scholarly journals Quantifying relative fishing impact on fish populations based on spatio-temporal overlap of fishing effort and stock density

2013 ◽  
Vol 70 (3) ◽  
pp. 618-627 ◽  
Author(s):  
Morten Vinther ◽  
Margit Eero
Keyword(s):  
Fishing Effort ◽  
Fish Populations ◽  
Fishing Mortality ◽  
Fishing Impact ◽  
Management Measures ◽  
Stock Assessments ◽  
Spatio Temporal ◽  
Substantial Decline ◽  
The Impact ◽  
Temporal Overlap

Abstract Vinther, M., and Eero, M. 2013. Quantifying relative fishing impact on fish populations based on spatio-temporal overlap of fishing effort and stock density. – ICES Journal of Marine Science, 70: 618–627. Evaluations of the effects of management measures on fish populations are usually based on the analyses of population dynamics and estimates of fishing mortality from stock assessments. However, this approach may not be applicable in all cases, in particular for data-limited stocks, which may suffer from uncertain catch information and consequently lack reliable estimates of fishing mortality. In this study we develop an approach to obtain proxies for changes in fishing mortality based on effort information and predicted stock distribution. Cod in the Kattegat is used as an example. We use GAM analyses to predict local cod densities and combine this with spatio-temporal data of fishing effort based on VMS (Vessel Monitoring System). To quantify local fishing impact on the stock, retention probability of the gears is taken into account. The results indicate a substantial decline in the impact of the Danish demersal trawl fleet on cod in the Kattegat in recent years, due to a combination of closed areas, introduction of selective gears and changes in overall effort.

Simulations of the impact of different temporal and spatial allocations of fishing effort on fishing mortality in a lobster (Homarus americanus) fishery

2002 ◽  
Vol 59 (5) ◽  
pp. 899-909 ◽  
Author(s):  
Louise Gendron ◽  
Jean-Claude Brêthes
Keyword(s):  
Homarus Americanus ◽  
Fishing Effort ◽  
Fishing Mortality ◽  
Management Scenarios ◽  
Spatially Explicit Model ◽  
Offshore Area ◽  
Management Measures ◽  
Exploitation Rate ◽  
Temporal And Spatial ◽  
The Impact

A spatially explicit model is proposed to assess the impact on fishing mortality of modifying effort patterns for an American lobster (Homarus americanus) fishery. A two-box (offshore and inshore grounds) model is developed for the 1995 lobster fishery season in the Magdalen Islands (Quebec). It considers lobster migration and fisher's temporal and spatial effort dynamics to estimate within-season catchability patterns and exchange rates between the two spatial units. Different management scenarios are simulated: reducing nominal fishing effort and changing its temporal (season's length) and spatial (area closures) allocations. Catchability showed a strong temporal trend, being highest during the first 3 weeks and declining regularly afterwards. The model indicated a continuous migration toward the inshore during the fishing season and that a significant amount of biomass remained offshore. As a result, reducing fishing effort at the beginning of the season would have the greatest impact on exploitation rate. Allowing less effort in the offshore area would also reduce the exploitation rate significantly. Restricting effort to the inshore area, as it was 25 years ago, reduced substantially the exploitation rate. This model represents the first attempt to analyze in-season fishery dynamics and should be useful to further assess the impact of management measures.

Spatial and Temporal Overlap of the American Lobster (Homarus americanus) and Sea Scallop (Placopecten magellanicus) as Related to the impact of Inshore Scallop Dragging

1992 ◽  
Vol 49 (7) ◽  
pp. 1486-1492 ◽  
Author(s):  
D. L. Roddick ◽  
R. J. Miller
Keyword(s):  
Nova Scotia ◽  
Homarus Americanus ◽  
Fishing Effort ◽  
The Other ◽  
American Lobster ◽  
Placopecten Magellanicus ◽  
Time And Space ◽  
Sea Scallop ◽  
The Impact ◽  
Temporal Overlap

Assessment of the damage of one fishery by another requires knowledge of the overlap, in time and space, of the damaging fishing effort and the abundance of the damaged species, as well as a measure of the rate of damage. This approach was used to measure the impact of inshore scallop dragging on lobsters in Nova Scotia. Areas of reported co-occurrence of lobster and scallop grounds were surveyed by divers to determine the extent of overlap. Only 2 of 52 sites surveyed had lobsters on scallop grounds that could be dragged. Divers surveyed one site six times during 1987 and 1988 and found lobsters most abundant during August and September. Only 2% of the lobsters in the path of scallop drags were either captured or injured. The estimated value of lobsters destroyed by dragging for scallops during periods of peak lobster abundance was minor: $757 at one site and $176 at the other. Restricting dragging to periods of low lobster abundance significantly reduces this cost.

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 First Assessment of the Thryssa vitrirostris (Engraulidae) Beach Seine Fishery in Northeastern Mozambique

J ◽  
2018 ◽  
Vol 1 (1) ◽  
pp. 116-132
Author(s):  
Bonifácio Manuessa ◽  
Eurico Morais ◽  
Teresa Cerveira Borges ◽  
Maria Teodósio ◽  
Francisco Leitão
Keyword(s):  
Standard Length ◽  
Growth Parameters ◽  
Mesh Size ◽  
Fishing Effort ◽  
Fishing Mortality ◽  
Beach Seine ◽  
Management Measures ◽  
Exploitation Rate ◽  
Exploitation Status ◽  
Sustainable Fishery

Monthly length-frequency data, from 2009 to 2014, was used to estimate the growth parameters, mortality, and spawning season, and to assess the exploitation status of Thryssa vitrirostris (Engraulidae) fisheries in Pebane. The von Bertalanffy asymptotic length (L∞) and growth rate (K) were 25.1 cm (standard length) and 0.41 per year (standard length), respectively. Two proxy recruitment peaks were found: the first peak of recruitment occurs from April to July, and the second recruitment peak from September to October. The total estimated mortality rates (Z), natural mortality (M), and fishing mortality (F) were Z = 1.31, M = 0.92, and F = 0.39. For the beach seine gear, the size at first catch of T. vitrirostris was Lc25 = 4.43 cm. The 50% retention size of the catch was Lc50 = 5.39 cm. The retention probability analyses revealed a large rate of juvenile fishing mortality (54.2%). The estimated exploitation rate (0.30) was below the maximum exploitation rate (0.48), and above the optimal sustainable exploitation rate (E50 = 0.28), evidencing a sustainable fishery. However, under such an exploitation regime, it is advised that a continuously monitoring-survey of T. vitrirostris is maintained. An increase in migration of fishermen has been recently recorded in Pebane, due to its rich fisheries, which can increase the fishing effort and the risk of overexploitation if management measures (such as mesh size increase) are not taken in advance.

scholarly journals The Impact of Price on the Profits of Fishermen Exploiting Tritrophic Prey-Predator Fish Populations

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Meriem Bentounsi ◽  
Imane Agmour ◽  
Naceur Achtaich ◽  
Youssef El Foutayeni
Keyword(s):  
Equilibrium Points ◽  
Price Change ◽  
Fishing Effort ◽  
Fish Populations ◽  
Bioeconomic Model ◽  
Top Predator ◽  
Nash Equilibrium Problem ◽  
Change Mechanism ◽  
The Stability ◽  
The Impact

We define and study a tritrophic bioeconomic model of Lotka-Volterra with a prey, middle predator, and top predator populations. These fish populations are exploited by two fishermen. We study the existence and the stability of the equilibrium points by using eigenvalues analysis and Routh-Hurwitz criterion. We determine the equilibrium point that maximizes the profit of each fisherman by solving the Nash equilibrium problem. Finally, following some numerical simulations, we observe that if the price varies, then the profit behavior of each fisherman will be changed; also, we conclude that the price change mechanism improves the fishing effort of the fishermen.

scholarly journals Impact of a simultaneous reduction in fishing subsidies and introduction of efficient management of rents: the case of the Northwest Spanish fleet

2017 ◽  
Vol 31 ◽  
pp. 1 ◽  
Author(s):  
Eugenia Merayo ◽  
Staffan Waldo ◽  
Max Nielsen
Keyword(s):  
Fishing Effort ◽  
Simultaneous Reduction ◽  
Effort Level ◽  
Efficient Management ◽  
Management Measures ◽  
Management Scheme ◽  
Fishing Sector ◽  
The Impact ◽  
The Eu

Subsidies to the fishing sector have long been criticized for fueling over-fishing, and a reduction in subsidies is currently on the agenda in the negotiations within the World Trade Organization (WTO). This article analyzes the role of subsidies and other management measures for Spain, one of the largest fishing nations within the EU. A static bio-economic model is used to analyze the effect of simultaneous elimination of subsidies and introduction of an economically efficient management system for the Northwest Spanish fleet. It is concluded that improvements in management would bring substantial rents to the industry, up to €164 million, irrespective of subsidy level, but also a reduction in fishing effort of almost 60%. Under a management scheme that maximizes economic rents, elimination of subsidies in the fishery would increase social welfare, induced by a decrease in the equilibrium fishing effort level. However, the impact of subsidies under this scheme is limited.

The importance of scale for fishing impact estimations

2009 ◽  
Vol 66 (5) ◽  
pp. 829-835 ◽  
Author(s):  
G. J. Piet ◽  
F. J. Quirijns
Keyword(s):  
Life History ◽  
Spatial Scale ◽  
Bottom Trawl ◽  
Spatial Processes ◽  
Temporal Scales ◽  
Fishing Impact ◽  
Trawl Fishery ◽  
Time Period ◽  
Spatio Temporal ◽  
The Impact

The impact of a bottom trawl fishery on fish or benthos is often determined by multiplying the frequency of the passing of the trawl by a factor for the effect (i.e., % mortality) of the singular passing of the gear. As fishing intensity in an area is not homogeneously distributed, it is necessary to determine the proportions of the area that are fished with different trawling frequencies, as these subareas together contribute to the overall species’ mortality. In this study, we show that the perceived proportion of the area fished with a specific trawling frequency depends upon the spatial and temporal scale used. A smaller spatial scale results in an increased perceived patchiness of the fishing intensity, while a longer time period does the opposite. The implication is that to determine the fishing-induced mortality of a particular species, the trawling frequency needs to be determined at those spatio-temporal scales that are appropriate considering the species’ spatial processes (e.g., dispersion) or temporal processes described by life history characteristics.

scholarly journals “The Elephant in the Room”: Exploring Natural Mortality Uncertainty in Statistical Catch at Age Models

2020 ◽  
Vol 7 ◽  
Author(s):  
Alessandro Mannini ◽  
Cecilia Pinto ◽  
Christoph Konrad ◽  
Paraskevas Vasilakopoulos ◽  
Henning Winker
Keyword(s):  
Stock Assessment ◽  
Assessment Process ◽  
Sensitivity Analyses ◽  
Fish Stock ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Food And Agriculture ◽  
Stock Assessments ◽  
The Mediterranean ◽  
The Impact

The natural mortality rate (M) of a fish stock is typically highly influential on the outcome of age-structured stock assessment models, but at the same time extremely difficult to estimate. In data-limited stock assessments, M usually relies on a range of empirically or theoretically derived M estimates, which can vary vastly. This article aims at evaluating the impact of this variability in M using seven Mediterranean stocks as case studies of statistical catch-at-age assessments for information-limited fisheries. The two main bodies carrying out stock assessments in the Mediterranean and Black Seas are European Union’s Scientific Technical Economic Committee for Fisheries (STECF) and Food and Agriculture Organization’s General Fisheries Commission for the Mediterranean (GFCM). Current advice in terms of fishing mortality levels is based on a single “best” M assumption which is agreed by stock assessment expert working groups, but uncertainty about M is not taken into consideration. Our results demonstrate that not accounting for the uncertainty surrounding M during the assessment process can lead to strong underestimation or overestimation of fishing mortality, potentially biasing the management process. We recommend carrying out relevant sensitivity analyses to improve stock assessment and fisheries management in data-limited areas such as the Mediterranean basin.

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.

scholarly journals Integrating spatial and temporal mortality from herring on capelin larvae: a study in the Barents Sea

2009 ◽  
Vol 66 (10) ◽  
pp. 2183-2194 ◽  
Author(s):  
O. P. Pedersen ◽  
T. Pedersen ◽  
K. S. Tande ◽  
D. Slagstad
Keyword(s):  
Experimental Data ◽  
Mortality Rate ◽  
Barents Sea ◽  
Field Surveys ◽  
Fish Stocks ◽  
The Barents Sea ◽  
Spatio Temporal ◽  
The Impact ◽  
Important Fish ◽  
Temporal Overlap

Abstract Pedersen, O. P., Pedersen, T., Tande, K. S., and Slagstad, D. 2009. Integrating spatial and temporal mortality from herring on capelin larvae: a study in the Barents Sea. – ICES Journal of Marine Science, 66: 2183–2194. Barents Sea herring and capelin are commercially very important fish stocks. We investigate the spatial and temporal mortality rate of capelin larvae in 2001 as a function of herring predation. Our methods are based on Lagrangian modelling, field surveys, and experimental data. The impact of juvenile herring predation on capelin recruitment is corroborated, in particular the importance of the integrated spatio-temporal overlap between the two stocks. Capelin larvae were reduced to 20–50% in two weeks in accordance with different simulation scenarios. Hamre advanced a hypothesis in 1994 that juvenile herring are important predators of capelin larvae and a main cause of poor capelin recruitment in years when herring are very abundant in the Barents Sea. This hypothesis is supported through the results of this work.

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