| Project title: |
Atresia and Potential Down-regulation of Fecundity in Walleye
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| Hypothesis or objectives: |
Walleye pollock (Gadus chalcogrammus) supports the largest fishery in the U.S., and accounts for 40% of the global whitefish production. Pollock is a semi-pelagic schooling fish that is widely distributed in the North Pacific Ocean, and displays a deterministic, partial-batch spawning strategy. Pollock stocks are managed by applying a harvest rate toward an assessment model estimate of spawning stock biomass (SSB), which is reliant on the assumption that SSB is proportional to total egg production (fecundity).
Studies testing the impacts of these assumptions were made by modeling weight-specific relative fecundity (i.e., increasing fecundity per unit body mass with weight) for pollock in the GOA. The results suggested that when fecundity per unit body mass increased with weight there was an increase in the estimate of FMSY (fishing mortality rate at maximum sustainable yield) compared to when using SSB as reproductive potential. This was due to the higher level of stock productivity associated with a higher level reproductive output when using relative fecundity instead of SSB. In addition, studies have shown that fecundity, even in determinate spawning fish, is not fixed but subject to down-regulation (the process of halting oocytes development and resorption of developing oocytes) through the developmental process. Oocyte development and the sequestering of vitellogen pose energetic costs to maturating females. These studies identify down-regulation of fecundity in several fish species to occur early in development preceding ovulation as a means of maintaining energy reserves while maximizing reproductive output.
This project will examine the potential biological and environmental drivers of atresia and down-regulation of fecundity in pollock. Specifically, we will test the hypotheses: (1) fish density compromises body condition and hence increases atresia (density-dependence); (2) temperature directly influences the metabolic rate of walleye pollock such that colder years lead to increased atresia during either the growing season (April to October) or during the final stages of maturation (November to March); and (3) increased ocean productivity during spring and summer translates into increased consumption of prey by pollock and accumulation of energy reserves for reproduction and thus decreased atresia.
To address the three hypotheses described above, we will need answer the following basic questions about the process of atresia in pollock reproductive biology:
1. At what time during the oocyte development is atresia manifested in walleye pollock (early development or at the end of spawning)?
2. Is atresia evenly distributed throughout the age range or more prevalent in young fish just about to mature?
3. Is atresia correlated with condition of the fish?
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| Duration: |
3 - 12 months
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| Area(s) of discipline: |
Science Teacher Education
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| Internship location: |
Seattle, WA
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| Duties and responsibilities: |
The intern candidate for this project will be trained to employ image analysis software to estimate oocyte diameter measures along with a measure of oocyte roundness to identify and count atresia. Atresia counts found through auto-diameteric methods will be compared by the candidate to estimates of atresia using the Weibel grid sampling scheme. The use of this stereological sampling grid accounts for potential bias in estimating shapes of various size ranges. To account for the impacts of atresia, a correction factor will be added to estimates of fecundity where appropriate.
Methods for identifying and quantifying atresia will be developed and applied to existing histological specimens of pollock gonads. Additional collections of gonads from the GOA will be made in 2016 and specimens from the Bering Sea NOAA pollock assessment cruises. Collections will incorporate the early development stages, spawning stages and post-spawning to capture atresia events occurring associated with these stages of maturation.
The occurrence and quantity of atresia will then be related to fish condition at the time of capture and to environmental factors impacting growth rates and conditions from the previous summer and through the time of early oocyte development. The candidate will develop multi-variate statistical models to relate atresia to environmental factors including temperature, salinity, chlorophyll a, and ocean stratification.
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| Special skills/training required: |
Prior knowledge and interest in fish reproduction and pattern analysis is helpful. We are seeking a candidate with a high interest in reproductive biology; who has good communications skills can work independently; and is able to apply established concepts to new research. Interest and skill in applying statistical models is also helpful.
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| Expected outcomes: |
The candidate will gain technical experience in the use of image analysis software, developing sampling protocol and methods for analysis for these data, and will participate in efforts to distribute research findings i.e. coauthor a publication, present findings at center meeting, workshops or fishery conferences). The candidate will gain experience applying statistical models to field and laboratory data. Candidate will work closely with FIT members as well as members of the larger Stock Assessment group to gain experience working with the latest fisheries management concepts.
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| Point of contact (Mentor): |
Sandi Neidetcher
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| Organization: |
National Marine Fisheries Service (NMFS)
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| Program office: |
Alaska Fisheries Science Center
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| Mailing address: |
7600 Sand Point Way Ne
Seattle, WA 98115
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| Phone number: |
206-526-4521
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| Fax number: |
206-526-7623
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| Email: |
sandi.neidetcher@noaa.gov
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| Co-Mentor name: |
Sandi Neidetcher
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| Co-Mentor email: |
sandi.neidetcher@noaa.gov
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| Co-Mentor gency or organization: |
NOAA AFSC REFM
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