Declining Traffic With Same Rankings

Hello

I would be grateful for any input on this.

I'm the webmaster of a site. Before May 22, 2013, penguin 2 updates, the site was getting around 720 hits per day

After penguin 2 Updates, there is no difference In ranking... But my traffic has halved.

Just checked on Moz for rankings update and I have used all 300 Keywords permitted with rankings of 220 In Top 3 & 288 On First Page

But traffic stats show

Week ending: 6/16 Change 6/23 6/16 Change 6/23 6/16 Change 6/23
Organic Search Visits
Total number of organic (unpaid) visits to your site from search engines.
1,782 -11% 1,589 37 -16% 31 1,745 -11% 1,558
URLs Receiving Entrances Via Search
The number of distinct URLs on your site that receive one or more organic (unpaid) visits from a search engine.
370 -4% 354 8 13% 9 362 -5% 345
Non-Paid Keywords Sending Search Visits
The number of distinct keywords that send one or more organic (unpaid) visits to your site.
886 -2% 865 8 0% 8 878 -2% 857

I have another serps tool which has the sites full 1100+ kws and I can see no difference here either.

I have checked historical analytics data to see how much can be allocated to seasonal variations but May 2102 traffic only reduced by a little over 6% compared against Apr 2012. Jun was 1.7% down on Apr 2012 so no great fluctuations.

Looking at 2013 on the other hand Apr traffic was up 2.375% against March. May, when the issue commenced, we were down against Apr 17.63%. Jun we have not recovered as traffic compared against Apr was down 52.79%

My questions are

1. Why is there a major decline in traffic when ranking is more or less the same

2. What is the possible solution?

This is a little frustrating and obviously would like to get to the bottom of it so would be grateful for any input. Thanks.