The cache should be here, not in the manager.

src/main/java/com/gmail/nossr50/skills/fishing/Fishing.java

@@ -1,7 +1,10 @@
 package com.gmail.nossr50.skills.fishing;
 
+import java.util.HashMap;
 import java.util.List;
 
+import org.bukkit.Material;
+import org.bukkit.enchantments.Enchantment;
 import org.bukkit.entity.LivingEntity;
 import org.bukkit.inventory.ItemStack;
 
@@ -49,6 +52,8 @@ public final class Fishing {
         abstract protected int getVanillaXPBoostModifier();
     }
 
+    protected static final HashMap<Material, List<Enchantment>> enchantableCache = new HashMap<Material, List<Enchantment>>();
+
     public static int fishermansDietRankLevel1 = AdvancedConfig.getInstance().getFishermanDietRankChange();
     public static int fishermansDietRankLevel2 = fishermansDietRankLevel1 * 2;
     public static int fishermansDietMaxLevel   = fishermansDietRankLevel1 * 5;

src/main/java/com/gmail/nossr50/skills/fishing/FishingManager.java

@@ -2,7 +2,6 @@ package com.gmail.nossr50.skills.fishing;
 
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.List;
 
 import org.bukkit.ChatColor;
@@ -49,7 +48,6 @@ import com.gmail.nossr50.util.skills.CombatUtils;
 import com.gmail.nossr50.util.skills.SkillUtils;
 
 public class FishingManager extends SkillManager {
-    private final HashMap<Material, List<Enchantment>> enchantableCache = new HashMap<Material, List<Enchantment>>();
     private final long FISHING_COOLDOWN_SECONDS = 1000L;
 
     private int fishingTries = 0;
@@ -438,8 +436,8 @@ public class FishingManager extends SkillManager {
     private List<Enchantment> getPossibleEnchantments(ItemStack treasureDrop) {
         Material dropType = treasureDrop.getType();
 
-        if (enchantableCache.containsKey(dropType)) {
-            return enchantableCache.get(dropType);
+        if (Fishing.enchantableCache.containsKey(dropType)) {
+            return Fishing.enchantableCache.get(dropType);
         }
 
         List<Enchantment> possibleEnchantments = new ArrayList<Enchantment>();
@@ -450,7 +448,7 @@ public class FishingManager extends SkillManager {
             }
         }
 
-        enchantableCache.put(dropType, possibleEnchantments);
+        Fishing.enchantableCache.put(dropType, possibleEnchantments);
         return possibleEnchantments;
     }