• Cliff Spital

    Cliff Spital
    Bradeis University
    Researched the response by walleye pollock to climate change in the Bering Sea.

    This summer I had the opportunity to work with Anne Hollowed of the Alaska Fisheries Science Center's Resource Ecology and Fisheries Management Division (AFSC). What can I say about my experience here this summer -- It was phenomenal!

    Like the other interns, I expected to spend the summer being a copy machine jockey. I was pleasantly surprised on my first day to have my own cubicle and computer, already things were looking up. Over the next few days I got to meet everyone who I would be working with on my project, and I was given some data I could use to learn the R statistics program that I would depend on during my internship.

    My first week at AFSC was dedicated to becoming familiar with the methods I would be using during the summer. This included a 400-page journey through journal articles reading about the work that led up to this project. When I was done catching up with the rest of my co-workers to the best of my ability, Steve Barbeaux (AFSC) showed me the ropes of R and Microsoft Access. We used data obtained by fishery observers on commercial fishing vessels, which Angie Greig (AFSC) had transformed into an ArcGIS geodatabase. This was very helpful because now each data point contained detailed information on location, fish caught, mean length, mean weight, sex ratio, time of day, day of the year, fishing gear used, bottom depth, fishing depth, sea surface temperature, etc. Steve and I used Access to create a database which we could use in R.

    I spent the next couple weeks working with Steve and my beloved R stats package creating general additive mixed models (GAMMs) in order to test the significance of our covariates (location, bottom depth,

  • map

    Figure 1.  Map of sea surface temperatures in 2003 (warm year), blue area in the north represents ice cover.


    distance from bottom, sea surface temperature, time of day, day of the year, and wind speed and direction) on the these four response variables (catch per unit effort, mean length, mean weight, and sex ratio). In our tests we used data from a warm year, 2003 (Fig. 1) and a cold year, 2006 (Fig. 2).


    map

    Figure 2. Map of sea surface temperatures in 2006 (cold year), blue area in the north represents ice cover.


  • Figure 3. Graph of the yearly effect on CPUE.


    This gave us a good contrast with which to test our hypotheses about the effects of climate change on the population dynamics and distribution of walleye pollock in the Bering Sea.

    After running the test GAMMs, I was able to weed out the insignificant covariates to make the model as simple but thorough as possible. Steve and I then made a couple of discoveries that have never been documented before and will hopefully be included in a publication. Using the 2003 data, we discovered that the walleye pollock are stratified by sex, and found that females were generally located closer to the bottom with the males hovering over them.

    We hypothesized that females could prefer slightly colder water, and in warmer years where there is more thermal stratification of the water column that would lead them to deeper water.

    Additionally, we found that the catch per unit effort (CPUE) was significantly higher in 2006 (Fig. 3), this could be caused by a smaller area suitable for foraging and spawning. The slightly colder water may have led to a more concentrated fish stock in 2006 and made pollock easier to catch in bulk.

  • Figure 4. CPUE by SST, 2003.


    Most importantly, we found that walleye pollock are sensitive to temperature of their surroundings (Figs. 4 and 5), and are mobilized by changes in the sea surface temperature (SST). This is good news for the fishery, it means that their foraging and spawning habitat will expand with rising sea temperatures allowing the population to expand and increase.

    Figure 5. CPUE by SST, 2006.




  • This experience has been one of a kind and I highly recommend this internship to anyone interested in fisheries, or deciding whether research is the right career for them. I learned so much this summer, I familiarized myself with a statistics program widely used in the fisheries management industry, improved my abilities in ArcGIS and Microsoft Access, and most importantly, I developed a more professional way of attacking problems in my research. I am looking forward to returning to the AFSC in November as a contractor to finish this project.