Reply to the comment by Francis on “Differences in predicted catch composition between two widely used catch equation formulations”Appears in Can. J. Fish. Aquat. Sci. 66: 126–132.

2010 ◽  
Vol 67 (4) ◽  
pp. 766-768
Author(s):  
Trevor A. Branch
Keyword(s):  
Entire Population ◽  
Fishing Gear ◽  
Fishing Mortality ◽  
Gear Selectivity ◽  
Catch Composition ◽  
Continuous Formulation ◽  
Discrete Formulation ◽  
Model Fits

Francis (2010. Can. J. Fish. Aquat. Sci. 67: 763–765) writes a thoughtful response detailing concerns with my suggestion that the continuous (Baranov) catch formulation is preferable to the discrete catch formulation when fishing mortality is high (T.A. Branch. 2009. Can. J. Fish. Aquat. Sci. 66: 126–132). He suggests the discrete formulation allows for multiple gear encounters and that formulation choice should depend on which formulation better fits the data. Here I first distinguish between gear selectivity and availability and then show that our two views are complementary: the original assumes fish groups with differing gear selectivity but full availability, whereas Francis assumes fish groups fully selected by fishing gear but with differing availability. I maintain that the discrete formulation only models a single instantaneous interaction between fish and fishing gear and therefore only part of the population can be caught if fish groups have equal gear selectivity that is less than 100%, whereas under the same assumptions, the continuous formulation would allow the entire population to be caught. Finally, when the balance between gear selectivity and availability is unknown, I agree that formulation choice could be driven by model fits to the data, although formulation choice could also be based on how the fishery operates.

Differences in predicted catch composition between two widely used catch equation formulations

2009 ◽  
Vol 66 (1) ◽  
pp. 126-132 ◽  
Author(s):  
Trevor A. Branch
Keyword(s):  
Age Groups ◽  
Correct Choice ◽  
Fishing Gear ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Gear Selectivity ◽  
Different Types ◽  
Catch Composition ◽  
Continuous Formulation ◽  
Discrete Formulation

Fishing gear selectivity varies among different types of fish (e.g., species, age, sex, or length groups), but their relative catch composition also depends on the fishing process. The continuous (Baranov) formulation assumes that fishing mortality and natural mortality occur together during the fishing season and that there are multiple encounters between fish and fishing gear. For this formulation, predicted catch composition depends on fishing mortality, and at high fishing mortality levels the entire population can be caught provided the selectivity is nonzero for all age groups. In contrast, the discrete formulation assumes that fishing mortality occurs separately from natural mortality and that fish encounter at most only one set of fishing gear. The discrete formulation is easier to compute, but the predicted catch composition is independent of fishing mortality, and some of the population remains unexploitable. The correct choice of equations depends on the particular fishery and fishing mortality levels; at low fishing mortality levels the predictions differ little, but at high fishing mortality levels where multiple gear encounters could occur, the continuous formulation is preferable.

Comment on “Differences in predicted catch composition between two widely used catch equation formulations”Appears in Can. J. Fish. Aquat. Sci. 66: 126–132.

2010 ◽  
Vol 67 (4) ◽  
pp. 763-765 ◽  
Author(s):  
R. I.C. Chris Francis
Keyword(s):  
Stock Assessment ◽  
Fishing Gear ◽  
Fishing Mortality ◽  
Instantaneous Rate ◽  
Exploitation Rate ◽  
Catch Composition ◽  
Continuous Formulation

Branch (2009. Can. J. Fish. Aquat. Sci. 66: 126–132) described the two most common catch equation formulations in stock assessment models: the continuous (Baranov) one, which represents fishing mortality as an instantaneous rate, F, and the discrete one, in which it is represented as an exploitation rate, u. He claimed that the continuous formulation is preferable at high fishing mortality where a fish could encounter multiple sets of gear within a year. This claim is wrong for two reasons. First, it is based on the false supposition that the discrete catch equations require the assumption that fish encounter at most only one set of fishing gear in a year. Second, it is not possible to determine, for a specific stock assessment, whether one formulation is preferable to another solely on the basis of information about the fishery. The appropriate way to make this decision is to see which fits the data better.

scholarly journals PENDEKATAN BIONOMI PADA PELUANG PENGEMBANGAN PERIKANAN TANGKAP DI KABUPATEN KEPULAUAN TALAUD

2012 ◽  
Vol 1 (2) ◽  
pp. 57
Author(s):  
Jeti Pulu ◽  
Mulyono S. Baskoro ◽  
Daniel R. Monintja ◽  
Budhi H. Iskandar ◽  
Akhmad Fauzi
Keyword(s):  
Open Access ◽  
Economic Value ◽  
Secondary Data ◽  
Primary Data ◽  
Fishing Gear ◽  
Fish Production ◽  
Resource Rent ◽  
Illegal Fishing ◽  
Fishing Gears ◽  
Catch Composition

The research is aimed to reveal opportunity development of the capture fisheries in Talaud Islands Regency by using bionomy approach with Gordon-Schaefer model (Fauzy, 2005) con-cerning the dominant of illegal fishing activities around the area. The research was started by co-llected some secondary data on fish production and number of fishing units. Primary data were collected on catch composition and types of fishing gear. Gordon-Schaefer methods was applied to evaluate the tuna and skipjack resources in the area. The troll and pole and line are indicated as the dominant fishing gears used to catch the skipjack and tuna. In case of open access condition, the production will end up to 25,09 tons, while the resource rent will be end up to zero. For the development, simulations were exercised in 3 scenarios: 1) scenario of enhancing domestic fleet, 2) scenario of illegal fishing, and 3) scenario of net surplus. With those scenarios, if the illegal fishing could be eliminated, the capture fisheries in this regency could render economic value to 10 billion rupiah.

scholarly journals Discard Avoidance by Improving Fishing Gear Selectivity: Helping the Fishing Industry Help Itself

2018 ◽  
pp. 279-296 ◽  
Author(s):  
Finbarr G. O’Neill ◽  
Jordan Feekings ◽  
Robert J. Fryer ◽  
Laurence Fauconnet ◽  
Pedro Afonso
Keyword(s):  
Fishing Gear ◽  
Fishing Industry ◽  
Gear Selectivity ◽  
Fishing Gear Selectivity

scholarly journals Using a double codend to reduce discard mortality

2009 ◽  
Vol 66 (10) ◽  
pp. 2077-2081 ◽  
Author(s):  
Matt K. Broadhurst ◽  
Russell B. Millar ◽  
Sebastian S. Uhlmann
Keyword(s):  
Cloud Cover ◽  
Marine Science ◽  
Total Catch ◽  
Fishing Mortality ◽  
Short Term ◽  
Discard Mortality ◽  
Conventional Design ◽  
Gear Selectivity ◽  
Negative Impacts

Abstract Broadhurst, M. K., Millar, R. B., and Uhlmann, S. S. 2009. Using a double codend to reduce discard mortality. – ICES Journal of Marine Science, 66: 2077–2081. Traditional technical strategies for mitigating collateral fishing mortality have involved improving gear selectivity (to reduce bycatch) and, more recently, concomitant changes to onboard handling procedures to reduce some of the negative impacts to the remaining discards. A less common approach is to modify gears physically to minimize deleterious catching mechanisms and subsequent mortalities during fishing. This study aimed to investigate the utility of the latter category of modifications for penaeid trawls by separating a codend into two compartments (termed a double codend) to alleviate interactions between catches. Compared with a conventional design, the double codend significantly reduced the immediate (from 17.1 to 13.8%) and short-term (22.5 to 17.1%) mortalities of discarded juvenile school prawns (Metapenaeus macleayi). The effectiveness of the double codend remained independent of other factors known to affect the fate of discarded juvenile M. macleayi, including cloud cover and, owing to minimal variability, the weight of the total catch. However, irrespective of the codend configuration, overall mortalities were also positively correlated with the quantity of jellyfish. We conclude that when combined with modifications to improve selectivity and appropriate onboard handling strategies, compartmentalizing codend catches could cumulatively reduce unaccounted fishing mortality.

scholarly journals Mapping nearly a century and a half of global marine fisheries: 1869 to 2015

2018 ◽  
Author(s):  
Reg Watson ◽  
Alex Tidd
Keyword(s):  
Satellite Tracking ◽  
Data Sources ◽  
Fishing Gear ◽  
Tracking Data ◽  
Marine Fisheries ◽  
Pelagic Species ◽  
Fishing Gears ◽  
Catch Composition ◽  
Marine Fishing ◽  
Spatial Cell

Understanding global fisheries patterns contributes significantly to their management. By combining harmonized unmapped data sources with maps from satellite tracking data, regional tuna management organisations, the ranges of fished taxa, the access of fleets and the logistics of associated fishing gears the expansion and intensification of marine fisheries for nearly a century and half (1869–2015) is illustrated. Estimates of industrial, non-industrial reported, illegal/unreported (IUU) and discards reveal changes in country dominance, catch composition and fishing gear use. Catch of industrial and non-industrial marine fishing by year, fishing country, taxa and gear by 30-min spatial cell broken to reported, IUU and discards is available. Results show a historical increase in bottom trawl with corresponding reduction in the landings from seines. Though diverse, global landings are now dominated by demersal and small pelagic species.

scholarly journals Spatiotemporal Variation in the Catch Composition and Abundance of Precious Corals Around Taiwan: Implications for Fisheries Management

2021 ◽  
Vol 8 ◽  
Author(s):  
Chih-Shin Chen
Keyword(s):  
Fisheries Management ◽  
Regional Cooperation ◽  
Fishing Effort ◽  
Spatiotemporal Variation ◽  
Northwest Pacific ◽  
Fishing Gear ◽  
Fishery Resource ◽  
Religious Importance ◽  
Fishing Fleets ◽  
Catch Composition

Precious corals are a fishery resource of cultural and religious importance. Because of their high commercial value, precious corals have been exploited for several centuries in the Mediterranean and for almost one century in the Northwest Pacific. Taiwanese fishing fleets have harvested precious corals since the 1920s; however, management regulations have only been promulgated since January 2009, when the catch and effort data of fisheries began to be collected. This study examined spatiotemporal variation in the catch composition and abundance of precious corals Corallium, Hemicorallium, and Pleurocorallium spp. around Taiwan using fishery data from 2009 to 2018 and discussed its implications for fisheries management. Licenses are issued for 60 vessels annually, and the annual total catch was 2.9–3.5 t between 2009 and 2018, peaking in 2015 and then decreasing sharply in 2016. Because of the use of non-selective fishing gear, dead and fossilized colonies were included in the total catches of the fishery. Fossilized colonies were predominant (average 78.5%) in the total catches, whereas the proportion of live colony catches accounted for less than 5%. Pink coral (Momo) was predominant in the total and live colony catches during the 10-year period. The Taiwanese precious coral fishing fleets are restricted to harvesting precious corals in five designated fishing grounds (DFGs; A–E). The fishing effort (vessel⋅day) was mainly concentrated in DFG-A (average 56.6%), which accounted for an average of 63.9% of the total catches. However, the live colony catches were largest in DFG-E (average 39.9%) and DFG-A (average 39.6%). The annual catch rates of live colonies decreased in two major fishing grounds (DFGs-A and DFG-B), whereas it increased in two minor fishing grounds (DFGs-C and DFG-D). The temporal variation in occurrence rates of live colonies decreased between 2015 and 2018, indicating a declining trend for precious coral populations around Taiwan. These results indicate that an unsustainable condition may occur in the near future if the precious corals continue to be harvested at the current scale. Revised regulations for the Taiwanese precious coral fishery should contain proposals on fishing gear modifications, a rotational harvesting scheme, or both; such measures can contribute to the conservation of precious coral populations. Regional cooperation in fisheries management is necessary to achieve the sustainable development of precious corals and their fisheries in the Northwest Pacific.

scholarly journals Assessment of a small-scale fishery: Lane Snapper (Lutjanus synagris) using a length metric method

2020 ◽  
Author(s):  
Liliana Sierra Castillo ◽  
Masami Fujiwara
Keyword(s):  
Small Scale ◽  
Fishing Gear ◽  
Optimal Length ◽  
Limited Availability ◽  
Small Scale Fisheries ◽  
Catch Data ◽  
Gear Selectivity ◽  
Fishing Gear Selectivity ◽  
High Level

ABSTRACTSmall-scale fisheries are hard to assess because of the limited availability of data. Therefore, a method requiring easy-to-obtain catch-data is important for the assessment and management of small-scale fisheries. The objectives of this study were to assess the effect of fishing gear selectivity on a length-based metric method proposed by Froese by estimating three indicators using catch-data from Lane Snapper (Lutjanus synagris) collected in Honduras. These indicators are (1) the percentage of mature individuals in the catch, (2) the percentage of fish within the range of estimated optimal lengths to be captured and (3) the percentage of fish larger than the optimal length. These indicators determine the level of overfishing. The indicators were estimated separately for catchdata corresponding to gillnets, and each indicator was estimated with and without selectivity correction. Selectivity and mesh sizes of the fishing gear had a major impact in the estimation of indicators 1 and 2. As for indicator 3, it consistently showed a high level of exploitation. The three estimated indicators suggested that the Lane Snapper fishery in Honduras, is experiencing overfishing. Overall, the method proposed by Froese appears to be promising for the assessment of small-scale fisheries, but it should be used cautiously.

scholarly journals Inferring genetic connectivity in real populations, exemplified by coastal and oceanic Atlantic cod

2018 ◽  
Vol 115 (19) ◽  
pp. 4945-4950 ◽  
Author(s):  
Ingrid Spies ◽  
Lorenz Hauser ◽  
Per Erik Jorde ◽  
Halvor Knutsen ◽  
André E. Punt ◽  
...  
Keyword(s):  
Genetic Differentiation ◽  
Population Size ◽  
Extreme Values ◽  
Atlantic Cod ◽  
Genetic Connectivity ◽  
Fishing Gear ◽  
The North ◽  
Empirical Estimates ◽  
Gear Selectivity ◽  
Fishing Gear Selectivity

Genetic data are commonly used to estimate connectivity between putative populations, but translating them to demographic dispersal rates is complicated. Theoretical equations that infer a migration rate based on the genetic estimator FST, such as Wright’s equation, FST ≈ 1/(4Nem + 1), make assumptions that do not apply to most real populations. How complexities inherent to real populations affect migration was exemplified by Atlantic cod in the North Sea and Skagerrak and was examined within an age-structured model that incorporated genetic markers. Migration was determined under various scenarios by varying the number of simulated migrants until the mean simulated level of genetic differentiation matched a fixed level of genetic differentiation equal to empirical estimates. Parameters that decreased the Ne/Nt ratio (where Ne is the effective and Nt is the total population size), such as high fishing mortality and high fishing gear selectivity, increased the number of migrants required to achieve empirical levels of genetic differentiation. Higher maturity-at-age and lower selectivity increased Ne/Nt and decreased migration when genetic differentiation was fixed. Changes in natural mortality, fishing gear selectivity, and maturity-at-age within expected limits had a moderate effect on migration when genetic differentiation was held constant. Changes in population size had the greatest effect on the number of migrants to achieve fixed levels of FST, particularly when genetic differentiation was low, FST ≈ 10−3. Highly variable migration patterns, compared with constant migration, resulted in higher variance in genetic differentiation and higher extreme values. Results are compared with and provide insight into the use of theoretical equations to estimate migration among real populations.

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