Title page for ETD etd-07122006-124938

Type of Document Master's Thesis
Author Lachica, Ronald B.
Author's Email Address ronaldlachica@yahoo.com
URN etd-07122006-124938
Title Using Life-History, Surplus Production, and Individual-Based Population Models for Stock Assessment of Data-Poor Stocks: An Application to Small Pelagic Fisheries of the Lingayen Gulf, Philippines
Degree Master of Science (M.S.)
Department Oceanography & Coastal Sciences
Advisory Committee
Advisor Name Title
Kenneth A. Rose Committee Chair
James H. Cowan Committee Member
Megan La Peyre Committee Member
  • length-based catch analysis
  • stock assessment
  • small pelagic
  • individual-based population model
  • life-history invariant
  • surplus production model
Date of Defense 2006-07-03
Availability unrestricted
Stock assessment methods that quantify the status of fishery resources are critical to effective fisheries management. There is a need for stock assessment methods applicable for management of tropical species based on limited, un-aged catch data. I applied four stock assessment approaches to situation with limited life-history information and with short-term, un-aged catch data. The four approaches are: life-history invariants, length-based catch analysis, individual-based modeling, and surplus production modeling. All four approaches were applied to catch data from Lingayen Gulf, Philippines. The life-history invariant, length-based catch analysis, and individual-based modeling were applied to monthly length-frequency data of commercial catch for each of the three commonly caught species (moonfish, short mackerel, and tropical anchovy); surplus production modeling was applied to total annual catch and effort (all species combined) of commercial and municipal fisheries. Catch data was analyzed to determine current fishing mortality rate (Fcurrent). The stock assessment approaches were used to compute the fundamental stock assessment benchmark of fishing mortality rate at MSY (Fmsy). Comparison of Fcurrent to Fmsy provides critical information on sustainability of current harvest rates. The application of surplus production modeling resulted in questionable parameter estimates but did suggest that Fcurrent have been increasing. The results using life-history invariant, length-based catch analysis, and individual-based modeling methods predicted that Fcurrent of moonfish and short mackerel likely were or exceeded Fmsy values. Estimated Fcurrent of tropical anchovy were lower than the other species and lower than the estimated Fmsy values, but the harvesting of many juveniles and the increasing fishing rates also make their status worth monitoring. I discuss the use of multiple approaches and year-specific analyses to bound the high uncertainty associated with the reliance of all of the species-specific methods on accurate identification of cohorts from the length-frequency catch data and other assumptions. The use of multiple methods and approaches to estimate and compare Fcurrent to Fmsy provided relatively higher degree of confidence in the results. I conclude with the implications of my results to the management of pelagic fisheries in Lingayen Gulf namely that harvesting rates of moonfish and short mackerel should be reduced from current levels.
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