Offshore Test Fishing Index (OTF) for Alaska's Cook Inlet Explained!

Ever since I posted the OTF chart along with the daily Kenai Sockeye Run Count chart I've gotten deluged with inquiries asking what is this number, how does it have any relationship to the Cook Inlet fisheries and most importantly how can I use this valuable information to fill my freezer in one trip to the river or beach? I must admit, if I didn't already know the answer these would be the same questions I'd ask. And not feel a bit of remorse for tasking that poor old webmaster with more work than he can already handle.

Perhaps its time to expand upon this mysterious number and for those who have complained in the past about my presentation of too much scientific trivia, you can leave the room at this point. The remainder of this dialog will only bore you.

OTF Index stands for OFFSHORE TEST FISHING INDEX and it is a somewhat complex index number used by the commercial fisheries management team in the Department of Fish & Game. Managing Cook Inlet's large sockeye salmon runs requires a number of sources of information. The OTF index is a primary one, aerial surveillance and spotter observations is another, along with reports from beach locations, as well as the amount of success the commercial fishers are having in various areas of Cook Inlet. Then throw in variables such as extreme tides, or the opposite, neap tides with little hi/low change, wind velocities and especially wind direction, the portion of the run entering the system based on "the front half or back half" of the run, and many unknowns. So the OTF index is just one tool and for the average JOE FISHERMAN, whether he/she is a rod and reel sport angler or a personal use dipnetter, this data may have limited value as you will see. I personally use it "sparingly" for making future theoretical predictions of fish arrival times at the rivers. But its more of a ball park figure as you will see - its not cut and dried science.

Down in Anchor Point a commercial salmon drift gillnet boat has been contracted out to engage in the offshore test fishing and provide ADFG the daily numbers they come up with. On days when extreme weather prevents the boat from working there will be no numbers available. The test boat has a specific length of net and SIX exact locations in Cook Inlet on a line from Anchor Point to the west side of the Inlet.

When the boat stops at the first station it deploys the net and fishes 30 minutes. The number of salmon caught at that location in that amount of time is recorded and the boat moves to the next location and repeats the process. This continues until they reach the last station. Then the process is repeated the following day beginning at the sixth station and working their way back across the Inlet to Anchor Point. This crude method provides a snapshot view of a cross section of what numbers of salmon are moving up the Inlet at that given time. We all see how this process can produce sketchy and misleading indications since the boat could pull its net and while working the other stations a 50,000 fish school could slip on up the Inlet. But you just can't perfect this approach any finer. Thus its only their guideline and does not provide them with hard facts to base every decision on.

The data from fishing each station is summed for the DAILY OTF Index that ADFG reports. The larger the number, the MORE FISH they caught in the net for the given amount of time. The lower the index number, the fewer the number of fish intercepted during the test fishing. As some reference, OTF indexes in the 100-200 range hit big numbers of fish pushing up the Inlet. 50-100 can indicate decent numbers coming in, but may be specific to one portion of the Inlet, perhaps only westside sockeye moving in. Low numbers indicate a lull in the fish movements, but you can see how that can still not be fully accurate.

Wind is a big factor. High seas drive fish deep and therefore pass below the net. Strong winds create cross currents interacting with the tidal currents to push fish farther offshore or the opposite, push them right onto the beaches. When pushed to the center of the Inlet they can often OVERSHOOT the river mouth they were headed for and must loop back on a returning tide to hit their home waters. (NOTE: As a general rule, probably 1/2 of the sockeye salmon that enter the Kenai River do so from the north of the river. The set gillnet fishermen that operate north of the Kenai will often experience stronger catches on the ebb tide than from flood tides.)

The big Minus Four & Five tide series in July will play a big factor too. Some salmon species tend to slow down and hold back when the big tides are running while other species prefer the extra "free ride" of faster currents to make up much more ground in their travels.

And LASTLY, and the most important factor if you plan to "second guess" Mother Nature to predict when you should be down there dipping - the FRONT HALF of the sockeye run tends to move SLOWER up the Inlet than the BACK HALF of the run whose biological clocks are ticking at the same rate as the early arriving fish. The only difference is they are coming LATE TO THE PARTY and therefore push up the Inlet at a faster speed generally speaking, given all those variables just explained above. Early fish may take 7-10 days to reach the Kenai and Kasilof rivers fisheries. The second half of the season may have fish moving from Anchor Point to their home waters in 5-7 days. And in concluding, IF the run timing is significantly LATER than a typical year, all the fish running up the Inlet will be in a hurry once they hit Anchor Point.

So there you have it folks. Make what you want or can from those numbers. Its a little more helpful to be referencing previous years' comparison charts to see when the big numbers at Anchor Point converted to big numbers at the rivers' sonar counters. Here is the 2010, 2011, & 2012 Charts for your reference. Good luck. Good fishing. Good dipping. And save a few for spawning! ~Klondike Kid~