323,861 research outputs found
Fisheries biology and management of pink snapper, Pagrus auratus, in the inner gulfs of Shark Bay, Western Australia
No full textThis study explored an important aspect of the basis for the highly complex population structure of pink snapper (Pagrus auratus) within the inner gulfs of Shark Bay, investigated how growth and reproduction differ among these closely-adjacent but separate stocks, and obtained biomass estimates for each stock that are essential for the sustainable management of the regionally-important recreational pink snapper fishery. Using ichthyoplankton data in combination with hydrodynamic modelling, P. auratus eggs and larvae were shown to be retained within localized meso-scale eddies that were coincident with the main inner gulf spawning areas. Such hydrodynamic retention, in conjunction with tagging and otolith chemistry data that indicates very limited movement of juvenile and adult fish, explains how separate pink snapper populations can exist in the adjacent waters of the Eastern Gulf, Denham Sound and Freycinet Estuary. The study found significant variation in maximum age, growth, maturity and spawning time at fine spatial scales. Such variation, unusual for a large, potentially mobile fish inhabiting a marine environment with no obvious physical barriers, is linked to the inner gulfs' marked environmental heterogeneity, the low levels of mixing and historic differences in fishing pressure among the three areas. The daily egg production method (DEPM) was used, for the first time with this species in Western Australia, to provide estimates of spawning biomass of the three separate inner gulf P. auratus stocks. While relatively imprecise, mostly due to imprecision in estimation of daily egg production, these estimates demonstrated that these stocks are very small (measured in tens of tonnes) compared with P. auratus stocks elsewhere in Australia and New Zealand. Biological data and DEPM estimates obtained from this study were incorporated in age-based stock assessment models that have been used to determine the status of inner gulf pink snapper stocks since 2002
Ichthyoplankton assemblages associated with pink snapper (Pagrus auratus) spawning aggregations in coastal embayments of southwestern Australia
No full textPink snapper (Pagrus auratus) form spawning aggregations during the austral spring/summer in three adjacent, sheltered, coastal embayments in southwestern Australia (Cockburn Sound, Warnbro Sound and Owen Anchorage). Larval fishes were sampled in these embayments, as well as in the more exposed adjacent waters of Five Fathom Bank, to ascertain which teleost species utilised these areas for spawning concurrently with P. auratus. Obliquely towed bongo nets (500 μm mesh) were used to collect icthyoplankton in November 2007 over three days during the new moon period when spawning of P. auratus is known to peak. A total of 13 270 larvae from 30 teleost families was collected with an overall mean larval fish concentration of 1.91 m -3 (± s.e. 0.28). Larval fish assemblages were significantly different in each of the three embayments and Five Fathom Bank, reflecting the degree of shelter, water-circulation patterns and associated benthic habitats. The highest larval fish concentrations were recorded in Cockburn Sound (3.69 m -3 ± s.e. 0.05) and the lowest along Five Fathom Bank (0.16 m -3 ± s.e. 0.02). P. auratus larvae were only present in samples from the three embayments. The most abundant larvae were those of the Australian anchovy (Engraulis australis), which occurred predominantly in Cockburn Sound and, to a lesser extent, Owen Anchorage. The most ubiquitous larvae included the longspine dragonet (Callionymus goodladi) and leatherjackets (Monacanthidae). This study provides circumstantial evidence that eggs and larvae of P. auratus and other teleosts are retained in the sheltered waters of Cockburn and Warnbro Sounds during spring/summer
Otolith chemistry, stomach contents and stable isotope analysis of a snapper (Pagrus auratus) caught in the Waikato River at Ngaruawahia
No full textAnalyses of stomach contents, stable isotopes and otolith microchemistry were carried out in order to ascertain the length of freshwater residence of a snapper (Pagrus auratus) caught in the Waikato River at Ngaruawahia in a net set for grey mullet(Mugil cephalus). Results of all analyses suggest that the snapper had spent all of its life in a marine environment with no evidence of freshwater residence in the otolith. Stable isotope analyses (δ15N = 17.0‰, δ13C = –17.1‰) indicated an entirely marine diet, and the stomach contents (two New Zealand screwshells, Maoricolpus roseus, and a hermit crab, Pagurus novizelandiae), suggested that the fish had not fed while in freshwater. However, this does not preclude the possibility that the snapper quickly travelled up the river, without eating, and was caught very soon after
Joint Estimation of Revealed and Stated Preference Data: An Application to Recreational Red Snapper Valuation
No full textThis study extends the joint estimation of revealed and stated preference data literature by accounting for truncation in the revealed preference data. The analytical model and estimation procedure are used to estimate the value of recreational red snapper fishing in the Gulf of Mexico. This recreational red snapper valuation is decomposed into its direct and indirect components. As expected, the value of recreational red snapper fishing using the joint revealed-stated preference model proposed in this analysis is bracketed on the upper limit by the value obtained using the contingent valuation method and on the lower limit by the travel cost method. The results also indicate that the joint model improves the precision of estimated recreational red snapper valuation.Resource /Energy Economics and Policy,
Latitudinal and temporal comparisons of the reproductive biology and growth of snapper, Pagrus auratus (Sparidae), in Western Australia
No full textThis study focused on obtaining sound quantitative data on the reproductive biology, length and age compositions and growth of the snapper Pagrus auratus in the waters off Carnarvon at ca 25oS and Perth at ca 32oS on the west coast of Australia and at ca 34oS on the south coast of Western Australia. Sampling thus encompassed both sub-tropical and temperate waters and the geographical range within which this species is abundant in Western Australia. The resultant data were used to explore the ways in which the biological characteristics of P. auratus differ with latitude and thus water temperature. An intensive sampling regime for eggs and spawning individuals of P. auratus was conducted in Cockburn Sound, a large marine embayment in the Perth region at ca 32oS. The resultant data were used to elucidate where and when spawning occurs in this large marine embayment and to determine more precisely the factors that influence the timing of spawning. The implications of the results presented in this thesis for the management of P. auratus, a species that has been subjected to very heavy fishing pressure in recent years, are discussed.
The time and duration of spawning of P. auratus in the subtropical waters of Carnarvon differed markedly from those recorded for this sparid in the temperate and cooler waters of the Perth and the south coast regions. Spawning at Carnarvon occurred predominantly in the five months between late autumn (May) and mid spring (September), whereas it took place mainly in the three months between mid spring (October) and early summer (December) in the Perth region. Spawning of P. auratus on the south coast occurred predominantly in October and November in 2003 and 2004 and scarcely at all in 2005. Gonadal recrudescence was thus initiated when water temperatures were close to their maximum but declining in Carnarvon, and close to their minima and rising in the Perth and south coast regions, respectively. The prevalence of fully mature and spawning females in all three regions was greatest in those months when water temperatures lay between 19 and 21oC. Collation of the data in this thesis and those provided in the literature for other populations showed that the spawning period was related to latitude, occurring far earlier in sub-tropical than temperate waters.
The females and males attained maturity at a far smaller total length (L50) in the Carnarvon region, i.e. 378 and 353 mm, respectively, than in the Perth region, 585 and 566 mm, respectively, and also the south coast region, i.e. 600 and 586 mm. The trends exhibited by the age at maturity parallel those for length, with the A50s for the two sexes increasing from ca 4 years in Carnarvon to ca 5.6 years in the Perth region and nearly 7 years in the south coast region. The L50 and A50 at maturity thus both increased with increasing latitude.
Marginal increment analysis demonstrated that, irrespective of the number of opaque zones in the otoliths of P. auratus, a single such opaque zone is laid down each year in these otoliths. Furthermore, the trends exhibited by the monthly marginal increments showed that the opaque zone is laid down predominantly in winter in the subtropical waters of Carnarvon, as opposed to mainly in spring in the temperate waters of the Perth and south coast regions. Thus, the timing of formation of the opaque zone in the otoliths of P. auratus along the Western Australian coast is not related to the trends exhibited by water temperature, but, in both the Carnvarvon and Perth regions, was coincident with the timing of spawning.
The maximum total lengths recorded for females and males in the Carnarvon region, i.e. 864 and 840 mm, respectively, were considerably less than the corresponding values of 1051 and 1056 mm in the Perth region, and 1083 and 1099 mm in the south coast region. Growth in the Perth and south coast regions was greater than in Carnarvon, as is reflected in, for example, the respective lengths of 820, 720 and 610 mm for females at 10 years of age, as determined from the von Bertalanffy growth equations.
The length and age compositions in the Carnarvon and south coast regions were essentially unimodal, whereas those in the Perth region were bimodal. However, the 'mode' in the length-frequency distribution for the south coast region was located well to the right of that in the Carnarvon region, reflecting relatively lower contributions by individuals of the age cohorts of 3 to 6 years. The marked bimodality in the length-frequency distribution for P. auratus in the Perth region was due to the presence of a group of mainly smaller individuals caught outside Cockburn Sound and another of mainly larger individuals that were caught in Cockburn Sound and which formed part of a spawning aggregation in that embayment.
The proportion of fish > 10 years old in the Carnarvon region declined markedly between 2003 and the following two years, presumably reflecting the effect of heavy fishing pressure. This contributed to the decision by fisheries managers to reduced the TAC in those waters after 2003. Age-frequency data demonstrated that annual recruitment success in Cockburn Sound varied greatly, with the 1991, 1992 and 1996 year classes being particularly strong, and recognizing that the relative numbers of the first two year classes did decline progressively between 2002 and 2004. Annual recruitment was particularly variable in the south coast region, with the catches of the 1996 year class dominating the samples.
The relative number of early stage P. auratus eggs in ichthyoplankton samples collected from Cockburn sound on each of four new moons during the spawning seasons of four consecutive years peaked in November in three of those years, i.e. 2001, 2003 and 2004, and in November/December in the remaining year, i.e. 2002. This showed that spawning in this embayment peaked during these months, at which times the mean sea surface temperatures ranged only from 19 to 20oC.
The prevalence of spawning fraction females in sequential samples demonstrated that spawning peaks at the new and, to a lesser extent, full moons. This helps account for the strong positive correlation between spawning fraction and tidal regime, with spawning being greatest when the tidal range is greatest.
Spawning times, back-calculated from the ages of the eggs collected during ichthyoplankton surveys in Cockburn Sound on each of 16 new moons within the spawning periods of four successive years, demonstrated that, in this embayment, P. auratus spawns at night and within the first three hours of the onset of the ebb tide. The distribution of egg concentrations on the 16 new moons showed that, each year, spawning occurred firstly in the north-eastern area of Cockburn Sound and then in the middle and finally north-western areas of this embayment.
In the Perth region, the marine embayments of Cockburn and Warnbro Sound act as nursery areas for P. auratus during the first two years of life. The majority of 2 to 5 year old fish and a large proportion of the 6 year old fish occupy the marine waters outside the embayments. The remaining 6 year old and almost all of the older fish begin to move in September into particularly Cockburn Sound, where they form relatively large spawning aggregations between October and December, before undergoing a massive emigration from this embayment in December/January. The limited returns from fish that were tagged in Cockburn Sound and were subsequently caught outside this embayment indicate that, following spawning, P. auratus does not tend to move in a particular direction.
Pagrus auratus stocks are heavily exploited in offshore, oceanic waters and in embayments, such as Cockburn Sound, where they are particularly susceptible to capture because of the tendency of this species to form spawning aggregations in these same easily accessible locations each year. The data obtained during this thesis show that the L50 at maturity of females and males in temperate waters, i.e. nearly 600 mm, is far greater than the current minimum legal length (MLL) of 410 mm TL. There is thus a need to increase the MLL and/or reduce fishing pressure on immature individuals in open waters. However, the effectiveness of an increase in the MLL may be limited because there is evidence that P. auratus suffers from fishing-induced barotrauma. Closures of specific areas during the spawning season of P. auratus, such as those that have been applied in Cockburn Sound and Shark Bay, are potentially a very effective method for reducing the effects of heavy fishing on spawning individuals
snapper boats
No full textsnapper nIn the 1940's another type of boat was added to the skiff, "snapper boats" (long-liner type which was from forty to forty-five feet in the keel). Those as well were still in use when the Trepassey fishery failed. The men owning those two types of boats carried on the fishery away from home. The "snapper boats" at first went to the Glace Bay and Dingwall areas of Nova Scotia from April to November. They fished by means of "long lines" and sold their catches to the fresh fish producing plants in that area.type of boatDNE-cit JH 7/72Used IUsed I2Used Isnapper-rigged, snapper fisherma
snapper
No full textsnapper nif there was one ocean-going skipper on the coast known to be more of a "snapper" than the rest, that man was Elijah Anderson.PRINTED ITEM DNE-citUsed IUsed I1Used Isnapper boat, snapper-rigged, snapper fisherma
snapper
No full textsnapper nAny undersized marketable fish. DAE � Prob an adaptation of DAE fish names - on that ship. ? What to do. File!Used IUsed INot usedsnapper boats, snapper fisherman, snapper-rigge
snapper
No full textsnapper nIt became harder and harder to close the home for six months and carry the children among the dangers of the Labrador coast, more especially as every year the "snapper" fishermen were pushing further and further north, where the coast is not only unlighted and unmarked but also unsurveyed and uncharted.PRINTED ITEM DNE-citUsed IUsed I1Used Isnapper boat, snapper-rigged, snapper fisherma
snapper
No full textsnapper nsnapper A civilian foreman on a government (military or naval) project. Origin undetermined. Bill: _any use_? Not at this time. Not at MUN Lib.a civilian foreman on a government projectDEC. 20 1979Used IUsed INot usedsnapper-boat, snapper-rigge
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