SEMINAR: MBF602 - Vallierre Deleveaux - Friday 04/22/2011 @ 1pm in SLAB seminar room

["Vallierre K. W. Deleveaux" <vdeleveaux@rsmas.miami.edu>]

Issues with the back-calculation of fish growth: A case study using the 
the Gulf of Mexico Red Snapper (Lutjanus campechanus)

	Back-calculation is used to estimate the size of an individual fish at a
previous age. Back-calculations are based on the assumption of
proportionality between the somatic growth and the growth of the hard
parts, commonly otoliths, that has recorded the previous age marks. In
the red snapper the sectioned otolith radius is measured from the core to
the edge along the dorsal side of the sulcus acousticus of the sagittae
for ageing and back-calculation purposes. Back-calculation is an
important tool used in stock assessments to determine the average growth
rate, hence the rate of weight increase which is then used to determine
the fishing effort required to obtain a desired yield target. Growth
studies of red snapper are hampered by the probable effects of
overexploitation, missing size classes from the data and the lack of
availability of all size classes due to the spatial-temporal dispersion
of the stock. Several models were used to back-calculate the individual
growth trajectories for red snapper from the Gulf of Mexico, but the
results were unsatisfactory due to a lack of strong correlation between
otolith growth .and somatic growth. To improve the correlation between
otolith and somatic growth additional otolith morphometric data was
collected along its primary axis of growth. This new data collection
resulted in a higher correlation between otolith length and fish total
length generally, and importantly, at age. Also, a multiple regression
model was developed that gave improved results to the total
length-otolith radius relationship. This model may be useful for
improving the growth rates used in red snapper stock assessments.






Vallierre K. W. Deleveaux
PhD Candidate, Graduate Research Assistant
Division of Marine Biology and Fisheries
RSMAS, University of Miami
4600 Rickenbacker Causeway
Miami, FL, 33149-1031

Ph:  305-421-4881
Fax: 305-421-4600


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