Update on Pacific Halibut Age, Growth, and Maturation Thesis Project

Miki Takada Halibut Leave a Comment

Miki
By: Miki Takada

In the summer 2015 HASA Newsletter, I reported that I had collected 219 Pacific halibut samples, from Northern California and Southern Oregon. Thanks to the assistance of many of you, I ended up with 268 samples by season’s end! With such a short season, I was definitely excited that I was able to obtain so many samples.

In the summer 2015 newsletter, I also mentioned that I had traveled to Seattle to learn from the International Pacific Halibut Commission (IPHC) staff how to age Pacific halibut otoliths. This past fall and winter, I aged all the otoliths I collected (Figure 1), and then sent them to Joan Forsberg, an IPHC scientist who reread them, double-blind, to verify my aging. I then used length measurements from the Pacific halibut I sampled to calculate their length-at-age. Comparing Pacific halibut landed in Northern California versus those caught in Southern Oregon, we learned that length-at-age for these two areas was similar, as you can see in Figure 2. For this reason, I pooled the data for these two bioregions for all subsequent analyses.

Figure 1. Otolith aged using break-and-bake method (11 years).

Figure 1. Otolith aged using break-and-bake method (11 years).

We also compared the Pacific halibut caught in 2015 in N. California and S. Oregon with those caught in 2013 and 2014. For 2013, we utilized the data from the HASA-sponsored project conducted by Liz Perkins, another HSU student who completed her Masters thesis last year; for 2014, we used setline data from the IPHC. Our findings show that fish from the 2015 survey were smaller for a given age than those from both the 2013 and 2014 studies, as shown in Figure 3. The two most likely explanations for this finding are that either unfavorable ocean conditions resulted in little growth between 2014 and 2015, or that slower-growing fish from other areas migrated in to our area over the past year. The fact that the outermost annulus (growth ring) of otoliths from fish in 2015 was not spaced more closely than other years suggests that migration rather than ocean productivity may be behind the reduced size-at-age. A very informative next step to verify this would be to investigate the migration patterns of Pacific halibut from our region, potentially using archival pop up satellite tags. After a preset period these tags release from the fish, pop up to the surface, and send data via satellite about the location of the fish at that time as well as the path it took to get there.

Figure 2. Mean length versus age of Pacific halibut in Northern California and Southern Oregon

Figure 2. Mean length versus age of Pacific halibut in Northern California and Southern Oregon

Figure 3. Mean length versus age of Pacific halibut landed in California

Figure 3. Mean length versus age of Pacific halibut landed in California

Lastly, we compared Pacific halibut caught in 2015 in N. California and S. Oregon with those caught in Washington, the Alaska Peninsula, and the Bering Sea. Again, data from Washington, the Alaska Peninsula, and the Bering Sea were from setline surveys conducted by the IPHC. Results show that fish from the 2015 study were still larger (for a given age) than those from the Alaska Peninsula and the Bering Sea, but similar to those from Washington (Figure 4).

Figure 4. Mean length versus age of Pacific halibut landed in different IPHC areas

Figure 4. Mean length versus age of Pacific halibut landed in different IPHC areas

I also collected gonad samples from Pacific halibut last year as part of the study, and analyzed them macroscopically (by eye) for sex and maturity. I am now analyzing the ovary samples of females histologically (looking under a microscope at stained, thin sections I have prepared) for maturity to validate the macroscopic staging methods currently used by the IPHC and others. I plan to complete this analysis in the next few months.

I am grateful to HASA and California Sea Grant for their generous support of this research. It is clear that the HASA organization and its members care enormously about the local fish stocks and the health of these fish stocks. This study would not be possible without all the support of HASA and the community of anglers who let me sample their fish.

 

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