From 3a88168aab39e8375531b5f5112986919f906582 Mon Sep 17 00:00:00 2001
From: Nathan Vaughan <nathan.vaughan@noaa.gov>
Date: Wed, 22 Jul 2026 13:51:14 -0400
Subject: [PATCH] Bug: Fix VBK sign for Nat_M case 6

---
 SS_biofxn.tpl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/SS_biofxn.tpl b/SS_biofxn.tpl
index 09094aed..d7572b8c 100644
--- a/SS_biofxn.tpl
+++ b/SS_biofxn.tpl
@@ -1229,7 +1229,7 @@ FUNCTION void get_natmort()
             //  SS_Label_Info_17.1.2.6  #case 6:  Calculate lorenzen M from survivorship over fixed age range
             case 6: //  Survivorship based Lorenzen M
             {
-              Loren_temp2 = L_inf(gp) * (mfexp(-VBK(gp, K_index) * VBK_seas(0)) - 1.); // need to verify use of VBK_seas here
+              Loren_temp2 = L_inf(gp) * (mfexp(VBK(gp, K_index) * VBK_seas(0)) - 1.); // need to verify use of VBK_seas here
               Loren_M1 = (natMparms(1, gp)); //This is the user specified average M over the input range of ages.
               for (s = nseas ; s >= 1; s--)
               {