• Brita Mjos

    Brita Mjos
    Western Washington Univ
    Researched the life history of four rockfish species commercially targeted in the Gulf of Alaska federal fishery.

    This summer I researched the life history of four rockfish species that are commercially targeted in the Gulf of Alaska federal groundfish fishery managed by NOAA's Alaska Fisheries Science Center. Little is known about most rockfish, but a comprehensive understanding of the life history and reproductive patterns is crucial for making effective fishery policies.

    The subjects of my research were rougheye rockfish (Sebastes aleutianus), Pacific ocean perch (S. alutus), shortraker rockfish (S. borealis), and sharpchin rockfish (S. zacentrus). Life history parameters that I examined were length, seasonal timing, and geographic location of maturity stages, and maximum ova diameter.

    Histology, the study of the microscopic structure of plants and animals, was a significant component of the project. I processed 180 ovaries that had been collected from NOAA trawl surveys and NMFS fishery observers.

    First, I took a cross-section of each ovary. Second, the samples were dehydrated in a tissue processing machine. Third, the dehydrated tissues were embedded in paraffin wax in batches of 90 each. Next, a 6 µm section was sliced from each sample, placed on a slide, and dyed with hematoxylin and eosin. Finally, I was able to look at each slide under a microscope and assigned a maturity stage to each sample.

  • graph

    Percent frequency of the most advanced oocyte stage present in femail rougheye rockfish for each month sampled. Sample sizes are shown above each bar. This chart is an example of maturity stages found for rougheye rockfish from September to June, 2009.



    Maturity stages included immature (stage 1), early development (stage 2), vitellogenesis (yolk formation, stage 3), fertilization (stage 4), eyed larvae (stage 5), and postovulatory or atretic (reabsorption, stage 6).

    I measured the maximum ova diameter, which is another criteria used to identify maturity stages, with photographs of several of the largest oocytes from each sample. After charting the maturity stages in relation to the months they were collected, trends were visible regarding seasonality of rockfish maturity. Preliminary data suggest all four species spawn in the spring months, February through June. Sample size was too small to estimate an accurate length at 50% maturity value, but sample collection continues and this parameter will be estimated in the future.

  • graph

    Preparing sample of rockfish ovary.



    Other life history parameters of interest include age at maturity, fecundity, and survival rates in relation to age. As data are collected, this project will expand to include these parameters. Detailed knowledge of rockfish life history parameters is necessary to manage these populations more effectively.

    During the internship I was able to participate in the Gulf of Alaska research cruise, sorting through sample trawls from the outer Alaska shelf. We saw many interesting creatures, processed thousands of fish, and saw the best of the North Pacific. The week at sea allowed me to see the beginning of the data collection process, where all of the samples originate for NOAA's research and policy.