Tab C, No. 7
From: Clay Porch [Clay.Porch@noaa.gov]
Sent: Friday, December 01, 2006 3:27 PM
To: Tom Jamir; Roy Crabtree; Joe Kimmel; Alex Chester; Jim Berkson; phil
Goodyear; John McGovern; Steve Branstetter
Subject: king mackerel stuff

Attachments: ATT326508.doc

All,

The attached document explains what was done in the SEFSC updates to the
SEDAR5 projections of king mackeral and why they may appear to differ. 
In a nutshell, the realized catches for 2002-2006 were quite different from the level of 2002 catch supposed by the SEDAR Panel. When the realized catches were used, the picture of stock status in 2002 is slightly more optimistic for the Gulf and less optimistic for the Atlantic as compared to SEDAR 5. Qualitatively, however, it is still true that increasing the fraction of the mixing zone allocated to the Gulf results in more optimistic perceptions of the status of the Gulf stock in 2002.

The pictures of stock status in 2006 have a different qualitative trend because they involve longer-term projections. Here it is important to remember that the projections assume relatively constant recruitment levels and do not account for any information relating to abundance trends (CPUE etc…); therefore they tend to interpret catch trends as declining fishing mortality rate trends and may be somewhat optimistic. 
In the case of the Gulf stock, for example, the decreasing observed catches associated with reducing the mixing zone allocation implies decreasing F/Fmsy ratios and therefore faster recoveries (increasing SS/SSmsy ratios). An alternative explanation could be declines in biomass (rather than declines in F), which would make the predictions of stock status in 2006 worse than shown in the phase plots. One should also keep in mind that that the projections become more uncertain with time. If a new assessment were conducted, including updated indices of abundance and catch at age information, then it is possible that somewhat different estimates of stock status in 2006 would be obtained. 
Thus, managers should weigh carefully whether they should set ABC levels based on more precise, but outdated projections to 2002, or less precise and possibly less accurate, but updated 2006 projections.

Under the 50:50 mixing assumption, the ABC's corresponding to a 50% chance of fishing at or above FOY (40% SPR) are Atlantic Gulf
2002 updated projections 7.0 5.8
2006 updated projections 7.6 6.5

Under the 50:50 mixing assumption, the ABC's corresponding to an 90% chance of fishing at or above FOY (40% SPR) are Atlantic Gulf
2002 updated projections 4.4 4.0
2006 updated projections 4.6 4.1