Some aspects of the dynamics of populations important to the management of the commercial marine fisheries

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Sexual maturity, fecundity and egg size of wild and cultured samples of Bagrus bayad macropterus

Twenty four matured samples of Bagrus bayad macropterus from the wild (Shiroro Lake, Nigeria) and under captivity, size ranging from 412.69-3300.00 g total body weight, were analysed for sexual maturity,fecundity and egg size. The average fecundity obtained were 53352.59 and 21028.32 eggs for the wild and cultured fish respectively.Positive relationship was observed between fecundity, body size and gonad weight. Fecundity increased as body size increased. A more positive and linear relationship was observed between fecundity and gonad weight than fecundity and total body weight. Egg diameter,length and weight were determined from the egg samples. The mean size range of eggs for cultured fish was 0.74-1.05 mm of diameter; 1.01-1.20 mm of length and 0.25-0.40 mg of weight. Wild samples had mean size range of 0.68-l.09 mm of diameter, 0.85-1.38 mm of length and egg mean weight range was 0.15- 0.40 mg. Sexual maturity is dependent on size (1 kg and above). The egg diameter, egg length and weight bear no relationship with each other. Gonad development study indicated that gonad development was faster under captivity than in wild

Poverty alleviation among fishermen within the floodplains of Kaduna River: implication for introducing commercial fish farming at village level in Doko local government area of Niger State, Nigeria

A diagnostic survey was conducted among the fishermen in six selected villages in Doko Local Government Area of Niger State. One hundred and fifty fishermen were randomly selected and interviewed to find out whether or not they had interest in commercial fish farming aimed at improving their livelihood. The dwindling fish catches in the natural flood plain ponds and Ex-bow Lakes continue to have a serious negative effect on the socio-economic well being of the village communities in question. A break on natural regular annual flooding of the plains had resulted into very low natural fish recruitment. Data analysis using simple descriptive statistics revealed that land tenure system, educational status, inadequate infrastructural facilities, religious taboos, existing fish species among others were found to be favourable indices for commercial fish farming. However, serious conflicts among the fishermen concerning the ownership status of these natural fish ponds are found to be major obstacles to commercial fish farming despite that the traditional ownership of the ponds were vested in the lands of individuals and village communities. Extensive fish farming and small-scale fish farming in the ponds and Ex-bow Lake with improved management practices are considered to be profitable venture. Despite the fact that fish seeds supply and extension effort are still inadequate, the fish farmers have indicated willingness to adopt commercial fish farming in the Ex-bow Lakes and flood plains in order to restore abundant fish production thereby providing for their food security and also increasing the daily income

Determination of optimum stocking density of Macrobrachium rosenbergii larvae using multiple feed in a commercial hatchery at Cox’s Bazar, Bangladesh

Experimental stocking density of Macrobrachium rosenbergii in larval rearing was conducted in A.G. Aqua Hatchery, Chakaria, Bangladesh to study the effect of different stocking densities on growth, survival rate and diseases stress under hatchery condition. The research work was conducted using six cemented rectangular tanks having 3m3 capacity (1.5mX2mX1m) each. Stocking density were maintained in three experimental setup as 200, 150 and 100ind/L of the T1, T2 and T3 respectively with one replicate each. The larvae were fed with Artemia nauplii, Custard, Maxima and brine shrimp flakes. Water quality was maintained by exchanging 20-30% (12ppt saline water) daily. During the study period, temperature, pH, DO, salinity, nitrite-nitrogen, ammonia and alkalinity were maintained from 28.5-31.5ºC, 7.5-7.8, 5.8-5.9mg/L, 12-13ppt, 0.14-0.2 mg/L, 0.22-0.3mg/L, and 140-160mg/L respectively. The growth rates of larvae at 11th stage were recorded in terms of body length 0.115, 0.136, and 0.169 mm/day whereas body weight were observed 0.000115, 0.000180, and 0.000240g/day. The survival rate of larvae were found 21.8%, 30.4% and 51.3% in treatments T1, T2 and T3 respectively. PL was obtained as 43, 45, and 51PL/L and days required of 41, 38 and 34 days in stocking density of 200, 150, and 100ind/L respectively. It was found that the minimum of 34 days was required to attain the PL (12th stage) using the stocking density of 100 individuals/L. Cannibalism, Zoothamnium, Exuvia Entrapment Disease (EED), and Bacterial Necrosis (BN) were found to be the threat to the commercial hatchery operation that might responsible for potential larval damages which can be reduced by lowering the stocking densities in larval rearing tank that also increased the survival and growth rate.

Aspects of the washout of salmonid eggs. 6. Information on gravel composition , redd sites, the dimensions of redds and the depth of egg burial

Sampling was concentrated on the North Moor region and the series of ditches which drained this area to the Bristol Channel. Although most ditches were not deep the mud substratum precluded sampling from within the habitat. All samples were taken with a pond net from the banks. Efforts were made to sample each part of the habitat although in some ditches the macrophyte growth was so intense as to make sampling difficult particularly of the sediments. Organisms were identified on the 10 sampling sites.

Report upon the commercial fisheries in the Lancashire River Authority Area and their effect upon rod angling and spawning stock in the rivers and particularly the River Lune

The stock of salmon in any river is largely dependent upon the escapement of sufficient fish to ensure that an adequate quantity of ova is deposited and full use is made of all suitable spawning areas. At the present time, no accurate information is available on the numbers of fish entering rivers. Therefore, catch returns provide valuable information on fish stocks. This report summarises the catch returns for salmon in the Lancashire River Authority in the North of England for the years 1960-1964. Rivers included are the Lune, Ribble, Kent, Leven and Duddon.

Environmental quality standards to protect identified uses of controlled waters: salmonid fisheries, cyprinid fisheries, migratory fisheries, commercial harvesting of marine fish for public consumption, commercial harvesting of shellfish for for public consumption

This report considers the development of environmental quality standards (EQSs) for the salmonid fishery, cyprinid fishery, migratory fishery, commercial harvesting of marine fish for public consumption and commercial harvesting of shellfish for public consumption uses of controlled surface waters. Previous reports have been used to identify those parameters necessary for the maintenance of these five uses. Each water use is considered in a separate section within which identified parameters are discussed and standards proposed, a summary of the proposed standards is presented at the beginning of the relevant section. For salmonid, cyprinid and migratory fisheries, EQSs for substances in water have been proposed for the protection of these fisheries. For the commercial harvesting of marine fish and shellfish for public consumption uses 'Warning Levels' of substances in waters have been proposed. These 'Warning Levels' have been proposed by considering data on bioaccumulation and food standards and aim to prevent acceptable intake values and concentrations in fish/shellfish flesh exceeding statutory or recommended levels. For the commercial harvesting of marine fish for public consumption it has been concluded that the current EQSs for most List II substances for the protection of salt water life should be adequately stringent to protect this use, however for the commercial harvesting of shellfish for public consumption, these List II EQSs do not appear adequate to protect this use and more stringent 'Warning Levels' have been proposed. For all five uses considered in this report there has been found to be limited information on a number of the parameters considered and in general for indigenous species, this has been found to be especially so when considering migratory fisheries and the commercial harvesting of marine fish and shellfish.

Report on an egg bioassay experiment

In October 1992, a fish population survey of the Swanside Beck system revealed that the densities of juvenile salmon present in the beck were generally poor. The survey highlighted that a potential reason for this may be due to a lack of spawning substrate resulting from siltation. Numerous workers have found that increased levels of A salmonid egg box experiment of Swanside Beck carried out in the spring of 1994, revealed that the survival rates in the majority of sites were good. While the in-site variability was relatively high, mean survival rates remained in excess of 70%. As a result egg survival rates were eliminated as the reason for low juvenile salmonid production. The only site with a relatively low survival rate was Swanside Beck downstream of Cowgill Beck. However, even at this site siltation was eliminated as the cause of the increased mortality rate. It is recommended that a salmonid stocking of Swanside Beck should be carried out this year. This should be followed by an electric fishing survey to evaluate juvenile salmonid survival rates.

1994 annual report on fisheries in the North west incorporating the annual summary of fishery statistics.

This report provides national and regional developments, statistics on fisheries finance, including income and expenditure, salmon and sea trout catches, including rod and line, commercial catches, and angler log book returns, monitoring and special projects, including salmon microtagging, salmon egg survival in Swanside Beck, and fish stock assessments, one with hydroacoustics, and one of surveys of different areas in Cumbria. The appendix includes a summary of fish statistics for 1994.

A study of salmonid egg and fry survival in the River Taff catchment

This report looks at previous findings that egg survival was related to the percentage of fine solids in the spawning gravels of the River Taff. Green salmonid eggs were planted out at 8 sites in the Taff catchment; and eyed salmonid eggs were planted out at 27 sites. Gravel cores were taken at 18 of these sites and an analysis of their composition was carried out, particular attention being given to the pecentage of particles less than 1mm. As well as its method, the report includes its own findings and recommendations, which includes other factors influencing egg survival such as the need for water quality improvements.

Egg survival [River Wyre].

The report looks at egg survival in the River Wyre with use of three different techniques, (burying eggs in Harris boxes, eggs recovered in freeze cores and excavating redds). The report provides a detailed method and the results for each of the three different techniques, and gives an overall discussion of the findings.

Prediction and confirmation of seasonal migration of Pacific sardine (Sardinops sagax) in the California Current Ecosystem

During the last century, the population of Pacific sardine (Sardinops sagax) in the California Current Ecosystem has exhibited large fluctuations in abundance and migration behavior. From approximately 1900 to 1940, the abundance of sardine reached 3.6 million metric tons and the “northern stock” migrated from offshore of California in the spring to the coastal areas near Oregon, Washington, and Vancouver Island in the summer. In the 1940s, the sardine stock collapsed and the few remaining sardine schools concentrated in the coastal region off southern California, year-round, for the next 50 years. The stock gradually recovered in the late 1980s and resumed its seasonal migration between regions off southern California and Canada. Recently, a model was developed which predicts the potential habitat for the northern stock of Pacific sardine and its seasonal dynamics. The habitat predictions were successfully validated using data from sardine surveys using the daily egg production method; scientific trawl surveys off the Columbia River mouth; and commercial sardine landings off Oregon, Washington, and Vancouver Island. Here, the predictions of the potential habitat and seasonal migration of the northern stock of sardine are validated using data from “acoustic–trawl” surveys of the entire west coast of the United States during the spring and summer of 2008. The estimates of sardine biomass and lengths from the two surveys are not significantly different between spring and summer, indicating that they are representative of the entire stock. The results also confirm that the model of potential sardine habitat can be used to optimally apply survey effort and thus minimize random and systematic sampling error in the biomass estimates. Furthermore, the acoustic–trawl survey data are useful to estimate concurrently the distributions and abundances of other pelagic fishes.

Species compositions of elasmobranchs caught by three different commercial fishing methods off southwestern Australia, and biological data for four abundant bycatch species

Commercial catches taken in southwestern Australian waters by trawl fisheries targeting prawns and scallops and from gillnet and longline fisheries targeting sharks were sampled at different times of the year between 2002 and 2008. This sampling yielded 33 elasmobranch species representing 17 families. Multivariate statistics elucidated the ways in which the species compositions of elasmobranchs differed among fishing methods and provided benchmark data for detecting changes in the elasmobranch fauna in the future. Virtually all elasmobranchs caught by trawling, which consisted predominantly of rays, were discarded as bycatch, as were approximately a quarter of the elasmobranchs caught by both gillnetting and longlining. The maximum lengths and the lengths at maturity of four abundant bycatch species, Heterodontus portusjacksoni, Aptychotrema vincentiana, Squatina australis, and Myliobatis australis, were greater for females than males. The L50 determined for the males of these species at maturity by using full clasper calcification as the criterion of maturity did not differ significantly from the corresponding L50 derived by using gonadal data as the criterion for maturity. The proportions of the individuals of these species with lengths less than those at which 50% reach maturity were far greater in trawl samples than in gillnet and longline samples. This result was due to differences in gear selectivity and to trawling being undertaken in shallow inshore waters that act as nursery areas for these species. Sound quantitative data on the species compositions of elasmobranchs caught by commercial fisheries and the biological characteristics of the main elasmobranch bycatch species are crucial for developing strategies for conserving these important species and thus the marine ecosystems of which they are part.

Observer-reported skate bycatch in the commercial groundfish fisheries of Alaska

We analyzed skate catch data collected by observers in the North Pacific Groundfish Observer Program (NPGOP) from 1998 through 2008 to document recent changes in the identification of skates by observers and to examine the species composition of observed skate catch in Alaska’s groundfish fisheries as well as recent trends in skate retention by commercial fishermen. Historically, almost all skate bycatch has been reported by NPGOP observers as “skate unidentified.” However, since 2004 observers have been trained to identify skates to the genus and species level. In 2008 over 95% of all skates were identified at least to the genus level, and over 50% were identified to species. The most common species of skates identified by observers in groundfish fisheries are Bathyraja parmifera (Alaska skate), Raja binoculata (big skate), and Bathyraja aleutica (Aleutian skate). Species composition of reported skate catch generally reflects recent survey-derived biomass estimates, with B. parmifera dominating the catches in the Bering Sea and, to a lesser extent, in the Aleutian Islands region, and species of the genus Raja dominating catches in the Gulf of Alaska. A relatively high percentage of the skate catch on longline vessels is still reported at the family or genus level because of difficulties in the identification of skates not brought onboard the vessel. For the larger skate species, the proportion retained for processing has increased in recent years as the market price for skate product has increased. Although observed skate catch does not give a complete account of skate bycatch in the fisheries of the region, observer data provide critical information for the appropriate management of skate populations in Alaska.

Effects of commercial fishing on local abundance of Pacific cod (Gadus macrocephalus) in the Bering Sea

Groundfish fisheries in the southeast Bering Sea in Alaska have been constrained in recent years by management measures to protect the endangered Steller sea lion (Eumetopias jubatus). There is concern that the present commercial harvest may produce a localized depletion of groundfish that would affect the foraging success of Steller sea lions or other predators. A three-year field experiment was conducted to determine whether an intensive trawl fishery in the southeast Bering Sea created a localized depletion in the abundance of Pacific cod (Gadus macrocephalus). This experiment produced strongly negative results; no difference was found in the rate of seasonal change in Pacific cod abundance between stations within a regulatory no-trawl zone and stations in an immediately adjacent trawled area. Corollary studies showed that Pacific cod in the study area were highly mobile and indicated that the geographic scale of Pacific cod movement was larger than the spatial scale used as the basis for current no-trawl zones. The idea of localized depletion is strongly dependent on assumed spatial and temporal scales and contains an implicit assumption that there is a closed local population. The scale of movement of target organisms is critical in determining regional effects of fishery removals.