Examinando por Autor "Oliva, Doris"

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    Ítem
    Assessing pinniped bycatch mortality with uncertainty in abundance and post-release mortality: A case study from Chile
    (Elsevier, 2021) Punt, André E.; Sepúlveda, Maritza; Siple, Margaret C.; Moore, Jeffrey; Francis, Tessa B.; Hammon, Philip S.; Heinemann, Dennis; Long, Kristy J.; Oliva, Doris; Reeves, Randall R.; Sigurðsson, Guðjón Már; Víkingsson, Gísli; Wade, Paul R.; Williams, Rob; Zerbini, Alexandre N.
    The effects of human-caused mortality, such as fisheries bycatch, of endangered, threatened and protected (ETP) species of marine mammals can be evaluated using population model-based stock assessments. The information available to conduct such assessments is often very limited. Available data might include fragmented time-series of abundance estimates, incomplete data on bycatch for the fisheries that interact with ETP species (often few years and low observer coverage), and perhaps some data on scale and trends in fishing effort. Such data are challenging to use as the basis for stock assessments, which generally assume that estimates of removals (bycatch, in our context) through time are available for at least the most recent decade or two. This paper describes a stock assessment method for use with sparse observer data on bycatch mortality, applied within the context of a Bayesian estimation framework. The method produces estimates, with associated measures of precision, of population size and historical time-series of bycatch mortality that are consistent with the observer and abundance data. It provides a rigorous way to account for the uncertainty arising from animals that are caught but released alive and then die subsequent to release, given a post-release mortality rate prior. Observer data from industrial and artisanal purse seine and trawl fisheries and survey data for South American sea lions (Otaria byronia) and South American fur seals (Arctocephalus australis) off Chile are used to illustrate the method.
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    Broodstock conditioning, spawning, embryonic and early larval development of a novel baby clam species for aquaculture in the southeast Pacific: Tawera elliptica (Lamarck, 1818)
    (Wiley, 2021) Barría, Camila; Abarca, Alejandro; Colivoro, David; Célis, Angela; Couve, Pablo; Cárcamo, Daniel; Durán, L. René; Oliva, Doris
    Tawera elliptica is a small size (baby) clam with an export fishery in southern Chile. The species is dioecious with external fertilization and without sexual dimorphism. The aim of this work was to optimize broodstock conditioning, induce spawning and describe embryonic development until the early larval stage in a hatchery. Broodstock were conditioned at 3 treatments (with/without sand; water circulation) for 48 days. The clams were fed with a mixed diet of macroalgae, with a daily ration of 250,000 cells/ml. Broodstock response was quantified using condition index and gonad development stages (histological techniques). For spawning induction, physical and biological methods were tested. The best response was achieved in males with physical induction. Histological analysis showed that the water circulation system treatment exhibited the highest percentage of maximum maturity. A fertilization ratio of 500:1 sperm:oocyte was used. The incubation was carried out in 3-L containers with filtered seawater at 10.7 ± 0.9°C without aeration. Observations, measurements and the duration of each embryonic and larval stage were recorded. The oocyte has a prominent gelatinous layer (= jelly coat) that disappears between the gastrula and trochophore stages. The status of the D-larval stage was reached at 107 h post fertilization with a mean valve length of 91.4 ± 8.9 µm. This is the first record of the complete embryonic development of this baby clam until the early larval stage and the conditioning in a water circulation system for 48 days are suitable for the species.
  • Miniatura
    Ítem
    Changes in aquaculture
    (United Nations, 2021) Subasinghe, Rohana; Barón, Pedro; Beveridge, Malcolm; Marschoff, Enrique; Oliva, Doris
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    Lethal and oxidative stress side effects of organic and synthetic pesticides on the insect scale predator Rhyzobius lophanthae
    (E. Schweizerbart’Sche Verlagsbuchhandlung, 2021) Palma-Onetto, Valeria; Oliva, Doris; González-Teuber, Marcia
    Although pesticides are the most widely used method for the control of agricultural pests, natural insect enemies can successfully suppress pest populations. However, side effects of pesticides can have strongly deleterious impacts on these biocontrol agents. In this context, lethal (mortality over time) and sublethal (oxidative stress) effects of organic and synthetic pesticides (seven of each) on the insect scale predator Rhyzobius lophanthae Blaisdell (Coleoptera: Coccinellidae) were evaluated. Adults of R. lophanthae were exposed to pesticide residues every seven days over a period of 49 days following pesticide application. Oxidative stress was measured only in the insects surviving the first day of pesticide application. We found that most organic pesticides were harmless, causing less than 30% mortality in R. lophanthae, whereas the majority of the tested synthetic pesticides led to 100% mortality, which was persistent over time. Some organic pesticides, however, caused significant oxidative stress in R. lophanthae. Overall, the results showed that organic pesticides were less harmful than synthetics, resulting in low mortality over time in R. lophanthae, although some may result in sublethal effects in biological control agents. Our findings offer useful insights into general impacts of organic versus synthetic pesticides on beneficial insects, suggesting that they could provide a safer and effective alternative to synthetics for the control of agricultural pests.
  • Miniatura
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    Long-term monitoring for conservation: closing the distribution gap of Arctocephalus australis in central Chile
    (Bmc, 2021) Cárcamo, Daniel; Pizarro, Marlene; Orellana, Muriel; Canto, Anahi; Herrera, Pablo; Muñoz, Lily; Vásquez-Calderón, Piera; Guerrero, Alicia; Sepúlveda, Maritza; René Durán, L.; Oliva, Doris
    Objectives. Here, we present the first record of stable colonies of the South American fur seal (Arctocephalus australis), in an area where their presence has never been documented (hereafter distribution gap), as well as an update of the current distribution range of the species in central Chile. Results. A national synoptic aerial census of pinnipeds was performed during the austral summer of 2019 on the Chilean coast. An additional aerial census was conducted in the same area during the austral spring of 2019 as well as a maritime census during the austral summer of 2020. The data showed the presence of South American fur seals in central Chile within their well-known distribution gap. The total abundance was registered in three colonies where fur seals were sighted: one non-breeding colony, Punta Topocalma (summer 2019: mean = 46 ± 3; spring 2019: mean = 9 ± 1); and two breeding colonies, Punta Curaumilla (summer 2019: mean = 595 ± 7; spring 2019: mean = 45 ± 4; summer 2020: mean = 744 ± 5) and Isla Santa María (summer 2019: mean = 246 ± 6). Specifically, we suggest that it is crucial to elucidate the origin of the described settled colonies, and to determine whether there has been an augment in the distribution range from either the northern population, the southern population, or both simultaneously.