Search results for "stock"
showing 10 items of 878 documents
The effect of random and density‐dependent variation in sampling efficiency on variance of abundance estimates from fishery surveys
2019
Abundance indices (AIs) provide information on population abundance and trends over time, while AI variance (AIV) provides information on reliability or quality of the AI. AIV is an important output from surveys and is commonly used in formal assessments of survey quality, in survey comparison studies, and in stock assessments. However, uncertainty in AIV estimates is poorly understood and studies on the precision and bias in survey AIV estimates are lacking. Typically, AIV estimates are “design based” and are derived from sampling theory under some aspect of randomized samples. Inference on population density in these cases can be confounded by unaccounted process errors such as those due …
Chlorophyll fluorescence, photosynthesis and growth of tomato plants as affected by long-term oxygen root zone deprivation and grafting
2020
A greenhouse experiment was conducted to study the effects of the O2 root zone level and grafting on chlorophyll fluorescence, photosynthesis and growth of cherry tomato grown in a hydroponic system. Two O2 concentrations in the root zone, namely Ox (saturation level) and Ox- (2&ndash
Marine reserves: size and age do matter
2008
Marine reserves are widely used throughout the world to prevent overfishing and conserve biodiversity, but uncertainties remain about their optimal design. The effects of marine reserves are heterogeneous. Despite theoretical findings, empirical studies have previously found no effect of size on the effectiveness of marine reserves in protecting commercial fish stocks. Using 58 datasets from 19 European marine reserves, we show that reserve size and age do matter: Increasing the size of the no-take zone increases the density of commercial fishes within the reserve compared with outside; whereas the size of the buffer zone has the opposite effect. Moreover, positive effects of marine reserve…
Hybrids and allied species as potential rootstocks for eggplant: Effect of grafting on vigour, yield and overall fruit quality traits
2018
Abstract Grafting of fruiting vegetables is an effective technique to overcome pests and diseases in modern cropping systems and it is often used to improve yield and fruit quality. Eggplant is an important vegetable crop that benefits significantly from grafting. In this regards, the exploitation, valorization and breeding of new rootstock genotypes as possible substitute to those commonly used (Solanum torvum and tomato hybrids) would permit an intensive eggplant crop system in those situations where a rootstock rotation is required. In the present article, we study the effects of several potential rootstocks including both wild/allied species of eggplant [S. torvum (STO), S. macrocarpon …
Causes of mortality in depleted populations of Atlantic cod estimated from multi-event modelling of mark–recapture and recovery data
2017
Knowledge on mortality causes is key for an effective management of animal populations and can help to restore depleted fish stocks. Here we investigated the mortality dynamics of coastal Atlantic cod (Gadus morhua) in Skagerrak, southern Norway, by analyzing local mark–recapture and recovery data collected from 2005 to 2013 (N = 9360 fish, mean length = 41 cm, range = 16–93 cm). By applying multi-event models to the data, we could link field observations to multiple “dead states” and estimate the proportion of deaths associated with different fishing gears while controlling for unobserved mortality and detection errors. Deaths due to hand lines and fixed gear types were dominant compared …
Genetic assessment of spatiotemporal evolutionary relationships and stocking effects in grayling (Thymallus thymallus, Salmonidae)
2002
Domestically reared introduced (or escaped) individuals can have detrimental genetic effects on the indigenous populations into which they are released. Consequently, numerous studies have attempted to estimate whether non-native specimens have contributed to the gene pool of wild populations. So far, the key limiting factor of such studies has been their lack of appropriate baseline genetic material. Here, microsatellite DNA analyses of historical scale samples and contemporary wild and introduced populations were used to assess spatiotemporal population structure and stocking effects among endangered Lake Saimaa (eastern Finland) grayling (Thymallus thymallus, Salmonidae). Significant dec…
Effect of stocking time on yield and location of recapture in two forms of brown trout (Salmo trutta) when stocked in respect to migration activity
2003
Abstract Tagged 2-year-old trout smolts, Salmo trutta , were stocked into River Isojoki in 1996, 1997 and 1998 (a sea trout strain), and Lake Konnevesi in 1997 and 1998 (a brown trout strain) in April, May or June–July. Stocking dates were determined in respect to the migration activity of 100 PIT-tagged fish held in the laboratory. Migration activity was relatively similar in both trout forms each year. In April, movement activity was low; in May, movement activity of the PIT-tagged fish increased and in June–July, movement had ceased. There was a general tendency for lower migration activity in maturing males than for immature fish, but differences were not statistically significant every…
Ticket to spawn: Combining economic and genetic data to evaluate the effect of climate and demographic structure on spawning distribution in Atlantic…
2019
Abstract Climate warming and harvesting affect the dynamics of species across the globe through a multitude of mechanisms, including distribution changes. In fish, migrations to and distribution on spawning grounds are likely influenced by both climate warming and harvesting. The Northeast Arctic (NEA) cod (Gadus morhua) performs seasonal migrations from its feeding grounds in the Barents Sea to spawning grounds along the Norwegian coast. The distribution of cod between the spawning grounds has historically changed at decadal scales, mainly due to variable use of the northern and southern margins of the spawning area. Based on historical landing records, two major hypotheses have been put f…
Who is fishing on what stock: population-of-origin of individual cod (Gadus morhua) in commercial and recreational fisheries
2018
AbstractAtlantic cod (Gadus morhua) in Skagerrak are structured into distinct ecotypes or stock components that have been severely depleted over the past decades. To improve our understanding of how local commercial and recreational fisheries influence cod stocks, we investigated whether these user groups target different stock components of cod. Cod were sampled from the recreational rod and line fishery and from commercial shrimp trawlers catching cod as by-catch. Based on a large set of single nucleotide polymorphisms (SNPs), we defined a subset of 27 semi-diagnostic SNPs designed to discriminate between two cod stock components: “inner fjord” cod and “North Sea” cod, designated by their…
Land Cover Trade-offs in Small Oceanic Islands: A Temporal Analysis of Pico Island, Azores
2017
Livestock production has been highly relevant in the Azores, boosted by European agricultural policies, increasing the demand for pasture and competing for space with other land uses. Therefore, it is important to understand the spatial evolution of pasture and related LULC trade-offs. This study describes a GIS-based LULC change detection approach to identify, map and assess pasture-related land use changes and respective trade-offs in Pico Island in the period between 1998 and 2013 (15 years). Pasture in 1998 occupied a total area of 17131 ha (about 39% of Pico Island surface), while in 2013 this same area was of 17621 ha (about 40% of Pico Island surface). During this period, about 16316…