Short-term stress and mortality of juvenile school prawns, Metapenaeus macleayi, discarded from seines and trawls

Abstract  Two experiments were carried out to assess the short-term impacts to juvenile school prawns, Metapenaeus macleayi (Haswell) discarded from commercial seining and trawling in New South Wales, Australia, and the potential utility of modifications to operational and/or onboard handling practices designed to improve survival. For both gears, discards were handled according to two general categories of treatment (termed mild and extreme) chosen to represent the plausible limits of severity during existing commercial operations. A total of 600 trawled and 480 seined school prawns (from both treatments), along with appropriate numbers of controls (previously collected and housed in acclimation tanks), were placed into cages (in groups of 10). Subsets of each of these groups were then destructively sampled over periods of up to 5 days and examined for their mortality and physiological response (measured as levels of l -lactate in the haemolymph). In both experiments, the temporal mortalities in the treatment groups ranged between 0% and 15% and, for the most part, were not significantly different to controls. Prawns in the treatment groups had similar, significantly elevated levels of l -lactate approximately 40 min after being caught, but these returned to levels approaching baseline estimates within 48 h. Under the conditions examined, juvenile school prawns appear capable of withstanding a range of stressors associated with being discarded from active gears, and their fate is not greatly influenced by the duration of gear deployment and subsequent air exposure. However, further work is required to quantify other sources of unaccounted fishing mortality and, ultimately, the impacts that discarding has on stocks.     

山东省群众渔业变水层绳拖网研究↑（*）

近几年，山东省群众渔业绳拖网发展很快，进入９０年代以来，先后在蓬莱、荣成和环翠等地的１３６－１４７Ｋｗ渔船上试验了目大０８ｍ、１ｍ、２２ｍ、３５ｍ、４ｍ、５ｍ、６ｍ、７ｍ、８ｍ、１０８ｍ的绳拖网，取得显著效果。本文对山东省各种绳拖网的试验情况，网型特点，网线配置和其他方面的性能进行了综合分析，并提出改进意见。     

南海北部拖网35．2与30．3mm方目网囊渔获选择性比较

根据1997年10月和2000年11~12月的拖网网囊网目选择性试验资料,对网目内径35.2mm方目和30.3mm方目网囊的渔获选择性进行了比较和分析。对比试验结果表明,35.2mm方目网囊渔获尾数总逃逸率为39.28%、重量总逃逸率为16.18%,高于30.3mm方目网囊的28.40%和7.47%,35.2mm方目网囊的渔获选择性有所提高;2种规格方目网囊及其套网中出现的渔获种类较为相似,具有释放鱼类种类少、数量低的共同特点,且在渔获选择性能上的差别还不明显,对渔获种类数量的释放效果都相当有限;作为优势释放种类,大头狗母鱼、条尾绯鲤和多齿蛇鲻在2种规格方目网囊中的尾数逃逸率和重量逃逸率分别在42.9%~65.8%和24.2%~45.0%之间;其中条尾绯鲤和多齿蛇鲻的50%选择体长均未达到最低可捕标准。总体来看,2种规格方目网囊对渔获的总体释放效果还不理想,要实现负责任捕鱼,需进一步放大拖网方目网囊的网目尺寸。     

福建海区单拖渔业现状浅析

本文根据1998-2003年福建海区拖网渔业资源监测以及1995-1997年间闽南台湾浅渔场单拖渔业资源调查、1998年和2000-2001年福建海区拖网定点调查的资料,论述和分析福建海区单拖渔业的现状。结果表明:目前整个单拖渔业虽然船数削减,实际却加大渔船功率,作业时间延长,促使年产量、单位产量不断提高,导致渔获组成发生很大变化,由低质小型鱼类、生命周期短的头足类、虾蟹类支撑,渔获鱼类质量较差,经济效益下降;另一方面头足类、虾蟹类资源量年间波动性较大,易受捕捞过渡影响,很难长时间承担目前捕捞压力。为此,文中提出加强严格实行"双控制度"及控制网目规格等管理建议和意见,为有关渔业管理和生产部门提供参考依据。     

主要作业参数对单船中层拖网性能的显著性分析

以网口高度和网具阻力作为单船中层拖网性能的表现,在拖速3.0~5.5kn的范围内,选择上、下手纲,重锤,沉力,浮力,上、下叉纲7个作业参数作为影响其性能的因子,共进行了27次不同因子相互组合的模型系列试验。结果显示:显著性因子个数随拖速增加而增加,但到一定拖速后显著性个数不变;在不同拖速条件下,上手纲和下手纲变化对网具性能的影响均不大;重锤和浮力在不同的试验条件下,均是网具性能的主要影响因子。     

乙纶发光网线在张网拖网上的初步应用

试验结果表明，发光网线应用于被动性张网渔具时，增产效果不明显，而且还必须考虑资源保护和解决光源激发问题。在拖网渔具上应用时，能提高渔获效率，夜间生产效果高于白天，而且调整方便。     

Life history and ecology of the glowbelly <Emphasis Type="Italic">Acropoma japonicum</Emphasis> in the Uwa Sea,Japan

ABSTRACT:   The life history and ecology of the glowbelly Acropoma japonicum a commercially important fishery resource, were investigated in the Uwa Sea, Japan. Newly settled juveniles (0⁺) appeared at the end of the breeding season and reached maturity in the next season, i.e. when they became yearlings (1⁺). The yearlings made a gametic effort comparable to that of older fish. During the breeding season, the somatic conditions were more deteriorated for males than for females. That the deterioration of male somatic conditions was not attributable to a sexual difference in energy gain from feeding suggests that the males incurred higher energetic costs of reproduction despite their relatively low gonadosomatic indices. Such an energy depletion may increase the mortality risk, resulting in female-biased sex ratios in the older age classes. Most of the 1⁺ fish disappeared in winter following their first breeding. For A. japonicum , the observed precocity and short life span is notable because it is a higher consumer that is generally expected to show later maturation and longer life. As possible explanations for their disappearances, predation and postbreeding emaciation were less likely. While fishing is one of the most influential factors, the possibility of age-specific migration toward deeper waters remains to be examined.     

Selectivity of flexible size-sorting grid in Mediterranean multispecies trawl fishery

ABSTRACT:   The demersal multispecies trawl fishery in the western Mediterranean Sea has a poor selectivity; large numbers of juvenile fish are caught when using the legislated 40-mm diamond mesh cod end. The selectivity of a flexible sorting grid with 20-mm bar spacing (BS20) installed in front the conventional trawl cod end was investigated. The standard covered cod end method was used. Data was adequate for analyzing the selectivity of European hake Merluccius merluccius , poor cod Trisopterus minutus , greater forkbeard Phycis blennoides and Norway lobster Nephrops norvegicus . The selectivity of the 20-mm sorting grid was compared with the performance of 40-mm diamond (DM40) and square mesh (SM40) cod ends. The effect of a guiding funnel on the performance of the grid (BS20-f) was also explored. Finally, the potential changes in yield per recruit (Y/R) and biomass per recruit (B/R) after implementing a sorting grid were explored. An overall improvement in the 50% selection length ( L ₅₀ ) with all four species was substantial when comparing the BS20 to the DM40. Higher improvement in L ₅₀ s was achieved when the grid was equipped with the guiding funnel. When comparing the performance of the BS20-f to the SM40, there was no marked difference in L ₅₀ s. The Y/R and B/R, however, are substantially higher with BS20-f for poor cod and about the same for European hake. BS20 compared to SM40 achieved lower Y/R and B/R for all four species; the smallest difference was observed for Norway lobster. Further development is required if the sorting grid is to be introduced into commercial fisheries.