Given your answer Andy,
I will assume you know where this came from.. just a differing view on the data provided.
· This stock assessment used a series of statistical analyses (generalised linear modelling, SALSA and SSRA population Models) to investigate to what extent, if any, the stock is overfished.
· Catch rates from the commercial sector were stable over time, appearing to indicate a low impact of fishing.
· Howerver, there are concerns that the commercial data were hyperstable (catch rates can remain stable while abundance is declining), and this concern is supported by charter data and two recreational data sources, which all showed consistent significant declines.
· Model uncertainties
· Although the best available data were used to determine the status of the stock, there was an inherent level of uncertainty associated with the data and model assumptions. Major levels of uncertainty exist in the key biological parameters of natural mortality and stock–recruitment, as well as in the fisheries data of the historical and recreational catches;
This one is brilliant..
· However, if there is a significant level of stochastic variation on top of a presumed deterministic stock-recruitment relationship (one level of stock size gives rise to a range of recruitment levels (then this interpretation is not the only one possible. A high proportion of smaller animals relative to larger ones could also be due to the appearance of numerous strong recruitment years. This confounding is particularly vexing because the possible interpretations are quite divergent – one of high fishing mortality and the other low fishing mortality and strong recruitment.
In order to remove this confounding it would be necessary to incorporate recruitment variation into the estimation process for the stock mode. One way to do this would be to estimate a recruitment ‘anomaly’ for each year of the fishery (for a concise summary of this topic and other approaches see Walters & Martell (2004, p. 96)). Preliminary runs of the model using this estimation approach ended up with very large recruitment anomalies estimated for the years 1993/94. The estimation process clearly preferred the strong recruitment interpretation to the high fishing mortality interpretation. The problem with this estimation is that we only had ‘snapshots’ of composition information (one in 1994/95 and one in 2006/07) to inform the model, not a time series. Time constraints prevented a detailed investigation of this issue; however, the following points are pertinent
Sensitivity to uncertain catch history
· The use of boat registration information and Fish Board records to construct historical changes in harvest has been criticised as a source of model bias. Likewise, there is uncertainty about the accuracy of recreational harvest estimates.
Regards
HOnda.
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Originally Posted by caster226
