Saltwater Fishing

Hal-ibut 2.0.14

256px-HAL9000.svg
The New Hal-ibut 2.0.14

Me: “Hal can you tell me where I am most likely to catch a halibut near shore from kayak? I would prefer to catch a big one.”

Hal 2.0.14: “I’m sorry, Tyler, I’m afraid I can’t do that.”

Me: “Stupid computer!”


Introduction

A major goal of this year’s big fishing year is to connect with a halibut from a kayak. I have almost no experience with halibut other than occasionally eating them beer-battered with fries and a frosty beer. While some fisherman scoff at the idea of learning to fish from the internet I really have no choice in this big year attempt. I only have so much time and resources to allocate to a particular fish species so it is imperative that I do everything I can to maximize the probability of catching a target species. You can fish with right tackle at the right time but if you are not in the right place you are just wasting time.

Each year the International Pacific Halibut Commission (IPHC) does a stock assessment of halibut off our coasts in July. To assess stocks they use a systematic sampling scheme (Fig. 1) and at each grid they deploy approximately six “skates”. A skate is nothing more than a long fishing line 1800’ long with a 16/0 circle hook every 18’ for a total of 100 hooks/skate. Total halibut catches (over and under 32”) and weights are recorded for each sampling grid. This data is made publicly available on the
IPHC website. You can download a data table in a pdf or in an Excel document but it really isn’t that useful for those like me who are visual learners. Additionally, I have an unhealthy obsession with maps and can spend many hours staring at them so I decided to combine my obsession of fishing, maps, and data analysis to answer the question that Hal-ibut 2.0.14 could not.

Halibut_Survey_Locations
Figure 1. The IPHC sampling design off the OR and WA coasts. A total of 47 points were sampled off OR and 49 off the WA coast.


Methods & Results

I will not get overly carried away in the detail here but I think it is useful to understand how I processed the data. First I georeferenced the IPHC sampling grids into a GIS (geographic information systems) program and attributed each point with catch data. The most important variables I was interested in were
halibut abundance and the average weight of each halibut caught. While just looking at the data in this form was useful it didn’t tell me a lot about the space in-between the sampling points which is what I was really interested in. Next I used a simple kriging algorithm to fill in the spatial data gaps. What this does is to interpolate the missing data by looking at known halibut catch data. The basic assumption is that if all the neighboring points had lots of halibut odds are they are lots of halibut in-between and vice-vera when your have a cluster of points with no halibut then the space in-between likely doesn’t support large numbers of halibut. The caveat here is that the further the points are apart the less certain you are about the accuracy of your guess of the space in-between.

Halibut Abundance

I figured first and foremost if I want to catch a halibut I would need to fish where there are fish and they need to be close to shore. Looking at the interpolated halibut abundance data maps I immediately noted that there were 4 primary areas where there are estimated to be large numbers of halibut nearshore (Fig. 2). These include the Neah/Makah Bay region, the wild coasts north of La Push, WA, the Gold Beach/Brookings region, and to a lesser extent off the mouth of the Columbia River. That isn’t to say there are not fish to be found elsewhere (the blue regions) but the model is simply predicting fewer fish to be present in those regions given the IPHC data. For those not kayak bound, like myself, there are large concentrations of halibut 30-50 miles off Wesport, WA and the central Oregon coast.

Halibut_Abundance
Figure 2. Halibut abundance (per 6 skates) off the OR and WA coasts.


Halibut Size

Nobody wants to catch smalI fish (they don’t make for very interesting Facebook photos) and with retention set at one fish you want to make it count. First I estimated the mean halibut weight by dividing the total catch weight by the number of halibut caught on the IPHC stock surveys. Looking at the mean weight of halibut off the PNW coast reveals a much different picture than the halibut abundance maps revealed (Fig. 3). The largest concentrations of large near shore halibut were found primarily from Brookings, OR to the Umpqua River mouth with fish averaging nearly 40 lbs. To a lesser extent large halibut were found in areas near La Push, WA and off the Quinalt River. However, remember from earlier that the relative abundance of halibut was much lower in general off the Oregon coast. In other words there are fewer fish off the Oregon coast but the ones that remain generally are large which might speak to problems of recruitment (reproduction) of halibut in the Oregon halibut fishery.

Mean Halibut Weight
Figure 3. A map of the mean halibut weight (lbs) off the OR and WA coasts.


Hal-indices of Success

While the thought of hooking into a big halibut from a kayak is enough to get my blood pumping I also know I would much rather catch a 15 or 20 lb fish then no fish at all. From the above maps it is clear that halibut abundance and mean fish weight are not necessarily correlated. To look more at how those two variables interact I developed a “
Hal-indices of Success” by multiplying the mean fish weight by the abundance of each fish at the IPHC points and interpolated as before. This is roughly a measure of halibut biomass with the idea being the more halibut meat under my boat the better my odds of bringing it on board. The Hal-indices map (Fig. 4) shows a strong correlation with abundance map suggesting biomass is driven largely by abundance (duh!). Again the hotspots are the Neah/Makah Bay, La Push, Brookings/Gold Beach, and Columbia River regions.

Hal_indices

Figure 4. The “Hal-indices of Success” which is an approximate measure of halibut biomass off the OR and WA coasts. Concentrating your efforts in yellow and red regions should lead to a successful outing.

Abundance and Mean Weight in Relation To Depth

Another concern of mine was the depth at which halibut can be found. Kayak fishermen are limited in the distance they can fish from shore and by definition have limited access to deep waters. Depth (fathoms) readings were made at each IPHC sample point. Using this data I explored the relationships between depth and mean halibut weight and abundance by plotting each against one another. The depth versus abundance data revealed that the majority of halibut were concentrated at depths between 30 and 150 fathoms (Fig. 5). More importantly for me there are large numbers of halibut available in certain locations in depths between 30-50 fathoms which are easily accessible from a kayak. However, no sampling was done in less than 30 fathoms so its difficult to know for sure what halibut abundance might look like in the shallower waters.

Abundance_Depths
Figure 5. The relationship between halibut abundance and water depth. Larger numbers of halibut are found between 30 and 150 fathoms.


Mean halibut weights versus depth paints a slightly different picture (Fig. 6). Halibut averaging 10 to 30 lbs can be found in depths from as shallow as 30 fathoms to extremely deep at more than 200 fathoms. However, the three sampling locations that averaged halibut at or in excess of 40 lbs were in shallower water between 30 and 80 fathoms suggesting that there are big fish to be had inshore.

Weight_Depth
Figure 6. Mean halibut weight versus water depth. Medium sized (10-30 lbs) halibut can be found in a wide range of depths but the largest averages (~ 40 lbs) are found primarily between 30 and 80 fathoms.


Conclusion

I am big believer that a confident fisherman catches more fish. Near shore halibut fishing is nothing new in the PNW and accomplished halibut fisherman have been targeting these fish for a long time. Using this information I believe that my best chances at connecting with a halibut from kayak this next season is going to be off the Olympic peninsula, Columbia River, or southern Oregon coasts. Typically seasons are set for halibut in March so for now it is a matter of waiting for the seasons and quotas to be published. Then all I need to do is find a window where the fishery is open with safe ocean conditions and the fish are biting. Easy right? While I know that this analyses far from guarantees success it does give me confidence to peddle out on the big blue and take on a beast from the deep.

Comments