diff --git a/src/rl4fisheries/envs/asm.py b/src/rl4fisheries/envs/asm.py
index 28341c9..b077bf1 100644
--- a/src/rl4fisheries/envs/asm.py
+++ b/src/rl4fisheries/envs/asm.py
@@ -249,7 +249,7 @@ def population_growth(self, n):
         return n
 
     def observe(self):
-        self.vulb = sum(p["vul"] * self.state * p["wt"]) # update vulnerable biomass
+        self.vulb = sum(p["vul"] * self.state * self.parameters["wt"]) # update vulnerable biomass
         observation = 2 * np.array([self.vulb]) / self.bound - 1
         observation = np.clip(observation, -1.0, 1.0)
         return np.float32(observation)
diff --git a/src/rl4fisheries/envs/asm_2o.py b/src/rl4fisheries/envs/asm_2o.py
index 5c3963a..397bbad 100644
--- a/src/rl4fisheries/envs/asm_2o.py
+++ b/src/rl4fisheries/envs/asm_2o.py
@@ -259,7 +259,7 @@ def observe(self):
         p = self.parameters
         self.vul_pop = p["vul"] * self.state
         self.vul_pop_total = sum(self.vul_pop)
-        self.vulb = sum(self.vul_pop * p["wt"]) # update vulnerable biomass
+        self.vulb = sum(self.vul_pop * self.parameters["wt"]) # update vulnerable biomass
         
         biomass_obs = 2 * self.vulb / self.bound - 1
         
diff --git a/src/rl4fisheries/envs/asm_esc.py b/src/rl4fisheries/envs/asm_esc.py
index 27a2607..9fe6ce5 100644
--- a/src/rl4fisheries/envs/asm_esc.py
+++ b/src/rl4fisheries/envs/asm_esc.py
@@ -179,7 +179,7 @@ def population_growth(self, n):
         return n
 
     def observe(self):
-        self.vulb = sum(p["vul"] * self.state * p["wt"]) # update vulnerable biomass
+        self.vulb = sum(p["vul"] * self.state * self.parameters["wt"]) # update vulnerable biomass
         observation = 2 * np.array([self.vulb]) / self.bound - 1
         observation = np.clip(observation, -1.0, 1.0)
         return np.float32(observation)