Differential Egg Mortality of Georges Bank Cod and Haddock Inferred from Two Independent Estimates of Seasonal Egg Production
Differential Egg Mortality of Georges Bank Cod and Haddock Inferred from Two Independent Estimates of Seasonal Egg Production
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从季节性产蛋量的两个独立估计推断出乔治银行鳕鱼和黑线鳕的差异蛋死亡率
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发表时间：
2008
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通讯作者：
L. Buckley
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作者：
R. Lough;L. O’Brien;L. Buckley
乔治斯浅滩大西洋鳕鱼(Gadus Morhua)和黑线鳕(Melanogrammus Aeglefinus)种群在过去40年中经历了重大变化，老年产卵者减少，年轻成熟鱼的发生率增加。来自其他调查的圈养研究已经注意到，第一次产卵的第二次产卵者表现出较低的卵孵化成功率，特别是与鳕鱼相比，黑线鳕的孵化成功率更低。从虚拟种群分析(VPA)得到的产卵种群生物量(SSB)被认为是对种群产卵潜力的高估，因为它没有完全考虑产卵者年龄或大小的差异。东北水产科学中心(NEFSC)的浮游鱼类调查(1979-1999)提供了季节性卵产量的独立估计，并与基于VPA繁殖力的估计进行了比较。由于这两个物种的早期卵是无法区分的，它们的数量是通过将一个站点的总卵丰度(鳕鱼和黑线鳕)与后期丰度比率进行分摊来估计的，假设这两个物种的死亡率相等。对于鳕鱼，调查高估了多年来VPA衍生的卵子产量高达一个数量级。然而，对于黑线鳕，来自VPA的鸡蛋产量估计大多高于调查得出的结果。比较两个产卵量估计值与鳕鱼和黑线鳕总产卵量之比，当黑线鳕丰富时，鳕鱼比率很高，特别是在1995-1999年期间，当鳕鱼占总数的较大部分时，鳕鱼比率更接近1。对黑线鳕的相应分析与鳕鱼的分析相反，进一步支持了这一假设，即减少年龄的黑线鳕种群的较高卵死亡率偏向于黑线鳕和鳕鱼的季节性产卵量估计。这些比率似乎解释了调查与VPA季节性产蛋量比率变化的60%-70%，而其他因素可能与SSB的繁殖力和年龄组成有关，或鸡蛋死亡率在时间序列中的变化。我们的调查估计还表明，黑线鳕卵的死亡率高于鳕鱼。因此，基于恒定鸡蛋死亡率的鸡蛋调查得出的季节性鸡蛋产量估计可能是不准确的，特别是自20世纪90年代中期以来。鳕鱼蛋的产量可能被高估了，而黑线鳕的产量被低估了。
Georges Bank Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) stocks have undergone significant changes over the last 40 years with the reduction of older spawners and increased incidence of young mature fish. Captive studies, from other investigations, have noted that firstand second-time spawners exhibit lower egg hatching success, and especially for haddock compared to cod. Spawning stock biomass (SSB), derived from virtual population analysis (VPA), has been considered as an overestimate of a stock’s spawning potential since it does not fully account for differences in age or size of spawners. The Northeast Fisheries Science Center’s (NEFSC) ichthyoplankton Surveys (1979–1999) have provided an independent estimate of seasonal egg production to compare with a VPA-fecundity based estimate. Since the early stage eggs of the two species are indistinguishable, their numbers were estimated by apportioning the total egg abundance (cod plus haddock) at a station by the late stage abundance ratio, assuming equal mortality for the two species. For cod, the Surveys overestimated the VPA-derived egg production in many years by as much as an order of magnitude. However, for haddock, the VPA-derived egg production estimates were mostly higher than those from the Surveys. Comparing the ratio of the two egg production estimates versus the total combined VPA egg production of cod and haddock, the cod ratios were high when haddock was abundant, especially during the years 1995–1999, and closer to one when cod comprised the greater part of the total. The corresponding analysis for haddock was the reverse to that of cod further supporting the hypothesis that the higher egg mortality of the reduced age population of haddock biased the seasonal egg production estimates of both haddock and cod. These ratios appear to explain 60–70% of the variability in the ratio of Survey to VPA seasonal egg production, while other factors might be related to fecundity and age-class composition of the SSB, or changes in egg mortality rates over the time series. Our Survey estimates also suggest that haddock egg mortality is greater than cod. Thus, the seasonal egg production estimates from egg Surveys based on constant egg mortality are probably inaccurate, especially since the mid-1990s. Cod egg production may have been overestimated and haddock’s underestimated.