Conflicting objectives in trophy trout recreational fisheries: evaluating trade-offs using an individual-based model

2011 ◽  
Vol 68 (11) ◽  
pp. 1892-1904 ◽  
Author(s):  
Martín Ignacio García-Asorey ◽  
Gabriela Escati-Peñaloza ◽  
Ana María Parma ◽  
Miguel Alberto Pascual
Keyword(s):  
Population Size ◽  
Size Structure ◽  
Somatic Growth ◽  
Maximum Size ◽  
Minimum Size ◽  
Recreational Fisheries ◽  
Trade Offs ◽  
Conflicting Objectives ◽  
Size Limits ◽  
Harvest Model

Standard fisheries models, based on average population metrics, are inadequate for analyzing recreational fisheries where fishing is size-selective and management objectives are related to preserving population size structure. We developed a framework for policy analysis of size-based harvest strategies in recreational fisheries. The framework combines a mixed-effects body growth model and an individual-based harvest model to describe the relationship of growth, mortality, and size structure. Fishery performance is quantified with indicators directly associated to catch-related components of anglers’ satisfaction: yield (kg), population size, and availability of trophy-size fish. We applied our analyses to the steelhead ( Oncorhynchus mykiss ) fishery in the Santa Cruz River (Patagonia, Argentina). Large declines in trophy-size fish are to be expected at fishing mortalities much too low to cause a sizeable decline in recruitment from virgin values. When somatic growth is density-independent, harvest occurs at the expense of other indicators associated with the quality of fishing experienced by individual anglers. Size limits provide a tool to better accommodate harvest without compromising fishing quality. When preserving population size is favored over preserving trophy-size fish, minimum size limits constitute the best policy overall, whereas maximum size limits are best when the emphasis is on preserving trophy-size fish.

Growth, reproduction, and population structure in four alpine lichens during 240 years of primary colonization

2004 ◽  
Vol 82 (9) ◽  
pp. 1356-1362 ◽  
Author(s):  
Geir Hestmark ◽  
Olav Skogesal ◽  
Øystein Skullerud
Keyword(s):  
Population Size ◽  
Life Histories ◽  
Size Structure ◽  
Growth Period ◽  
Maximum Size ◽  
Strongly Correlated ◽  
Interspecific Differences ◽  
Population Size Structure ◽  
The Relationship ◽  
Plant Life Histories

The increase in thallus diameter and apothecium production, and the population size structure of the saxicolous lichens Umbilicaria cylindrica (L.) Del., Umbilicaria hyperborea (Ach.) Hoffm., Umbilicaria proboscidea (L.) Schrad, and Umbilicaria torrefacta (Lightf.) Schrad, were measured in a chronosequence of 240 years in a glacier foreland in the alpine Jotunheimen National Park in Norway. All four species exhibited a pattern of fast growth in the early decades of their life history, followed by a rapid decrease in growth, slowly approaching a maximum body size. There were clear interspecific differences in initial estimated growth rate, growth period, and maximum size. In all species, apothecium production is strongly correlated with thallus size, but in U. hyperborea the relationship approximates an exponential function, while in the other species the trend is more linear. In U. proboscidea, the slowest to mature, a fairly high proportion of sterile individuals also occur in the higher size classes. There was no observed trade off between growth and reproduction. Quite the contrary: the species that grow faster also start to reproduce abundantly and early. The relatively slow growth and reproductive maturation of the species implies that a population of 40- to 50-year-old individual thalli is still a population consisting mainly of immigrants. The population size structure of all four species remains strongly skewed during the entire chronosequence, with a predominance of small thalli.Key words: plant life histories, lichen growth rates, size structure, Umbilicaria.

Optimal management of recreational fisheries in the presence of hooking mortality and noncompliance — predictions from a bioeconomic model incorporating a mechanistic model of angler behavior

2015 ◽  
Vol 72 (1) ◽  
pp. 37-53 ◽  
Author(s):  
Fiona D. Johnston ◽  
Ben Beardmore ◽  
Robert Arlinghaus
Keyword(s):  
Fish Species ◽  
Mechanistic Model ◽  
Strong Dependence ◽  
Fish Population ◽  
Minimum Size ◽  
Optimal Management ◽  
Bioeconomic Model ◽  
Recreational Fisheries ◽  
Regulatory Constraints ◽  
Size Limits

Using a bioeconomic model, we systematically investigated how hooking mortality and regulatory noncompliance influenced management outcomes across a range of freshwater fish species exploited by diverse angler populations. The model integrated an empirically based submodel describing the behaviour of three angler types with an age-structured fish population submodel calibrated to five life-history types (LHTs). Increased hooking mortality generally undermined regulation effectiveness, decreased socially optimal input (license numbers) and output regulations (minimum-size limits), and eroded the social welfare anglers derived from the fishery. However, the results strongly varied with LHT and angler type. Noncompliance had an isolated effect, primarily affecting fish species with low compensatory reserves when hooking mortality was low. However, in the absence of regulatory constraints on effort, noncompliance facilitated recruitment overfishing and increased the minimum-size limit required to avoid it. Despite added mortality from hooking and noncompliance, the strong dependence of angler utility on catch rates usually meant socially optimal management safeguarded biological sustainability. Yet, ignoring hooking mortality and noncompliance when predicting optimal regulations often led to population collapse. To conclude, models designed to derive recommendations for recreational fisheries management must consider both hooking mortality and noncompliance. Otherwise, dissatisfied anglers or biologically overfished stocks are possible.

scholarly journals Populations of wild and feral reindeer in Siberia and Far East of Russia

Rangifer ◽  
2007 ◽  
Vol 27 (4) ◽  
pp. 227 ◽  
Author(s):  
Leonid M. Baskin ◽  
Frank L. Miller
Keyword(s):  
Population Size ◽  
Rangifer Tarandus ◽  
Far East ◽  
Renewable Resource ◽  
Maximum Size ◽  
Range Size ◽  
Minimum Size ◽  
Far East Of Russia ◽  
Lack Of Information ◽  
Population Structure And Dynamics

Identification and cataloging of discrete reindeer (Rangifer tarandus) populations in Siberia and the Far East of Russia has not been carried out. This prohibits accurate measures of population structure and dynamics that would allow more intensive management of this important renewable resource. To rectify the lack of information, an inventory was made that identifies 84 wild populations and 3 feral populations originating from domestic reindeer. This inventory summarizes the information available on the location, approximate population size, approximate range size, and occurrence by ecoregions and habitat types of each of those 87 reindeer populations. The 87 reindeer populations used a collective landmass of about 3 000 000 km2. The range size for each population was calculated to be between 446 km2 and 392 267 km2, with a mean ± SE of 34 033 ± 5734 km2. The 86 populations for which population size could be approximated totaled 790 655 reindeer, with an approximate mean ± SE of 9194 ± 2517, a minimum size of 50, and maximum size of 145 000. The location of the calving grounds could be determined for only 26 (30%) of the 87 reindeer populations.

Comparing size-limit and quota policies to increase economic yield in a lobster fishery

2015 ◽  
Vol 72 (9) ◽  
pp. 1292-1305 ◽  
Author(s):  
Richard McGarvey ◽  
André E. Punt ◽  
Janet M. Matthews ◽  
John E. Feenstra ◽  
Caleb Gardner ◽  
...  
Keyword(s):  
Egg Production ◽  
Maximum Size ◽  
Catch Rate ◽  
Minimum Size ◽  
Control Rule ◽  
Exploitation Rate ◽  
Harvest Control Rule ◽  
Lobster Fishery ◽  
Size Limits ◽  
Rule Setting

To advance economic and sustainability objectives in a lobster fishery, four broadly different management policies were evaluated: minimum and maximum size limits, constant catch quotas, and quota set yearly in proportion to the previous year’s catch per unit effort (CPUE). The performance of each policy was evaluated based on its discounted economic yield, together with egg production, catch, and catch stability. Maximum size limits performed poorly for all indicators. Raising the minimum size increased economic yield by improving yield-per-recruit. Output controls, both constant and dynamic, uniformly outperformed size limits, leading to substantially higher economic yield and egg production. A dynamic harvest control rule, setting quota in proportion to the previous year’s catch rate, achieved the highest economic yield, catch, and egg production over 20 years. The optimal (30%) exploitation rate under this policy produced a 182% improvement in economic yield compared with a baseline strategy of only minimum size, but led to a mean year-to-year change in quota of 11.5% in response to yearly variable recruitment. This quota-setting management regime is straightforward to implement, using only catch rate as input. When absolute exploitation rate estimates are not available, this quota-setting harvest control rule can be constructed using only a target level of effort.

Persistence of giants: population dynamics of the limpet Scutellastra laticostata on rocky shores in Western Australia

2020 ◽  
Vol 646 ◽  
pp. 79-92
Author(s):  
RE Scheibling ◽  
R Black
Keyword(s):  
Population Dynamics ◽  
Western Australia ◽  
Size Structure ◽  
Survival Rates ◽  
Maximum Size ◽  
High Rate ◽  
Adult Survival ◽  
Rocky Shores ◽  
Adult Size ◽  
Decadal Time Scale

Population dynamics and life history traits of the ‘giant’ limpet Scutellastra laticostata on intertidal limestone platforms at Rottnest Island, Western Australia, were recorded by interannual (January/February) monitoring of limpet density and size structure, and relocation of marked individuals, at 3 locations over periods of 13-16 yr between 1993 and 2020. Limpet densities ranged from 4 to 9 ind. m-2 on wave-swept seaward margins of platforms at 2 locations and on a rocky notch at the landward margin of the platform at a third. Juvenile recruits (25-55 mm shell length) were present each year, usually at low densities (<1 m-2), but localized pulses of recruitment occurred in some years. Annual survival rates of marked limpets varied among sites and cohorts, ranging from 0.42 yr-1 at the notch to 0.79 and 0.87 yr-1 on the platforms. A mass mortality of limpets on the platforms occurred in 2003, likely mediated by thermal stress during daytime low tides, coincident with high air temperatures and calm seas. Juveniles grew rapidly to adult size within 2 yr. Asymptotic size (L∞, von Bertalanffy growth model) ranged from 89 to 97 mm, and maximum size from 100 to 113 mm, on platforms. Growth rate and maximum size were lower on the notch. Our empirical observations and simulation models suggest that these populations are relatively stable on a decadal time scale. The frequency and magnitude of recruitment pulses and high rate of adult survival provide considerable inertia, enabling persistence of these populations in the face of sporadic climatic extremes.

scholarly journals A Comparison of Genetic Representations and Initialisation Methods for the Multi-objective Shortest Path Problem on Multigraphs

2021 ◽  
Vol 2 (3) ◽  
Author(s):  
Lilla Beke ◽  
Michal Weiszer ◽  
Jun Chen
Keyword(s):  
Shortest Path ◽  
Time Budget ◽  
Exact Algorithm ◽  
Simple Graph ◽  
Shortest Path Problem ◽  
Future Application ◽  
Multi Objective ◽  
Trade Offs ◽  
Conflicting Objectives ◽  
Problem Instances

AbstractThis paper compares different solution approaches for the multi-objective shortest path problem (MSPP) on multigraphs. Multigraphs as a modelling tool are able to capture different available trade-offs between objectives for a given section of a route. For this reason, they are increasingly popular in modelling transportation problems with multiple conflicting objectives (e.g., travel time and fuel consumption), such as time-dependent vehicle routing, multi-modal transportation planning, energy-efficient driving, and airport operations. The multigraph MSPP is more complex than the NP-hard simple graph MSPP. Therefore, approximate solution methods are often needed to find a good approximation of the true Pareto front in a given time budget. Evolutionary algorithms have been successfully applied for the simple graph MSPP. However, there has been limited investigation of their applications to the multigraph MSPP. Here, we extend the most popular genetic representations to the multigraph case and compare the achieved solution qualities. Two heuristic initialisation methods are also considered to improve the convergence properties of the algorithms. The comparison is based on a diverse set of problem instances, including both bi-objective and triple objective problems. We found that the metaheuristic approach with heuristic initialisation provides good solutions in shorter running times compared to an exact algorithm. The representations were all found to be competitive. The results are encouraging for future application to the time-constrained multigraph MSPP.

Population size structure and sex ratios in some woodlice (Crustacea: Oniscidae) from southern Africa

1994 ◽  
Vol 10 (2) ◽  
pp. 261-271 ◽  
Author(s):  
J. M. Dangerfield ◽  
S. R. Telford
Keyword(s):  
Population Size ◽  
Southern Africa ◽  
Life Histories ◽  
Mating Systems ◽  
Size Structure ◽  
Sex Ratios ◽  
Interspecific Variation ◽  
Sexual Competition ◽  
Population Size Structure ◽  
Adult Sex Ratio

ABSTRACTThe population size structure and adult sex ratio were recorded for four indigenous and one introduced species of terrestrial isopod from southern Africa. Interspecific variation was considerable with either discrete or continuous distributions indicative of the production of separate cohorts or continuous recruitment. Intraspecific variation was also considerable particularly in species such as Aphiloscia vilis which can be found in diverse habitats. Sex ratios were consistently female biased, a result consistent with observations made on temperate species. These observations, and a consideration of sexual dimorphism based on body mass, suggest that phenotypic plasticity may be an important tactic in the life histories of tropical woodlice and that in some populations the potential exists for strong sexual competition and complex mating systems.

Sign in / Sign up

Export Citation Format

Share Document