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S De Lestang - One of the best experts on this subject based on the ideXlab platform.
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spatial and temporal changes in egg production in the western rock lobster panulirus cygnus fishery
New Zealand Journal of Marine and Freshwater Research, 2009Co-Authors: Roy Smith, S De Lestang, A J ThomsonAbstract:Abstract Size at maturity in the western rock lobster (Panulirus cygnus) fishery in Australia increases from north to south and female lobsters carry either one or two batches of eggs per season depending on their carapace length. There has been a steady decrease in the Size at first maturity of western rock lobster over the last 30 years, and there are now significantly more small females, many below the legal minimum Size, contributing to the brood stock than any time since the fishery has been researched. Biological data were used to show the current contribution to egg production in different management regions of the fishery and historical length‐frequency data were used to show how egg production has changed in those regions overtime. Reasons for the change in Size at maturity in this fishery are unclear, but the outcome has been that egg production is now more evenly distributed across management zones. Egg production was high at Abrolhos Islands in the 1990s owing to strong year classes of breedin...
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spatial and temporal variation in the Size at maturity of the western rock lobster panulirus cygnus george
Marine Biology, 2006Co-Authors: Roy Melvillesmith, S De LestangAbstract:The Sizes at which female and male western rock lobster Panulirus cygnus become mature were examined over 32 years from records at six localities along the coast of Western Australia. The Size of males at maturity was estimated from a subset of these data by a morphometric and a physiological method, with both producing statistically similar results. Males were larger at first maturity than females at the same sites. For both sexes, the Sizes at first maturity at each location correlated (P<0.05) with the mean annual water temperature at that location, decreasing from south to north along the mainland coast and being smallest at the offshore Abrolhos Islands. Smaller Sizes at maturity were recorded for both sexes than have been published previously. One certain explanation for these differences is that management measures protecting females with ovigerous setae have distorted Size compositions and the ratio of immature to mature females, thereby increasing the likelihood of capturing small mature females. However, these fishing effects cannot fully account for the progressive decline in CL50 observed over the past 20 years. Other possible hypotheses considered include increases in water temperature over this period, as well as whether this change could be consistent with a genotypic response caused by the selective removal of large lobsters combined with high exploitation rates.
Graham J Pierce - One of the best experts on this subject based on the ideXlab platform.
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Size at maturity of brown crab cancer pagurus in scottish waters based on gonadal and morphometric traits
Fisheries Research, 2020Co-Authors: Graham J Pierce, Carlos Mesquita, Helen Dobby, Stephanie Sweeting, Catherine S JonesAbstract:Abstract Minimum landing Sizes (MLS) are commonly used to manage crustaceans and are generally set above the Size at first maturity to ensure that some protection is afforded to exploited stocks. Despite the economic importance of the brown crab fishery in Scotland, the species is considered data-poor and only limited information is available on Size-at-maturity. This study provides, for the first time, estimates of the Size-at-maturity of brown crab on the east and west coasts of Scotland using gonadal and morphometric criteria. Gonadal maturity was determined from female ovary and male testes, which were classified macroscopically into development stages and their relationship with body Size modelled using a logistic regression. Body morphometric maturity was studied by analysing morphometric changes in growth in the male chelae and female abdomens using generalized additive models and regression models to estimate the Size at which changes in allometric relationships occur. Estimates of Size-at-maturity using gonad development were 101-106 mm carapace width (CW) for males and 127-128 mm for females. Size-at-maturity based on the morphometric characters were 120-148 mm CW for males and 131-142 mm for females. Results show that brown crab maturity is likely to occur at lower Sizes than the current MLS in Scotland, implying that crabs may be able to reproduce at least once before being harvested. Regional variations in local populations should be considered when setting a MLS and this study suggests that the current MLS of 150 mm is appropriate for both areas considered.
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comparisons of Size at maturity and fecundity of two scottish populations of the european lobster homarus gammarus
Fisheries Research, 2003Co-Authors: Hector A Lizarragacubedo, I D Tuck, N Bailey, Graham J Pierce, J A M KinnearAbstract:Abstract Sampling of Homarus gammarus on commercial boats and regular visits to local ports were carried out during 1999–2001 for the Firth of Forth and Hebrides fisheries. Biological data on Size, sex, morphometric measurements and egg samples were collected. Size at the onset of sexual maturity (SOM), fecundity and egg development were compared between populations. Techniques that require transformed (Logarithm base e) or untransformed morphometric data, were applied to the data. Lobsters from the Firth of Forth had smaller SOM ( ♂=80 mm carapace length (CL) and ♀=79 mm CL) than those from the Hebrides ( ♂=98 and ♀=110 mm CL). Fecundity ( x =8154 eggs) for the Firth of Forth was lower than for the Hebrides ( x =14 238 eggs). ANCOVA showed no significant differences in the Size–fecundity relationship between locations (F1,1=2.62,P>0.05) for lobsters with eggs in which the eye spot index (ESI) was between 0.29 and 0.54, using CL and ESI as co-variates. The reliability of the methods and the resulting estimates are discussed.
Adrian Linnane - One of the best experts on this subject based on the ideXlab platform.
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spatial and temporal variations in female Size at maturity of a southern rock lobster jasus edwardsii population a likely response to climate change
PLOS ONE, 2019Co-Authors: Lachlan J Mcleay, Mark J Doubell, Adrian LinnaneAbstract:The Size at which sexual maturity is reached is a key population parameter used to guide the setting of minimum legal Size limits in fisheries. Understanding spatial and temporal variations in Size at maturity is fundamental to management because the relationship between Size at maturity and minimum legal Size limits affects the fraction of the mature population biomass that is harvested, and resulting egg production, larval settlement and recruitment. This study measured the Size at maturity of female Southern Rock Lobster (Jasus edwardsii) across South Australia between 1991 and 2015 in relation to known oceanographic characteristics, surface and subsurface temperature data, and relative changes in lobster abundance. There was pronounced north to south spatial variation in estimates of Size at maturity. Larger average Size at maturity was recorded in warmer north-western areas of the fishery relative to the cooler waters of the south-east. Estimates of Size at maturity also differed over 25 years across the fishery. However, the nature of temporal responses varied spatially, and were more consistent with variations in surface and subsurface water temperature at local-scales than changes in lobster density. In the well-mixed waters of the north-western, western and south-eastern parts of the fishery, relatively high rates of increase in sea-surface temperature and Size at maturity were recorded since 1991, indicating that Size at maturity may be responding to ocean warming associated with global climate change. In more central parts of the fishery, contrasting temporal signals in sea-surface temperature (positive) and bottom temperature (negative) indicated increases in upwelling strength over the study period, and formation of a bottom cold pool below a warm surface layer, with corresponding decreases in Size at maturity recorded. The spatio-temporal changes in Size at maturity measured in this study highlight the need for oceanographic information to be integrated into future stock assessment models to enhance harvest strategy development, allow timely adaptive management decisions and increase the resilience of fisheries to the impacts of climate change.
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contrasting fecundity Size at maturity and reproductive potential of southern rock lobster jasus edwardsii in two south australian fishing regions
Journal of the Marine Biological Association of the United Kingdom, 2008Co-Authors: Adrian Linnane, S S Penny, Tim M WardAbstract:The annual commercial catch from the Southern Zone of the South Australian rock lobster ( Jasus edwardsii ) fishery is ~1900 tonnes, representing ~50% of total landings from south-east Australia. A single minimum legal Size (MLS) of 98.5 mm carapace length (CL) exists across the entire zone. Fecundity (F), Size at onset of maturity (SOM) and relative reproductive potential (RRP) of female rock lobsters were investigated in two major fishing regions, i.e. the North Southern Zone (NSZ) and South Southern Zone (SSZ) with a view to providing a basis for future fine-scale spatial management of the resource. F ranged from 45,292 to 466,800 eggs per female and increased proportionally with CL according to the relationship: F = 0.0584 × CL 3.1642 . F was significantly higher in the NSZ compared to the SSZ but was attributed to differences in lobster Size between regions. There was no significant difference in the number of eggs · g −1 of egg mass between areas. SOM, estimated as the Size at which 50% of females reached sexual maturity (L 50 ) was higher in the NSZ (104.1 mm CL) compared to SSZ (92.3 mm CL). Approximately 20% of lobsters above the MLS in the commercial catch in the NSZ were under the L 50 estimate. RRP, as a measure of egg production, was calculated for each Size-class from the product of F, SOM and population length–frequency. The modal RRP Size-classes in the NSZ were 117.5–122.5 mm CL, while in the SSZ it was 97.5–102.5 mm CL. Only 6% of RRP was contributed by female rock lobsters below the MLS in the NSZ, compared to 34% in the SSZ. Regional differences in SOM and RRP in the Southern Zone of South Australia suggest that different MLSs may be beneficial, particularly if the fishery is to be effectively managed at finer spatial scales.
Kentaro Morita - One of the best experts on this subject based on the ideXlab platform.
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increase in maturation Size after the closure of a high seas gillnet fishery on hatchery reared chum salmon oncorhynchus keta
Evolutionary Applications, 2008Co-Authors: Masaaki Fukuwaka, Kentaro MoritaAbstract:Gillnet fisheries are strongly Size-selective and seem to produce changes in Size at maturity for exploited fishes. After Word War II, large-scale gillnet fisheries targeted Pacific salmon (Oncorhynchus spp.) in the high seas area of the North Pacific and the Bering Sea, but these fisheries were closed in 1993. To assess the effects of this high seas gillnet fishery (and its closing) on Size at maturity, we examined long-term trends in Size at 50% probability of maturing (L50) for chum salmon (O. keta) from three populations in Hokkaido, Japan. The L50 trends were statistically different among rivers, but showed similar temporal patterns with decreases in the 1970s and early 1980s and increases after the 1985 brood year. While fishery-induced evolution seemed largely responsible for this temporal change in L50 during the fishing period, natural selection and phenotypic plasticity induced by environmental changes could contribute to the increases in L50 after the relaxation of fishing pressure.
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why age and Size at maturity have changed in pacific salmon
Marine Ecology Progress Series, 2007Co-Authors: Kentaro Morita, Masaaki FukuwakaAbstract:Over the last few decades, the Size at which Pacific salmon Oncorhynchus spp. attains maturity has decreased in many populations, whereas the age at maturity has increased. Both fish- eries-induced evolution and environmentally-induced phenotypic plasticity could contribute to the changing age and Size at maturity of Pacific salmon. We evaluated the potential for genetic changes in the maturation schedule of Japanese chum salmon using the probabilistic maturation reaction norm (PMRN) method. We found that the recent decrease in Size at maturity, and increase in age at maturity, of Japanese chum salmon can be largely attributed to a phenotypic response to a reduced growth rate, but that fisheries-induced evolution should not be ruled out. Recent claims concerning fisheries-induced evolution of the maturation schedule are based on the decline in the age-specific body Size at which the probability of maturing is 50%, a feature of PMRNs. However, the PMRN could change with changing environmental conditions. Therefore, a genetic change cannot be diagnosed only by the PMRN method.
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rule of age and Size at maturity of chum salmon oncorhynchus keta implications of recent trends among oncorhynchus spp
Canadian Journal of Fisheries and Aquatic Sciences, 2005Co-Authors: Kentaro Morita, Shoko H Morita, Masaaki Fukuwaka, Hiroyuki MatsudaAbstract:In the last quarter of the 20th century, the Size at maturity of many North Pacific salmon (Oncorhynchus spp.) populations decreased. During this same period, the age at maturity increased, implying that the growth rate of Pacific salmon decreased, probably owing to environmental changes. To elucidate these trends, we identified the rule of age and Size at maturity of Japanese chum salmon (Oncorhynchus keta), which was that slow-growing salmon initiated maturation at an older age and smaller Size than did fast-growing salmon. We then simulated the potential modification of age and Size at maturity in response to changing growth rate using a Size-structured model with age- and Size- specific maturation rates. This showed that reducing the growth rate without assuming a genetic change was sufficient for realistic modeling of recent changes. In addition, the observed rule of age and Size at maturity was consistent with the optimal age and Size at maturity in terms of maximizing the fitness. Our results attributed the recent trends in chum salmon's increasing age and decreasing Size at maturity to an adaptive phenotypic response to a reduced growth rate.
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rule of age and Size at maturity individual variation in the maturation history of resident white spotted charr
Journal of Fish Biology, 2002Co-Authors: Kentaro Morita, S H MoritaAbstract:Individual growth and maturation histories, age, and Size at maturity of resident white-spotted charr Salvelinus leucomaenis were examined in a tag-recapture study in a natural river over 3 years. Slow-growing fish reached sexual maturity not only at an older age, but also at a smaller Size than fast-growing fish, although females had a larger threshold Size at maturity than males at each age. It is suggested that these patterns result from adaptive phenotypic plasticity that depends on individual growth conditions.
Masaaki Fukuwaka - One of the best experts on this subject based on the ideXlab platform.
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increase in maturation Size after the closure of a high seas gillnet fishery on hatchery reared chum salmon oncorhynchus keta
Evolutionary Applications, 2008Co-Authors: Masaaki Fukuwaka, Kentaro MoritaAbstract:Gillnet fisheries are strongly Size-selective and seem to produce changes in Size at maturity for exploited fishes. After Word War II, large-scale gillnet fisheries targeted Pacific salmon (Oncorhynchus spp.) in the high seas area of the North Pacific and the Bering Sea, but these fisheries were closed in 1993. To assess the effects of this high seas gillnet fishery (and its closing) on Size at maturity, we examined long-term trends in Size at 50% probability of maturing (L50) for chum salmon (O. keta) from three populations in Hokkaido, Japan. The L50 trends were statistically different among rivers, but showed similar temporal patterns with decreases in the 1970s and early 1980s and increases after the 1985 brood year. While fishery-induced evolution seemed largely responsible for this temporal change in L50 during the fishing period, natural selection and phenotypic plasticity induced by environmental changes could contribute to the increases in L50 after the relaxation of fishing pressure.
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why age and Size at maturity have changed in pacific salmon
Marine Ecology Progress Series, 2007Co-Authors: Kentaro Morita, Masaaki FukuwakaAbstract:Over the last few decades, the Size at which Pacific salmon Oncorhynchus spp. attains maturity has decreased in many populations, whereas the age at maturity has increased. Both fish- eries-induced evolution and environmentally-induced phenotypic plasticity could contribute to the changing age and Size at maturity of Pacific salmon. We evaluated the potential for genetic changes in the maturation schedule of Japanese chum salmon using the probabilistic maturation reaction norm (PMRN) method. We found that the recent decrease in Size at maturity, and increase in age at maturity, of Japanese chum salmon can be largely attributed to a phenotypic response to a reduced growth rate, but that fisheries-induced evolution should not be ruled out. Recent claims concerning fisheries-induced evolution of the maturation schedule are based on the decline in the age-specific body Size at which the probability of maturing is 50%, a feature of PMRNs. However, the PMRN could change with changing environmental conditions. Therefore, a genetic change cannot be diagnosed only by the PMRN method.
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rule of age and Size at maturity of chum salmon oncorhynchus keta implications of recent trends among oncorhynchus spp
Canadian Journal of Fisheries and Aquatic Sciences, 2005Co-Authors: Kentaro Morita, Shoko H Morita, Masaaki Fukuwaka, Hiroyuki MatsudaAbstract:In the last quarter of the 20th century, the Size at maturity of many North Pacific salmon (Oncorhynchus spp.) populations decreased. During this same period, the age at maturity increased, implying that the growth rate of Pacific salmon decreased, probably owing to environmental changes. To elucidate these trends, we identified the rule of age and Size at maturity of Japanese chum salmon (Oncorhynchus keta), which was that slow-growing salmon initiated maturation at an older age and smaller Size than did fast-growing salmon. We then simulated the potential modification of age and Size at maturity in response to changing growth rate using a Size-structured model with age- and Size- specific maturation rates. This showed that reducing the growth rate without assuming a genetic change was sufficient for realistic modeling of recent changes. In addition, the observed rule of age and Size at maturity was consistent with the optimal age and Size at maturity in terms of maximizing the fitness. Our results attributed the recent trends in chum salmon's increasing age and decreasing Size at maturity to an adaptive phenotypic response to a reduced growth rate.
