◽  
Early Life ◽  
Mortality Rates ◽  
State Space Models ◽  
Natural Mortality ◽  
Juvenile Growth ◽  
Life Stages ◽  
Grey Seal ◽  
Early Life Stages ◽  
Scotian Shelf

Mature thorny (Amblyraja radiata), winter (Leucoraja ocellata), and smooth (Malacoraja senta) skates have declined to very low abundance in the southern Gulf of St. Lawrence (SGSL) and on the eastern Scotian Shelf (ESS). We used stage-structured state-space models to examine decadal patterns in mortality rates in these skates. Mortality at early life stages (embryos in egg cases, hatchlings, and (or) small juveniles) appeared to decrease between the 1970s and the 2000s. In contrast, estimated mortality rates increased for larger individuals over this period. Although potentially confounded in models with effects of any changes in juvenile growth, the estimated increases in mortality could not instead be attributed solely to changes in growth. Increases in the mortality of large individuals appeared to reflect increases in natural mortality, possibly due to predation by grey seals. Increases in natural mortality were not evident for skates on the neighbouring western Scotian Shelf, where grey seal abundance has remained lower. Even in the absence of fishing, recovery of skates is unlikely under current ecosystem conditions in the SGSL and on the ESS.

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